Help on HVAC system and refrigeration?

Let's say we have an r134a new refrigerant cylinder which i believe is in a liquid and vapour state.

Since the two states exist we can say it's at saturation.

So what ever the room temperature is, it's the r134a temperature inside the cylinder(if I'm correct)

Assuming the room temp is 25°c, the saturation pressure corresponding to it is 6.4atm

The boiling temp of r134a is -26.3°c at 1atm

Here comes my confusion, if I open the cap and release some of the refrigerant then close it, will the pressure drop??

If so, how do i read the corresponding pressure on the chart??since there is no change in the room temperature and I'd have to go to the chart with the same 25°c (I just don't get the science I believe) 

3 Answers

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  • 1 month ago
    Favorite Answer

    As long as there is liquid in the container some will evaporate to fill the space caused by the vapor you have released. The pressure in the container will still be equal to the vapor pressure at that temperature. That is true until there is no liquid left.

    If you wish to determine the amount of refrigerant still in the container you will need to use a scale to weight the container before and after the release.

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  • 1 month ago

    If you open the valve and bleed off some pressure then close the valve, the liquid inside will boil off some vapor until the pressure reaches the original pressure again and re establishes equilibrium.

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  • Anonymous
    1 month ago

    < if I open the cap and release some of the refrigerant then close it, will the pressure drop?? >

    Depends how much you open the valve.  If the valve is opened just a little so the amount of vapor leaving is 'small', then as it leaves, the pressure in the container starts to drop.  Liquid however vaporizes to maintain the vapor pressure or a constant pressure.  The liquid vaporization requires energy which comes from the liquid and directionally, the temperature will start to drop (which in turn reduces the vapor pressure).  However, if the rate is low, then the ambient temperature of the room will keep the liquid at a constant temperature and therefore the pressure in the cylinder at a constant pressure.

    If the amount of vapor leaving is relatively large, then the vaporization of the liquid will still occur but heat transfer from the room can't maintain the liquid temperature and it starts to drop.  As the liquid temperature drops, the pressure above the liquid drops (following the saturation curve).  Once you close the valve (assuming there is any liquid left), that liquid will warm back up to room temperature and the pressure will go back to the original value.

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