Results Of Flow Patterns Research Articles

Flow behavior over well-escape weirs

ABSTRACT Weirs play an important role in controlling and managing water in irrigation canal networks through several functions, such as discharge measurements, water distribution, and lowering the water level. Weirs also play a crucial role in protecting canals from flooding, which might cause the earthen banks to collapse, by eliminating surplus water at the ends of the canals. Over the previous decades, the flow over the traditional sharp-crested weirs was extensively investigated by many researchers; however, the well-escape weirs have not received sufficient attention. These types of weirs were mostly constructed in the form of vertical wells that may be circular or rectangular in shape, and water may flow through the entire perimeter of the weir or part of the perimeter. In the present research, the effect of the well-escape-weir shape on the characteristics of flow over the weir was studied. A set of models were constructed in different shapes, circular and square, and the entire perimeter of the weir or part of the perimeter is working as the weir crest length. The discharge passing over the unit length of the weir crest (q) is investigated and compared for the circular and square weirs of various crest lengths and positions. The results indicated that the discharge capacity of the circular weirs increases by a rate ranging between 7.5% and 15% more than that of the square weirs at the same head. Also, results indicated that the discharge coefficient of the circular weirs increases by a rate ranging between 9.3% and 10.3% more than that of the square weirs. This behavior can be attributed to the interference between the orthogonal water nappes at the corners of the square models. In addition, the flow direction has little effect on the discharge coefficient at small discharges, and this effect becomes more obvious at higher discharges. Additionally, the well-escape weirs of the upstream crest have a slightly higher discharge capacity than those of the downstream crest due to the effect of the approach velocity, which increases the water entrance velocity at the upstream crest. The results of flow patterns around the weir showed that the locations of maximum flow velocities (u, v, w) are mostly near the weir crest and depend entirely on the crest length and position.

Evaluation of Three-Dimensional Environmental Hydraulic Modeling in Scour Hole

The main goal of this study was comparing the performance of an open-source code OpenFOAM and a commercial software Ansys Fluent in simulating the turbulent flow through a scour hole developed in a sand bed channel, which helps to give a hint in choosing the appropriate calculating tool. Both models were set with the same mesh and as similar as possible numerical settings, with RANS turbulence modeling, applying the k-ωSST model, in transient simulations. The results of flow pattern, velocity, and turbulence properties were collected and compared with laboratory experimental data. The analyzed results showed that, although both of the two models cannot perfectly reproduce the values from a laboratory experiment, they can quite well capture the flow in scour hole near the wall, with a bit higher performance coming from the OpenFOAM model application.

Experimental Study of (Water–Oil) Flow Patterns and Pressure Drop in Vertical and Horizontal Pipes

This paper provides the results of experimental stream flow patterns (water–oil) investigated in vertical and horizontal pipes with an elbow. The pipes are made from Perspex; the inner diameter is 0.024[Formula: see text]m, and the lengths of the vertical and horizontal pipes are 6 and 3[Formula: see text]m, respectively. The values of pressure at the four locations where [Formula: see text], 138, 248, and 304 are measured in various cases. The superficial velocities of the water range from 0.1 to 0.4[Formula: see text]m/s and of the oil from 0.1 to 0.9[Formula: see text]m/s. The pressure decreases with an increase in the height and the speed. Droplet/elongated/churn and annular streams are observed in a vertical pipe. The flow patterns are the stratified wavy stream with droplets at the interface, scattering (dispersion) of oil in water with a water layer, and annular flow in the horizontal pipe. These results of flow patterns are determined by a digital camera.

Oil-Water flow patterns, holdups and frictional pressure gradients in a vertical pipe under high temperature/pressure conditions

We conducted experimental measurements to examine the upward oil-water flow patterns in a vertical pipe (0.02 m I.D.) under high temperatures up to 130 °C and high pressures up to 20.51 MPa. The viscosity of the oil sample was 85.113 mPa·s at 40 °C. All the experiments were conducted with an in-house-built high pressure/temperature flow apparatus. This apparatus is equipped with a view window that allows us to visually observe the upward flow patterns of oil-water two-phase flow in a 0.02 m I.D. stainless steel pipe. The effects of pressure, temperature, input water fraction (IWF) and mixture flow rate on the flow patterns and friction pressure gradients were systematically investigated. We plot the observed flow patterns on a flow pattern map in which input water fraction was used as the y-axis and the mixture flow velocity was used as the x-axis. Based on the measurement results, we observed nine flow patterns including four water-in-oil flow, transition flow and four oil-in-water flow patterns. With an increase in temperature at a given input water fraction, slug flow, plug flow with large water drops tended to transform into bubbly flow and dispersed flow with smaller water drops, water-in-oil very dense bubbly flow (VDB W/O) was observed at high temperature due to the significantly increasing of in-situ water holdups. The transition flow and the boundaries in the flow pattern maps tend to occur at lower input water fraction values. The effect of pressure on the flow patterns was found to be opposite to that of temperature. The possible causes leading to the changes in the flow patterns subjected to pressure/temperature variations were provided in terms of changes in density ratio, interfacial tension, and viscosity ratio between oil and water. The phase inversion points at different temperatures and pressures reflected from friction pressure gradients were found to be in agreement with the results of flow patterns. This work contributes to a better understanding of oil-water two-phase flow behavior under high temperature/pressure.

CFD in Continuous Stirred Tank: Comparison between Rushton and Paddle Turbines

Biogas produced from palm oil mill effluent (POME) is common in Thailand. A 2-step digestion system, which consists of a continuous stirred-tank reactor (CSTR) and a UASB, is being implemented for biohythane (biohydrogen and biomethane) production. This paper describes three-dimensional computational fluid dynamics (CFD) simulations of POME flow in a laboratory-scale CSTR. The study focuses on comparisonof impellers, the Rushton and the paddle turbines, for the best POME mixing with minimum loss of granules. The result of flow patterns in CFD showed that better mixing in the bottom through the middle of the tank can be achieved by proper selection of impellers and baffles to avoid the loss of granules by effluent.

Numerical Simulation on Forced Convective Condensation of Steam Upward Flow in a Vertical Pipe

A transient three-dimensional volume of fluid (VOF) simulation on condensation of upward flow of wet steam inside a 12 mm i.d. vertical pipe is presented. The effect of gravity and surface tension are taken into account. A uniform wall temperature has been fixed as boundary conditions. The mass flux is 130~6400 kg m−2's−1and the turbulence inside the vapor phase and liquid phase have been handled by Reynolds stress model (RSM). The vapor quality of fluid is 0~0.4. The numerical simulation results show that, in all the simulation conditions, the bubbly flow, slug flow, churn flow, wispy annular flow, and annular flow are observed; in addition, the results of flow pattern are in good agreement with the regime map from Hewitt and Roberts. The typical velocity field characteristic of each flow pattern and the effect of velocity field on heat transfer of condensation are analyzed, indicating that the slug flow and churn flow have obvious local eddy. However, no obvious eddy is observed in other flow patterns and the streamlines are almost parallel to the flow direction. The simulation results of heat transfer coefficients and frictional pressure drop show good agreement with the correlations from existing literatures.

Optimization of SO2 Scrubber Using CFD Modeling

The reduction of environmental contaminants that contribute to smog and soot is a worldwide goal that has seen an increased focus in recent years. In the United States, for example, it is estimated that by 2014 new rules will lead to a 71% reduction of sulfur dioxide emissions and 52% of nitrogen oxide emissions as compared to 2005 level. Thus, medium-sized plants (100-500MW) that currently do not have flue gas desulfurization (FGD) units or selective catalytic reduction systems (SCRs) will be required to adapt. Similar emission reduction efforts are expected to be adopted globally, albeit at different levels. Wet-scrubber FGD is characterized as one of the most effective SO2 removal techniques with low operating costs. However capital cost for implementation is considered high. Hence an effective optimization procedure is required to reduce these capital costs of conversion.Power plants commonly use a lime slurry spray reaction to reduce SO2 emissions. Control of the droplets throughout the tower geometry is essential to ensuring maximum reduction while minimizing scale. The liquid slurry is known to have density, surface tension and viscosity values that deviate from standard water spray characteristics, which complicates process optimization. In order to improve the scrubber, nozzle characteristics and placement must be optimized to reduce the cost of the system implementation and mitigate risks of inadequate pollution reduction. A series of large flow rate, hydraulic, hollow cone sprays were investigated for this study.A Computational Fluid Dynamics (CFD) model was used to examine potential scrubber designs for optimization of the system. Nozzle parameters were modeled to allow particle tracking through the system. An ANSYS Fluent Lagrangian particle tracking method was used with heat and mass transfer. The alkaline sorbent material and SO2 reaction is modeled to determine uniformity and efficacy of the system. Volumetric chemistry mechanisms were used to simulate the reaction. These results demonstrate the expected liquid-gas interaction relative to the system efficiency. Drop size, liquid rheology, and spray array layout were examined to achieve SO2 removal above 90%. Wall impingement and flow pattern results were evaluated due to their impact in minimizing equipment plugging and corrosion required as for long-term scrubber utilization.

A Test Bench for Validation of CFD Analysis for Air Flow in Thin Electronic Casing Model

This paper describes accuracy between experimental and calculated results of air flow pattern in thin electronic equipment. To measure flow patterns in the model of a thin electronic equipment, PIV measurement technique was employed. Dummy components (obstacles in the flow path in the thin electronic equipment) were set in the model and those configurations were altered for evaluating several flow patterns. For a CFD calculation, "OpenFOAM" was employed and the results of flow patterns from the CFD calculation were compared with the experimental results. A heat source was set in the model and temperature rise of the heat source was also measured. Then the relationship between flow patterns and the cooling performance were examined. As a result, the numerical results showed a good agreement with the experimental results when seeing in the over all velocity filed.

Study on Flow Pattern and Characteristics of Sediment Deposition in Tidal Reach of Yangtze River

Taking Nanjing macha river mouth of Yangtze river for example, a two-dimensional flow and sediment mathematical model was established to study flow pattern and characteristics of sediment deposition. The results of flow pattern show that there isn’t flood tidal current in the Nanjing baguazhou reach, but with tidal level alternating between flood tide and ebb tide, there is flood tidal current inside the river mouth under the condition of flood water. The calculation results of sediment deposition show that the sediment deposition is connected with the flow character and the incoming water and sediment condition. The deposition thickness at macha river mouth is much more than that of inside the macha river, and the sediment deposition in 1998 is much more than that of in 2006. With the increasing of calculational time, the deposition thickness per year decreases.

Analyzing unsaturated flow patterns in fractured rock using an integrated modeling approach

Characterizing percolation patterns in unsaturated fractured rock has posed a greater challenge to modeling investigations than comparable saturated zone studies, because of the heterogeneous nature of unsaturated media and the great number of variables impacting unsaturated flow. This paper presents an integrated modeling methodology for quantitatively characterizing percolation patterns in the unsaturated zone of Yucca Mountain, Nevada, a proposed underground repository site for storing high-level radioactive waste. The modeling approach integrates a wide variety of moisture, pneumatic, thermal, and isotopic geochemical field data into a comprehensive three-dimensional numerical model for modeling analyses. It takes into account the coupled processes of fluid and heat flow and chemical isotopic transport in Yucca Mountain's highly heterogeneous, unsaturated fractured tuffs. Modeling results are examined against different types of field-measured data and then used to evaluate different hydrogeological conceptualizations and their results of flow patterns in the unsaturated zone. In particular, this model provides a much clearer understanding of percolation patterns and flow behavior through the unsaturated zone, both crucial issues in assessing repository performance. The integrated approach for quantifying Yucca Mountain's flow system is demonstrated to provide a practical modeling tool for characterizing flow and transport processes in complex subsurface systems.

Numerical simulation for aerodynamic characteristics of two circular cylinders in staggered arrangement by a third-order upwind finite element method

We present numerical results for flow patterns around two circular cylinders in a staggered arrangement, and fluid forces of the cylinders which are placed in a uniform flow. The numerical results for flow around two circular cylinders are obtained by two- and three-dimensional computations. The distances of the in-line and transverse directions between the centers of two circular cylinders are taken into consideration as the parameters of the computation. Stabilization of numerical solutions is achieved by using a third-order upwind finite element method. In the case of tandem arrangement of the circular cylinders, it is well known from experimental data that, when two circular cylinders are placed at a distance of approximately diameters between the centers of cylinders, the fluid forces of both cylinders vary suddenly. Therefore, in this paper, the circular cylinders are put at two kinds of distances of 3- and 4-diameters to the in-line direction and are also put at distances of diameters to the transverse direction. The obtained results for two circular cylinders in the staggered arrangement are qualitatively compared with experimental data.

Study on enhancement of evaporating heat transfer in narrow horizontal annular crevices

This study is intend to improve flow pattern within evaporator, which is low quality and low mass flux, by installing narrow horizontal annular crevice so that enhance heat transfer coefficient. The motive, which made to study heat transfer enhancement by using narrow annular crevice, came from capillary phenomena and pumping force of generating vapor on refrigerant boiling. Tests were run about 5 models of turbulence promoter with CFC-12, in the range of evaporating temperature (15.deg. C), mass flux (50 to 100 kg/m2/s), heat flux (3.4 to 6.7 kW/m2/), quality (0.1 to O.5). It is observed that flow pattern within evaporator is changed closely to semi-annular flow or annular flow, of which refrigerant liquid is reached to the upper side of tube by using narrow annular crevice. When the narrow annular crevice is installed in the evaporator tube, local heat transfer coefficient is generally more improved than that of smooth tube. That fact is according to observed result of flow pattern. It is learned that narrow annular crevice has more efficiency at a low mass flux. At the TP-5, enhancement of heat transfer rate is about 170% compare to that of smooth tube on a low mass flux (50 kg/m2/s), and it is about 134% on a high mass flux (100 kg/M2/S), so that we know that it is on a very high condition.