ENGINEERING APPLICATION Suppose the Brayton cycle engine

Chapter , Problem 84

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ENGINEERING APPLICATION Suppose the Brayton cycle engine (see 83) is run in reverse as a refrigerator in your kitchen. In this case, the cycle begins at temperature and expands at constant pressure until its temperature is Then the gas is adiabatically compressed until its temperature is And then it is compressed at constant pressure, until its temperature is Finally, it adiabatically expands until it returns to its initial state at temperature (a) Sketch this cycle on a diagram. (b) Show that the coefficient of performance, is (c) Suppose your Brayton cycle refrigerator is run as follows. The cylinder containing the refrigerant (a monatomic gas) has an initial volume and pressure of 60 mL and 1.0 atm. After the expansion at constant pressure, the volume and temperature are 75 mL and The pressure ratio for the cycle is 5.0. What is the coefficient of performance for your refrigerator? (d) In order to absorb heat from the food compartment at the rate of 120 W, what is the rate at which electrical energy must be supplied to the motor of this refrigerator? (e) Assuming the refrigerator motor is actually running for only 4.0 h each day, how much does it add to your monthly electric bill. Assume 15 cents per kWh of electric energy and 30 days in a month.