Abstract
A Knudsen pump operates under the thermal transpiration effect or the thermal edge effect on the micro-scale. Due to the uneven temperature distribution of the walls in the channel axis direction or the constant temperature of the tips on the walls, directional thermally-induced flow is generated. In this paper the Direct Simulation Monte Carlo (DSMC) method is applied for N2–O2 gas mixtures in the ratios of 4:1, 1:1, and 1:4 with different Knudsen numbers in a classic rectangular Knudsen pump to study the flow characteristics of the gas mixtures in the pump. The results show that the changing in the gas physical properties does not affect the distribution of the velocity field, temperature fields, or other fields in the Knudsen pump. The thermal creep effect is related to the molecular mass of the gas. Even in N2 and O2 gas mixtures with similar molecular masses, N2 can be also found to have a stronger thermal creep effect. Moreover, the lighter molecular weight gas (N2) can effectively promote the motion of the heavier gas (O2).
Highlights
It is well known that the thermally-induced flow of rarefied gas is generated by the temperature gradient along the walls of the Knudsen pump and that the gas is driven to flow from the lowtemperature side to the high-temperature side
With the development of materials technology and micro-machining technology, the pump structure can be produced by using poly-silicon material, and using the inter-molecular gaps in porous materials such as aerogel membranes [10,11,12], mixed cellulose ester (MCE) [13,14], zeolite [15,16], porous ceramics [17,18] and Bi2 Te3 [19,20] to construct the flowing channel of the Knudsen pump
If collisions with the walls occur in the process of the free movement, the collision will be calculated first, and the post-velocity will be used for the free movement and inter-molecular collisions
Summary
It is well known that the thermally-induced flow of rarefied gas is generated by the temperature gradient along the walls of the Knudsen pump and that the gas is driven to flow from the lowtemperature side to the high-temperature side. The Knudsen pump can provide consistent gas flow and has the advantage of having of no moving parts, a simple structure, ease of operation, long life span, low energy consumption, and wide energy sources. It is widely applied in Micro Electro Mechanical Systems (MEMS) such as gas separators [2,3], gas analysis [4,5,6], micro combustors [7,8], and micro-air vehicle systems [9,10]. Since the rectangular Knudsen pump has been proposed, many structures for the channel were successively designed and studied (Figure 1), including the sinusoidal micro-channel [21], matrix micro-channel [21], curved micro-channel with
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