| Flexible protective material is a fundamental condition for normal moving in special occasions to explore the world and the universe. There is much demand to develop light weight materials with stability and flexibility under high/low temperature in practical applications, such as space technology, adventure, sport, special engineering etc. Flexible thin thermal insulation material is the basic material of personal thermal protection and deformable thermal insulation. Flexibility or movement without obstacle can be realized through two methods usually. One is fiber aggregate which is thick and has poor airproof properties. The another is multilayer films combination material which will impact the flexibility and thermal insulating performance in applications.In this paper, the flexible multilayer insulation composite materials which are mainly used for high (150℃), low (-150℃) temperature insulation were discussed. Based on the analysis about the relationship between the properties of the insulation materials and their heat transfer process, the structure of the flexible multilayer insulation material which is combined by reflecting shields and spacers was designed. And the ultra-thin, flexible and high efficient insulation materials were obtained. Furthermore, the preparation and the processing technology for the materials were introduced simply. Compared with the metal foils, the films evaporated with metal are high strength and good reusability. Especially, the performance of aluminum and polyester is much better and low price. So it is reasonable to choose the aluminized polyester film as a reflecting shield. The performance of six different aluminized polyester films were tested. As a result, the composite film (6μm PET+0.03μm Al+8μm PET) was selected as the reflecting shield of the flexible multilayer insulation composite material. The thermal conductivity and thermal resistance of multilayer insulation materials with four different spacers were compared, and the best spacer structure is the polyester mesh that had down added into the mesh. Meanwhile, the properties of the multilayer insulation material with different surface contact state and different combination structures were studied, and then the optimal combination structure of the multilayer insulation materials was obtained.The final forming sample which met the requirements were obtained through the experiments about the multilayer insulation samples. The structure of the final forming sample is outer fabric+ the middle layers (11 composite films with polyester mesh between adjacent reflecting shields, and down was fixed into the mesh in order to improve the insulation performance)+inner fabric. Meanwhile, the composite films were crumpled in order to achieve the best insulating effect. The weight per unit area of the final forming sample is 475.52 g/m2, the thermal conductivity is 0.0326 W/m-K, the temperature preservation rate is 87.72%, the average heat transfer coefficient is 1.333 W/m2·℃, and the clo value is 4.862. After the forming sample at 160℃two-hours treating, the temperature of inner side of fabric remained at about 43.2℃. After the forming sample treating under a low temperature -120℃～-110℃for 2 hours, the temperature of inner side of the fabric remained at about -5.4℃. Under the low temperature -120℃～110℃, the flexibility decreases of both warp and weft directions were less than 6%, and there was no frost and low temperature embrittlement phenomenon. The mechanism and airtight properties of the multilayer insulation material at high/low temperature condition were measured. And it can be found that the multilayer insulation materials could meet the requirements of bending, compressing, the hanging etc applications. Furthermore, the change rate of flexibility was less than 3%, and there was no leaking phenomenon of the samples.Firstly, the ideal heat transfer model and the solid thermal conductivity transfer model of multilayer insulation material were given based on previous studies. And the temperature distributions of reflecting shields and heat fluxes through the materials were calculated using Newton’s iterative method. Then, for the dependence of the thermal conductivity of the temperature about reflecting shields and spacers, and the dependence of the surface reflecting emission of the temperature, the ideal heat transfer model and practical heat transfer model of the materials which discussed in this paper were investigated on the basis of the simple heat transfer models. Heat transfer fluxes through the material which consists of thermal radiation flux, solid heat transfer flux and gas heat transfer flux have been investigated according to the practical heat transfer model. The temperature distributions and heat fluxes of multilayer insulation materials have been solved by practical heat transfer model using iterative method combining with dichotomy method. The comparison between the experimental results and the calculated values which are obtained from the model shows that the model is feasible to be applied in engineering. The errors between experimental thermal conductivity and the theoretical results by heat transfer model are less than 10%, and errors between experimental heat fluxes and the calculated results by model in this paper are below 3%. So the numerical model of the flexible multilayer material can be applied to practical engineering.The theoretical temperature distributions of reflecting shields of multilayer insulation materials from high temperature (433K)/low temperature (123K) to 273K were obtained using ideal heat transfer model, solid heat transfer model and the practical heat transfer model. The increase of the temperature gradient of practical model is smaller than that of ideal model approaching the cold boundary. And the decrease of the temperature gradient of practical model is larger than that of ideal model approaching the hot boundary. The results show that the temperature distribution of practical heat transfer model is between distribution of ideal heat transfer model and solid conductive heat transfer model.The heat fluxes and the ratios of heat fluxes for radiation heat transfer, solid conductive heat transfer, and gas heat transfer have been discussed in this paper from high temperature (433K)/ low temperature (123K) to 273K were calculated and analyzed. In atmospheric pressure, the ratio of gas heat transfer flux through multilayer insulation material is less than 0.6; the radiation resistance is the largest; and the heat transfer flux is the least. The radiation heat transfer flux is almost negligible compared with the gas and solid heat transfer fluxes. While the gas heat transfer flux was reduced by reducing gas pressure, and the solid heat transfer flux was reduced by reducing the thermal conductivity of the material, the apparent thermal conductivity and heat transfer process of the multilayer insulation material were analyzed. When the gas and solid heat transfer fluxes were reduced, the radio of radiation heat transfer flux increases. With the increase of the proportion of radiation thermal transfer flux for multilayer insulation materials, the insulation performance of the material would be more closed to the ideal state of vacuum multilayer insulation. |
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