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10-04-2009, 02:55 AM #1
Student Project (Cascade Refrigeration System)
Hi,
I am working on a project to optimize the evaporating temperatures, superheat and subcooling on a 2 stage cascade refrigeration cycle using R404a and R744 (CO2). I've setup everything in EES but I have a few concerns regarding the solution I'm getting:
My ltc evap temp is -45C and im testing 10C superheat. When I ran the equations, I got a temperature of 58C at the ltc compressor outlet at almost 4 MPa, which seems a bit high to me, but I really dont know for sure.
I tried to parametrically plot my COP vs. the htc evap temperature, and the COP just keeps going up without bound. I was expecting to see an inverse parabola, but the COP never decreases.
If anyone has any suggestions for me please let me know. Thanks!
David
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10-04-2009, 12:17 PM #2
Re: Student Project (Cascade Refrigeration System)
I'm not sure what exactly you input in the calculation, but I'm pretty confident that 58°C at compressor discharge is quite normal, provided the condensing temperature is subcritical (let's say around 50K discharge superheat)
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12-04-2009, 02:36 AM #3
Re: Student Project (Cascade Refrigeration System)
ok, thats good to know, i wasn't sure.
But now, my problem is that when I plot the COP vs. the cascade temp for a specific set of design conditions, the COP just increases almost linearly without a limit. Any ideas?
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19-04-2009, 12:00 AM #4
Re: Student Project (Cascade Refrigeration System)
That's also normal. As the evap temperature increases, the COP increases as much, and the reason is the higher mass flow at suction together with a better volumetric efficiency. Please note that the evap temperature in a real case scenario is bound to the physical constraint of the testing setup
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22-03-2010, 02:26 PM #5
Re: Student Project (Cascade Refrigeration System)
hey buddy may i have ur analysis on EES..??? if u dont have any prob plz send it to me....i thnk i m working on somewhat similar project so i need ur help
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24-03-2010, 10:23 AM #6
Re: Student Project (Cascade Refrigeration System)
is there any way to plot property curve (say T-s diagram) for two different fluids on same graph, i.e. overlaying one's property plot over another in 'EES'?
if anyone knows plz reply.
actually i need combined T-s diagram for ammonia and ethane on one plot.
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24-03-2010, 12:01 PM #7
Re: Student Project (Cascade Refrigeration System)
Coolpack can assist. It's a free download based on the EES platform.
Engineering Specialist - Cuprobraze, Nocolok, CD Technology
Rarefied Technologies ( SE Asia )
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24-07-2010, 06:46 AM #8
Re: Student Project (Cascade Refrigeration System)
Hey guys,
I am also working on a project based on CO2 cascade refrigeration systems......if anybody can send me the code pertaining to the optimisation of cascade system in terms of intermediate temp.(IT) and overlap temp(DT) I would be highly thankful.
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29-05-2011, 01:11 AM #9
Re: Student Project (Cascade Refrigeration System)
I am also working on a project based on CO2 cascade refrigeration systems......if anybody can send me the code pertaining to the optimisation of cascade system in terms of temp(DT) .
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