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首页> 外文期刊>International Journal of Heat and Mass Transfer >CO_2 based natural circulation loops: New correlations for friction and heat transfer
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CO_2 based natural circulation loops: New correlations for friction and heat transfer

机译：基于CO_2的自然循环回路：摩擦和热传递的新关联

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摘要

Results obtained from CFD analysis of 3-dimensional natural circulation loops (NCL) that employ carbon dioxide and water as loop fluids are presented for various isothermal wall temperatures of source and sink in the range of 278-341 K. Such a temperature range would be useful in various heat transfer applications of NCL, e.g. air conditioning, solar collectors, extraction of geothermal energy, etc. For the same wall temperature and geometrical parameters, comparison is made between CO_2 and water in terms of heat transfer rate. Water is considered at atmospheric pressure whereas CO_2 is either in subcritical (liquid) or supercritical state. Liquid CO_2 exhibits very high heat transfer rate, approximately seven times higher than water, whereas performance of supercritical CO_2 depends on the operating pressure and temperature. Effect of loop operating pressure on the system performance is also investigated. Results show that near pseudo-critical region, CO_2 yields very high heat transfer rate, approximately seven times higher than water. Results also show that, due to the presence of bends and local buoyancy effects, fluid parameters such as local velocity and temperature vary in all three dimensions. Validation of simulation results against experimental results reported in the literature with respect to modified Grashof number (Gr_m) and Reynolds number (Re) exhibit good agreement. Additionally, new correlations are proposed for Re in terms of Gr_m, friction factor (f) in terms of Re, and Nusselt number (Nu) in terms of Re and Prandtl number (Pr).
机译：给出了使用二氧化碳和水作为回路流体的三维自然循环回路（NCL）的CFD分析获得的结果，显示了源和汇的各种等温壁温范围为278-341K。在NCL的各种传热应用中有用，例如空调，太阳能集热器，地热能的提取等。在相同的壁温和几何参数的情况下，根据传热速率比较了CO_2和水。认为水是在大气压下，而CO_2处于亚临界（液态）或超临界状态。液态CO_2的传热速率非常高，约为水的7倍，而超临界CO_2的性能取决于工作压力和温度。还研究了回路工作压力对系统性能的影响。结果表明，在伪临界区附近，CO_2的传热速率非常高，约为水的7倍。结果还表明，由于存在弯曲和局部浮力效应，流体参数（例如局部速度和温度）在所有三个维度上均发生变化。相对于文献报道的关于修改的Grashof数（Gr_m）和雷诺数（Re）的实验结果，仿真结果的验证显示出很好的一致性。另外，提出了关于以Gr_m表示的Re，以Re表示的摩擦因数（f）以及以Re和Prandtl数（Pr）表示的努塞尔特数（Nu）的新的相关性。

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