Effects of Impeller Rotational Speed and Immersion Depth on Flow Pattern, Mixing and Interface Characteristics for Kanbara Reactors using VOF-SMM Simulations

The Kanbara Reactor (KR) is a primary desulfurization technology in the hot metal pretreatment refining process that is widely employed in the modern steelmaking industry. The operating parameters of KR impeller immersion depth (IID) and rotation speed (IRS) have a crucial impact on the process performance and the desulfurization effect. Still, their influences have not been fully understood. This study systematically investigated the effects of IID and IRS on the flow pattern, mixing behavior, vortex core depth, and free surface characteristics for KR processes based on a 3D Volume of Fluid (VOF) model coupled with the sliding mesh method (SMM). The model was validated via scale-down water model experiments and then applied to the KR process, and simulations found that IID and IRS have different impacts on the flow pattern. Specifically, the discharge flow location moves downward with IID increasing, but the discharge strength and mean velocity hardly changes. Comparatively, the rise of IRS significantly increases the mean velocity, but few changes occur to the discharge flow position. Increasing IRS improves bath hydrodynamics, strengthens recirculation, and efficiently shortens mixing time, but IID has a neglectable effect on these features. The minimum mixing time is 55 s at a maximum IRS of 260 rpm. Moreover, the vortex core depth and free surface velocity visibly increase with the increase of IRS. Comparatively, IID has a limited effect on the flow and mixing behavior but directly impacts the distribution of recirculation regions at the axial direction and the velocity gradient on the free surface at the radial direction. Furthermore, the correlation equations of these critical parameters as a function of the operating parameters were obtained. The results from this study may provide references for operating optimizations and industrial practices of KRs.

Analysis of flow field characteristics of cycloidal pump based on fluid solid interaction

At present, in the aspect of numerical simulation of a cycloid pump, most researchers are based on CFD (computational fluid dynamics) to analyze the pump under different operating conditions (such as speed, temperature), and the performance of a pump under FSI (fluid solid interactions) is rare. Firstly, a model of cycloidal pump is established in COMSOL. The simulation results obtained by applying CFD and FSI are verified by experiments. Then, the flow in the rotating region and the inlet and outlet cavities are analyzed. Finally, through further analysis of the internal flow, improved design scheme of the cycloid pump is put forward, the inlet flow of the cycloid pump increased by 5.8% compared with the unoptimized, the inlet flow pulsation decreased by 32.7%. The discharge flow of the cycloid pump increased by 16.3%, the pulsation rate of discharge flow decreased by 47%. It provides a reference for other pump research, analysis and improvement design.

Rotating Mechanism of Diffuser Stall in a Centrifugal Compressor With Vaneless Diffuser

The rotating mechanism of diffuser stall in a centrifugal compressor with a vaneless diffuser is investigated via experimental and computational analyses. Diffuser stall is generated as the mass flow rate decreases, and it rotates at 25%–30% of the impeller rotational speed. First, a diffuser stall cell emerges at 180° from the cutoff by the hub-side boundary layer separation. Subsequently, the diffuser stall cell develops further owing to boundary layer separation accumulation and an induced low-velocity area. The low-velocity region forms a blockage across the diffuser passage span. The diffuser stall cell expands owing to the boundary layer separations that occurred on the shroud and hub wall by turns. Finally, the diffuser stall cell vanishes when it passes the cutoff because mass flow recovery occurred. Furthermore, the static pressure ahead of the rotating stall decreases because of the merging of the impeller discharge flow and the reverse flow from the casing. Accordingly, a reverse flow occurred owing to the evolution of the separation vortex at the diffuser exit. In addition, the flow angle decreases by the merging of the impeller discharge flow and reverse flow from the casing. Therefore, boundary layer separations start occurring on the shroud and hub wall ahead of the stall cell. The rotating mechanism of the diffuser stall is induced by the reverse flow development and a decrease in the flow angle ahead of the stall cell.

Experimental Measurement on Pebble Flow Discharge in a Hopper Silo Based on a Drainage Method

The dropping of absorption sphere from the storage vessel under accident conditions and the transportation of spent fuel elements in the reactor will both lead to the pebble flow discharging process driven by gravity in a hopper silo. Therefore, the research on the gravity-driven discharging rate of pebbles in a hopper silo has significant engineering guidance for reactor safety. In general, the idea of falling pebbles weighing to obtain the discharging rate becomes the most common experimental measurement method. However, due to the limitation of response frequency and the disturbance of pebbles falling, the resolution of experimental results is limited, and the uncertainty is introduced into the data error, which is difficult to eliminate. In this experiment, a volume measurement based on drainage method is adopted. This is a new experimental method to measure the discharge process of hopper silo. The magnetostrictive liquid level sensor is applied to measure the rise of liquid level caused by the volume of falling pebbles. Compared with the weighing method, this method has two advantages. First, the resolution of this method has a higher controllability. On the one hand, the disturbance caused by the momentum of falling pebbles will not be introduced into this method, on the other hand, the measurement accuracy is determined by the multiple controllable factors. Second, this method can obtain higher measurement frequency. the sampling frequency of liquid level sensor is 1–2 orders of magnitude higher than that of electronictong balance. Based on this new experimental method, the reliability of the method is validated by comparing the experimental results of discharge flow rate with the Beverloo’s and Nedderman’s empirical formula. Furthermore, the effect of silo outlet size on pebble discharge flow rate fluctuation have been also analyzed in this study. By use of fast Fourier transform, the fluctuation of particle discharge flow rate is separated from the discharging sampling results of liquid level sensor.

EXPERIMENTAL INVESTIGATION OF ENHANCEMENT IN EFFICIENCY OF CENTRIFUGAL PUMP BY REDUCTION IN CAVITATION OF PUMP

Cavitation phenomenon is basically a process formation of bubbles of a flowing liquid in a region where the pressure of the liquid falls below its vapour pressure and it is the most challenging fluid flow abnormalities leading to detrimental effects on both the centrifugal pump discharge characteristics as well as physical characteristics. In this low pressure zones are the first victims of cavitation. Due to cavitation pitting of impeller occurs and wear of internal walls of pumps occurs due to which there is creation of vibrations and noize are there. Due to this there is bad performance of centrifugal pump is there. Firstly, description of the centrifugal pump with its various parts are described after that pump characteristics and its important parameters are presented and discussed. Passive discharge (flow rate) control methods are utilized for improvement of flow rate and mechanical and volumetric and overall efficiency of the pump. Mechanical engineers is considering an important phenomenon which is known as Cavitation due to which there is decrease in centrifugal pump performance. There is also effect on head of the pump which is getting reduced due to cavitation phenomenon. In present experimental investigation the cavitation phenomenon is studied by starting and running the pump at various discharges and cavitating conditions of the centrifugal pump. Passive discharge (flow rate) control is realized using three different impeller blade leading edge angles namely 9.5 degrees, 16.5 degrees .and 22.5 degrees for reduction in the cavitation and increase the of the centrifugal pump performance at different applications namely, domestic, industrial applications of the centrifugal pump.