Thermal-economic Optimization and Structural Evaluation for an Advanced Intermediate Heat Exchanger Design

Download or read book Thermal-economic Optimization and Structural Evaluation for an Advanced Intermediate Heat Exchanger Design written by Xiaoqin Zhang and published by . This book was released on 2016 with total page 139 pages. Available in PDF, EPUB and Kindle. Book excerpt: Coupling the s-CO2 Brayton cycle to the advanced nuclear reactors generally requires an intermediate heat exchanger (IHX). From an economic viewpoint, it is important to reduce the size and cost of IHX, but at the same time, the thermal hydraulic performances should not be deteriorated. Printed-circuit heat exchanger (PCHE), one of advanced compact heat exchangers, has been demonstrated as a competitive candidate. This thesis mainly focuses on designing a PCHE-type advanced IHX with innovative surface geometry with thermal, economic and mechanical consideration. Among the four outstanding surface geometries, zigzag and S-shaped fin channels are selected for a helium-to-s-CO2 IHX. Since the thermal-hydraulic correlations of the zigzag channel with a variety of geometrical parameters are available, a thermal-economic optimization is carried out to optimize the design of zigzag channel. For such multi-objective optimization problem, the annual total cost and heat exchanger thermal effectiveness are selected as two objectives functions. NSGA-II (a fast and elitist non-dominated sorting genetic algorithm), one of the widely used multi-objective genetic algorithms, is used for searching a group of Pareto-optimal designs. It is found that among the Pareto-optimal solutions, the total cost gradually increases with the thermal effectiveness between 88 and 95% while rises rapidly after the heat exchanger effectiveness exceeds around 95%. The sensitivity study shows that for the solutions with thermal effectiveness below around 95% the heat exchanger core physical length is the dominant factor that causes conflict between the total cost and thermal effectiveness. A similar trend can be observed from both the basic and extended design space. The final selection of the optimal designs obtained from the thermal-economic optimization requires a structural evaluation of surface geometry, especially for high-temperature high-pressure applications. S-shaped fin channels are chosen for preliminary structural assessment using numerical simulation due to the geometrical complexity and expected severe stress concentration. It is found that the excessive stress concentrations occur at tips of S-shaped fins when imposed with high-pressure differential loading. A small portion of the fin yields while the rest of the fin body remains low-stress level. The design and service limit prescribed in the ASME BPVC code is used to evaluate local stresses of the S-shaped fin, and according to the criterion, the reference model was allowed for 11.5 years of service with small portion of fin body yielded.