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A refrigerator using R-12 as the working fluid keeps the refrigerated space at ?16? in an...

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Mechanical Engineering

A refrigerator using R-12 as the working fluid keeps therefrigerated space at ?16? in an environment at 27?. You are askedto upgrade this refrigerator by replacing R-12 with theozone-friendly R-134a. What changes in the pressure levels wouldyou suggest in the new system? How do you think the COP of the newsystem will compare to the COP of the old system?

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3.9 Ratings (812 Votes)

properties of r-12

At -16C p=175.6 kPa , hf=185.2 KJ/kg hg=345.5 KJ/kg

At 27C p=686.7 kPa hg=364.2 KJ/kg

properties of r-134a

At -16C p=157.3 kPa ,hf=30.69 KJ/kg ,hg=240.87 KJ/kg

At 27C p=707.308 kPa ,hg=413.3 KJ/kg

By changing refrigerent evaporator pressure will reduce while condensor pressure will increase.

Consider latent heat of vaporization of r-12 =160.3KJ/kg

prssure ratio with r-12=3.90

latent heat of vaporization of r134a =210.18

prssure ratio with r134a=4.5

COP is ratio of refrigerating effect to work required.

Now for r134a system refrigerating effect is more mean while work input is more so COP may increase or decrease.
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