Chemical Engineering License Review, Second Edition
This text contains 146 problems with detailed step-by-step solutions, and is an ideal study guide and the first truly practical, no-nonsense review for the difficult PE Exam.
TABLE OF CONTENTS Chemical Engineering License Review, Second Edition
Chapter 3: Heat Transfer
There are three modes of heat transfer: conduction, convection, and radiation. The basic laws governing these are covered in this chapter.
Thermal Conduction
Fourier's law states that
| where q k | = heat transferred by conduction, Btu/h |
| k | = thermal conductivity of material, Btu/(h ft 2 F/ft) |
| A | = area of cross section perpendicular to direction of heat flow, ft 2 |
| dT/ dx | = temperature gradient in the direction of heat flow, F/ft |
If k is independent of temperature,
where L is the distance between the hot and cold surfaces in the direction of heat flow, in feet.
Thermal Radiation
By the Stefan-Boltzmann law, the heat transfer by radiation for a blackbody is
| where q r | = heat transfer by radiation, Btu/h |
| ? | = Stefan-Boltzmann constant |
| = 0.173 10 ?8 Btu/h ft 2 R 4 | |
| = 5.67 10 ?8 W/m 2 K 4 | |
| A 1 | = area of radiating surface, ft 2 |
| T 1 | = radiating surface temperature, R |
Real bodies emit radiation at lower rates than blackbodies. Gray bodies emit a constant fraction of the blackbody emission at each wavelength at a given temperature. The net rate of the radiation heat transfer from a gray body at T 1 to a surrounding blackbody at T 2 is given by
where ? 1 is the emissivity of the gray surface.
Heat transfer between two gray bodies is given...
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