Analysis Of Thermal Comfort About Textiles And Fabric Design Of Knitting Products

Heat transfer process, effective factor to heat comfort of knitting underwear and the effect of knitting technique and fabric structure on heat comfort were discussed in this paper.On the basis of basic physical theories about heat conduction, convection and radiation, a comprehensive mathematic model was given to describe the transient heat transfer process which took into account the three heat transfer mechanisms of conduction, convection, radiation and their tripled effects.After the establishment of mathematic equations which describes the complex transient heat transfer process through fabric, the solving of these equations is very time-consuming by traditional method, especially when taking into account the changes of so many conditions such as fabric parameters, wearing situation of the fabric, environment conditions and so on. So, trying to get the rules of how so many conditions affect transient heat process is almost impossible by traditional calculation. There seems to have been no definitive descriptions about the details of transient heat transfer through the textile system. Finite Element Method was used to solve this problem in this paper.Heat transfer mainly involves two aspects: temperature and heat flux. This paper focus on the temperature distribution and the changes of heat flux through the cross section of the fabric system which consists of fabric and air layers.Because we mainly dealt with knitting underwear which normally contacts with human body directly, so, transient cool feeling when putting clothes on is another key content of the analysis.1. Mathematic EquationsFibers and air tangle together form textile material. As far as focusing on the overall heat transfer properties of the fabric and measuring and calculating the average values of fabric parameters used by theoretical analysis, it is reasonable to premise that the fabric is a uniform and isotropic system.In normal wearing, the size of the thickness direction is much smaller than the sizes of the other two directions in the coordinates, so heat transfer through the fabric deduced to one dimension problem. The transient heat transfer process through the fabric system could be described as:There is a temperature difference between the outer surface of the textile that covered the human body and the environment which cause heat transfer between the textile and the environment by convection and radiation. Convection and radiation combined together to act as boundary condition at the outer surface of the textile. This boundary condition couple together with conduction to determine the total heat transfer process through. When the air flows through the out surface of the fabric, the velocity of air flow slows down near the surface because of the stickiness of the air. The thin air layer at the surface is still, so, the way for heat transfer through this thin layer must be conduction. When Fourier's law of conduction and energy conservation equation were used to this surface air layer, we got the combined heat transfer equation:d" (2)Where q=heat flux (W.m )-2 -1h=film coefficient (W.m . K );0Tf=out surface temperature of the fabric ( C);and0Tr=temperature of the ambient atmosphere ( C).o = Stefan-Boltzmann constant s = emissivity of the surfaceEquations (1) and (2) are the theoretical background for dry heat transfer through textile system.2. Detail Description of Heat Transfer Process through Textile SystemThe theoretical model of the combined conductive convective and radiative heat flow through fabrics is presented and studied using the finite element method. By the aid of software MSC MARC/Mentat, details of heat transfer through textiles and air trapped within the textile assembly were simulated. Significant findings through this study include the change in heat flux against time and the transit temperature distribution at the cross section of the fabric assembly. This research also investigated on the influence of structural parameters of the fabric assembly on the heat transfer performance of the fabric assembly. The structural parameters of the fabric assembly range from the materials used in the assembly, the number of fabric layers, the presence of air between fabric layers, and the size of the gap betweenfabrics layers. Besides, this paper also studied the influence of environment conditions, such as environment temperature and wind condition, on heat comfort of the textiles system and the effective factors on cool-feeling when put clothes on.3. Experimental TestTo test the theoretical predictions about heat transfer process and the influence factors, relevant samples were tested in an artificial climatic chamber, comparisons showed good agreement between the theoretical and tested results4. Application of the Theoretical ConclusionsAccording to the theoretical conclusions, 6 different knitting fabrics with different surface characters were designed. Tested results showed that the thermal comfort characteristics of the fabric showed agreement with the theoretical prediction.