Energy to compress gases...

[Externet]

To compress one litre of refrigerant gas, from atmospheric pressure to say 100 psi; takes X amount of energy

 

To compress one litre of air, from atmospheric pressure to say 100 psi; does it take the same amount of energy ?

 

In the examples above, none the gases will become liquified at a condenser; just cooled to ambient temperature.

 

If both gases take the same amount of energy for the task; why air is not a good to use as refrigerant gas yielding a poor coheficient of performance COP ?

 

If both gases take different amount of energy for the task; is the one that will take less energy the one that will be a poorer refrigerant ?

 

Would a good refrigerant gas be good only if in the compression/cooling/expanding process the change of state -gas to liquid to gas- is achieved ?

 

If there is no change of state; are the COPs equal for all gases ?

[csmyth3025]

To compress one litre of refrigerant gas, from atmospheric pressure to say 100 psi; takes X amount of energy

 

To compress one litre of air, from atmospheric pressure to say 100 psi; does it take the same amount of energy ?

 

In the examples above, none the gases will become liquefied at a condenser; just cooled to ambient temperature.

 

If both gases take the same amount of energy for the task; why air is not a good to use as refrigerant gas yielding a poor coefficient of performance COP ?

 

If both gases take different amount of energy for the task; is the one that will take less energy the one that will be a poorer refrigerant ?

 

Would a good refrigerant gas be good only if in the compression/cooling/expanding process the change of state -gas to liquid to gas- is achieved ?

 

If there is no change of state; are the COPs equal for all gases ?

I'm no expert on refrigeration, but I think you'll find an answer to most of your questions in the Wikipedia article on refrigeration here:

 

 

http://en.wikipedia....i/Refrigeration

 

Chris

[John Cuthber]

To a fair approximation, if the gas doesn't condense then the energy needed to compress it to some given pressure is the same.

But they don't use gases like that for refrigerants; they use ones that do condense because they can then use that phase change to move energy around more efficiently.

[Enthalpy]

A part of the gas' enthalpy comes from rotations and vibrations of the molecule, also from excited electronic states and dissociation in some circumstances. This part does change the energy needed for compression between one molecule and an other one.

 

Then, the chosen gas must fit the technological job: melting and boiling point, heat of vaporization, heat capacity, toxicity, flammability, corrosion, environment, price, and many more.

[alpha2cen]

The difference is like this.

--->compress, heat release--->storage ---------------------------------------------------->evaporation or expansion----->heat absorption

air:------------------------------- much more volume is needed to storage air ----using expansion--------------------heat absorption rate is slow :very large volume is required

refrigerant:----------------------small volume is needed------------------------------------using evaporation(latent heat)---heat absorption rate is fast :small volume is needed

 

if used energy is the same, i.e.,

 

E_air = E_refrigerant

 

Air------------------large volume*small temperature difference

Refrigerant--------small volume* large temperature difference

 

But at the point of heat transfer large temperature difference is more good to use.

 

This is heat transfer equation

q= U A (dT)_{log average}