Contact Heat And Warmth Of Fabric Sand Their Heat Transfer Under Cold Stress

With the advancement of society and the development of science and technology,people’s living standards have gradually increased.The role of clothing is not limited to the past warmth and beauty.People have put forward higher requirements for the functional aspects of clothing,especially in high-tech fields and aviation.The field and special operating environment have certain functional requirements for the comfort of the clothing.Clothing comfort is a science that studies the relationship between man-clothing and the environment.It provides a scientific basis for the comfort and satisfaction of people’s lives and work,and maintains the thermal balance of the body-clothing-environment system.The basis of clothing comfort.Over the years,many domestic and foreign scholars have conducted extensive research on it.The comfort of the garments mainly refers to the temperature and comfort of the human body.Therefore,the heat transfer of the garments is an important research direction for the comfort of the garments.Due to the complex and diverse climate in China,in many regions,especially in the“Three North”region,the winter is extremely cold,with a minimum of-50°C or even lower.Therefore,whether it is normal life or winter outdoor work,the cold stress problem is more prominent.Cold stress may cause local or systemic damage to the body and even death.Therefore,how to reasonably evaluate the human body’s safety dress under cold stress conditions and predict the protective measures that should be taken under different cold environments are very important.Since cold stress conditions are not physically easy to achieve,this paper establishes a numerical simulation of the skin-clothing-environment mathematical heat transfer model to simulate changes in the temperature field and flow field of the entire system,and perform transient heat transfer processes on the system.Analysis,the skin temperature to reflect the body’s degree of cold stress.The research content of this topic is mainly divided into three parts:The first part（fabric exposure to cold and warmth）analyzes the physiological mechanism of human skin perceptual cooling and the mechanism of fabric contact cooling and warmth.It outlines important indicators for evaluating human skin temperature changes,is temperature drop timeΔt,maximum temperature drop T_max.The five parameters that produce the maximum temperature drop time t_max,the maximum temperature drop rate vmax,and the maximum transient heat flux density qmax are used as indicators for evaluating the feeling of warmth and warmth.Based on the bio-heat transfer model,a skin-to-fabric heat transfer model was established to simulate the heat transfer occurring when the human body came into contact with different fabrics,and the effect of fabric structure,fabric material,and fabric temperature on the contact cooling and warmth of the fabric was analyzed based on the characterization index.The results showed that the greater the contact area with fabric material,the more pronounced the cold feeling of the fabric;fabrics with different fabric materials,the thermal conductivity coefficient of the fabric,the cold feeling is more obvious;the same fabric with different initial temperature will lead to human body The skin produces different degrees of coldness.The lower the fabric temperature,the stronger the cold feeling.The second part（the cold stress reaction of wearing human body）establishes the human body heat transfer mathematical model under the cold stress condition according to the actual situation,and uses the same numerical solution method to simulate and calculate the skin temperature field after the human body is stimulated by cold in the cold environment.,Analysis of environmental temperature,clothing materials,clothing material porosity,clothing thickness and the air layer under the clothing on the body’s cold stimulus response.Finally,it is concluded that:（1）Under a certain state of wear,the human body’s ambient temperature is the main influencing factor of the body’s cold stress response.The reduction of the ambient temperature will make the human skin’s cooling rate faster,and the body’s cold stress level.It is also the greater;（2）When the ambient temperature is constant,the body’s clothing state will affect the body’s cold stimulation.Clothing materials with low thermal conductivity,high porosity,and large clothing thickness will weaken the body’s cold stimulation,and will experience a decline in skin temperature after a lag;（3）clothing under the air layer is equivalent to clothing and clothing In the microclimate,below the optimum air layer thickness,the greater the thickness of the air layer,the stronger the warmth of the garment,and the degree of cold stimulation felt by the human body.The third part（experimental verification）uses the YG406LF plate type warming apparatus to simulate the dynamic heat transfer process of human skin temperature after different fabrics are exposed to human body under low temperature conditions.The experimental results are in accordance with the theory.Through the theoretical analysis of human perception cold and warm and using numerical simulation methods to predict the dynamic heat transfer process of human body under cold stress conditions,the main influencing factors of human body’s degree of cold stimulation are analyzed to guide people in cold stress environment.How to dress safely,and provide theoretical basis for the design of related protective products,their functional evaluation and optimization.