| Sleeping bag is a warm and portable sleeping equipment,which is generally composed of three parts:outer fabric,filling material and inner fabric,and it is widely used in indoor infant protection,field camping to keep warm,professional outdoor athletes heating,and military marching sleep protection.With the improvement of country’s economic level and the vigorous development of outdoor sports,the market of outdoor sleeping bag shows great potential on growth.Thermal comfort is one of the most important properties that determine the use of outdoor sleeping bag,which is determined by the fabric,filling material and structure.Therefore,it is necessary to take the sleeping bag as the whole thermal insulation system and investigate the structure and property of the fabric used in the sleeping bag,the heat and mass transfer mechanism of the sleeping bag,the influence of the sleeping bag structure on the heat transfer of the sleeping bag,and the evaluation method of the thermal comfort of the sleeping bag,thoroughly.However,the research on thermal comfort of the sleeping bag is scattered and partial at present,usually focusing on a certain aspect,such as:Improve the warmth and lightness of the sleeping bag by changing the filling material or adding external auxiliary devices;Improve the windproof performance of the sleeping bag by designing special sleeping bag structures;Study the moisture permeability of the sleeping bag and its influencing factors;Determine and verify the temperature ratings of the outdoor sleeping bag and so on.Therefore,the outdoor down sleeping bag was taken as the research object,the fabrics for the outdoor sleeping bag were selected,the phenomenon and mechanism of the heat and mass transfer of the down filled sheet under dry and wet conditions were investigated,the heat transfer and air flow model of the interior and the surface of the sleeping bag with different structures was proposed,and the global and local thermal comfort of the sleeping bag were evaluated.The subject can provide systematic research method for outdoor sleeping bag and provide theoretical basis and technical support for the design and application of outdoor sleeping bag.The major work and conclusions of the subject are as follows:(1)Heat transfer and mechanism analysis of down filled sheet under dry condition20 kinds of fabrics for outdoor sleeping bag were taken as objects,the mechanical properties,water resistance and moisture permeability of the fabrics were tested and evaluated.It was found:Calendered high-density nylon fabrics and PVC-coated fabrics had lightweight and excellent mechanical properties as well as moderate water resistance and moisture permeability,which were suitable for outdoor sleeping bag using as outer fabric.30 cm×30 cm down filled sheets were made by covering down with the selected fabrics.24kinds of down filled sheets was taken as objects,the heat transfer mechanism of down filled sheets was analyzed,and their thermal resistance and thermal conductivity under dry condition as well as their influencing factors were tested and evaluated.It was found:The heat transfer under dry condition in the down filled sheets was mainly conduction and convection,and the thermal resistance under dry condition of them ranged from 0.33-0.80 m~2·K/W.Down fill weight,air permeability of fabric,down filling rate and down fill power were the main factors affecting the thermal properties of down filled sheets under dry condition,and a multiple regression formula between thermal resistance and its influencing factors was proposed.(2)Heat and mass transfer and mechanism analysis of down filled sheet under wet conditionA simulated skin sweating device including heating controller,temperature controller,water storage device and other components was designed and built,the moisture absorption and thermal resistance under wet condition of the down filled sheets were tested,and the heat and moisture transfer mechanism of the down filled sheet was analyzed.It was found:Under the condition of simulating human body’s 8 h latent sweat sleep,the thermal performance of the down filled sheets reduced due to the moisture absorption.The maximum mean change rate of thermal resistance was between 11.3%-33.5%.The air permeability of the fabric,the moisture absorption time of the sheet,the down fill weight and the down filling rate were the main factors affecting the thermal resistance under wet condition of the sheet.Under the moisture absorption time of 8 h,when the down fill weight,the down filling rate,and the air permeability of the fabric were 10.93 g,91.31%,and 11.80 mm/s,respectively,the maximum change of the thermal resistance under wet condition was tiny.(3)Heat transfer modeling and heat transfer analysis of sleeping bag with different structures4 sleeping bag samples with different structures which made by covering down with fabrics were taken as objects,a model of heat transfer of sleeping bag with different structures was developed using the CFD approach through geometric drawing,mesh division,parameter setting and other steps.The thermal resistance and thermal conductivity under dry condition of the sleeping bag samples were measured,and the surface temperature of the samples was photographed,then the results were compared and verified with the model calculation results.The natural convection,conduction and radiation in the whole computational domain were calculated by the CFD model,and the heat transmission and air movement inside and on the surface of the samples were analyzed.It was found:Under tiny wind velocity condition,among the samples with a similar porosity,the thermal insulation of the V-tube,the Trapezoidal and the Box structures were good,while the Sewn-through structure shared the least warmness.The difference of thermal resistance between the Box structure and the Trapezoidal structure was 2.6%.The difference of thermal resistance between the Box structure and the Sewn-through structure was 20.3%.The experiment data were in good agreement with simulation data,with a maximum difference of 11.2%.The heat exchange of the sleeping bag samples was simulated by the model,it was found that the heat transfer inside the samples was dominated by convection and conduction,and the ratio of convection and conduction was around 30%:70%.On the surface of the samples,convective and radiation dominated.The convective heat flux of the Box structure was the largest,and the radiation heat flux of the Sewn-through structure was the largest.(4)Global and local thermal comfort evaluation of sleeping bagAn outdoor down sleeping bag was designed and made,5 females were taken as subjects,the global thermal comfort of the sleeping bag was evaluated at 3 temperature ratings.It was found:At the comfort temperature,subjects were not sweating,the comfort and thermal sensation were almost the same as the neutrality sensation,but the hands and feet had stronger cool sensation.The body heat storage rate was nearly 0 W/m~2.The mean heart rate ranged from 64-86 bpm.The sleep was dominated by the deep sleep stage,accounting for 58.6%.The mean skin temperature was in the thermal neutrality range,that is 32-34℃.At the extreme and the maximum temperatures,the amount of sweat increased,and the body heat storage rate,mean heart rate,and sleep quality changed.The limbs of subjects were more sensitive to temperature changes than the rest of the body.4 sleeping bag units with different structures were made,and 5 males and 5 females were taken as subjects,the local thermal comfort of sleeping bag units with different structures were evaluated.It was found:For sleeping bag units with similar porosity,subjects’hands felt the warmest in the V-tube structure,and the Sewn-through structure was claimed the coldest.For the same sleeping bag structure,the thermal sensation ratings of male were generally higher than that of female. |
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