Difference between revisions of "Solar powered refrigeration/dehumidification"

Jump to navigation Jump to search
Line 54: Line 54:
[http://www.nrel.gov/docs/fy11osti/49722.pdf DevAPP nrel report - desiccant evap cooler under vacuum]
[http://www.nrel.gov/docs/fy11osti/49722.pdf DevAPP nrel report - desiccant evap cooler under vacuum]
[[File:devapp.pdf local copy of devapp]]

Latest revision as of 12:04, 10 April 2015



I beleive the above system is doable for dehumdification - open A,A' and close B at night and turn on fan, drying air past CaCl2 hygroscopic desiccant. During day, close A,A' and open B, allowing sun to boil water off desiccant. See graph below showing 180C is enough for boiling.



Would like to do simple solar icemaker . One nagging question - is it 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-water phase diagram it seems that at 80wt% CaCl there is no liquid and thus nothing to evaporate.

Useful graph CaCl vapor pressure from the CaCl handbook

water phase diagram water phase diagram

Another more or less encouraging graph from here CaCl pressure

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

absorption refrigeration

raplin ice maker

ammonia absorption ice maker

army desiccant manual

solar air conditioning - EC manual

Delft U Solar AC report

solar icemaker

DevAPP nrel report - desiccant evap cooler under vacuum

Question eagle.gif