ABSTRACT
CONTENTS
3.1 Introduction ................................................................... 58 3.2 Steady State Conduction .............................................. 60 3.3 The Shape Factor .......................................................... 72 3.4 Graphical Method for Wall Heat Transfer
and Design ..................................................................... 75 3.5 Convection...................................................................... 80 3.6 Forced Convection ......................................................... 85
3.6.1 Boundary Layer and Convection..................... 86 3.6.2 Forced Convection over Flat Plate.................. 88 3.6.3 Forced Convection inside Tubes...................... 97 3.6.3A Laminar Flow ................................................... 98 3.6.3B Turbulent Flow................................................. 99 3.6.4 Heat Transfer in Coils ................................... 108
3.7 Natural Convection (Flat Walls) ................................ 113 3.7.1 Free Convection over Horizontal Pipes .......... 116 3.7.2 Free Convection inside Enclosures ................. 121
3.8 Radiative Heat Transfer ............................................. 124 3.9 Radiation Exchange between Bodies......................... 128
3.9.1 Radiative Exchange between Two Parallel Surfaces............................................... 129
3.9.2 Radiative Exchange between Article and Enclosure ................................................... 132
3.10 Radiation Screens........................................................ 133 3.11 Radiation Exchange inside and outside
Furnaces....................................................................... 137 3.12 Radiation in Absorbing Media ................................... 140 3.13 Radiation Loss from Furnace Openings.................... 146 3.14 Extended Surfaces....................................................... 161
3.1 INTRODUCTION
Industrial heating is based on the science of “heat transfer.” Heat (
Q
◊ q
) is produced or is available from a heat source such as a combustion flame, a hot surface, and a hot filament or wire. From these sources it is transferred to a cold surface or medium such as an object or work, a cold wall, or the surrounding cold environment. Studying the rate (
dq
/
d
t
) of heat transfer and obtaining the quantity of heat transferred (
∫
q d
t) are the principal objectives of studying heat transfer. The flow of heat is always from a higher temperature to a lower one, i.e., under a temperature gradient. The thermal state of a body or surface is indicated by its temperature (
T
,
t
). Heat will always flow from a higher to lower temperature, i.e., a positive temperature gradient.
