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I have a doubt about expansion process.

Some people say it's an adiabatic expansion, but other say it's something related to the nozzle.

What is the actual cause for cooling in expansion process?

According to me, pressure drop of the gas, takes the gas to its boiling point. Since the boiling point of the gas is very low, cooling takes place.

Am i correct?

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    $\begingroup$ Have you tried Googling "refrigeration cycle?" $\endgroup$
    – Chet Miller
    Commented Jul 30, 2018 at 16:37
  • $\begingroup$ still need more clarity $\endgroup$
    – Hvac Engineer
    Commented Jul 30, 2018 at 16:51
  • $\begingroup$ You have a heat exchanger (evaporator) with working fluid entering at one end as a liquid and exiting at the other end as a vapor. The vaporization/boiling takes place at a constant low pressure and temperature, with heat supplied by the warm air blowing over the outside of the tubing. The heat balance on the evaporator (heat exchanger) is $\dot{Q}=\dot{m}\Delta H_{vapor}$, where $\dot{Q}$ is the rate of heat removal from the air and $\dot{m}$ is the mass flow rate of working fluid passing through the evaporator. $\endgroup$
    – Chet Miller
    Commented Jul 30, 2018 at 17:05
  • $\begingroup$ @HvacEngineer, as a start, see swtc.edu/Ag_Power/air_conditioning/lecture/basic_cycle.htm $\endgroup$
    – David White
    Commented Jul 30, 2018 at 17:14
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    $\begingroup$ Dude its still more deeper, my question is about throttling process in refrigeration cycle $\endgroup$
    – Hvac Engineer
    Commented Jul 30, 2018 at 17:17

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It seems that there are no contradictions in all those statements.

Some people say it's an adiabatic expansion.

What they probably mean is that the initial expansion of the coolant at the output of a throttling device does not involve heat exchange with the surroundings, i.e., the cooling occurs due to evaporation - not due to the cooling effect of some external agent.

other say it's something related to the nozzle

This is a reasonable statement. A nozzle, as a throttling device, restricts the flow of coolant, which causes pressure drop.

According to me, pressure drop of the gas, takes the gas to its boiling point. Since the boiling point of the gas is very low, cooling takes place.

This is a reasonable summary as well.

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  • $\begingroup$ which one will be best answer? $\endgroup$
    – Hvac Engineer
    Commented Jul 31, 2018 at 5:39
  • $\begingroup$ @HvacEngineer I'd say all answers have a valid point and complement each other, so it would be subjective to rate them. I'd rephrase the second part of your answer to "and as the coolant boils/evaporates, its temperature drops. I'd add that the adiabatic expansion of gas (with no evaporation involved) also decreases its temperature (unless it expands into vacuum). $\endgroup$
    – V.F.
    Commented Aug 1, 2018 at 1:12

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