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The two-phase flow is a vital topic of thermal-hydraulic research in light-water nuclear reactors. The fluid dynamics and heat transfer characteristics of two-phase flow impact the safety and efficiency of nuclear power plants. The two-phase flow results in various transients in the nuclear reactor: The change of the pressure drop redistributes the flow rate of the channels, and the generation of the void in the core alters the reactivity and consequently the power. The two-phase flow is among the most complex flows since the interface structure evolves and the mass/momentum/energy transfers across the interface. The two-phase flow research of the nuclear system started in the 30s and 40s of the last century, when the pioneer scientists studied the flow instability and the pressure drop. Along with the rise of commercial nuclear reactors in the 50s, the interests lay in the critical flow, the critical heat flux, and the void distribution. In the 70s, the industry shifted its interest to the blow and the flooding, which are compound flow phenomena in specific geometries of the reactor system. In the 90s, the focus was to improve the ability of the nuclear safety codes, such as developing the constitutive models and conducting benchmark experiments. Since this century, the growth of the measuring techniques has supported fundamental research, like the interface evolution and the behavior under extreme conditions. Also, the development of the computers enables the multi-dimensional study using computational fluid dynamics codes and enables the multi-physics study using the codes-coupling platform. This paper aims to understand the research trend of the two-phase flow in the nuclear system by reviewing the history, summarizing the critical problems, and presenting the status. Five phenomena, which lack knowledge and need to be investigated, are described in the current review: the two-phase flow structure, the interfacial drag, the heat transfer crisis, the interphase heat/mass transfer, and the counter-current flow limitation. Three research directions are suggested: advanced modeling, advanced measuring techniques, and cross-cutting fields. Concluding remarks, with research recommendations from the local scale to the system scale, are given to the two-phase flow in the nuclear system.

Mid-deep geothermal heat pump systems (MD-GHPs) use mid-deep borehole heat exchangers (MDBHEs) to extract heat from the geothermal energy at a depth of 2–3 km, and have been used for space heating in China over the last decade. This paper proposes a comprehensive and multilevel evaluation-index system to analyze and evaluate the energy performance of MD-GHPs. The multilevel evaluation index system consists of a target layer, a criterion layer, and an index layer, where the criterion layer is subdivided into six aspects and the index layer includes 26 specific indices, reflecting the geothermal resources, heat transfer performance of the MDBHEs, energy efficiency of the heat pump systems, building space heating demand, grid dynamic response capability, and energy-saving and economic benefits. Then, based on both expert survey results and case study data, the entropy weight method and the analytic hierarchy process are integrated to determine indicator weight coefficients among the multilevel evaluation indices, comprehensively considering both subjective and objective analyses. Furthermore, a fuzzy comprehensive evaluation model is conducted to integrate these weighted indices into a multi-criteria evaluation of MD-GHP performance. Finally, the proposed method was applied to evaluate the practical performance of four projects, returning scores of 61.56, 58.33, 72.73, and 78.41. These evaluations enable an overall assessment of the energy performance of MD-GHPs, reflecting the technical weaknesses and offering optimization guidance for system design and operation. [ABSTRACT FROM AUTHOR]

Urbanization‐driven biotic homogenization has been recorded in various ecosystems on local and global scales; however, it is largely unexplored in developing countries. Empirical studies on different taxa and bioregions show conflicting results (i.e. biotic homogenization vs. biotic differentiation); the extent to which the community composition changes in response to anthropogenic disturbances and the factors governing this process, therefore, require elucidation. Here, we used a compiled database of 760 bird species in China to quantify the multiple‐site β‐diversity and fitted distance decay in pairwise β‐diversities between natural and urban assemblages to assess whether urbanization had driven biotic homogenization. We used generalized dissimilarity models (GDM) to elucidate the roles of spatial and environmental factors in avian community dissimilarities before and after urbanization. The multiple‐site β‐diversities among urban assemblages were markedly lower than those among natural assemblages, and the distance decays in pairwise similarities in natural assemblages were more rapid. These results were consistent among taxonomic, phylogenetic, and functional aspects, supporting a general biotic homogenization driven by urbanization. The GDM results indicated that geographical distance and temperature were the dominant predictors of avian community dissimilarity. However, the contribution of geographical distance and climatic factors decreased in explaining compositional dissimilarities in urban assemblages. Geographical and environmental distances accounted for much lower variations in compositional dissimilarities in urban than in natural assemblages, implying a potential risk of uncertainty in model predictions under further climate change and anthropogenic disturbances. Our study concludes that taxonomic, phylogenetic, and functional dimensions elucidate urbanization‐driven biotic homogenization in China. [ABSTRACT FROM AUTHOR]