Difference between Conduction, Convection, and Radiation

Heat transfer is a phenomenon that can be achieved by any matter that is made of atoms and molecules. It is found that the atoms will not stay still but are in a varied motion from time to time. The movement of atoms and molecules inside a body is the main reason heat is generated. Because of the increase in heat, thermal energy is also increased. Every matter or body possesses heat and thermal energy. If the movement of molecules is more in number, then more heat is produced. Heat transfer is the transfer of heat from a hot body to a cold body.

Heat transfer

Heat transfer, according to thermodynamics, means the motion of heat particles across any system’s border based on the difference in temperature among the system and its surroundings. The difference obtained while taking temperature is called its ‘potential’. It causes heat transfer from one body to another. Heat can also be called flux.

The following are the three basic modes of heat transfer:

• Conduction
• Convection
• Radiation

Conduction

Conduction is a process that happens when the flow of heat is from high-temperature object to lower temperature object. Here, a specific area that contains higher kinetic energy is capable of transferring thermal energy towards the area that consists of lower kinetic energy. During this process, the particles that contain high speed collide with low-speed particles. Hence, the low-speed particles gain some speed which also increases their kinetic energy. This heat transfer happens through physical contact. This type of action is also described as heat conduction or thermal conduction.

Conduction equation

A metal body can conduct heat way better according to the coefficient of thermal conductivity. Given below is the equation for the rate of conduction,

Where,

Q = heat transferred per unit time
K = thermal conductivity of the body
A = area of heat transfer
T(hot) = hot region temperature
T(cold) = cold region temperature

Examples of conduction

• While ironing the clothes, heat is transferred from the iron plate to the clothes.
• During summer days, on beaches, heat can be conducted through the sand as sand particles are considered good conductors of heat.
• When we place an ice cube in our hands, due to the heat present in our hands, the ice cube starts to melt and becomes liquid.

Convection

Convection is the motion of fluid molecules from the regions that contain higher temperature to the lower temperature ones.

Convection equation

The volume of the liquid will increase if the temperature increases. This type of effect is called displacement. Following is the equation to calculate the convection rate,

Where,
Q = heat transferred per unit time Hc = coefficient of convective heat transfer
A = area of heat transfer
Ts = surface temperature
Tf = fluid temperature
 

Examples of convection

• Circulation of blood in warm-blooded animals happens with the aid of convection. They also increase body temperature.
• While boiling water, denser molecules move towards the bottom whereas the less dense molecules travel towards the top surface of the water. Due to this transfer, a circular motion of molecules is created which helps the water to heat up.
• Water present around the equator is warm and it moves towards the poles, whereas on the other hand, water contained in the poles is way cooler and moves towards the equator.

Radiation

In our daily life, we can experience radiant heat in many forms. Radiant heat is thermal radiation. The emission of electromagnetic waves helps generate thermal radiation. These waves can carry the energy that is contained in the emitting body. Radiation occurs if the medium is in a vacuum or transparent, and it can be solid or liquid. This radiation occurs when molecules present in matter move randomly. Electromagnetic radiation is emitted due to the motion of charged protons and electrons. Therefore, while looking at the radiation heat transfer, it can be measured by a device called a thermocouple. This device can be utilized for the measurement of temperature.

Radiation equation

When the temperature keeps on increasing, the wavelengths contained in the spectra of the emitted radiation see a downfall. This can result in the emission of shorter wavelengths. The equation given below is the Stefan-Boltzmann law for thermal radiation,

Where,
P = net power of radiation A = area of radiation
Tc = temperature in the surroundings
Tr = radiator temperature
e = emissivity
o = Stefan’s constant

Examples of radiation

• Ultra-violet rays from the sun.
• Radiation emitted by a microwave oven.
• Release of alpha particles during the decay of Uranium-238 into Thorium-234.