| The research on thermal and moisture comfort of clothing comes from people’s need to maintain their own physiological comfort after wearing.To quantitatively study the role of clothing in heat and moisture transfer,it is necessary to measure relevant indicators and simulate and calculate the process of heat and moisture transfer and the relationship between them.In 1962,Woodcock put forward the moisture permeability index to describe the relative relationship between thermal resistance and moisture resistance of clothing and tested it with a cylinder.Meanwhile,the maximum ratio S=0.0165 ℃/Pa of the thermal resistance and moisture resistance of air layer at wind speed greater than 3 m/s was regarded as a constant,which was also the reference value for calculating the moisture permeability index of clothing.However,some scholars theorized from the perspective of heat and mass transfer and found that the value would change with wind speed and clothing size.Therefore,the value of relative reference value ’S still needs to be discussed.In terms of measurement,to fit the dress situation of the human body,scholars constructed the human body-clothing-environment system to carry out related heat and moisture transfer experiments.In this paper,the heat and moisture transfer process and moisture permeability index of multi-layer fabric systems were studied by using SGHP-10.5 sweating guarded hotplate.First of all,to explore the relative reference value ’S,the thermal resistance and moisture resistance of empty plate under 0.1～1.5 m/s were measured.Through curve fitting and theoretical derivation,’S under different wind speeds were obtained,which represented the maximum ratio of thermal and moisture resistance of clothing or fabric.The ratios of ’S and S under different wind speeds were the maximum moisture permeability index of clothing or fabric under the corresponding wind speed,which could define the range of permeability index.Secondly,multi-layer fabric systems were designed to explore the mechanism of heat and moisture transfer and the change of moisture permeability index.The multi-layer fabric system simulated the dress situation in autumn and winter: underwear layer + thermal insulation layer+ outer clothing layer.According to the different outer clothing fabrics,the systems were divided into two types: ordinary fabric system and waterproof and breathable fabric system.In the systems,glass fiber mesh material was used to simulate the air gap under clothes,and three combination modes were designed.Considering the limitation of measuring instrument and previous studies,the total thickness of air gap under clothing was set as 0～11.184 mm.The results showed that: 1)the total thermal resistance and total moisture resistance of fabric systems increased linearly with the increase of the thickness of the air gap;2)there was no significant difference in the total thermal resistance and moisture resistance of different air gap combinations,and the thickness of air gap had a significant effect on the total thermal resistance and moisture resistance;3)the total isothermal moisture resistances of the fabric systems were larger than that of the total non-isothermal moisture resistances,which could be considered to be caused by the moisture resistance of air(boundary layer,air gap under clothing)and fabric layer.Although the moisture resistances of the boundary layer under the two conditions were different,the influence was limited.If the moisture pressure difference of the air gap under the clothing was larger in the non-isothermal environment,the moisture resistance was smaller.At the same time,there was condensation on the surface of the fabric under the non-isothermal environment,which aggravated the moisture absorption of the fabric.On the one hand,it would cause systematic errors in measurement.On the other hand,the different transmission performance of fabrics to water vapor and liquid water would also lead to greater differences in the measured results of fabric moisture resistance.It could be considered that in the process of sweating hotplate,the sweat precipitated from the skin in the isothermal environment evaporated and then transmitted in the form of water vapor(without considering that the fabric was close to the skin).In the non-isothermal environment,there was a transmission mode of sweat: evaporation-condensation,re-evaporation and re-condensation.Finally,the moisture permeability index in isothermal and non-isothermal environment was compared and the permeability index calculated by ’S was discussed.The experimental results showed that the difference between isothermal and non-isothermal permeability index was related to the difference of moisture resistances under the two conditions,which could reflect the relative change of heat and moisture transfer.The moisture permeability index calculated by ’S was the degree that the relative moisture permeability capacity of clothing could reach in the actual environment,which had certain guiding significance for the measurement and improvement of moisture permeability of clothing or fabric. |
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