Modes of Heat Transfer

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DEFINITION OF HEAT TRANSFER|
Heat transfer is energy in transit due to temperature difference . Whenever there exists a temperature difference in a medium or between media, heat transfer must occur. The basic requirement for heat transfer is the presence of temperature difference . There can be no net heat transfer between two mediums that are at the same temperature. The temperature difference is the driving force for heat transfer, just as the voltage difference is the driving force for electric current flow and pressure difference is the driving force for fluid flow. The rate of heat transfer in a certain direction depends on the magnitude of the temperature gradient (the temperature difference per unit length or the rate of change of temperature) in that direction. The larger the temperature gradient, the higher the rate of heat transfer|

PHYSICAL ORIGINS AND RATE EQUATIONS:It is important to understand the physical mechanisms which underlie the heat transfer modes and that we are able to use the rate equations that quantify the amount of energy being transferred per unit time. Conduction:Conduction can be imagined as a atomic or molecular activity which involves the transfer of energy from the more energetic to the less energetic particles of a substance due to interactions between the particles. |  | Explanation: The physical mechanism of conduction is explained as follows: Consider a gas in which there exists a temperature gradient and assume that there is no bulk motion. The gas may occupy the space between two surfaces that are maintained at different temperatures, as shown in Figure 1.2. The temperature at any point is associated with the energy of gas molecules in proximity to the point. This energy is related to the random translational motion, as well as to the internal rotational and vibrational motions, of the molecules. | Higher temperatures are associated with higher molecular energies, and when neighboring molecules collide, as they...
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