Refrigeration problem 2
From https://www.nzifst.org.nz/resources/unitoperations/httrapps4.htm
10. A refrigeration plant using ammonia as refrigerant is evaporating at -30°C and
condensing at 38°C, and extracting 25 tons of refrigeration at the evaporator. For
this plant, assuming a theoretical cycle, calculate the:
(a) rate of circulation of ammonia, kg s-1
(b) theoretical power required for compression, kW
(c) rate of heat rejection to the cooling water, kW
(d)COP,
(e) volume of ammonia entering the compressor per unit time, m3 s-1
[(a) 0.0842 kg s-1 ;(b) 31.6 kW ;(c) 0.12 MJ s-1 ;(d) 2.8 ;(e) 0.08 m3 s-1 ]
First, we need to draw the cycle on the ammonia refrigerant P-H diagram (see
next page). A good way to remember what each of the sides represent, is that
they are in the same arrangement and order as in the diagram above.
1. Draw horizontal lines at the evaporating and condensing temperatures to
represent those operations.
2. Then draw the straight vertical line on the left representing the expansion
process from where the phase boundary intercepts the condenser
temperature straight down to the evaporator temperature
3. And finally, the isentropic line representing the compression process.
a) We can use the evaporation tons to work this out.
.
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