气体传热对多层绝热性能影响的试验研究

文中通过建立的能进行夹层气体置换的稳态量热器试验系统,试验分析了夹层气体传热对多层绝热材料有效热导率的影响,重点对置换气体种类、气体压强、材料层数及冷热边界温度对多层材料的影响进行试验研究。试验表明在10—60层/cm层密度范围,真空度低于100Pa时,Kn数属于自由分子状态区域和中间压强区域,此时材料的有效热导率随残留气体热适应系数的增大而减小,并随着真空度的降低而增大,当残留气体为空气时,为保证多层材料的绝热性能,应尽量维持真空度不低于10-2Pa。同时,分析表明为有效降低低真空下稀薄气体传热对多层绝热性能的影响,可以采用综合热适应系数较低的气体置换夹层中的空气,以减少低真空多层绝热材料的有效热导率,改善绝热性能。

Experimentally analysis of the effects of rarefied gas heat transfer characteristics on degraded vacuum multilayer insulation material

The investigations were carried out using a static liquid nitrogen boil-off rate measure technique in the case of the small temperature perturbations of cold and hot boundaries.A developed test facility with two cryogenic end-boxes was designed and commissioned for the testing.The heat fluxes for a number of inert and some polyatomic gases were analyzed at different heat transfer conditions ranging from a molecular to a continuum regime.Effective thermal conductivities of the Multilayer Insulation(MLI) were measured over a wide range of temperature(77K—300K) and pressure(10-3—105Pa) using the apparatus.Experimental results indicate that under degraded vacuum condition,the effect of rarefied gas inner space on the MLI thermal performance very depends on the gas rarefaction degree which is impacted by the MLI vacuum degree.Compared to the results of N2,Ar,CO2,Air and He as residual gas,using the gas with low EAC and conductivity on the condition from high pressure to low pressure as residual gases can improve the insulation performance of low vacuum MLI.