Refrigeration evaporation temp

[HD109]

Hi I'm 20 years old I just started on the refrigeration end this past month,I previously worked on the steam end for two years with boilers and turbines for ship propulsion and electricity. my question is in refrigeration how can an evaporator which just absorbed heat from a process fluid still be at such a cold temperature be superheated and considered a low pressure vapor returning back to the compressor? Ive been told refrigeration just really is reverse basic steam cycle can someone please help me clear this up.

 

[berkshire]

Google airconditioning courses,this stuff is freely available on the web.
B.E.

"A free people ought not only be armed and disciplined, but they should have sufficient arms and ammunition to maintain a status of independence from any who might attempt to abuse them, which would include their own government."
-George Washington, President of the United States----

 

[MintJulep]

Heat is not the same as temperature.

Low is relative to high.

Heat transfer happens from high temperature to low temperature.

 

[Adnan86]

It all depends on the type of refrigerent that is flowing in the cycle. The refreigerent boiling temperature is itself so low that even at ambient temperature it boils therefore it gets evaporated.

 

[MTES93]

Phase change. Refrigerant absorbs heat in the evaporator by changing phase (liquid to gas). A lower state to a higher state which requires energy 'in' ie... heat. This is essentially an Isothermal process if I remember by refrigerant cycle correctly. The super heat setting on the thermal expansion valve will control how much sensible heat is added to the refrigerant. Meaning a SH of 10 degrees the refrigerant will be 10 degrees warmer than the incoming liquid temp at the expansion valve.

berkshire is right, google a basic refrigerant cycle first and then expand on that. Look at a refrigeration cycle and a steam cycle and you will see similarities.

It is just like steam, which gives up its heat by going from a higher state (gas-vapor) to a lower state (liquid-H20) This is an exothermic or heat out process. However the heating process may include 'sensible' heating where the condensate is cooled below the steam temperature.

 

[Allen1973]

Hi HD109,
There is one term that you are probably familiar with, from dealing with steam, saturated.
The refrigerant in the refrigeration cycle is saturated in the condenser and the evaporator.
In the evaporator, once all of the liquid has been boiled off to a vapor at its saturation temperature any
additional heat added is superheat. Ideally, all liquid has been boiled off and a few degrees of superheat has been added
to the refrigerant vapor, this protects the compressor from slugging liquid refrigerant that the compressor cannot compress.
As an example, an air conditioning evaporator typically operates with a 45 degree saturated refrigerant temperature. If the temperature
of the suction refrigerant is measured at the suction inlet to the compressor and a reading of 55 degrees is obtained, the refrigerant
has 10 degrees of superheat.

Good Luck
Allen

Steamfitters Local 602
Washington, DC
I'm not paranoid, but I know everyone is out to get me.