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Avapour compression system using R12 works between

-15°C and 35°C as evaporator and condenser temperature respectively. Using PH chart determine

i. COP

ii. Mass flow of refrigerant per TR

iii. Piston displacement per TR using volumetric efficiency = 80%

iv. Heat rejected in the condenser per TR

v. Ideal COP

Marks: 5M, 6M

Year: Dec2014, Dec2015, Dec2013, May2014

1 Answer
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$T_E=T_{sat_{Pe}}=-15℃,T_C=T_{at_{Pc}}=35℃$

From P-H chart of R12,

$h1=345 kJ/kg,$

$h2=374 kJ/kg$,

$h3=h4=234 kJ/kg$

COP of given system = $\frac{R.E.}{Wc}=\frac{h1-h4}{h2-h1}$ COP=3.83

Also, $Q ̇_a=m ̇_R×(h1-h4)$

For 1 TR capacity, $1 x 3.5= m ̇_R×(345-234)$

mass flow rate,$m ̇_R=0.031 \frac{kg}{sec}=1.842 \frac{kg}{min}$

$Also,\ m ̇_R×v1=piston \ displacement \ per \ TR×η_{vol}$

$v1=0.091 \frac{m3}{kg} \ from \ p-h \ chart$

Therefore, piston displacement per TR = 0.2095m3/min

Rate at which heat is rejected in condenser per TR=Q ̇_r=m ̇_R×(h2-h3)=4.34 kJ/sec

We know, ideal COP = $\frac{T_E}{T_C-T_E }$= 5.16

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