***** expansion fundamentals

[sgtech]

Hello,

I would like to know the thermodynamics of why liquid ***** R22 at about pressure of 17.64kg/cm2A and temperature of 45 degrees celcius is expanded to about 0.56 degrees celcius at 5.2kg/cm2. After the expansion valve, is the ***** in liquid form or a mixture of gas and liquid, how come being expanded the temperature is able to drop so much, where all the HEAT went ?

thanks,

[Brian_UK]

The HEAT went into the space being cooled.

[DTLarca]

Hello,

I would like to know the thermodynamics of why liquid ***** R22 at about pressure of 17.64kg/cm2A and temperature of 45 degrees celcius is expanded to about 0.56 degrees celcius at 5.2kg/cm2. After the expansion valve, is the ***** in liquid form or a mixture of gas and liquid, how come being expanded the temperature is able to drop so much, where all the HEAT went ?

thanks,

The first thing we have to remember about science is that it is a merely descriptive discipline. We do not know why there is gravity, for instance, but we do have some very good mathematical tools for describing the way gravity works.

So why is there cooling when there is expansion?

If you accelerate a mass you are applying a force. Keep accelerating a mass over a distance and you are applying a force through a distance and are therefore doing work. Work is energy.

Force = mass x acceleration
F = ma = kg x m/s² = N

Work = force x distance
W = mas = kg x m/s² x m = kg x m²/s² = Nm = J

Pressure = force per area
P = F/A = N/m²

Therefore F = PA = Pressure x Area = N/m² x m² = N

But if work = force x distance and pressure x area = force...

...then work = pressure x area x distance = PAs = N/m² x m² x m = Nm

But since area x distance is volume then work = pressure x volume = N/m² x m³ = Nm

So any substance expanding within any other substance has to do work expanding because it is a change in volume against a pressure i.e. pressure x volume. Where does the energy comes from? It comes from within - the energy within is kinetic energy of motion of the molecules - that is what temperature is. The gas expanding or changing phase is a conversion of kinetic energy to potential energy and so to gain the potential in occupying a greater volume the gas converts its kinetic energy - in other words it takes energy from itself that is in the form of temperature and converts it to energy of a pressure over a greater volume.

We can calculate temperature (K) if we know the mass of each molecule and its average velocity.



T = ⅓.m.v²
k
Take a look at different refrigerants on their PH charts - you will find that those with higher net refrigeration effects tend to also produce gases of greater volume for the same pressure.

[Segei]

Hello,

I would like to know the thermodynamics of why liquid ***** R22 at about pressure of 17.64kg/cm2A and temperature of 45 degrees celcius is expanded to about 0.56 degrees celcius at 5.2kg/cm2. After the expansion valve, is the ***** in liquid form or a mixture of gas and liquid, how come being expanded the temperature is able to drop so much, where all the HEAT went ?

thanks,
It is very simple. Liquid R22 goes through expansion valve pressure and temperature will drop. To achieve lower temperature, portion of liquid R22 will evaporate. I would call it selfcooling. For example. 10% of liquid will evaporate to cool down the rest 90%. After expansion valve you will have mixture of liquid and gas.

[sgtech]

Thanks for information everyone, but after the expansion valve, it becomes a mixture of vapor and liquid *****, am i right to say that the vapor takes the away the heat leaving behind the cold liquid *****(~0.5degrees celcius) then would the vapor be
'warm' ?

[mad fridgie]

Thanks for information everyone, but after the expansion valve, it becomes a mixture of vapor and liquid *****, am i right to say that the vapor takes the away the heat leaving behind the cold liquid *****(~0.5degrees celcius) then would the vapor be
'warm' ?
When you boil a kettle is steam the same temperature of the boiling water or is it cold, theres the answer

[DTLarca]

Thanks for information everyone, but after the expansion valve, it becomes a mixture of vapor and liquid *****, am i right to say that the vapor takes the away the heat leaving behind the cold liquid *****(~0.5degrees celcius) then would the vapor be
'warm' ?

Yes - the vapour is just what you get when the liquid does work on its surrounds (P x V = Nm = J) and the energy to do this work came from the molecular kinetic energy of the liquid and now with less kinetic energy in the liquid its temperature drops because the temperature of anything is nothing other than an indication of the average velocities of the molecular masses.

[desA]

Thanks for information everyone, but after the expansion valve, it becomes a mixture of vapor and liquid *****, am i right to say that the vapor takes the away the heat leaving behind the cold liquid *****(~0.5degrees celcius) then would the vapor be
'warm' ?

Have you studied Thermodynamics? There are some useful principles in this, that will assist with your understanding.

The expansion process (within the orifice of a TXV, for instance) is generally considered to occur at constant enthalpy.