Which branch of physics is devoted to the study of heat and related phenomenon?

Thermodynamics is a branch of physics concerned with heat and temperature and their relation to energy and work. The behavior of these quantities is governed by the four laws of thermodynamics, irrespective of the composition or specific properties of the material or system in question. The laws of thermodynamics are explained in terms of microscopic constituents by statistical mechanics. Thermodynamics applies to a wide variety of topics in science and engineering, especially physical chemistry,chemical engineering and mechanical engineering.

The four laws of thermodynamics are:

Zeroth: If two systems are each in thermal equilibrium with a third, they are also in thermal equilibrium with each other.

First: The internal energy of an isolated system is constant.

Second: Heat cannot spontaneously flow from a colder location to a hotter location.

Third: As a system approaches absolute zero, all processes cease and the entropy of the system approaches a minimum value.