Heat Transfer Characteristics of Printed Circuit Heat Exchanger with Supercritical Carbon Dioxide and Molten Salt
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https://doi.org/10.1007/s11630-020-1374-3
Article ID: 1003-2169(2020)00-0000-00
Heat Transfer Characteristics of Printed Circuit Heat Exchanger with Supercritical Carbon Dioxide and Molten Salt LAO Jiewei, FU Qianmei, WANG Weilong, DING Jing*, LU Jianfeng* School of Material Science and Engineering/School of Intelligent Systems, Sun Yat-Sen University, Guangzhou 510006, China © Science Press, Institute of Engineering Thermophysics, CAS and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract: Molten salt and supercritical carbon dioxide (S-CO2) are important high temperature heat transfer media, but molten salt/S-CO2 heat exchanger has been seldom reported. In present paper, heat transfer in printed circuit heat exchanger (PCHE) with molten salt and S-CO2 is simulated and analyzed. Since S-CO2 can be drove along passage wall by strong buoyancy force with large density difference, its heat transfer is enhanced by natural convection. In inlet region, natural convection weakens along flow direction with decreasing Richardson number, and the thermal boundary layer becomes thicker, so local heat transfer coefficient of S-CO2 significantly decreases. In outlet region, turbulent kinetic energy gradually increases, and then heat transfer coefficient increases for turbulent heat transfer enhancement. Compared with transcritical CO2 with lower inlet temperature, local heat transfer coefficient of S-CO2 near inlet is lower for smaller Richardson number, while it will be higher for larger turbulent kinetic energy near outlet. Performance of PCHE is mainly determined by the pressure drop in molten salt passage and the heat transfer resistance in S-CO2 passage. When molten salt passage width increases, molten salt pressure drop significantly decreases, and overall heat transfer coefficient slightly changes, so the comprehensive performance of PCHE is improved. As a result, PCHE unit with three semicircular passages and one semi-elliptic passage has better performance.
Keywords: heat exchanger, molten salt, supercritical carbon dioxide, numerical simulation
1. Introduction Concentrating solar thermal power (CSP) has attracted great attention due to its high efficiency, low operating cost and good scale-up potential [1]. In order to make CSP more efficient and cost-effective, thermal energy storage [2] should be used to store heat during sunshine period and release it during weak solar irradiation period. Molten salt is a promising heat transfer fluid due to its good properties [3]. A common technique is based on Received: Jul 25, 2019
steam Rankine cycle to utilize heat from molten salt and generate electricity. The ultra-supercritical steam cycle is used as operating temperature is higher than 550°C, but it is limited by material degradation under high temperature and steam pressure condition [4]. Brayton cycle with supercritical carbon dioxide (S-CO2) [5] can be used in a large temperature range, and it has many advantages such as small compression work and no phase change process. Dostal et al. [6] proposed
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