RogueRose
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Dehydration chamber - methods to remove humidity from air
My project of making an old dishwasher into a dehydrator is coming along and I'm trying to figure out the best methods of drying the air.
The chamber is about 8ft^3 and temps will be up to 250F but most often probably 130-180F.
Option 1- Desiccant Chamber - a .35ft^3 chamber of desiccant like NaOH/KOH/CaCl2 or MgSO4 (anhyd). I can also use P2O5 but it would be pretty
expensive and I don't know how to regenerate it. This option seems plausible for drying smaller amounts (1-10lbs of material) and is good b/c it
retains heat that is input and recirculated.
Option 2 - Dehumidifier chamber / heat exchangers - Here the air would slowly circulate at like 1CFM (maybe less, IDK I have to see stats on
evaporation rates). It would pass into hot stage of heat exchanger (slow moving air here) then into something like a condenser with a center core
cooled as well, so inner & outer wall of condenser is cooled. This is 4 24" sections in parallel with a downward slope to allow water to drip
down. After the condenser it moves to the final drying chamber of one of the above mentioned desiccants. After final drying air moves into heat
exchanger to absorb any heat extracted from the first stage. Finally air moves into heater - (5, 10, 25, 50, 100, 200, 500 watt resistors digitally
controlled). The hardest part will be the programming of the controller and I have most parts already. Biggest issue is the temp of the fluid in the
condenser (should it be below freezing, at freezing or just above?)
Option 2 is much more involved but will be pretty slick when it is done and less work dealing with desiccants, which such to dry, break up and replace
in large quantities.
Which option would you choose? Any suggestions on what temp the cold fluid should be?
I'm kind of worried about the heat exchanger and am curious about using a similar setup for the dehumidifier. I have access to a lot of old PC
(mainly server) heat sinks which I could use with custom make square PVC tubing & JB Weld to seal the fluid under the heatsink from the air
chamber above. So the fluid would circulate under the heatsink and air on the fins. I could also do a double layer with the heatsink slightly offset
and upside down, to create more surface area to transfer heat.
I could do the same thing with the dehumidifier using the heat sinks instead of a condenser tube.
My plan for option 2 was to use round heatsinks (fins radiating from solid central core) with fluid running through the center for the 2 heat
exchangers. I would use 4-6 for each section of the exchanger.
[Edited on 19-6-2016 by RogueRose]
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NEMO-Chemistry
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Could you maybe have a guard tube (large) for a air inlet and use a vac pump now and then to remove wet air?
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PHILOU Zrealone
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From Merck Memento p14
Residual humidity in mg H2O /L of air after dehydration at 25°C:
White CuSO4 1,4
Molten ZnCl2 0.8
CaCl2 0.14-0.25
CaO 0.2
Molten NaOH 0.16
MgO 0.008
Anhydrous CaSO4 (plaster of Paris) 0.005
Concentrated H2SO4 (95-100%) 0.003-0.3
Dry Al2O3 0.003
Molten KOH 0.002
Silica gel (SiO2) 0.001
Anhydrous Mg(ClO4)2 0.0005
P2O5 below 0.000025
[Edited on 19-6-2016 by PHILOU Zrealone]
PH Z (PHILOU Zrealone)
"Physic is all what never works; Chemistry is all what stinks and explodes!"-"Life that deadly disease, sexually transmitted."(W.Allen)
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Dr.Bob
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The simplest, cheapest, way to dry large amounts of stuff that I know of is to just pour dryrite or similar materials into a Pyrex baking dish (I have
a few available which have been used in a lab, so I would not bake in them, but they are great for this use.) and warm it or pull a vacuum. The
entire plate of drying agent can be reactivated in a real oven or even better a vacuum oven. If you want really dry, do several cycles with cheap
dryiung agent first, then use P2O5 or the like as the final step, but using much P2O5 is a mess.
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PHILOU Zrealone
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Quote: Originally posted by Dr.Bob  | | The simplest, cheapest, way to dry large amounts of stuff that I know of is to just pour dryrite or similar materials into a Pyrex baking dish (I have
a few available which have been used in a lab, so I would not bake in them, but they are great for this use.) and warm it or pull a vacuum. The
entire plate of drying agent can be reactivated in a real oven or even better a vacuum oven. If you want really dry, do several cycles with cheap
dryiung agent first, then use P2O5 or the like as the final step, but using much P2O5 is a mess. |
I have one of those in Polycarbonate with silicone joint and anti return vacuum stopper.
If into the vacuum circuit you introduce a cold condenser (liquid N2 or safer dry ice/aceton), you may also dry sublimate (lyophilisate) the compound
you wish to dry...
PH Z (PHILOU Zrealone)
"Physic is all what never works; Chemistry is all what stinks and explodes!"-"Life that deadly disease, sexually transmitted."(W.Allen)
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