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)?

VIDEO TRANSCRIPT

This is Giancoli Answers with Mr. Dychko. The ideal efficiency the best efficiency in other words that you can get with a heat engine with liquid nitrogen as the low temperature reservoir and ambient room temperature as the high temperature reservoir is one minus the low temperature divided by the high temperature. So it's one minus seventy seven Kelvin divided by two hundred and ninety three Kelvin which is seventy four percent.