A calorimetric sensor has been designed to measure the heat flow dissipated by a 2 x 2 cm2 skin surface. In this work, a non-invasive method is proposed to determine the heat capacity and thermal conductance of the area of skin where the measurement is made. The method consists of programming a linear variation of the temperature of the sensor thermostat during its application to the skin. The sensor is modelled as a two-inputs and two-outputs system. The inputs are 1) the power dissipated by the skin and transmitted by conduction to the sensor, and 2) the power dissipated in the sensor thermostat to maintain the programmed temperature. The outputs are 1) the calorimetric signal and 2) the thermostat temperature. The proposed method consists of a sensor modelling that allows the heat capacity of the element where dissipation takes place (the skin) to be identified, and the transfer functions (TF) that link the inputs and outputs are constructed from its value. These TFs allow the determination of the heat flow dissipated by the surface of the human body as a function of the temperature of the sensor thermostat. Furthermore, as this variation in heat flow is linear, we define and determine an equivalent thermal resistance of the skin in the measured area. The method is validated with a simulation and with experimental measurements on the surface of the human body.
Keywords: direct calorimetry; heat capacity; heat conduction calorimeters; human skin; medical calorimetry; thermal resistance.