The efficiency of a heat engine is to be improved by lowering the temperature of its low-temperature reservoir to a valuer τl, below the environmental temperature τl, by means of a refrigerator. The refrigerator consumes part of the work produced by the heat engine. Assume that both the heat engine and the refrigerator operate reversibly. Calculate the ratio of the net (available) work to the heat Qh supplied to the heat engine at temperature τh. Is it possible to obtain higher net energy conversion efficiency in this way?