Improved buoyancy-driver hybrid ventilation system for multiple-heat-source industrial buildings

An industrial building may have several heat sources which together create a high-temperature working environment that puts the health of workers at risk. Ventilation is an effective way to remove heat, but improperly designed systems may fail to create a healthy thermal environment. The performance of buoyancy-driven hybrid ventilation in a multi-heat-source industrial plant was investigated in this study. The effects of the height of the inlet above the floor and exhaust velocity on the hybrid ventilation performance were studied; properly increasing the above-floor inlet height appears to improve the thermal environment while excessive mechanical exhaust velocity leads to increased energy consumption with a negative impact on ventilation efficiency. The optimum parameters of the improved ventilation system were determined and compared against existing ventilation systems. In summer, the improved ventilation system shows an average temperature of 34.61 °C, which is 3.40 °C lower than the existing system. The allowed exposure time (AET) is 52 min, which is 18 min longer than the existing system. In winter, the improved ventilation system shows an average temperature of 18.68 °C, which meets the design requirements for industrial buildings. The improved ventilation system can provide thermally comfortable conditions in both summer and winter

Time-Variant Reliability Optimization for Stress Balance in Press-Pack Insulated Gate Bipolar Transistors

Stress imbalance significantly affects the performance of a press-pack insulated gate bipolar transistor (IGBT). Time-variant loads and conditions lead to the stress fluctuations, exacerbating the impacts. The conventional reliability optimization faces efficiency barriers due to the nested time-variant reliability analysis and design optimization. In this paper, a time-variant reliability optimization approach for press-pack IGBTs is proposed to address the efficiency issue of the IGBT reliability optimization. The performance functions of the maximum and typical stresses are formulated as the optimization objective and constraint. A time-variant reliability optimization model is formulated considering the stress balance reliability degradation within the service cycle. A decoupling algorithm is proposed to transform the nested optimization into a sequential iteration of static reliability optimization and time-variant reliability analysis. The reliability analysis utilizes the performance function continuity in the time domain to reduce the evaluations for the most likelihood points, thereby enhancing efficiency. Numerical and experimental results on an actual IGBT demonstrate the accuracy of the stress balance performance analysis. The time-variant reliability optimization based on the performance functions improves the stress balance performance by 16.3% and meets the reliability requirements within the service cycle. Compared with the conventional double-loop approach, the difference between the solution of the proposed approach with the reference solution is 0.4%, and the efficiency is 334 times that of the double-loop approach. The performance advantages in accuracy and efficiency exhibit the application potential of this approach