Heat Transfer – Conduction, Convection, and Radiation

Heat transfer refers to the phenomenon of transferring energy from one point to another. This specific mechanism includes heat conduction, heat convection, and radiation heat transfer. The transfer of heat in natural and man-made conditions involves all of these processes.

In this article, we will be discussing the concept of heat transfer- conduction, convection, and radiation. We will also discuss conduction, convection, and radiation. 

Conduction, Convection, and Radiation 

Conduction 

• Heat is transferred between adjacent molecules during the heat conduction process, which is a slow process. 

• The flow of heat energy during the conduction process is by direct contact. Therefore, heat energy is emitted from a warmer object and is absorbed by a colder object. The best example of this phenomenon is heating a frying pan kept on a stove. 

• The transfer of heat within solid materials and between two solid materials occurs because of heat conduction. 

• Metals are highly conductive substances. The transfer of heat occurs because the molecules of the hotter substance begin to vibrate faster than the molecules of the cooler object. Thermal equilibrium is maintained during heat transfer because the heat absorbed by one object is balanced by the heat emitted by another object. 

• The factors affecting heat transfer rate through conduction are temperature and the thickness of the substance through which the heat energy is transferred. Therefore, the thicker the material of the substance, the longer it will take to transfer heat energy through it. Therefore, when we feel cold during the night, we sleep with a thicker blanket. 

• The thermal conductivity of a material refers to the constant of proportionality K. A material will conduct more heat if the value of K for that material is high. 

• The SI unit of thermal conductivity K is (J s-1 m-1 K-1) or W m-1 K-1.

• Conductors are instruments/tools through which heat energy can easily flow, whereas an insulator is an instrument that doesn’t allow heat energy to transfer. 

• We can observe in our day-to-day lives several combinations of instruments that have a good conductor and a good insulator. For example, cooking pots are made from metals such as copper or brass, which are great conductors. But if we notice closely, their handles are made from insulators such as plastic foam or wood. 

Convection 

• The heat convection process is faster and more efficient than the conduction process and involves the rapid movement of heated fluid.

• The convection process occurs only within gases and liquids and refers to the transfer of heat while mixing a fluid. 

• Heat convection can be caused due to both natural and forced conditions; however, gravity plays a huge role during the natural convection process. 

• The molecules in a liquid vibrate faster when heated, and at a higher temperature, these molecules begin to expand to occupy their space. When the liquid is heated, less dense fluid begins to rise to the surface, the cooler fluid takes its place. And this repeated rising and falling between warmer liquids and cooler liquids sets up the convection current. 

• An example of a naturally occurring convection process is sweating. When our surrounding temperature exceeds our body temperature, sweating allows us to cool off as it evaporates from our body. 

• Another example of naturally occurring convection is the cool wind phenomenon at sea. As we all know, the specific heat of water is higher than the specific heat of any other substance. Therefore, as the warm air from the land rises during the daytime, the cooler air from the sea moves in and takes its place. And with this, a thermal convection cycle is set up. 

Radiation heat transfer 

• Radiation heat transfer refers to the transmission of electromagnetic radiation. The energy radiated by electromagnetic radiation is called radiant energy. 

• While the transfer of heat through conduction and convection cannot be completed without a transport medium, conduction and convection modes of heat transfer are also incapable of transferring heat energy between bodies separated by a distance in a vacuum. Heat transfer through radiation does not require a medium through which heat is transferred. 

• Different electromagnetic waves have different wavelengths and travel in a vacuum with the same speed as the speed of light, 3 x 108 m s-1. This is how, even in a vacuum, the earth receives heat and ultraviolet radiation from the sun. 

• An ideal radiator, or blackbody, is an object that absorbs all of the radiation that falls upon it. An ideal radiator is the same colour as an ideal absorber. 

• Thermal radiation refers to the electromagnetic radiation emitted by all bodies that emit radiation by its temperature. 

• Thermal radiation is partially absorbed and partially reflected when it falls on a body. The amount of heat energy absorbed by a body when thermal radiation falls on it depends upon the colour of the body. 

• We can see the application of this property in our day-to-day lives, too, as we can observe that black bodies absorb more radiant energy than bodies of other lighter colours. Therefore, we wear lighter colours during summers and darker colours during winters. This is because lighter shades absorb less heat from the sun, and darker shades absorb more heat from the sun and keep our bodies warm during winters. 

• Similarly, cooking utensils have blackened bottoms that maximise heat absorption from the stove and allow the vegetables to cook quickly. 

Conclusion 

Heat transfer refers to the phenomenon of transferring energy from one point to another. This specific mechanism includes heat conduction, heat convection, and radiation heat transfer. With this, we conclude our article on heat transfer- conduction, convection, and radiation. This article discussed the meaning of conduction, convection, and radiation heat transfer and how these processes are applied in our day-to-day lives.