换热面裕量对再生式换热器热工特性的影响分析

Effect of the Heat Transfer Area Margin on Thermal Characteristics of the Regenerative Heat Exchanger

再生式换热器由再生段和冷却段共同构成,凭借再生段的加入,再生式换热器有助于减小换热器承受的热应力以及回收部分热量,而广泛应用于研究型反应堆的各试验回路中。在再生式换热器设计中,通常会对换热面积保留一定的裕量以应对换热管破损、阻塞以及工况波动等情况发生。结合再生式换热器的结构特点,在不利因素未发生时,将设计裕量效果计入实际的换热中,分析不同的设计裕量对再生式换热器理论运行功率、流质流量以及出口温度等的影响。分析结果表明,再生式换热器的理论运行功率随着冷却段设计裕量的增加而逐渐增加,而随着再生段设计裕量的增加而逐渐减小。再生段及冷却段设计裕量对再生式换热器的功率调节跨度影响不大,但再生式换热器的理论功率调节区间在再生段设计裕量增加时会逐渐下移,而在冷却段设计裕量增加时会逐渐上移。要克服再生段裕量对运行功率带来的不利影响,可以选择增加相应的冷却端设计裕量以及加大二次水流量。再生式换热器运行于功率调节下边界以下时,再生段保持一定设计裕量有利于一次水的流量更为接近设计流量。鉴于分析的结果,对于处于稳态试验回路中的再生式换热器,建议再生段裕量小于10%以满足设计功率,而对需要具备降功率运行的再生式换热器,建议可以取较大的再生段裕量以减小一次水流量的波动。

The regenerative heat exchanger consists of the regeneration section and cooling section. Due to the existence of the regeneration section, the regenerative heat exchanger can weaken the thermal stress and recovery some heat, as a result, it is widely used in the loop test of the research reactors. In the design of heat exchangers, some margin of the heat transfer area is usually kept to cope with some unfavorable occurrence, such as the heat transfer tubes damage and obstruction, conditions fluctuate, etc. The structural characteristics of the regenerative heat exchanger were considered, and the excess heat transfer area resulting from the margin existence was applied to participate in the heat transfer when no unfavorable factor had occurred. Furthermore, the effect of the heat transfer area margin on the theory power, fluid flow and outlet temperature during the regenerative heat exchanger operation were investigated. The results show that the theory power of the regenerative heat exchanger increases with the heat transfer area margin of cooling section increasing, while it shows an opposite tendency for that of regenera-tion section. The heat transfer area margins of the regeneration and cooling sections has little impact on the power adjustment span. However, the interval of the theory power regulation gradually moves down and upward with the heat transfer area margins of regeneration and cooling sections increasing, respectively. The measures, including increasing the flow of the secondary water and keeping a certain margin for the cooling section, are effective to over-come the adverse effect of margin from the regeneration section on the power during the regenerative heat exchanger operation. Below the lower boundary of power regulation, some margin occurrence from the regeneration section fa-vors the primary water flow close to the designed value. Moreover, the study demonstrates that a margin less than 10% for the regeneration section can be taken to meet the designed power during the regenerative heat exchanger operating in the steady loop experiment, however, a larger value can be taken to reduce the flow fluctuation of the primary water during the regenerative heat exchanger running under a lower and variable power.