Effect Of Human Postures On The Heating Performance And Thermal Comfort Of Human Body In Electric Heating Suit

In the extreme cold environment,it is hard for traditional winter clothes to keep human body in thermal balance.As a typical clothing for active heating,electric heating clothes have been becoming an effective equipment to provide cold protection for wearers due to its quickly heating ability,portability and simple structure.Previous researches on electric heating clothing focued on the design of heating area and the thermal comfort of human body.However,the researches are generally based on the standard standing posture,without considering the influence of human postures on the heat transfer performance of the heating clothing system,which has a significant effect on the heat exchange process between human body,clothing and environment.Therefore,aiming at the difference of the heat transfer in the heating clothing system caused by human postures,this paper selects three typical human postures(standing,sitting and squatting)to explore the heating performance of electric heating clothing,and put forward the heating design scheme for different postures.The main research contents and conclusions are as follows:(1)Based on the analysis of human postures,there are two key factors: the air layer under clothing and clothing pressure,which have a significant influence on the heat transfer performance.Three-dimensional body scanning experiment and clothing pressure experiment were used to obtain the air layer thickness and clothing pressure of different human parts in three postures,and they were divided by cluster analysis.This part of the experiment provides quantitative basis for subsequent heat transfer analysis.The results show that the average thickness and volume of air layer under clothing are the largest in standing,followed by sitting and squatting.From standing and sitting to squatting posture,the air layer gradually increases under the clothes of upper chest and the lower middle part of lower leg since the human body leans forward.The air layer in middle back,lower back and abdomen gradually decreases due to the change of spine curvature.The air layer under the clothes of lower chest and upper back is the largest in sitting posture.The air layer in thighs and knees only exists in standing posture.When the human body is in a standing position,there is only about 0.5 k Pa pressure on the upper chest.In the sitting position,the knee and the upper part of the calf form a larger clothing pressure due to the knee bending,which reaches 2.5 k Pa.In the squatting position,less pressure on the back is generated due to garment stretching.The clothing pressure of abdomen,thigh,knee and upper leg increase obviously compared with the standing and sitting posture,and the clothing pressure of knee reaches 6 k Pa.The clothing pressure of the lower limbs decreases with the center of knee.Cluster analysis was used to divide the thickness of air layer under clothing in 12 parts and clothing pressure in 20 parts in three human postures.The thickness of air layer is divided into 7 categories: 0 cm,0.3 cm,0.6 cm,1.2 cm,1.5 cm,1.9 cm and 2.4 cm respectively.Clothing pressure is divided into 6 categories: 0 k Pa,0.5 k Pa,1 k Pa,1.5 k Pa,2.5 k Pa and 6k Pa respectively.(2)The multi-layer fabric of electric heating clothing has been used to explore the heating performance of heating sheet in various fabric combinations under different air layer thicknesses and clothing pressure levels,and a preliminary heating design scheme for different human parts is put forward.Research shows that the heating performance is the best as the air layer is 0.3 cm.When the air layer increases to 0.6cm,the heating performance decreases,at this time,the air layer plays a role of heat insulation in the multilayer fabric.When the air layer increases from1.2cm to 1.5cm and 2.1cm,the heating performance decreases obviously,at this time,natural convection has been formed.The heating performance is the best as the clothing pressure is0.5k Pa.When the clothing pressure increases from 1k Pa to 1.5k Pa,the heating performance decreases,since the thickness of multilayer fabric decreases and the heat dissipation to the external environment increases.And there is no significant difference of heating performance when the pressure is further increased to 6k Pa.It is also found that the heating area is mainly concentrated in the coverage of the heating sheet,and the surface temperature of the fabric at a distance of 4 cm away has dropped significantly.The surface temperature of the fabric in the uncovered area of heating sheet is related to the external heat,which plays a certain role.According to the conventional distribution of heating sheets on the market,the dressed human body is divided into 9 heating areas: chest,abdomen,upper back,lower back,thighs,knees,calves,upper arms and lower arms.Combined with the heating performance of different fabric combinations,the preliminary heating design scheme is determined.Among them,the chest,upper back and lower arm are set to the second or third heating temperature in three postures,and the upper arm is set to the first or second heating temperature.From sitting to squatting posture,the heating temperature of abdomen and lower back needs to be lowered.And from standing to sitting posture,the heating temperature of thighs,knees and calves needs to be raised.(3)According to the skin temperature and subjective evaluation,the thermal comfort performance of different human parts in three postures was explored based on the dressing experiment of electric heating suit,and the specific design scheme of heating was further optimized.It turned out that in the three postures,the overall skin temperature and thermal sensation of human body are the highest in squatting,followed by sitting and standing.The overall thermal comfort shows a downward trend during the fourth gear heating in squatting posture,and the overall thermal tolerance shows a slightly unbearable phenomenon during the fourth gear heating in sitting and squatting posture.The human body’s thermal sensation not only reflects the thermal physiological,but also is influenced by external heat.The acceptance range of thermal comfort of human body is relatively wide.When heating in the fourth gear,some parts of the human body is overheated,such as the abdomen in sitting and squatting position,the lower back,thighs and knees in squatting position.The optimization of heating design scheme is mainly based on the heat production and reactions of different human parts and the change of heat dissipation area.The final scheme is as follows: in standing and sitting posture,the abdomen,thighs and knees are set as the third heating gear;and the chest,upper back,lower back,upper arm,lower arm and lower leg are set as the fourth heating gear.When squatting,the abdomen and thighs are set to the second heating gear;the chest,upper back,lower back and knees are set to the third heating gear;and the upper arm,lower arm and lower leg are set to the fourth heating gear.To sum up,based on the change of human postures,this paper explores the heating performance of electric heating sheet in different human parts and the thermal comfort performance of human body,which provides a quantitative basis for the actual production of electric heating clothing and provides a direction for improving the thermal comfort of wearing heating clothing.