Yuanzineng kexue jishu (Dec 2024)
Development of Sub-channel Program and Multi-objective Optimization Method Research for Printed Circuit Heat Exchanger
Abstract
The helium-xenon Brayton cycle system is one of the most feasible small reactor power technology solutions. The performance of the regenerator directly affects the conversion efficiency of the Brayton cycle system. The printed circuit heat exchanger (PCHE) is a microchannel heat exchanger with a hydraulic diameter usually in the range of 0.5-2.0 mm. Therefore, PCHE has a high degree of compactness and performs well under high temperature and high pressure conditions. It has become one of the best choices for Brayton cycle system regenerators. The regenerator used in the small Brayton cycle system is subject to multiple constraints, such as total mass, total pressure drop, and flow channel length, which must be lower than a certain limit. Taking it as the objective function, the purpose of the research is to optimize the regenerator from multiple dimensions. To this end, a sub-channel calculation program for the PCHE for helium-xenon working fluids was developed. The input parameters include the structural dimensions of the flow channel and the flow rate of a single flow channel. The output results are the total mass, total pressure drop, and flow channel length of the heat exchanger, which are used to study the sensitivity of the structural parameters to multiple objectives. An orthogonal experimental table of flow channel structural parameters was designed. By analyzing the numerical simulation results of the orthogonal experimental table, the effects of different flow channel structural parameters on flow, heat transfer and energy utilization efficiency were obtained, and the structural parameters with the greatest influence were added to the thermal correlation in the form of influencing factors. According to the analysis results, the flow channel width has the greatest influence on energy utilization efficiency, followed by the flow channel height, while the lateral and upper and lower partition wall thicknesses have almost no effect. An empirical relationship between Nu and f factors with high accuracy was fitted in the range of Re=4 700-35 400 and Pr=0.186-0.196, which greatly improved the reliability of the sub-channel program. The results of sensitivity analysis show that as the flow channel width and height of the cold side flow channel increase, the sensitivity of the objective function to the variables continues to decrease, the optimization effect gradually becomes worse, and there are optimal design points, which are 4 mm and 1 mm respectively. The sensitivity of the hot side flow channel height to the total pressure drop continues to increase, and is opposite to the optimization direction. Therefore, the hot side flow channel height should be as small as possible. Considering the optimal optimization point of total mass and total pressure drop, the value is 1.4 mm. The total pressure drop after optimization decreases by 12.0%, and the total mass decreases by 28.8%. The optimization design method studied in this paper is more in line with the design requirements of the small Brayton cycle system scheme, and has a guiding role in the design of PCHE for special application scenarios.
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