Chapter 5, Problem 5.35P

a student, observed that she can focus more in her lessons if the air conditioning unit in her spacious room is opened. She usually set the temperature to be maintained in her room at 10 C. The temperature outside of her room is 40 C. The refrigerant of her AC unit is HFC-134 a. What is the coefficient of performance of her AC unit if it is operating on a Vapor Compression refrigeration cycle? The compressor efficiency is 0.7.

3. A Carnot engine is coupled to a Carnot refrigerator so that all the work produced by the engine is used by the refrigerator in extraction of heat from a heat reservoir at 0 °C at the rate of 35 kJ/s. The source of energy of the Carnot engine is a heat reservoir at 250 °C. If both devices discard heat to the surroundings at 25 °C, how much heat does the engine absorb from its heat-source reservoir ? Draw a schematic diagram of the coupling of the heat engine and the refrigerator showing the direction of heat absorbed and discarded and the work involved.

5. A refrigerator is to remove heat from the cooled space at a rate of 300 kJ/min to maintain its temperature at 28°C. If the air surrounding the refrigerator is at 25°C, determine the minimum power input required for this refrigerator. in min 300 Odo Refrigerator kJ/min -8°C 25°C

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Problem 2 A window air conditioner consumes 0.8 kW of electricity during steady-state operation. If the COP of the air conditioner is 3, calculate the rate at which the AC unit removes thermal energy from the room. If this is a Carnot air conditioner and the room is maintained at 27°C, what is the outside temperature? Do you think this is a Carnot AC unit?

3.) When a gas surrounded by air is compressed or expands adiabatically, its temperature rises or decreased even though there is no heat input or dissipated to the gas. Where does the energy come from to raise or lower the temperature? 4.) Why must a room air conditioner be placed in a window rather than just set on the floor and plugged in? Why can a refrigerator be set on the floor and plugged in?

A food compartment is to be maintained at 21°C by a refrigeration system. The total cooling load of the food compartment is estimated to be 330 kJ/h and the heat rejection by the condenser is 480 kJ/h. The outdoor air temperature is 35°C. draw the schematic diagram of the refrigeration system determine the power input required to operate the refrigeration system in kW.

Two Carnot engines are hooked up in series so that the waste thermal energy at constant tempera- ture TM for the first engine is used as the heat source for the second engine. The high temperature reservoir for engine 1 is at TH = 327 C. The low temperature reservoir for engine 2 is at TL = 27 C. TL < TM < TH. For what value of TM in C will the combined engine produce the greatest total work output, wi + w2? TH 1 W1 TM 2 W2 TL Figure 2: Two Carnot engines operate in series.

1. A Carnot refrigerator operates between two reservoirs, one at 250K and the other at 300K. It is claimed that the refrigerator has a COPr of 6. Determine: a. If the energy removed from the low temperature reservoir is 160 kJ, then what is the energy delivered to the high temperature reservoir and how much work must be put into the system. b. Is the refrigerator even possible?