布雷顿循环冷端空冷换热器设计与变工况运行特性分析

Design and off-design operating characteristics analysis of Brayton cycle cold end air-cooled heat exchanger

作为布雷顿循环系统中的重要冷端部件,气体冷却器的性能对循环系统结构紧凑性和运行高效性有重要影响。分析了一种新型横流印刷电路板式换热器(printed circuit heat exchanger,PCHE)—板翅混合式气体冷却器的工作性能及影响因素,对该种换热器建立了一个数值计算模型,并编写MATLAB程序验证其可靠性;基于此,对该类冷却器进行了设计,其功率密度均在1 MW/m^(3)以上,属于紧凑型换热器;其次进行了变工况性能分析,给出了冷却器的压降和换热性能随循环工质和冷却空气进口状态的变化规律,并比较了布雷顿循环工质为超临界二氧化碳、氮气、空气时冷却器的换热特性和压降特性,结果表明,冷、热流体流量的改变对换热特性的影响最明显。研究结果对布雷顿循环空冷换热器的设计与运行具有参考意义。

The gas cooler,as an essential heat exchange device in Brayton cycle system,has a significant influence on structural compactness and operational efficiency of the cycle system.The performance and influencing factors of a cross flow printed circuit heat exchanger(PCHE)-plate-fin gas cooler are analyzed.A calculation model is established for this type of heat exchanger,and a MATLAB program is written to verify its reliability.Based on this,the coolers are designed,and the power density is above 1 MW/m^(3),indicating the cooler is compact heat exchanger.Moreover,the design and performance analysis of the heat exchanger are carried out under varying working conditions,and the change law of the pressure drop and heat transfer performance of the gas cooler with the inlet state of the circulating working medium and cooling air is given.The pressure drop and heat transfer performance are compared when the working medium of the Brayton cycle is supercritical carbon dioxide,nitrogen and air.The results show that,the change of cold and hot fluid mass flow has the most obvious influence on the heat transfer performance.The research has reference significance for the design and operation of Brayton circulating air cooling heat exchangers.