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Chapter 21: Q. 15 (page 595)
What are (a) the thermal efficiency and (b) the heat extracted from the hot reservoir for the heat engine shown in
a.Thermal efficiency heat engine is.
b.The heat extracted from the hot reservoir for the heat engine is.
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A heat engine running backward is called a refrigerator if its purpose is to extract heat from a cold reservoir. The same engine running backward is called a heat pump if its purpose is to exhaust warm air into the hot reservoir. Heat pumps are widely used for home heating. You can think of a heat pump as a refrigerator that is cooling the already cold outdoors and, with its exhaust heat , warming the indoors. Perhaps this seems a little silly, but consider the following. Electricity can be directly used to heat a home by passing an electric current through a heating coil. This is a direct, conversion of work to heat. That is, of electric power (generated by doing work at the rate of at the power plant) produces heat energy inside the home at a rate of . Suppose that the neighbor鈥檚 home has a heat pump with a coefficient of performance of , a realistic value. Note that 鈥渨hat you get鈥� with a heat pump is heat delivered, , so a heat pump鈥檚 coefficient of performance is defined as.
a. How much electric power does the heat pump use to deliver of heat energy to the house?
b. An average price for electricity is about per dollar. A furnace or heat pump will run typically hours per month during the winter. What does one month鈥檚 heating cost in the home with a electric heater and in the home of the neighbor who uses a heat pump?
An ideal refrigerator utilizes a Carnot cycle operating between and . To turn of liquid water at into of ice at ,
How much heat is exhausted into the room and
How much energy must be supplied to the refrigerator?
A heat engine doesof work and exhaustsof waste heat during each cycle.
a. What is the engine's thermal efficiency?
b. If the cold-reservoir temperature is , what is the minimum possible temperature in of the hot reservoir?
What are (a) the heat extracted from the cold reservoir and (b) the coefficient of performance for the refrigerator shown in Figure Ex-?
A gas following the trajectory of FIGURE does of work per cycle. What is ?
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