The Research Of Unsteady-State Test Method For Fiber Material’s Thermal Physical Properties

With rapid development of modern material science, the application and research of fiber material becomes more and more important. Fiber material has a large number of applications, not only in the clothing area, but also in the aerospace, energy, machinery, medicine, construction and other engineering fields. With its unique mechanical and thermal properties, light weight, good flexibility performance, fiber material has been becoming essential for material area.The thermal property of fiber material is significant. It is a very good insulation material caused by its poor heat transfer capacity. Historically, at the very beginning fiber material became raw materials of clothing and textile products for keeping human being from cold conditions. In the engineering field, fiber material is a suitable insulation material due to its excellent shape adaptability as well. And now, fiber material will be also involved in a large number of heat transfer problems, such as in the production and application of composite material. So it is very important to study the thermal property of fiber material.However, for its complex structure, the heat transfer research of fiber material has lagged behind its application. Fortunately, lots of researchers have made contributions in this area, but many researches are still inadequate. Take the unsteady thermal test of heat transfer performance for example, current researches are still very lack.The aim of fiber heat transfer performance testing is mainly to obtain thermal conductivity of fiber material, which is based on steady-state test method generally from past test methods. But this steady-state test method has its own defect:it will take a long period of sample balance. This process may affect the moisture regain of fiber material, which will lead to inaccurate measurement results. In addition, we cannot distinguish whether there are other heat transfers occurring including heat conduction, so the thermal conductivity obtained from this test cannot be known if it has true thermally physical significance.Unsteady-state measurements can be a good solution to these problems. However, the reliability of this test method has always been controversial in recent researches, some scholars believe that the thermal conductivity can be obtained from this test method, but some scholars hold the opposite view that the result difference between unsteady-state test and stead-state test is too large, which is not suitable for fiber material. In this paper, quite a few drawbacks have been found in previous unsteady-state test methods by detailed analysis. The question arises for the fiber unsteady-state test method should have the characteristics.According to unsteady-state test requirements analysis to fiber material, the Step-wise Transient Method is selected as the objective of this study.In this paper, the Step-wise Transient Method is improved. The relationship between test time and sample size is analyzed through numerical analysis. And the numerical analysis of conclusions is verified through grease sample as well. In this paper, the associated sample size and maximum measurement time is further proposed for fiber material through numerical results.Using the theory of Step-wise Transient Method, an unsteady test device for fiber material is set up in this pilot testing, which includes framework, specimen thickness stabilizer, heat source circuit, measuring circuit, data acquisition modules, computer processing and so on. In order to verify the accuracy of this test equipment, plexiglass sample is adapted in this paper, and the results show this measuring device is reliable and accurate for solid material.In the data processing algorithms, this paper improves previous methods of data processing. By the new method, it can not only easily be identified whether the heat is transferred through heat conductivity way inside of the fiber material, which can avoid interfere of non-conductive in normal test, but also can effectively eliminate effect of other error factors. According to the testing results of weaving, knitting and nonwoven samples, this paper concludes that the thermal conductivity can be achieved through an unsteady-state method, but some test parameters need to be carefully controlled, such as the heat flow of heat source.In this paper, through numerical simulation analysis, we find the test result error for material with low thermal conductivity is greater than the one with high thermal conductivity, so this measurement need to be still need to be optimized through lots of work.Subsequently, the unsteady-state test of multi-layer composite material is proved from theory and experiment. And it is proved by theory that one general thermal conductivity cannot be characterized the multi-layer composite material structure under the unsteady state thermal conditions. The heat transfer performances of multi-layer composite material not only relate to thermo-physical properties of each component, but also relates to the orders of each components. This paper is confirmed the correctness of theoretical analysis through the research of unsteady-state test for fiber material.In conclusion, the thermal conductivity for fiber material can be measured by using unsteady-state test through the research of this test method. However, the testing of fiber material has certain condition, namely need to avoid thermal convection and mass transfer phenomenon. The research of unsteady-state test methods for fiber heat transfer has important implications, it not only improves the test speed, but also make we get lots of specific information through this test.