Question

differentiate between conduction convection and radiation as a means of transportation of energy state the equation for each and explain each symbol used

Answer 1

Conduction : It is the flow of heat through solids and liquids by vibration and collision of molecules and free electrons. For example, the heat transfer by conduction through the bodywork of a car.

formula of conduction is given as,

q = - kA (T / n)

Where, T / n = temperature gradient

A = area of cross-section

k = thermal conductivity

Convection : Flow of heat through currents within a fluid (liquid or gas). Convection is the displacement of volumes of a substance in a liquid or gaseous phase. For example, when heating up water on a stove, the volume of water at the bottom of the pot will be warmed up by conduction from the metallic bottom of the pot and its density decreases.

formula of convection is given as,

q = hA (T_s - T)

Where, h = for convective heat transfer coefficient

A = area implied in the heat transfer process

T_s = temperature of the system

and T = reference temperature

Radiation : It is heat transfer by electromagnetic waves or photons. It does not need a propagating medium. The energy transferred by radiation moves at the speed of light. For example, if I place an object (such as a coin, a car, or myself) under the direct sunbeams, I will note in a little while that the object will be heated.

formula of radiation is given as,

q = A [(T)⁴]

where, q = heat transferred by radiation

emissivity of the system

= Stephan-Boltzmann constant