Numerical simulation of heat transfer in electrically heated footwear in a severely cold environment

The purpose of this study was to investigate the mechanisms of heat transfer and thermal regulation of electrically heating pad in footwear through numerical simulation. A one-dimensional heat transfer model was developed based on parameters of footwear materials, heating pad and skin tissues, which was validated by small-scale fabric experiments. Two modes of temperature control for the heating pad (HPTC) and human skin (STC) were compared, and a parametric analysis was conducted. It was showed that the model predictions were in agreement with the experimental results. Generally, the STC mode had better thermal regulative performance and less energy consumption than the HPTC mode. Results from the parametric analysis demonstrated that the properties of the heating pad and inner fabric layer were the most important factors for affecting the thermal regulative performance of the electrically heated footwear. No significant changes were found in the thermal regulative performance, but the environmental temperature had a clear influence on the energy saving effect. Besides, the energy efficiency could be remarkably improved by lowering the heating power. Even in a severely cold environment of −30 °C, the common lithium battery was able to function the HPTC mode of the typical four-layer fabric system for 7.7 h. This research provides suggestions for the design of the heating pad as well as the upper of the electrically heated footwear.