Conventional parallel capacitive RF MEMS switches have a large impact during the suction phase. In general, RF MEMS switches have to be switched on and off in a considerably fast manner. Increasing the driving voltage enables fast switching but also increases the impact force, which causes the beam membrane to be prone to failure. In the present study, the addition of two support pillars was proposed for slowing down the fall of the beam membrane based on the conventional RF MEMS parallel switch, so as to reduce the impact velocity. As such, a novel RF MEMS switch was designed. Further, simulation software was used to scan and analyze the positioning and height of the support pillars with respect to electromechanical and electromagnetic performance. The simulation results show that the optimal balance of impact velocity and pull-in time was achieved at a height of 0.8 um, a distance of 10 um from the signal line, and an applied voltage of 50 V. The impact velocity was reduced from 1.8 m/s to 1.1 m/s, decreasing by nearly 40%. The turn off time increased from 3.9 us to 4.2 us, representing an increase of only 0.05%. The insertion loss was less than 0.5 dB at 32 GHz, and the isolation was greater than 50 dB at 40 GHz.
The residual heat exchanger in nuclear power plant is the key component of secondary side passive residual heat removal system, where the performance of removing decay heat by condensation and pool boiling to the secondary water storage tanks in the residual heat exchanger is crucial to the safety of the nuclear power plant. In the present paper, an experimental facility is built to evaluate the heat removal capability of the residual heat exchanger in both steady state natural circulation and forced circulation at different pressures. The high pressure steam is forced to flow and enter into heat exchanger with a slight inclined tube, which is installed in a large water pool. Experiments are carried out to study the characteristics of the steam condensation in the residual heat exchanger at different parameters. A calculation code for modeling this process and predicting the outlet temperature is also developed.
The results show that the temperature difference between inlet and outlet increases with the increase of the inlet steam pressure due to the variation of latent heat. Meanwhile, the outlet temperature also increases with increasing flow rate. The calculation results accord with the experimental data at low mass flow rate. It is also found that the two calculation models proposed by J.R. Thome predict the flow pattern well, and the Shah’s equation is more suitable to estimate the heat transfer characteristic.
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