论文标题
在稀有气氛中非常薄的水平电线的自由对流传热相关性
A free convection heat transfer correlation for very thin horizontal wires in rarefied atmospheres
论文作者
论文摘要
近年来，火星和地球大气层任务蓬勃发展，增加了对稀土气体热传递的兴趣。在这些低压力下，涉及小几何形状的传热问题，其特征长度是气体分子平均自由路径的顺序，这会带来新的困难。在自由对流的情况下，气体的速度与传热问题密切相关，这一点尤其严重。直径为$ 12.7 \μ\ mathrm {m} $和$ 25 \μ\ mathrm {m {m {m} $的水平电线的实验是在量身定制的真空室内进行的，其压力为0.03 $ $ MILIBAR到环境压力到环境压力，达到$ 80 $ K之间的温度差异到$ 80 $ K之间。实验数据由瑞利号码从$ 10^{ - 13} $到$ 10^{ - 5} $组成，涵盖了从自由分子流到连续体制的广泛范围。特别是对于过渡方案，Knudsen数量在0.1到10之间，实验数据表明，自由对流传热不能仅仅是瑞利数字的函数，但是对Knudsen数字的依赖也必须引入相关性。 $ 10^{ - 8} $低于瑞利号的Nusselt号码的结果表现出了与文献中可用相关性的明显不同。提出了从水平薄电线到连续体制的新经验相关性。目前的工作阐明了当前的热工程问题，这些问题涉及其系统中非常细的电线，这些电线与周围环境相互作用，并具有很大的稀疏度。
Mars and upper Earth atmosphere missions are booming in recent years increasing the interest in heat transfer in rarefied gases. At these low pressures, the heat transfer problems involving small geometries whose characteristic length is of the order of the mean free path of the gas molecules, raises new difficulties. This being especially severe in the case of free convection, where the velocity of the gas is closely linked to the heat transfer problem. Experiments with horizontal wires with diameters of $12.7\ μ\mathrm{m}$ and $25\ μ\mathrm{m}$ were conducted in a tailored vacuum chamber with pressures from $0.03$ milibar to ambient pressure, reaching temperature differences of up to $80$ K between the wire and the air. Experimental data is comprised of Rayleigh numbers from $10^{-13}$ to $10^{-5}$ that cover a wide range from free molecular flow to continuum regime. Particularly for the transition regime, with Knudsen numbers ranging between 0.1 and 10, the experimental data shows that the free convection heat transfer cannot be represented solely as a function of the Rayleigh number, but a dependence on Knudsen number must be introduced into the correlation as well. The presented results for the Nusselt number below Rayleigh numbers of $10^{-8}$ exhibit a clear departure from the available correlations in the literature. A new empirical correlation for free convection from horizontal thin wires from the transition to continuum regime is presented. The present work sheds light on current thermal engineering problems which involves very thin wires in their systems which interact with a surrounding environment with a significant level of rarefaction.
