Advanced Materials Research Vols. 516-517

Abstract: Pressure fluctuations strongly affect the performance stability of the Pump-turbine unit. According to previous research, pressure fluctuations observed between runner and guide vanes (vaneless area) have the large amplitudes and complicated sources. This article analyzed this type of pressure fluctuations in transient operating period, by carrying out observations in a pump-storage power station. Amplitudes and frequencies were analyzed to show the characteristics of pressure fluctuations caused by rotor-stator interaction, vibration and vortex.

Abstract: The three-dimensional pulsating velocity distribution of fluid in the three different structure of SMX static mixers were measured by using laser Doppler velocimetry. The results show that the three different structure of SMX static mixers all have good turbulent reinforcement. Especially in the third and the fourth elements are more obvious. The pulse RSM after them gets stability in the main. With the increase of inlet flow, not only the pulse of axial speed increase ,but also the pulse RSM of axial speed and turbulent energy are approximate linear increase .

Abstract: Numerical simulation of gas-solid two-phase flows in circulating fluidized bed is proved to be a low-cost and high-efficient method to research the instability essence of flow character. In this work, numerical simulation based on the discrete element (DEM) method is applied to analyze behaviors in a rectangular cross-section fluidized bed. The models of physical and mathematical models are introduced in detail, and the schematic of DEM method also described clearly. It indicates that the DEM method may be used as a powerful tool for the simulation of the gas-solid flow.

Abstract: To understand the spatial representation of flux measurement of the eddy covariance system in the Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL), footprint was analyzed during representative seasons (summer and winter) from March 2007 to February 2011 by FSAM (Flux Source Area Model). The results indicated that wind direction and atmospheric stability have important effect on footprint. 1) The analysis at different wind directions showed that the location of the maximum footprint function (X_m) in winter was farther from the observation point than that in summer; the source area was the largest in SW, and smallest in NW in both summer and winter; the source area in summer was bigger than that in winter at all directions except for NE. 2) The analysis under different atmospheric stabilities showed that X_m was the farthest from the observation point under stable condition and nearest under unstable condition; the source area was the largest under stable condition and smallest under unstable condition; the source area in summer was bigger than that in winter under all atmospheric stabilities. 3) Moreover, the results showed that the flux measurements of SACOL were representative of two types of topography: flat terrain and mountain terrain.

Abstract: The flow character in riser is important for deep understanding the steady and high-efficient running of CFBs. In this paper, the 2D numerical simulation research for bench-scale circular cross-section riser based on EMMS methods is carried out. The solids’ transient moving profiles are captured. By analyzing the axial solids concentration profiles by simulation and experimental methods, the practicability of the EMMS model is verified.

Abstract: For the problem of incapable to determine the width of spherical diffuser, four groups of spherial diffusers with different width were designed by using the speed coefficient method. Numerical investigation of internal flow in the nuclear coolant pumps with these diffusers was made based on ANSYS-CFX software. Aimed at the efficiency, ditribution of pressure and velocity vector on the meridian plane of each volute scheme was analysised emphatically. By comparing the performance curves of the coolant pumps predicted by the numerical simulation, we can draw that the head and efficiency of pump decreased as the increasing of diffuser width and performanced worst at the width of d=1.7R, then the performance no longer changes when diffuser width continue to reduce.

Abstract: The flow characteristics of deposited water displaced by flowing oil in hilly terrain tube were studied experimentally and numerically. Lab-scale experiments were carried out on the transparent organic glass test loop with I.D. 50 mm to investigate the distributions of oil-water interface by diesel flowing from a lower horizontal test section into the up-inclined test section. Two-dimensional numerical simulation was conducted by VOF model and CSF model based on the test geometrical model. Comparisons of the oil-water interface distribution and the critical superficial oil velocity show that the numerical simulations favorably compare with the measurements.

Abstract: Supersonic gas separation (SGS) is a novel gas separation technology proposed in recent years. The Inner-core SGS device with droplet enlargement measure has been proved to perform effectively for processing low-pressure gas mixture with one condensable component. The effectiveness of the droplet enlargement measure depends largely on the adding location of extra nuclei. A two-phase flow model was established in which the droplet movement was simulated by dispersed phase model. Using the model, movements of nuclei from three potential locations of Inner-core SGS device, inlet of swirl generator (Ⅰ), throat of supersonic nozzle (Ⅱ) and inner-taper core (Ⅲ), were simulated and the possibility of vapor condensation on nuclei was predicted. The simulation results showed that the droplets injected from location Ⅲ had smaller size (0.0183mm~ 0.0953mm), longer residence time (0.43 ms) and longer axial running distance (58.9 mm). The gas flow near that region had bigger supersaturation (larger than 1). Thus, the best location of Inner-core SGS device for nuclei injection was determined at the throat of the inner-taper core (Ⅲ).

Abstract: Fluid flow and heat transfer characteristics of pulsating flow around the vibrating tube was numerically investigated by the dynamic meshing technique of FLUENT. The results showed the combined action of pulsating flow and vibration enhances the coefficient of heat transfer, and the surface heat transfer coefficient of vibrating tube increases with the increment of the tube vibration amplitude, frequency and pulsating flow amplitude, and pulsating flow frequency has less affected. The main reason that pulsating flow enhances heat transfer is the secondary flow, generated by the combined effect of pulsating flow and tube vibration, enhances momentum and energy transfer.

Abstract: The mechanism of heat transfer enhancement of pulsating flow in a spiral fluted tube was researched by CFD (computational fluid dynamics) software FLUENT. Numerical results showed that pulsating flow leads to cyclical fluctuation of outlet pressure and the extent of fluctuation increases with increasing the pulsating flow frequency. Moreover, the pulsating flowing causes whirlpools near the spiral flute and the vortices generate, drift, and fall off periodically. The optimum pulsating frequency in the spiral fluted tube is 6HZ and the optimum amplitude A is equal to 0.7 approximately when the Reynolds number is 1683.