Reciever Use

[sdumper]

When is a Receiver needed for a cascade and where in the loop is it placed?

[marru]

In a cascade the only stage a receiver would be used in is the first stage, and you put the receiver after the condensor like in any single stage.

The only time the receiver is used in a higher stage is when you plan an explosion.

[tiborrr]

Good point, marru. One should use recieved only on the high stage (by high stage I mean high temperature stage -> 1st stage of the cascade), e.g. before the metering device (TXV, AEV = CPEV). Cap tube systems does not require liquid reciever.

It's also not needed if you use large enough condenser and a properly sized / oriented tubing.

[sjg0]

The only time the receiver is used in a higher stage is when you plan an explosion.

Could you clarify what you mean by this?

Do you mean your higher stage might explode with a receiver on it, or your higher stage might explode so you put a receiver in it to prevent this?

[Patrickclouds]

but this is not called receiver.
i think he means an expansion tank

[sdumper]

Cool so I shouldnt be concerned with adding a seperate reciever...for my 2 stage

[sacha35]

Cool so I shouldnt be concerned with adding a seperate reciever...for my 2 stage

No but an expansion tank is a must have if your using R1150, in hot weather the expansion of the refrigerant can easy hit 300PSI when the system is not switched on.

[marru]

In a cascade the only stage a receiver would be used in is the first stage, and you put the receiver after the condensor like in any single stage.

The only time the receiver is used in a higher stage is when you plan an explosion.

I meant upper stage (eg. 2nd, 3rd stage) and i was ironic .
Consider the situation when you would charge a second stage up to the point of filling up or partially filling up a liquid receiver (which could only be done while cascade is running btw). At this point when you turn off the cascade the low boiling refrigerant would warm up, pass the critical temperature point and go well beyond the 100bar pressure.

Bada Bing Bada Bang

[EvoCarlos]

sd imo you dont need one evocade dont use one and when i did it made no diffrence to the way it ran idle and load

No but an expansion tank is a must have if your using R1150, in hot weather the expansion of the refrigerant can easy hit 300PSI when the system is not switched on.

hey paul what size exspantion tank you got ?
also i would of thougth if it ever got to 300psi static what ever the ambent temp i say it was over chargerd
with a 2l exspntion tank and 26c ambent i get a 175psig static and 175psig running pressure

I meant upper stage (eg. 2nd, 3rd stage) and i was ironic .
Consider the situation when you would charge a second stage up to the point of filling up or partially filling up a liquid receiver (which could only be done while cascade is running btw). At this point when you turn off the cascade the low boiling refrigerant would warm up, pass the critical temperature point and go well beyond the 100bar pressure.

Bada Bing Bada Bang

nm you edited
was gona say yes if you had like 3kg of r1150 in the system :0

[sdumper]

I dont see an oil return on this does it not trap oil?

[sacha35]

hey paul what size exspantion tank you got ?
also i would of thougth if it ever got to 300psi static what ever the ambent temp i say it was over chargerd
with a 2l exspntion tank and 26c ambent i get a 175psig static and 175psig running pressure

The PSI quoted is if you did not use an expansion tank, mine sits at around 10 bar static no matter even with it being 30c at the moment.

I cannot remember what the size of my tanks are but I know they are about the size of my first stage Compressor

[sacha35]

I dont see an oil return on this does it not trap oil?

If you're going to use it as an expansion tank then block of one side and run a cap tube to the other from the suction side of your compressor, when the compressor is switched off it will drain some of the refrigerant into the expansion tank slowly, when you switch the compressor on it will draw the refrigerant slowly back into the loop.

In this picture you can see two rotolock valves on each expansion tank and two hennery shut off valves in line from the compressor, this will allow me to shut and open different valves which will allow me to recover most of the refrigerant into the expansion tanks if any work is need at all like adjusting cap tubes ECT.

[sdumper]

If you're going to use it as an expansion tank then block of one side and run a cap tube to the other from the suction side of your compressor, when the compressor is switched off it will drain some of the refrigerant into the expansion tank slowly, when you switch the compressor on it will draw the refrigerant slowly back into the loop.

In this picture you can see two rotolock valves on each expansion tank and two hennery shut off valves in line from the compressor, this will allow me to shut and open different valves which will allow me to recover most of the refrigerant into the expansion tanks if any work is need at all like adjusting cap tubes ECT.

Not as an expansion on the second but was considering using it as a reciever on the first.

I have a VERY large Parker expansion on the second stage already.



By the way that is one beautiful / clean build!! What do you use it for?

[runmc]

The receiver let's the liquid and gas separate and the liquid drops to the bottom of the receiver. The liquid is then picked up and fed to the expansion valve. An expansion valve works at it's maximum efficiency when fed liquid only with no gas bubbles.
Cap tube system does not use receiver because you want some gas moving through the cap tube with the liquid



Now that's a cascade!!!

[SoddemFX]

Cap tube system does not use receiver because you want some gas moving through the cap tube with the liquid

I don't agree with this. At the entrance of the capillary tube the refrigerant will be a sub-cooled liquid, the degree of sub-cooling depending on how the system was built.

The pressure drop experienced by the refrigerant along the length of the capillary tube will cause an ever increasing percentage of refrigerant to be in gas phase, but at the entrance to the capillary tube the refrigerant will be pure liquid.

The reason for usually not using a receiver in a capillary tube system is more to do with the dynamics (for lack of a better word) of the system with regards to load -> idle transitions.

Essentially, a capillary tube system with no receiver is able to better adapt the refrigerant flow rate to the load applied to the evaporator.

Tom

[runmc]

I was under the impression that a small amount of gas would help let the system adjust to load. That's why I said that.
No doubt Tom knows the dynamics much better than myself. Thank you Tom

[SoddemFX]

Imagine you have a capillary tube single stage running on a processor, the processor is idling at 100W

The single stage is running well - the evaporator exit superheat is a few degrees and at the filter drier you have a few degrees of sub-cooling.

Because of the low superheat you have a large mass of dense gaseous refrigerant in the suction line and because of the small amount of sub-cooling, only the last few inches of the condenser is filled with liquid.

The processor now goes into load with the processor putting out 250W.

The added evaporator heat load causes the suction superheat to raise dramatically, the dense gas occupying the suction line is replaced by highly superheated (and much less dense) suction gas. The mass of refrigerant in the suction line is reduced, with the displaced mass of refrigerant being moved into the condenser.

This added refrigerant condenses and fills up a much larger proportion of the condensers volume than was previously occupied by liquid. This process has reduced the condensers effective size, so in the long term the discharge pressure rises

Capillary tube flow rate is highly dependant on the pressure drop across it and the increased discharge pressure increases the mass flow though the capillary tube.

The increased flow rate is much better suited to handling the evaporator load and subsequently the suction superheat falls and the transition reaches a steady state.

If you had a receiver, you wouldn't have anywhere near as much increase in discharge pressure.

I was trying to avoid typing this as I’m tired but I realised that my previous post could have been taken as arrogant hence the explanation.

Tom

[sdumper]

Thanks for the assist...Receiver added



I have never used a Reciever before and certainly not this type but I brazed the long copper pipe to my filter drier and the short exit pipe to my copper tube running to my site glass and then TXV.

Vacuuming right now and will charge at 9:00pm EST if all goes well.

Im assuming I dont need to adjust this thing and that it wont trap oil since fluid and not gas will be exiting...

[sdumper]

Evidently it has a valve of sorts on the bottom of the outlet ... im loosening it now because it was not feeding any refrigerant at all...

Would have been nice to have some instructions on this thing...

--edit-- Yep that was it and it made a huge difference in my required running pressure...much lower now...

[marru]

The added evaporator heat load causes the suction superheat to raise dramatically, the dense gas occupying the suction line is replaced by highly superheated (and much less dense) suction gas. The mass of refrigerant in the suction line is reduced, with the displaced mass of refrigerant being moved into the condenser.

This added refrigerant condenses and fills up a much larger proportion of the condensers volume than was previously occupied by liquid. This process has reduced the condensers effective size, so in the long term the discharge pressure rises

Tom

You are missing one thing. When the evaporator experiences a bigger load, the suction pressure will increase as a result of the increased discharge pressure and of the flow rate. So under a higher load, you have a bigger flow rate through the suction side@a higher pressure and you actually have a higher mass of fluid in the suction line thus a lower liquid level in the condenser.

In my point of view the existence of a receiver in a single evaporator sistem would only be justified by the lack of condensing pressure control and a very big load variation on the evaporator. This is only the case for our sistems where we cant afford the on/off termostatic control over the compressor as you find in a commercial application.