A piston-cylinder assembly contains m = 5 kg steam as shown in the figure. The a

Question

A piston-cylinder assembly contains m = 5 kg steam as shown in the figure. The assembly undergoes an expansion from state 1, where the specific internal energy is u_1 = 2709.9 kJ/kg, to state 2, where the specific internal energy is u_2 = 2659.6kJ/kg. During the process, there is heat transfer to the steam with a magnitude of 80kJ. Also, a paddle wheel transfers energy to the steam by work in the amount of 18.5 KJ There is no significant change in the kinetic or potential energy of the steam. Determine the energy transfer by work from the system (steam) to the surroundings. A gas is contained within a piston-cylinder assembly as shown in the figure. Initially, the piston face is at x = 0, and the spring exerts no force on the piston. As a result of heat transfer, the gas expands, raising the piston until it hits the stops. At this point the piston face is located at x = 0.06m, and the heat transfer ceases. The force exerted by the spring on the piston as the gas expands varies linearly with x according to F = kx where k = 9,000N/m, Friction between the piston and the cylinder wall can be neglected. The acceleration of gravity is g = 9.81 m/s^2 Additional information is given on the figure. Find the initial pressure of the gas in kPa. Find the work done by the gas on the surroundings in J. If the specific internal energies of the gas at the initial and

Explanation / Answer

2) Energy transferred by work = 80 + 18.5 + 5 * ( 2709.9 - 2659.6)

                                                   =   350 kJ

3) a) Initial pressure = (9000 * 0.06)/(0.0078)

                                    = 69.23 kPa

     b) work done = 69.23 * 1000 * 0.0078 * 0.06

                           = 32.4 J

     c) specific internal energy =   32.4/(0.5 * 10-3)

                                                   = 64.8 kJ/kg

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