Large Flow Rate Research Articles

A study on the dynamic characteristics of surface suction vortices in an open inlet pool

The surface suction vortices in the open pump intakes were systematically investigated by using numerical and experimental methods. A 3D open inlet pool model has been applied to numerically simulate the flow pattern in the sump based on the shear stress transfer k–ω model, and the volume of fluid method was used to analyze flow fluctuations in the free surface in order to capture and identify the developing status and the evolution process of surface suction vortices as well. The results show that the surface suction vortices easily occur at large flow rates, and the suction ability of these vortices has a positive linear relationship with the flow rate, submerged depth, and the Froude constant. Moreover, it can be observed that the extended direction of the dynamic vorticity is determined by the vortex component along the Z axis (ωz), which played a major role in the stretching effect during the vortex deformation.

Transmission model of transient flow wave signal in intelligent layered water injection system

Fluid wave code communication is used in layered water injection intelligent monitoring system, but model of fluid transient flow wave signal transmission is still unknown. Based on the fluid energy equation of steady flow, a transmission mathematical model of fluid transient flow wave signal in intelligent layered water injection system was established. The model can accurately describe the transient flow wave transmission characteristics in the tubular string of water injection wells. The transient flow wave signals and influencing factors generated by the ground electric control valve and the downhole water distributor were studied, and the transmission mechanism of the signal in the water injection tubular string was revealed. Studies show that ground and downhole transient flow wave signals are generated by discharge changes caused by changes in the opening degree of the ground valve and the downhole water distributor. The length of the water injection tube has no effect on the downlink transmission of the wellhead signal, but has a certain influence on the uploading of the downhole signal. Numerical calculations show that the flow rate of the water injection tube has a great influence on the amplitude of the pressure signal. The larger flow rate can generate larger signal amplitude, which is beneficial to the signal transmission, signal detection and processing. It was verified by the experiments and simulations that the pressure and flow changes in the downhole and wellhead had good consistency during the transmission of transient flow waves. It is found that the greater the variation of opening degree, the greater the amplitude of transient flow wave signal, which is beneficial to the wave signal transmission. The optimal settings for the valve opening are selected as 100% rightleftarrows 0%. This study has theoretical guiding significance for the design and performance improvement of fluid wave code communication systems.

An experimental model of the pharyngoesophageal segment in tracheoesophageal phonation.

Tracheoesophageal (TE) speech is an important method of speech rehabilitation for those who undergo a total laryngectomy. Despite the many advantages over other methods, there is still room for improvement in terms of the overall quality of the TE voice as well as its success rate. These points could be greatly assisted by an improved knowledge on the mechanics of TE speech. Here, an experimental model of the pharyngoesophageal segment (PES), based on the idea of a collapsible tube, is proposed. To implement the model, considerable simplifications had to be made, most notably in the use of a thin flexible tube to represent the PES. The model was used to assess the minimum amount of tonicity required for the onset of phonation in terms of the flow rate and longitudinal tension. Additionally, comparisons with a mathematical model [Tourinho, da Silva, dos Santos, Thomaz, and Vieira, J. Acoust. Soc. Am. 149, 1979-1988 (2021)] have been made, yielding similar trends for sufficiently large flow rates. The measurements also suggest that the phonation frequency is most affected by the tonicity of the PES, which highlights the question of which physiological mechanism is responsible for the control of the fundamental frequency of phonation.

Thermal response analysis of a medium-deep coaxial borehole heat exchanger by circulating CO2

Geothermal energy is abundant and renewable. It is of great interest to extract geothermal energy efficiently and sustainably. In this paper, a composite coiled tubing (CCT) is put forward and a coaxial borehole heat exchanger (CBHE) technology is utilized to extract heat from the medium-deep geothermal reservoir using phase-change CO2 as the working fluid. CCT has all the advantages of coiled tubing, and thermal insulation could be realized more easily. Considering the transient heat transfer of the formation, a mathematical model of the CBHE system is established and validated by two field tests. Then, both the phase change process of CO2 in the CCT and the long-term heat extraction performance are predicted. Effects of key parameters on the heat output are discussed. It is shown that extracting medium-deep geothermal energy by the phase-change CO2 is realized, and the latent heat of vaporization accounts for a high proportion of the heat carried by production CO2. The larger the mass flow rate is, the more heat could be carried out. But the larger flow rate would lead to the lower temperature of the production CO2 and the more frictional loss. The results provide a reference for exploiting the medium-deep geothermal energy sustainably.

Identification of cavitation state of centrifugal pump based on current signal

Centrifugal pump, which is widely used in water conservancy, electric power, petrochemical, ship, aerospace, and other technical fields, is the core equipment used to ensure all kinds of energy transfer. Cavitation not only affects the service life of the centrifugal pump but also seriously impacts the reliability of the process flow or device system. Due to the influence of the life, position and number of vibration sensors, the existing cavitation fault feature identification accuracy is not enough. The state analysis and characteristic recognition of the current signal under the cavitation state of the centrifugal pump are conducted in this paper based on soft sensing technology, and the signal component and judgment threshold representing the cavitation state are obtained. The following results are presented. Under different critical cavitation numbers, a small number of bubbles appeared near the suction surface of the inlet edge of the impeller, which verified the reliability of criterion for the critical cavitation number when the head coefficient decreased by 3%. The overall accuracy of binary classification cavitation recognition based on the current signal is 12.9% higher than that of three classification cavitation recognition. The recognition rate of VMD decomposition under different working conditions is higher than that of EMD, in design conditions, for example, overall accuracy improved by 7.3%, which also indicates that the obtained cavitation information of each component by VMD decomposition is richer than that obtained by EMD decomposition. Comparing different working conditions, a large flow rate easily leads to cavitation and high recognition current rate, compared with the flow of 0.75 Q and 1.25 Q, the overall accuracy is improved by 9.6%.

Analysis of flow characteristics and cavitation in the vanes of a reversible pump-turbine in pump mode

In reversible pump-turbines, cavitation erosion can be found at the leading edge of stay vanes (SVs), which is generally considered related to the undesirable flow regime in the double radial vanes in pump mode. In this study, the flow characteristics in the vanes were studied at small guide vane (GV) openings in pump mode to evaluate the easily-ignored stay vane (SV) cavitation. Numerical simulations for three-dimensional (3D) flow passages of pump-turbine revealed that a large pressure drop was induced at SV leading edge in the situation of large velocity magnitude in the GV-SV vaneless space with a backflow flow pattern in the SV channel. Since a quasi-two-dimensional characteristic was confirmed for the flow regime in the vanes, refined simulations for GV-SV region with a two-dimensional (2D) approach were conducted to analyze the evolution of flow regime and the influence of flow rate coefficient. A low-frequency pressure fluctuation was found at SV leading edge, in which the minimum pressure appeared when the flow separation occurred near SV inlet in the situation with backflow in SV channel. This special flow pattern transferred to the adjacent SV channel in the direction of runner rotation. Moreover, the increase of flow rate coefficient resulted in a larger pressure drop at SV leading edge and accelerated the evolution of the flow regime in the vanes. This implies that a high cavitation risk at SV leading edge appears when operating at small GV opening angles with large flow rate coefficients. The outcomes of this study may help researchers to focus on the SV cavitation and improve the start-up and shutdown processes in pump mode.

Research on stability and control strategies for a spring-loaded valve with bypass outlet

The stability and control strategies of a spring-loaded valve with bypass outlet have been studied by combining numerical and theoretical analysis. First, a nonlinear dynamical model and a CFD model of a spring-loaded valve with bypass outlet are developed. The theoretical analysis requires parameters such as discharge coefficients and fluid forces obtained from CFD simulations. The equivalent area of the fluid forces and discharge coefficients are similar at different pressure differences, leading to a reduced-order formulation that serves the theoretical analysis of nonlinear dynamics. Second, the valve disc oscillates at small constant flow rates by nonlinear dynamical analysis. The oscillation frequency is a superposition of the Helmholtz cavity and the mass spring system, which increases as the valve disc impacts the seat or the upper limiter. More importantly, there is a frequency lock-in phenomenon at small fluctuating flow rates, which vanishes at large flow rates. The oscillations are not symmetric during the opening and closing processes, and the oscillations are more severe during the opening processes. Finally, the bypass outlet has a great effect on the stability of valve disc, which can appropriately kill the nonlinear component in the dynamic equation. A reasonable bypass sleeve design can reduce the unstable flow range and oscillation amplitude. This paper provides a reference for the design of spring-loaded valves.

Modelling the film fragmentation of industrial-scale centrifugal granulation of high-temperature molten slag

Centrifugal-granulation-assisted thermal energy recovery (CGATER) is one of the most promising routes to enable waste heat harvest from molten slags. However, it remains a grand scientific and technological challenge to produce fine particles from the bulk high-temperature molten slag, especially at large slag throughput. In this work, we established an improved model to simulate the centrifugal granulation at the large flowrate comparable to the laboratory- pilot-scale trials. For the first time, film fragmentation has been successfully reproduced by modelling. On this basis, we elucidated the intricate film fragmentation by quantifying the off-atomizer film characteristics at various operational conditions, with a strong focus on the metrics of the off-atomizer slag film. The present study provides an important and valuable CFD model to approach the underlying physics of film fragmentation. Most importantly, it opens up new possibilities for predicting slag droplet formation at experimentally unavailable operational conditions.

Multiple parameters and multiple conditions optimization based on two steps strategy for an axial flow pump

Axial flow pump with high specific speed and large flow rate has been widely used for ship propulsion, water transfer and pump station, and now it meets the demand to work in a wide operation region with high performance. In the present work, a multiple parameters and multiple conditions optimization system based on two steps strategy is proposed and established for an axial pump. The multiple parameters and multiple conditions optimization system includes the controllable blade load design method, Kriging surrogate model, numerical simulation, parameter sensitively analysis method and multiple islands genetic algorithm. A two steps strategy is proposed for multiple conditions optimization. In this optimization strategy, the first step is to optimize the pump performance under the design condition, and the second step is to optimize the pump performance under other multiple operation conditions. In application of the multiple parameters and multiple conditions optimization for an axial pump, eight parameters are as follows: two cascade solidity parameters, two blade load parameters, two blade angle parameters, blade number and axial length. At design condition of 70 kg/s, the efficiencies of baseline pump and optimal pump are 84.249% and 85.419%, respectively, improving by 1.170%. For the multiple conditions optimization, the average efficiency of optimal pump in flow rate range of 30 kg/s to 100 kg/s is 2.562% higher than that of baseline pump. In comparison of baseline pump, the backflow of optimal pump near the shroud is obviously reduced, and the turbulent kinetic energy of optimal pump is greatly improved.

104 Application of CFD Simulation for Development Cyclone Samplers

Abstract Aerosol sampling is one of the largest and growing application areas of small-scale cyclone separators. A series of limit values are already or will be reduced in the future and therefore there is a need for samplers operating at larger flow rates that can collect the required amount of particles for analysis at lower aerosol concentrations. Therefore, the main goal of this work was to develop and validate a Computational Fluid Dynamics (CFD) model that can be used for simulation and optimisation of cyclone samplers. For aerosol flow modelling the Euler-Lagrange method was applied where the continuous phase is treated in an Eulerian manner, whereas the dispersed phase is treated in a Lagrangian approach. For a proper simulation of the flow field, the Large Eddy Simulation (LES) technique was used. A dynamic Smagorinsky-Lilly model was applied to calculate subgrid-scale turbulence. The developed model was validated on two cyclone samplers, a 9.5 mm in diameter sampling cyclone of the HD design and a 23 mm in diameter FSP 10 cyclone. For that, the simulated performance characteristics, such as a cut-size, a slope of the penetration curve, and the pressure drop, were compared with the experimental measurements. The simulation results agree well with experimental data. The deviation in cut-size, the slope of the penetration curve, and the pressure drop between the experimental data and LES simulations of the HD cyclone do not exceed 7%, 18.4%, and 10.3% respectively. Regarding the FSP10 cyclone, the deviations in cyclone performance characteristics are even lower.

Effect of wellbore layout and varying flow rate on fluid flow and heat transfer of deep geothermal mining system

Optimal wellbore layout and fluid flow supplying scheme are crucial in thermal breakthrough alleviation and performance improvement for geothermal energy recovery. This study aims to evaluate the effect of wellbore layout and fluid flow injection scheme on heat extraction performance and determine the optimal scheme for a sCO2-based deep geothermal mining system. A three-dimensional numerical model is established and the fluid flow and heat transfer characteristics for six types of wellbore layouts is comparatively analyzed. Then the system performance under increasing and decreasing type of varying flow injection scheme is evaluated. The results show that the wellbore layout has great impact on the sufficient degree of heat exchange between the cold working fluid and the hot rock. The triplet triangle layout is superior to the other kinds of wellbore layouts in heat transfer and gives moderate pressure loss. Quintuplet and doublet diagonal layouts give moderate performance, while doublet center straight-line has slightly poorer heat transfer performance than these two layouts. The triplet center straight-line and triplet diagonal layouts provide the two worst wellbore layouts with obvious dead zone visualized in system temperature contour. Besides, the injection flow rate needs to be supplied into the reservoir cautiously. Too large mass flow rate makes too fast heat extraction, and the thermal breakthrough time is shortened and temperature drops dramatically. Moreover, the increasing type of varying flow rate scheme can extend thermal breakthrough time by 50% and significantly raise reservoir outlet temperature, while the decreasing type of varying flow rate scheme deteriorate the system heat transfer performance due to excessive heat extraction in early operation period. Overall, the triplet triangle layout combined with increasing type of varying flow rate scheme can improve the heat extraction performance, enabling a more stable and sustainable geothermal mining system.

The mathematical model of kitchen smoke exhaust system in high-rise residential buildings considering the Influence of Stack effect

In high-rise buildings with large indoor and outdoor temperature difference, neglecting the effect of stack effect in smoke exhaust shafts may cause calculation error of the fluid network model. In this paper, the mathematical model of kitchen smoke exhaust system considering the influence of stack effect was put forward and it can be inserted different range hood sub-models. Compared with the results of six working conditions of the model without considering the stack effect, the error of the proposed model were reduced by 7.6%, 4.3%, 4.1%, 2.8%, 2.4%, and 2.1%. While the indoor and outdoor temperature difference varies from −5 °C to 49 °C, the effect of stack effect on the pressure in the flue and the flow rate for each user was studied for six operating rates s. The results show that under the combined effect of stack effect and flue resistance, the static pressure of the kitchen smoke exhaust system showed a low-high-low distribution, and the maximum static pressure in the flue moved toward the bottom with the increase of temperature difference. User flow rates exhibit a low-high-low-high distribution, with an increased flow rate in the bottom users and the largest flow rate in the top users.

Numerical Simulation and Wind Tunnel Test of a Variable Geometry Auxiliary Inlet for a Wide-Body Aircraft Environmental Control System

A variable geometry auxiliary inlet for a wide-body aircraft environmental control system with moveable deflectors operating in a large mass flow rate range is studied through numerical simulation and wind tunnel tests, which yields a design method for the variable geometry auxiliary inlet with high performance. The characteristics of the flow field are studied by numerical simulation. The results show that the favorable pressure gradient and the roll-up vortices are the major impetus that inhales the incoming flow into the inlet. The law of regulation and the performance variation under different conditions are obtained by wind tunnel test. The flow coefficient increases first but then decreases with the increase in the inlet opening, and the pressure rise ratio and total pressure recovery coefficient increase first and then decrease with the increase in the mass flow rate. In general, under the condition of a high Mach number (Ma > 0.4), the inlet opening of this test configuration should not exceed 50%. The deflectors can maintain the normal work of the environmental control system by moving properly to control the mass flow rate of the auxiliary inlet.

Water distribution and scheduling model of an irrigation canal system

A complete water distribution scheme should include the scheduling of the check gates and turn out gates. This study aims to resolve the water distribution problem in irrigation districts based on channel hydrodynamic simulation and using the hydraulic factor of water level increase in backwater areas. The supply-decided water distribution and scheduling model(SD-WDSM), the demand-decided water distribution and scheduling model(dd-WDSM) were established respectively. The model was applied to the Bojili irrigation district to verify it’s applicability. The results show that the SD-WDSM can adjust the length of the backwater area through the operation of the check gate, ensuring a large flow rate at the turn out gate. The dd-WDSM was established to group the water diversion canals by rotation irrigation, and the turn out gate in the same group could open and close simultaneously, which is convenient for the administrator to operate. The two models also ensure that the water is diverted as early as possible, and the operation numbers of the check gates and the turn out gates are less. The model obtains the complete scheduling scheme of the check gates and the turn out gates in the water distribution system. This model can improve agricultural water use efficiency and promote sustainable agricultural development. The proposed model is universal and can be applied to other irrigation districts.

Investigation of flow characteristics in a twin-surface dielectric barrier discharge reactor by Schlieren imaging

Dielectric barrier discharges are an emerging technology for the plasma-catalytic removal of volatile organic compounds and other gas purification challenges such as the removal of O2 traces from H2. Packed-bed reactors are mainly used for these applications, but surface dielectric barrier discharges (SDBDs) typically printed on thin dielectric plates are promising alternatives for the treatment of large volumetric flow rates due to their low flow resistance causing a low pressure drop. Especially for SDBDs the flow conditions are crucial, because the active plasma filled volume covering the mentioned plates with a typical thickness of 0.1 mm is small in comparison to the overall reactor volume with a typical distance of some tens of millimeters to the reactor wall. In this study, the flow conditions of a twin-SDBD were investigated by Schlieren imaging applied in converting O2 traces in H2 containing gas mixtures to H2O and compared to fluid dynamics simulations. Schlieren imaging was used to visualize local gradients of the refractive index inside the SDBD reaction chamber, while gas composition, dissipated power, or flow rate were varied. Without a plasma discharge, laminar flow dominates, resulting in a conversion below 10% over a Pt-coated electrode configuration in the reaction of O2 traces with H2. With the plasma discharge, full conversion was achieved for the same reaction without catalyst, although the plasma is also confined to the surface of the electrode configuration. Schlieren structures covering the complete cross section of the reaction chamber were observed, showing that strong radial mass transport is induced by the plasma. The shape and extent of the Schlieren structures is ascribed to a superimposition of gas flow, thermal expansion from the plasma volume, thermal buoyancy as well as an electrohydrodynamic force between the electrodes and the grounded reactor walls. Fluid dynamics simulations show vortex formation above and below the electrode, created by the electrohydrodynamic force further implying extensive mass transport by the plasma, which is visualized in addition by carbonaceous deposits on the reactor lid. This emerging deposition pattern during toluene decomposition closely corresponds to the electrode geometry. It is proposed that the reaction proceeds only in the active plasma volume and that reactive species transported to the bulk gas phase only have a minor contribution. Thus, the degree of conversion of the SDBD reactor is not only determined by the chemical reactivity in the plasma volume, but also by its plasma-induced mass transport resulting in efficient gas mixing. These findings reveal new possibilities to improve SDBD reactors for gas purification applications based on their favorable flow conditions.

Multi-objective optimization of the oil-free centrifugal air compressor in hydrogen fuel cell vehicles based on grey relational analysis

Centrifugal air compressor is critical to hydrogen fuel cell vehicles due to it guarantees the air provided to the stack is higher pressure ratios and a larger flow rate. However, the compressor has low efficiency and high energy consumption. In this paper, the multi-objective optimization was performed based on experimental data, which considered both the maximum isentropic efficiency and minimum total power consumption. The effects of the factors on the performance of the compressor were obtained by mean S/N ratios. The contributions of the factors to the optimization objectives of the compressor were investigated by analysis of variance. The optimal parameters combination providing the larger isentropic efficiency and lower total power consumption was found by grey relational analysis. The isentropic efficiency increased by 34.5% and total power consumption decreased by 48.5% in comparison with the average value in all Taguchi cases for the optimal compressor.

Characteristics of Double-Layer, Large-Flow Dielectric Barrier Discharge Plasma Source for Toluene Decomposition

The direct decomposition of toluene-containing humidified air at large flow rates was studied in two types of reactors with dielectric barrier discharge (DBD) features in ambient conditions. A scalable large-flow DBD reactor (single-layer reactor) was designed to verify the feasibility of large-flow plasma generation and evaluate its decomposition characteristics with toluene-containing humidified air, which have not been investigated. In addition, another large-flow DBD reactor with a multilayer structure (two-layer reactor) was developed as an upscale version of the single-layer reactor, and the scalability and superiority of the features of the multilayer structure were validated by comparing the decomposition characteristics of the two reactors. Consequently, the large-flow DBD reactor showed similar decomposition characteristics to those of the small-flow DBD reactor regarding applied voltage, flow velocity, flow rate, and discharge length, thus justifying the feasibility of large-flow plasma generation. Additionally, the two-layer reactor is more effective than the single-layer reactor, suggesting multilayer configuration is a viable scheme for further upscaled DBD systems. A high decomposition rate of 59.5% was achieved at the considerably large flow rate of 110 L/min. The results provide fundamental data and present guidelines for the implementation of the DBD plasma-based system as a solution for volatile organic compound abatement.

A realistic analysis of hydrogen production based on flare gas considering life cycle assessment

Among the different methods for flare gas recovery, the comprehensive evaluation of hydrogen production has yet to be studied. The techno-economic evaluation and life cycle assessment of using flare gas to produce hydrogen are performed in this study. The Aspen HYSYS software is used to simulate the different units of hydrogen production, and the economic assessment is performed to calculate the hydrogen production expenditures. The results illustrated that the mass flow rate and the capacity of the hydrogen production plant are 117600 kg/h and 4856.4 MW, respectively. The obtained results demonstrate that the hydrogen production costs can be considered reasonable using flare gas with a low price and large flow rate. In this regard, the breakeven price of hydrogen is US$ 0.27, and the share of Capital expenditure in hydrogen production cost is 55.4%, as well. Moreover, the life cycle assessment (LCA) of hydrogen production has been conducted to evaluate the environmental effects of hydrogen production. Thanks to the novel CO2 capturing process considered in this study, GHG and CO2 productions have been reduced, respectively, by 59 and 63 percent, demonstrating the necessity of using the CO2 capturing process.

Performance analysis of multi-well EGS system based on unique network structure — Voronoi fractures

Fracture network is an important factor in the utilization of geothermal energy, its composition and structure have an important influence on the development of geothermal energy. As a component of EGS system, fractures have various forms. Therefore, this paper studies the influence of fracture morphology on reservoir heat extraction. The Voronoi is used to describe the unique network structure and is applied to geothermal development system as a form of fracture network. Therefore, a THM coupled EGS model with Voronoi fractures is established to observe its thermal extraction performance. In present work, the effects of fracture block numbers, well length, well spacing, injection mass flow rate and injection temperature on the thermal extraction performance of EGS system are numerically investigated. The results show that the model has higher production temperature when the number of Voronoi blocks is 77, and the production temperature in the 30th year is 494.01 K. The influence of the change of well spacing on the production temperature of the model is more obvious than that of the change of well length. At the same time, the longer the well length, the smaller the injection pressure, the stronger the connectivity between the injection and production wells, and the narrower the end of the injection well in the temperature diagram. Furthermore, the increase of injection mass flow rate reduces the production temperature of the model, when the injection mass flow rate increases from 80 kg/s to 140 kg/s, the production temperature decreases from 494.01 K to 450.99 K. However, because the increase of the total injection mass flow rate, the large mass flow rate still has a high heat extraction ratio. The higher the injection temperature is, the smaller the pressure difference between injection wells and production wells is. The temperature changes the permeability and liquid viscosity of the reservoir, thereby reducing the pressure difference. In addition, with the increase of injection wells, the production temperature of the model increases, and the injection pressure decreases. However, the pressure difference between injection wells and production wells increases, indicating that the pressure of production wells is large, so the production cost increases. Therefore, in the actual production situation, reasonable selection of geothermal operation parameters should consider the operation cost and the difficulty of development.

Effects of tip clearance on energy performance of three-stage electrical submersible pump

In order to investigate the influence of tip clearance on the energy performance of electrical submersible pump (ESP), numerical simulation and experimental study were carried out. The three-dimensional transient Reynolds-Averaged Navier–Stokes (RANS) equation is solved by using the ANSYS CFX software. The experimental results were used to verify the reliability of the numerical method. The results shown that the increase of tip clearance leads to the decrease of energy performance. The increase of tip clearance leads to a proportional drop in energy performance under part-load flow rate conditions, while the increase of tip clearance leads to a significant loss under large flow rate conditions due to increased leakage. The rotor-stator interaction between the impeller and the diffuser is the main factor for the enhanced turbulence at part-load flow rate conditions, resulting in energy losses. The maximum turbulence intensity along the axial direction in the tip clearance is 4.4 times and 4.7 times of the minimum turbulence intensity at rated flow rate 1.0Qdes and large flow rate 1.4 Qdes operating conditions, respectively. The results could be referred to predict the internal flow loss and optimize the design of ESPs.