Looking for endothermic reactions

I am not having a lot of luck finding a list of reversible, endothermic reactions, that could be used in a cooler. The ones I am aware of:

• ammonia water - cools when exposed and separates when aqueous solution is heated to drive off ammonia.
• calcium chloride and water - like ammonia, fewer side effects like ammonia attacking some metals.

My goal is to find endothermic reactions that can be used for cooling using engine exhaust as the heat source that separates the reactants. The separated reactants still have to dump their heat to the atmosphere but then they can be recombined to cool a car cabin.

Water works until it freezes but this is OK as cooling is usually not required then. Just make sure the frozen water does not damage the storage container. But I suspect some alcohols might substitute for water without the freezing risk. But so far, Google is being too high level.

Suggestions on where to look?

Bob Wilson

 

Google scholar found a useful paper:

Reversible formation of alcohol solvates and their potential use for heat storage

Kathrin Korhammer1 • Judith Miha ́ly2 • Szabolcs Ba ́lint2,3 • La ́szlo ́ Trif2 • A ́da ́m Vass2 • Andra ́s Tompos2 • Em ́ılia Ta ́las2

Received: 22 May 2018 / Accepted: 14 February 2019 / Published online: 5 March 2019

Ó The Author(s) 2019
​

This answered my questions. It does cover both methanol and ethanol and compounds to use.

Bob Wilson

 

There is no free lunch. But I'm looking a using low quality solar heat and I'm not adverse to 'swamp cooling' without the humidity. I already live in Dixie.

Bob Wilson

 

I'm not adverse to hybrid cycles as long as they don't require the 1 kWh of my current A/C. To keep it in scale, 1 kWh is 4 miles of EV range and costs $0.12/kWh. Also, we have freezing temperatures in the winter which means avoiding freezing damage.

Bob Wilson

 

I was aware of the Peltier coolers but cost and efficiency put me off. In an ideal world, the only moving part would be the fan which might be accomplished by a set of high voltage grids. But again, cost and operational requirements to deal with 'field' conditions limit utility.

The paper provides excellent detail on how to replicate their results. But many practical problems limit this research to a general application. I certainly appreciate being exposed.

My goal is to look at space cooling that does not require the refrigeration cycle, grid electrical power. Ideally, it uses direct solar heating to drive the cooling system:

• photocell to refrigeration - high capital costs, even today's solar cells. Low operational cost but attractive as incident solar heating is somewhat mitigated by the photoelectric effect. I certainly admire solar shingles.
• thermal mass storage - my latitude often has good night temperatures that could cool a large mass providing cooling during the day. Examples include several tons of sand that cool night air blows through to provide cool air during the day. Another variation is earth heat sink best handled by two wells: one earth cooled water extraction and the other warm water insertion. But the high clay, costs, and local regulations makes this impractical. For now, I turn off refrigeration cooling once the night temperatures fall below 75 F and use window fans to cool the house interior.
• water evaporative cooling - requires low humidity as the dew point defines the lower temperature. Examples include the old 'swamp coolers' which worked fine except on high humidity days which are all too common in my area.
• endothermic chemical reactions - two chief approaches are CaCl{s} and ammonia absorption. Both can be driven by concentrated solar to separate the reactants. There are material challenges that modern PVC piping can handle the low temperature side. Of the two, CaCl{2} is most attractive as there is no gas leakage to worry about.
• bleed air - a solar concentrator could drive a heat engine that could also provide compression heated air. Run through a heat exchanger that could include water evaporation cooler, the compressed air could be expanded to provide cool air source. The past practice is to run the air through an expansion valve but from my thermodynamic class, I would prefer to pass the compressed, ambient cooled gas through a mechanical 'engine' that also drives the fan and/or helps the compressor. I happen to have a pair of two cylinder, two cycle engines that could easily meet these needs.

So the two leading approaches are CaCl{2} and bleed air driven by concentrated solar heating. I have not rulled out ammonia absorption. Regardless, there are non-trivial design issues to minimize capital costs but both appear to be practical approaches for this home experimenter.

Bob Wilson