Compressor Use in Refrigeration Cycle?

Question

Hi

I understand the overview of the refrigeration cycle:

The gas goes into compressor and comes out with higher temp and pressure

This gas then goes through condenser (water or air cooled) and comes out in liquid state with same temp and pressure as what came in.

The liquid then goes through an expansion valve to reduce temp and pressure

The liquid now goes through the evaporator and heat transfer occurs with the glycol coils that are used to cool down the equipment/room. Refrigerant liquid absorbs enough heat to leave the evaporator as a gas. The temp and pressure leaving the evaporator are the same as what they came in as, just a different state.

The system starts all over again.

My question:
What is the use of the compressor specifically, as opposed to just using a standard pump? Why would you want to increase the temperature and pressure of the refrigerant, if you are going to be reducing them in the expansion valve stage of the cycle?

Thank you

Answer 1

The compressor increases the pressure and therefore the temperature rises. The gas emerging from the condenser is at a similar temperature but a HIGHER pressure than before compression. When the gas expands, it becomes cooler.

Answer 2

Based on your additional details:

(1) Vapor leaves the compressor at high press and temp 55-65C(correct).

(2) The condenser cools the hot vapor to a liquid state for the corresponding temperature (30-40C).

(3) Warm liquid is metered by the expansion valve (at constant pressure) into a lower pressure evaporator where change of phase ( liquid to vapor) absorbs heat.



( A refrigerator which is unplugged for several days will come to equilibrium.

as the compressor starts, it will begin reducing pressure in the evaporator causing any

liquid refrigerant to boil and absorb heat. The vapor will be pumped through the condenser to re-liquefy and back to the evaporator to boil again.)

Answer 3

Regarding the use of a compressor vs a standard pump, a compressor is a standard pump. Every pump application is different; different fluids, pressures, flows, connections, applications, life requirements, etc, A standard shallow well water pump is different from a standard oil pump for an automobile is different from a standard refrigerant compressor. I worked on a project where I needed a pump that generated 4000 atmospheres of pressure. I bought one out of a catalog. My point is that there is no one "standard pump."



Your second question of why do you want to squeeze it and heat it when you are only going to cool it later can be most easily answered by looking at the thermodynamics of the refrigerant cycle. The link describes it quite well and I would only be repeating what they say. Please look at the two figures on the right side that show the refrigerant cycle and the thermodynamics. It will all be very clear then.

Answer 4

The refrigeration cycle begins with the compression of the vapor

so it can be cooled. The removal of heat causes the vapor to

condense to a liquid. This is necessary so that the liquid referigant

can be expanded back to vapor which is colder due to the expansion

Then the cold refrigerant vapor absorbes heat and returns to the

compressor to complete the cycle. Compression is an essential part

of the cycle as it allows the vapor to be compressed so that it will

condense to liquid when cooled. The heat that accompanies the compression

is rejected it the cooler when the vapor is cooled to return to liquid.