Process for determining thermal conductivity and electrical resistivity of porous materials is described. Characteristics of materials are identified and used in development of mathematical models. Limitations of method are examined

Fortini, A.

Koh, J. C. Y.

English

NASA Technical Reports Server

October 1972
	 CORRECTED COPY
	 B72.10587 
Q NASA TECH BRIEF Lewis Research Center 
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Thermal Conductivity and Electrical

Resistivity of Porous Materials 
0
Thermal conductivity of porous material is an impor-
tant property in determining the temperature distribu-
tion in a coolant and in the porous structure in transpi-
ration cooling. Due to the irregularity of the micro-
structures, confident, theoretical calculation of thermal 
conductivity of porous materials is extremely difficult. 
Existing prediction methods are based on certain simplifi-
cations such as parallel cylinders, laminates in series, 
spheres dispersed in a conducting medium, etc. Even 
with a well-defined microstructure, the problem remains 
complex due to the existence of the interface resistance. 
Therefore, with the exception of parallel cylinders, a 
semi-empirical approach employing experimental data 
has been the only practical way of predicting the thermal 
conductivity of porous materials. 
A study was conducted to provide experimental data 
of thermal conductivity and electrical resistivity of 
(1) woven and sintered wire mesh made from 304L 
stainless steel wire, (2) 304L stainless steel sintered 
spherical powder, and (3) OFHC (oxygen free high con-
ductivity) copper sintered spherical powder. Three 
different porosities (.093, .203, .385) of each material 
were tested from a temperature range of 100°C to 
10000C and the data tabulated in a series of tables and 
charts. The data were correlated into equations and 
compared with other published data and correlations. 
It was found that the thermal conductivity, A, and 
electrical resistivity, p, can be related to the solid 
material properties, NO and Po, and the porosity, , of 
the porous matrix regardless of the matrix structure by 
the following correlation equations:
(1) For sintered powder and woven wire mesh, the 
dimensionless thermal conductivity can be repre-
sentedby x 
NO	 l+l0 
and the dimensionless electrical resistivity is given by 
P	 1+1l2 
(2) Within the temperature range where there is no 
magnetic transformation; the thermal conductivity 
of porous metals is related to the electrical re-
sistivity and temperature, T, by the Wiedermann-
Franz-Lorenz equation: 
A = LT 
P 
For a high conductivity material, the Lorenz 
constant, L, and the lattice component of conduc-
tion, b, are independent of porosity. For low con-
ductivity materials, the lattice component depends 
on the porosity. 
For low porosities, the calculated data compared well 
with published data and correlations. The departure of 
the high porosity data from existing correlations was 
cause for development of correlation equations appli-
cable to the full span of porosities (0 to 100%). Utilizing 
only the experimental data of the above porous materials, 
full span correlations were developed. The published 
data of others covering the full span were then applied to 
the correlations in order to establish their validity 
throughout the span. The materials of others differed 
nil
(continued overleaf) 
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https://ntrs.nasa.gov/search.jsp?R=19720000586 2020-03-17T03:35:30+00:00Z
	not only in matrix structure (e.g., foametal, feltmetal, 	 2. Technical questions may be directed to: 
	
and nonspherical sintered powders), but also in solid	 Technology Utilization Officer 
	
material properties. Such variances in material properties 	 Lewis Research Center 
	
did not cause departures from the new correlations and 	 21000 Brookpark Road 
proved the correlations applicable. 	 Cleveland, Ohio 44135 
Reference: B72.10587 
Notes: 
	
1. The following documentation may be obtained from: 	 Patent status: 
National Technical Information Service 	 NASA has decided not to apply for a patent. 
Springfield, Virginia 22151 
Single document price $3.00 	 Source: J.C.Y. Koh of 
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The Boeing Company 
under contract to 
	
Reference: NASA CR-120854 (N72-19634), 	 Lewis Research Center and 
	
Thermal Conductivity and Electrical Resistivity	 Anthony Fortini 
of Porous Material
	
	
Lewis Research Center
(LEW.11754) 
B72-10587	 Category 04	 S
A


Thermal conductivity and electrical resistivity of porous materials

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