318 Chapter 11 Temperature and Temperature-Related Parameters
The temperature differenceT 1 T 2 over material thickness is commonly referred to as the
temperature gradient. Again, keep in mind that a temperature gradient must exist in order for
heat transfer to occur. Thermal conductivity is a property of materials that shows how good the
material is in transferring thermal energy (heat) from a high-temperature region to a low-
temperature region within the material. In general, solids have a higher thermal conductivity
than liquids, and liquids have a higher thermal conductivity than gases. The thermal conduc-
tivity of some materials is given in Table 11.3.Example 11.5 Calculate the heat transfer rate from a single-pane glass window with an inside surface tem-
perature of approximately 20C and an outside surface temperature of 5C. The glass is 1 m tall,
1.8 m wide, and 8 mm thick, as shown in Figure 11.8. The thermal conductivity of the glass
is approximatelyk1.4 W/mK.L 8 1 mm2a
1 m
1000 mm
b0.008 m
TABLE 11.3 Thermal Conductivity of Some Materials at 300 K
Material Thermal Conductivity (W/mk)
Air (at atmospheric pressure) 0.0263
Aluminum (pure) 237
Aluminum alloy-2024-T6 (4.5% copper, 1.5% magnesium, 177
0.6% manganese)
Asphalt 0.062
Bronze (90% copper, 10% aluminum) 52
Brass (70% copper, 30% zinc) 110
Brick (fire clay) 1.0
Concrete 1.4
Copper (pure) 401
Glass 1.4
Gold 317
Human fat layer 0.2
Human muscle 0.41
Human skin 0.37
Iron (pure) 80.2
Stainless steels (AISI 302, 304, 316, 347) 15.1, 14.9, 13.4, 14.2
Lead 35.3
Paper 0.18
Platinum (pure) 71.6
Sand 0.27
Silicon 148
Silver 429
Zinc 116
Water (liquid) 0.61Copyright 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).圀圀圀⸀夀䄀娀䐀䄀一倀刀䔀匀匀⸀䌀伀䴀圀圀圀⸀夀䄀娀䐀䄀一倀刀䔀匀匀⸀䌀伀䴀