Throttling in Refrigeration Cycles

[multiviya]

Hi all,

The process of throttling in refrigeration is taken to be isenthalpic. And as enthalpy remains constant then so should the temperature. But in the TS diag of the process it shows a drop of temperature from T_higher to T_lower. Please help me regarding this.

Thanks!

 

[256bits]

To which process are you referring?
Isenthalpic
http://en.wikipedia.org/wiki/Isenthalpic
Isentropic
http://en.wikipedia.org/wiki/Isentropic_process

 

[multiviya]

for isenthalpic process, for which temperature decreases despite enthalpy remaining constant. But from what i know enthalpy is directly proportional to temperature, so temp should remain constant when enthalpy does. But clearly that's not the case in RAC cycle. Plz explain

 

[Q_Goest]

Hi multiviya,

But from what i know enthalpy is directly proportional to temperature, so temp should remain constant when enthalpy does.

This is only true for an ideal gas.

 

[jack action]

The reason is that there is a (partial) phase change from liquid to liquid & vapor during the expansion process.

Normally, to go from liquid to gas, you need to add energy to break the molecular bonds, i.e. boil the liquid. But since we have a process which have no heat transfer to or from the surroundings by definition, the energy needed has to come from within, thus the temperature drop.