Question

A freon 12 simple saturation cycle operates at temperatures of ${35}^{o}C$ and -${15}^{o}C$ for the condenser and evaporator respectively. If a liquid vapour heat exchanger is installed in the system, with the temperature of the vapour leaving the heat exchanger at ${15}^{o}C$, the enthalpy of subcooled liquid at exit will be given as

	Superheated by
	20k	40k
(kPa)	h(c)	H(KJ/Kg)	S(KJ/KgK)	S(Kj/KgK)	H(KJ/kgK)	S(KJ/KgK)	H(KJ/Kg)	S(kJ/kgK)
$P_2$	55	09.5	201.5	0.6839	216.4	0.731	231.0	0.7741
$P_1$	-15		181.0	0.7052	195.2	0.751	205.7	0.7942

• A. 57.23 KJ/Kg
• B. 53.11 KJ/Kg
• C. 51.05 kJ/Kg
• D. 59.51 kJ/Kg

Answer 1

The correct option is C 51.05 kJ/Kg


Degree of superheat at suction
$t_2-t_1=15-(-15)=30k$

By interpolating for superheated vapour
$h_2=193.2+\frac{30-20}{20}\times (205.7-193.2)$

$h_2=199.45kJ/kg$

Now,
$h_2-h_1=h_4-h_5$

$199.45-181=69.5-h_5$

$h_5=51.05KJ/kg$