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GreenRabbit
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Thermodynamic Analysis of Monotub Air Currents 17
#21371089 - 03/06/15 02:11 PM (8 years, 10 months ago) |
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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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GreenRabbit
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Re: Mathematical Analysis of Monotub Ventilation [Re: GreenRabbit] 1
#21399118 - 03/12/15 06:12 PM (8 years, 10 months ago) |
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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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Abshroom
Cause he can


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Re: Mathematical Analysis of Monotub Ventilation [Re: GreenRabbit]
#21445525 - 03/23/15 01:10 AM (8 years, 10 months ago) |
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Mr. Alien
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Re: Mathematical Analysis of Monotub Ventilation [Re: GreenRabbit] 1
#21447337 - 03/23/15 01:45 PM (8 years, 10 months ago) |
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I don't undertand anything. But right on GR
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GreenRabbit
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Re: Mathematical Analysis of Monotub Ventilation [Re: Mr. Alien]
#21447374 - 03/23/15 01:54 PM (8 years, 10 months ago) |
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Quote:
Mr. Alien said: I don't undertand anything. But right on GR 
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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blindingleaf
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Re: Themodynamic Analysis of Monotub Air Currents [Re: GreenRabbit]
#21464558 - 03/27/15 08:31 AM (8 years, 9 months ago) |
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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!
-------------------- A few thoughts on cultivation MICROBIAL HUSBANDRY!!!! The whole is greater than the sum of its parts
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spacechildo
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Re: Themodynamic Analysis of Monotub Air Currents [Re: blindingleaf]
#21475732 - 03/29/15 06:36 PM (8 years, 9 months ago) |
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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 )
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GreenRabbit
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Re: Themodynamic Analysis of Monotub Air Currents [Re: spacechildo] 1
#21480218 - 03/30/15 05:07 PM (8 years, 9 months ago) |
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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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spacechildo
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Re: Themodynamic Analysis of Monotub Air Currents [Re: GreenRabbit]
#21480330 - 03/30/15 05:36 PM (8 years, 9 months ago) |
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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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GreenRabbit
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Re: Themodynamic Analysis of Monotub Air Currents [Re: spacechildo]
#21480477 - 03/30/15 06:21 PM (8 years, 9 months ago) |
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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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FarOutMushROOM4849
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Re: Themodynamic Analysis of Monotub Air Currents [Re: GreenRabbit]
#21550026 - 04/15/15 07:18 AM (8 years, 9 months ago) |
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Awesome write up. Been thinking about monos for awhile. Saved this thread.
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tedoro
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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
-------------------- -------------------- Deep pour soft agar plates-->bags of WBS-->Low Profile Monos Clean spawn thread | Put a thermometer on your PC
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tedoro
ToadStool Tender



Registered: 02/06/15
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Re: Themodynamic Analysis of Monotub Air Currents [Re: tedoro]
#21654285 - 05/08/15 05:25 PM (8 years, 8 months ago) |
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Ooooo, and I like the top lid vents. That works for me. I don't stack. And its totally higher.
t
-------------------- -------------------- Deep pour soft agar plates-->bags of WBS-->Low Profile Monos Clean spawn thread | Put a thermometer on your PC
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drfunk
Stranger
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Re: Themodynamic Analysis of Monotub Air Currents [Re: tedoro]
#21686964 - 05/16/15 12:43 PM (8 years, 8 months ago) |
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WOW, I have been looking for this thread for YEARS I just didn't know it
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GreenRabbit
Plutonium Pollinator



Registered: 04/28/13
Posts: 2,667
Loc: In a forest
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Re: Themodynamic Analysis of Monotub Air Currents [Re: tedoro]
#21687166 - 05/16/15 01:56 PM (8 years, 8 months ago) |
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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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Tmethyl
Smear in the shale


Registered: 07/16/12
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Re: Themodynamic Analysis of Monotub Air Currents [Re: GreenRabbit]
#21689512 - 05/17/15 06:24 AM (8 years, 8 months ago) |
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-------------------- ¯\_(ツ)_/¯
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Tmethyl
Smear in the shale


Registered: 07/16/12
Posts: 16,431
Loc: Florida
Last seen: 1 year, 4 months
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Re: Themodynamic Analysis of Monotub Air Currents [Re: Tmethyl]
#21689533 - 05/17/15 06:38 AM (8 years, 8 months ago) |
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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.
-------------------- ¯\_(ツ)_/¯
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GreenRabbit
Plutonium Pollinator



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Re: Themodynamic Analysis of Monotub Air Currents [Re: Tmethyl]
#21689632 - 05/17/15 07:42 AM (8 years, 8 months ago) |
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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
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Buck513

Registered: 04/17/14
Posts: 5,682
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Re: Themodynamic Analysis of Monotub Air Currents [Re: GreenRabbit]
#21689939 - 05/17/15 09:57 AM (8 years, 8 months ago) |
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-------------------- Fail to plan and you plan to fail. Enter the Ban Lottery
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Tmethyl
Smear in the shale


Registered: 07/16/12
Posts: 16,431
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Re: Themodynamic Analysis of Monotub Air Currents [Re: Buck513]
#21690069 - 05/17/15 10:42 AM (8 years, 8 months ago) |
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A glorious conclusion then. Thank you for the reply.
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