多重耦合自然循环载热系统瞬态特性及其热工水力解耦

多重耦合自然循环载热系统热工水力具有流动换热耦合和回路间耦合的特点，本文采用理论分析结合数值计算的方法对自然循环的建立时间、流动方向及多重耦合自然循环系统的热工水力解耦等问题进行了研究。提出了自然循环载热系统瞬态流动的理论模型，该模型能预测自然循环建立时间、流动衰减等现象，模型计算结果与数值计算结果吻合。初始流速为零的自然循环流动方向与系统的加热及冷却设备布置位置有关，垂直布置换热面使系统具有固有循环流动方向。具有初始流速的自然循环系统，即使换热面垂直布置，初始反向流速超过临界流速后也可使自然循环系统流动方向发生翻转，从而使系统在与固有循环流动方向相反的方向运行。提出了多重耦合自然循环载热系统热工水力的简单解耦计算方法，能快速对多重耦合自然循环载热系统热工水力进行分析计算，理论分析和计算结果均表明，以水为工质的自然循环回路载热能力近似与冷热源温差的1.5次方呈正比。

Transient Characteristics and Thermo-hydraulic Decoupling of Multi-coupled Natural Circulation Heat Transport Systems

The thermo-hydraulic of multi-coupled natural circulation heat transport systems has the characteristics of flow-and-heat-transfer coupling and between-loop coupling. In this paper, theoretical and numerical methods were used to investigate the natural circulation start-up time, circulation direction and thermo-hydraulic decoupling of the multi-coupled natural circulation systems. A transient flow model for a natural circulation loop was proposed, which can predict the start-up time and flow decay of a natural circulation loop. The predictions coincide with numerical simulation. The circulation direction of a natural circulation loop with zero initial velocity was determined by the orientations of the heating and cooling surfaces. The vertical arrangement of the heating and cooling surfaces will make the system have an intrinsic circulation direction. However, when the initial velocity is reverse to the intrinsic circulation direction and exceeds a critical value, it can make the circulation direction reverse to its intrinsic direction. A simple decoupling analysis method of the thermo-hydraulic of multi-coupled natural circulation heat transport systems was proposed. It can quickly predict the thermal-hydraulic parameters of a multi-coupled natural circulation system. Both theory and calculation show that the heat transfer capacity of a natural circulation loop is proportional to 1.5 power of the temperature difference of the heating and cooling sources.