Fault size estimation is of great importance to bearing performance degradation assessment and life prediction. Until now, fault size estimation has generally been based on acoustic emission signals or vibration signals; an approach based on current signals has not yet been mentioned. In the present research, an approximate estimation approach based on current is introduced. The proposed approach is easy to implement for existing inverter-driven induction motors without complicated calculations and additional sensors, immune to external disturbances, and suitable for harsh conditions. Firstly, a feature transmission route from spall, to Hertzian forces, and then to friction torque is simulated based on a spall model and dynamic model of the bearing. Based on simulated results, the relation between spall size and the multiple characteristic vibration frequencies in friction torque is revealed. Secondly, the multiple characteristic vibration frequencies modulated in the current is investigated. Analysis results show that those frequencies modulated in the current are independent of each other, without spectrum overlap. Thirdly, to address the issue of which fault features modulated in the current are very weak, a fault-feature-highlighting approach based on reduced voltage frequency ratio is proposed. Finally, experimental tests were conducted. The obtained results validate that the proposed approach is feasible and effective for spall size estimation.
Enhancing flow distribution to mitigate heat transfer dead zones and intensify heat transfer efficiency constitutes the crux of augmenting the effectiveness of plate heat exchangers (PHEs). To this end, a two-phase fluid topology optimization approach suited for PHE conditions was developed to devise a novel channel structure of topology PHE. Next, 3D printing technology was employed to fabricate topology plate samples, whose geometrical parameters were akin to those of the traditional dimple plates. To compare the performance of the two plate types, CFD simulation, performance experiment, and visual test were implemented. The CFD simulation results showed that compared to the dimple plate, the temperature disparity between the fluid inlet and outlet of the topology plate escalated by 21.8%, the heat transfer coefficient increased by 6.2%, and the pressure drop grew by 7.4%. Moreover, the experimental results demonstrated that the temperature difference between the topology plate inlet and outlet increased by 13.7%, and the pressure drop surged by 16.9%. These results were mainly attributable to the more homogeneous distribution of the two-phase fluid and the reduced flow resistance in the turning area of the topological plate, which were corroborated by the visual test. The discoveries of this study proffer guidelines for future research endeavors aimed at assessing prospective solutions to boost the heat transfer of PHEs and foster their implementation for heat management.
Abstract In order to enhance heat transfer performance of the reactor core coolant in the narrow rectangular channel of nuclear power system and ensure the safety of the reactor core without local high temperature as well as not cause excessive pressure loss, three different shapes of protruded elliptic dimple were adopted in the channel for numerical research. Firstly, the angle between long axis of the elliptic dimple and direction of the mainstream was rotated, which was defined as a rotated angle θ ranging from 0° to 90°. Secondly, streamwise (in line with the mainstream) slit was processed on the dimple. The last, inclined slit was processed on the dimple. There were five quantitative and two qualitative indicators to account for comprehensive effects of heat transfer, flow resistance and temperature distribution on the wall of the channel, namely, Nu for heat transfer capacity, f for flow resistance, performance evaluation criteria PEC for combination of heat transfer and flow resistance, Tmax and Tavg for maximum and average temperature on the outer wall respectively, velocity field near the inner wall and temperature distribution on the outer wall to show more detail information of the flow and heat transfer characteristics. The study results showed that with increase of θ, heat transfer efficiency and flow resistance all increased. Dimple with whether streamwise slit or inclined slit helped to reduce flow resistance. The dimple with streamwise slit performed best in flow resistance performance and the dimple with inclined slit performed best in heat transfer performance.
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