2016 Apr

Modes of Heat Transfer

April 4, 2016


Thermodynamics can be defined as the study of the relationship between heat and other energy forms. Thermal equilibrium is attained when macroscopic variations in the system stop occurring. When you place ice-cube in a glass of water, since the water is at a higher temperature, thermal energy will be transferred to the ice-cube. This continues until the melt completely to form water that’s precisely the same temperature as that in the glass. Hence, a state-of thermal equilibrium is attained. Thermodynamics is applied to systems which are in thermal equilibrium. The heat transfer phenomenon deals with systems those aren’t in thermal equilibrium.

Temperature gradient or temperature variation between the systems of interest is a necessity for heat-transfer. Temperature gradient can be defined as the temperature rate of change or the temperature difference per unit length. Heat transfer in virtually any direction is dependent upon the temperature gradient magnitude towards that direction. Heat transfer is founded on these essential laws, namely: 1) Laws of Thermodynamics, 2) Newton’s laws of motion, 3) Law of conservation of mass

Modes of Heat Transfer learnt during our Physics Tuition classes

Conduction: It occurs in either solids or fluids. It’s the transfer of heat though a medium or between objects that are in physical contact. When you touch a hot pan on fire, your hand burns because heat conduction occurs from the heated pan to your hand.

Convection: Convection can be defined as the heat transfer within a fluid or from a fluid into a solid surface. It’s a combination of random molecular movement (diffusion) and bulk fluid movement (advection). The best instance of this mode of heat-transfer is the convection currents. When a cast-iron frying pan containing water is put on a burner, convection currents forms in the water. Less dense molecules, which are warmer, move up while the ones which are colder sink down.

Radiation: At finite temperature, matter emits energy in the form of electromagnetic waves in space. This is referred to as ‘radiation’. An excellent example is the radiation from the Sun surface. Folks can take a pew around a camp-fire and warm their hands over it due to the heat radiated by the fire. Availability of a medium is unimportant for the propagation of the radiation electromagnetic waves. Actually, radiation effectively most takes place in a vacuum. It also occurs in solids, gases, and liquids.

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