Numerical Analysis on the Cooling Performance of a Hybrid Personal Cooling System (HPCS) under Different Hot Environments

Abstract

The hybrid personal cooling system (HPCS) consisted of ventilation fans and phase change materials (PCMs) covered with insulation pads is a promising wearable cooling system to mitigate heat strain and heat-related illnesses of occupational workers with heavy labor in hot environments. Effects of clothing characteristics (e.g., thermal resistance of insulation pads, latent heat and melting temperature of PCMs) on the thermal performance of the HPCS have been investigated in detail in our previous study. Apart from the aforementioned factors, environmental conditions, i.e., environmental temperature and relative humidity, also significantly affect the thermal performance of the HPCS. In this paper, a numerical parametric study was performed to investigate the effects of the environmental temperature and relative humidity (RH) on the thermal management of the HPCS. Five levels of air temperature under environmental RH=50% were chosen (i.e., 32, 34, 36, 38 and 40 ºC) to study the impact of environmental temperature on the HPCS’s cooling performance. In addition, four levels of environmental RH at ambient temperatures of 36 and 40 ºC were selected (i.e., 30, 50, 70 and 90%) to examine the effect of RH on cooling performance of the HPCS. Results show that high environmental temperatures could accelerate the PCM melting process and thereby weaken the cooling performance of HPCS. In the moderately hot environment (36 °C), the HPCS presented good cooling performance with the maximum core temperature at around 37.5 °C during excise when the ambient RH≤70%, whereas good cooling performance could be only seen under RH≤50% in the extremely hot environment (40 °C). Thus, it may be concluded that the maximum environmental RH for the HPCS exhibiting good cooling performance decreases with the increase in the environmental temperature.

Advanced Functional Materials for Intelligent Thermoregulation in Personal Protective Equipment

“…Some work has also been devoted to the numerical analysis of the performance of PCM/fan garments under different conditions [256,304,305]. In one of these studies, a mathematical model was proposed to calculate the transient transfer of heat and humidity through layers of clothing incorporating PCM pouches and fans.…”

“…According to numerical analyses of T c and T s values, high ambient temperature and RH ≥ 70% would weaken the performance of such a suit. However, for better cooling efficiency in conditions of very high environmental temperatures or RH, the properties of the PCM used and their level of insulation should be optimized [304].…”

Advanced Functional Materials for Intelligent Thermoregulation in Personal Protective Equipment

“…4.5.2. Numerical analysis of hybrid cooling garments Some work has also been devoted to the numerical analysis of the performance of PCM / fan garments under different conditions [235], [283], [284]. In one of these studies, a mathematical model was proposed to calculate the transient transfer of heat and humidity through layers of clothing incorporating PCM pouches and fans.…”

“…However, for better cooling efficiency in conditions of very high environmental temperatures or RH, the properties of the PCM used and their level of insulation should be optimized [283].…”