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scarecrow75
28-08-2016, 02:53 PM
Hi

I'm new here and was hoping for some guidance. As part of my engineering course I have been asked to carry out some analysis of the performance of refrigeration plant incorporating a water cooled condensor. I logged 5 sets of data based on varying heat loads on the evaporator using R134a refrigerant noting that my pressures are Gauge not Abs.

My problem really is how to start my p-h chart. I somewhat understand the process involved in my own head but am struggling to convey it in chart form. For example, if I take t4 and t2 as my evaporator and condensor temperatures respectively why are my recorded pressures not matching my temperatures on the p-h chart for R134a (t2=57.9degC does not equate to 11.6bar nor t4=12.7degC does not equate to 3.6bar.) Also worth noting although I waited 5mins after every alteration to heat load for stabilization no-one verified results.

If anyone can get me started in particular with the plotting of these results I'm pretty sure I can calculate COP, CC, Power absorbed, etc.

Thanks



14288)

scarecrow75
29-08-2016, 01:52 PM
Hi

I'm new here and was hoping for some guidance. As part of my engineering course I have been asked to carry out some analysis of the performance of refrigeration plant incorporating a water cooled condensor. I logged 5 sets of data based on varying heat loads on the evaporator using R134a refrigerant noting that my pressures are Gauge not Abs.

My problem really is how to start my p-h chart. I somewhat understand the process involved in my own head but am struggling to convey it in chart form. For example, if I take t4 and t2 as my evaporator and condensor temperatures respectively why are my recorded pressures not matching my temperatures on the p-h chart for R134a (t2=57.9degC does not equate to 11.6bar nor t4=12.7degC does not equate to 3.6bar.) Also worth noting although I waited 5mins after every alteration to heat load for stabilization no-one verified results.

If anyone can get me started in particular with the plotting of these results I'm pretty sure I can calculate COP, CC, Power absorbed, etc.

Thanks



14288)


Anyone????

seanf
29-08-2016, 02:37 PM
Does your discharge temperature and pressure not put you into the superheated vapour region, and your evaporator inlet temp and pressure put you only just into the liquid region. rather than expecting saturated temperatures at those pressures?

scarecrow75
29-08-2016, 06:59 PM
Does your discharge temperature and pressure not put you into the superheated vapour region, and your evaporator inlet temp and pressure put you only just into the liquid region. rather than expecting saturated temperatures at those pressures?

yes, I expect some superheating prior to compression and accept that my refrigerant is a mixture of fluid/vapour on entry to evaporator. What's is really getting me is that my evaporator inlet temp is higher than the compressor suction temp in all 5 cases above. How can this be?

seanf
29-08-2016, 08:26 PM
Are the instruments reading correctly and temps taken at the same time. Would also depend on the system as well and where you mean by compressor suction and evap inlet. Is there a change in pressure between the inlet and where you take your evap pressure reading.

RANGER1
29-08-2016, 09:05 PM
Some helpful information, maybe

https://www.parker.com/literature/Sporlan/Sporlan%20pdf%20files/Sporlan%20pdf%20Miscellanous/5-200.pdf

https://www.youtube.com/watch?v=yHExWd1LtIM

https://www.youtube.com/watch?v=vu9aNXlhbEI

el_donks
19-09-2016, 11:06 AM
As i see it, condenser temperature should be t3 and not t2, which is discharge temp i guess.

In this case, you'd have a p(cond)= 11,6 bar -> t(p,cond)~=48C

t3=42C so you're working with subcooling of 48-42= 6K

For the evaporator, if you name evaporator inlet as the suction side of the evaporator, then maybe there's liquid out of the evaporator┐?┐?

p(evap)=3,6 bar -> t(p,evap)~=13C

t(evap)= 12,7C -> there's no superheating -> compressor suction is lower because there's liquid evaporating┐?┐?