Question

State Second Law of Thermodynamics. How is heat engine different from a refrigerator?

Answer 1

The Second Law of Thermodynamics states that the state of entropy of the entire universe, as an isolated system, always increases over time. The second law also states that the changes in the entropy in the universe can never be negative.

Difference in heat engine and refrigerator:
In a heat engine, heat is transferred from a higher temperature level called source to a lower temperature level called sink. Work is obtained during this process.

A refrigerator is a reversed heat engine. Heat is transferred from the lower temperature level to higher temperature by applying external work to maintain the temperature below atmospheric temperature.