Question

Why is there always some waste heat in a heat engine?

Answer 1

Heat is wasted in the heat engine because:

1. Heat engines work in a cycle where each step has different working conditions.

1. For example, the above-given cycle.
2. In stage 1, the heat is converted to work by the expansion in the cylinder, and in stage 2, the piston return to the initial state for the next cycle.
3. Of the net output work, a very less amount of work is required for the cylinder to return to its initial position.
4. The hot gas from stage 1 is expelled into the environment, which is waste energy that gets continuously expelled as the cycle continues.
5. Some amount of energy is to be dumped for the reason that the heat when it flows into the system, it brings some entropy along with it, which must be removed before the starting of the cycle.
6. To remove this entropy, every heat engine must dump some amount of waste heat into the surrounding.

Hence, there is always some waste energy in a heat engine.