Advanced Materials Research Vols. 732-733

Abstract: The numerical simulations of the flow around different pillars acted by the cnoidal internal waves have been made by building numerical wave flume based on FLUENT software. The cnoidal internal wave was created by using the push-pedal method, and the free surface was tracked by using VOF (volume of fluid) method. The three-dimensional different amplitude and period cnoidal internal waves were simulated. The inertia force and viscous force trends were analyzed, and for different pillars the total wave force were compared. There were some significance for stress analysis of the offshore terminal pillars. The converted wave force could alternative and treatment problems about square columns.

Abstract: In this paper, a set of wellbore multiphase flow experimental system with several functions is designed. The system can complete a flow loop of the two-phase flow or the multiphase flow of oil, gas, and water in a level, vertical or tilt angle tube, used to study the flow law of these different mixed modes in the inner tube and the annular space of the wellbore and the heat transfer law between the fluids in the inner tube and the annular space. It is a set of large-scale and complete experimental system to research the multiphase flow.

Abstract: Two centrifugal cardio pumps with recirculation region and anti-recirculation region are designed by speed coefficient method. We can obtain the flow distribution of impeller and inside the shell at design conditions from geometric modeling and numerical simulation of two cardio pumps by using related software, and compared the interior shear stress distribution of two cardio pumps at the same condition. The results show that the maximum shear stress in the cardio pump with the recirculation region is lower about 10% than the pump with the anti-recirculation region and the region of the shear stress is exceed the critical shear stress (150Pa) which produced hemolytic is less about 2/3 than the cardio pump with the anti-recirculation region from the shear stress distribution. As a result a tiny destroys are caused to the blood cell and the pump with the anti-recirculation region model correspond with the demand of the haemophysiology, the research results provide the theory reference and basis in the optimization design for such artificial cardio pump.

Abstract: Flow characteristics of stirred tanks with different structures were calculated by taking RNG k-ε model as the turbulent flow model. The results showed that at the same rotational speed, a large number of axial and radial vortexes were formed in the stirred tank with the baffle. The velocity in the blade area was high, and it decreased rapidly with the increasing distance to the blade. The double peak area of the radial velocity was formed in the stirred tank with baffle, and the high and low speed cycles were obtained in the cross-section. The baffle increased not only the axial circulation of the liquid in the tank but also the radial circulation, which help to mix the liquid.

Abstract: A small hydraulic turbine more still remains to improve the mechanical performance because it does not come fully similarity as compared with the large-scale hydraulic turbine. Many studies on the small hydraulic turbine focused on the increase of performance. In this study, the characteristics of axial propeller turbine which is appropriate equipment for low head conditions and high flow rates were numerically investigated using the commercial code, ANSYS CFX. A parametric study was carried out with two different geometrical parameters, such as blade number and tip clearance between casing and blade. Results showed that the hydraulic loss was increased and the efficiency of small hydraulic turbine was decreased because of increasing tip clearances, which lead to the increase of absolute velocity at the exit of the runner blade.

Abstract: The horizontal axial turbine could extract kinetic energy from both wind and tidal stream. In this paper, a type of horizontal axial turbine was designed with a crown stalled on the blade tip and the turbine was analyzed in a tidal stream. Several turbines with different geometries of the crowns were compared, whose power coefficients were numerically simulated by the CFD method. Effects of the crown design parameters, such as crown setting directions and different widths on turbine efficiency were discussed. Furthermore, when the turbine worked at different tip speed ratio, the results were discussed, either. By analysis of the results, it is could be concluded that a circular crown was sufficient to eliminate blade tip loss caused by tip leakage flow. The upstream semicircle crown modified the corresponding side foil pressure distribution to the design value, and so did the downstream semicircle crown. In the ellipse crowns testing, turbine efficiency was approximately in line with the value of crowns width. When the turbine with the circular crown worked at a little higher tip speed ratio than the design value, the crown was effective as before.

Abstract: The increase in speed and system hydraulic pressure may cause major accidents during the transient of load rejection, especially in high-water head hydropower plants. The current study presents a wicket gate step-by-step closure control law, where two guide vanes will be closed asynchronously to reduce the increase in pressure and improve the transient quality of a waterturbine. Compared with the calculated data in the routine closure law, the control law obviously improved the dynamic qualities of the transient in load rejection and decreased the rising hydraulic pressure from the water diversion system of the plant. The proposed control law can replace the role of a surge tank under certain conditions.

Abstract: The turbulent characteristics of stratified shear flow in braided rivers have not been known until now. The physical model experiment was conducted to study the turbulence kinetic energy distribution of stratified shear flow in the typical braided rivers with a mid-bar between two symmetrical anabranches. Firstly, the distributions of depth-averaged turbulence intensity components in different sections of the anabranch were analyzed. The turbulent intensity peak occurs at the boundary of the separation zone near outer bank and the high velocity zone near inner bank in the entrance region of the anabranch. In the outlet section of the anabranch, turbulent intensity increased at the inner bank. Secondarily, Lateral-averaged turbulence intensity components were compared between different sections. There was obvious high turbulence appearing at the interface of hot and cold water in the inlet section of the anabranch. Finally, the distributions of total turbulence intensity were analyzed by the sectional contours.

Abstract: Start up and heat transfer performances of improved closed loop pulsating heat pipe (ICLPHP) charged with water and silver/water nanofluid, respectively, were investigated experimentally with angles of 90° and 60°. Both the average evaporator wall temperature and the overall thermal resistance of the ICLPHP with different working fluids and at the volume filling ratio of 35% were tested and compared. Experimental results showed that nanofluid caused different thermal performances of ICLPHP. Within the experiment range, silver/water nanofluid can improve operation stability and heat transfer limit and reduce starting power compared with water. With high heating power, thermal resistance of nanofluid was lower than that of water. With inclination of 60°, ICLPHP with nanofluid operated better and reduced sensitivity of inclination.

Abstract: Gas residence time is an important parameter for gas-liquid agitated tank. Two approaches, i.e., Euler-Tracer method and CFD-DPM method are proposed for predicting gas residence time distribution (RTD) in an aerated agitated tank by using a Fluent 6.2 software package. The simulation results show that the characteristic of the gas-RTD is a curve with single peak and long tailing. Bubble size, stirring speed and gas inlet flow rate have great effect on gas-RTD in the stirred tank. Small bubbles have wider residence time distribution and stay in the vessel longer than the large bubbles and tend to complete mixing. With increasing of impeller speed or decreasing of gas inlet rate, gas-RTD become wider and have longer average gas residence time, which is in favor of gas effectively utilization.