Heat transfer as the name suggests is a discipline of thermal engineering which deals with the transfer of heat energy from one point to another point. Unlike thermodynamics which deals with the change of state of matter, Heat transfer deals with rate of flow of heat from one place to another. The practical use of this subject cannot be stressed upon. From industries to every household, the implication of this subject can be found everywhere. Study of Heat Transfer helps us in reducing the loss of heat energy with proper insulation in industries, in insulation of walls during winters, in cooking and many more. Similarly study of Heat Transfer also helps us increase the Heat Transfer rate in automobiles; Electrical systems may damage critical components.
There are three main modes of Heat Transfer, namely conduction, convection and radiation. In conduction heat transfer, free electrons play the main role. 70% of the heat transferred in a body is due to the movement of free electrons after gaining energy from the hot part of the body. 30% of conduction heat transfer is due to molecular momentum transfer by the molecules as they vibrate more vigorously after gaining the heat energy. In fluids, convection is the primary mode of Heat Transfer, where there is actual movement of the fluid due to difference of density. Under normal condition, the hotter, less dense fluid rises up and the colder, heavier fluid moves inside to fill the void. Radiation is a form of Heat Transfer which takes place in the form of electro-magnetic waves. Radiation Heat Transfer requires no material medium. Radiation is the dominant mode of Heat Transfer where temperature differences are large. These electro-magnetic waves travel in straight path and can transverse large distance. Radiation is the only mode of energy transfer between the Sun and the Earth. In GATE Exam, Heat Transfer has a weightage of about 6 to 8 marks out of 100 on an average. With proper understanding, dedication and practice, it is very easy to score these 6 to 8 marks. Syllabus of HT: Modes of heat transfer, one dimensional heat conduction, resistance concept, electrical analogy, unsteady heat conduction, fins; dimensionless parameters in free and forced convective heat transfer, various correlations for heat transfer in flow over flat plates and through pipes; thermal, boundary layer; effect of turbulence; radiative heat transfer, black and grey surfaces, shape factors.
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