Uniform Mass Flow Research Articles

Improving heat transfer and compressed air consumption in low pressure die casting of aluminum wheels

Automotive wheels made from aluminum alloys are generally manufactured using the Low-Pressure Die Casting (LPDC) method. The molten aluminum is pressurized and filled into the cavities between the molds, and it is cooled using cooling channels in the LPDC. While the cooling fluid can be either air or water in industrial applications, only air cooling is utilized within the scope of this study. The primary expenditures of the process are attributed to the cycle time and the consumption of compressed air. In industrial settings, the primary coolant supply, emanating from either one or two inlet sources, is systematically channeled through a series of nozzles. These nozzles are strategically designed to impinge air onto specific areas of the mold pockets, ensuring efficient cooling.This research focuses on enhancing the cooling channels and mold pocket regions in LPDC through a combination of experiments and Computational Fluid Dynamics (CFD) integrated with Conjugate Heat Transfer (CHT) analyses. The study involves designing cooling channels to achieve a uniform mass flow distribution at the nozzle outlets, and optimizing the mold pocket regions. This optimization resulted in a 46% reduction in compressed air flow while maintaining comparable levels of heat transfer in the optimized mold pocket design. Moreover, flow rate non-uniformity at nozzle outlets was reduced from 11.5% to 2.0% to achieve uniform cooling and temperature distribution across the wheel spokes. An experimental setup with a cooling pipe network allowed simultaneous flow rate measurements from 20 outlets using flow rate sensors.The improved cooling channel and mold pocket design were adapted to the LPDC, and 20 aluminum alloy wheels were successfully cast with a 46% lower mass flow rate. All these wheels were tested in accordance with the relevant test specifications and the results obtained were assessed as compliant according to certain limits.

A comparison of oscillating sweeping jet and steady normal jet in cooling gas turbine leading edge: Numerical analysis

Impinging jets have emerged as a prominent cooling technology in the gas turbine industry. With the addition of fluidic oscillators as heat removal devices, steady-state impinging jets can be converted to sweeping impinging jets, presenting an opportunity to improve the heat transfer performance of current impinging jets by covering a larger cooling surface area on the leading edge of a gas turbine blade. Sweeping jets are self-oscillating devices that operate based on the Coanda effect, making them self-sustaining. In this study, the flow and heat transfer performance of an array of seven steady and sweeping impinging jets were investigated using the unsteady Reynolds-averaged Navier-Stokes turbulent SST k-ω model. The sweeping jet impingement improved the heat removal performance by cooling a larger surface area of the leading edge with a constant heat flux and by improving the overall time-averaged cooling effectiveness. Compared with the steady jet case, the sweeping jet case shows an improvement in heat transfer of 12.2%. Further, the use of fluidic oscillators (sweeping jets) produced a more uniform mass flow rate distribution from all jets compared with a simple jet.

Modeling of a continuous physical vapor deposition process: Mass transfer limitations by evaporation rate and sonic choking

• Novel evaporation boundary condition is proposed to consider Hertz-Knudsen limitation. • A comprehensive numerical model for continuous PVD processes in OpenFoam is presented. • Non-isentropic losses reduce discharge; this effect decreases with melt temperature. • The isentropic overestimate is 110%–150%, that of the new CFD model only 30%. • Numerical model predictions are relatively insensitive to unknown process parameters. In recent years, Physical Vapor Deposition has been advanced to a continuous process which makes it amenable for in-line, high-quality and energy-efficient galvanization. To achieve the high and uniform mass flow required for in-line production, a Vapor Distribution Box is used, in which the zinc is evaporated. The zinc fills the Vapor Distribution Box at a relatively high pressure and leaves into the coating chamber via nozzles. A reliable modeling approach that can be used in the design and optimization of Vapor Distribution Boxes is as yet not available in the literature. The present paper analyses which phenomena play a major role and therefore have to be included in a simulation model of continuous Physical Vapor Deposition processes, and identifies process parameters which have a significant impact on deposition rate and uniformity. To this end, a model for the flow and heat transfer is developed based on the numerical solution of the compressible Navier–Stokes-Fourier equations in combination with the Launder and Sharma low-Reynolds k- ∊ turbulence model, using the open-source CFD-library OpenFOAM. To account for the vapor mass flow to be limited by both evaporation and sonic choking, a novel inlet boundary condition is proposed based on the Hertz-Knudsen condition. Results from the CFD model are compared to those of analytical models based on isentropic flow, the influence of various modeling parameters is evaluated against experiments, and sensitivity of the process to various process parameters studied. The proposed numerical model predicts mass flow rates with a much better accuracy than analytical models previously proposed in the literature. The latter overpredict the mass flow rate by a factor of 2.1–2.5, whereas the proposed numerical model overpredicts only by a factor of 1.3. Next to the novel Hertz-Knudsen boundary condition, the inclusion of viscous effects is found to be crucial to achieve this improvement, since viscous effects – especially in the boundary layer inside the nozzles – severely reduce the mass flow. The numerical model is shown to be only weakly sensitive to uncertainties in the evaporation coefficients and metal vapor viscosity. For the device studied, the mass flow discharge efficiency was found to be relatively low ( ≈ 40 % ). To increase this efficiency, viscous losses in the nozzle boundary layers have to be reduced, for instance by employing shorter or a bigger radius nozzles (possibly impairing nozzle-to-nozzle uniformity) or by employing a higher melt temperature and vapor pressure.

A novel mass flow controller for tandem hot rolling mills

In tandem hot strip rolling mills, the roll speed of the mill stands is synchronized to ensure a uniform mass flow. A uniform mass flow is desirable to keep the strip tension constant and thus avoid large movements of the loopers which are located between the mill stands in order to control the strip tension. This also improves the general thickness quality and prevents the strip from necking in case of too excessive strip tension. In typical state-of-the-art implementations, the roll speed is synchronized in a cascade master–slave control structure where the very last downstream mill stand serves as speed master and the upstream mill stands operate in a slave mode to make sure that the mass flow is kept constant. While the relation between the roll speeds in the classical synchronization control concept is typically constant, a thorough analysis of the mass flow reveals that the slip between the work rolls and the strip is time varying. Therefore, in order to ensure a uniform mass flow, a novel adaptive speed synchronization controller is proposed, which can be easily added to the existing control structure and is computationally undemanding. To this end, a mathematical model of the whole tandem mill including the complete control structure is derived and validated by measurements. Simulation results for this validated model prove that the proposed mass flow controller clearly outperforms the existing solution.

Unsteady Steam Turbine Optimization Using High-Fidelity Computational Fluid Dynamics

Abstract This paper presents the computational methodology and experimental investigations accomplished to enhance the efficiency of a turbine stage by applying non-axisymmetric profiling on the rotor hub wall. The experimental setup was a two-stage axial turbine, which was tested at “LISA” test facility at ETH Zurich. The first stage was considered to create the flow history for the second stage, which was the target of the optimization. The hub cavity of the second stage was designed with large dimensions as a requirement of a steam turbine. The goal was to optimize the interaction of the cavity leakage flow with the rotor passage flow to reduce the losses and increase efficiency. The computational optimization was completed using a genetic algorithm coupled with an artificial neural network on the second stage of the test turbine. Unsteady time-accurate simulations were performed using in-house developed “MULTI3” solver. Besides implementing all geometrical details (such as hub and tip cavities and fully 3D blade geometries) from the experimental setup into the computational model, it was learned that the unsteady upstream effect could not be neglected. A novel approach was introduced using unsteady inlet boundary conditions to consider the multistage effect while reducing the computational cost to half. The importance of this implementation was tested by performing a steady simulation on the optimized geometry. The predicted efficiency gain from steady simulations was 4.5 times smaller (and negligible) compared to the unsteady approach. Excluding the cavity geometry was also assessed in a different simulation setup showing 3.9% over-prediction in the absolute efficiency value. Comprehensive steady and unsteady measurements were performed utilizing pneumatic, fast response aerodynamic probe (FRAP), and fast response entropy probe (FENT) on the baseline and profiled test cases. The end wall profiling was found to be successful in weakening the strength of the hub passage vortex by a 19% reduction in the under-over turning. As a result, the blockage was reduced near the hub region leading to more uniform mass flow distribution along the span. The flow angle deviations at the higher span position were also corrected due to better control of the flow angles. Furthermore, the improvements were confirmed by reductions in entropy, secondary kinetic energy, and pressure unsteadiness. The accurate computational implementations led to an excellent agreement between the predicted and measured efficiency gain.

Visualization of refrigerant two-phase flow before and through distributor and evaluation of its performance

Abstract This paper presents an evaluation of the performance of a refrigerant distributor with visualization of the two-phase flow. The distributor is a typical conical design w/o the orifice for about 4 kW R134a system. Three factors influencing two-phase flow distribution are varied: mass flow rate, distributor inlet quality, and orientation. We looked at the uniformity of mass flow rates, evaporator inlet qualities, and capacities of each circuit. The authors built a transparent distributor following the exact geometry of an original distributor to visualize two-phase flow regimes exiting the expansion device and entering the distributor. We related flow regimes with distributor performance. A high-speed camera is used to capture two-phase flow regimes. After acquiring results for a baseline situation, the authors applied two approaches in an attempt to improve flow distribution: The first is manual adjustment of the resistance of each circuit individually to achieve uniform mass flow rates, and the second is the homogenization of the flow regime before division by adding an orifice in the distributor before separation to four channels. The average deviations of capacity for each branch are 9% for the baseline case, 3.3% for manual adjusting, and only 1.6% for the homogenization approach, stressing the importance of that simple strategy.

Granular flow behavior in a conveyor system: From local velocity profiles to mass flow rates

Predictability of consistent granular flow is critical in many industries. This exploration of behavior in a conveyor apparatus aims to fill a gap in knowledge of achieving a uniform mass flow rate by correlating local velocity profile data with summative mass measurements in both experiments and simulations. Differences between the two types of flow measurements indicate unwanted energy dissipation. In experiments, image data was collected for uniformly-sized particles in the bottom-driven flow conveyor belt system for which edge velocity profiles could be produced to measure local shear rates and estimate mass flow. These velocity relationships under different speeds of the belt and varied outlet sizes are compared to shear rates from gravity driven flow. Similarity in the linear profile transitioning to an exponential decay are observed but at shear rates substantially lower than dilated, free-surface flows. Simulations were conducted using LIGGGHTS discrete element model framework using the same dimensions for the conveyor system and particle sizes. Results show unique three-dimensional velocity profiles can produce similar mass flow rate behavior. The work continues to demonstrate computational models of granular flows with experimental validations can be used to evaluate customized designs in industrial applications, such as feeding unsteady biomass conversion reactors. Future work can be developed to evaluate granular materials that have random distribution of sizes, aspect ratios, and orientation.

Analysis and optimization of the manifolds of the HCCB blanket for CFETR

ABSTRACT Thermal-hydraulic performance is a challenging issue in helium-cooled ceramic breeder (HCCB) blanket design due to the extremely complicated working environment and the strict limits of materials temperature. The heat loads deposited on the HCCB blanket comprises of severe surface heat flux from plasma and the volumetric nuclear heat from neutron irradiation, which can be exhausted by the built-in cooling channels of the components. High pressure helium with 8 MPa, distributed from the coolant manifolds is employed as coolant in the blanket. The design and optimization of the manifolds configuration was performed to guarantee the accurate flow control of helium coolant. The flow distribution in the coolant manifolds was investigated based on the structural improvement of manifolds aiming at overall uniform mass flow rates and better flow streamline distribution without obvious vortexes. The peak temperature of different functional materials in the blanket under normal operating condition is below allowable material limits. It is found that the components in the current blanket module could be cooled effectively under the intense thermal loads due to the updated design and optimization analysis of manifolds.

Optimum design of the injection duct system of a stenter machine

Stenter machines are used for drying fabrics in the textile industry and have a heater, injection duct system, and fans inside a chamber. The injection duct system has ducts and air-injecting holes. Plane-type injection duct systems were investigated to obtain uniform airflow at the air-injecting holes. The flowfield of the injection duct systems was computed using ANSYS CFX with different heights of the duct end and different shapes for the air-injecting holes. There was a high mass flow rate at the air-injecting holes and high airflow circulation inside both plane-type and mountain-type ducts at the ends. The height of the duct end was varied between 40 mm and 160 mm. The injection duct systems were analyzed with four different shapes of air-injecting holes. The circular and elliptical holes had lower standard deviations of the mass flow rate than other shapes. Relatively uniform mass flow rates were obtained in the plane-type and mountain-type duct systems when the height of the duct end was 40 mm and the shape of the air-injecting holes was circular or elliptical. The developed injection duct systems were improved by obtaining a uniform mass flow rate at the air-injecting holes. A stenter prototype was fabricated with the developed injection duct system to confirm the numerical results. The developed injection duct system had better performance than the original system.

Numerical simulation of cell-to-cell performance variation within a syngas-fuelled planar solid oxide fuel cell stack

The cell-to-cell voltage variation in a planar solid oxide fuel cell (SOFC) stack is numerically investigated, considering the coupling effect of the heat transfer and uniform mass flow rate distribution between cells. The model integrates validated three-dimensional electro-chemical button cell sub-models with the structure of a real counter-flow planar SOFC stack. A uniform characteristic diagram is defined to analyse the variation of the cell voltage distribution in a planar SOFC stack. A quantitative index of uniformity is proposed to compare and explain the difference in the cell voltage distribution uniformity in planar SOFC stacks. The simulation results indicate that the distribution characteristics of the cell voltage within a planar SOFC stack are primarily determined by the combined effects of the mass flow rate distribution and temperature distribution. The mass flow rate distribution dominates the overall cell voltage distribution trend, and the temperature distribution mainly dominates the cell voltage distribution of the cell near the top and bottom of the stack due to the thermal effects. The simulation results also indicate the relative uniform cell voltage distribution in planar SOFC stacks in the case of using syngas as a fuel instead of hydrogen.

A screw-brush feeding system for uniform fine zinc oxide powder feeding and obtaining a homogeneous gas–particle flow

The most important requirements of gas–solid two phase flow feeding are a very uniform mass flow of fine particles and providing a homogeneous dispersed cloud of them. In this study, a screw-brush feeding device has been developed to feed fine zinc oxide powders and to achieve a homogenous gas–particle two phase flow by a minimum gas flow rate. The results of these experiments indicated that the performance of this feeding system without gas flow was better than a screw feeder alone, to stabilize the feeding of fine ZnO powder at low flow rates. Moreover, the results of experimental micrographs showed that the screw-brush system with a minimal amount of gas flow rate is able to reduce the mean aggregate size of the particle size distribution and could provide a homogeneous gas–particle flow.

Optimum design of the injection nozzle system of a three-drive jigger dyeing machine

A jigger dyeing machine is used to dye fabric across the width, which enables the fabric to be passed back and forth in a perfect dyeing bath. A three-drive jigger dyeing machine contains an injection nozzle system. The flowfield inside the injection nozzle system was computed using ANSYS CFX software and was evaluated by mass flow rate, velocity, and pressure. The injection nozzle system was observed by installing two different division plates and by changing the diameter and distance of the outlet holes to improve dyeing efficiency. The division plates have slits and holes help to distribute the dye liquid evenly over all the holes. The standard deviations of the mass flow rate of the division plates with slits and holes were 0.000551 and 0.000368, respectively. The effects of distance and diameter of the outlet holes were analyzed and evaluated by mass flow rate and standard deviation. The developed injection nozzle system of the jigger machine has more uniform mass flow rate. A diameter of 5 mm for the outlet holes and a distance of 50 mm between them were selected to manufacture a prototype. The prototype of the injection nozzle system of the three-drive jigger machine was manufactured and tested. The test results were compared with the computational results from the developed three-drive jigger dyeing machine, the original three-drive jigger dyeing machine, and a classic jigger dyeing machine.

Impact of flow-corrective insert on flow patterns in two-dimensional moving bed

This paper presents the study of the flow patterns inside a granular moving bed in a quasi-two-dimensional (2D) model of a granular moving bed filter (GMBF) vessel with vertical walls and a mass flow hopper. Fine quartz sand was chosen as the granular filter media in experiments. The related flow properties were measured by a Jenike Shear Tester. According to the flow properties of fine silica sand and Johanson's theory, a 2D moving-bed apparatus was built, with transparent walls and the flow-corrective insert to diminish the quasi-stagnant zones along the side walls. The flow patterns and velocity profiles of silica sand in the system with flow-corrective insert were studied experimentally, and the effect of the location of the flow-corrective insert on the internal flow patterns was investigated. The optimal placement of flow-corrective insert according to Johansson's theory was demonstrated to efficiently diminish the quasi-stagnant zones near the side walls. Little vertical shift of the flow-corrective insert from optimal position changed the stable and uniform mass flow pattern of moving bed into the funnel flow.

New Composite Models of Partially Ionized Protoplanetary Disks

We study an accretion disk in which three different regions may coexist: MHD turbulent regions, dead zones and gravitationally unstable regions. Although the dead zones are stable, there is some transport due to the Reynolds stress associated with waves emitted from the turbulent layers. We model the transport in each of the different regions by its own $\alpha$ parameter, this being 10 to $10^{3}$ times smaller in dead zones than in active layers. In gravitationally unstable regions, $\alpha$ is determined by the fact that the disk self-adjusts to a state of marginal stability. We construct steady-state models of such disks. We find that for uniform mass flow, the disk has to be more massive, hotter and thicker at the radii where there is a dead zone. In disks in which the dead zone is very massive, gravitational instabilities are present. Whether such models are realistic or not depends on whether hydrodynamical fluctuations driven by the turbulent layers can penetrate all the way inside the dead zone. This may be more easily achieved when the ratio of the mass of the active layer to that of the dead zone is relatively large, which in our models corresponds to $\alpha$ in the dead zone being about 10% of $\alpha$ in the active layers. If the disk is at some stage of its evolution not in steady-state, then the surface density will evolve toward the steady-state solution. However, if $\alpha$ in the dead zone is much smaller than in the active zone, the timescale for the parts of the disk beyond a few AU to reach steady-state may become longer than the disk lifetime. Steady-state disks with dead zones are a more favorable environment for planet formation than standard disks, since the dead zone is typically 10 times more massive than a corresponding turbulent zone at the same location.

연료전지 공기판의 구조적 변형을 고려한 유동 해석과 실험

연료전지의 박막면은 공기판에 비해 변형이 쉬운 재질로 이루어져 있다. 박막면의 구조적 변형에 따라 채널 단면의 형상이 바뀔 수 있고, 채널의 형상이 변하면 유통특성은 크게 달라질 수 있다. 연료전지의 공기판을 설계할 때에 유동 특성은 성능을 좌우하는 중요한 요소이다. 설계된 공기판의 검증을 위해서는 유동 특성을 파악하고, 유동 특성이 효율적인 성능을 갖기 위한 조건을 만족시키는가를 알아보아야 한다. 본 연구에서는 공기판의 유동 특성을 파악하기 위해 유동해석을 수행하였고, 동일한 조건에서의 실험을 수행하여 해석결과를 검증하였다. 그리고 박막면의 구조적 변형에 의한 유동 특성의 변화를 알아보기 위하여 박막면과 공기판의 구조해석을 수행한 결과를 이용하여 박막면의 구조적 변형을 고려한 유동해석을 수행하여 박막면의 구조적 변형을 고려하지 않은 유동해석의 결과와 그 특성을 비교하였다. 그 결과 상당한 차이가 발생함을 알 수 있었다. 연료전지의 설계를 위해 해석 및 실험시 구조변형이 고려되어야 함을 규명할 수 있다. The porous media of a proton exchange membrane fuel cell (PEMFC) is made of deformable materials. The shape of cross sectional area in air plate channels has been changed by structural deformation of the porous media. The uniform mass flow rate and pressure are major factors for safe and efficient operation in the PEMFC. Two kinds of models are provided for the flow analyses. Deformable and undeformable porous media are considered for numerical analysis and experiment of the air plate model. The numerical flow analysis results with deformable and undeformable porous media has some discrepancy in pressure distribution. The pressure differences are measured in order to compare with numerical analysis results. Pressures are measured between inlet and outlet of the air plate. The numerical analysis and experimental results show similar pressure distribution. It is shown that the pressure drops in the two approaches are well matched each other. It is proven that the consideration of structural deformation is required in the numerical analysis/experiment for the PEMFC design.

Numerical and experimental studies to predict properties of gas discharged from a number of nozzles on a blow pipe

This study numerically and experimentally investigates the properties of pressure, temperature and mass flow rate of air discharged from a number of nozzles drilled on a blow pipe. In addition to deriving a set of equations to express the physical phenomena, this study also uses measurement equipment to measure the indispensable data used in the above equations. Consequently, the theoretical and experimental works complement each other. According to the results, the mass flow rate of the air pulse discharged from a nozzle depends on the position and diameter of the nozzle on the blow pipe. Furthermore, the direction of the discharged air pulse is not perpendicular to the blow pipe and has an inclined angle which also depends on the position of the nozzle on the blow pipe. Employing the model proposed herein, a uniform mass flow rate discharged from each nozzle can be obtained by adjusting the sizes of the nozzles on the blow pipe.

Design and Performance of Vaneless Volutes for Radial Inflow Turbines: Part 3: Experimental Investigation of the Internal Flow Structure

An experimental study is presented which considers the flow structure in the vaneless volute of a radial inflow turbine. The data show evidence of significant secondary flows around the volute. The volute tested generated a uniform ‘free vortex’ type structure and produced a uniform mass flow distribution around the periphery of the rotor. The flow within the volute was turbulent although this did not appear to have a detrimental effect on the overall performance of the volute. However, the turbine performance appears to be insensitive to variations in the inlet conditions in the axial direction.