Page 305 - Academic Press Encyclopedia of Physical Science and Technology 3rd Chemical Engineering

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Encyclopedia of Physical Science and Technology En007c-310 June 30, 2001 17:30

Heat Exchangers

Kenneth J. Bell
Oklahoma State University

I. Applications in Chemical Engineering
II. Criteria for Selection
III. Types of Heat Exchangers
IV. Basic Heat Exchanger Equations
V. The Design Process
VI. Further Developments in Design and Application

GLOSSARY rosion, and/or thermal degradation of organic process
fluids.
Condensation Conversion of a vapor to a liquid by Heat exchanger Any device that allows two or more flu-
removing the latent heat of condensation from the ids at different temperatures to transfer heat from the
vapor. hotter stream(s) to the colder stream(s). Usually the
Condenser Heat exchanger with the primary function of streams are separated by solid walls, but the streams
condensing a vapor by transferring heat to a coolant are allowed to mix in direct-contact heat exchangers.
stream. Heat transfer coefficient Ratio of the rate of heat trans-
Conduction Heat transfer within a substance by molec- fer in a heat exchanger (in watts) to the product of the
ular motion (and also by electron flow in electrical heat transfer area of the heat exchanger (in square me-
conductors). The molecular motion may be actual dis- ters) and the mean temperature difference between the
placement of molecules (the predominant mechanism hot and cold streams (in kelvins). The higher the heat
in gases) or may be collisions between adjacent vibrat- transfer coefficient, the more effective the heat transfer
ing molecules (the predominant mechanism in liquids process.
and nonmetallic solids). Latent heat transfer Transfer of heat required to bring
Convection Heat transfer within a flowing fluid by phys- about a phase change (e.g., condensation or vaporiza-
ical translation of one element of the fluid (consisting tion) in a fluid. (Compare to sensible heat transfer.)
of a very large member of molecules) characterized by Many heat exchangers involve both latent and sensible
one temperature to another part of the flow field at a heat transfer.
different temperature. The heat is carried as the internal Mean temperature difference Effective difference be-
energy of the molecules. tween the temperature of the hot stream and the tem-
Fouling Unwanted deposit on heat transfer surface due perature of the cold stream in a heat exchanger. This is
to sedimentation, crystallization, biological films, cor- the driving force for the heat transfer process.

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