Large Flow Rate Research Articles

A Novel Stacked Rotary Cup Atomizer Toward Efficient Centrifugal Granulation of Molten Blast Furnace Slag

Atomizer is one of the most important facilities in molten slag centrifugal granulation heat recovery system, which concerns the heat recovery rate of the system as well as the quality of slag particles. Aim to large slag flow rate in industrial application, a novel stacked rotary cup atomizer (SRCA) is proposed to achieve high‐quality centrifugal granulation performance. The authentic molten slag is adopted as working medium and the centrifugal granulation phenomena are visually investigated including the molten slag fragmentation on the surface of atomizer and the impacting of slag droplets on the water cooled wall. A film perforation fragmentation mode is found in the experiments under high slag flow rate. The granulated particle size distribution, average particle size, and slagging mass fraction produced by the atomizer are obtained. Moreover, the granulation performances of the SRCA with divergent structures are tested. The results demonstrate that the SRCA has excellent granulation performance in large slag flow rate to produce smaller particles and suppress slagging. Comparing with the typical rotary cup atomizer, the largest decrement in average particle size and slagging mass fraction for the SRCA is ascertained as 28.1% and 71.1%, respectively.

Study of flow effects on temperature-controlled radiofrequency ablation using phantom experiments and forward simulations.

Blood flow is known to add variability to hepatic radiofrequency ablation (RFA) treatment outcomes. However, few studies exist on its impact on temperature-controlled RFA. Hence, we investigate large-scale blood flow effects on temperature-controlled RFA in flow channel experiments and numerical simulations. Ablation zones were induced in tissue-mimicking, thermochromic phantoms with a single flow channel, using an RF generator with temperature-controlled power delivery and a monopolar needle electrode. Channels were generated by molding the phantom around a removable rod. Channel radius and saline flow rate were varied to study the impact of flow on (i) the ablated cross-sectional area, (ii) the delivered generator power, and (iii) the occurrence of directional effects on the thermal lesion. Finite volume simulations reproducing the experimental geometry, flow conditions, and generator power input were conducted and compared to the experimental ablation outcomes. Vessels of different channel radii affected the ablation outcome in different ways. For mm, the ablated area decreased with increasing flow rate while the energy input was hardly affected. For mm and mm, the energy input increased toward larger flow rates; for these radii, the ablated area decreased and increased toward larger flow rates, respectively, while still being reduced overall as compared to the reference experiment without flow. Directional effects, that is, local shrinking of the lesion upstream of the needle and an extension thereof downstream, were observed only for the smallest radius. The simulations qualitatively confirmed these observations. As compared to performing the simulations without flow, including flow effects in the simulations reduced the mean absolute error between experimental and simulated ablated areas from 0.23 to 0.12. While the temperature control mechanism did not detect the heat sink effect in the case of the smallest channel radius, it counteracted the heat sink effect in the case of the larger channel radii with an increased energy input; this explains the increase in ablated area toward high flow rates (for mm). The experiments in a simple phantom setup, thus, contribute to a good understanding of the phenomenon and are suitable for model validation.

Thermal and mechanical performance of a hybrid printed circuit heat exchanger used for supercritical carbon dioxide Brayton cycle

Printed circuit heat exchangers with high heat transfer efficiency, small volume and high pressure resistance are usually chosen as a precooler for the supercritical carbon dioxide Brayton cycle. The supercritical carbon dioxide channel has high pressure and small mass flow rate, but the water channel has low pressure and large mass flow rate. The conventional printed circuit heat exchanger does not consider the difference between the two-side channels, and thus the weight is large. In this work, a diffusion-bonded hybrid printed circuit heat exchanger is put forward as the precooler used for supercritical carbon dioxide Brayton cycle. The new structure uses chemical-etching channels for the supercritical carbon dioxide side and plate-fin channels for the water side. Thermal design of the hybrid printed circuit heat exchanger based on a segmented Log-Mean Temperature Difference method is conducted. The results indicate that the hybrid printed circuit heat exchanger can effectively improve the heat transfer performance. Compared with the conventional printed circuit heat exchanger, the core volume of the optimized hybrid printed circuit heat exchanger is reduced by 49%, and the heat transfer rate per unit volume is increased by 145%. The optimized hybrid printed circuit heat exchanger in both channels can satisfy the mechanical stress requirement.

Experimental and numerical studies of stress fields of a branched polybutadiene in a flat die

There is a growing body of laboratory and industrial evidence that the viscoelastic characteristics of molten polymers contribute to improving the efficiency of polymer extrusion molding. Understanding the behavior of molten polymers in manufacturing processes requires the qualitative and quantitative determination of flow kinematics and stress distribution. The optimization of forming processes and final properties of transformed products requires the mastery of high-performance simulation models. So, it is necessary to be able to correctly describe the non-linear rheological behavior of the molten polymers by appropriate constitutive equations and a relatively easy implementation in computer codes. In this work, experimental and numerical studies are performed to investigate the rheological behavior of branched polybutadiene into a two-dimensional channel of a capillary rheometer. The stress field in the flow was analyzed with a birefringence device to identify areas of stress concentration and to show its progress in different areas of the extrusion die. Also, we obtain the stress field with numerical simulations using ANSYS Fluent 16.0 as a solver and Gambit as a mesh generator. The power law model, or Ostwald-de Waele, adopted in this numerical study is a rheophysical approach used to simulate the rheological behavior of branched polybutadiene during extrusion molding. Furthermore, this numerical approach can be adopted for large flow rates where experimental study becomes very difficult.

Experimental investigations and optimization of machining performance during turning of EN-31 steel using TOPSIS approach

Machining of difficult to cut material at advanced range of process parameters is the requirement of modern day machining scenario for achieving the goals of sustainable machining through utilization of modern cooling techniques to minimizing the friction, heat generation and tool damage. Consequently, leads to profitable machining under the provision of suitable volume, application method and environmental friendly cutting fluids. Contrary to this, larger flow rate and inferior methodology of cutting fluid application leads to various health problems, environment issues and imperfect product quality. So, to achieve targets the sustainable machining, the firm has to meet certain environmental norms regarding the application and disposal of cutting fluids. Therefore, to tackle the aforementioned ecological issues the dry machining is preferred which exhibit solution, but this option does not endure economic plan at accelerated machining parameter levels due to lower tool life and impaired quality of product. Hence, the alternative to all these situations are the requirement of such a cooling system which does not pollute the environment, operator friendly as well as economical to use. Henceforth, the minimum quantity lubrication using soybean oil has been used in present investigation as a replacement to flood lubrication. The experiments have been conducted on EN-31 Steel taking advanced ranges of machining parameter in dry and M.Q.L system. Research outcomes revealed that the M.Q.L machining improved the surface finish, lowered the cutting temperature and enhanced the chip reduction coefficient with comparison to dry machining system. The Parametric optimization evaluated by TOPSIS approach pointed out that the best machining combination has been observed at 196 m/min, 0.088 mm/rev in vegetable oil environment.

Proton Exchange Membrane Fuel Cell Ejector Test Platform Design and Ejector Test Analysis

The hydrogen recirculation system is essential to the performance of the fuel cell system; the ejector device plays an important role in the hydrogen recirculation system. In this paper, a test platform which can simulate the fuel cell anode system is integrated for ejector performance testing. Based on the ejector test platform, an ejector device was tested under different operating conditions. The design of the ejector test platform, the test method and test process are introduced in detail. The test results of the ejector are compared with the Computational Fluid Dynamics (CFD) simulation results of different turbulence models. The results show that the standard k-e model is more accurate than other turbulence models at small and medium flow rates. At a large flow rate, the realizable k-e model has a higher simulation accuracy than other turbulence models.

Thermal Efficiency and Economics of a Boil-Off Hydrogen Re-Liquefaction System Considering the Energy Efficiency Design Index for Liquid Hydrogen Carriers

This study analyzes the thermodynamic, economic, and regulatory aspects of boil-off hydrogen (BOH) in liquid hydrogen (LH2) carriers that can be re-liquefied using a proposed re-liquefaction system or used as fuel in a fuel cell stack. Five LH2 carriers sailing between two designated ports are considered in a case study. The specific energy consumption of the proposed re-liquefaction system varies from 8.22 to 10.80 kWh/kg as the re-liquefaction-to-generation fraction (R/G fraction) is varied. The economic evaluation results show that the cost of re-liquefaction decreases as the re-liquefied flow rate increases and converges to 1.5 $/kg at an adequately large flow rate. Three energy efficient design index (EEDI) candidates are proposed to determine feasible R/G fractions: an EEDI equivalent to that of LNG carriers, an EEDI that considers the energy density of LH2, and no EEDI restrictions. The first EEDI candidate is so strict that the majority of the BOH should be used as fuel. In the case of the second EEDI candidate, the permittable R/G fraction is between 25% and 33%. If the EEDI is not applied for LH2 carriers, as in the third candidate, the specific life-cycle cost decreases to 67% compared with the first EEDI regulation.

A novel low pressure-difference fluctuation electro-hydraulic large flowrate control valve for fuel flowrate control of aeroengine afterburner system

To address the control accuracy of large fuel flowrate during pressure fluctuation, a novel electro-hydraulic fuel metering unit (FMU) is constructed for afterburner fuel system of military aeroengine. Different from the previous FMU, the proposed FMU can achieve the higher precision opening control by a new metering valve with double control chambers (MVDCC), and realize the lower pressure difference fluctuation regulating by a novel two-stage constant pressure difference compensated valve (CPDCV) with dynamic damping orifice and damping piston. The experimental and AMESim simulation results verify the validity and superiority of the novel FMU. Since the temperature-induced variation in fuel properties and device capabilities may degrade or even impair the properties of novel FMU, the discharge flowrate is analyzed by global sensitivity analysis to research the effect proportion of each factor, the temperature effect is explored to ensure the working reliability in long-span temperature variation. Finally, the optimization of structure parameters for novel CPDCV can further reduce pressure difference fluctuation during pressure regulation, and the overshoot, adjust time and the integral of time multiplied by absolute value of error (ITAE) can be reduced by 24%, 30% and 26%, respectively. This paper provides a reference for improving the stability of large flowrate during pressure fluctuation.

Experimental research on using CO2-Ar microjets to control liquid fuel combustion instability and pollutant emission

Combustion instability has become an obstacle to the development of modern gas turbines. In this study, four categories of jet tubes inject CO2-Ar mixture to the flame root at different total injection volume flow rates and mixing ratios. These jets do not change the dominant combustion instability frequency, yet the large flow rate jets can significantly weaken the pressure and the heat addition oscillations. The tube type or the CO2-Ar volume fraction in the jets has no apparent influence on the control efficacy. When the total jet volume flowrate reaches 10 L/min, the maximum amplitude reduction ratio of pulsating pressure and CH∗ chemiluminescence intensity is 90% and 89%, respectively. Meanwhile, the jets caused a significant drop in the flame temperature, and the NOx emission was reduced by at least 35%. However, the side effect of the jets is that the flame is on the verge of blowing out, and the CO emission increases sharply. The higher the volume fraction of CO2 in the jets, the more likely it is to generate CO. Designers need to compromise the impact of jets on the safety and cleanliness of the combustors.

A resonant piezoelectric proportional valve for high-flowrate regulation operated by a bending sandwich actuator

A resonant piezoelectric proportional valve for large flowrate regulation was proposed in this work. The large flowrate of the valve and its proportional regulation under high differential pressure were achieved using a bending sandwich actuator (BSA). First, the configuration and operation principle of the valve were depicted, and its structural parameters were determined by simulated analyses. Then, the theoretical analysis method was accomplished to predict the flowrate, and the direct fluid structure interaction simulation was used to validate the theoretical model. Ultimately, a prototype was fabricated and experimentally measured for the output performances. The results denoted that the output displacement of the BSA under the loaded condition was 91.69 μm when the resonant frequency and voltage were 2.19 kHz and 100 Vp-p; and the corresponding flowrates for the deionized water (DIW) and silicone oil (SLO) were 1.256 L/min and 0.221 L/min at 344.75 kPa. Besides, the cut-off pressures for the DIW and SLO were 289.59 kPa and 310.275 kPa under −300 V0-p; and the leakages were 0.5 mL/min and 0.2 mL/min under 344.75 kPa. This valve is expected to be applied to the cooling systems, hydraulic actuators.

The impact of isothermal flow assumption on accuracy of pressure transient analysis results

AbstractAdiabatic expansion and viscous dissipation of fluid flow in porous media result in considerable heating or cooling of hydrocarbon fluids when pressure gradients are very large. Traditionally, fluid flow in porous media has been assumed isothermal in hydrocarbon reservoirs. While this assumption helps with simplifying the physics of fluid flow by neglecting the thermal effects, it imposes a dominant impact on fluid properties in situations where flow undergoes fast paced and abrupt changes in flow rate and or pressure. The analytical solutions of fluid flow for pressure transient analysis rely on the isothermal flow assumption. Since the variations of fluid properties are not accounted for in temperature fluctuations, there is an inherent error in standard methods of well test analysis. In this paper, the errors in pressure transient analysis as a consequence of the assumption of isothermal fluid flow are investigated. The magnitude of error is quantified as a function of flow rate and pressure drop. Error analysis shows that at higher flow rates, the thermal impacts are elevated such that the application of isothermal flow models becomes erroneous and invalid. It can be shown that oil well tests are more influenced by thermal effects compared to gas well tests in conventional dry gas reservoirs. This study highlights an important thermal impact that is often neglected and should be considered in the design, execution, and analysis stages of well testing. Also, it suggests that isothermal analytical models should be avoided for well test analysis with large flow rates.

Effect of the liquid–gas interface curvature for a superhydrophobic surface with longitudinal grooves in turbulent flows

A superhydrophobic (SH) surface has shown great potential in reducing flow resistance and saving energy in hydrodynamic applications. In this paper, we have tried to investigate the effects of liquid–gas interface curvature of a SH wall in turbulent flows with the wall-resolved large eddy simulation (LES). The LES is first validated against direct numerical simulation results before the curvature shape is parameterized and examined at various Reynolds numbers (Reτ = 180, 395, and 590). The parametric study shows that a positive curvature angle leads to a higher flow rate, while the effect of a negative curvature angle on the flow resistance is minimal. In addition, the effect of the interface curvature on the flow rate is weakly dependent on the Reynolds number. Analysis shows that larger flow rate can be obtained by reducing the spanwise momentum exchange. A positively curved interface bows into the liquid and shifts the transverse flow circulation (in the cross-sectional plane) away from the solid wall, which helps to reduce spanwise momentum exchange and thus the flow resistance significantly. In contrast, a negatively curved interface does not change the location of the transverse circulation but deforms its shape, which hardly affects the spanwise momentum exchange or the flow rate. The near-wall streak patterns above the SH wall distribute with roughly the same spacing of the surface texture. In addition, the absolute distance plays a more important role than the viscous distance in the variation of the streaks with the distance from the SH wall.

Investigation of suction flow characteristic in the inertance hydraulic converters for efficiency improvement

The inertance hydraulic converter relies on fluid inertance to modulate flow or pressure and is considered to be a competitive alternative to the conventional proportional hydraulic system due to its potential advantage in efficiency. As the quantification of fluid inertance, the suction flow characteristic is the crucial performance indicator for efficiency improvement. To explore the discrepancy between the passive inertance hydraulic converter featured by the check valve and the active inertance hydraulic converter driven by an equivalent 2/3 way fast switching valve in regard to suction flow characteristics, analytical models of the inertance hydraulic converters were established in MATLAB/Simulink. The validated models of the respective suction components were incorporated in the overall analytical models and their suction flow characteristics were theoretically and experimentally discussed. The analytical predictions and experimental measurements for the current configurations indicated that the active inertance hydraulic converter yields a larger transient suction flow rate than that of the passive inertance hydraulic converter due to the difference of the respective suction components. The suction flow characteristic can be modulated using the supply pressure and duty cycle, which was confirmed by experimental measurements. In addition, the suction flow characteristics are heavily affected by the resistance of the suction flow passage and switching frequency. There is a compromise between the resistance and switching frequency for inertance hydraulic converters to achieve large suction flow rate.

Numerical Simulation of the Nonlinear Flow Properties in Self-Affine Aperture-Based Fractures

In order to study the effect of fracture geometry on the nonlinear flow properties in aperture-based fractures, a fractal model based on the self-affinity is proposed to characterize the three-dimensional geometry of rough-walled fractures. By solving the N–S (Navier–Stokes) equation directly, the relationships between the Forchheimer-flow characteristics, fractal dimension, and standard deviation of the aperture have been obtained. The Forchheimer equation is validated to describe the nonlinear relationship between flow rate and pressure gradient. For lower flow rate, the influence of the fractal dimension almost can be ignored, but the linear coefficient increases and the hydraulic aperture decreases with increasing standard deviation of the aperture, respectively. For larger flow rate, the nonlinear coefficient increases with the growth of the standard deviation of the aperture and fractal dimension. Thus, an empirical relationship between the nonlinear coefficient, fractal dimension, and standard deviation of aperture is proposed. In addition, the critical Reynolds number decreases with the increase of the standard deviation of the aperture and the fractal dimension, and the numerical results are generally consistent with the experimental data.

Numerical study on Unstable Hydraulic Factors of Kaplan turbine with semi-spiral case at large flow rate conditions

The operation of semi-spiral case Kaplan turbines at large flow rate conditions is restricted by factors such as severe cavitation and severe vibration, which limit the maximum output of the unit. In order to explore the main hydraulic factors that cause the poor operating stability of the unit at large flow rate conditions, and provide a reference for the operation and design of the turbine, the numerical simulation method is adopted to conduct the performance study of an semi-spiral case Kaplan turbine at different operating conditions, by comparing and analysing the results at the optimal conditions and large flow rate conditions, the unstable hydraulic factors at large flow rate conditions is obtained. The research results show that: at large flow rate conditions, the uneven flow distribution in the semi-spiral case cause vortices between the guide vanes, lead to the large fluctuations of blade torque, and generate unstable back-flow and vortices in the draft tube. These phenomena combined with the various gap flows in the runner, make the internal flow of the Kaplan turbine at large flow rate conditions deteriorate, cavitation increase, efficiency decrease, and cause severe vibration, thereby limiting the stable operation of Kaplan turbine at large flow rate conditions.

3D transient numerical simulation of a helical roots air compressor for FCVs

Oil-free helical Roots air compressors which have great application potential in air circulation systems for high-power fuel cell systems, such as commercial fuel cell vehicles (FCVs), have the advantages of active adaptation, low cost, large flow rate and high reliability. In this study, a three-dimensional transient numerical simulation model of a helical Roots air compressor was established by considering all leakage clearances. In this study, hexahedral structured dynamic grids were generated in the working chamber and the rotating angle was updated at an increment of 1° to ensure the mesh quality of the entire solving domain. The accuracy of the simulation model was validated using experimental data, and the maximum deviation was less than 4.0%. Based on the simulated results, the pressure field and variation of the pressure field with the rotation angle are presented. It shows that the pressure fluctuation at the discharge side was larger than that at the suction side. The influence of various leakage clearance on the volumetric efficiency was analyzed comparatively. Additionally, the flow field characteristic of clearance was revealed. It is found that the rotor tip clearance was the major factor for the reduction of volumetric efficiency when the size was larger than 0.12 mm instead of the interlobe clearance. It is suggested that more attention should be paid to control the clearance size to ensure the performance of helical Roots air compressors.

Effect of Tip Clearance on Rotating Stall in a Mixed-Flow Pump

Abstract The non-uniform disturbance in the circumferential direction is the essential cause of the occurrence of rotating stall in a turbomachinery. In order to study the effect of tip clearance leakage flow on rotating stall, the mixed-flow pump models with different tip clearances were numerically calculated, and then the energy performance curves and internal flow structures were obtained and compared. The results show that the pump efficiency and the internal flow field of the numerical calculation are in good agreement with the experimental results. A saddle region appeared in the energy performance curves of the three tip clearances, and with the decrease of clearance, the head and efficiency of the mixed-flow pump increased to varying degrees, but the critical stall point shifted to the large flowrate, and the stable operating range of the mixed-flow pump decreased, which indicating that the mixed-flow pumps were easier to stall under small tip clearance. Under the deep stall condition, the influence of the leakage flow on the end wall area increases gradually with the decrease of clearance. Under the small clearance, the leakage flow flows away from the suction surface for a certain distance to form a number of tip leakage vortex strips with the mainstream action, overflows the leading edge of the next blade, and then flows downstream into different flow passages, aggravating backflow and secondary flow separation at the blade inlet, which seriously damaged the spatial structure of the inlet flow. This resulted in the earlier occurrence of stall. With the increase of tip clearance, the tip leakage vortex develops along the radial direction to the middle of the flow channel and serious flow separation phenomenon occurs in the downstream channel, which induces the deep stall. Under the 0.8 mm tip clearance, the whole impeller outlet passage is almost blocked by the backflow of the guide vane inlet, and a deep stall was induced.

Aerodynamic analysis and design optimization of a centrifugal compressor impeller considering realistic manufacturing uncertainties

Centrifugal compressor impeller blades inevitably suffer from manufacturing uncertainties. Such manufacturing uncertainties result in geometric deviations of blade profiles, and have been increasingly recognized to be detrimental to compressor performance. However, relevant studies on the uncertainty analysis and design optimization of centrifugal impeller blades are quite rare. The effect of realistic manufacturing uncertainties on impeller aerodynamic performance and flow field still remains unclear. Here we present a comprehensive investigation on deterministic analysis, uncertainty analysis and design optimization of a centrifugal compressor impeller with considerations of three-dimensional realistic manufacturing uncertainties. Through statistical analysis of blade profile measurements of machined centrifugal impellers, both the blade camber and thickness errors are confirmed to obey Gaussian distributions. The deterministic analysis results show that the positive thickness errors near the main blade leading edge are mainly responsible for impeller performance degradations because of aggravated flow separations especially at large flow rate. A bi-fidelity metamodel, namely sparse grid stochastic collocation-support vector regression (SGSC-SVR), is used to balance the efficiency and accuracy of the uncertainty analysis. The mean impeller performance is found to become more deteriorated as the mass flow rate increases while the uncertain band is smaller at the design point than at off design points. Finally, a sequential infilling sampling-based optimization method is employed to solve the design optimization. It is demonstrated that reduced blade angles are able to compensate the adverse effect of positive blade thickness errors and thus enhance the impeller performance robustness against manufacturing uncertainties. The present study lays a theoretical foundation for the further uncertainty quantification and robust design of advanced centrifugal compressors.

Theoretical Evaluation of Flow Electronic Rate at Au/TFB Interface

This investigation presents a quantum model for electron transfer allows us to calculate the flow electronic transfer rate through metal/molecule devices. The flow electronic transfer rate at interfaces between Au metal contact with poly(9,9’-dioctylfluorene-co-bis-N, N’-(4-butylphenyl)-diphenylamine) (TFB) and solvents media with polarity is ranging from 0.315 for Diethyl ether to 0.5361 for Methanol is investigated via quantum theory of donor acceptor model. The flow rate are large with Au energy level alignment with TFB levels has been found when the potential barrier at interface is 0.066 eV with Diethyl ether solvents. Flow electronic transfer rate for Au/TFB system with methanol solvent decreased cross interface when the potential barrier is as large as 0.122 eV. This lead to produce accumulate the charges on the both side of Au and TFB when the potential at interface is large. The resulting slow transfer of electrons cross interface. Furthermore, Au metal contact on TFB molecule interface frequently with different solvents media and have large flow rate with Diethylether solvents and low flow rate with Methanol.

Effect of Different Blade Numbers on the Radial Force of Pump as Turbine in Transient Process

In order to analyze the influence of the number of blades on the radial force characteristics of pump as turbine during the variable flow rate transition process, six impellers with different number of blades are designed. On the basis of verifying the correctness of the numerical calculation method by the external characteristic experiment, the steady and unsteady numerical simulation of each scheme is carried out by ANSYS-CFX software, the radial force characteristics on impellers with different schemes are compared and analyzed. The results show that during the transition process of variable flow rate, the radial force vector and its fluctuation range on the impeller gradually decreases with the increase of the number of blades. The radial resultant force obviously increases with the increase of time in the transition to large flow rate, and obviously decreases with the increase of time in the transition to small flow rate. The dominant frequency of the radial force is equal to leaf frequency, and the pulsation amplitude of the radial force of Z9 is the minimum in both transition processes. In the transition process of variable flow rate, when the number of blades is Z9, the efficiency is the highest, the radial force on the impeller is the minimum, and the pulsation amplitude of the radial force is also the smallest, so for this pump as turbine, the value of blade number equals 9 is the optimal.