Heat and mass transfer equation; continuity equation; momentum equation;

The document outlines principles of heat and mass transfer, focusing on three-dimensional heat transfer equations in various coordinate systems, including Cartesian, cylindrical, and spherical coordinates. It discusses assumptions for steady-state conditions and the derivation of key equations related to thermal energy generation, thermal diffusivity, and the continuity equation for fluid flow. The content emphasizes fundamental concepts like conservation of mass, momentum, and thermal resistance in heat transfer scenarios.