High Flow Rate Region Research Articles

Multiobjective hydraulic optimization of the diffuser vane in an axial flow pump

Separation flows tend to induce a chaotic flow field that eventually leads to energy losses and reduced efficiency. The present study performed a multiobjective optimization to improve the hydraulic performance of an axial flow pump at the best efficiency point (BEP) and critical stall point based on the diffuser vane (DV) geometry. Computational fluid dynamics were applied to predict the hydraulic performance of a series of DV models with design points generated through design of experiment. Six different surrogate models were evaluated based on the R-squared criteria. The nondominated sorting genetic algorithm II was also employed to search for optimum solutions for design variables. Hydraulic performance balance between low and high flow rate conditions was analyzed based on the velocity triangle. After optimization, the efficiency and total head at the BEP of the optimum model were increased by 2.341% and 2.779%, respectively, compared to the reference model. Despite the minimal changes to the hydraulic performance at the critical stall point, the optimal operating range was notably expanded in the high flow rate region. Thorough evaluation of losses attributed to horseshoe, corner, and trailing-edge vortices was conducted in meridional planes, multiple spans, and various cross sections in the DV domain. Additionally, the formation and development of turbulent flow were analyzed in detail by transient simulation. Vibration and noise caused by instabilities in the flow characteristics of the reference model were substantially reduced by 36.76% and 67.342% at the first higher-harmonic frequencies at the BEP and the critical stall point, respectively.

Design method based on a new slip-diffusion parameter of centrifugal pump for multiple conditions in wide operation region

Centrifugal pumps are widely used in industrial production, agricultural irrigation, water transportation, energy storage pump station and ocean engineering, and the development prospect of centrifugal pump is to work in a wide operation region with high efficiency. In this work, the achievement of high-efficiency operation for multiple conditions in a wide operation region is strenuously realized by a new design method from the perspective of flow mechanism analysis and theoretical derivation. A new dimensionless slip-diffusion parameter Φ on consideration of the slip effect and diffusion effect in impeller is proposed. On the basis of the new parameter Φ, a new design method of centrifugal pump is established to improve the pump efficiency for multiple conditions in a wide region. Two centrifugal pumps with different specific speeds of 102 and 127 are designed to validate the proposed design method. When the slip-diffusion parameter Φ ≈ 0.677, the centrifugal pump can achieve the maximum average efficiency for multiple conditions. For Φ < 0.677, the pump efficiency rapidly drops at the high flow rate region. For Φ > 0.677, the pump efficiency rapidly drops at the low flow rate region. Two centrifugal pumps are numerically simulated to obtain the flow pattern, and the entropy production method is used to analyze the relationship between flow field and energy performance of the pumps. Entropy production mainly appears at the blade suction side and the impeller outlet. For different flow rates, the total entropy productions of pumps with Φ ≈ 0.677 are always the minimum.

Effect of Pre-Swirling Flow on Performance and Flow Fields in Semi-Opened Axial Fan

In this study, we tried to improve the performance by giving a pre-swirling flow to the radial inflow that occurred in the semi-opened axial fan. In addition, the flow fields of rotor outlet were clarified experimentally, and the effect of pre-swirling flow was considered. The experiment was carried out using a performance test wind tunnel with a square cross section of 880 mm. Three types of casings were prepared, in which the blade tip protruded 0%, 20%, and 40% of the meridional chord length. They were called R25, R15, and R05, respectively, in the casing bellmouth model code. Guide blades for generating a pre-swirling flow were installed on the vertical wall surface of the casing. In addition, a vertical wall was installed 60% upstream of the meridional chord length as an obstacle to prevent axial inflow. The velocity fields of the rotor outlet were measured using a hot-wire anemometer. From the results, the pre-swirling flow did not significantly affect the fan performance. When there was no obstacles wall upstream, there was a partial increase in efficiency, but the difference was not so large. When there was an obstacle wall upstream, the efficiency increased overall in the case of R15, but in the case of R05, the efficiency increased only in the low flow rate region, and conversely decreased in the high flow rate region. By observing the blade outlet flow fields when the performance was improved, it was confirmed that the influence of the tip leakage vortex was weakened.

Thermo-economic analysis of a solid oxide fuel cell-gas turbine hybrid with commercial off-the-shelf gas turbine

The thermodynamic and economic performance of a natural gas-fueled solid oxide fuel cell (SOFC)-gas turbine (GT) hybrid system with a commercial off-the-shelf GT is investigated. Until today, commercial GTs are primarily engineered for the direct use of energy dense fuels, such as natural gas, and the integration of commercial GTs into a SOFC-GT hybrid remains challenging. In this work technically feasible and economically viable GT operating modes are identified to gauge the technology’s competitiveness on the free market. Steady state, full load operating conditions were established for various GT operating modes: I) constant spool speed operation, II) variable spool speed operation and III) partially closed compressor inlet guide vanes. For each GT operating mode, the performance was investigated over a range of SOFC fuel utilization factors, while considering physical constraints inside the SOFC, such as local temperature gradients in flow direction as well as overall cell temperature differences. The results of the thermodynamic evaluation served as inputs for the economic analysis of the SOFC-GT hybrid power plant. The results show that the integration of an off-the-shelf GT not only results in a significant derating of the GT, but also substantially impacts the SOFC operation, the main power producer in this SOFC-GT hybrid. To maximize the SOFC power output it is desirable operate the GT in a region of high air mass flow rates and low pressure ratios, which increases the number of stacks that can be accommodated and reduces the SOFC cooling requirement. The lowest costs of electricity are obtained at constant spool speed operation, while the highest efficiencies are reached at variable spool speed operation. Critical for the integration of off-the-shelf GTs, which historically have been designed for natural gas, is the surge margin. The largest surge margins are obtained by closing the compressor inlet guide vanes. Furthermore, higher SOFC fuel utilization factors are shown to increase the surge margin as the turbine firing temperature is decreased.

Study of Pressure Drops and Heat Transfer of Nonequilibrial Two-Phase Flows

Currently, there are no universal methods for calculating the heat transfer and pressure drop for a wide range of two-phase flow parameters in mini-channels due to changes in the void fraction and flow regime. Many experimental studies have been carried out, and narrow-range calculation methods have been developed. With increasing pressure, it becomes possible to expand the range of parameters for applying reliable calculation methods as a result of changes in the flow regime. This paper provides an overview of methods for calculating the pressure drops and heat transfer of two-phase flows in small-diameter channels and presents a comparison of calculation methods. For conditions of high reduced pressures pr = p/pcr ≈ 0.4 ÷ 0.6, the results of own experimental studies of pressure drops and flow boiling heat transfer of freons in the region of low and high mass flow rates (G = 200–2000 kg/m2 s) are presented. A description of the experimental stand is given, and a comparison of own experimental data with those obtained using the most reliable calculated relations is carried out.

Development of MEMS-based thermal mass flow sensors for high sensitivity and wide flow rate range

In the natural gas trade, mass flow metering is preferred to volume flow metering. In order to improve the measurement performance related to sensitivity within wide flow rate range of the mass flow meter, a novel design of a MEMS-based thermal mass flow sensor is proposed. To determine of the correlation between the sensing performance and geometry of sensor components, in this case the heater and the thermopile, models with various designs were fabricated using MEMS technology. Flow characteristic tests of the fabricated models were conducted in the low pressure gas flow standard system of KRISS. The effect of the distance ratio between the heater and thermopiles on the measurement performance of the thermal flow sensor was examined according to the flow rate range. The results presented that the basic models with the different distance ratio show different sensitivity characteristics. The non-uniform model proposed in this study show high sensitivity in both low and high flow rate region compared with models with a certain distance ratio.

Optimal design of current collectors for microfluidic fuel cell with flow-through porous electrodes: Model and experiment

Design optimization of current collectors has been performed to reduce the significant ohmic resistance observed in microfluidic fuel cell (MFC) with flow-through porous electrodes. A three-dimensional computational model is developed to investigate the electron transport characteristics in the porous electrodes, where lateral electron transport is found to encounter high resistance. Influences of different current collector design parameters on the transport resistances are examined and analyzed. The modeling results indicate that current collector position is the most influential factor due to the non-uniform flow rate distribution. Optimal current collector position is located at the high flow rate region instead of the conventional exposed end of the porous electrode. Experimental studies are performed to support the modeling analysis. The experimental results demonstrate that the optimized current collector position can boost the maximum power density by 61%. This study highlights the significance of the current collector design in achieving high performance MFC with flow-through porous electrodes. Based on the results, some general rules have been set for the current collector designs in this energy system, which can provide useful guidance for the future development of MFC.

Design Principles of Current Collectors in Microfluidic Fuel Cell with Flow-through Porous Electrodes

Abstract Computational and experimental studies have been performed to investigate the effects of current collector design on the performance of microfluidic fuel cell (MFC) with flow-through porous electrodes. Characteristics of electron transport in MFC with flow-through porous electrodes are investigated based on a three-dimensional computational model. The lateral electron transport in the porous electrode is found to encounter high resistance. To improve the cell performance, influences of different current collector design parameters on the transport resistances are examined. Physical origins for the influences of different design parameters are also discussed. The results demonstrate that current collector position is the most influential factor due to the non-uniform flow rate distribution. In the experimental study, cell performances revealed maximum power density when current collectors were located at the high flow rate region. An increase of 61% was observed when the current collectors moved from the conventional exposed ends of the electrodes to the high flow rate regions in the electrode active area. Based on the results, some general rules are set for the current collector designs of MFCs.

Effects of bending-torsional duct-induced swirl distortion on aerodynamic performance of a centrifugal compressor

A turbocharger compressor working in commercial vehicles, especially in some passenger cars, often works together with some pipes with complicated geometry as an air intake system, due to limit of available space in internal combustion engine compartments. These pipes may generate various distortions of physical parameters of the air at the inlet of the compressor and therefore the compressor aerodynamic performance deteriorates. Sometimes, the turbocharging engine fails to work at some operation points. This paper investigates the effects of various swirl distortions induced by different bending-torsional intake ducts on the aerodynamic performance of a turbocharger compressor by both 3D numerical simulations and experimental measurements. It was found that at the outlet of the pipes the different inlet ducts can generate different swirl distortions, twin vortices and bulk-like vortices with different rotating directions. Among them, the bulk-like vortices not only affect seriously the pressure distribution in the impeller domain, but also significantly deteriorate the compressor performance, especially at high flow rate region. And the rotating direction of the bulk-like vortices is also closely associated with the efficiency penalty. Besides the efficiency, the transient flow rate through a single impeller channel, or the asymmetric mass flow crossing the whole impeller, can be influenced by two disturbances. One is from the upstream bending-torsional ducts; other one is from the downstream volute.

Study on Performance Evaluation of Small Axial Fan

In order to establish the design methodology of a small axial fan, the axial fan with impeller diameter of 36 mm was designed, manufactured and tested. Especially, in order to investigate the influence of difference in blade cord length and blade thickness on performance characteristics, the performance characteristics obtained by the designed axial fans with difference blade shapes were examined. Also, by using CFD, the same flow field as the experiment was visualized. It was found that the lift of the blade was increased and the performance was improved in high flow rate region by thinning of the blade thickness and by extending the blade chord length.

Optimisation of the Sputnik-VAD design.

Miniaturisation of VADs can offer important benefits, including less invasive implantation techniques and more versatility in patient selection. The aim of this work was to reduce the weight, size, and energy consumption of the Sputnik VAD. The second generation of the Sputnik VAD was developed with a set of changes in construction. The head pressure-flow rate (H-Q) and power consumption-flow rate curves for the Sputnik VADs were measured at different rotational speeds. Computational fluid dynamics (CFD) were used for operating condition simulation and the LVADs were compared under the simulated physiological conditions. The slope of the H-Q curves for the Sputnik 1 VAD remains almost invariable over the entire range of the measured flow rate, in contrast to the curves for the Sputnik 2 VAD, which become flat in the high flow-rate region. Despite the design modification, the operating rotor speed remained invariable. The preload sensitivity of the Sputnik VAD is higher than that of the other rotary blood pumps and amounts to 0.111 ± 0.0092 L min-1 mmHg-1. The power consumption for the Sputnik 2 VAD is lower over the entire speed range, except for at 5,000 rpm. The pump weight was reduced from 246 to 205 g, the pump length was decreased from 82 to 66 mm, and the pump diameter was decreased from 32 to 29 mm. The total energy consumption of the pump was reduced by 15%.

Optimization study of a batch chromatographic process based on Amberchrom-CG161C adsorbent for separation of valine from a ternary amino acid mixture

The optimal design of the batch chromatographic process for separation of valine (product) from isoleucine and leucine (side-products) was carried out by using the relevant optimization tool that was prepared on the basis of an up-to-date genetic algorithm. In such an optimal design, the flow rate, feed size (?feed), eluent gap size (?gap), and product collection time were optimized to maximize the valine productivity of the batch chromatographic process under consideration. The results showed that the valine productivity was governed by the flow rate in the region of low flow rates, whereas it was governed by the Δ gap /Δ feed factor in the region of high flow rates. Finally, the effect of valine yield on the productivity was investigated, followed by providing the proper operating conditions that could be advantageous to both valine productivity and valine yield.

Silicon-based guided-wave optical flow sensor using a diaphragm with a small opening as an orifice

Our proposed silicon-based guided-wave optical flow sensor consists of a diaphragm with a small opening used as an orifice and a waveguide across the diaphragm. The sensor operates based on Bernoulli’s theorem and the elasto-optic effect. A sensor, which had a 10×10-mm 2 , 50- μ m -thick diaphragm with a 0.34 × 0.34-mm 2 opening, was fabricated to demonstrate and confirm the sensor operation. Measured output power as a function of flow rate using oxygen gas agreed quite well with the theoretical prediction although slight deviation was seen in the high flow rate region. Moreover, according to Bernoulli’s theorem, sensitivity is strongly dependent on sectional area of opening. So, three sensors with different opening areas, such as 0.28 × 0.28 , 0.34 × 0.34 , and 0. 55× 0.55 mm 2 , were fabricated to examine such a dependence, which would be helpful to design the sensor. The measured sensitivity was found to be almost proportional to area of the opening, similar to the theoretical prediction.

CFD simulations of the fluid flow behavior in a spacer-filled membrane module

In this study, the effects of the angles of spacer filaments and the different feed Reynolds number on the fluid flow behavior have been investigated. Three-dimensional computational fluid dynamics (CFD) study is carried out for fluid flow through rectangular channels within different angles (30°, 40°, 50°, 60°, 70°, 80°, 90°, 100°, 110°, 120°, respectively) between two filaments of spacer for membrane modules. The results show that the feed Reynolds number and the angles of spacer filaments have an important influence on pressure drop. While the feed Reynolds number is fixed, the optimal angle of spacer should be between 80° to 90°, because the pressure drop is not only relatively small, but also high flow rate region expanded significantly with the increase of the angles between 80° to 90°.The Contours of velocities and change of the average shear stress with the different angle of spacer filaments confirm the conclusion.

Effect of Trailing-Edge Modification of a Mixed-Flow Pump

Modern pumps are designed to guarantee a sufficiently large operating range or to satisfy the performance requirements relative to more than one operating point. This study applies trailing-edge (TE) modification method based on TE rounding in the suction surface to widen the operating range of a mixed-flow pump. The effects of TE modification on the performance and internal flow of the mixed-flow pump are investigated through computational fluid dynamics (CFD) analysis. Local Euler head distribution is introduced to reveal the pattern of energy growth along the blade-aligned (BA) streamwise location. A pump model with TE modification is tested, and numerical results agree well with experimental data. The results show that TE modification significantly improves pump efficiency in the high flow rate region by more than 10%. The best pattern of normalized local Euler head distribution (NLEHD) is a convex curve of nearly constant growth rate. The overall heads are also improved, and the flow near the exit of the impeller exhibits better uniformity. This finding demonstrates that a small change in the TE of the impeller can influence flow structure in most areas of impeller channels and that the local Euler head distribution is closely related to pump efficiency. TE modification can effectively improve the performance of the mixed-flow pump with high flow rate.

Simulation and Modeling of Flow in a Gas Compressor

The presented research demonstrates the results of a series of numerical simulations of gas flow through a single-stage centrifugal compressor with a vaneless diffuser. Numerical results were validated with experiments consisting of eight regimes with different mass flow rates. The steady-state and unsteady simulations were done in ANSYS FLUENT 13.0 and NUMECA FINE/TURBO 8.9.1 for one-period geometry due to periodicity of the problem. First-order discretization is insufficient due to strong dissipation effects. Results obtained with second-order discretization agree with the experiments for the steady-state case in the region of high mass flow rates. In the area of low mass flow rates, nonstationary effects significantly influence the flow leading stationary model to poor prediction. Therefore, the unsteady simulations were performed in the region of low mass flow rates. Results of calculation were compared with experimental data. The numerical simulation method in this paper can be used to predict compressor performance.

The effect of the solution flow rate on the final mass of metals deposited into a porous electrode at individual and joint deposition. Rear delivery of solution

Calculations in terms of the model of metal codeposition into a porous electrode (PE) and experimental measurements are used for studying how the flow rate m v and the volume of circulating solution at its frontal delivery affect the final mass of the cathodic deposit and its spatial distribution. For both individual and joint deposition of metals, the correlation between the final mass of the cathodic deposit m f and the uniformity of its distribution in PE is demonstrated: the more uniform the deposit distribution the higher its final mass. Due to peculiarities of the frontal delivery (the fixed position of the maximums of polarization and metal concentration and the same direction of their shift within the PE), the dependence of the final deposit mass on the volume flow rate demonstrates a very flat maximum shifted to sufficiently high m v. The increase in cathodic polarization and the transition to circulation with a small solution volume lead to the analogous shift. As a result, for the frontal delivery, the region of high flow rates turns out to be relatively more advantageous for the metal deposition into PE. For codeposition of silver and copper from their alkaline thiosulfate solution at the frontal solution delivery, the qualitative agreement between experimental and calculated m f = f(m v) dependences is demonstrated.

Response surface methodology for the modeling and optimization of oil-in-water emulsion separation using gas sparging assisted microfiltration.

Response surface methodology (RSM) and central composite design (CCD) were used to develop models for optimization and modeling of a gas sparging assisted microfiltration of oil-in-water (o/w) emulsion. The effect of gas flow rate (Q G ), oil concentration (C oil ), transmembrane pressure (TMP), and liquid flow rate (Q L ) on the permeate flux and oil rejection were studied by RSM. Two sets of experiments were designed to investigate the effects of different gas-liquid two-phase flow regimes; low and high gas flow rates. Two separate RSM models were developed for each experimental set. The oil concentration and TMP were found to be the most significant factors influencing both permeate flux and rejection. Also, the interaction between these parameters was the most significant one. At low Q G , the more the gas flow rate, the higher the permeate flux; however, in the high gas flow rate region, higher Q G did not necessarily improve the permeate flux. In the case of rejection, gas and liquid flow rates were found to be insignificant. The optimum process conditions were found to be the following: Q G = 1.0 (L/min), C oil = 1,290 (mg/L), TMP = 1.58 (bar), and Q L = 3.0 (L/min). Under these optimal conditions, maximum permeate flux and rejection (%) were 115.9 (L/m(2)h) and 81.1 %, respectively.

A numerical study for the effect of flow skirt geometry on reactor internal flow

A series of 1/5 scale reactor flow distribution tests had been conducted in order to determine the hydraulic characteristics of the APR+ (Advanced Power Reactor Plus) which were used as the input data for the open core thermal margin analysis code. In this study, in order to examine the applicability of computational fluid dynamics with the porous model in the analysis of reactor internal flow, simulation was conducted with the commercial multi-purpose computational fluid dynamics software, ANSYS CFX V.14. In addition, among the various reactor internals the effect of flow skirt geometry on reactor internal flow was investigated. It was concluded that depending on the shape of flow skirt the flow distribution was locally somewhat different. Standard deviation of mass flow rate (σ) for the original shape of flow skirt was smaller than that for the modified shape of flow skirt. This means that the original shape of flow skirt may give the more uniform distribution of mass flow rate at core inlet plane, which may be more desirable for the core cooling. Porous model for some reactor internal structures could adequately predict the hydraulic characteristics inside reactor in a qualitative manner. However, while the predicted high core inlet flow rate region was located in the core center zone, the measured one was located in the core outer boundary. This difference may result from the fact that some internal structures including the lower support structure assembly were not modeled with the real geometry but treated as the porous domain. If the sufficient computation resource is available, the predicted core inlet mass flow distribution is expected to be more accurate by considering the real geometry of the internal structures, especially located in the upstream of core inlet.

Analysis and Optimization of a Vaned Diffuser in a Mixed Flow Pump to Improve Hydrodynamic Performance

Hydrodynamic analysis and an optimization of a vaned diffuser in a mixed-flow pump are performed in this work. Numerical analysis is carried out by solving three-dimensional Reynolds-averaged Navier-Stokes equations using the shear stress transport turbulence model. A validation of numerical results is conducted by comparison with experimental data for the head, power, and efficiency. An optimization process based on a radial basis neural network model is performed with four design variables that define the straight vane length ratio, the diffusion area ratio, the angle at the diffuser vane tip, and the distance ratio between the impeller blade trailing edge and the diffuser vane leading edge. Efficiency as a hydrodynamic performance parameter is selected as the objective function for optimization. The objective function is numerically assessed at design points selected by Latin hypercube sampling in the design space. The optimization yielded a maximum increase in efficiency of 9.75% at the design flow coefficient compared to a reference design. The performance curve for efficiency was also enhanced in the high flow rate region. Detailed internal flow fields between the reference and optimum designs are analyzed and discussed.