Smaller Slot Width Research Articles

Experimental and Numerical Investigation of Pressure Fluctuation in a Low-Specific-Speed Centrifugal Pump with a Gap Drainage Impeller

In order to analyze the effect of impeller with different slot widths on the performance of the low-specific-speed centrifugal pumps, based on the impeller of a single-stage pump with the specific speed of 21, two gap drainage schemes with slot widths of 1.5 mm and 6.0 mm, slot diameter of 180 mm, and lap length of 5 mm were designed. Both experimental and numerical simulation methods were applied to compare the steady performance, which includes the head, efficiency, and the internal flow field distribution, and the unsteady pressure pulsation performance between new designed pumps and the original pump. The results show that gap drainage would cause a certain degree of head reduction, but a smaller slot width could achieve higher efficiency. Meanwhile, a reasonable open seam scheme can reduce the development of pressure pulsation, which provides experience and reference for the stable operation of low-specific-speed centrifugal pumps.

Effects of the Impeller Blade with a Slot Structure on the Centrifugal Pump Performance

An impeller blade with a slot structure can affect the velocity distribution in the impeller flow passage of the centrifugal pump, thus affecting the pump’s performance. Various slot structure geometric parameter combinations were tested in this study to explore this relationship: slot position p, slot width b1, slot deflection angle β, and slot depth h with (3–4) levels were selected for each factor on an L16 orthogonal test table. The results show that b1 and h are the major factors influencing pump performance under low and rated flow conditions, while p is the major influencing factor under the large flow condition. The slot structure close to the front edge of the impeller blade can change the low-pressure region of the suction inlet of the impeller flow passage, thus improving the fluid velocity distribution in the impeller. Optimal slot parameter combinations according to the actual machining precision may include a small slot width b1, slot depth h of ¼ b, slot deflection angle β of 45°–60°, and slot position p close to the front edge of the blade at 20–40%.

A numerical study of dynamics in thin hopper flow and granular jet**Project supported by the National Natural Science Foundation of China (Grant Nos. 11705256 and 11905272), the National Postdoctoral Program for Innovative Talents, China (Grant No. BX201700258), Young Scholar of CAS "Light of West China" Program for Guanghui Yang (Grant No. 2018-98), and the Strategic Priority Research Program of the

The dynamics of granular material discharging from a cuboid but thin hopper, including the hopper flow and granular jet, are investigated via discrete element method (DEM) simulations. The slot width is varied to study its influence on the flow. It is found the flow in the cuboid hopper has similarity with the flow in two-dimensional (2D) hopper. When the slot width is large, the flowrate is higher than the predicted value from Beverloo’s law and the velocity distribution is not Gaussian-like. For granular jet, there is a transition with varying slot width. For large slot width, there is a dense core in the jet and the variations of velocities and density are relatively small. Finally, the availability of continuum model is assessed and the results show that the performance with large slot width is better than that with small slot width.

Numerical modeling, simulation, and experimental validation of predicting fiber diameter in wide‐slot positive‐pressure spunbonding process

An air‐drawing model of polypropylene (PP) polymer and an air jet flow field model in wide‐slot positive‐pressure spunbonding process are established. The influences of the density and the specific heat capacity of polymer melt at constant pressure changing with polymer temperature on the fiber diameter have been studied. The predicted fiber diameter agrees with the experimental data as well. The effects of the processing parameters on the fiber diameter have been investigated. The air jet flow field model is solved by means of the finite difference method. The numerical simulation computation results of distribution of the fiber diameter match quite well with the experimental data. The air‐drawing model of polymers is solved with the help of the distributions of the air velocity. It can be concluded that the higher air velocity and air temperature can yield the finer fibers diameter. The higher inlet pressure, longer drawing segment length, smaller air knife edge, longer exit length, smaller slot width, and smaller jet angle can all cause higher air velocity and air pressure along z‐axis position, which are beneficial to the air drawing of the polymer melt and thus to reduce the fiber diameter. The experimental results show that the agreement between the predicted results and the experimental measured data is very better, which verifies the reliability of these models. Also, they reveal great prospects for this work in the field of computer‐assisted design (CAD) of spunbonding process. POLYM. ENG. SCI., 58:1371–1380, 2018. © 2017 Society of Plastics Engineers

CFD and infrared thermography of particle curtains undergoing convection heat transfer: Image analysis and edge prediction

In this paper infrared thermographic images of falling hot particle curtains are compared to Eulerian-Eulerian Computational Fluid Dynamics (CFD) model simulations. The hot particle curtains were made to fall through a narrow slot in a rectangular box. The shapes of the formed curtains at different slot widths, particle sizes and mass flow rates were predicted using gradient-based image analysis techniques. Small slot width and low mass flow rate situations were found to show excellent correlation. Larger particle sizes led to greater uncertainty in the thermographic data, and large slot width and high mass flow rate CFD simulations were less reliable.

Computational fluid dynamics simulation and theoretical study the air jet flow field of a wide slot positive pressure drawing assembly in the spunbonding nonwoven process

The polymer air‐drawing model of polyethylene terephthalate spunbonding nonwovens and the air jet flow field model in wide slot positive pressure spunbonding process have been established. The influence of the density and the specific heat capacity of polymer melt at constant pressure changing with polymer temperature on the fiber diameter have been studied, which is solved by introducing the numerical computation results of the air jet flow field of attenuator. It is simulated by means of the finite difference method. The predicted fiber diameter agrees with the experimental data. The effects of the processing parameters on the fiber diameter with the help of the image analysis method have been investigated. A higher inlet pressure, smaller slot width, and smaller jet angle will all cause higher z‐axis position of air velocity and air pressure, which are beneficial to the air drawing of the polymer melt and thus to reducing the fiber diameter. The experimental results show that the agreement between the results and experimental data is better, which verifies the reliability of these models. The results present great prospects for this research in the field of computer assisted design of spunbonding process, technology, and equipment. POLYM. ENG. SCI., 55:231–242, 2015. © 2014 Society of Plastics Engineers

Filtration flows in the upper wedge of an earthen dam

Investigation of questions related to the stability of the thrust slopes of earthen dams subject to rapid drawdown of the reservoir level is currently extremely urgent. Reservoirs are rapidly drawn down both at daily-regulated hydroprojects, and during emergency discharges to the tailrace, and evacuation of trenches. Analysis of the performance of the upper wedge of a dam during rapid emptying of the reservoir indicated that its stability is appreciably diminished by the effect of hydrodynamic forces directed toward the upper pool. A procedure for determination of the direction of the hydrodynamic forces and construction of streamlines and lines of equal heads under conditions of nonsteady filtration during rapid lowering of the reservoir level has yet to be sufficiently formulated. To continue study of these phenomena, we have conducted model investigations to determine the influence exerted by a rapid drop in water level in reservoirs on the stability of the thrust slopes of earthen dams with a core. A “slotted” model was used to investigate the process. This is a special type of model, in which study of filtration is based on the analogy between the laminar movement of a liquid between two parallel plates and plane filtration in the soil. It was first used by E. A. Zamarin in a filtration study [1]. The flow of liquid in a thin slot formed by plates under appropriate boundary conditions is a filtration-flow model. The boundary conditions for the slotted model are realized by the same means as for a model created from soil. In the impermeable sections of the boundary perimeter, the slot is blocked by a partition impermeable to water. In sections of the boundary perimeter where the head is constant, the thin slot transitions into a broad slot playing the role of the open reservoir. As for the depression curves and the surfaces leaking filtration flow onto slope, they are formed on the slotted model itself. This method makes it possible to record the mechanical “trajectory” of liquid particles in any region of the slope. The dimensions of the model are determined by the clearance dimensions of the laboratory, and by convenience of observation during the experiment. We selected a model with a height of 20 cm and an embankment slope of 1:2 (Fig. 1). The width of the slot was 1.3 and 5.3 mm for the slope and pool, respectively. In Fig. 1, the zone investigated is indicated by the hatchures (the thrust slope of the dam). The slot into which the liquid flows is bounded on one side by sight glass, and on the other by the profile of the dam (model of slope), which is fashioned from glass. In conducting the experiment, the liquid overflows from the region with the small slot width (1.3 mm) into the broader slot. This process is similar to filtration in an actual soil. In the case of gravity filtration when the scale of the heads is assumed to be linear, the head at each point of the filtration flow in the field is expressed in terms of the head at the corresponding point of the model in accordance with the formula

MODIFICATION OF SLOT MODEL BY COINCIDING WITH THE LATERAL MODEL

Preissmann Slot concept is one of the most extensively accepted numerical approaches in unsteady free surface pressurized flow. However Courant's stability condition has imposed this method with limitation on the size of the time step. The slot concept produces large wave celerity and a corresponding strict time step limitation with too small slot width, while inaccuracies may result with too large slot width. The equations for a surcharged flow which form the lateral model are derived incorporating the relaxation effect and compared with corresponding equations of slot model. The friction loss is evaluated in slot model by introducing the coefficient, which modifies the slot model. The pair of differential equations of Slot Model and Modified Slot Model are solved and presented in forms for direct substitution into FORTRAN programming for numerical analysis. The numerical result justifies Modified Slot Model to be more efficient for the modeling of transient flow in sewer network.

CPW‐fed bow‐tie slot antenna

A CPW-fed bow-tie slot antenna is presented. Experimental results show that the widest bandwidth can be adjusted by the slot width when the extended angle is zero, while the far field is in the broadside direction and the cross polarization is kept at a low level. The bow-tie slot antenna can obtain at least 36% bandwidth (VSWR<2) with a 20° extended angle. A smaller slot width needs a larger extended angle to reach the widest bandwidth; meanwhile, the far field has a wider 3 dB beamwidth in the H-plane than that using a larger slot width. © 1998 John Wiley & Sons, Inc. Microwave Opt Technol Lett 19: 358–360, 1998.

CPW-fed bow-tie slot antenna

A CPW-fed bow-tie slot antenna is presented. Experimental results show that the widest bandwidth can be adjusted by the slot width when the extended angle is zero, while the far field is in the broadside direction and the cross polarization is kept at a low level. The bow-tie slot antenna can obtain at least 36% bandwidth (VSWR<2) with a 20° extended angle. A smaller slot width needs a larger extended angle to reach the widest bandwidth; meanwhile, the far field has a wider 3 dB beamwidth in the H-plane than that using a larger slot width. © 1998 John Wiley & Sons, Inc. Microwave Opt Technol Lett 19: 358–360, 1998.