Analytical Model for Thermoregulation of the Human Body in Contact with a Phase Change Material (PCM) Cooling Vest

Abstract

Cooling vests containing phase change materials (PCMs) are used to reduce heat stress in hot environments and maintain the body core temperature within a safe range. The performance of such cooling vests depends in a complicated way on the PCM material and mass, the insulation value of the clothing layers and heat loss to the environment. Conventionally, these performance parameters are evaluated experimentally or using a numerical model, both of which do need a certain amount of evaluation time. The objective of this paper is to develop a transient heat transfer model which includes metabolic heat production in the human body, as well as clothing and PCM layers and radiation to the environment but which is presented as a series of closed-form equations that can be evaluated without the need of a numerical solver. We present solutions for the body and PCM temperature as well as for the heat flux, cooling power and cooling duration. The model equations are validated by comparing them with experiments of ice PCM packs on a hotplate, as well as with published experimental and numerical data for the core temperature, heat flux and percentage of environmental heat loss using a Glauber salt type of PCM. Both the hotplate experiments and the model predictions show that the cooling power during PCM melting drops from about 70 to 32 W for increasing insulation layer thicknesses. In addition, the model is seen to compare well with experimental and simulation data in the literature. In a parametric study, we show how the equations can be used to evaluate the effects of PCM melting temperature and PCM thickness on cooling performance. The paper, therefore, can be considered as a practical means to help select the best cooling vest configuration for workers in a hot and humid environment.