MadSci Network: Engineering |
This is a tough question, mainly because the concept of getting cooling out of a flame seems rather bizarre. I couldn't find a source that really explains it well, but I will attempt to at least give you the theoretical concept. To explain how a propane refrigerator works, lets look at a normal refrigerator first. A refrigerator is an insulated box of cold air separated from the outside. In a normal refrigerator, a compressor compresses a refrigerant such as freon, which causes it to get very warm, even hot to the touch. The air surrounding the outside of the refrigerator cools the fluid back to room ambient. It then enters the inside of the refrigerator. Now the fluid, still under high pressure, is allowed to expand inside the refrigerator coil, reducing the pressure, and turning it into a gas. When that happens, it turns cold. (Sort of like the air escaping from a tire valve.) Because the air in the refrigerator is warmer than the cold fluid in the tubing, the cold refrigerant gets warmer (and the air in the refrigerator gets a little colder). The compressor sucks the freon gas/fluid out of the refrigerator coil and back outside the box. When the fluid is compressed, increasing the pressure again, the cycle starts over. A propane refrigerator works much the same way, except it uses an absorption cycle instead of a compressor. This is where it gets a little tricky to understand. The refrigerant inside the tubing is actually a mixture of water and ammonia. When inside the refrigerator, the water absorbs the ammonia, which leaves the inside at low pressure and temperature. The propane gas is used to heat this mixture, which causes the mixture to reach high temperature and pressure. The ammonia escapes the mixture, and the heat from this ammonia is allowed to disipate to the outside air the same way as in the normal refrigerator described above. The ammonia is then expanded inside the refrigerator and collects heat from the inside in the same manner. It is re-absorbed by the water at the lower pressure and the cycle starts over. Try http://homedoctor.net and ask your question. They answered a question about a faulty propane refrigerator and may be able to give more details. Most of the manufacturers of such units seem to be in Canada, and you might also find them on the web.
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