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Refrigeration System

refrigeration condenser propylene

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#1 abcdssjenfl


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Posted 12 March 2018 - 09:38 AM


I am trying to design refrigeration system with propylene refrigerant. This course is pretty new for me, so I read from book "Principles of Refrigeration" by R. J. Dossat. I have some questions related with my findings.

Refrigeration system is needed to cool H2 and lisght hydrocarbons (C1-C3) from sistillation column from -26C to -35. Distillation columnn operating at 18 bar

So I want to describe my cycle

1. I assumed that saturated liquid propylene leaves the condenser at 0.4 MPa and -13C

2. It passes through  the heat excahnger for subcooling, cools down to -20C (0.4Mpa)

3. then passes through throttling valve decreases to evaporater temperature and pressure -38C and 0.16Mpa

4. Leaves evaporater as saturated vapor same temp same pressure

5. Saturated vapor propylene enters same heat exchanger for superheating and leaves HE at -25C and 0.16 Mpa

6. Superheated vapor enters the compressor and leaves compressor at 12C and 0.4 MPa (I assumed entropy is constant during compression and from enthaply pressure diagram I got this temperature)

7. It enters back to 1st condition within condenser -13Cand 0.4 MPa


I hope this information is clear. Could you please check it. I wanted to upload my work on enthalpy/pressure diagram but I dont know how to upload files here.

I used heat exchanger for subcooling, as I read subcooling process increases COP. There were two phase of subcooling. One is to use subcooler and other is HE.

In the book it was written as superheating is unavoidable even without HE, so I though that HE will be reasonable choice for both achieving subcooling and superheating. However, this sentence in the book made me confused "advantages from subcooling of the liquid in the HE are approximately offset by the disadvantages of superheating the vapor"


I hope someone can help me. Sorry for long explanation


#2 PingPong


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Posted 12 March 2018 - 11:04 AM

Without a process flow scheme it is difficult to visualize your design.


To upload use the [More Reply Options] button under the reply window.

Then scroll down to Attach Files.


By what means do you intend to condense the propylene at -13 oC ?

#3 abcdssjenfl


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Posted 12 March 2018 - 11:26 AM

Flow scheme will look like this I think.  Evaporation temperature is fixed at -38 oC.  After condenser there will subcooling and throttling valve, so I decided -13 oC will be enough to reach evaporation temperature.



Is it wrong?


In Pressure-Enthaply

A - after condenser

A* - after subcooling HE

B - after throttling valve

C - after evaporator

C* - after superheating HE

D - after compressor

E - condenser

Attached Files

#4 PingPong


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Posted 12 March 2018 - 05:05 PM

.... so I decided -13 C will be enough to reach evaporation temperature
I have no idea what that means.


Anyway, you can't simple "decide" to use any number.


You need to condense the propylene from the compressor using a cooling medium that is available in your unit.

If that is cooling water then the condensing temperature could be around 40 oC at resulting pressure.

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