3
Heat and mass transfer, basic principles ....................................................... 69
3.1 Introduction ......................................................................................... 69
3.2 Basic relations in transport phenomena ................................................. 69
3.2.1
Basic laws of transport .............................................................. 69
3.2.2 Mechanisms of heat and mass transfer ....................................... 70
3.3 Conductive heat and mass transfer ........................................................ 70
3.3.1
The Fourier and Fick laws ........................................................... 70
3.3.2 Integration of Fourier’s and Fick’s laws for
steady-state conductive transport ............................................ 71
3.3.3 Thermal conductivity, thermal diffusivity
and molecular diffusivity ............................................................ 73
3.3.4 Examples of steady-state conductive heat and
mass transfer processes .............................................................. 76
3.4 Convective heat and mass transfer ......................................................... 81
3.4.1
Film (or surface) heat and mass transfer coeffi cients ................... 81
3.4.2 Empirical correlations for convection heat and mass
transfer
..................................................................................... 84
3.4.3 Steady-state interphase mass transfer ......................................... 87
3.5 Unsteady state heat and mass transfer ................................................... 89
3.5.1
The 2 nd Fourier and Fick laws .................................................... 89
3.5.2 Solution of Fourier’s second law equation for an
infi nite slab ............................................................................... 90
3.5.3 Transient conduction transfer in fi nite solids ............................... 92
3.5.4 Transient convective transfer in a semi-infi nite body .................... 94
3.5.5 Unsteady state convective transfer .............................................. 95
3.6 Heat transfer by radiation ..................................................................... 96
3.6.1
Interaction between matter and thermal radiation
96
3.6.2 Radiation heat exchange between surfaces .................................. 97
3.6.3 Radiation combined with convection ........................................ 100
3.7 Heat exchangers ................................................................................. 100
3.7.1
Overall coeffi cient of heat transfer ............................................ 100
3.7.2
Heat exchange between fl owing fl uids ....................................... 102
3.7.3
Fouling ................................................................................... 104
3.7.4
Heat exchangers in the food process industry ............................ 105
3.8 Microwave heating .............................................................................. 107
3.8.1
Basic principles of microwave heating ....................................... 108
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