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作者提出了一个理论模型,即增强黑腔模型,用来解释通过低温装置中多层绝热裂缝(或狭缝)的热流意外大的原因。首先,把绝热层中的裂缝仅看作一个黑腔,估算了从外热源直接进入裂缝的辐射能量;然后加上裂缝外辐射热流多次反射的影响及由裂缝引起的绝热层温度分布变化的影响,在分析中,还指出存在一个降低黑腔效率的几何因子,它是裂缝尺寸的函数。用增强模型和最近的实验数据,可说明如何计算角系数F、辐射能量Q_(s,b)和总增强系数η。最后,在该模型的基础上,预示了一些有裂缝的多层绝热系统的传热现象,并提出了几种减小裂缝影响的方法。这些方法已通过实验检测,其结果由另一论文发表。
The authors propose a theoretical model that enhances the black cavity model to account for the surprisingly large amount of heat flow through multi-layer adiabatic cracks (or slits) in cryogenic plants. First, the crack in the insulation layer is only regarded as a black cavity, and the radiation energy which directly enters the crack from the external heat source is estimated. Then, with the influence of the multiple reflection of the radiative heat flux outside the crack and the temperature distribution of the insulation layer caused by the crack In the analysis, it is also pointed out that there is a geometrical factor that reduces the efficiency of the black cavity, which is a function of the size of the crack. Using the augmented model and the recent experimental data, we show how to calculate the angular factor F, the radiant energy Q_ (s, b), and the total enhancement factor η. Finally, based on the model, the heat transfer phenomena of some cracked multilayer thermal insulation systems are predicted, and several methods to reduce the influence of cracks are proposed. These methods have been experimentally tested and the results are published in another paper.