Which factors will decide the temp and pressure in the end of condenser (before TXV)?

[david2008]

The surface of cond? or TD of cond? Or compressor? Thanks.


David

[US Iceman]

Let's assume the condenser is air-cooled.

Ambient air temperature + condenser TD = saturated condensing temperature (SCT). The SCT is the temperature of the liquid coming out of the condenser without subcooling. If the condenser is equipped/designed to provide sub-cooling then you have: SCT - subcooling = liquid feed temperature from condenser (this then flows into the receiver).

If the receiver is exposed to air temperature greater than the sub-cooled liquid temperature then the liquid can warm up a little, hence causing a reduction in sub-cooling.

If the liquid line is warmer than the surrounding ambient air temperature then the heat is rejected from the liquid line to the ambient air.

Then, if the drier is clean the liquid arrives at the TXV as long as the liquid line pressure loss (or elevation increase) does not cause any subcooling effect to be lost.

I think that covers the major items...

[GXMPLX]

US_Iceman is right as usual, but as for the pressure there are three main variables that affect it:

The pumping capacity of the compressor makes the pressure of the condenser go up.

The energy/time (heat) the condenser gives off reduces the refrigerant volume therefore lowering the pressure. This
is affected by TD and surface and heat transfer coefficients (refrigerant, velocities, densities, cooling fluid
temperature and density etc.)

The amount of liquid leaving the condenser. If you flood the condenser you are definitely changing its pressure.

Anything going on before the condenser is attenuated by the condenser so the pressure at the expansion valve (or any
point in between) is condensing pressure minus the pressure drop you have caused by the flow of the liquid
refrigerant from the condenser to that point.

And as US_Iceman says, you may get a little more or less depending on heat gains/losses in between the condenser and
where you measure.

Am I doing their homework again, you think?

[david2008]

US_Iceman is right as usual, but as for the pressure there are three main variables that affect it:

Am I doing their homework again, you think?

Thank you Iceman and GXMPLX.

[US Iceman]

The pumping capacity of the compressor makes the pressure of the condenser go up.

The energy/time (heat) the condenser gives off reduces the refrigerant volume therefore lowering the pressure. This is affected by TD and surface and heat transfer coefficients (refrigerant, velocities, densities, cooling fluid temperature and density etc.)

Ahhh, now you are talking about transient or temporary conditions that occur outside of the normal design window. I was assuming clean condensers and everything designed properly.

If this is homework then at least someone is asking good questions!

[GXMPLX]

Ahhh, now you are talking about transient or temporary conditions that occur outside of the normal design window.

No, no transient. The question asked wich factors affect, I simply mentioned in which direction it affects.

Refrigerant pumped makes it go higher, reduction of volume due to condensation makes it go lower and of course the higher the mass flow you take out as liquid will also make it go lower, if you stop or reduce the out mass flow pressure will go higher like when you flood the condenser.

These effects when combined can give a stable condensing pressure.

I was assuming clean condensers and everything designed properly.

Me too.

If this is homework then at least someone is asking good questions!

The right questions yes, but you are givin' away the answers! As usual, you started it, ... I simply got carried away!

[Contactor]

TD 15K Ambient 25C SCT= 37C ?