TABLE OF CONTENTS Engineering thermal science includes thermodynamics and heat transfer. Thermodynamic analyses consider only systems in equilibrium. The role of heat transfer is to supplement thermodynamics with additional laws that allow the prediction of rates of energy transfer. These laws are based on different modes of heat transfer, namely conduction, radiation, and heat transfer by convection.
In this chapter, many of the heat transfer problems encountered in air-cooled heat exchangers and cooling towers are addressed. Specific solutions are presented for application in later chapters.
The mechanism by which heat is transferred in physical equipment is quite complex; however, there appear to be two rather basic and distinct types of heat transfer processes conduction and radiation.
Conduction is the transfer by molecular motion of heat between one part of a body to another part of the same body or by one body and another in physical contact with it. In fluids, heat is conducted by nearly elastic collisions of the molecules or by an energy diffusion process. Theory of heat conduction in solids distinguishes between conductors and nonconductors or dielectrics of electricity. In a dielectric, heat is conducted by lattice waves caused by atomic motion; in electrical conductors, free electrons behaving almost like gas molecules contribute additionally to heat conduction.
Radiation, or more precisely thermal radiation, is a phenomenon identical to the emission of light and is significant across the entire range of wave lengths from zero to infinity.
Frequently, the processes of conduction...
