Determination of the equivalent thermal conductivity of complex material systems with large-scale heterogeneities

• A measuring procedure for determination of equivalent thermal conductivity is proposed.
• The method is suitable for complex material systems with large-scale heterogeneities.
• A laboratory experiment in a combination with 3D computational modeling is applied.
• The combined standard uncertainty of the measurement is 10%.
• The simplicity and cost effectiveness, together with an acceptable accuracy, are the main advantages of the method.

A method for determination of the equivalent thermal conductivity of heterogeneous systems with large representative elementary volumes is proposed. The laboratory experiment is based on the guarded hot plate principle but the heat transfer in the designed setup is generally 3D. Therefore, 3D computational modeling is applied for the analysis of heat transport in the system. The measuring procedure begins with the calibration which is performed using a material of the known thermal conductivity and typical specimen dimensions. Then, the experiment is carried out with the investigated specimen and the steady-state values of temperatures and heat fluxes in the characteristic positions are measured. The equivalent thermal conductivity is determined in an iterative procedure, utilizing the results of the laboratory experiment as input data of the computational model. The application of the proposed method is illustrated on an example of two types of advanced hollow clay bricks. The uncertainty analysis including both the standard uncertainties of types A and B and sensitivity-aimed calculations shows that the combined standard uncertainty of the equivalent thermal conductivity is 10% which can be considered satisfactory for this kind of experiment. The main advantages of the proposed method can be seen in its simplicity and cost effectiveness, together with an acceptable accuracy. This makes good prerequisites for its successful application in future experiments.