Advanced Materials Research Vols. 243-249

Abstract: With the increase of mining depth, an investigation of the convective heat transfer of airflow in deep airway is urgently required. The velocity and temperature distribution were derived by using the turbulence model for smooth tube. In order to simplify calculation and avoid the complicated calculation of integration, with the help of velocity-temperature distribution analogy, the criterion equation of convective heat transfer was obtained by using the model of constant heat flux. The coefficient of convective heat transfer between airflow and airway was calculated, and criterion correlation of convective heat transfer was regressed according to test data. Test results show that the axial temperature distribution of airflow is linear, which is encouraging agreement with theoretical calculating results. Hence model of constant heat flux is a viable method for studying the convective heat transfer of airflow in deep airway.

Abstract: To evaluate the security of urban water distribution network, one model based on LS-SVM was put forth. On the basis of summary and analysis of influential factors for urban water distribution network security, a set of indexes used in the evaluation model above was constructed. The nonlinear mapping between the water distribution networks security classification and its conditions were learned from the finite samples and a water distribution network example was simulated using this model. In addition, the BP ANN model was used to simulate the same example. Through the analysis of the result of the actual security level, the security level acquired by the LS-SVM model and BP ANN model, it may be found that the result acquired by the LS-SVM model has high accuracy, and may used in actual engineering.

Abstract: This paper mainly analyzes the high efficiency characteristic of cross-critical carbon dioxide cycle refrigeration, especially when this refrigeration system works as a heat pump. When this refrigeration system is used as heat recycle system with larger different temperature and high level temperature, the solely superiority and energy saving capability of this system will reveal. However, the development localization of cross-critical CO₂ cycle refrigeration system also exists, which includes immature cross-critical CO₂ flow and heat exchange theory, and seal problem of compressor, expansion ratio of expansion equipment.

Abstract: For the study of human thermal sensation in Xi'an and adaptive thermal comfort situation, the measurement of environmental parameters and questionnaires as the way to analyze and explore the indoor and outdoor weather conditions, clothing thermal resistance, thermal sensation and so on. This paper studies human thermal sensation within the civil construction and thermal neutral temperature relationship changes with the seasons. The results showed that: the study of adaptive thermal comfort, human neutral temperature and outdoor ambient temperature has a strong correlation, the resulting models in Xi'an.

Abstract: The operation reliabilities of heating systems are always of great importance. As to the reliability assessment of a combined heating system with peak load compensation in the secondary heating network, it is suggested to use reliability ensuring coefficient based on quota heating coefficient rather than traditional reliability criteria. It is clear that the reliability ensuring coefficient S is capable of assessing the reliability of combined heating system in the most critical condition. Besides, peak load heat sources in secondary heating network can backup the primary heating network and augment the reliability to a certain extent.

Abstract: Based on the statistical method of the heating outdoor design temperature in HVAC design code, we use two calculation methods to analyze the outdoor design temperature and the heating load of some typical cities for intermittent heating . The results show that: the heating outdoor design temperature is higher 3.8 °C and 4.6 °C than that of the current standard value for long-term and short-term intermittent heating respectively, accordingly, the heating load of the long-term and short-term intermittent heating can be reduced by 9% and 15% according to the new outdoor design temperature calculated by this paper.

Abstract: Downburst winds with their great destructive power have caused destruction of numerous engineering structures around the world. Study on wind loadings of downburst is essential and hot in the wind engineering field. But various meteorological factors of downburst formulation are not considered in existing research methods in the wind engineering field. In this paper, a downburst case is simulated by using a numerical weather prediction model ARPS from the meteorological point of view. The simulation results successfully reproduce the wind field characteristics while downburst occurring. The study in this paper aims at introducing meteorological method and knowledge to the wind engineering field, and the results of mesoscale numerical simulation in this study will be used in the small-scale numerical simulation as initial data in further study.

Abstract: Thunderstorm microbursts, which are sources of extreme wind loadings in nature, have caused numerous structural failures, especially collapses of transmission tower around the world. It is important to study wind field characteristics of thunderstorm microbusts from the perspective of wind-resistant design. In this paper, the three-dimensional wind field characteristics of thunderstorm microbursts were studied using computational simulation method. Firstly, the three-dimensional wind field of microburst was computational simulated using time-filtered Reynolds Averaged Navier-Stokes (RANS) numerical computational method. Then, the three-dimensional wind field characteristics including the wind distribution of wind velocity at different heights, the wind contours at lower altitude positions were studied in detail. The results indicate that the three-dimensional wind field of microbursts winds presents quite different characteristics at different heights and radial positions.

Abstract: Downburst is a strong downdraft generated below a cumulonimbus cloud, which hits the ground rapidly and causes significant low-level wind shear. It is a strong destructive regional weather phenomenon, which is the main reason for the transmission towers. In recent years, some scholars have researched the finer wind field characteristics and wind load of downburst by using the method of CFD. But the initial conditions are all assumed due to the small synoptic scale, the short lifecycle and the big measurement difficulty of downburst. So downburst wind load can not be taken into account in structural design. Based on the 3-D convective storm numerical model, by inputting temperature, humidity and wind fields detected in Wuhan radiosonde station at 8pm on July,27^th,2007, simulation has been accomplished to understand the characteristics of the wind field in the place where the downburst incurred actually. The result provides model data and parameters for CFD simulation, which has directive significance to concern the high intensity downburst wind load in structure design.

Abstract: The roof is cemented backfill in underhand drift cut-and-filling stopping, stability of cemented fills is the key to safety of mining. Through numerical simulation test, simply supported beams subjected to uniform was considered mechanical model of backfill roof. and failure modes of backfill roof was found through physical modeling experiment. The results show that the failure of backfill roof is first happening from the center at the bottom of backfill, the final result is that falling arch. Based on the the result of the experiment, finally, The reasonable reinforcement pattern was proposed to avoid failure of backfill roof.