Refrigerant-134a is contained in a closed piston and cylinder assembly with the

Question

Refrigerant-134a is contained in a closed piston and cylinder assembly with the arrangement shown in the figure. There is no friction between the piston and cylinder walls. The piston has a mass of 4080 kg and the cross-sectional area of the piston is 0.4 m2. The initial temperature and volume of the R- 134a are 50degreeC and 2 m3. The refrigerant is heated until its temperature reaches 80degreeC. Calculate the following quantities: the initial and final pressure of the R-134a the mass of the R- 134a in the cylinder the internal-energy change of the R-134a during the process

Explanation / Answer

pressure on the fluid is only due to piston weight

so pressure is constant during the process

P(initial) = P(final) = m(piston)*g/A + P(atm)= 201.382 kpa

(b) at P=201.382kpa & T = 50'c

specific volume = .1277m3/kg(from table)

so mass of refrigerant = volume/specific vol.=2/.1277=15.66kg

(c)u = m*c*T= 15.66*1.92 *30=902.016 kj (taking specific heat value from table)

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