Refrigeration Cycle temperatures

Main Question or Discussion Point

Please look at the picture on this link of a refrigeration cycle:

http://ffden-2.phys.uaf.edu/212_fall2003.web.dir/Dane_Lenaker/img/pics/frigcycle.gif

Would the temperature at position 1 be the temperature leaving the evaporator or the temperature entering the compressor? or should they in theory be the same? Because according to results i have obtained in a lab, the temp entering the compressor and leaving the evaporator are different. Also, what is the compressor discharge temperature?
Would the temperature of the refrigerant at position 2 be the temperature leaving the compressor? Or would it be also dependent on the compressor discharge temperature?
Thank you
 
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Answers and Replies

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In an ideal cycle the state of the working fluid is the same at the compressor inlet as it is at the evaporator outlet. This means the pressure and temperature will be the same at these locations (with a quality of 1).

However, in a real cycle some things are different. First, a real compressor does not like fluid in it so the cycle is designed in such a way that the inlet gas is superheated a little bit as opposed to sitting exactly on the outer edge of the two-phase region. Also, in a real cycle fluid must be transported from place to place using tubing (copper tubing in a lot of commercial refrigerators). Within the tubing there are frictional losses which can cause a small pressure drop when going from the outlet of the evaporator to the inlet of the compressor. Also, there is often heat transfer between the tubing and whatever environment it is in.

So, long post short. You are likely noticing the differences caused by heat transfer and frictional effects within the tube connecting your evaporator to your compressor.

Also, state 2 is, again, the ideal compressor outlet temperature, but you will likely see similar effects there too.
 

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