0.4 kg of R-134a is contained in a cylinder with a piston attached to a spring.T

Question

0.4 kg of R-134a is contained in a cylinder with a piston attached to a spring.The initial volume and pressure inside the cylinder are 5 liters and 504.16 kPa respectively. Heat is transferred into the gas and the piston moves to compress the spring such that the pressure increases linearly with volume until the cylinder hits some stops. Just when the piston hits the stops, the volume and pressure are 10 liters and 800 kPa. Heat is further added without the piston moving until the pressure reaches 1200 kPa.

a)  What are the initial and final temperatures?

b)  How much work is done by the R-134a during the entire process?

c)  How much heat is transferred into the R-134a ove the entire process?

0.4 kg of R-134a is contained in a cylinder with a piston attached to a spring.The initial volume and pressure inside the cylinder are 5 liters and 504.16 kPa respectively. Heat is transferred into the gas and the piston moves to compress the spring such that the pressure increases linearly with volume until the cylinder hits some stops. Just when the piston hits the stops, the volume and pressure are 10 liters and 800 kPa. Heat is further added without the piston moving until the pressure reaches 1200 kPa.

Explanation / Answer

R-134a molecular weight=102gm/mole

no. of moles in cylinder=400/102

=3.92 mole

P1=504.16 kPa

V1=5 liter=5*10^-3 m^3

PV=nRT

T1=504.16*10^3*5*10^-3/(3.92*8.314)

=77.34 K

T2=800*10^3*10*10^-3/(3.92*8.314)

=245.47 K

work done on R-134a=P2V2-P1V1

=800*10^3*10*10^-3-504.16*10^3*5*10^-3

=5497 J

work done by R-134a=-5497 J

Heat Transfered Q=change in internal energy+work done

  

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