Abstract
The behavior of the rarefied gas in the thermal transpiration pump with the porous material is investigated numerically by the direct simulation Monte Carlo method. The mass flux achieved by the pump is analyzed for a wide range of Knudsen numbers and ratios of the pore length to the pore diameter. The results show that the thermal edge flows around the ends of the pore play an essential role in determining the maximum performance. The effect of the thermal edge flow leads to a qualitative difference in the driving mechanism from a similar thermal transpiration pump by Knudsen. The mass flow takes a maximum value at a considerably large Knudsen number when the pore length is much larger than the pore diameter. The numerical tests show that a larger mass flux is possible when the edge flow is suppressed. The mass flux is investigated for several values of accommodation coefficient and complex pore geometries. The present results show that only the latter leads to the reduction in the mass flux. The compression ratio, including the performance curve of the pump, is also analyzed for several cases. The results show that the small accommodation coefficient decreases the compression ratio of the pump.
Highlights
We investigate the behavior of the gas in the thermal transpiration pump by Direct Simulation Monte Carlo (DSMC) method for the rarefied gas to clarify how the performance of the pump is determined and whether there is a qualitative difference between the pump by Knudsen and that by Reynolds
The maximum mass flux analysis shows a qualitative difference between the pump of the Kn-type and that with the porous material (Retype)
Reynolds type pump’s mass flux shows the dependency on the space around the porous material, e.g., a narrow space around the porous material may limit the size of the mass flux obtained by the pump
Summary
The micropump becomes increasingly important as the emerging MEMS (micro-electro mechanical systems) technology finds new applications in the diversity of industries. Scitation.org/journal/adv materials, including those fabricated by MEMS technologies Note that they include several applications of the thermal transpiration pump to other fields, e.g., gas chromatography, gas mixture separation, heat pump, and power generation device.. Such a pressure gradient cannot play any role in the driving mechanism This leads to the idea that the performance of porous type devices is to be described only by the theory of the thermal transpiration flow in the pipe of infinite length. This strategy has a drawback of the absence of the effects of ends of the pore. We investigate the behavior of the gas in the thermal transpiration pump by Direct Simulation Monte Carlo (DSMC) method for the rarefied gas to clarify how the performance of the pump is determined and whether there is a qualitative difference between the pump by Knudsen and that by Reynolds
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