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OfflineGreenRabbit
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Thermodynamic Analysis of Monotub Air Currents * 17
    #21371089 - 03/06/15 02:11 PM (9 years, 10 months ago)

Most of this was calculated and written before I found this: http://www.shroomery.org/forums/showflat.php/Number/20307891 which pretty much explains everything you need to know. I just decided to take it way further to understand the effects of different atmospheres and different vent geometries. This write-up is not simple and I expect the reader to understand the basics already. This is not a tek, just an analysis of different monotub ideas. A tek may follow after experiments.



Monotub Function and Effect of Geometry

This journal is to explain the function of a properly dialed in monotub. If you need help with that go here:
http://www.shroomery.org/forums/showflat.php/Number/17332777/fpart/1/vc/1/nt/16

This is an analysis of the currently accepted monotub tek and examination of possible improvements, either functional or to simplify production. Although vent size and placing affects the direction of airflow, mushrooms tend to grow randomly or from the entire surface area of the substrate.
Regardless, creating a tub with good air circulation and steady airflow across the entire surface of the substrate would be ideal in obtaining even pinsets and evenly sized fruits.

The monotub is essentially a and can be modeled as a mixing chamber. Outside air enters through the top holes, mixes with the air in the tub, and exits through the bottom holes. It is an isobarric, isothermal, irreversible process that generates entropy while maintaining semi-equilibrium. I originally called the monotub adiabatic but this is not true as the fungi do produce some heat. Since the system is not insulated though the heat is lost and the process remains isothermal.

Pure Dry Air

Air is a mixture of gases, vapors and contaminants. Dry, clean air exists only theoretically.
Dry, clean air consists of:
N2: Nitrogen; 78.1%Volume; 75.5%weight
O2: Oxygen; 21.0%V; 23.2w
Ar: Argon; .93%V; 1.29%w
CO2:Carbon Dioxide; .03%V; .04%w
H2:Hydrogen; 0.01%V; .001%w
Ne: Neon; .002V; .001%w
He, K, Xe: Helium, Krypton, Xenon; .008%V; .008%w

Humid Air

Absolutely dry air does not exist in the atmosphere, there is always some amount of water vapor. Moist air is a mixture of dry air and water vapor. The largest possible amount of water vapor in the air amounts to only a few grams per kilogram of dry air.
Air with a humidity that is very low will increase surface evaporation but also quickly dry out a substrate.

Absolute (x) vs Relative (rH) Humidity

Absolute humidity is the amount of water in grams per kilogram (g/kg) of air.

At a given temperature and pressure, air can only hold a certain maximum amount of water vapor. The higher the temperature and air pressure, the higher the maximum possible water content.
This maximum water content for any given state of air is referred to as saturation.

Dew Point Temperature (Saturation Temperature)



Saturation can be reached by a temperature drop more easily than by the addition of water to the air.
The saturation line cannot be reached simply by increasing the water content.
If cooled below the saturation temperature, condensation occurs.
Water vapor condenses on surfaces and bodies, whose temperature is below the dew point, that is, droplets form.



The comfort range shown is for people if that isn't obvious.

Mixing Two Quantities of Air

If two air flows are mixed, a third state results. A psychrometric chart cannot be used here because the chemical composition of each state is different.
Absolute humidity can be calculated however by
xmix=(xtubmflowtub+xfreshmflowfresh)/](mflowtubmflowfresh)

Air Density

Higher humidity decreases density. Some people think this is counter-intuitive but, um... Clouds float, don't they?
Dry air has a density of 1.293 kg/m3
Humid air has a density of 0.804 kg/m3
02 has a density of 1.185 kg/m3
C02 has a density of 1.98 kg/m3

The air density is increased due to a change in chemical composition caused by the breakdown of the substrate. As carbon is added and mixed into the air the density drops significantly.
The humidity of the air in the tub is not actually much higher than the ambient humidity of the room. As fresh air comes in it evaporates the mist or condensation on the sub and creates >90% humidity at the substrate level where it matters. The air itself is not carrying that much water vapor.
Condensation is a result of a temperature drop after 100% humidity has been reached. Condensation does not necessarily mean your humidity is 100%. If the rH is high and you have a temperature drop of a few degrees, you will still get condensation. If the temperature of the surface is below the dew point, there will be condensation. This is how car defoggers work, if your windshield is above the dew point, fog cannot form on your windshield. Plastic, like glass, radiates heat, though not as well as glass. This leads the temperature of the sides of the tub to be slightly lower than the air, so you can get some condensation even when the air temperature is still above the dew point.

The density of humid air is dependent on three different criteria:

Air pressure:
Ambient air pressure is determined by atmospheric air pressure and indoor temperature.
Monotub aip pressure is determined by indoor air pressure and tub air temperature.
Due to polyfill stuffing, heat generated by substrate, and increase in CO2 by the substrate, the air pressure is constantly being lowered.
If there is a difference in pressure, air will travel in the same direction through all holes. Air will move faster through the top holes as the stuffing is lighter.
Pressure facilitates movement and mixing of air in the monotub, but most flow of air in or out of the tub is caused by a difference in buoyancy.
When air leaves through only the top , the resulting pressure differential causes air to be sucked in through the bottom holes.


Temperature:

The temperature of the monotub is generally higher than the ambient. This is due to the mycelium metabolizing the substrate. As a result, pressure in the tub rises slightly which helps to mix air.
As temperature rises though, the density of the air in the tub decreases, and if the density of the tub becomes lower than ambient, air will flow out of the top holes and air will be drawn in through the bottom holes. Temperatures increases also tend to drive evaporation, which also lowers density, so a hot dry tub will quickly evaporate water and flow will likely be upward.
If temperatures drop though the opposite can happen if the density drops below ambient.
When temperature drops below the 100% line on the Mollier diagram, the air can no longer hold all the air was holding at the higher temperature drop, creating condensation on the substrate and walls of the tub.

Water vapor content:

The higher density in the tub creates a higher pressure on the vents of the tub and a force on the air pushing it out. Since the air in the tub is heavier it goes out the bottom holes and fresh air is drawn in through the top holes. The tubs air pressure should be equal to atmospheric. When air is pushed out of the tub, the pressure differential causes air to be drawn in through the other set of holes to equalize the pressure again. The ideal is to always have this pressure differential to create constant fresh air flow. As far as FAE goes, the direction of flow doesn't matter.
The motion of air is driven by potential energy, which is greatest when the height difference between bottom and top holes is at a maximum.
It would be logical to make this density difference as large as possible.

Air is not flowing in and 'pushing' the air out the bottom as I have read around here. The air in the tub 'falls' out of the tub and fresh air is actually sucked in through the top.
Air can flow the opposite direction still, however the air is being pushed out by its buoyant force, and air is sucked in through the bottom holes.
The addition of a fan does not change the pattern of airflow inside the tub, but it  does increase the velocity of the incoming air slightly. If there is no polyfill in the top holes, a fan makes a big difference, as air can flow freely through the top.
A fan should not be pointed directly at a tub as it could force air in through the bottom holes, which would make air move sideways in a tub instead of downwards. Air would only be able to flow out through the bottom holes on the side away from the fan.

This analysis suggests it is not beneficial to have any unstuffed holes in the tub.
Allowing air to travel freely into to tub does not help. That air would not mix very well, and likely float at the ceiling of the tub. Also, you do not have control of the direction of airflow through the top holes. Top holes should have a minimal but not negligible amount of stuffing.
Polyfill in the tub holes ensures that air is not randomly flowing into the tub, but actually being sucked in due to air leaving the tub.


Basic Monotub Tek
Shown in Top drawing


air does not follow the lines directly, it circulates around and mixes while it is in the tub and then exits. The lines are just possible average paths of any single air particle.


Topics to cover:
x Effect of fan in the room
_ Effect of various ambient air rH
_

Things to cover:
x Geometry
x Air Composition
x Dry vs Humid Air
x Absolute vs Relative Humidity
_


Ok, from here its a lot of math.

Known values:
L, W, & H ; measurable
Vtub ; available airspace in tub from LxWx(H-Hsubstrate)
d1 or L; top holes or squares, measurable
d2 or L & H; bottom holes
Patm=P[sub ]tub [/sub ] ; 1 atm, 101.325 kPa
Tatm ; measurable
Ttub ; measurable
Mair components ; reference periodic table

Used values:
L : 14"; 35.56cm
W : 10"; 25.40cm
H :  6"; 15.24cm
Vtub: 840 in2; 0.542 m3
d1: 2"; 5.08cm
d2: 4"; 10.16cm
P : 1 atm, 101.325 kPa
Min: M=29.09 kg/kmol
Mout: M=29.958 kg/kmol

Values to calculate:
xx A1,A2
xx Asurface ratio
xx Dtub possible levels
xx Daily Air Flow Rate
xx yz comparison of hole centers
_x Volumetric Flow Rates
xx Force Balance (why air does not got out your top holes)
xx Mdry air, Mtub air
xx v1/v2
xx Mass Flow Rates
xx Heat Output of Substrate
xx True Humidity of Air in tub
_x Entropy balance

Hole Shape


It is important to note that shape DOES matter. A round hole stuffed with polyfill will let more air in through the center of the hole than near the sides.

Airflow is not consistent throughout the holes surface area.

Square holes act the same way as circles, but rectangular holes create an even linear horizontal flow through the hole.



Difference in yz due to Hole Shape


Air flows fastest through the lightest packed zone of a hole. This is always going to be the center of a round hole and the center plane of a rectangular slit.



yz.circle=r= 2" from edge of circle
yz.rectangle=(0.5)H= 1" from bottom or top of slit.

yz is always double for a circle compared to rectangle with a height equal to the radius of the circle.

Having the exit airflow slightly lower will increase the effect of the density difference.
The optimal level for the slits is just barely above the substrate level. This is why rectangular holes would be superior to round holes; even if the bottom of the circle were at the top of the substrate, the air would flow out at double the height compared to the rectangular slit.
Rectangles at the bottom increase the chances of air getting to the whole surface of the substrate. Also, once a flush starts, the fruits can mess with air flow once they get tall, and lower air vents would draw fresh air to the bottom of the tub more effectively.

It may be better not to put the holes as low as possible to avoid mushrooms growing right in front of the holes.



Surface Area (As) Ratio


2 2" holes at top on narrow side of tub and 2 4" holes at bottom on wide sides of tub.
This means the ratio of surface area between the top and bottom holes is related to r squared, which would mean about the same thing as a square hole and increasing both x and y dimension by the same value as r.

Bottom As 4:1 Top As



Close Equivalent with Rectangular holes


Drawing 2
To equate the round holes to rectangular holes, the top holes would be about 1.75" wide squares and the bottom holes would use a 2" high window requiring a length of around 6.25". Numbers have been rounded down to a simple measurment.

The ratio is still 4:1 off by only half a percent.

Top Holes: 4"*1" = 4 in2
Bottom Holes: 2*(3.75"*1.5") + 4"*1.75" = 18.25 in2
Exact As Ratio: 3.97 (Less than 1% away from standard monotub ratio

I used a larger middle hole to help draw air toward the center, away from the narrow sides and corners.
The addition of a middle hole is to improve air circulation near the corners by pushing the holes apart.

Overall, it should not make much of a difference, but it is the ideal theoretical setup.





Hole Placement


Drawing 3
Could achieve the same surface area ratio with 3 rectangular slits, each 2" high and 4.15" long.
This pattern would give the best chances of having good air circulation across the whole substrate while making no changes to the velocity or mass flow rate of air.

Drawing 4 shows the top holes moved to the lid instead of the side. This design maximizes the potential energy of the system by using the greatest height difference possible.

Future Experiments:
x_ Monotub based on Drawing 3 & 4 EDIT: 3 done, need to try 4 with top holes
 
x_ Eye Shaped Holes (Minimono done, need to make 70qt version.)



Air Velocity


The volumetric flow rate through the top holes is equal to the volumetric flow rate of the bottom holes. The top holes are half the radius and diameter of the bottom holes, and there are twice as many bottom holes as top holes.

Using diameters of 2" for top holes and 4" for bottom holes

V1=V2 ; 2d1=2d2
A1=3.14in2 & A2=12.57in2

Regardless of hole diameter, A2=4A1

Vrate = vA
v1A1=2v2A2
v2=(v1A1)/2A2



Volumetric Flow Rate


Assuming v1 to be 1 mm/sec
v2= 0.000125 m/sec = 0.125 mm/sec

v2=(1/8)v1 when you have twice as many bottom holes as top holes & they are twice the diameter.

This tub would cycle 0.175 cubic meters of air every day.
It would take 3.92 days to replace a cubic meter.



Air Density Calculation


Fresh dry air composition: 78% N2, 20% O2 1% CO2, 1% Ar
M=29.09 kg/kmol
Patm=101.325kPa

vs=(RT)/(PM) at Patm and 295K
vs=0.832 m3/kg
D=1.201 kg/m3

Air in the tub could have up to 20% CO2 and 1% O2 not likely

For compositions:
15% O2 + 5% CO2 : 29.251 g/mol ; 1.208 kg/m3
10% O2 + 10% CO2 : 29.851 g/mol ; 1.233 kg/m3
5% O2 + 15% CO2 : 30.452 g/mol ; 1.2577 kg/m3
1% O2 + 20% CO2 : 31.373 g/mol ; 1.2958 kg/m3

This means the density of the air in the tub can never be more than 10% more dense than the atmosphere. Realistically though, you probably won't even reach 105% of the density of ambient air due to constant airflow and mixing.
EDIT: I have learned that concentrations of 20% - 30% C02 will make a person unconscious and concentrations greater than 30% are lethal.
Concentrations like these only happen near volcanoes, so I doubt our tubs are getting anywhere near there, even with holes taped up.




Force Balance on Air in Tub


FBuoyancyAir.tub= D*g*V= 1.2958 kg/m3*9.81 m/s2*0.542 m3= 6.890 N

Fgravity= m*g= (0.7 kg)(9.81 m/s2)= 6.887 N

Fnet= 3 mN
Which seems like a small number, but the force of air moving unrestricted can be expected to be almost negligible.
Also, gravity was left positive so that's why Fnet is positive. It is in fact a downward force on the air.



Mass of Air in Tub


mtub= D*V = 1.2958 kg/m3*0.542 m3= 0.7 kg



Mass Flow Rates


Volumetric flow rates are equal while densities are not, therefore,
mratein<mrateout

mrate=DVrate

mratein=(1.201kg/m3)(.175m3)=0.210 kg per day

mrateout=(1.2958kg/m3)(.175m3)=0.227 kg per day

These masses are not the same because the air leaving the tub has picked up a significant amount of Carbon, which came from the mushrooms using up the substrate.
Evaporation decreases the mass of outgoing air so it appears that the difference in mass flow rates is actually the mass of substrate being used up by the mushrooms.



Heat Output of Monotub


To calculate the heat output of a monotub: (assuming the air in the tub is dry, the mass of air in the tub is 1kg, and a temperature difference of 5 degrees Celsius)

U=Cp*m*dT

U=1 J/(gK) * 1000g * 5K

U=5000 J or 5kJ

If this temperature was reached in 1 hour:

Qrate=U/dt

Qrate= 1.38 J/s



True Humidity of Air in a Monotub


From keeping a hygrometer in a monotub I've found that the rH of the tub can vary from anywhere between ambient rH and 99%. It is quite easy to get 99% rH in a tub with a mister, and I actually believe some electric hygrometers can be quite accurate even at high rH. If misting with a quality mister and a super fine mist, the rH can be brought from 60% to above 90% in a matter of minutes.
Misting the substrate provides your surface evaporation source while misting the air and sides of the tub raises the rH even more.

Important here:
You do NOT want your tub rH high. This seems counter intuitive but as long as your substrate is not dry on the surface you have evaporation. Keeping the rH high will lower the evaporation and likely reduce a pinset.

Ideally, you would actually want very LOW rH in the tub provided that the substrate is never dry on the surface. This would boost evaporation and likely cause more pins.
Just make sure the substrate never dries out.

So really, you should not mist the sides of the monotub nor the air itself. Just mist the substrate until it looks like water is going to pool, then stop.
If you are not a noob, you likely don't mist your monotubs at all, and if your monotub can fruit for several weeks without drying out:
Congratulations, you've practically mastered making monotubs and substrates.



Entropy Balance


Srategen= -mratetubstub+mratefresh airsfresh air
A monotub generates entropy. Yep, growing mushrooms increases the randomness of the universe! I doubt I'll ever go so far as to calculate this numerically.

Edited by GreenRabbit (06/28/16 11:48 PM)

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OfflineGreenRabbit
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Re: Mathematical Analysis of Monotub Ventilation [Re: GreenRabbit] * 1
    #21399118 - 03/12/15 06:12 PM (9 years, 10 months ago)

Quote:

Ghatti said:
Dude, thank you soooooo much for acknowledging that humid air rises and leaves through the top holes.

I don't know how many times I argued this with frank on a diff account.

He swore that the fresh air got pushed in the top holes and out through the bottom.




Frank is right on this one. The air in the tub is more dense than the air in the room. Without a fan, this would cause the the denser air in the tub to slowly 'fall' out. The center of mass of the air in the tub is the center of the airspace in the tub, so there is no way air that is more dense is going to fall up and out through the top holes. The density difference forces the tub air out the bottom and it is this action that pulls air in through the top holes. Otherwise, why would the less dense, fresh air enter the tub at all?

If your monotubs holes are all on the same plane, at the same height, there would be minimal forces driving air in and out of the tub, resulting in poor FAE.

Adding a fan increases mass flow rate and the air circulation inside the tub but does not do much to affect the pattern of airflow. This is mainly determined by the vent geometry.

If you put the fan really close to the tub and point it right at it, then you would be forcing air through the bottom holes on that face as well. In this case, you would have air entering through all the top holes and the bottom holes on that face. Air would only be able to exit through the bottom holes away from the fan.


EDIT: I believe this can actually vary. It is possible for the air in the tub to be less dense due to humidity and temperature, in which case the flow would be upward. If the tub dries out however, the CO2 will have a greater effect on density than humidity and flow would be downward.

Edited by GreenRabbit (08/04/15 03:28 PM)

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InvisibleAbshroom
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Re: Mathematical Analysis of Monotub Ventilation [Re: GreenRabbit]
    #21445525 - 03/23/15 01:10 AM (9 years, 9 months ago)

:threadmonitor:

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InvisibleMr. Alien
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Re: Mathematical Analysis of Monotub Ventilation [Re: GreenRabbit] * 1
    #21447337 - 03/23/15 01:45 PM (9 years, 9 months ago)

I don't undertand anything. But right on GR :thumbup:

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OfflineGreenRabbit
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Re: Mathematical Analysis of Monotub Ventilation [Re: Mr. Alien]
    #21447374 - 03/23/15 01:54 PM (9 years, 9 months ago)

Quote:

Mr. Alien said:
I don't undertand anything. But right on GR :thumbup:




Most things relevant to using a monotub are in green. The point was originally to equate the round holes to rectangular ones because I don't have a hole saw, and making straight cuts is way easier for me.

Also, rectangular holes make more sense to me; I think they would help the airflow by letting the air escape as low as possible.

I also wanted to explain mathematically why air does not flow in the bottom holes at all.


If there are any questions, I can answer them and clarify the OP as well.

Edited by GreenRabbit (05/16/15 01:57 PM)

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Invisibleblindingleaf
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Re: Themodynamic Analysis of Monotub Air Currents [Re: GreenRabbit]
    #21464558 - 03/27/15 08:31 AM (9 years, 9 months ago)

wow!
nice write up brother!
this is one of hose posts i need to read like 3 times to get.
thanks for thinking clearly about something we take for granted most of the time!


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MICROBIAL HUSBANDRY!!!!

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Re: Themodynamic Analysis of Monotub Air Currents [Re: blindingleaf]
    #21475732 - 03/29/15 06:36 PM (9 years, 9 months ago)

From OP:

-Condensation is a result of a temperature drop after 100% humidity has been reached

-The addition of a fan does not change the pattern of airflow inside the tub

But you dont need a 100% rh to have condensation as the mollier diagram shows..
and a fan does change the pattern because with top holes looser than bottom
more air comes in top than bottom. path of least resistance for theair would then be to exit the bottom holes.
even tho the air inside the chamber is denser it will rise without a fan, because hot and humid air rises.

I've also thought about square holes. air from a fan likes to make turbulence around the holes
so I'd think you'd get more air flowin through the chamber wiht square holes.
but then again with turbulence and stuff like that you'd need a wind tunnel to do proper tests, cant just calculate stuff like that (at least I cant :tongue2:)

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OfflineGreenRabbit
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Re: Themodynamic Analysis of Monotub Air Currents [Re: spacechildo] * 1
    #21480218 - 03/30/15 05:07 PM (9 years, 9 months ago)

Quote:

spacechildo said:

But you dont need a 100% rh to have condensation as the mollier diagram shows..






How does the Mollier diagram show this? In a practical sense you do not need 100% rH to have condensation, as in, all of the air does not need to be saturated for condensation to occur. When you have high (>80%) rH there is enough water in the air for it to condense due to a temperature difference. The fact that the inside of the tub is just slightly warmer than the outside is what causes condensation on the sides of a tub. When the temperature drops, 100% humidity is reached because the air can not hold as much water as it could at the higher temperature.

Again,
Condensation is a result of a temperature drop after reaching 100% humidity.
But to clarify, if you have 80% rh at 20 C, and you drop the temp to 10 C, you will have reached 100% rH at some point around 15 C and any temperature drop below that will lead to condensation as the air simply cannot hold the same amount of water it was previously holding.

Quote:

spacechildo said:
a fan does change the pattern because with top holes looser than bottom
more air comes in top than bottom. path of least resistance for theair would then be to exit the bottom holes.
even tho the air inside the chamber is denser it will rise without a fan, because hot and humid air rises.





First, this part
Quote:

spacechildo said:more air comes in top than bottom




No, it doesn't. Refer to Volumetric Flow Rate calculation above for proof. If more air came in than out you would have a slowly inflating balloon. The volume of air leaving is exactly equal to the volume coming in. However, as densities are different, this means that the air leaving the tub is actually heavier than the air coming in, and overall the tub loses mass.

Air cannot come in and 'push' other air out. The carbon laden air in the tub is pulled out of the tub by gravity, this would create a vacuum, except air is sucked in the top to keep pressures equal. Air cannot come in and push other air out unless it has a significantly higher pressure, which is never the case in fruiting a monotub.

And now
Quote:

spacechildo said:even tho the air inside the chamber is denser it will rise without a fan, because hot and humid air rises.




Refer to Mixing Two Quantities of Air, fresh and and stale tub air are constantly mixing. The hot humid air does not rise because it mixes with the carbon dioxide and overall, the mixture has a higher specific gravity than the fresh air outside still.
Refer to Force Balance for proof that the force of bouyancy on the air in the tub is lower than the force of gravity, therefore gravity wins and the air overall must travel down, in the direction of gravity.
EDIT: This depends on the humidity and temperature. I believe air can travel either direction through the tub. Having tightly stuffed holes will also increase CO2 content.
A warm, humid tub with lots of FAE will almost always have flow going upwards. After they dry out a bit, if the bottom holes are stuffed tight, flow could reverse.


The main function of the fan is to keep the air in the room circulating. It would only affect airflow inside the tub if pointed directly at loose or empty holes. Then it absolutely has an effect on airflow patterns, but it is often advised not to point the fan directly at the tub because this can dry out the substrate rather quickly, especially if there are uncovered holes.

This analysis is done assuming that no holes are empty, and that top holes have enough polyfill to stop air from freely flowing into the tub.
This is in fact the goal and purpose of a monotub, so I will not debate tubs with empty or almost empty top holes. I know they can work if managed properly, but I cannot analyze a system that lets air flow in freely. Too many variables; at that point, the speed and placement of the fan is extremely important as is it is the main driving force for airflow in the tub.

Edited by GreenRabbit (08/04/15 03:41 PM)

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Offlinespacechildo
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Re: Themodynamic Analysis of Monotub Air Currents [Re: GreenRabbit]
    #21480330 - 03/30/15 05:36 PM (9 years, 9 months ago)

Re: 100% rh for condensation, I think we mean the same but say it differently.
A room with 40% RH and say 25C can still have condensation on a metal door handle which only is 10C. just examples.
you just say that rh is 100% around the door handle.


  spacechildo said:more air comes in top than bottom

No, it doesn't. Refer to Volumetric Flow Rate calculation above for proof. If more air came in than out you would have a slowly inflating balloon. The volume of air leaving is exactly equal to the volume coming in.

I'm just saying that some air is entering both top and bottoms. but more air is entering top
because that is where the resistance is lowest. I'm not saying the same amount that comes in isnt pushed out somewhere else.


    spacechildo said:even tho the air inside the chamber is denser it will rise without a fan, because hot and humid air rises.


This is just wrong, sorry if I sound like a dick.
Refer to Mixing Two Quantities of Air, fresh and and stale tub air are constantly mixing. The hot humid air does not rise because it mixes with the carbon dioxide and overall, the mixture has a higher specific gravity than the fresh air outside still.


have you ever done any tests on this? hot and humid air does rise, just like smoke from a fire.

Back in the days before Frank and the fans everyone just stuffed top and bottom the same and let hot humid air rise out the top and new air being drawn in the bottom.

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Re: Themodynamic Analysis of Monotub Air Currents [Re: spacechildo]
    #21480477 - 03/30/15 06:21 PM (9 years, 9 months ago)

If the bottom holes are stuffed tight, there should be no air going in through the bottom holes. If the top holes are stuffed very loosely, then yes, air will travel in both directions.
Lets at least agree that volumetric flow rates are equal. They have to be or you would have a pressurized system.
Now, if the top holes are stuffed loosely, but still enough to stem free air travel, then the air would actually be sucked in the top holes as air is pulled out the bottom by gravity. This is why monotubs can be on the ground, and SGFCs need to be raised. And SGFC works in a totally different way, so air flows upwards instead.
I'll have to run some in depth calculations on density, but I'm waiting to get my monotub running so I can use some experimental data.

Hot humid air rises, sure, but the air in the tub isn't the same chemical composition as the incoming air. It mixes and on average is more dense than the ambient air. Refer to Air Density Calculation for densities of different compositions of air.

Edited by GreenRabbit (05/16/15 01:56 PM)

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Re: Themodynamic Analysis of Monotub Air Currents [Re: GreenRabbit]
    #21550026 - 04/15/15 07:18 AM (9 years, 9 months ago)

Awesome write up. Been thinking about monos for awhile. Saved this thread.

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Re: Themodynamic Analysis of Monotub Air Currents [Re: FarOutMushROOM4849]
    #21654273 - 05/08/15 05:22 PM (9 years, 8 months ago)

I love this thread.

I am reconsidering the placement of my lower holes. I think they are too high. Four 1.5 inch holes at 1" above substrate. I have a hard time believing the mushrooms would block the air flow of the lower holes, because its sooooo slow. But I do think my holes are too high (pun intended)

I'm liking six lower holes (equaling the accepted hole volume) As low as possible.

I feel like my little guys have been wanting the fresh air level to be lower.

T


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Re: Themodynamic Analysis of Monotub Air Currents [Re: tedoro]
    #21654285 - 05/08/15 05:25 PM (9 years, 8 months ago)

Ooooo, and I like the top lid vents. That works for me. I don't stack. And its totally higher.

t


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Re: Themodynamic Analysis of Monotub Air Currents [Re: tedoro]
    #21686964 - 05/16/15 12:43 PM (9 years, 8 months ago)

WOW, I have been looking for this thread for YEARS I just didn't know it

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Re: Themodynamic Analysis of Monotub Air Currents [Re: tedoro]
    #21687166 - 05/16/15 01:56 PM (9 years, 8 months ago)

Quote:

tedoro said:
I love this thread.

I am reconsidering the placement of my lower holes. I think they are too high. Four 1.5 inch holes at 1" above substrate. I have a hard time believing the mushrooms would block the air flow of the lower holes, because its sooooo slow. But I do think my holes are too high (pun intended)

I'm liking six lower holes (equaling the accepted hole volume) As low as possible.

I feel like my little guys have been wanting the fresh air level to be lower.

T




An inch above the substrate is fine, I like to keep the polyfill off of the substrate.

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Re: Themodynamic Analysis of Monotub Air Currents [Re: GreenRabbit]
    #21689512 - 05/17/15 06:24 AM (9 years, 7 months ago)

:kaneclap:


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Re: Themodynamic Analysis of Monotub Air Currents [Re: Tmethyl]
    #21689533 - 05/17/15 06:38 AM (9 years, 7 months ago)

I especially enjoy your optimal theoretical setup. Are there any final changes you would make to this now that you've had time to marinate on it a bit?
I don't just mean the hole placement, but the entire system.


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Re: Themodynamic Analysis of Monotub Air Currents [Re: Tmethyl]
    #21689632 - 05/17/15 07:42 AM (9 years, 7 months ago)

Quote:

Tmethyl said:
I especially enjoy your optimal theoretical setup. Are there any final changes you would make to this now that you've had time to marinate on it a bit?
I don't just mean the hole placement, but the entire system.




No, I've been making edits quite often. I wrote this up to see where I can apply thermo and fluid dynamics to mycology. Anyone that has built a flow hood has done half the math here with a different application.

The most important factor to getting a monotub to work properly is adjusting the polyfill properly. Hole placement is really not that important as long as the holes aren't just at the top.

I don't quite see a point to stuffing the bottom holes as tight at possible as people say. I think as long as air doesn't flow in freely (no polyfill) then the stagnant air will pick up CO2 and gravity will pull it out the bottom. So it seems to me that light polyfill in both top and bottom holes would be the way to go. More airflow overall.

Pins need a wet substrate and humid microclimate not humid air. Casings are good for this, I like to sprinkle verm on top of my brf/coir subs to pick up excess water so there aren't any pools.

Dry air aids evaporation, monotubs can be fanned often should misted to keep the sub glistening. Definitely have a fan in the room, more airflow is always good and is ultimately controlled by polyfill.

There's some new info here about the fluid dynamics involved but as far as being applied to an actual grow, there's nothing I've concluded here that experienced growers didn't already know. But a nice summary for anyone looking to design their own tubs I think:mushroom2:

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Re: Themodynamic Analysis of Monotub Air Currents [Re: GreenRabbit]
    #21689939 - 05/17/15 09:57 AM (9 years, 7 months ago)

:vibin:


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Re: Themodynamic Analysis of Monotub Air Currents [Re: Buck513]
    #21690069 - 05/17/15 10:42 AM (9 years, 7 months ago)

A glorious conclusion then.
Thank you for the reply.
:thumbup:


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Re: Themodynamic Analysis of Monotub Air Currents [Re: Tmethyl]
    #21690744 - 05/17/15 02:12 PM (9 years, 7 months ago)

:nothingtoadd:


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Re: Themodynamic Analysis of Monotub Air Currents [Re: Dekozn]
    #21748443 - 06/01/15 01:13 PM (9 years, 7 months ago)

Just so much freaking information...

I am trying to figure out a how to on a mono and there are so many different ideas and ways....

Great writeup GR...


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Re: Themodynamic Analysis of Monotub Air Currents [Re: Fog1]
    #21748841 - 06/01/15 02:33 PM (9 years, 7 months ago)

Yea it did end up being quite long..

One thing I want to mention at this point is that rectangular holes are a bitch to stuff with polyfill. It doesn't get in the corners very well so I would recommend long elliptical holes. But if you have a hole saw just use that...

Also, don't make holes too low, keep them above 4 inches so you can have a 2-3" substrate in there.

Actually, my next idea is to make 6" high subs but keep them 2-4" thinner than the tub, so it would not cover the bottom at all. Just something I want to try.Side pins like a mother-fucker...

Edited by GreenRabbit (08/04/15 12:19 AM)

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Re: Themodynamic Analysis of Monotub Air Currents [Re: GreenRabbit]
    #22040143 - 08/03/15 10:59 PM (9 years, 5 months ago)

Sorry for jumping onto this thread so late, but I'm curious if changing the rectangular openings that are so hard to stuff with polyfil with a row of smaller holes might achieve the same results you were aiming to achieve. I know you were wanting to avoid using a hole-saw, but for those with access to one I think the following might work:



Four 2-in. diameter holes equals the area of one 4-in. diameter hole and they put the exiting air low to substrate, which I think has merit. Unless there there are serious issues I'm overlooking, I might try something along these lines.

Great analysis by the way, thanks for all the hard work.

NRustler

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Re: Themodynamic Analysis of Monotub Air Currents [Re: NRustler]
    #22040335 - 08/04/15 12:17 AM (9 years, 5 months ago)

Even though your surface area is the same, it might be harder for air to flow through the smaller holes still, since air will flow faster in the center.
I would expect faster airflow through the larger hole even with equivalent surface area due to the friction from the walls of the holes.
(Your overall circumference is higher, therefore more surface friction.)
Of course, this can all be balanced by properly stuffing the holes, so for that reason I would prefer having less holes to stuff.

To make my most recent minimono, I used a 4" diameter metal can like people around here have mentioned, except I bent the can so that the hole was in the shape of an eye. (I'll add a pic soon)

The eye shape allows for a lower air exit point compared to the round circle. The max air velocity is still in the middle, but you are able to place the entire hole an inch lower.

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Re: Themodynamic Analysis of Monotub Air Currents [Re: GreenRabbit]
    #22040538 - 08/04/15 02:38 AM (9 years, 5 months ago)

Nice write up. I will definitely give this a more thorough read when I have a few minutes.

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Re: Themodynamic Analysis of Monotub Air Currents [Re: insanemike]
    #22042458 - 08/04/15 02:43 PM (9 years, 5 months ago)

Quote:

Even though your surface area is the same, it might be harder for air to flow through the smaller holes still, since air will flow faster in the center.
I would expect faster airflow through the larger hole even with equivalent surface area due to the friction from the walls of the holes.
(Your overall circumference is higher, therefore more surface friction.)




It's always something :crazy: ... Thanks for pointing out the increased circumference/area ratio. My combined circumference would be double a single hole of the same area, whereas the perimeter of your rectangular hole was only about 31% greater (I'll wait until you post pics before taking the integral to find the circumference of the ellipse :wink: ).


Edited by GreenRabbit (08/04/15 02:57 PM)

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Re: Themodynamic Analysis of Monotub Air Currents [Re: NRustler]
    #22042521 - 08/04/15 02:58 PM (9 years, 5 months ago)

lol sorry didn't mean to edit your post. I switched it back, no edit has been made...

Perimeter of the ellipse is the same. I used a bent can, so it is using the same length of can that makes the circle, just in a different shape.

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Re: Themodynamic Analysis of Monotub Air Currents [Re: GreenRabbit]
    #22042717 - 08/04/15 03:41 PM (9 years, 5 months ago)

No worries - I wasn't at my computer to even notice, lol. You're right about the circumference of the ellipse; I was just joking about needing to take an integral (and not a very friendly integral, at that) to find the circumference of an ellipse. I'd actually forgotten that, but I'm sure I saw it in a calculus class long, long ago. Based on the thoroughness of your air flow analysis I'm guessing you saw a semester or two (or three or four...) of calculus and beyond at some point in time.


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Re: Themodynamic Analysis of Monotub Air Currents [Re: NRustler]
    #22182967 - 09/03/15 12:56 PM (9 years, 4 months ago)

thank you for this write up. i'll have to re-read this again but still learned something through my first read

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Re: Themodynamic Analysis of Monotub Air Currents [Re: GreenRabbit]
    #22826725 - 01/26/16 01:08 PM (8 years, 11 months ago)

Added Pressure and Temperature sections and made corrections to other sections.

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Re: Themodynamic Analysis of Monotub Air Currents [Re: GreenRabbit]
    #22828738 - 01/26/16 10:07 PM (8 years, 11 months ago)

I have to say, you really put a lot of hard work into this. This thread is very well organized and easy to follow. Your research and explanations of each dynamic are impeccable. Keep up the awesome work that you are doing.

Have you tested air quality yet?

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Re: Themodynamic Analysis of Monotub Air Currents [Re: insanemike]
    #22832014 - 01/27/16 08:38 PM (8 years, 11 months ago)

Quote:

insanemike said:
Have you tested air quality yet?




You mean humidity? No. Analog hygros are the best way to do that, haven't ran a monotub in a while. Got jars on the way though, I'll add more pictures when that gets going.

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Re: Themodynamic Analysis of Monotub Air Currents [Re: GreenRabbit]
    #22832062 - 01/27/16 08:53 PM (8 years, 11 months ago)

No. Not humidity. I'm talking ppm oxygen and co2 levels. I'm talking cellular respiration. The idea of the perfect monotub would be to get as close to atmospheric oxygen levels without drying out the growing chamber. Or to just know at what levels a typical monotub sustains and how these levels change hour by hour, day by day and over the course of the monotub run.

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Re: Themodynamic Analysis of Monotub Air Currents [Re: insanemike]
    #22832366 - 01/27/16 10:13 PM (8 years, 11 months ago)

:eek:


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Re: Themodynamic Analysis of Monotub Air Currents [Re: insanemike]
    #22848036 - 01/31/16 07:54 PM (8 years, 11 months ago)

Quote:

insanemike said:
No. Not humidity. I'm talking ppm oxygen and co2 levels. I'm talking cellular respiration. The idea of the perfect monotub would be to get as close to atmospheric oxygen levels without drying out the growing chamber. Or to just know at what levels a typical monotub sustains and how these levels change hour by hour, day by day and over the course of the monotub run.




Well, I would love to be able to test that, but I have no equipment for testing air quality, and I'm guessing separate detectors would be needed for each molecule. That, or a Gas Chromatography machine, which I don't have access to, and they cost about $7000 soo..
Best advice I can offer as far as air quality goes is to have as much FAE as possible (and fresh ambient air), just don't let your sub dry out.
Some of the large grow rooms I have seen would have stale ambient air, but most of them have some sort of ventilation and filtration system to deal with that.
For a small time grower, opening a window once a day would be fine.

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Re: Themodynamic Analysis of Monotub Air Currents (moved) [Re: GreenRabbit]
    #22921698 - 02/19/16 12:17 AM (8 years, 10 months ago)

This thread was moved from the user's journal.

Reason:
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Re: Themodynamic Analysis of Monotub Air Currents (moved) [Re: cronicr]
    #22921728 - 02/19/16 12:36 AM (8 years, 10 months ago)

Wooooow. Nice write up.

I was thinking about rectangles too.
But using ironed poly filters. Figured it would be easy to dial in by simply changing the amount the hole (slot?) is blocked with an over lapping solid door-type-thing.

Thoughts?

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Re: Themodynamic Analysis of Monotub Air Currents (moved) [Re: MajorDick]
    #22921742 - 02/19/16 12:44 AM (8 years, 10 months ago)

You could do that..
I would recommend against rectangles though after trying them.
They make stuffing the holes annoying; the corners are hard to get right.

I much prefer an eye shaped hole.
Take the can you would use to make the normal round hole, and bend it into a eye shape.
This will give you the lower vertical center, and is much easier to stuff evenly with polyfill.
Honestly though, I doubt there is a difference between this and the standard monotub tech.

This write-up isn't meant to promote new ideas.
It is a mathematical analysis and the main purpose was to refute the idea of air going in one way out the other.

However, the conclusion was that air will go in either direction, the main deciding factor being how much water is in the substrate.

If there is enough heat and humidity, air will go in through the bottom holes and out the top holes.
If the tub dries out though, and the air is allowed to build CO2 without the addition of water vapor, density will increase the flow will reverse.
In through top holes, out through bottom.

And as mention in the OP, if there is no stuffing in the top holes at all, this entire analysis means nothing to that specific system.
Due to this, I prefer to have monotubs with minimal stuffing in the top holes, and I never have a monotub with empty top holes.

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Re: Themodynamic Analysis of Monotub Air Currents (moved) [Re: GreenRabbit]
    #22921755 - 02/19/16 12:52 AM (8 years, 10 months ago)

I think you sum it up pretty good by calling it an "air mixing chamber"

The idea with the flat ironed poly filters is too eliminate the need for stuffing all together. No reason it can't be put over any shape hole... Or array of holes....

You've really laid good ground work for experimentation and development.

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Re: Themodynamic Analysis of Monotub Air Currents (moved) [Re: MajorDick]
    #22921760 - 02/19/16 12:55 AM (8 years, 10 months ago)

Ironed polyfill is stuffing...
I wouldn't bother with an array of holes.
Theoretically it would be the same, just really annoying to stuff.

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Re: Themodynamic Analysis of Monotub Air Currents (moved) [Re: GreenRabbit]
    #22921789 - 02/19/16 01:08 AM (8 years, 10 months ago)

https://www.shroomery.org/forums/showflat.php/Number/20115107

Idk if we're thinking the same thing here..

Anyways. My daydream is more related to crafting a cabinet that would function like a stack of monos. Using spawn trays. Or i guess more like a stack of home fabricated tubs. http://m.instructables.com/id/HomemadePlastic/

But now i feel like I'm derailing your awesome thread so i digress.

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Re: Themodynamic Analysis of Monotub Air Currents (moved) [Re: MajorDick]
    #22921821 - 02/19/16 01:36 AM (8 years, 10 months ago)

We're talking about the same thing.
I consider ironed polyfil stuffing... Same material, same idea..
A cabinet full of trays sounds like a greenhouse.

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Re: Themodynamic Analysis of Monotub Air Currents (moved) [Re: GreenRabbit]
    #22921826 - 02/19/16 01:40 AM (8 years, 10 months ago)

Dude- thank you so much. This is amazing and seriously I value al the input you've had in this community.

"I've got to science the shit out of this"

Mycology has given me so much, and you, along with others in this community have made helped to make it so.


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Re: Themodynamic Analysis of Monotub Air Currents (moved) [Re: TravelAgency]
    #22921829 - 02/19/16 01:43 AM (8 years, 10 months ago)

Quote:

TravelAgency said:
"I've got to science the shit out of this"




Thanks.
Lol, some people waste their time designing automated monotubs that will never work.
I spend my time analyzing systems that work to understand why.

Fuck, I should be studying nuclear reactor thermal hydraulics...
I wrote this when I was studying thermodynamics..
I'm well beyond that and am still not studying.
ahaha. Fuck school. I just want my degree.
Gimme goddamit...

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Re: Themodynamic Analysis of Monotub Air Currents (moved) [Re: GreenRabbit]
    #22921839 - 02/19/16 01:49 AM (8 years, 10 months ago)

Quote:

GreenRabbit said:
Quote:

TravelAgency said:
"I've got to science the shit out of this"




Thanks.
Lol, some people waste their time designing automated monotubs that will never work.
I spend my time analyzing systems that work to understand why.

Fuck, I should be studying nuclear reactor thermal hydraulics...
I wrote this when I was studying thermodynamics..
I'm well beyond that and am still not studying.
ahaha. Fuck school. I just want my degree.
Gimme goddamit...




I understand but from a completely other perspective. This hobby has truly brought out the best science mind in me- my parents always thought I'd become a scientist- but I don't think they had a clue as to what kind

And hey, seriously and honestly- mycology is more the future than nuclear power is. From cleaning up oil spills, to creating vaccines, to providing cues, to tasting delicious, to parting from yourself, to experiencing something more spiritual than all the time you've spent in church combined- mycology is the way of the future- and I hope I can help.


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Re: Themodynamic Analysis of Monotub Air Currents (moved) [Re: GreenRabbit]
    #22921846 - 02/19/16 01:59 AM (8 years, 10 months ago)

Quote:

GreenRabbit said:
A cabinet full of trays sounds like a greenhouse.




...kinda... But more like a stack of decorated monos... That's easy to disguise, hide or cover when needed.

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Re: Themodynamic Analysis of Monotub Air Currents (moved) [Re: MajorDick]
    #22921904 - 02/19/16 03:17 AM (8 years, 10 months ago)

Quote:

TravelAgency said:

I understand but from a completely other perspective. This hobby has truly brought out the best science mind in me- my parents always thought I'd become a scientist- but I don't think they had a clue as to what kind

And hey, seriously and honestly- mycology is more the future than nuclear power is.




No, it's not. I'm rarely so blunt about directly refuting someones statements haha.
There is nothing more relevant to the future than nuclear power.

Quote:

TravelAgency said:From cleaning up oil spill



Mycelium and mushrooms are slow and inefficient at this...

Quote:

TravelAgency said:creating vaccines



Please elaborate

Quote:

TravelAgency said: to providing cues



Lol what?

Quote:

TravelAgency said: to tasting delicious, to parting from yourself, to experiencing something more spiritual than all the time you've spent in church combined- mycology is the way of the future- and I hope I can help.




And you lost me.. And I've spend more time on psychedelics than in church haha.
I don't see how mycology is advancing humanity in general.

Quote:

MajorDick said:
Quote:

GreenRabbit said:
A cabinet full of trays sounds like a greenhouse.




...kinda... But more like a stack of decorated monos... That's easy to disguise, hide or cover when needed.




Ok... But covering monotubs is effectively choking them off from FAE. That's fine if it is for a short period of time, but why not just have them in a room you keep people you don't trust out of?
This also begs the questions, why do you need to hide anything? Do you have people you don't trust in your house?
I mean... I know you aren't growing out of your parent's house haha.

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Re: Themodynamic Analysis of Monotub Air Currents (moved) [Re: GreenRabbit]
    #22921916 - 02/19/16 03:33 AM (8 years, 10 months ago)

Dammit! I was hoping for "how do disguise a monotub".. I was gonna say "fake glasses and a rubber nose".

...reasons... That's why.

I got to have a dedicated room once. It was pretty cool. I just don't like explaining that stuff to everyone who sees it.

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Re: Themodynamic Analysis of Monotub Air Currents (moved) [Re: MajorDick]
    #22921972 - 02/19/16 04:51 AM (8 years, 10 months ago)



This SGFC was kept under a bed and worked well for my first grows. My roommates didn't even know it was there, and I had apartment maintenance coming in randomly (but not unannounced) and was never worried. I just turned off the light when they came so that there wasn't a bright ass light coming out from under my bed.
Air flow isn't ideal in any situation where you are trying to hide a tub.

Just keep the tubs in your bedroom if you have nowhere else, and keep people in your living room, out of your bedroom.

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Re: Themodynamic Analysis of Monotub Air Currents (moved) [Re: GreenRabbit]
    #22921985 - 02/19/16 05:13 AM (8 years, 10 months ago)

Oh fuf. I haven't fruited atop perlite since ought nine. Sgfg had been developed.. But i didn't know cuz i didn't have an internet connection at the time.

I try to do exactly what you said, but sometimes other things happen. Explaining it to girls is mostly what i try to avoid... Especially in the bedroom.

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Re: Themodynamic Analysis of Monotub Air Currents (moved) [Re: MajorDick]
    #22922046 - 02/19/16 06:09 AM (8 years, 10 months ago)

This is an awesome write up, I kind of wish you applied this to a hypothesis on how to make a better design that pushed the envelope a little more. It seems though after your analysis that the square holes is the only major change you would make to the standard mono design, which makes a lot of sense. Simplicity is key and the mono is already a pretty great design I guess!

So what I got out of this very informative post:

1. Rectangular holes have the ability to control airflow out of the bottom holes at a more consistent level. This could create a more ideal air dynamic that would be most beneficial for the shrooms. This means however that holes on top don't have to be square, they could be oblong star shaped. Whatever. But why have just 2 large points of entry for fresh air? What if you now put a line of smaller holes, at let's say for arguments sake, 3.5" apart, lining the very top of your mono single-file. To attempt to create a more even airflow from top to bottom, instead of just having air coming from 2 points and creating stale air points on the sub surface because of uneven airflow.

2. That the fan can be your enemy in terms of air entering the bottom holes. I think I had this problem with one of my minis, now that I think about it. Fan was pointed at a wall to disperse its trajectory, but in a way that it could have bounced and had a clear path to those bottom holes in this mono. You can see which side the fan was on and how nothing wanted to grow there.


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Re: Themodynamic Analysis of Monotub Air Currents (moved) [Re: SloppyJoseph]
    #22922065 - 02/19/16 06:22 AM (8 years, 10 months ago)

1. I much prefer an eye shaped hole.
Take the can you would use to make the normal round hole, and bend it into a eye shape.
This will give you the lower vertical center, and is much easier to stuff evenly with polyfill.
Rectanglular holes are annoying to stuff. Polyfill tends to leave gaps in the corners which leak air freely.

2. Fans shouldn't be pushing air through any holes. They shouldn't be pointed directly at the tub at all. The point of the fan is to circulate the ambient air.
Let the pressure differential control your air flow.
You control the pressure differential by stuffing the hole appropriately.

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Re: Themodynamic Analysis of Monotub Air Currents (moved) [Re: GreenRabbit]
    #22922087 - 02/19/16 06:30 AM (8 years, 10 months ago)

The concept of the fan the issue, I get that it should only be used to create air movement indirectly. But I think the way I had it positioned it might have affected the tub adversely. So a physical inability to see the issue with the fans position was the problem I think, which was giving my mushrooms some fuzzy feet.


But what do you think about a series of smaller holes lining the top of the tub?


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Re: Themodynamic Analysis of Monotub Air Currents (moved) [Re: SloppyJoseph]
    #22922128 - 02/19/16 06:45 AM (8 years, 10 months ago)

Fuzzy feet are due to lack of FAE, your issue was more likely stuffing that was too tight, rather than fan placement.

A series of smaller holes would be fine, but more annoying to stuff.

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Re: Themodynamic Analysis of Monotub Air Currents (moved) [Re: GreenRabbit]
    #22922171 - 02/19/16 07:03 AM (8 years, 10 months ago)

:popcorn: One of my favorite threads. Thanks


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Re: Themodynamic Analysis of Monotub Air Currents (moved) [Re: GreenRabbit]
    #22922180 - 02/19/16 07:06 AM (8 years, 10 months ago)

FAE is fresh air exchange, and fresh air can't exchange properly when fresh air is coming through both holes, right? So the 2 aren't coinciding in this instance?


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Re: Themodynamic Analysis of Monotub Air Currents (moved) [Re: GreenRabbit]
    #22922251 - 02/19/16 07:59 AM (8 years, 10 months ago)



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Re: Themodynamic Analysis of Monotub Air Currents (moved) [Re: SloppyJoseph]
    #22922564 - 02/19/16 10:32 AM (8 years, 10 months ago)

Quote:

SloppyJoseph said:
FAE is fresh air exchange, and fresh air can't exchange properly when fresh air is coming through both holes, right? So the 2 aren't coinciding in this instance?




Your wording is confusing me a bit.. Air will flow either up or down, depending on humidity and CO2 concentration.
It does not flow in or out through both the top and bottom holes. If it did that, then it would have to go through one side (left or right) and out the other.
The only time this will happen is if air is forced into one side (fan blowing directly at polyfill)

The pressure differential is immeasurable. It is minute, and constantly being forced into equilibrium.
The only time a monotub will be at true equilibrium with ambient temperature and pressure is when a substrate is dry and dead.
As long as there is heat being generated or water is being evaporated (it's almost always both) there will be a differential that causes air to travel either up or down.

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Re: Themodynamic Analysis of Monotub Air Currents (moved) [Re: GreenRabbit]
    #22925163 - 02/20/16 12:15 AM (8 years, 10 months ago)

Good explanation, thanks GreenRabbit


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Re: Themodynamic Analysis of Monotub Air Currents (moved) [Re: TravelAgency]
    #22964752 - 03/02/16 08:52 AM (8 years, 10 months ago)

What about monotube without CO2? If you pour just some warm water in it, it will also "work" over some time, after water cools down. You'll be able to see downward dry traces from upper holes. Why? Why air density in monotube without CO2 is higher than ambient? Or it's not? What's the physics without CO2 and warm substrate?

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Re: Themodynamic Analysis of Monotub Air Currents (moved) [Re: disassembler]
    #22965212 - 03/02/16 11:30 AM (8 years, 10 months ago)

Quote:

disassembler said:
What about monotube without CO2?



That isn't possible, unless you have an O2 as your air supply, and nobody does that.

Quote:

disassembler said:
If you pour just some warm water in it, it will also "work" over some time, after water cools down. You'll be able to see downward dry traces from upper holes.



I'm not sure what you are talking about, and I see no reason why you would add warm  water.

Quote:

disassembler said:
Why? Why air density in monotube without CO2 is higher than ambient? Or it's not?



It's not. CO2 is more dense, if you fan less or have low airflow, CO2 concentrations will increase, density will increase, and you have a higher chance of airflow reversing.

Quote:

disassembler said:
What's the physics without CO2 and warm substrate?



Without CO2 makes no sense... The substrate is already warm, if you mean without a warm substrate, that would only happen if your substrate is dead and no longer producing heat.

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Re: Themodynamic Analysis of Monotub Air Currents (moved) [Re: GreenRabbit]
    #22968044 - 03/03/16 01:04 AM (8 years, 10 months ago)

Sorry for my bad English.

Quote:

GreenRabbit said:
Quote:

disassembler said:
If you pour just some warm water in it, it will also "work" over some time, after water cools down. You'll be able to see downward dry traces from upper holes.



I'm not sure what you are talking about, and I see no reason why you would add warm  water.




To check if monotube works. And yes, it works. Even without CO2 and substrate. There are downward air streams in monotube. And I don't understand why they are.

Edited by disassembler (03/03/16 01:05 AM)

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Re: Themodynamic Analysis of Monotub Air Currents (moved) [Re: disassembler]
    #22968382 - 03/03/16 05:47 AM (8 years, 10 months ago)

Quote:

disassembler said:
Sorry for my bad English.

Quote:

GreenRabbit said:
Quote:

disassembler said:
If you pour just some warm water in it, it will also "work" over some time, after water cools down. You'll be able to see downward dry traces from upper holes.



I'm not sure what you are talking about, and I see no reason why you would add warm  water.




To check if monotube works. And yes, it works. Even without CO2 and substrate. There are downward air streams in monotube. And I don't understand why they are.



You can expect updrafts in the center due to heat from the substrate and downdrafts on the sides of the tub do to cooling effect of the plastic. With adequate holes though it's mainly an updraft on the inside. You can get a good idea of how the currents are moving if your mushrooms start sporulating. Where there's an updraft you'll see spores landing on the cap of the mushroom dropping them.


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Re: Themodynamic Analysis of Monotub Air Currents (moved) [Re: Kizzle]
    #22968651 - 03/03/16 08:39 AM (8 years, 10 months ago)

Thank you Kizzle. I always fucking argued with Frank about this. Don't get me wrong, Frank could grow circles around me, but when we came to discussing that humid air rises up even though it's heavier he just wouldn't listen lol


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Re: Themodynamic Analysis of Monotub Air Currents (moved) [Re: maddchef]
    #22969012 - 03/03/16 10:55 AM (8 years, 10 months ago)

Quote:

disassembler said:
Sorry for my bad English.

Quote:

GreenRabbit said:
Quote:

disassembler said:
If you pour just some warm water in it, it will also "work" over some time, after water cools down. You'll be able to see downward dry traces from upper holes.



I'm not sure what you are talking about, and I see no reason why you would add warm  water.




To check if monotube works. And yes, it works. Even without CO2 and substrate. There are downward air streams in monotube. And I don't understand why they are.




Oh you meant without CO2 from the substrate. How do you know there are downward air streams if there is nothing in there?
As long as there is a difference in pressure caused by either humidity, temperature, or CO2 increase there will, be some airflow.

Quote:

Kizzle said:
You can expect updrafts in the center due to heat from the substrate and downdrafts on the sides of the tub do to cooling effect of the plastic. With adequate holes though it's mainly an updraft on the inside. You can get a good idea of how the currents are moving if your mushrooms start sporulating. Where there's an updraft you'll see spores landing on the cap of the mushroom dropping them.




What you are describing is a convection current, and I don't believe they exist in a monotub. I don't think air is circling around like you say.
I think the updrafts are caused by air leaving the tub and air being pulled in the bottom holes.
I've been looking for photos of grows with good tracks from spore deposits and I've found many with mushrooms in the corners with spores on them, suggesting a updraft throughout the whole tub, not just in the center.

Quote:

maddchef said:
Thank you Kizzle. I always fucking argued with Frank about this. Don't get me wrong, Frank could grow circles around me, but when we came to discussing that humid air rises up even though it's heavier he just wouldn't listen lol




That's because you are wrong. Humid air is lighter than dry air. Read the OP....

Edited by GreenRabbit (03/03/16 10:56 AM)

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Re: Themodynamic Analysis of Monotub Air Currents [Re: GreenRabbit]
    #22969093 - 03/03/16 11:18 AM (8 years, 10 months ago)

Quote:

GreenRabbit said:
If the bottom holes are stuffed tight, there should be no air going in through the bottom holes. If the top holes are stuffed very loosely, then yes, air will travel in both directions.




Some air does come in through the tightly stuffed bottom holes. That's why you get a dry ring. But, most of the air exchange is through the top. As the air flows out the top, somewhat of a vacuum is created that pulls dry air in the bottom. The higher the flow rate, the bigger the dry ring gets. Because the bottom holes are close to the substrate, slowing the flow coming in helps prevent the substrate surface from drying out.


Quote:

GreenRabbit said:
Now, if the top holes are stuffed loosely, but still enough to stem free air travel, then the air would actually be sucked in the top holes as air is pulled out the bottom by gravity.




There's no stuffing scenario that will cause air to be sucked in to the top. Air coming in the top is because of natural currents and drafts in the room. The only way to get air to suck in through the top holes is to attach a device that sucks or pushes air out the bottom that causes enough vacuum to reverse the natural rise of heat and water vapor. If the holes on top are loose and the bottom is tight, a fan in the room pushes more air through the top than normal, but the tub is not sucking in, the air is being pushed in and most of it will still flow right back out the top top because that would still be the path of least resistance for the added internal pressure caused by the fan.


Quote:

GreenRabbit said:This is why monotubs can be on the ground, and SGFCs need to be raised. And SGFC works in a totally different way, so air flows upwards instead.




Monos can be on the ground because there are no holes on the very bottom. The laws of fluid and aerodynamics don't change between a mono and SGFC. Air in both naturally flows upwards. If you block the bottom of a SGFC, the flow slows just like stuffing the bottom holes of a mono. The principles of both are essentially the same. Bulk substrate in a mono just provides enough evaporation and heat to create the flow need for adequate FAE on its own and a SGFC needs help from perlite. The difference in design is essentially due to using bulk substrate vs wet perlite and their abilities to create flow.

Quote:

GreenRabbit said:Hot humid air rises, sure, but the air in the tub isn't the same chemical composition as the incoming air. It mixes and on average is more dense than the ambient air. Refer to Air Density Calculation for densities of different compositions of air.




The difference in chemical make up is not enough to counter the forces created by heat and water vapor's natural inclination to rise. Yes, CO2 is more dense than the air we breath, but the tiniest amount of turbulence will mix it with the surrounding air and the amount that is produced in a mono is not enough to counter the rise of heat and water vapor. All the chemicals created get mixed in with the warm humid air and is carried out the top. Math doesn't tell the whole story when it leaves out too many variables.

I didn't read the entire OP, but it looks pretty in depth.


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Re: Themodynamic Analysis of Monotub Air Currents [Re: SpitballJedi]
    #22969137 - 03/03/16 11:29 AM (8 years, 10 months ago)

Quote:

SpitballJedi said:
Some air does come in through the tightly stuffed bottom holes. That's why you get a dry ring. But, most of the air exchange is through the top. As the air flows out the top, somewhat of a vacuum is created that pulls dry air in the bottom. The higher the flow rate, the bigger the dry ring gets. Because the bottom holes are close to the substrate, slowing the flow coming in helps prevent the substrate surface from drying out.




The same amount of air overall is going in the bottom holes as it is going out the top holes. Due to the larger size of the bottom holes, the air will flow through them slower.

Quote:

GreenRabbit said:
Now, if the top holes are stuffed loosely, but still enough to stem free air travel, then the air would actually be sucked in the top holes as air is pulled out the bottom by gravity.




Quote:

SpitballJedi said:
There's no stuffing scenario that will cause air to be sucked in to the top. Air coming in the top is because of natural currents and drafts in the room. The only way to get air to suck in through the top holes is to attach a device that sucks or pushes air out the bottom that causes enough vacuum to reverse the natural rise of heat and water vapor. If the holes on top are loose and the bottom is tight, a fan in the room pushes more air through the top than normal, but the tub is not sucking in, the air is being pushed in and most of it will still flow right back out the top top because that would still be the path of least resistance for the added internal pressure caused by the fan.




Yea, I should edit the OP. Air flow can reverse but it has nothing to do with stuffing. It will reverse if the sub dries out and humidity drops.

Quote:

GreenRabbit said:This is why monotubs can be on the ground, and SGFCs need to be raised. And SGFC works in a totally different way, so air flows upwards instead.




Quote:

SpitballJedi said:
Monos can be on the ground because there are no holes on the very bottom. The laws of fluid and aerodynamics don't change between a mono and SGFC. Air in both naturally flows upwards. If you block the bottom of a SGFC, the flow slows just like stuffing the bottom holes of a mono. The principles of both are essentially the same. Bulk substrate in a mono just provides enough evaporation and heat to create the flow need for adequate FAE on its own and a SGFC needs help from perlite. The difference in design is essentially due to using bulk substrate vs wet perlite and their abilities to create flow.




Another edit to be made..

Quote:

GreenRabbit said:Hot humid air rises, sure, but the air in the tub isn't the same chemical composition as the incoming air. It mixes and on average is more dense than the ambient air. Refer to Air Density Calculation for densities of different compositions of air.




Quote:

SpitballJedi said:
The difference in chemical make up is not enough to counter the forces created by heat and water vapor's natural inclination to rise. Yes, CO2 is more dense than the air we breath, but the tiniest amount of turbulence will mix it with the surrounding air and the amount that is produced in a mono is not enough to counter the rise of heat and water vapor. All the chemicals created get mixed in with the warm humid air and is carried out the top. Math doesn't tell the whole story when it leaves out too many variables.




I agree, the effect of the humid air is much greater than that of the additional CO2. As a result, the air will be going upwards until the sub dries out or is spent and dies. The heat generated by the substrate is the most important part. Once that is gone, you lose the ability to evaporate water and heat the air in the monotub, and the air flow can reverse.
In any properly functioning monotub, the airflow should be upward.

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Re: Themodynamic Analysis of Monotub Air Currents [Re: GreenRabbit]
    #22969317 - 03/03/16 12:29 PM (8 years, 10 months ago)

:popcorn:

Thanks for the write up GreenRabbit!


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Re: Themodynamic Analysis of Monotub Air Currents [Re: GreenRabbit]
    #22969357 - 03/03/16 12:46 PM (8 years, 10 months ago)

Quote:

GreenRabbit said:
Quote:

SpitballJedi said:
Some air does come in through the tightly stuffed bottom holes. That's why you get a dry ring. But, most of the air exchange is through the top. As the air flows out the top, somewhat of a vacuum is created that pulls dry air in the bottom. The higher the flow rate, the bigger the dry ring gets. Because the bottom holes are close to the substrate, slowing the flow coming in helps prevent the substrate surface from drying out.




The same amount of air overall is going in the bottom holes as it is going out the top holes. Due to the larger size of the bottom holes, the air will flow through them slower.

The top and bottom holes are the same size on most peoples monotubs, including mine and it's the tightness of the poly that restricts the flow and more air can flow through larger holes if otherwise not covered or stuffed. In a vacuum or still air room, then yes, the air coming in the mono's bottom would likely equal the flow going out the top due to simple displacement. But, most grow rooms we have at home are drafty and the poly plays a role in how much additional air can move in either direction of any given hole. Air will follows the path of least resistance and/or greater force.

Quote:

GreenRabbit said:
Now, if the top holes are stuffed loosely, but still enough to stem free air travel, then the air would actually be sucked in the top holes as air is pulled out the bottom by gravity.




Quote:

SpitballJedi said:
There's no stuffing scenario that will cause air to be sucked in to the top. Air coming in the top is because of natural currents and drafts in the room. The only way to get air to suck in through the top holes is to attach a device that sucks or pushes air out the bottom that causes enough vacuum to reverse the natural rise of heat and water vapor. If the holes on top are loose and the bottom is tight, a fan in the room pushes more air through the top than normal, but the tub is not sucking in, the air is being pushed in and most of it will still flow right back out the top top because that would still be the path of least resistance for the added internal pressure caused by the fan.




Yea, I should edit the OP. Air flow can reverse but it has nothing to do with stuffing. It will reverse if the sub dries out and humidity drops.

Actually, it can have a lot to do with the stuffing in a drafty room. The poly restricts flow in either direction. No poly on top means more air can be blown in. Stuffed tightly and less air can be blown in. The natural drafts in a room are often over looked when thinking about the dynamics of an FC.

Quote:

GreenRabbit said:This is why monotubs can be on the ground, and SGFCs need to be raised. And SGFC works in a totally different way, so air flows upwards instead.




Quote:

GreenRabbit said:Hot humid air rises, sure, but the air in the tub isn't the same chemical composition as the incoming air. It mixes and on average is more dense than the ambient air. Refer to Air Density Calculation for densities of different compositions of air.




Quote:

SpitballJedi said:
The difference in chemical make up is not enough to counter the forces created by heat and water vapor's natural inclination to rise. Yes, CO2 is more dense than the air we breath, but the tiniest amount of turbulence will mix it with the surrounding air and the amount that is produced in a mono is not enough to counter the rise of heat and water vapor. All the chemicals created get mixed in with the warm humid air and is carried out the top. Math doesn't tell the whole story when it leaves out too many variables.




I agree, the effect of the humid air is much greater than that of the additional CO2. As a result, the air will be going upwards until the sub dries out or is spent and dies. The heat generated by the substrate is the most important part. Once that is gone, you lose the ability to evaporate water and heat the air in the monotub, and the air flow can reverse.
In any properly functioning monotub, the airflow should be upward.




yes, heat will definitely cause evaporation to happen faster, air to rise faster and also cause humid air to rise even faster. But, even if the temperatures are the same inside and outside, which doesn't happen in a live sub in a mono, water will still evaporate, albeit slower, and the vapor will still rise. The flow will not reverse unless some other force is added to make it happen, such as drafts or the sub becomes cooler than the room. But, once your sub is dead or spent, none of it really matters because you're done...lol.

As I mentioned earlier, natural drafts and currents in a room play a bigger role than some may realize. It may seem subtle, but so are the currents created in our FCs. Many of the ways we understand flows and dynamics don't take into consideration how much impact tiny changes around the tubs can have. The environment in a mono is pretty delicate and easily impacted. Just ask people who put fans in a room as a matter of coarse instead of waiting to see if they need one.

Your willingness to change your opinion in light of new information is a great credit to your character. We need more people like you. I still update my write-ups when I get new info or understanding and your openness to do the same is a great value often missed. There's not a word I wouldn't change in any write-up I've done if someone pointed out the error. Evolving the community begins with evolving our self.


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OfflineGreenRabbit
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Re: Themodynamic Analysis of Monotub Air Currents [Re: SpitballJedi]
    #22969696 - 03/03/16 02:51 PM (8 years, 10 months ago)

This analysis was written with the assumption that the top holes are stuffed.
I acknowledged that open top holes would allow air to flow in freely, and that is a system that is far too random to be able to analyze.
When a tub has no stuffing in the top holes, air doesn't have to flow up or down. It can flow in one top hole and out the other.

I like having smaller holes up top, but yea, if your holes are the same size, and there are 2 bottoms holes total then air velocities have to be equal, even with a difference in stuffing. Volume in always has to equal volume out.

As far as tubs being the same temperature as the ambient air, this is more likely to happen in a tub with light stuffing, which would allow more airflow, and less time for the air in the tub to warm up. I've run several tubs with thermometers inside the tub and sitting just outside, and have observed at least a 3-5 degree F difference at most times of the day. They tend to equal out in the middle of the day, then when the ambient air cools, the tub air holds its heat a little longer. The tub is almost always warmer than ambient at night.

Yes, water will still evaporate if the temperatures are equal, and the density of the tub air will be lower than that of the ambient, causing the rise.

I don't think we are disagreeing anywhere anymore.

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Re: Themodynamic Analysis of Monotub Air Currents [Re: GreenRabbit]
    #22970409 - 03/03/16 06:05 PM (8 years, 10 months ago)

:youthemandawg:


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Offlinecamplo
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Re: Themodynamic Analysis of Monotub Air Currents [Re: SpitballJedi]
    #22971195 - 03/03/16 09:30 PM (8 years, 10 months ago)

Quote:


Your willingness to change your opinion in light of new information is a great credit to your character. We need more people like you. I still update my write-ups when I get new info or understanding and your openness to do the same is a great value often missed. There's not a word I wouldn't change in any write-up I've done if someone pointed out the error. Evolving the community begins with evolving our self.



:glorious:  :dandyzoom:  :singletear:


I did come across this text book explanation in case its needed "You might also say: “Water is heavier than air.” True, a glass of liquid water weighs more than a glass filled only with air. But, humidity is water vapor, not liquid water, and water vapor molecules are lighter than the molecules of nitrogen and oxygen that make up approximately 99% of the atmosphere."


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Re: Themodynamic Analysis of Monotub Air Currents [Re: camplo]
    #22971207 - 03/03/16 09:38 PM (8 years, 10 months ago)

and warm humid air rises best. clouds how do they work

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Re: Themodynamic Analysis of Monotub Air Currents [Re: bodhisatta]
    #22971634 - 03/04/16 02:05 AM (8 years, 10 months ago)

Humid air: 0.804  kg/m3
Dry air  : 1.293  kg/m3

02      : 1.185  kg/m3
C02      : 1.98  kg/m3

Humid air is only 62% of the density of dry air.

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Re: Themodynamic Analysis of Monotub Air Currents [Re: GreenRabbit]
    #22974595 - 03/05/16 02:16 AM (8 years, 10 months ago)

Quote:

What you are describing is a convection current, and I don't believe they exist in a monotub. I don't think air is circling around like you say.
I think the updrafts are caused by air leaving the tub and air being pulled in the bottom holes.
I've been looking for photos of grows with good tracks from spore deposits and I've found many with mushrooms in the corners with spores on them, suggesting a updraft throughout the whole tub, not just in the center.



I said the air circles inside without the holes. Although the air is still circling with adequate holes and both the top and bottom, the downdraft will on the outside the tub and the updraft will be inside.

It makes sense to have the polyfil tighter on the top or bottom because for air to leave the top the same amount needs to be able to enter on the bottom. Pointing a fan at a hole has the same as simply making the hole bigger or loosening the polyfil in it.

Edited by Kizzle (03/05/16 02:51 AM)

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Re: Themodynamic Analysis of Monotub Air Currents [Re: GreenRabbit]
    #23392196 - 06/28/16 08:37 PM (8 years, 6 months ago)

Thank you so much for your analysis GR, I was just about to make a new mono and since it's a big 80 litre tub I wasn't sure what to do for holes. Your math work (which I had to read multiple times to understand) allowed me to scale up and decide the position for the openings effectively and efficiently.
I must say I also had much more fun applying your more complex design as opposed to just 4 holes.
Thanks again.


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Re: Themodynamic Analysis of Monotub Air Currents [Re: Captain67]
    #23392601 - 06/28/16 10:56 PM (8 years, 6 months ago)

Thanks for reading.
You might want to use a few smaller holes and spread them out. Bigger holes are harder to stuff.


I don't use polyfill anymore.



The holes can be taped up if it dries out too quickly, but usually I just fruit them open and mist them when they dry out.

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Re: Themodynamic Analysis of Monotub Air Currents [Re: GreenRabbit]
    #23392735 - 06/29/16 12:05 AM (8 years, 6 months ago)

I've been trying to figure out a good filter media to replace the polyfil. Faux silk made from polyester seems like it might work if layered and crosshatched. It'd be flat instead of balled. The threads are very fine. The part I can't work out is how many layers to put on top and bottom to make an equivalent to the "dialed in" density used in Frank's tek.


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OfflineTheBlackCat
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Re: Thermodynamic Analysis of Monotub Air Currents [Re: GreenRabbit]
    #24389791 - 06/08/17 10:53 PM (7 years, 7 months ago)

:takingnotes:


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Offlinechejacho
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Re: Thermodynamic Analysis of Monotub Air Currents [Re: GreenRabbit]
    #25480213 - 09/22/18 08:32 AM (6 years, 3 months ago)

!!!!!!! master. thx

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OfflineLangfordjoey
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Re: Themodynamic Analysis of Monotub Air Currents [Re: GreenRabbit]
    #26639946 - 04/30/20 08:56 PM (4 years, 8 months ago)

Wow! Awesome read! Thanks for this.  I'm a super noob and just figuring out my mono systems. Having a little bit of paralysis by analysis.

After so many years do you mind me asking how you currently design your monos? I'm thinking of doing the rectangular holes on top and bottom with  layered micropore tape to adjusted internal climate.

Thanks!

-J

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