4 replies to this topic

[acjeson]

I am try to determine the flow rate of propane refrigerant given only the suction and discharge pressure of the compressor, cooling water supply temperatures to the condenser and subdewpoint cooler, and areas of the evaporator, condenser, and subdwpoint cooler.  I was also given the inlet temperature of the ethane on the tubeside of the evaporator and outlet temperature and volumetric flowrate.  I was trying to do an energy balance around the evaporator to determine the flow rate but am unable to get an accurate rate.  Any recommendations?

 

 

Thank you.

[kabtik]

1. Propane is use as the refrigerant for cooling ethane.

2. Propane evaporates in the evaporator while cooling ethane

3. The evaporated propane is compressed to a higher pressure and sent to condenser where it is condensed using cooling water

4. The propane is condensed below its dew point temperature and the cycle continues.

 

Hope this is exactly what you are trying to say. Please furnish a sketch and the temperatures and pressures you talked about. If you leave your post like this, not many experience persons will give you a helping hand. It looks too vague.

 

I have attached a simple sketch that you may want to improve on.

 Propane loop.xls   51.5KB   68 downloads

[Art Montemayor]

Aaron:

 

You fail to submit a Process Flow Diagram (PFD) of the mechanical refrigeration cycle that you are working with.  This is what you should do first in order to fully explain your queries.  Kabtik shows you a very simple block diagram, but what you need to supply is a PFD with the flow conditions at each location within the cycle.  A drawing is far better than your written explanation.  For example, we don’t know if you are using an economizer or not.

 

What I understand is that you are to determine the Propane refrigerant flow rate within the cycle (you don’t say where in the cycle).  To calculate this, you need to know the evaporator pressure or temperature on the refrigerant side as well as the duty the evaporator handles.  Lacking the duty, you have to calculate it using the process fluid’s (ethane) flow rate and the difference in temperature it undergoes.  What doesn’t make for good sense is that you claim you can’t calculate an “accurate” answer to the ethane flow rate.  There can be only ONE answer when done properly.  How it that you know your answer is wrong?  Where did you get the “right” answer?  We can’t comment on your “answer” if you don’t submit your detailed calculations (in an organized and orderly electronic spreadsheet) we can’t check them or comment on your inability to get the “right” answer.

 

I have developed detailed spreadsheets calculating various refrigeration cycles – including many propane examples – in the past and have uploaded them here in our Forums on many threads.  To obtain this information all you have to do is use our SEARCH engine, study the threads and download all the workbooks.  One such example is found at:

http://www.cheresour... +refrigeration

 

[acjeson]

Yes sir, Kaptik, that is the process.  I updated your diagram with all the parameters that were given to me related to this process. 

Attached Files

•  Propane loop.xls   68KB   58 downloads

[kabtik]

I love to stand behind my senior friend, Art. Mine is just a block diagram to bring you out of your reticence. Follow him and you are safe. I have downloaded the spreadsheet in one of the threads he responded to and it's a piece of work. Cheers.