复合换热管过冷沸腾换热实验与关联式评价

以去离子水为实验介质，在单面受热流密度条件下，开展了聚变装置偏滤器的过冷流动沸腾强化换热特性实验研究，将内肋强化换热技术与内插扭带结构相结合，利用两者的协同强化传热效应，设计出一种复合换热管。实验参数为：质量流速，992～4 960 kg/(m2·s)；压力，04～2 MPa；入口过冷度，8701～11921 ℃；热流密度，1～163 MW/m2。对4种强化换热管（光管、内插扭带管、内螺纹肋管和复合换热管）的管内过冷流动沸腾换热特性和综合性能评价指标（PEC）进行了对比实验。结果表明：与其他3种管道相比，复合换热管的对流换热系数和PEC最高，传热特性最好。研究了复合换热管的扭带扰动比、螺距、压力和质量流速对管内两相流动对流换热系数的影响规律，发现对流换热系数与螺距、质量流速呈正比，与扭带扰动比、压力呈反比。最后对比了4个现有的过冷流动沸腾换热经验公式，并在无量纲模型基础上，增加了扰动比和螺径比（t/Dh）进行修正，利用非线性拟合方法提出了适合复合换热管过冷流动沸腾的努塞尔数新公式。

Experiment and Correlation Evaluation for Subcooled Flow Boiling Heat Transfer in Compound Heat Transfer Tube

Under the condition of a one sided heating flux, an experimental research on the enhanced heat transfer characteristics of the subcooled flow boiling for the fusion reactor divertor was carried out. Deionized water was used as the experimental medium. The compound heat transfer tube was designed by using the synergistic enhanced heat transfer effects of the internal thread tubes and twisted tape inserts. The experimental parameters are as follows: mass fluxes from 992 kg/(m2·s) to 4 960 kg/(m2·s), pressures from 04 MPa to 2 MPa, inlet subcoolings from 8701 ℃ to 11921 ℃, and heat fluxes from 1 MW/m2 to 163 MW/m2. The heat transfer characteristics and performance evaluation criteria (PEC) were compared and studied for the four kinds of enhanced heat transfer tubes (plain tubes, tubes with twisted tape inserts, internal thread tubes and compound heat transfer tubes). The results show that: Compared with the other three kinds of tubes, the heat transfer coefficient and PEC of the compound heat transfer tubes are the highest, and the heat transfer characteristics are the best. Within the range of experimental conditions, the heat transfer coefficient of the compound heat transfer tubes is about 5% 98%, 99% 102% and 179% 184% higher than that of the internal thread tubes, tubes with twisted tape inserts and plain tubes, while the overall PEC of the compound heat transfer tubes varies between 091 141. Then, the influences of the twist ratios, pitches, pressures and mass fluxes on the heat transfer coefficient for the compound heat transfer tubes in the two phase flow boiling were also conducted. It is found that the heat transfer coefficient is directly proportional to the pitches and mass fluxes, and inversely proportional to the twist ratios and the pressures. In addition, according to the experimental data, the wall superheat temperature and heat flux at ONB point increase with mass flux, which indicates that the larger mass flux can postpone the generation of ONB point. Finally, the four existing empirical correlations for subcooled flow boiling heat transfer were compared and evaluated. Based on the dimensionless models and the nonlinear fitting method, the Nusselt number correlation modified by adding the twist ratios and ratio of the pitches to the hydraulic diameter of the tube (t/Dh) for the compound heat transfer tubes in the subcooled flow boiling is proposed. It is found that the deviation between predicted values and experimental values is within ±15%, the new correlation has a MAE of 569% and a RMSE of 755%, respectively. Therefore, it is indicated that the new developed correlation has the excellent agreement and effectiveness to predict the values for the compound heat transfer tubes.