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The focus of this paper is on the measurement and calculation model of void fraction for the vertical upward co-current air–water slug flow in a circular tube of 15 mm inner diameter. High-speed photography and optical probes were utilized, with water superficial velocity ranging from 0.089–0.65 m∙s–1 and gas superficial velocity ranging from 0.049–0.65 m∙s–1. A new void fraction model based on the local parameters was proposed, disposing the slug flow as a combination of Taylor bubbles and liquid slugs. In the Taylor bubble region, correction factors of liquid film thickness Cδ and nose shape CZ* were proposed to calculate αTB. In the liquid slug region, the radial void fraction distribution profiles were obtained to calculate αLS, by employing the image processing technique based on supervised machine learning. Results showed that the void fraction proportion in Taylor bubbles occupied crucial contribution to the overall void fraction. Multiple types of void fraction predictive correlations were assessed using the present data. The performance of the Schmidt model was optimal, while some models for slug flow performed not outstanding. Additionally, a predictive correlation was correlated between the central local void fraction and the cross-sectional averaged void fraction, as a straightforward form of the void fraction calculation model. The predictive correlation showed a good agreement with the present experimental data, as well as the data of Olerni et al., indicating that the new model was effective and applicable under the slug flow conditions.

In order to investigate the heat transfer characteristics of hypervatron in the divertor dome of the International Thermonuclear Experimental Reactor (ITER), the off-center electrically heating method was used simulate the one-side heating condition in the engineering application. The heat transfer experiments of subcooled water were carried out in a vertically upward hypervapotron under the system parameters as follows: system pressure P = 2.7, 3.2, 3.7 MPa, mass flux G = 2000–5000 kg·m−2·s−1, and equivalent one-side radiating heat flux qe = 2–5 MW·m−2. The effects of parameters on heat transfer were discussed in detail. The results show that the heat transfer coefficient h is significantly affected by G in the single phase (SP) region; the h is synthetically influenced by P, G, q in the partially boiling (PB) region; the h is only affected by q in the fully developed boiling (FDB) region. The experimental data were compared with the typical correlations in single phase region and subcooled boiling region, respectively. The results show that the Dittus-Boelter correlation and the modified Shah correlation have good agreement with the experimental data. The typical CHF correlations for smooth tubes were assessed by the CHF data, the results indicate that experimental Bocr are overpredicted by most CHF correlations, so it can be speculated that the hypervapotron can obtain higher CHF values than smooth tubes.

Experimental investigation on vertical upward co-current air–water slug flow was carried out at atmospheric pressure, employing optical probes and high-speed photography. Experiments were performed with water superficial velocity ranging from 0.089 to 1.52 m/s and gas superficial velocity ranging from 0.049 to 1.06 m/s in a polymethyl methacrylate tube of 15 mm inner diameter. Taking advantage of the time-domain characteristics of optical probes, slug flow has been disposed as a combination of Taylor bubbles and liquid slugs. Slug flow identification, characteristic parameters measurement and analysis were conducted in the present study. Firstly, combined with subjective observation, a developed methodology of flow pattern identification based on machine learning was proposed, with emphasis on slug flow. Results showed that the proposed method exhibited an outstanding advantage in the identification in the flow pattern transition region. More importantly, extensive data on local void fraction in liquid slugs (αl,LS) and in continuous slug units (αl), gas-phase velocity of Taylor bubble (UTB) and liquid slug (ULS), length of Taylor bubble (LTB) and liquid slug (LLS), were obtained. Through comprehensive analysis, it was found that turbulence intensity and flow pattern transitions were the dominant factors in affecting the characteristics of slug flow parameters.

Region: The Nagqu River Basin in the Qinghai-Tibet Plateau. Focus: Climate change and human activities have altered the type of land use in the Qinghai-Tibet Plateau (QTP), which has affected the variation laws of water resources. We calibrated and verified the Water and Energy Transfer Process for a Large basin model (WEP-L), and calculated the impacts of climate change and human activities on runoff change and separated the impact of land use. New hydrological insights: The Archimedean Copula function was used to diagnose the variance between precipitation and runoff. The contribution of climate change to the runoff in the Dasa and Jiayuqiao subbasin was 81.7% and 71.5%, of which the contribution of land use was 39.3% and 32.6%, respectively. Human activities contributing to the runoff in the Dasa and Jiayuqiao subbasins were 18.3% and 28.5%, of which the contribution of land use is 7.9% and 2.8%, respectively. Climate change has led to the melting of glaciers, permanent permafrost and the shift of the vertical distribution of vegetation, which is the main reason for the runoff variation in the NRB. This research provides a scientific basis for the rational protection and utilization of water resources, as well as soil and water conservation work. Keywords: Precipitation–runoff, Mutation diagnosis, Climate change, Human activities, Land use, Hetao area