Development of gas mixture separation method by using thermally driven pumps

在稀薄气体中，气体分子的平均自由程与系统的尺度相比是不可忽略的，气体的温度场与气体的运动密切相关。利用这些流动，已经做了几项工作来开发一种没有运动部件的泵。这种类型的泵在现代技术中很有价值，特别是在与微型设备相关的领域。2006年，我们通过数值模拟发现，这些泵--热力驱动泵--具有气体分离效果。在某些情况下，泵内出现浓度梯度，在某些情况下，两种不同的物质以相反的方向流动。本研究旨在促进这种气体混合物分离新方法的发展。热驱动泵的要求之一是由直径为气体平均自由程数量级的通道组成。因此，在大气压下工作的泵需要微米或亚微米通道，这在许多情况下是气体分离系统的最小压力。在这项研究中，我们开发了一种有效的方法来构建这种具有气体流动驱动力的微尺度通道。这只是两个不同温度的平行金属丝网。在本工作中，我们成功地在实验上观察到当网格内部结构的尺度为气体的平均自由程数量级时，气体流过该对网格。另一项研究结果是热泵的气体分离效果。在本研究中，我们利用宏观尺度热缘压缩机和氦-氩混合气体，成功地测量了泵内的浓度梯度，正如先前数值结果所预期的那样。

In a rarefied gas, where the mean free path of the gas molecule is not negligible compared with the scale of the system, the temperature field of the gas is deeply related to gas motion. Several works has been done to develop a pump without a moving part by using these flows. Such types of pumps are valuable in modern technologies, especially in the fields related to micro-scaled devices. In 2006, we have found by the numerical simulation that these pumps.-thermally driven pumps-has a gas separation effect. In some case there appears a concentration gradient in the pump, and in some case two different species flow in opposite direction. The present study aims to contribute to the development of this new method of gas mixture separation.One of the requirements of the thermally driven pump is that it should consist of channels with diameter of order of the mean free path of gases. Thus micron or sub-micron channel is required for the pumps that work at atmospheric pressure, which would be the minimum pressure for the gas separation system in many cases. In this study we have developed an effective method to construct such micro-scaled channel that has driving force of gas flows. It is just a two parallel wire meshes with different temperatures. In the present work we have succeeded to observe experimentally the gas flows through the pair of meshes when the scale of inner structure of the mesh is the order of the mean free path of the gas.Another result of present research is on the gas separation effect of thermally driven pump. In this research, by using the macro-scale thermal edge compressor and He-Ar mixture, we have succeeded to measure the concentration gradient in the pump as expected in the previous numerical results.