pressure difference in TXV system

[david2008]

Hi there,

For a TXV system, what is the pressure difference between condenser and evaporator during cycle off? Thanks.

[monkey spanners]

How long is a piece of string?

It would depend on the refrigerant, the respective standing temperatures of the condenser and evaporator, the temperature range of the tev/txv, if the valve has a bleed port, pumpdown/solenoid etc.

Are you thinking about a specific system or just wondering?

Jon

[david2008]

Jon,
I am wondering, for a cap system, they will equal to each other. For a txv system, will they? We assume it is a R134a system. No bleed port. Cond is about 100F, evap is about 10F.
Thanks.

David

[Brian_UK]

If you know the temperatures then you have your answer already.

[david2008]

If you know the temperatures then you have your answer already.

My fault. Temperature is refer to cycle on. I don't know the temp of cycle off.

[GXMPLX]

Depends on system design.

If you don't use pump down or a special kind of expansion valve the difference is CERO ZIP NADA NIE.

If you use pumpdown it'll vary slowly and be saturation pressure at condenser temperature minus the cut out pressure for the compressor. If the pressure moves above low pressure cut in the compressor will start and leave it at cut out.

If you have a special type of valve, depends on what else is closing the system.

[david2008]

Depends on system design.

If you don't use pump down or a special kind of expansion valve the difference is CERO ZIP NADA NIE.

After I google, I know CERO ZIP NADA NIE means zero. Thank you.

David

[GXMPLX]

After I google, I know CERO ZIP NADA NIE means zero. Thank you.

David

What? You mean you don't whatch Stallone movies?

[david2008]

[GXMPLX]

I’m not too fond of politics! May get you in trouble.

[david2008]

I’m not too fond of politics! May get you in trouble.

me too. . .

[GXMPLX]

me too. . .

I can't believe it! Tried to post the answer here yet got the internal error again.

Well to sumarize the example you gave in other post lacks fundamental data like the system volume yo need it to estimate the refrigerant charge.

The only new thing is that to estimate the amount of liquid refrigerant in the receiver at maximum load you'll get a minimum height in the receiver and can calculate the height by equating potential energy of the fluid=maximum kinetic energy of the fluid at the vena contracta.

Use half the area of the outlet pipe of the receiver as the size of the vena contracta and apply bernoulli to calculate the height needed in the receiver.

With this height and refrigerant densities at the conditions you mentioned you can estimate the mass of refrigerant in the receiver.

Collect manufacturer data for condenser and evaporator. If you don't have estimate 70/30 percent of volume for vapor/liquid in the condenser and 30/70 percent of vapor/liquid in the evaporator. With this and densities at the corresponing temperatures give you the mass of refrigerant.

Add the volume of the liquid line times the density

And you have an estimation.

You read in other threads you have to check by measuring superheat at minumum load and this is about it!

[GXMPLX]

This got through! I must have a non printable character somewhere in my original answer!

[david2008]

I can't believe it! Tried to post the answer here yet got the internal error again.

Well to sumarize the example you gave in other post lacks fundamental data like the system volume yo need it to estimate the refrigerant charge.

The only new thing is that to estimate the amount of liquid refrigerant in the receiver at maximum load you'll get a minimum height in the receiver and can calculate the height by equating potential energy of the fluid=maximum kinetic energy of the fluid at the vena contracta.

Use half the area of the outlet pipe of the receiver as the size of the vena contracta and apply bernoulli to calculate the height needed in the receiver.

With this height and refrigerant densities at the conditions you mentioned you can estimate the mass of refrigerant in the receiver.

Collect manufacturer data for condenser and evaporator. If you don't have estimate 70/30 percent of volume for vapor/liquid in the condenser and 30/70 percent of vapor/liquid in the evaporator. With this and densities at the corresponing temperatures give you the mass of refrigerant.

Add the volume of the liquid line times the density

And you have an estimation.

You read in other threads you have to check by measuring superheat at minumum load and this is about it!

Thanks. I will have a try using the method above.