Metal Foams: A Design Guide

52 Metal Foams: A Design Guide
Thermal conductivity (W/m.k)
100
10
1
T-Conductivity vs.
Volumetric specific heat
Alulight (1)
Alulight (0.751)
Manual2.CMS; MFA 5-12-97; MetFoam DB
Duocel (0.254)
Fraunhofer (0.551)
Duocel (0.235)
Fraunhofer (0.4)
Duocel (0.198)
Duocel (0.162)
Cymat (0.355)
Fraunhofer (0.8)
Alulight (0.55)
Alporas (0.21)
Alporas (0.245)
Alulight (0.49)
Alulight (0.372)
a = 10 −4
Cymat (0.083)
a = 10 −5
Hydro (0.143)
a = 10 −6
Cymat (0.155)
Cymat (0.166)
Hydro (0.3)
INCO (0.385)
Hydro (0.4)
60 80 100 200
Specific heat x Density (kJ/m3 400 600 800 1.0E+3
K)
Figure 4.11 Thermal conductivity, , plotted against volumetric specific
heat Cp for currently available metal foams. Contours show the thermal
diffusivity a D /Cp in units of m 2 /s
They are shown as full lines on the chart. Thermal conductivity is the property
which determines steady-state heat response; thermal diffusivity determines
transient response. Foams are remarkable for having low values of thermal
conductivity. Note that the open-cell aluminum foams have relatively high
thermal diffusivities; the nickel foams have low ones. All closed-cell aluminum
foams have almost the same value of a.
4.4 Scaling relations
Tables 4.2(a)–(c) give scaling relations for foam properties. They derive partly
from modeling (for which see Gibson and Ashby, 1997) most of it extensively
tested on polymeric foams, and partly from empirical fits to experimental data
of the type shown in the previous section.
The properties are defined in the first column. In the rest of the table a
symbol with a subscripted s means ‘property of the solid metal of which the
foam is made’; a symbol with a superscript ‘*’ is a property of the foam. The