Study of the thermal measurement depth of a skin calorimeter using simple RC and TF models

• A theoretical study has been carried out, using FEM and RC models, to analyze the measurement of the heat capacity performed by a skin calorimeter. • Simulations are a good tool to reproduce the behavior of the skin calorimeter (deviation < 5 %). • For heat conducting materials, with a brief measurement (5 min) it is possible to determine the heat capacity of the sample. • For heat-insulating materials, it takes a long time (15 – 60 min) to determine the heat capacity of the sample and the measurement is limited by the time-dependent thermal penetration depth. • This study has been completed with experimental measurements on inert samples and on human skin. An experimental and theoretical study of the heat capacity thermal measurement depth of a skin calorimeter has been carried out. This calorimeter consists of a thermopile placed between a thermostat and an aluminum measuring plate, which is placed on the sample to be measured. We performed simulations using the finite element method (FEM) with inert samples of different sizes. From these simulations, Transfer Functions (TFs) between the calorimeter's thermostat temperature and the temperature of the measuring plate were determined. Compact thermal models (RC models) able to determine the heat capacity of the sample were also determined. We conclude that, in the case of heat-conducting materials, a single time constant is enough to represent the TF. However, at least two time constants are required for heat-insulating materials. In this work we also studied the time dependence of the thermal measurement depth, concluding that this dependence is exponential. Finally, we present some experimental measurements performed on inert samples and on human skin, which are coherent with the results of the simulation.