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Direct contact condensation affects the performance of pressure suppression system of nuclear reactor. Since the heat and mass transfer varies with the condensation regimes as well as steam-water interface shapes, the identification and classification of the condensation regimes are important. The experiment of steam direct contact condensation was carried out and the corresponding condensation regimes were studied. Specifically, the experiment was studied by injecting steam vertically into a wet well with subcooled water. The physical process of steam condensation phenomenon with varying undercooling degree of wet well was recorded by high-speed camera. According to the location of the steam-water interface and the shape of the steam bubble, the four condensation regimes were studied, namely internal chugging, external necking, spheroidal upward bubble and T-shaped upward bubble. Besides, it is found that thermal stratification occurs in the wet well at low steam mass flux, the influence of each condensation regime on the thermal stratification of wet well was studied. The experimental results show that the internal chugging and external necking cause a large downward circulation of subcooled water, which enhance the flow mixing around the discharge tube and the bottom of the wet well. Consequently, the thermal stratification phenomenon does not happen in those condensation regimes. However, the regimes like spheroidal upward bubble and T-shaped upward bubble cause the upward circulation of subcooled water in wet well, which cause the thermal stratification. The critical Richardson number (Ri) determines the condensation regimes. Furthermore, when the Ri is smaller than 1, the condensation regime is external necking. Besides, when the Ri is greater than 1, the condensation regimes are spheroidal upward bubble and T-shaped upward bubble.

Due to the adoption of operational data storage method, the coal mine safety monitoring system can't use massive data effectively and the data analysis capability is poor. In order to solve the above problems, this paper proposes the key technologies of data warehouse for coal mine safety monitoring. According to the business requirements of coal mine safety monitoring, the functional structure of coal mine safety monitoring data warehouse is proposed. Moreover, the five business subjects are designed, including overrun analysis, calibration analysis, abnormal data analysis, measuring point network interruption analysis and personnel management analysis. The logical model of coal mine safety monitoring data warehouse is established by using the fact constellation model. The fact table and dimension table are designed by subject. The physical model of data warehouse is established by using SQL Server. According to the characteristics of coal mine safety monitoring data warehouse, data extraction, conversion and loading strategies are proposed. The different data extraction rules are used to extract data by subject. The data from different sources are processed through format conversion, cleaning and sorting. In the process of data loading, pre-loading, loading and post-processing operations are carried out.

Poor wind conditions in metropolitan areas can result in inadequate ventilation and degradation of the thermal environment. Several researches have demonstrated that the building ground floor elevation (BGFE) enhances the wind conditions surrounding buildings. Further investigation is required to thoroughly examine the BGFE's impact on the wind conditions in the courtyard area. We researched how the various overhead placements affect the ventilation of a U-shaped school building's courtyard space in different wind directions. We performed Computational Fluid Dynamics (CFD) numerical simulation experiments on 93 overhead scenarios based on field measurements and validation. The statistical analysis of the experimental data revealed that the BGFE had significant effects on reducing the mean air age (p < 0.001), standard deviation of air age (p < 0.01), standard deviation of wind speed (p < 0.001), and mean wind speed (p < 0.01) in the courtyard space. The BGFE in the northeastern zone of the U-shaped school building significantly increased the mean air age (p < 0.05), while the BGFE in the middle and southwestern zones significantly decreased the mean air age (p < 0.001), and the BGFE in the southeastern zone significantly decreased the mean wind speed (p < 0.05). The BGFE facilitates the entry of fresh air and offers even ventilation while significantly reducing wind speed. Choose sites C and D to enhance the U-shaped courtyard's ventilation and avoid locations B and E. This paper's findings provide theoretical guidance for designing the elevation of courtyard space from a ventilation perspective and for the green rehabilitation of existing buildings. [ABSTRACT FROM AUTHOR]

Compressed sensing is a novel information collection theory. Compared with the Nyquist sampling theorem, compressed sensing can obtain all the information of a signal with very few samples. The deterministic construction of the measurement matrix is an important research area in compressed sensing. Inspired by the observation that the parity-check matrix of low-density parity-check code can be used as a deterministic measurement matrix, in this paper, a special balanced incomplete block design proposed by Bose is exploited to construct the deterministic measurement matrix. The incidence matrix of the balanced incomplete block design proposed by Bose is used as the deterministic measurement matrix. The experimental results show that the proposed measurement matrix has lower mutual coherence than some widely used measurement matrices and shows better performance than the progressive edge-growth measurement matrix. Moreover, by using the embedding operation, the modified measurement matrix with a more flexible size and improved performance is constructed. In our simulation, the modified measurement matrix has lower mutual coherence and better performance than some widely used measurement matrices.