Chapter 5, Problem 5.132EP

An air conditioner is a device used to cool the inside of a home. It is, in essence, a refrigerator in which mechanical work is done and heat removed from the (cooler) inside and rejected to the (warmer) outside. A home air conditioner operating on a reversible Carnot cycle between the inside, absolute temperature T2, and the outside, absolute tempera- ture T1 > T2, consumes P joules/sec from the power lines when operating continuously. (a) In one second, the air conditioner absorbs Q2 joules from the house and rejects Q1 joules outdoors. Develop a formula for the efficiency ratio Q2/P in terms of T1 and T2. (b) Heat leakage into the house follows Newton's law Q = A(T, – T2). Develop a formula for T, in terms of T1, P, and A for continuous operation of the air conditioner under constant outside temperature T and uniform (in space) inside temperature T2. (c) The air conditioner is controlled by the usual on-off thermostat and it is observed that when the thermostat set at 20°C and an…

Q2: Source 1 can supply energy at the rate of 12000 kJ/min at 320°C. A second source 2 can supply energy at the rate of 120000 kJ/min at 70°C. Which source (1 or 2) would you choose to supply energy to an ideal reversible heat engine that is to produce large amount of power if the temperature of the surroundings is 35°C?

Heat engine and refrigerator. Consider a heat engine operating between temperatures Th and Tj. During each cycle with time At, work W is extracted, so Pout = W/At. (a) Assuming the processes are all reversible, what is the efficiency of this heat engine, n = Wout/Qn? (b) Now assume that the low temperature of the heat engine is lowered by a reversible refrigerator, such that the heat engine operates between Th and T. The refrigerator takes input power Pin = Win/At and operates between T and T, where Ti < T. Draw an energy- entropy flow diagram. (c) Calculate the net efficiency (Wout - Win)/Qh. Is the efficiency of this system higher, lower, or the same as your answer for (a)?