thermal

Thermal is an adjective relating to heat or temperature. In science and engineering, it describes properties or processes connected with thermal energy, heat transfer, or temperature differences. The term comes from the Greek therme, meaning heat.

Thermal energy is the internal energy of a system due to microscopic motion of its particles. Temperature measures the average kinetic energy of those particles. Heat transfer occurs by conduction, convection, and radiation, and is governed by properties such as thermal conductivity, specific heat capacity, and thermal diffusivity. Materials may expand or contract with temperature changes, a phenomenon described by the coefficient of thermal expansion.

Applications include thermal management in buildings and electronics, thermal insulation to reduce heat loss, and HVAC systems. Thermal imaging uses infrared cameras to visualize temperature distributions. The design and analysis of thermal processes rely on thermodynamics and heat transfer theory, often with standards for thermal performance such as R-values or U-factors in construction.

Units and measurements follow the physical quantities involved: energy in joules, power in watts, and temperature in kelvin or degrees Celsius. Absolute zero is 0 K, the lower limit of the thermodynamic temperature scale. The concept of thermal performance is central to energy efficiency, safety, and comfort across many disciplines.