Determine...
a.) The mass flow rate of R-134a through each compressor in lbm/h.
b.) The power input to each compressor in Btu/h.
c.) The coefficient of performance of the cycle.
Tuesday, May 22, 2007
HW #9, P6 - Ammonia Cascade Refrigeration Cycle - 8 pts
The diagram shows a two-stage, vapor-compression refrigeration system that uses ammonia as the working fluid. The system uses a flash drum to achieve intercooling. The evaporator has a refrigeration capacity of 30 tons and produces a saturated vapor effluent at -20oF. In the first compressor stage, the refrigerant is compressed adiabatically to 80 psia, which is the pressure in the mixer. Saturated vapor at 80 psia enters the second compressor stage and is compressed adiabatically to 250 psia. Each compressor stage has an isentropic efficiency of 85%. Ther are no significant pressure drops as the refrigerant passes through the heat exchangers. Saturated liquid enters each expansion valve.
Determine...
a.) The mass flow rate of R-134a through each compressor in lbm/h.
b.) The power input to each compressor in Btu/h.
c.) The coefficient of performance of the cycle.
Determine...
a.) The mass flow rate of R-134a through each compressor in lbm/h.
b.) The power input to each compressor in Btu/h.
c.) The coefficient of performance of the cycle.
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6 comments:
I assume that part a) meant to say ....ammonia... and not R-134a, right?
Sunshine:
Yes, I meant to say ammonia, not R-134a. Sorry, I changed this problem at the last minute.
How does a ton translate into a unit of power?
Anon:
1 ton of refrigeration = 200 Btu/min. If you remove 200 Btu/min from 1 ton (2000 lbm) at 32 degF, it will freeze solid in 24 hours.
how does an ammonia thermostatic expansion valve differ from a typical expansion valve
Anonymous, 9:45 AM
The word thermostatic means that the valve position (and therefore the pressure drop across the valve) changes in response to changes in response to any deviation between the set-point temperature and the actual temperature in the refrigerated space.
Other than that important aspect, the expansion valves shown in this problem are the same as a thermostatic expansion valve.
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