Cooling is the process of removing heat from an object or system. The most common methods of cooling are convection, conduction, and radiation.
Convection is the transfer of heat by the movement of fluids. When a fluid (liquid or gas) is heated, it expands and becomes less dense than the surrounding fluid. The warmer fluid rises and the cooler fluid sinks, creating circulation that transfers heat from one area to another. Convection can be used to cool objects by circulating air or water around them.
Conduction is the transfer of heat through direct contact between two objects. When two objects with different temperatures are in contact, heat will flow from the hotter object to the cooler object until they reach equilibrium (the same temperature). Metals are good conductors of heat, which is why they are often used in cookware and heating elements. Insulators are materials that do not conduct heat well, making them ideal for use in insulation and thermal clothing.
Radiation is the transfer of heat through electromagnetic waves. All objects emit radiation; however, hot objects emit more radiation than cold objects. This is why we feel warm when we stand in sunlight but not when we stand in shade – even though both locations may have identical air temperatures. Radiation can be used to cool objects by directing infrared waves (heat) away from them using mirrors or other reflective surfaces.