Abstract:The Knudsen pump (KP) is a kind of micro-pump that can form thermally induced flows induced by temperature fields in rarefied gas environments. It has the advantages of having no moving parts, simple structure, easy construction and extension, a wide range of energy sources, and low energy consumption. With the development of Micro/Nano Electro Mechanical Systems (MEMS/NEMS), extensive studies have been conducted on KPs, and the applications of KPs have widened. In order to obtain efficient flow fields in KPs,… Show more
“…The mass flow rate of 1.33 10 −9 kg/s was obtained over a vertical line connecting the substrate to the top freestream. Thus, case 6 demonstrates that micro-configuration has potential in the application of gas pumping such as the Knudsen pump (compressor) [ 51 , 52 , 53 , 54 ].…”
Knudsen force generated by thermally driven gas flow in a microscale structure has been used for gas detection and has shown immeasurable potential in the field of microelectromechanical system (MEMS) gas sensors due to its novel sensing characteristics. In this article, the performances of three kinds of Knudsen force gas sensors with improved isosceles triangular shuttle arm structures were studied. In the first design, the top side and right side lengths were equal; in the second, the top side and bottom side lengths were equal; and for the third, the bottom side and right side lengths were equal. A detailed investigation including gas flow, thermal characteristics, Knudsen force, and coupling effects between the shuttle-heater pairs was conducted using the direct simulation Monte Carlo (DSMC) method and the main mechanisms for gas flow presented were almost the same in this work. However, the second design returned the highest Knudsen force performance. The value increased by 42.9% (P = 387 Pa) compared to the Knudsen force of the original square shuttle arm. The results also demonstrate that the coupling effects become weak toward the right with an increase in the number of shuttle-heater pairs.
“…The mass flow rate of 1.33 10 −9 kg/s was obtained over a vertical line connecting the substrate to the top freestream. Thus, case 6 demonstrates that micro-configuration has potential in the application of gas pumping such as the Knudsen pump (compressor) [ 51 , 52 , 53 , 54 ].…”
Knudsen force generated by thermally driven gas flow in a microscale structure has been used for gas detection and has shown immeasurable potential in the field of microelectromechanical system (MEMS) gas sensors due to its novel sensing characteristics. In this article, the performances of three kinds of Knudsen force gas sensors with improved isosceles triangular shuttle arm structures were studied. In the first design, the top side and right side lengths were equal; in the second, the top side and bottom side lengths were equal; and for the third, the bottom side and right side lengths were equal. A detailed investigation including gas flow, thermal characteristics, Knudsen force, and coupling effects between the shuttle-heater pairs was conducted using the direct simulation Monte Carlo (DSMC) method and the main mechanisms for gas flow presented were almost the same in this work. However, the second design returned the highest Knudsen force performance. The value increased by 42.9% (P = 387 Pa) compared to the Knudsen force of the original square shuttle arm. The results also demonstrate that the coupling effects become weak toward the right with an increase in the number of shuttle-heater pairs.
“…An abrupt temperature variation near a heated edge (or tip) introduces a strong anisotropy in the momentum transfer to the tip, which results in a flow near the tip by reaction 13 . In this paper, we are concerned with the application of the thermal edge flow with an emphasis on the possibility to induce a one-way flow, which is potentially significant, e.g., for microelectromechanical systems (MEMS) 14 , 15 . Figure 1 Schematics of the concept.…”
Section: Introductionmentioning
confidence: 99%
“…Thus, though localized near the edge, the order of magnitude of the flow velocity is more significant for the thermal edge flow than for the thermal creep flow, which makes it attractive for various applications. Moreover, unlike the thermal creep flow, there is no need to maintain the temperature gradient of the plate, making it easy to use in practice 13 , 15 . In this regard, a prototypical thermal edge pump has been fabricated in ref.…”
The thermal edge flow is a gas flow typically induced near a sharp edge (or a tip) of a uniformly heated (or cooled) flat plate. This flow has potential applicability as a nonmechanical pump or flow controller in microelectromechanical systems (MEMS). However, it has a shortcoming: the thermal edge flows from each edge cancel out, resulting in no net flow. In this study, to circumvent this difficulty, the use of a U-shaped body is proposed and is examined numerically. More specifically, a rarefied gas flow over an array of U-shaped bodies, periodically arranged in a straight channel, is investigated using the direct simulation Monte-Carlo (DSMC) method. The U-shaped bodies are kept at a uniform temperature different from that of the channel wall. Two types of U-shaped bodies are considered, namely, a square-U shape and a round-U shape. It is demonstrated that a steady one-way flow is induced in the channel for both types. The mass flow rate is obtained for a wide range of the Knudsen numbers, i.e., the ratio of the molecular mean free path to the characteristic size of the U-shape body. For the square-U type, the direction of the overall mass flow is in the same direction for the entire range of the Knudsen numbers investigated. For the round-U type, the direction of the total mass flux is reversed when the Knudsen number is moderate or larger. This reversal of the mass flow rate is attributed to a kind of thermal edge flow induced over the curved part of the round-U-shaped body, which overwhelms the thermal edge flow induced near the tip. The force acting on each of the bodies is also investigated.
“…In recent years, with the progress of micro-fabrication techniques and the advent of micro-electromechanical systems (MEMS), researchers have become increasingly interested in thermal creep flow and the Knudsen pump [ 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 ]. Wang et al [ 15 ] have recently reviewed more than 200 works in the literature to present a comprehensive literature review on the origin of Knudsen pump and its historical development. Based on the design of Knudsen pump, researchers have suggested some configuration variants [ 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 ].…”
In Knudsen pumps with geometric configuration of rectangle, gas flows are induced by temperature gradients along channel walls. In this paper, the direct simulation Monte Carlo (DSMC) method is used to investigate numerically the flow characteristics of H2–N2 mixtures in the Knudsen pump. The variable soft sphere (VSS) model is applied to depict molecular diffusion in the gas mixtures, and the results obtained are compared with those calculated from a variable hard sphere (VHS) model. It is demonstrated that pressure is crucial to affecting the variation of gas flow pattern, but the gas concentration in H2–N2 mixtures and the collision model do not change the flow pattern significantly. On the other hand, the velocity of H2 is larger than that of N2. The velocities of H2 and N2 increase if the concentration of H2 rises in the gas mixtures. The results of velocity and mass flow rate obtained from VSS and VHS models are different. Finally, a linear relation between the decrease of mass flow rate and the increase of H2 concentration is proposed to predict the mass flow rate in H2–N2 mixtures.
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