Probe Length and Filling Material Effects on Thermal Conductivity Determined by a Maximum Slope Data Reduction Method

The influence of probe length to diameter ratio (X) and filling material on the thermal conductivity (k) probe technique was studied using glycerol with probes of four different λs (4.1, 7.5, 13.6, and 54.3) filled with either high k paste or air by applying a maximum slope data reduction method. Statistical analysis showed the highly significant influence of X and significant influence of the filling material. Noncalibrated k values of the smallest X probes were 93% above the published value, whereas those of the largest λ probes were virtually identical to the published value. Separate measurements on chocolate pudding and starch gels showed that 7.5 X k were virtually identical to the largest X probe k when the former probes had been calibrated using glycerol. The use of short air-filled probes is not recommended when the maximum slope method is applied.

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