Question

Help I System Announcements is ul Englheering Thermodynamics, 9e PRINTER VERSION BACK NEXT Problem 2.045 SI As shown in the figure below, a gas contained within a piston-cylinder assembly, initially at a volume of 0.1 m3, undergoes a expansion at p 3 bar to a final volume of V2 - 0.16 m3, while being slowly heated through the base. The change in internal energy of the gas is 0.25 KJ. The piston and cylinder walls are fabricated from heat-resistant material, and the piston moves smoothly in the cylinder. The local atmospheric pressure is 1 bar. V,-0.1 m (U2-U) 0.25kJ Gas (a) For the gas as the system, evaluate work and heat transfer, each in kl. (b) For the piston as the system, evaluate work and change in potential energy, each in k Part A 13

Answer 1

a) The work done for the system is, W = p(V_2 - V_1) = (3 bar) (1 times 10^5 Pa/1 bar) (0.16 m^3 - 0.1 m^3) (1 kJ/1000 N-m) W = 1.8 kJ The heat transfer is, Q = W + (U_2 - U_1) = (1.8 kJ) + (0.25 kJ) = > Q = 2.05 kJ b) For the piston system, Applying the first law of thermodynamics, Q = delta PE + delta KE + (U_2 - U_1) + W For this system change in kinetic energy is negligible, thus, delta KE = 0. In this process when the gas expands the piston rises up. It means the work is done on the system. The sign for work done on the system is negative. Thus, the work done for the piston system is, W_piston = -W_gas = > W_piston = 1.8 kJ The heat transfer for the system is, Q_piston = -Q_gas = > Q_piston = -2.05 kJ