about refrigeration?

Question

In a capillary tube enthalpy remains constant. but how it happens because there is temperature drop
Cp=dH/dT.
so if there is change in temperature then enthalpy should change being Cp is constant .but it is not happening in capillary tube. can you please explain this?

Answer 1

Enthalpy by definition is a measure of heat content and unless there is heat or work input or output there is no change in enthalpy. However when the pressure of a condensed refrigerant is lowered the liquid/vapour phase equilibrium is different. Vapour forms and the latent heat of evaporation cools the mix until the equilibrium temperature is reached for the lower pressure. The refrigerant liquid/vapour mix can then absorb heat at low temperature in the refrigeration system (enthalpy rises) as the liquid vapourises.

Answer 2

In the summertime, have you ever gotten out of a swimming pool and then felt very cold standing in the sun? That's because the water on your skin is evaporating. The air carries off the water vapor, and with it some of the heat is being taken away from your skin.

This is similar to what happens inside older refrigerators. Instead of water, though, the refrigerator uses chemicals to do the cooling.

There are two things that need to be known for refrigeration.

A gas cools on expansion.
When you have two things that are different temperatures that touch or are near each other, the hotter surface cools and the colder surface warms up. This is a law of physics called the Second Law of Thermodynamics.

Answer 3

Cp = dH/dT at constant pressure. In the expander (capillary tube) pressure drops.

Answer 4

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