Design And Evaluation Of Cooling Workwear For Underground Mines Based On Phase Change Materials

With the increase of coal mining depth,the heat hazard problem in deep coal mines has become increasingly prominent.In order to attenuate the heat stress suffered by deep coal mine workers and improve their thermal and wetness comfort,this article developed the cooling workwear for coal miners using phase change materials(PCM)and evaluated its performance based on the human thermal balance theory and personal cooling strategies.This article developed a set of cooling workwear for coal miners,selecting and designing cooling methods,clothing structure,and clothing materials.The final application of PCM cooling is portable and suitable for the highly humid environment.15 ? PCM was selected and a new arrangement was proposed that used PCM with different temperatures: 15 ? PCM was used as the inner layer,and 23 ? PCM with higher latent heat was used as the outer layer(15&23).According to the heat dissipation,sweat production and thermal sensitivity at different parts of the human body surface,the PCM packs were designed to be placed on the torso and front thigh areas.Based on the needs of coal mining,clothing fabrics should be antistatic and flame-retardant.Fuzzy mathematical analysis methods were used to comprehensively evaluate their physical properties and wearing comfort and determine the proper fabrics.Secondly,this article applied the sweating manikin test to objectively evaluate the performance of the developed mining workwear.The 15&23 was compared with the workwear without PCM(CON)and the workwear with only 15 ? PCM(15&15)in a climate chamber at 30 ? and 80% relative humidity.The results showed that the PCM cooling workwear significantly increased the heat dissipation of manikin,and the cooling duration of 15&23 was longer than that of 15&15.The increased cooling duration could improve the cooling performance of workwear,reduce the time for replacing PCM packs and increase the work efficiency.Finally,human wearing trials were performed to evaluate the thermal and wetness comfort of the developed workwear.By simulating the working and resting periods of workers in a climate chamber under hot and humid condition(30 ? and 80% relative humidity),the effects of CON,15&15,15&23,and workwear with completely melted PCMs(mPCM)on body thermal regulation were compared.Skin temperatures,sweat production and heart rate were measured,and subjective sensations of thermal sensation,thermal comfort,wetness sensation and received perceptual exertion were recorded.The results showed that the PCM cooling workwear significantly attenuated the rise of skin temperatures and improved the thermal sensation and comfort.There was no significant difference in physiological responses,thermal sensation,thermal comfort,and received perceptual exertion between CON and mPCM,which indicated that the PCM packs would not greatly affect the thermal resistance of workwear,and the weight of PCMs would not significantly increase the wearers' workload.The cooling duration of 15&23 was longer than 15&15,which could reduce skin temperatures and heat sensation and improve thermal comfort during the resting period.The experiment also evaluated the movement comfort when wearing PCM cooling workwear and performing 6 typical work movements.It was proved that no matter whether the PCM packs were added or whether they were melted,it will not cause a sense of resistance and discomfort to the physical activities in the mining work.In summary,the PCM cooling workwear developed in this study improved the thermal comfort of the wearers and achieved the purpose of improving the occupational health of coal miners.The study proposed the use of PCMs with different temperatures in PCM cooling workwear,which can improve the performance of such clothing.The achievement of this study could provide a reference for the design of similar workwear or protective clothing and have certain practical application value.