Comparison Of Cooling Performance And Thermophysiological Response Between Cooling Clothing Combining Phase Change Materialand Different Dehumidification

Workers in high temperature environments not only have higher metabolic heat production,but also cannot dissipate heat to environment.Therefore,human body cannot maintain thermal balance only by its own thermoregulation mechanism,which is easy to cause heat stress and heat disease.When environmental cooling measures cannot be used,cooling clothing based on phase change materials(PCMs)has become an important thermal protection equipment to protect the thermal safety of workers because of its simple structure,energy saving and renewable.However,the poor moisture permeability of PCMs prevents the water evaporation from clothing microclimate to environment,resulting in poor thermal-wet comfort.Therefore,this paper studied the thermal insulation and moisture permeability performance of adding desiccant layers and ventilation fan to the cooling clothing based on PCMs(PCS).And then,the interaction of human activity level,ambient relative humidity and dehumidification methods on the cooling effect of PCS was explored.Finally,the thermal-wet comfort of PCS with different dehumidification methods was compared.Based on this,the cooling effect and human thermophysiological reaction of PCS,cooling clothing based on PCMs and desiccant layers(PCS-Des),cooling clothing based on PCMs and ventilation fans(PCS-Fan)were studied by combining the research methods of thermal manikin test and human test.The research results can be used to evaluate the cooling effect and thermal-wet comfort of PCS with different dehumidification methods under different conditions of human body and environment,so as to provide reasonable suggestions for the use of cooling clothing.The main research contents and relevant conclusions are as follows:A)To compare the influence of adding PCMs,desiccant layers and ventilation fans on the thermal-wet performance of the clothing,the thermal and wet resistance of the experimental clothing were studied.The results showed that PCMs obstructed the heat and moisture transfer between human body and environment,which increased the thermal resistance(p<0.05)and the wet resistance(p<0.05)of clothing.It also caused the skin surface relative humidity to exceed100% and the microclimate relative humidity to rise continuously,which increased the risk of condensation.The addition of desiccant layers further hindered the moisture evaporation of the torso,which significantly reduced the heat flow of the torso(p<0.01).However,the moisture absorption of desiccant not only reduced the relative humidity of the appropriate area,but also promoted the heat transfer from the skin.Ventilation effectively enhanced convection and evaporation by promoting air exchange between microclimate and environment.While the overall thermal resistance and wet resistance was significantly reduced(p<0.01),the differences of thermal insulation and moisture permeability performance between different parts were also weakened.And in the upper back,waist and other parts with large gap under clothing showed a relatively strong role in promoting heat and moisture transfer.B)To explore the interaction of human body,environmental and dehumidification methods on the cooling effect,the cooling effect of PCS,PCS-Des and PCS-Fan under the different conditions of sweat rates,motion states and ambient relative humidity was tested.Both PCS-Des and PCS-Fan showed better dehumidification and cooling effects under the condition of high sweating rate.When the sweating rate was low,desiccant could not only promote the evaporation by increasing the moisture difference between skin surface and microclimate,but also reduced the cooling power by releasing adsorption heat and hindering heat and moisture transfer.The effect of promoting water evaporation by ventilation was also limited,and the microclimate temperature was increased due to the strengthening of convection with hot air.With the increase of sweating rate,the cooling power of PCS-Des and PCS-Fan was significantly increased(p<0.01).The evaporation heat loss promoted by desiccant was obviously greater than its negative effect.Moreover,the time point when the evaporative heat loss of ventilation enhancement was greater than the environmental heat transfer was obviously advanced.PCS-Des and PCS-Fan were suitable for high and low ambient relative humidity respectively.The whole and torso cooling power of PCS-Des was greater than that of PCS in hot and humid environment.Because desiccant could better play a hygroscopic role,by increasing the moisture difference between skin surface and microclimate to promote moisture evaporation.The cooling power of PCS-Fan was significantly higher in hot and dry environment than in hot and humid environment(p<0.01).Ventilation could enhance convection and evaporation more effectively through the larger humidity difference between skin surface and low humidity air.Compared with PCS-Fan,the motion promoted the cooling effect of the other two cooling clothing more strongly.By promoting the air convection between microclimate and environment through movement,the obstruction of heat and moisture transfer of PCMs and desiccant layers could be made up,and the hygroscopic effect of desiccant layers could be enhanced.Thus,the cooling power of PCS-Des was significantly enhanced(p<0.01 in hot and dry environment,p<0.05 in hot and humid environment).However,the motion-enhanced convection was negligible compared with the ventilated forced convection,so the motion state didn’t significantly affect the cooling effect of the PCS-Fan.And the influence of the motion state on the torso cooling power was affected by the ambient relative humidity.C)To compare the thermal-wet comfort of PCS-Fan and PCS-Des,the human test was conducted for two cooling clothing.The results showed that the cooling effect and evaporation effect of PCS-Fan were more significant.Since the actual human sweat production was less than that of the thermal manikin under high sweat rate,the desiccant couldn’t enhance evaporation by increasing the humidity difference between skin surface and microclimate.The heat loss of convection and evaporation enhanced by ventilation was much greater than the heat transfer from environment to human body.Therefore,the mean torso temperature of PCS-Fan was significantly lower than that of PCS-Des(p<0.05).However,due to the strong cooling effect,the core temperature of PCS-Fan in the initial stage was higher than that of PCS-Des.Moreover,ventilation not only significantly enhanced the sweat evaporation(p<0.05),but also significantly reduced the sweat production(p<0.05)due to the better cooling effect,thus reducing the mean torso relative humidity of skin and microclimate.Therefore,wearing PCS-Fan significantly reduced the thermal sensation and wet sensation(p<0.05),thus improving the overall comfort(p<0.05),so as to effectively relieve the perceived fatigue and thermal strain caused by long-term exercise.To sum up,this paper has explored the thermal insulation and moisture permeability performance and thermal-wet comfort of PCS with different dehumidification methods in depth.The interaction of sweat rates,motion states,ambient relative humidity and dehumidification methods on the cooling effect was explored.It provided guidance and suggestions for rational use and performance improvement of cooling clothing.