# Different ways of 'Heat Transfer'

This resource deals with the overview or some highlights of basics of heat transfer process in the real world. There are mainly three modes of heat transfer viz. heat conduction in solids, heat convection in fluid-solid interaction and radiation from any object with a finite temperature.

## Introduction:

Heat transfer is the process of transferring the heat from higher temperature body to lower temperature body (due to temperature gradient). In actual practice, there are main three modes via heat can be transferred.

1. Heat Conduction (in solids)
2. Heat Convection (in liquids and gases)
3. Thermal Radiation (applicable to all)

## Heat Conduction:

• Conduction is the heat transfer between bodies and matters which are in direct contact. Conduction occurs at a macroscopic level between adjacent molecules of solids. Conduction happens due to diffusive transfer of kinetic energy of molecules with adjacent molecules.

• The material with higher thermal conductivity(a property of material) can rapidly absorb and reject the heat compared to the material with lower thermal conductivity. E.g. Silver is more conductive than iron.

• Conduction is governed by Fourier's Law. According to the law, heat transfer by conduction is directly proportional to the amount of temperature difference and inversely proportional to the distance between them.

• Heat conduction always requires solid body medium for heat transfer.

• ## Heat Convection:

• Convection is the transfer of the heat between solid and liquid interface due to bulk motion of particles of fluid with a solid body. Normally stationary fluid in contact with solid body transfers the heat by mainly due to conduction only not by convection. Convection is dominant than conduction when fluid is in motion.

• Heat convection is governed by 'Newton's law of cooling' which tells that amount of heat transfer by convection is directly proportional to the temperature difference between the solid and fluid and heat transfer coefficient. Heat transfer coefficient is dependent on geometry, flow property.

• Heat transfer cup of tea during heating on stove is an example of convection.

• Heat convection requires fluid-solid interface as a medium for heat transfer.

• Thermal radiation (not radioactive radiation) is heat transfer due to finite temperature of body itself. The body emits thermal radiation proportional to the fourth power of its temperature multiplied by Stephan Boltzmann Constant.

• Thermal radiation takes in form of electromagnetic waves and it does not required any medium for heat transfer. Even in vacuum, thermal radiation can happen. In actual practice, we feel hotter due to sunlight which is nothing but the example of thermal radiation.

• One can reduce the thermal radiation by putting radiation shield of high reflective material to add resistance to the flow of thermal radiation. This is the only way to reduce thermal radiation. Other modes like conduction and convection can be removed by use of vacuum but thermal radiation cannot be removed completely.

• Heat transfer in furnace is example of thermal radiation.

• Note: In actual practice, all of the three modes can be present for heat transfer.

Author: Revanth16 Dec 2013 Member Level: Gold   Points : 4

Heat Transfer in Human Body:
The principles of heat transfer applied in engineering also applicable for Human body in heat transfer.Heat is provided in the body by continuous metabolism of nutrients that supplies energy to our body.Human body also maintain continues temperature to make body healthy.So like meachines our human body also remove excesses heat from body in order to maintain its temparature.It use the principles of latent heat to remove excesses temperature from our body.Human body is the complex machine in the earth.

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