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To study the pressure drop characteristics of hypervapotron, which was designed as a water-cooling structure in the divertor dome of the fusion reactor, the pressure drop tests of subcooled water were carried out in a vertically upward hypervapotron. To simulate the one-side radiant heating condition in the engineering application, the non-uniform heat fluxes were obtained by using the off-center electrically heating method. The system parameters were as follows: mass flux G = 2000–5000 kg·m−2·s−1, inlet pressure p = 2–4 MPa, and equivalent one-side radiating heat flux qe = 0–5 MW·m−2. The effects of the parameters on the pressure drop were discussed in detail. It was observed that in the single-phase (SP) region, the pressure drop was little influenced by the inlet fluid temperature (Tb,in). However, in the subcooled boiling region, the pressure drop increased rapidly with the increasing Tb,in. A higher G leads to a high pressure drop. In the SP region, the influence of p on the pressure drop is not obvious, and the pressure drop decreased with the increasing qe. The test data are used to evaluate the typical pressure drop correlation, and the results show that none of these correlations can predict the pressure drop well under the test conditions. Therefore, a new pressure drop correlation is proposed for subcooled water in a hypervapotron under high and non-uniform heat fluxes. The new correlation has a high prediction accuracy for the test data, and the mean relative error (MRE) and root mean square error (RMSE) are 0.72% and 4.33%, respectively. The test results have a reference value for the design of the water-cooling structure of the diverter.

The hypervapotron structure was considered to be a feasible configuration to meet the high heat-dissipating requirement of divertors in nuclear fusion devices. In this work, symmetric CuCrZr-based transverse microchannels (TMHC) and longitudinal microchannels (LMHC) with an integrated hypervapotron channel were proposed and manufactured, and subcooled flow boiling experiments were conducted using deionized water at an inlet temperature of 20 °C with a traditional flat-type hypervapotron channel (FHC) for comparison. The LMHC and TMHC obtained lower wall temperatures than the FHC for all conditions, and the TMHC yielded the lowest temperatures. The heat transfer coefficients of the LMHC and TMHC outperformed the FHC due to the enlarged heat transfer area, and the TMHC had the greatest heat transfer coefficient (maximumly increased by 132% compared to the FHC) because the transverse-arranged microchannels were conductive, promoting the convection and liquid replenishment ability by introducing branch flow between fins; however, the microchannels of the LMHC were insensible to flow velocities due to the block effect of longitudinal microchannels. The LMHC obtained the largest pressure drop, and the pressure drop for the FHC and TMHC were comparable since the transverse-placed microchannels had little effect on frictional pressure loss. The TMHC attained the greatest comprehensive thermohydraulic performance which might bring significant insight to the structural design of hypervapotron devices.

In this study, a subcooled flow boiling experiment was conducted to analyze the critical heat flux (CHF) of a hypervapotron (HV) channel based on the one-side high-heat load condition. The experimental loop used in this study was operated at high values of pressure (20 bar), flow rate (1.5 kg/s), and fluid temperature (150 °C) with a one-side joule heating system capable of loading a high heat of 14.8 MW/m 2 . We analyzed the effect of the system parameters on the CHF of the HV channel and determined that the CHF increased at high subcooling and flow rate. This can be attributed to the strengthening of forced convective heat transfer and rapid condensation of the vapor under the aforementioned conditions. Additionally, the CHF tended to increase with the increasing pressure, owing to the decreased bubble size under pressure ranges of 1 to 10 bar. Furthermore, we evaluated the prediction performance of the existing subcooled flow boiling correlations considering the CHF of HV. However, most correlations tended to underpredict as they were developed based on smooth channels. Therefore, we modified the Inasaka and Nariai CHF correlation and developed a novel HV CHF correlation using PYTHON and the artificial intelligence regression method. The mean absolute error and root mean square error of the proposed correlation are 10.68% and 11.99%, respectively, which are significantly lower than those of existing correlations. It is recommended that the newly developed CHF correlation be utilized at an inlet bulk temperature of 40–140 °C, a mass flow rate of 0.071–0.284 kg/s, and a pressure of 1–10 bar.