(I) A heat engine's high temperature $T_H$ could be ambient temperature, because liquid nitrogen at 77 K could be $T_L$ and is cheap. What would be the efficiency of a Carnot engine that made use of heat transferred from air at room temperature (293 K) to the liquid nitrogen "fuel"(Fig.15$-$25)?
FIGURE 15-25 Problem 22. (CANT COPY FIGURE)