An insulated piston-cylinder device initially contains 0.03 m^3 of air at 120 Kp

Question

An insulated piston-cylinder device initially contains 0.03 m^3 of air at 120 Kpa and 27 degree C. Air is now heated for 300 sec by a 50 W resistance heater placed inside the cylinder. The pressure of air is maintained constant during this process. The surrounding are at 27 degree C and 100 KPa. Calculate the use PV = m RT mass of air. Find the h_1 (initial) and h_2 (final); (may use table A-17) Calculate the irreversibility for this process (I; X_destrayed) Calculate (X_2 - X_1) given (PV = mRT h_2 - h_1 = (u_2 - u_1) + P(V_2 - V_1) R_air = 0.287 kJ/kg k

Explanation / Answer

a)

m = PV/RT

= 120*10^3 * 0.03 / (287*(27+273))

= 0.0418 kg

b)

Work done W = Heat input = 50*300 = 15000 J = 15 kJ

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