CONFIT: a computer code for thermal conductivity probe data reduction with the use of parameter estimation techniques

Abstract

The basis and operation of the computer code CONFIT are described, and a sample case provided. The code uses parameter estimation techniques to obtain thermal conductivity and other parameters of interest from temperature versus time data acquired with the use of line-source type thermal conductivity probes. The basic estimation approach consists of fitting (in the least-squares sense) analytical problem solutions to the experimental data. Problem parameters (e.g., thermal conductivity) are used as curve fit variables, and are thus determined when the least-squares fit is achieved. Some advantages of the method include the following: requirements for development of the straight line region of the log-time versus probe temperature curve are minimized. (This permits shorter runs with low conductivity materials and more rapid return to equilibrium after the run is completed when compared to standard data reduction techniques); deviations between the experimental data and the analytical model are easily observed and analyzed. (Statistical tests on the residuals, the differences between the experimental data and the analytical solution, can be used to confirm the validity of the results); and contact resistance between the probe and the test material can be estimated simultaneously with the conductivity, simplifying data reduction. The code is written in Fortran IV (based on ANSI 1966 Fortran) and has been implemented on a Control Data Corporation 6600 computer and on a Hewlett-Packard 1000 minicomputer system in an interactive mode. With minor modifications, the program can be used with more recent Fortran compilers, e.g., Fortran V, based on ANSI 1977 Fortran.