Measurement of directional thermal properties of biomaterials

This paper presents an experimental technique to measure the directional th ermal conductivity and thermal diffusivity of materials, A heated thermisto r heats the sample and a sensing thermistor placed about 2.5 mm away measur es the temperature rise due the heating pulse at the heated thermistor, An empirical relation between the power delivered by the first thermistor and the temperature rise recorded by the sensing thermistor is used to measure the thermal conductivity of the material along the line joining the thermis tors. Diffusivity of the material is determined from the delay between the power pulse in the heated thermistor and the temperature pulse at the sensi ng thermistor. Signal processing was done to eliminate errors in the measur ement due to change of base line temperature, Uncertainty of the measuremen t technique was found to be 5% when tested in media of known thermal proper ties. The thermal conductivity and thermal diffusivity of swine left ventri cle in normal and ablated conditions were measured using this technique. Th e thermal conductivity of the tissue dropped significantly from 0.61 to 0.5 0 W . m(-1) . K-1 after ablation while the diffusivity dropped from 2.1 x 1 0(-7) to 1.7 x 10(-7) m(2) . s(-1).