冷却水流量调节对超临界二氧化碳印刷电路板式预冷器瞬态特性的影响

Effect of Cooling-Water Flow Adjustment on the Transient Characteristics of a Supercritical CO₂ Printed Circuit Heat Exchanger Precooler

摘要: 为研究冷却水流量调节对超临界CO₂印刷电路板式预冷器动态性能的影响，建立CO₂与水逆流换热的三维共轭传热模型，在CO₂出口压力为8.0 MPa和9.5 MPa下，设置流量增减20%的阶跃及2 s、10 s线性调节工况，共12个瞬态算例。结果表明，减流引起的CO₂出口温升幅度比增流引起的降温幅度大28.2%~42.0%。与阶跃调节相比，10 s线性调节使出口温度最大变化速率降低68.6%~79.7%，但温度稳定时间延长6.51~6.68 s；流量达到终值后，出口温度仍需2.75~4.54 s达到稳定。与阶跃调节相比，10 s线性调节使固体净吸热功率的绝对值峰值降低67.2%~75.6%，而相同压力和调节方向下的固体内能变化量近似不变。冷却水流量增加20%时，换热功率提高5.07%~5.79%，水侧压降增加22.73%~23.22%。结果说明，延长调节时间可降低温度变化速率及固体净吸热功率的绝对值峰值，但会延长出口温度稳定时间；评价预冷器动态性能时，应同时考虑流体温度、固体储热、换热功率及流动阻力。

Abstract: To investigate the effect of cooling-water flow adjustment on the transient performance of a supercritical CO₂ printed circuit heat exchanger (PCHE) precooler, a three-dimensional conjugate heat transfer model was developed for counterflowing CO₂ and water. Twelve transient cases were considered at CO₂ outlet pressures of 8.0 and 9.5 MPa, combining 20% increases or decreases in water flow with step changes and linear ramps lasting 2 or 10 s. The results show that the CO₂ outlet-temperature rise caused by flow reduction was 28.2%~42.0% greater than the temperature drop caused by the corresponding flow increase. Compared with step changes, 10 s ramps reduced the maximum outlet-temperature change rate by 68.6%~79.7% but extended the temperature settling time by 6.51~6.68 s. After the flow reached its final value, a further 2.75~4.54 s was required for the outlet temperature to settle. The 10 s ramps also reduced the peak absolute net heat-transfer rate to the solid by 67.2%~75.6%, while the change in solid internal energy remained approximately unchanged for a given pressure and flow-adjustment direction. A 20% increase in cooling-water flow raised the heat-transfer rate by 5.07%~5.79% and the water-side pressure drop by 22.73%~23.22%. These results indicate that extending the flow-adjustment duration reduces the rate of temperature change and the peak absolute net heat-transfer rate to the solid, but prolongs the outlet-temperature settling time. The transient performance of the precooler should therefore be assessed by considering fluid temperature, heat storage in the solid, heat-transfer rate, and flow resistance together.