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
Endothermic chemical reactions I think of first do not seem to be what you are looking for here. Break a cold pack (TM) and ammonium and nitrate ions go into solution and liquid temperature goes down. They 'like it' and you cannot to do things (inside your planned working space) to get them back out. I think you are looking for reversible phase changes that are 'endo' or 'exo' depending on direction. You already know several classic examples. New ones are surely underdevelopment, but googlish internet searches do not seem efficient without some, um, curation. I suggest (as usual) that you locate practitioners in the field and chat them up. Describing your proposed layout seems like a good idea. It is likely to be an inefficient way of fishing, but not time costly. A few things popped up Sustainability | Free Full-Text | Latent Heat Phase Change Heat Transfer of a Nanoliquid with Nano–Encapsulated Phase Change Materials in a Wavy-Wall Enclosure with an Active Rotating Cylinder https://link.springer.com/chapter/10.1007/978-4-431-55951-1_8 Their lists of referenced titles should be examined. This is new and different, yet reminds us of 'the old days' of tailpipe heat recovery https://www.nature.com/articles/s41467-023-38446-0
I would reject the idea that googl is too high level even though I use Bing instead because of 'regional limitations'. It is too low level. If you cannot exactly explain what you are looking for (sorry), search algorithms will guess poorly on your behalf.
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
Salts dissolving are endothermic but don’t have a proper pathway to reverse without the immense energy input to remove the water
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
What’s strange is there should be. Most endothermic reactions are reversible, dissolved salt on the microscopic scale is technically possible to recrystalize using strong fields but at the macro scale we don’t recrystalize salt we instead remove the water. I’ve always believed we are missing something fundamental as there should be a low energy path to recrystalize and remove without attacking the water. Such a discovery would rewrite the math on desalinization as you wouldn’t need pressure or heat.
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
Another new publication presents itself: https://onlinelibrary.wiley.com/doi/10.1002/adma.202303341 Our Bob seems to be in an unusual situation, with a clear engineering goal, but confronting even more nerdly nerds who may not be perfectly impedance matched. Happy that it is not me. Meanwhile I just happen to notice related publications. That happens in ways not easily described. Maybe other readers see that as a small thing. I inhale new scientific research broadly with most being elsewhere. I have not found a student/acolyte/kid inclined to use my tips and tricks Y'all might not see how challenging it is to examine new scientific research. I don't know how many journals now emit but they are many. Internet informs us broadly but not usefully what the heck is happening. My tips and tricks will soon fail to capture the real action. This will become ever more an AI-based game.
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
somebody says "most ammonium salts have endothermic energies when simply dissolved in water. Several systems are known (listed in CRC Handbook of Chemistry & Physics, etc). Many of these systems can cool down to - 20 or - 30 C. These are cheap, safe and simple"
Another one bubbled up: Electrocaloric cooling technologies for a sustainable world | TUP Journals & Magazine | IEEE Xplore
