Solar powered refrigeration/dehumidification

Revision as of 08:11, 25 July 2012 by Jeremy.rutman (talk | contribs)
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We have a 1m x 2m x 0.5mm sst sheet with mirror finish for a parabolic trough absorber. Would like to do either icemaker or dehumidifier . One nagging question - is it not possible to avoid ammonia/libr by use of water and low pressure (e.g. 0.01atm)

Dror Zchori has been doing some expts hooking up his absorption refrigerator absorption refrigerator (normally gas powered) to a solar collector - he reached over 200C in oil in a vacuum tube collector at the focus of a ~20cm width ~180cm length parabolic trough but so far it doesnt seem to run the refrigerator

turnip based refrigeration

One thing to think about is that if we are using water at a gas pressure of 0.01atm, then what keeps the water in the salt from boiling? We need the salt to 'grab' the water enough that the vapor pressure of water at lets say 20C at night is less than 0.01atm. From the phase diagram CaCl phase diagram it seems that at 80wt% CaCl there is no liquid and thus nothing to evaporate.

Another more or less encouraging graph from here CaCl pressure

And another CaCl vapor pressure from the CaCl handbook

Another way to look at it is how much the boiling point of water is increased by solute addition; there is a formula 'Raoult's law' stating that the partial pressures are equal to the partial mass fractions; thus if there is 1/100 water in the salt then 1/100 of the water's normal vapor pressure is present. So if at 30C the vapor pressure of water is 0.04atm and we need 0.01atm then we can use 1 part water in 3 parts salt for 1/4 of 0.04atm or 0.01atm. The boiling point increase is quantified thru the Ebullioscopic constants ebulliosities - boiling point increase factor


video of CaCl2 absorbing water and deliquescing

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