Numerical Analysis of Heat Transfer Characteristics of Hexamethyldisiloxane (MM) at Supercritical Pressures

J. Fu, Guoqiang Xu, Yongkai Quan, Yanchen Fu, Bensi Dong
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引用次数: 3

Abstract

Organic Rankine cycle (ORC) is one of the most promising solutions to utilize low-grade thermal energy for the worldwide energy crisis, environment deterioration, and climate change. Organic fluids, commonly with relatively low critical temperature and pressure, can be heated and compressed directly to the supercritical state in order to obtain better match with the heat source temperature and lower corresponding exergy destruction. Supercritical ORC has therefore attracted increasing attention in recent years. Supercritical fluids in the heated channels experience sharp changes in thermal properties during the pseudo-critical temperature range, leading to abnormal supercritical heat transfer characteristics. However, to the best of our knowledge, as one of the most challenging aspects related to the ORC modeling, heat transfer mechanisms for supercritical organic fluids have not been completely explained. To fill this gap, this work numerically analyzes the heat transfer to supercritical hexamethyldisiloxane (MM) with characteristics of high thermal stability and low critical parameters and therefore it is applicable for high temperature supercritical ORC system. In the numerical analysis, the shear stress transport k–ω turbulence model is employed to simulate the supercritical heat transfer process in a vertical upward tube under different boundary conditions of pressure, mass flux, and heat flux. Further insight is provided about the physical mechanisms of heat transfer deterioration with numerical results. The results show that the distributions of specific heat and turbulent kinetic energy are the key factors in determining the deterioration degree of heat transfer.
超临界压力下六甲基二硅氧烷(MM)传热特性的数值分析
有机朗肯循环(ORC)是解决全球能源危机、环境恶化和气候变化等问题最有前途的低品位热能利用方案之一。有机流体通常具有较低的临界温度和压力,可以直接加热压缩到超临界状态,以获得与热源温度更好的匹配,并降低相应的火用破坏。因此,超临界ORC近年来受到越来越多的关注。在准临界温度范围内,受热通道内的超临界流体热性能发生剧烈变化,导致超临界传热特性异常。然而,据我们所知,作为与ORC建模相关的最具挑战性的方面之一,超临界有机流体的传热机制尚未得到完全解释。为了填补这一空白,本文对具有高热稳定性和低临界参数的超临界六甲基二硅氧烷(MM)的传热进行了数值分析,因此它适用于高温超临界ORC系统。在数值分析中,采用剪切应力传递k -ω湍流模型模拟了不同压力、质量通量和热流密度边界条件下垂直向上管内的超临界换热过程。数值结果进一步揭示了传热恶化的物理机制。结果表明,比热和湍流动能的分布是决定传热恶化程度的关键因素。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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