Mechanisms of Heat Transfer

FE 546 Thermal Process Engineering
Heat Transfer
CONDUCTION
Mechanisms of Heat Transfer
There are three modes of heat transfer:
Conduction is the transfer of heat by molecular motion in solid bodies.
Convection is the transfer of heat by fluid flow, created by density differences and buoyancy effects, in fluid products.
Radiation is the transfer of electromagnetic energy between two bodies at different temperatures.
Heat Transfer by Conduction
Energy transfer by conduction takes place when different parts of a solid body are at
different temperatures. Energy flow in the form of heat takes place from the hotter, more energetic state, to the colder, less energetic state.
The quantity of heat transferred under steady-state conditions:
Formulation of Problems Involving Conduction Heat Transfer
The mathematical basis of the problems encountered in the determination of the temperature distribution in heating canned foods by conduction.
Unsteady-state conduction heat transfer equations is Fourier’s equation
A simpler equation is generally used
1. The surface temperature is prescribed and does not vary with time, i.e. a surface is exposed to an instantaneous change in temperature. It applies to steam heating and is often assumed in heat transfer modeling work.
The average temperature will be signified by putting a bar over the temperature term, thus the volume-average temperature is given by
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