Evaluation Of The Influence Of Ventilation Opening On Heat Transfer Performance Of Clothing Under Low Temperature Environment

When people engage in work or sports wearing cold-resistant clothing in a low-temperature environment,they will be faced with the thermal balance demand between the thermal insulation responding to the cold environment and the heat releasing responding to the heat stress in human body.Therefore,the development of cold-resistant clothing should not only guarantee adequate cold protective performance but also provide solutions for heat and moisture dissipation from human body.Clothing ventilation has always been regarded as an important pathway for adjusting human body’s thermal balance.Therefore,the widely used opening design is an important method for promoting the heat exchange between the air gaps underneath the clothing and the environment.For the study of the heat transfer performance of clothing,although the influence of the factors such as fabric performance,clothing opening design,clothing ease allowance,wind,and body movement are considered,there is a lack of systematic research on the heat dissipation of ventilation openings.In addition,researches on the design of ventilation openings have mainly focused on neutral or hot environments,but neglected the need for heat dissipation under low-temperature environment.This paper takes the design of the ventilation opening of outdoor cold-resistant clothing in a low-temperature environment as a research subject.In the manikin tests,8 kinds of opening designs(including the control group)were examined,includingthe thermal insulation of the clothing and the heat dissipation capacity of the manikin.By analyzing the changes of the total thermal insulation,local thermal insulation,surface temperature of the manikin and the temperature of the air gaps underneath the clothing in both the open and closed states of the natural opening,design opening and the combination openings,the heat transfer in the clothing and the influence of opening type on the body’s heat balance are clarified.The factors,including air gaps underneath the clothing,wind speed and body movement,are involved in the research scope to explore their effects on the clothing ventilation and heat dissipation.Accordingly,three conclusions are generated:A)The influence of ventilation opening on clothing heat transfer performance and human thermal balanceBy studying the influence of different opening types on the heat dissipation of clothing,it is found that the ventilation openings in different parts can reduce the overall thermal insulation of the clothing,promote the heat dissipation of the human body,and play a positive role in maintaining the human thermal balance,the effect of the opening type on the total thermal insulation of the clothing has a significant difference(p<0.05).By comparing the two types of clothing openings of natural opening(neckline,hem)and design opening(chest,armpits,back),the overall heat dissipation capacity of natural openings is stronger than the other.The chest opening of three design openings has the strongest heat dissipation capacity,and the armpit opening is inferior.The weakest is the back opening.The combination of the design opening and the natural opening shows a relatively stronger effect on promoting heat loss in the waist,chest and abdomen of the human body.Meanwhile,it reduces the accumulation of heat in the space underneath the clothing as a whole to avoid uneven heating and cooling at different parts of the body.It also alleviates the difficulty of heat dissipation t the back and shoulders to a certain extent.B)The influence of the air gap underneath the clothing on the heat dissipation through the ventilation openingsAs the clothing opening is closed,the total thermal insulation of the clothing increases with the increment of the ease allowance.Differently,it generally decreasesfirst and then rises as the clothing opening is open.There is a significant difference between the total thermal insulation of different ease allowance(p<0.05).Under different ease allowance,the change of the opening type has a significant effect on the total thermal insulation of the clothing(p<0.05).For the experimental clothing with a bust looseness of 6 cm and 12 cm,the effect of the chest opening is better than the opening of the armpit and back,while for the experimental clothing with a bust looseness of 18 cm,the heat dissipation effect of the armpit opening is the most obvious.The results of the local thermal insulation show that the uniformity of the local thermal insulation distribution of loose clothing is better.Therefore,avoiding body-fitting styling and choosing appropriate clothing looseness to reduce the thermal insulation of the clothing is helpful to maintain the heat balance of the human body.Especially when the ease allowance is large,it has a positive effect on the heat accumulation at the shoulder and back.C)The influence of wind and body movement on the heat dissipation through the ventilation openingThere is a significant difference between the influence of wind and body movement on the thermal insulation of clothing(p<0.05),which can promote the convection and heat dissipation of the air layer on the outer surface of the clothing,thereby reducing the thermal insulation of the clothing.When the opening is closed,the movement of the human body has a greater influence on the thermal insulation performance of the clothing,and when there is an opening,the effect of the wind on the heat dissipation through the opening is stronger than that of the body movement.There is an interaction between the type of opening,wind and body movement,which is closely related to the position of the opening(p<0.05).The heat dissipation performance of the chest opening is the strongest,while the underarm opening only performs better than the back opening under the dynamic condition with wind and body movement.There are interactions between ease allowance,wind,body movement and opening type.It is revealed that wind speed has the largest contribution to the clothingheat dissipation,followed by ease allowance,human body movement and opening type.It is shown that at the wind speed of 2 m/s(headwind)for a standing human body wearing clothing with a looseness of 12 cm,opening the neckline,hem and the chest opening contributes to a best heat dissipation performance of the clothing(headwind).Both ease allowance and ambient wind have a greater impact on the heat dissipation of the opening,followed by the movement of the human body and the type of opening.The research in this paper can provide theoretical guidance and support for the ventilation design,optimal configuration,functional evaluation and scientific dress of the cold-resistant clothing,and provide a reference for the development of related products.