Simultaneous Thermal Conductivity, Thermal Resistivity, and Thermal Diffusivity Measurement of Selected Foods and Soil

Abstract

There is a need for accurate and rapid thermal conductivity (k), thermal resistivity (R) and thermal diffusivity (D) measurements of food products and soils. Knowledge of the thermal properties of foods allows design of novel food processing techniques in the food industry. In soils, knowledge of the thermal properties allows energy balance and heat transfer calculations. Existing thermal conductivity probes only measure conductivity and cannot be used on liquid samples. A new, simple, easy to use system allows rapid and simultaneous conductivity, resistivity and diffusivity measurements, including liquid samples. The system consists of a hand-held readout and a single-needle sensor. The single-needle sensor consists of a stainless steel needle containing a heater and thermistor. The thermal conductivity and diffusivity are calculated by monitoring the dissipation of heat versus time given a known voltage applied. The range of thermal conductivity measurements is 0.1 to 2.0 Wm -1 C -1 with an accuracy of 5%. The range of thermal resistivity is 0.5 to 10 mCW -1 with an accuracy of 5%. The range of thermal diffusivity measurements is 0.1 to 1.0 mm 2 s -1 with an accuracy of 10%. The objective of this study is to evaluate the performance of the new thermal properties system on selected foods and soils, then compare the data to published literature values. The accuracy and repeatability of the probe is evaluated using glycerin as a reference material. This new thermal properties system provides rapid, accurate and economic means for simultaneously measuring thermal conductivity and thermal diffusivity on selected foods and soils, including liquid samples.