Thermodynamics: An Engineering Approach 6th Edition, Yunus A. Cengel, Michael A.

Question

Thermodynamics: An Engineering Approach 6th Edition, Yunus A. Cengel, Michael A. Boles, problem 3-31; A piston-cylinder device contains 0.85 kg of refrigerant-134a at -10 degree Celsius. The piston that is free to move has a mass of 12 kg and a diameter of 25 cm. The local atmospheric pressure is 88 kPa. Now, heat is transferred to refrigerant-134a until the temperature is 15degree Celsius. Determine (a) the final pressure, (b) the change in volume of the cylinder, and (c) the change in the enthalpy of the refrigerant-134a. I have part (a) done, but i need (b), and (c). thanks you.

Explanation / Answer

a) Final pressure = Initial pressure

P2 = P1= Patm + m.g/(.D2/4) = 88 + (12 x 9.81)/(.0.252/4) x 10-3 = 90.4 KPa

b) at P1 = 90.4 kPa and T1 = -10°C , from table for 134-a

v1 = 0.2302 m3/kg h1 = 247.76 kJ/kg

also at P2 = 90.4 Kpa and T2 = 15 C

v 2 = 0.2544 m3/kg h2 = 268.16 kJ/kg

b) change in volume = m.(v2 - v1)

   =0.85 x (0.2544 -  0.2302)

   = 0.0205 m^3

c) change in enthalpy = m.(h2 - h1)

   = 0.85 x ( 268.16 - 247.76  )

   = 17.4 KJ

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