Page 162 - Mechanical Engineers' Handbook (Volume 4)

1 Conduction Heat Transfer 151

Table 3 Thermal Properties of Building and Insulating Materials (at 300 K) a
Thermal Specific
Density Conductivity, k Heat, C p 10 6
2
3
Description/Composition (kg/m ) (W/m K) (J/kg K) (m /s)
Building boards
Plywood 545 0.12 1215 0.181
Acoustic tile 290 0.058 1340 0.149
Hardboard, siding 640 0.094 1170 0.126
Woods
Hardwoods (oak, maple) 720 0.16 1255 0.177
Softwoods (fir, pine) 510 0.12 1380 0.171
Masonry materials
Cement mortor 1860 0.72 780 0.496
Brick, common 1920 0.72 835 0.449
Plastering materials
Cement plaster, sand aggregate 1860 0.72 — —
Gypsum plaster, sand aggregate 1680 0.22 1085 0.121
Blanket and batt
Glass fiber, paper faced 16 0.046 — —
Glass fiber, coated; duct liner 32 0.038 835 1.422
Board and slab
Cellular glass 145 0.058 1000 0.400
Wood, shredded/cemented 350 0.087 1590 0.156
Cork 120 0.039 1800 0.181
Loose fill
Glass fiber, poured or blown 16 0.043 835 3.219
Vermiculite, flakes 80 0.068 835 1.018
a Adapted from Ref. 1.

x and the thermal conductivity by k for n 1, 2,..., N. Assuming that the interfacial
n n
resistance is negligible, (i.e., there is no thermal resistance at the contacting surfaces), the
overall thermal resistance can be expressed as
R x n
N
n 1 kA
n
Similarly, for conduction heat transfer in the radial direction through a number of N con-
centric cylinders with negligible interfacial resistance, the overall thermal resistance can be
expressed as
R ln(r n 1 /r )
N
n
n 1 2 kL
n
where r inner radius, r N 1 outer radius.
1
For N concentric spheres with negligible interfacial resistance, the thermal resistance
can be expressed as
R 1
1
N
n 1 4 k
r n r n 1
where r inner radius, r N 1 outer radius.
1