基于回热器温度滑移匹配的以CO_2为工质的布雷顿循环优化分析

Optimization Analysis of a Brayton Cycle Using CO_2 as Working Substance based on Temperature Glide Matching in Heat Exchanger

以CO_2为工质的高温闭式布雷顿循环具有高效、简单和紧凑的特点。其高效率的实现有赖于回热器内良好的温度滑移匹配以充分回收乏气的热量。提高回热器温度滑移匹配性的关键是使流经回热器的高低压力流体的热容相接近。本文从超临界CO_2的热物性特点出发,分析了部分冷却的再压缩超临界CO_2布雷顿循环对温度滑移匹配的优化效果。根据对物性的分析结果,提出了流量调节应该覆盖高低压流体物性变化剧烈的所有温区,通过模拟计算对其进行了优化分析,认为对于一定的高低温热源,存在最优的透平进、出口压力。

Closed-loop supercritical CO_2( s-CO_2) Brayton cycles have advantages of higher cycle efficiency,smaller weight and volume,and less complex. The realization of higher cycle efficiency depends on a perfect thermal match in heat exchanger to fully recover heat energy from the exhausted gases from turbine. The key to increase the temperature glide matching performance of the heat exchanger is to make the heat capacity of two streams flowing through the heat exchanger match well. This paper analyzes the cause of the recompression and partial cooling cycles increasing the performance of the cycle from the point of CO_2 thermalphysical properties. The simulation results suggest that the flow mass regulation to make the heat capacity of the two streams match well should cover the whole region of the specific heat changing greatly with temperature. System optimization analysis indicates that optimal operation and exhausted pressures exist for a given operating temperature.