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| Simulation Analysis of Stretch Induced Breakup of a Liquid-Metal Bridge for the Development of Micro-Switches |
| Zhu Xiaonan1, Yang Fei2, Zhang Yunxuan2, Sun Jinru2, Rong Mingzhe2 |
1. The 705 Research Institute China State Shipbuilding Corporation Limited Xi'an 710077 China;
2. School of Electrical Engineering Xi'an Jiaotong University Xi'an 710049 China |
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Abstract Traditional mechanical switches use a pair of solid-metal sheets as conductive contacts to achieve switch operations. Existence of conductive spots leads to a series of electrical contact stability problems such as the increase of contact resistance, electrodynamic repulsion force between closed contacts and the generation of switching arcs in current breaking, which seriously affect the service life of mechanical switches, especially microswitches like relays and miniature circuit breakers. Stretching a liquid-metal bridge to breakup could realize rapid arc breaking of low-voltage DC ampere-level currents, thereby eliminating the above electrical contact problems caused by solid conductive spots. Constructing a simulation model can effectively analyze the fluid dynamics of a liquid-metal bridge during the stretch induced breakup, providing guidance for the regulation of the liquid-metal bridge's arc breaking performance. Most existed models for liquid bridge's breakup simulation are based on moving mesh or other mesh deformation methods, which cannot simulate the wide range deformation or geometric rupture of a liquid bridge.
To address the above issue, a finite element simulation method that doesn't rely on grid deformation for liquid bridge's breakup is proposed here. This method approximates solids by setting a maximum viscosity for liquids, and simulates the liquid bridge's stretch process by moving the boundary of the maximum viscosity area cooperating with the liquid mass flowing out of the calculating domain. Fluid variations of the liquid bridge obtained from the model are in good agreement with experimental results, in terms of time scale and geometric shape. The model could be used to accurately track the boundary movement and profile development of a liquid bridge during the whole breakup process. Based on this model, fluid dynamics of a liquid bridge during stretch induced breakup could be accurately predicted.
Based on the model, the effects of liquid metal volume and stretching speed on the breakup characteristics of a liquid bridge are explored. Transition law of a liquid bridge's breakup characteristics within the full stretching speed range is also obtained. Liquid bridges with a larger volume have higher curvature tolerance towards external stretching effect, thus could develop larger rupture distances. Increasing the stretching speed can generally increase the rupture distance and bottom distance of a liquid bridge, which helps to create larger space for the development of single arc and double arc in series, shortening the arcing time and improving the breaking performance in the end. The stretching speed also affects the order of two times ruptures of the liquid bridge through competition with the effect of gravity. As the stretching speed increases, two times ruptures of the liquid bridge follow a transition pattern of firstly rupturing at the lower end, simultaneous rupturing at both ends, and firstly rupturing at the upper end.
Combined with experimental results, the influence of liquid bridge breakup characteristics' transition on the arc regimes was analyzed, and the phase diagram of the arc regimes' transition within the full stretching speed range was given, providing a basis for regulating the arc breaking performance of the liquid bridge-based switch. Within the full stretching speed range, electrical arc regimes' transition routes of the liquid bridge are more diverse. At the critical transition speed, breakup of the liquid bridge will directly give birth to the Regime Ⅱ where two electrical arcs elongate in series. At higher stretching speeds, “Regime Ⅱ Plus” of electrical arcs emerge due to multiple breakups of the liquid bridge. In the above two situations, electrical arc breaking performance of the liquid bridge is superior.
This study has strong reference significance for the study of both fluid simulation methods for liquid bridge breakup and the development of liquid bridge-based microswitches such as relays and contactors.
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Received: 17 July 2023
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2024, Vol. 39 
