Heat Transfer And Thermal Protection Of Woven Structural Materials Under Strong Heat Conditions

In strong thermophysical fields such as high and low temperature,thermal radiation and fire field,clothing is required to have heat insulation function.Thermal protective clothing has attracted much attention because of its unique heat insulation function and wide application prospect.However,due to the complexity and variability of fabric structure,it is difficult to describe the transient heat transfer process in the fabric by physical experiments,and many tests in the preparation process of thermal protection fabric are carried out at high temperature,which undoubtedly increases the development cost and wastes resources.Therefore,this paper simulates the transient heat transfer process of different woven structural materials by finite element software,explores the factors affecting the thermal insulation and protection performance of fabrics,and verifies the simulation results through experiments.The main contents are as follows:(1)Based on the real interwoven structure of yarns,six kinds of model fabrics(including plain weave,2/1～6/1 twill)with different thicknesses and 20 kinds of double-layer woven fabrics with different stacking orders were created by using modeling software.(2)Considering the anisotropy of fabric heat transfer,under the same conditions of material,linear density and warp-weft density,the transient heat transfer of fabric is simulated,and the time-varying temperature rise of fabric after heating is analyzed,and the effects of floating length,heat source intensity,thickness and stacking order on the thermal protection performance of fabric are discussed.(3)By observing the physical process of heat transfer of woven fabrics,five indexes are put forward to evaluate the thermal insulation and protection performance of woven structural materials from two dimensions of thermal insulation time and thermal insulation temperature,namely,the lag time of initial temperature rise of the lower surface,the temperature rise speed of the lower surface,the stable temperature of the upper and lower surfaces,the maximum temperature difference between the upper and lower surfaces and the stable temperature difference.(4)Observing the temperature distribution nephogram of fabric heat transfer,we can know that the length of floating line in fabric will affect the heat transfer law in fabric.The results show that the heat transfer along the floating length of the yarn increases the temperature of the yarn body on the surface of the fabric,and the yarn temperature in the interwoven area increases rapidly,resulting in the upper and lower surface temperatures and temperature differences related to the floating length.The simulation results show that the thermal insulation performance of six kinds of structures is from low to high:plain grain<2/1<3/1<4/1<5/1<6/1.(5)Under the condition of a conventional heat source of 0.8k W/m~2,a single layer of fabric can effectively prevent the transfer of heat flow.Under strong heat conditions,it is necessary to increase the protective thickness or add other materials to improve the thermal insulation ability.(6)Under the condition of strong heat of 2.4 k W/m~2 and constant thickness,the thermal protection performance of the six fabric structures ranges from low to high:plain<2/1<3/1<4/1<5/1<6/1,which meets the requirements that the larger the fabric float length and the less the interlacing points are,the better the thermal protection performance of the fabric.The simulation law of multi-layer fabrics is consistent with that of single-layer fabrics;When the float length is fixed,the thermal protection ability of the fabric gradually increases with the increase of the fabric thickness,but there is an optimal thickness.The research results show that the optimal thickness is 5 layers of fabric.(7)Under the condition of strong heat of 2.4 k W/m~2,when the surface texture/inner texture structure is the same,with the increase in the floating length of the inner texture/outer texture,the thermal protection performance of the fabric gradually increases,meeting the requirements of plain<2/1<3/1<4/1<5/1<6/1,and the simulation law is consistent with that of single layer fabrics.(8)The correctness and reliability of the numerical simulation results were verified through RPP thermal protection performance testing experiments,and the research results provide theoretical guidance for the design of thermal insulation structures for thermal protection clothing.