层间稀薄气体传热对多层绝热材料性能的影响分析

通过建立的热量传递模型,分析了不同的气体稀薄程度(Knudsen数)时,气体传热对多层绝热材料有效热导率和各层温度分布的影响。分析表明:由多层绝热材料真空度变化引起的稀薄气体传热量波动较大,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,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。

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

The numerical calculation model of MLI was developed to simply analyze a hybrid heat transfer with different degree of gas rarefaction or Knudsen number(Kn).The heat fluxes for a number of inert and some polyatomic gases have been analyzed at different heat transfer conditions ranging from a molecular to a continuum regime.The results indicated that under degraded vacuum condition,the effect of rarefied gas inner space on the MLI thermal performance is not neglected,when vacuum was degraded to 10Pa,the MLI thermal performance was greatly affected by energy accommodation coefficients and thermal conductivity of rarefied gas.So in order to improve the insulation performance of low vacuum MLI,different residual gases can be utilized according to the vacuum degree and gas energy accommodation coefficient.