Chapter 5, Problem 5.42P

Baseboard heaters are basically electric resistance heaters and are frequently used in space heating. A homeowner claims that her 5-year-old baseboard heaters have a conversion efficiency of 100 percent. Is this claim in violation of any thermodynamic laws? Explain.

A heat engine working with a thermal efficiency of 35% receives 2 kW of heat from a furnace. The waste heat rejected from the engine is

A heat pump is used to extract heat from the outside atmosphere to heat the inside of a building. On a day when the outside air temperature is Tc°C, the heat pump is operating to a COP of 2.7, maintaining the inside temperature of the building at Th°C. If the building is losing heat at the rate of 62,893 kJ/hour in these conditions, determine how much power (kW) must be supplied to a heat pump.

A heat engine that propels a ship produces 500 Btu/lbm of work while rejecting 300 Btu/lbm of heat. What is its thermal efficiency?

The coefficient of performance of a residential heat pump is 1.6. Calculate the heating effect in kJ/s this heat pump will produce when it consumes 2 kW of electrical power.

2. Consider a heat engine that operates between high temperature reservoir at 650°C and a heat sink at 30°C. Part of the work generated by the heat engine is used to drive the refrigerator where the food compartment is kept at -12 °C in an environment of 30°C. The total heat gain to the food compartment is 2500 kJ/h and the heat rejection to the condenser is 4000 kJ/h. Determine (0.416 kW, 1.667, 2233.14 kJ/h, 2791.43 kJ/h, 732 kJ/h) a) Power input to the compressor in kW and COP of the refrigerator b) Maximum heat that is required by the heat engine to drive the refrigerator c) Maximum heat that is required by the heat engine to drive the refrigerator if there is a 20% loss of power during transmission. d) Total rate of minimum heat rejection to the environment.

1. Is a temperature difference necessary to operate a heat engine? State why or why not. 2. Definitions of efficiency vary depending on how energy is being converted. Compare the definitions of efficiency for the human body and heat engines. How does the definition of efficiency in each relate to the type of energy being converted into doing work? 3. Why-other than the fact that the second law of thermodynamics says reversible engines are the most efficient-should heat engines employing reversible processes be more efficient than those employing irreversible processes? Consider that dissipative mechanisms are one cause of irreversibility. 1. (a) What is the efficiency of a cyclical heat engine in which 75.0 kJ of heat transfer occurs to the environment for every 95.0 kJ of heat transfer into the engine? (b) How much work does it produce for 100 k) of heat transfer into the engine? 2. The engine of a large ship does 2.00×10°J of work with an efficiency of 5.00%. (a) How much heat…

A heat pump is used to extract heat from the outside atmosphere to heat the inside of a building. On a day when the outside air temperature is Tc°C, the heat pump is operating to a COP of 3.7, maintaining the inside temperature of the building at Th°C. If the building is losing heat at the rate of 53,709 kJ/hour in these conditions, determine how much power (kW) must be supplied to a heat pump? Keep two decimal places

(1) Explain how a heat engine works. (2) Explain the 2nd Law of thermodynamics.