Temperature difference across thermal expansion valve
Temperature difference across thermal expansion valve
(OP)
Why is there a temperature difference across a thermal expansion valve, such as one used in a refrigeration cycle? If there is no work or heat transfer in the device then the internal energy of the fluid remains the same and so should the temperature, regardless of pressure difference across the valve.





RE: Temperature difference across thermal expansion valve
h1 = c*T1 + p1*v
h2 = c*T2 + p2*v
being:
h1 = enthalpy of state 1
h2 = enthalpy of state 2
c = specific heat
T1 = temperature of state 1
p1 = pressure of state 1
v = specific volume
T2 = temperature of state 2
p2 = pressure of state 2
h1 = h2 implies
c*T1 + p1*v = c*T2 + p2*v
rearranging
T2-T1 = (p2-p1)*v/c
RE: Temperature difference across thermal expansion valve
RE: Temperature difference across thermal expansion valve
If you are talking about why say freon gets cold during an expansion, since the energy is zero, 1 molecule of freon transfers it's energy to another molecule. The first loses energy so it gets cold, the second one gains energy and changes energy state from liquid to gas (it vaporizes). Energy is conserved, cold is not flowing to hot, laws of thermo are maintained.