Diffusion Angle Research Articles

Orthogonal Experiments on the Key Structural Parameters Optimization of Mine Dust Removal Foam Generator by Fluent Numerical Simulation

As an important countermeasure of dust control in mine, the efficiency of foam generator is seriously affected by the key structural parameters itself, including the baffle inclination angle (θ), the disturbance flow distance (L) and the diffusion angle (α). To ascertain the relation of the three parameters, the axial cross section velocity field and gas phase distribution field in the foam generator were simulated by FLUNET software and mixture method, standard κ-ε turbulence model and SIMPLEC algorithm. At the same time, the orthogonal tests were conducted for reducing amount of calculation. The results show that when θ = 30°, L = 22mm, α = 74°, the foam generator is on the optimal working condition. And the importance degree of the key structural parameters is successively θ, L and α. It can play a certain reference role in the actual design of the foam generator for the dust removal technology improvement of the foam generator.

Structure optimization of submerged water jet cavitating nozzle with a hybrid algorithm

ABSTRACTIt is critical to obtain a suitable geometry for a cavitating nozzle of submerged water jet, since a suitable geometry determines its cavitation intensity and cavitation distribution. This paper puts forward a water jet cavitating nozzle optimization platform aiming to improve its axial maximum vapor volume fraction. Considering the influence of all eight geometric parameters of the nozzle itself, a hybrid optimization algorithm is developed to optimize the nozzle by combining with the CFD technique. After the optimization, the optimal geometry results to a 9.41% increment in the axial maximum vapor volume fraction at 50 m underwater depth, and improves the cavitation effect obviously especially in deeper water. From the results, it is found that the cylindrical section diameter, contraction angle and diffusion angle have a great influence on the axial maximum vapor volume fraction, while the inlet diameter have the least effect on the same. The optimization presented in this study can lay the foundation for further study on water jet cavitating nozzle.

Design and Enhancement of Thermal Flow Characteristic in an Annular Diffuser under Turbulent Flow

The annular diffuser is an expansion area, which, despite its simple structure, is very important in some engineering and thermal applications. In the present research, numerical simulations were performed to investigate the temperature field and flow structure characteristics in an annular diffuser. The hub of the annular diffuser consisted of a straight semi-dimpled tube SSDT. Three different diffuser wall angles (α) 1.8°, 3.6° and 5.4° with inlet Reynolds number 1.5 × 104 were studied in details with air as a working fluid. The computational fluid dynamics CFD was used to simulate the model in a turbulent flow. The standard k-ε turbulence model was used to complete the governing equations. The numerical results, mainly the temperature distribution, pressure drop and velocity distribution for the airflow in the annular diffuser fitted with SSDT for different diffuser wall angles α were obtained and compared. It was observed that as the wall diffuser angle α increases, the enhancement of the temperature distribution and the velocity distribution decrease while the pressure drop rate increases. The maximum temperature distribution and velocity distribution were completed by diffuser wall angle α1 = 1.8° whereas, the highest pressure drop achieved by diffuser wall angle α3 = 5.4°.

Experimental Study on Jet Breakup Morphologies and Jet Characteristic Parameters of Non-circular Nozzles under Low-intermediate Pressures

Abstract. A High-Speed Photography (HSP) technique was used to investigate the breakup process and flow behavior of low-intermediate pressure water jets issued from square and triangular shaped nozzles. The non-circular orifices were designed based on the principle of equal flowrate with the same pressure in relation to the circular orifice. The breakup morphologies and boundary structures of the jets were studied under different nozzles and working pressures. Two forms of droplet formation and the process of droplet formation, in addition to the jet breakup lengths, initial amplitudes of surface waves and jet diffusion angles of different nozzles were evaluated. It was found that the jet presented a good continuity and fluidity in the initial section, and the fluid bands gradually appeared due to the air resistance and the jet break up as the disturbance intensifies. The degree of jet breakup was enhanced with the increase of pressure and cone nozzle angle. The random appearance of the fluid band structures and the dactylitic textures near the nozzles for non-circular jets appeared earlier than those produced by the circular jets. The small satellite droplets with different shapes and sizes were seen inside and outside the jet interface. Triangular jets exhibited the shortest breakup length, the initial amplitude of surface wave, and the diffusion angle of the jet at the same pressure were largest compared with square and circular jets. Two index equations of jet characteristic lengths and equivalent diameters of both circular and non-circular nozzles were fitted with a relative error of less than 10%, which means the fitting formulas are accurate. Keywords: Breakup length, High-speed photography, MATLAB simulation, Non-circular nozzle, Surface wave amplitude.

A modified Langevin-Debye model for investigating the electro-optic behaviour of de Vries smectic liquid crystals

ABSTRACTAn external electric field applied across a planar-aligned cell in Smectic A* phase of de Vries smectic liquid crystal induces director redistribution over a cone, resulting in a substantial increase in the birefringence and the apparent optical tilt angle. Such an electro-optic response is modelled by Shen et al. [Y. Shen et al., Phys. Rev. E 88, 062504 (2013)], who modified their previous hollow cone with a diffuse cone model by introducing the molecular distribution function limited over a range of tilt angles, that lie in between θmin and θmax. The limits in these two tilt angles are assumed to be temperature independent though the tilt angle in between the two values can be temperature dependent. However, the high resolution measurements of birefringence and the layer thickness indicate the presence of temperature dependent diffuse cone angle in SmA* phase.. In the proposed model, we replace θmin by θT, a temperature dependent fitting parameter and the change shows that a better fit of the experimental data to the model is obtained. We determine the temperature dependence of θmin and show that this angle increases as SmA* to SmC* phase transition temperature is approached.

Ultrasonic Transmission Tomography Sensor Design for Bubble Identification in Gas-Liquid Bubble Column Reactors.

Scientists require methods to monitor the distribution of gas bubbles in gas-liquid bubble column reactors. One non-destructive method that can potential satisfy this requirement in industrial situations is ultrasonic transmission tomography (UTT). In this paper, an ultrasonic transmission tomography sensor is designed for measuring bubble distribution in a reactor. Factors that influence the transducer design include transmission energy loss, the resonance characteristics and vibration modes of the transducer, and diffusion angles of the transducers, which are discussed. For practical application, it was found that an excitation frequency of 300 kHz could identify the location and size of gas bubbles. The vibration mode and diffusion also directly affect the quality of the imaging. The geometric parameters of the transducer (a cylinder transducer with a 10 mm diameter and 6.7 mm thickness) are designed to achieve the performance requirements. A UTT system, based on these parameters, was built in order to verify the effectiveness of the designed ultrasonic transducer array. A Sector-diffusion-matrix based Linear Back Projection (SLBP) was used to reconstruct the gas/liquid two-phase flow from the obtained measurements. Two other image processing methods, based on SLBP algorithm named SLBP-HR (SLBP-Hybrid Reconstruction) and SLBP-ATF (SLBP-Adaptive Threshold Filtering), were introduced, and the imaging results are presented. The imaging results indicate that a gas bubble with a 3 mm radius can be identified from reconstructed images, and that three different flow patterns, namely, single gas bubble, double gas bubble with different diameters, and eccentric flow, can be identified from reconstructed images. This demonstrates that the designed UTT sensor can effectively measure bubble distribution in gas-liquid bubble column reactors.

Experimental study on jet flow characteristics of fire water monitor

Fire water monitor is an important part of a sprinkler system. In this study, the jet flow characteristics of the external jet of the fire water monitor are studied. The water jet system is used to launch the water jet experiment under six pressures. A high-speed camera is used to obtain the water jet images. The feature extraction of water jet is obtained based on image processing technology, and it is used to study the jet diffusion angle and bundling of the fire water monitor under different pressures. The results of this study show that the jet pressure is an important parameter, which has a great influence on the cluster and surface characteristics of the jet. The fire water monitor has a limited range of pressure. When the pressure is constant, the jet distance determines the size of the air acting on water column, so the cluster and surface characteristics of the water column have changed obviously with the jet distance.

Investigation of the Influence of Inclination Angle and Diffusion Angle on the Film Cooling Performance of Chevron Shaped Hole

The film cooling performance of chevron holes with different inclination angles and exit lateral diffusion angles has been studied experimentally and numerically. The inclination angles include 35° and 55°. The exit lateral diffusion angles include 20° and 25°. The film cooling effectiveness, heat transfer coefficient and discharge coefficient were measured on a flat plate model by transient liquid crystal measurement technique under four blowing ratios. The results show that the large inclination angle reduces the film cooling effectiveness. The influence of diffusion angle has two aspects: the large diffusion angle leads to mainstream ingestion and decreases film cooling effectiveness at M=1.0 and 1.5; however, the large diffusion angle increases the film cooling effectiveness at high blowing ratio of 2.0, because the larger hole exit area decreases the normal momentum component of the film jet. The large inclination angle decreases the heat transfer coefficient in the right downstream region at M=0.5 and 1.0. The large diffusion angle enhances the heat transfer in the right downstream of the holes in M=0.5~1.5 conditions. The chevron hole with large inclination angle generally has the highest discharge coefficient.

Modeling hydrodynamic cavitation in venturi: influence of venturi configuration on inception and extent of cavitation

Hydrodynamic cavitation (HC) is useful for intensifying a wide variety of industrial applications including biofuel production, emulsion preparation, and wastewater treatment. Venturi is one of the most widely used devices for HC. Despite the wide spread use, the role and interactions among various design and operating parameters on generated cavitation is not yet adequately understood. This article presents results of computational investigation into the cavitation characteristics of different venturi designs over a range of operating conditions. Influence of the key geometric parameters such as the length of venturi throat and diffuser angle on the inception and extent of cavitation is discussed quantitatively. Formulation and solution of multiphase computational fluid dynamics (CFD) models are presented. Appropriate turbulence and cavitation models are selected and solved using a commercial CFD code. Care was taken to eliminate the influence of numerical parameters like mesh density, discretization scheme, and convergence criteria. The computational model was validated by comparing simulated results with three published data sets. The simulated results in terms of velocity and pressure gradients, vapor volume fractions and turbulence quantities, and so on, are critically analyzed and discussed. Diffuser angle was found to have a significant influence on cavitation inception and evolution. The length of the venturi throat has relatively less impact on cavitation inception and evolution compared to the diffuser angle. The models and simulated flow field were used to simulate detailed time–pressure histories for individual vapor cavities, including turbulent fluctuations. This in turn can be used to simulate cavity collapse and overall performance of HC device as a reactor. The presented results offer useful guidance to the designer of HC devices, identifying key operating and design parameters that can be manipulated to achieve the desired level of cavitational activity. The presented approach and results also offer a useful means to compare and to evaluate different designs of cavitation devices and operating parameters. © 2018 American Institute of Chemical Engineers AIChE J, 65: 421–433, 2019

A design analysis of piezoelectric-polymer composite-based valveless micropump

ABSTRACTThis paper presents the three-dimensional numerical simulation of a micropump, including diffuser and analytical modelling of the micropump flow rate. The numerical simulation of the diffuser is performed in all possible flow regimes to optimize its geometry for maximum efficiency. The deflection of the piezoelectric polymer composite circular actuator is analytically solved by theory of bending plates to determine the volumetric change and flow rate. The result is then extended for actuator bonded to diaphragm of the micropump considering it as bilaminar plates. From the simulation results, it is found that and the diffuser angle >30° results in flow recirculation and reduction in the efficiency. The flow rate of the micropump obtained from analytical model and the numerical simulation are found to be similar.

Analytical and numerical prediction of the flow and performance in a claw vacuum pump

This paper presents the use of a 0-D thermodynamic chamber model and 3D Computational Fluid Dynamics (CFD) to predict the performance of a claw vacuum pump. The 0-D model can be used for pump sizing during the initial design or concept phase. Parameters such as the compression ratio (π), the built-in volume ratio (θ), the volumetric efficiency (ην), the isentropic efficiency (ηis), the volume compression ratio (υi) and the intermediate pressures (pz, pi) are essential to the performance of such machines. To determine these parameters, the volume-curve of the pump is determined as a function of the rotational angle. Using this model, it is possible to enhance the pump performance. For example, by decreasing the carry-over volume and by limiting or preventing over and under compression which can lead to an increase in the power consumption. This paper presents the results of the 0-D thermodynamic chamber model followed by the results of the 3D CFD simulations and validation with measurement data. After the benchmarking, CFD was used to improve the aerodynamic design of the pump discharge tube which led to a decrease in the power consumption of the pump compared to the baseline case. The diffuser angle was decrease to limit the boundary layer size and flow separation and recirculation at the discharge. When left unchecked, it can lead to large pressure drop and to an increase in the power consumption. Using CFD, other phenomenon such as such as pressure jump, which is commonplace in such machines, can be prevented. Otherwise, it can lead to shock wave generation and to noise in the pump.

Improvement of Centrifugal Pump Performance by Using Different Impeller Diffuser Angles with and Without Vanes

ABSTRACTThis study aims at improving the performance of a centrifugal pump by using different angular diffusers on the downstream side of the centrifugal pump impeller. Numerical and experimental studies have been carried out on different vaned and non-vaned diffuser with three different wall divergence angle (α) of 0°, 5° and 10° to achieve that purpose. The data analyses show good agreement between the numerical and experimental results. They reveal profound effect of the divergence angle (α) of angular vaned diffuser on the head and overall efficiency of centrifugal pumps especially at high flow rates as they broaden operating region of the centrifugal pump. In fact it is found that the head and overall efficiency of impeller with vaned diffuser α = 10° enhance by 15.4 and 9 percent respectively compared to that of centrifugal pump with no vaned diffuser at high flow rates. Furthermore the head and overall efficiency of impeller with vaned diffuser α = 10° increase by 5.7 and 7 percent respectively in comparison with the impeller with vaned diffuser α = 0°.

A Novel Method for Designing Fan-Shaped Holes With Short Length-to-Diameter Ratio in Producing High Film Cooling Performance for Thin-Wall Turbine Airfoil

An experimental investigation of the geometrical parameter effects on the film cooling performance of a fan-shaped hole was conducted on a low speed flat-plate facility. The pressure sensitive paint (PSP) technique and steady liquid crystal (SLC) technique were employed to determine the adiabatic film cooling effectiveness and heat transfer coefficients, respectively, for a blowing ratio ranging from 0.3 to 3 and a density ratio of DR = 1.5. Several geometrical parameters were investigated, including lateral expansion angle, length-to-diameter ratio, and hole entrance shape. Local, laterally averaged, and area-averaged adiabatic film cooling effectiveness, heat transfer coefficients, and net heat flux reduction (NHFR) were shown to provide a comprehensive understanding on the geometrical parameter effects on the thermal performance. A novel method was proposed for designing a fan-shaped hole with short length-to-diameter ratio to design to achieve high film cooling performance. The original and optimized fan-shaped holes were compared in terms of adiabatic film cooling effectiveness, heat transfer coefficients, and NHFR. Results showed that the optimized fan-shaped hole with short length-to-diameter ratio, large lateral diffusion angle, and slot hole entrance shape obtained highest overall thermal performance. It demonstrated the feasibility of adopting the proposed design method to design fan-shaped holes applied in thin wall gas turbine blades.

ANALISIS UNJUK KERJA VENTURI VAKUM DENGAN VARIASI DIMENSI DAN VISKOSITAS FLUIDA

In the venturi vacuum, to produce a vacuum condition, a liquid fluid flow is
 required which is driven by a centrifugal pump through the venturi passage. The
 amount of vacuum pressure generated by venturi is influenced by the increase of flow
 velocity due to the diminution of the cross-section which follow Bernoulli principle.
 The flow velocity on the channel is influenced by the discharge generated by the
 pump following the continuity law. In addition to speed, channel input pressure is
 also a variable that affects venturi vacuum pressure. Performance of a setrifugal pump
 in the form of flow and pressure discharge greatly affect venturi vacuum
 performance, so that the variables affecting the performance of a setrifugal pump
 such as fluid viscosity, will also affect the venturi vacuum performance.
 Therefore, it is necessary to evaluate the effect of viscosity and venturi dimension on
 vacuum pressure and discharge into the main objective of this study so that the
 variables can improve the venturi vacuum pump performance.
 In this study liquid fluid with three variations of viscosity flowed through three
 different venturi dimension variations. Then measured parameters that occur, such as
 fluid flow fluid flow, fluid pressure fluid and vacuum pressure that occurs in the tube.
 From this study obtained, at the angle of diffuser 5o the lowest vacuum pressure of -
 66.75 cmHg occurs in water fluid with viscosity of 17 centipoise. Similarly, at the
 angle of the diffuser 6.5o the value of the lowest vacuum pressure is also produced by
 a water fluid of -68 cmHg which is the lowest value compared to other diffuser angles
 and other fluid viscosities. While at 8o diffuser angle, the lowest vacuum pressure
 value is also produced by water fluid of -64.5 cmHg.

Efficient photocatalytic hydrogen production by doped ZnS grown on Ni foam as porous immobilized photocatalysts

Ni-doped ZnS nanomaterials were decorated on the surfaces of porous Ni foam as immobilized photocatalysts for H2 production by a solvothermal process. Effects of the Ni dopant content on the photocatalytic hydrogen production activity, morphology, optical property, crystalline properties, surface wetting, and photocurrent were studied by scanning electron microscopy (SEM), X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), photoluminescence (PL), photocurrent response, and contact angle meter. The surface changed from hydrophobic to superhydrophilic by decorating Ni-doped ZnS on the NiO/Ni foam substrate. A mechanism is proposed to elucidate the band positions of ZnS and NiO, together with the transfer of photoinduced electrons among ZnS, NiO, and Ni foam. The Ni-doped ZnS/NiO/Ni foam photocatalyst NZ5 showed much higher photocatalytic activity because of the matched band structure and the high conductivity of Ni foam. Meanwhile, the porous texture and superhydrophilic nature of the photocatalyst favor the light trapping, effective mass transfer of reactant molecules, and provide large contact area. Ni doping leads to a decreased band gap. The highest photocatalytic H2 generation activity reached 2500 μmol/g−1 h−1. After being operated for 3 cycles, the activity of the third run was 85% of that obtained at the first run.

Simulation of positron and electron elastic mean free path and diffusion angle on DNA nucleobases from 10 eV to 100 keV

Positron and electron interaction collisions in living cells are efficiently simulated by Monte Carlo (MC) codes where huge data tables are needed. Present study provides detailed results of charged particles elastic interactions needed in MC on DNA nucleobases (adenine, thymine, cytosine and guanine, deoxyribose, and phosphoric acid). Indeed, electron and positron elastic cross sections, elastic mean free paths, and elastic angular distributions P(θ) are calculated from 10 eV to 100 keV using a corrected form of the independent atom method taking into account the geometry of the biomolecule. Our calculated results are compared with theoretical data available in the literature in absence of experimental data, in particular for positron. Moreover, our numerical results are presented in analytic format modeled to be used for fast sampling in the MC simulation of elastic collisions; particularly, we provide a useful analytic expression for sampling the elastic diffusion angle. For positron collisions on adenine, the relative error between numerical and analytic elastic diffusion angles is not exceeding 2% in the energy full range 10 eV to 100 keV.

Numerical and Experimental Investigations on Aerodynamic Behavior of the Ahmed Body Model with Different Diffuser Angles

Due to many restrictions applied by the necessity of fulfilling dimensional analysis in a numerical-experimental research and also the limits in experimental facilities a Low Reynolds Number simulation seems to be widespread. In this paper, effects of the diffuser angle on the aerodynamic behavior of the Ahmed body have been investigated for low Reynolds number flows. Numerical simulations were performed by solving the Reynolds Averaged Navier-Stokes (RANS) equations combined with different turbulence models. The Finite Volume Method (FVM) is used for simulations in Fluent 6.3.26 Software. The main objectives of the study are to improve the aerodynamic design of the body, analyzing the flow field to understand the nature of these improvements and reaching a suitable and reliable experimental-numerical setup for such a flow. Finally, it was concluded that the SST k-ω turbulence model with transitional flow corrections is the best choice. From the flow simulation and obtained experimental data, it was concluded that that drag coefficient is a function of three main phenomena. Results showed that the drag coefficient has its minimum value at a specific diffuser angle (8◦) and further increases in the angle lead to higher drag coefficient. On the other hand, the lift coefficient constantly decreases by increasing the diffuser angle. In order to show the validity of the numerical results, experimental data were obtained by measuring the drag and lift coefficients of scaled standard Ahmed body and a model with the diffuser angle of 8 degrees in a wind tunnel. Results confirmed that improvement of drag and lift coefficients occurs when diffuser region is considered for the Ahmed body. In addition, the flow field around the body was studied in detail to show the effects of the diffuser geometry on the aerodynamic characteristics of the body.

Characteristics of the pulsating jet flow through a dynamic glottal model with a lens-like constriction.

A computational study of the pulsating jet in a squared channel with a dynamic glottal-shaped constriction is presented. It follows the model experiments of Triep and Brücker (J Acoust Soc Am 127(2):1537-1547, 2010) with the cam-driven model that replicates the dynamic glottal motion in the process of human phonation. The boundary conditions are mapped from the model experiment onto the computational model and the three dimensional time resolved velocity and pressure fields are numerically calculated. This study aims to provide more details of flow separation and pressure distribution in the glottal gap and in the supraglottal flow field. Within the glottal gap a 'vena contracta' effect is generated in the mid-sagittal plane. The flow separation in the mid-coronal plane is therefore delayed to larger diffuser angles which leads to an 'axis-switching' effect from mid-sagittal to mid-coronal plane. The location of flow separation in mid-sagittal cross section moves up- and downwards along the vocal folds surface in streamwise direction. The generated jet shear layer forms a chain of coherent vortex structures within each glottal cycle. These vortices cause characteristic velocity and pressure fluctuations in the supraglottal region, that are in the range of 10-30 times of the fundamental frequency.

동익 피치각 및 디퓨져 각도가 축류팬의 공력 성능에 미치는 영향

동익 피치각 및 디퓨져 각도가 축류팬의 공력 성능에 미치는 영향

Numerical investigation of water droplets trajectories during natural gas dehydration inside supersonic separator

Reliable estimation of the condensed water droplets trajectories inside Supersonic separators (3Ss) during the dehydration process is essential for proper design and safe operation. Most of previous researches ignored the actual sizes of condensed droplets and predicted the particles trajectories for pre-specified diameters. In this article and for the first time, real trajectories are computed by considering the actual particle size distribution (PSD) of the condensed droplets in the presence of swirl, nucleation and growth processes during the dehydration of methane rich natural gas (MRNG) inside Laval nozzle for various diffuser angles. Furthermore, the injection of water droplets to facilitate the condensation process has not been addressed previously.Our simulation results indicate that even for the most optimal geometry and at extremely large centrifugal accelerations of 500,000 g, the condensed particles from MRNG are exceedingly small and can't reach the 3S walls for practical straight tube lengths. Our findings are verified with several previously reported experimental measurements and theoretical investigations results, borrowed from literature. To ensure proper dehumidification, sufficiently large water droplets are assumed to be injected preferably after the throat location. The computed results indicate that by injecting 5 μm diameter particles into MRNG of Khangiran refinery sweet gas stream and increasing its wetness fraction up to 0.12, the dehydration process is successfully achieved in an optimally designed supersonic separator.