Engineering Fundamentals: An Introduction to Engineering, 4th ed.c

11.5 Some Temperature-Related Material Properties 331

11.5 Some Temperature-Related Material Properties

Thermal Expansion

As we mentioned earlier in this chapter, accounting for thermal expansion and contraction of

materials due to temperature fluctuations is important in engineering problems, including the

design of bridges, roads, piping systems (hot water or steam pipes), engine blocks, gas turbine

blades, electronic devices and circuits, cookware, tires, and in many manufacturing processes.

In general, as the temperature of a material is increased, the material will expand — increase in

length — and if the temperature of the material is decreased, it will contract — decrease in length.

The magnitude of this elongation or contraction due to temperature rise or temperature drop

depends on the composition of the material. The coefficient of linear thermal expansion pro-

vides a measure of the change in length that occurs due to any temperature fluctuations. This

effect is depicted in Figure 11.13.

The coefficient of linear expansion, aL, is defined as the change in the length, ¢L, per orig-

inal lengthLper degree rise in temperature, ¢T, and is given by the following relationship:

aL (11.24)

¢L

L ¢T

L

L

■Figure 11.13

The expansion of a material

caused by an increase in its

temperature.

TABLE 11.9 Typical Insulating Values for Clothing

Insulation Values (clo)

1 clo 0.155 m

2

C / W or

Clothing 1 clo 0.88Fft

2

h /Btu

Walking shorts, short-sleeve shirt 0.36

Trousers, short-sleeve shirt 0.57

Trousers, long-sleeve shirt 0.61

Trousers, long-sleeve shirt, plus suit jacket 0.96

Same as above, plus vest and T-shirt 1.14

Sweatpants, sweatshirt 0.74

Knee-length skirt, short-sleeve shirt, panty hose, sandals 0.54

Knee-length skirt, short-sleeve shirt, full slip, panty hose 0.67

Knee-length skirt, long-sleeve shirt, half slip, panty hose,

long-sleeve sweater 1.10

Same as above, replace sweater with suit jacket 1.04

Source:Copyright © 1997 American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc.

http://www.ashrae.org. Reprinted by permission from ASHRAE 1997 Handbook-Fundamentals.

Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).

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