1. Refrigerant 134a at 30 lbf/in.2, 408F enters a compressor operating at steady state with a mass flow rate of 150 lb/h and exits as saturated vapor at 160 lbf/in.2 Heat transfer occurs from the compressor to its surroundings, which are at 408F. Changes in kinetic and potential energy can be ignored. A power input of 0.5 hp is claimed for the compressor. Determine whether this claim can be correct.
2. Ammonia enters a horizontal 0.2-m-diameter pipe at 2 bar with a quality of 90% and velocity of 5 m/s and exits at 1.75 bar as saturated vapor. Heat transfer to the pipe from the surroundings at 300 K takes place at an average outer surface temperature of 253 K. For operation at steady state, determine
(a) the velocity at the exit, in m/s.
(b) the rate of heat transfer to the pipe, in kW.
(c) the rate of entropy production, in kW/K, for a control volume comprising only the pipe and its contents.
Rate of entropy production, in kW/K, for an enlarged control volume that includes the turbine and enough of its surroundings that heat transfer occurs at the ambient temperature, 278C.