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- A gas is contained in a vertical piston-cylinder assembly, as shown in the figure below. Determine the gage pressure of the gas, in kPa, needed to maintain static equilibrium in the piston-cylinder assembly if an external force 𝐹ex = 1,000 N acts on the piston in the downward direction. The mass of the piston is 24.5 kg and the piston diameter is 0.1 m. The atmospheric pressure is 1 bar. Assume the piston can move smoothly (with no friction) in the cylinder and the gravitational acceleration is g = 9.81 m/s2
- The refrigerator shown in the figure below steadily receives a power input of 0.1 kW and rejects energy by heat transfer to the surroundings. Heart transfer occurs by convection and radiation from the refrigerator’s external pipe to the surroundings. Calculate the refrigerator’s coefficient of performance if the outer surface area, the temperature and the emissivity of the refrigerator’s pipe are 0.75 m2, 47C and 0.96, respectively. The heat transfer coefficient for convection between the pipe and the surroundings, which are at a temperature of 27C, is 25 W/m2·K.
- A radioactive gas undergoes an adiabatic process in a piston-cylinder assembly during which the pressure-volume relation is 𝑝𝑉 = constant. The mass of radioactive gas is 0.25 kg. It is known that the initial pressure and volume are p1 = 1.5 bar and V1 = 0.75 m3, respectively. The final pressure is p2 = 1 bar. The change in kinetic energy is 13 kJ and the change in potential energy is -25 kJ. Determine the change in specific internal energy of the radioactive gas, in kJ/kg.

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