1 reply to this topic

I am a mechanical engineer with 3 years experience working on a system which requires the use of a refrigerant, most likely R-134 or R-507a. The setup will consist of a 1000lb refrigerant cylinder, connected through a regulating valve and a line into a pipeline. The pipeline conditions are approximately 106 psia an 152 degF with the same refrigerant as the medium. At intermittent times, pressure in the pipeline will drop below the 106 psia and the regulating valve will open in order to bring the pressure back up. My question is: How can I calculate the flow rate of the gas leaving the cylinder in order to find out my recovery time back to full pressure? Also, I need to know if the conditions will necessitate the use of cylinder heaters in order to keep the refrigerant at a temperature where the vapor pressure remains at acceptable levels, ie. how quickly does the liquid refrigerant in the cylinder drop in temperature once the gas starts to be removed? Any help to push me in the right direction will be appreciated as I have hit a brick wall with this at this point.

[Art Montemayor]

CWB:

There is some basic data missing from your post that makes it necessary for me to assume in order to be able to address what you propose to do:

• The refrigerant storage cylinder will contain saturated LIQUID refrigerant at ambient temperatures;
• The refrigerant is assumed to be R134a – one of the most popular ones in the market;
• The vapor pressure of the saturated refrigerant minus the existing pipeline pressure (defined as the driving force) will need to be such that it is sufficient to force the desired flow rate of R134a. The driving force will be proportional to the R134a flow rate.
• Nothing is known about the system that receives the makeup refrigerant and why makeup is required. Consequently the procedure or method to determine the “recovery time” is unknown;
• At ambient conditions of 60 and 90 ^oF, the vapor pressure of the saturated R134a liquid is 72 and 119 psia.
• The saturated temperature of R134a at 106 psig is 230 ^oF.

From the above, it is obvious that you can’t generate enough vapor pressure in your storage cylinder in excess of 106 psig without heating the cylinder in excess of 230 ^oF. In other words, you can’t generate enough driving force in the system unless you heat the storage cylinder – and then it has to be in excess of 230 oF. And even if you do that, you still will have to keep on heating the storage cylinder at a rate that ensures that you continue to vaporize enough saturated R134a to maintain the storage cylinders vapor pressure at the desired value.

The important thing to consider is that you are dealing with a saturated liquid – not with a superheated vapor system as the stored refrigerant. All refrigerants are stored as saturated liquids; that’s a typical characteristic of a refrigeration system.

If you don’t want to go through all the above hassle, then you only have one alternative to feed in make up refrigerant: install a feed makeup pump system that operates automatically – together with all the required instrumentation and controls.

I hope this helps you out in deciding what to do. If you need specific details, you have to furnish specific basic data in order to fully understand your scope of work and the application.