An Apparatus for Measuring the Effective Thermal Conductivity of the Body Surface

Abstract

Abstract To prevent body from injury during the hyper- and hypo-thermic therapy, knowledge of the temperature distribution in the body surface (e.g. skin or tissue) close to the therapy location is needed. In order to predict, by calculation, the correct temperature field, it is essential to input meaningful values of the thermal properties of the body surface into numerical and analytical simulation models of its behavior during heating or cooling. A simple experimental apparatus for measuring effective thermal conductivity of the body surface has been developed. It differs from the previously developed apparatus. In experiments, a fine platinum wire (0.01 mm in diameter) with electrical resistance R (0.4Ω)is embedded between a tested specimen (body surface) and a silicone rubber. When the wire, specimen and rubber are in thermal equilibrium, and a constant electrical power is applied to the wire, the temperature increase of the wire against logarithm time in predetermined time interval was measured. The kinetics of this temperature rising is related to the thermal conductivity of the tested specimen and silicone rubber. The thermal conductivity of the silicone rubber is known from reference or measured. So the thermal conductivity of tested specimen can be calculated by measuring the temperature rise of platinum wire at predetermined time interval. It is assumed that (1) the wire is infinite long and the heat source is steady, (2) the tested medium (e.g. the tested specimen and the silicone rubber) are infinite large in space, and contact resistance between the fine wire and soft medium is negligible. The apparatus’ validity has been demonstrated by the following tests. First, as the standard specimen, thermal conductivity of glycerol and fused quartz glass (99.9% SiO2) were respectively measured using the apparatus. The relative errors between measured thermal conductivity and data provided by Thermophysical Properties Research Center (TPRC) are less than 0.7%. The validity of the theory model was also confirmed using several inorganic specimens and biological materials (e.g. rabbit sin, in vivo). Conditions and prerequisites for application of the technique and apparatus to measuring thermal conductivity of biomaterials (in vivo) were discussed.