MadSci Network: Engineering
Query:

Re: Propane refrigerator operation?

Date: Tue Sep 22 22:46:00 1998
Posted By: Jim Stana, , Mechanical Design/Analysis Manager, Lockheed Martin Orlando
Area of science: Engineering
ID: 905800515.Eg
Message:

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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