Air Conditioners - The Refrigerant Cycle

[Peter G.]

I was taking a look at how air conditioners work. After reading some texts in websites I decided to try a video. The concept seems pretty simple but I came across two things I did not quite grasp:

1st. When the refrigerant enters the compressor it is a hot gas because the air in the room lost heat to it. The video says that the gas heats up and increases its pressure when it goes through the compressor. I understand that the pressure increases as the collisions with the walls of the container are more frequent. The video says the rise in temperature is due to the greater friction between the molecules of the refrigerant. I did a quick research and seen that some people claim that in an ideal gas the temperature increases because work is being done on the gas and in this process energy is transferred in form of internal energy to the molecules, allowing them to move faster and thus, since temperature is the average kinetic energy of molecules, the temperature increases. Is it the friction or the work the compressor does responsible for the increase in temperature?

The second one is a bit simpler. There is also an expansion valve: It is used to reduce the pressure of the refrigerant so it can evaporate at a lower temperature?

Thanks in advance,
Peter G

 

[jbsteele]

.The answer to the first question is that it is the work done by the compressor that is responsible for the increase in temperature. The compressor compresses the refrigerant gas, increasing its pressure and temperature. The increase in temperature is due to the work being done on the gas, which increases its internal energy, allowing the molecules to move faster, thus increasing its temperature. The answer to the second question is yes, the expansion valve is used to reduce the pressure of the refrigerant so that it can evaporate at a lower temperature. This is because when the pressure is reduced, the boiling point of the refrigerant also decreases, allowing it to evaporate at a lower temperature.