Chapter 7, Problem 7.30P

An electrically-driven pump operating at steady state draws water from a pond at a pressure of 1 bar and a rate of 40 kg/s and delivers the water at a pressure of 4 bar. There is no significant heat transfer with the surroundings, and changes in kinetic and potential energy can be neglected. The isentropic pump efficiency is 80%. Evaluating electricity at 8 cents/kWh estimate the hourly cost of running the pump.

A system executes a power cycle while receiving 1000 Btu by heat transfer at a temperature of 900oR and discharging 600 Btu by heat transfer at a temperature of 540oR. There are no other heat transfers.Determine the cycle thermal efficiency.  Use the Clausius Inequality to determine σcycle, in Btu/oR. Determine if this cycle is internally reversible, irreversible, or impossible.

A heat pump cycle is used to maintain the interior of a building at 25°C. At steady state, the heat pump receives energy by heat transfer from well water at 9°C and discharges energy by heat transfer to the building at a rate of 120,000 kJ/h. Over a period of 14 days, an electric meter records that 1500 kW · h of electricity is provided to the heat pump.Determine:(a) the amount of energy that the heat pump receives over the 14-day period from the well water by heat transfer, in kJ.(b) the heat pump’s coefficient of performance.(c) the coefficient of performance of a reversible heat pump cycle operating between hot and cold reservoirs at 25°C and 9°C.