Question

a rigid 14 l vessel initially contains refrigerant 134a at 30 c and has a specific volume of 0.07m^3/kg. the mixture is having heat transfer to reach a pressure of 200kPa. calculate the heat transfer required for this process. state the process is heat addition or rejection to or from the system.

Answer 1

Case 1: T=30^oC = 303K; v = 0.07 m³/kg

We know that,

P=RT/v

=>

(8.314J.mol .Kx 303K) P1 0.07m3.kg 1

=36 kPa

Case 2: P₂ = 200 kPa

Since, the vessel is rigid, so volume is constant (Isochoric process).

So,

P2 T2

From Ideal Gas Law, we know that,

Cu V (P2 - P) R

Also, refrigerant 134a is a polyatomic gas (1,1,1,2-Tetrafluoroethane), so,

Cv=3R (for polyatomic gases)

So, heat transferred,

=

3R x 14(200 36) =6888.J

So, heat transferred is 6.88 kJ