Direction Of Fluid Flow Research Articles

Novel cross-flow electrostatic precipitator: Numerical and experimental study

ABSTRACT Electrostatic precipitators (ESP) are used extensively for removing particulates from a gas flow by charging the particles and then removing them in the presence of an electric field. Traditional ESP designs use the walls of the flow channel as the grounded collection surface. The objective of this present study is to evaluate a novel ESP configuration, recently patented by Ohio University’s Electrostatic Laboratory, in which an array of vertical surfaces of cylindrical geometry are placed in a crossflow configuration and used as grounded collection surfaces. A numerical approach was adopted by developing and implementing User-Defined Functions (UDFs) in ANSYS Fluent computational fluid dynamics (CFD) software to build a two-dimensional cross-flow ESP model, for the first time, for the gas flow and particulate capture. The two-dimensional numerical models proved useful in shedding light on the basics of the collection process in the novel cross-flow ESP. In the studied configuration, the collection of the particles on the collector surface was limited to the anterior and posterior surfaces of the first and second collection rows, respectively. The collection at the posterior surface of the second row presented interesting behavior, with the particles becoming entrained in the wake of the collectors and the electric field from the discharge electrode located downstream that was opposite to the fluid flow direction. The output of the simulation underestimated the experimental data. The lower efficiency prediction of the model could have been due to the vibration of the collection electrodes, collection by the mist formed in the wet system, and particle agglomeration in the experiments. The results of this study provide critical information in improving the particulate efficiency of novel cross-flow ESP and other similar cross-flow ESP systems. Implications: A novel Electrostatic precipitator (ESP) configuration (recently patented) was evaluated. A numerical approach was adopted to build a cross-flow ESP model, for the first time, for the gas flow and particulate capture. The collection of the particles on the collector surface was limited to the anterior and posterior surfaces of the first and second collection rows. Also, the particles were entrained in the wake of the collectors. The output of the simulation underestimated the experimental data. The results of this study provide critical information in improving the particulate efficiency of novel cross-flow ESP and other similar cross-flow systems.

Formation of Chromitite Seams and Associated Anorthosites in Layered Intrusion by Reactive Volatile-rich Fluid Infiltration

Abstract Drilling related to development of the platinum-group element deposit of the J-M Reef of the Stillwater Complex returned samples of a rare chromitite seam between anorthosite and norite in a discordant anorthositic body. Plagioclase core An concentrations are marginally higher and modestly reversely zoned on the norite side (average Ancore = 83·8; average Ancore – Anrim = –1·1) as compared with the anorthosite side (average Ancore 82·5; average Ancore – Anrim = +1·0). The anorthosites are also characterized by a slightly smaller average plagioclase grain size than plagioclase in the norite (1·41 mm and 1·54 mm, respectively). The chromite can contain single and polyphase inclusions of orthopyroxene, plagioclase, amphibole, biotite and Cl-rich apatite. These and other compositional and textural features, as well as inference from other discordant anorthositic bodies in the Banded series, are all consistent with a chromatographic model of chromite precipitation at a reaction front as a norite protolith reacts with a Cl-rich aqueous fluid saturated in plagioclase alone. Chromitite seam formation is modeled using an infiltration metasomatic model, in which a fluid becomes progressively undersaturated in pyroxene as it rises into the hotter part of the crystal pile. As this pyroxene-undersaturated fluid moves through a noritic protolith, it dissolves the Cr-bearing orthopyroxene to produce an anorthosite. Chromite precipitates at the reaction front between the anorthosite and the norite owing to liberation of Mg and Cr from pyroxene. Continuous redissolution and reprecipitation of chromite occurs as the pyroxene dissolution front moves in the direction of fluid flow, collecting the Cr lost from the anorthosite. Owing to Cr dissolved mainly as a neutral divalent cation complex, CrCl(OH)0, in the solution, but incorporated as a trivalent cation in chromite, the required redox reaction can involve concurrent precipitation of sulfide with chromite. This mechanism differs from some recent models in that the anorthosites are themselves replacement bodies and are not original precipitates from a magma nor formed by loss of mafic material by partial melting. The results show the need for experimental mineral solubility data at T and P conditions appropriate to upper crustal mafic–ultramafic intrusions.

CFD analysis of compressible flows in a convergent-divergent nozzle

A Nozzle is a mechanical device that uses pressure energy and fluid enthalpy to increase the outflow velocity and control fluid flow direction. To obtain the nozzle duct's shock pattern, the flow inside the nozzle must be supersonic with a Mach number greater than one. Experimentally, the shock pattern is obtained for a nozzle with a Mach number 2 and nozzle pressure ratio (NPR) equivalent to 7 and below. For Mach M = 2, the needed NPR is equal to 7.82 for correct expansion.. When the NPR is greater than 7.82, flow from the nozzles is under-expanded. For NPR less than 7.72 the flow from the nozzle is over-expanded. In this paper, the computational fluid mechanics (CFD) technique was used to simulate the nozzle flow based on the experimental investigation. A two-dimensional transient compressible flow of air through a supersonic nozzle was simulated using ANSYS fluent software. A time-dependent flow using the density-based implicit solver was useds to analyze the simulation results. The results illustrate that the CFD technique simulates the fluid flows and the formation of shock in a duct and gives useful information about fluid dynamics analysis.

Numerical Analysis of Thermal Convection in a CPU Chassis

Flow distribution and the effects of different boundary conditions are achieved for a steady-state conjugate (Conduction & Convection) heat transfer process. A plate fin heat sink with horizontal fin orientation along with a computer chassis is numerically investigated and simulated using software ANSYS CFX. Fin orientation of a heat sink changes the direction of fluid flow inside the chassis. For predicting turbulence of the flow inside the domain, a two-equation based k-ε turbulence model is chosen. The Reynolds number based on inflow velocity and geometry is found 4.2 × 103 that indicates that the flow is turbulent inside the chassis. To get proper thermal cooling, the optimum velocity ratio of inlet/outlet, dimension of inlet/outlet and different positions of outlet on the back sidewall of the chassis are predicted. Aspect velocity ratio between the inlet airflow and the outlet airflow has an effect on the steadiness of the flow. Mass flow rate depends on the dimension of the inlet/outlet. The horizontal fin orientation with 1:1.6 inlet-outlet airflow velocity ratio gives better thermal performance when outlet is located at the top corner of the chassis, near to the inner sidewall. Flow distribution and heat transfer characteristics are also analyzed to obtain the final model.

Percolation and Reynolds Flow in Elastic Contacts of Isotropic and Anisotropic, Randomly Rough Surfaces

In this work, we numerically study the elastic contact between isotropic and anisotropic, rigid, randomly rough surfaces and linearly elastic counterfaces as well as the subsequent Reynolds flow through the gap between the two contacting solids. We find the percolation threshold to depend on the fluid flow direction when the Peklenik number indicates anisotropy unless the system size clearly exceeds the roll-off wave length parallel to the easy flow direction. A critical contact area near 0.415 is confirmed. Heuristically corrected effective-medium treatments satisfactorily provide Reynolds fluid flow conductances, e.g., for isotropic roughness, we identify accurate closed-form expressions, which only depend on the mean gap and the relative contact area.Graphic

A tripartite graph based methodology for steady-state solution of generalized multi-mode vapor compression systems

The vapor compression system is the dominant technology in providing cooling and heating for residential, commercial, and industrial applications, and thus has significant energy and environmental impact. To predict the steady-state performance of vapor compression systems with a wide variety of configurations and operating modes, a general-purpose representation and solution methodology for vapor compression systems was developed using a component-based simulation architecture. The proposed methodology uses mass flow sign propagation to determine the working fluid flow directions. A tripartite-graph based tearing method was applied to reveal the most efficient component execution order, and to identify the corresponding tearing variables and residual equations. The resulting equations are solved using quasi-Newton method. The representation and solution methods are applied to six test systems: five R410A systems and one CO2 system, with capacities ranging from 10 to 100 kW. The test systems were chosen to represent a wide range of HVAC&R applications and operating modes, including residential heat pump, dual-circuit chiller, vapor injection system, supermarket system, and VRF system. The steady-state solutions of the test systems were verified and/or validated against existing simulations and experimental data. The observed worst case simulation energy imbalance across all cases was 0.91%, and the maximum system performance deviation was 8.94% compared to existing data.

Adopting inclined channel to decline the salinity mixing for rotary energy recovery device: Simulation and optimization

After years of research, the energy efficiency of energy recovery device has been raised to a high level, but the salinity mixing has not been effectively improved. Mixing will lead to a rise of high-pressure seawater salinity, which will increase the operating cost. In this paper, the computational fluid dynamics (CFD) simulation of the rotary energy recovery device (RERD) is carried out. It is found that the unstable flow caused by the non-parallel between the channel and the flow direction of fluid is an important reason for mixing. After the inclined channel structure is adopted, the non-parallel problem is improved. The formation of unstable flow is effectively controlled. Under the commercial product operating conditions, the volumetric mixing of the optimized device is reduced from 3.34% to 1.29%, showing the effectiveness of the structure.

Effects of variable heat flux at supercritical pressure in vertical pipe flow

It is a well-established fact that the heat transfer at supercritical pressure is complex and several numerical investigations have been conducted to address this issue. However, the focus of such studies remains uniform heat flux. Therefore, here we report the outcomes of direct numerical simulations performed with different profiles of non-uniform heat flux for supercritical carbon dioxide. Flow in a small pipe with a diameter of 2 mm is considered and vertical orientation with upward direction of fluid flow was chosen. The heat flux was varied in the axial and circumferential direction of the pipe. The circumferential heat flux induces the thermal stratification which resulted in a higher wall temperature at one side where heat flux was maximum. While axially varying wall heat flux results in the peak and valley in the wall temperature. The study also suggests that axially varying heat flux can be a possible strategy to control the heat transfer deterioration.

Effective fractures and their contribution to the reservoirs in deep tight sandstones in the Kuqa Depression, Tarim Basin, China

The Mesozoic Cretaceous reservoirs with a burial depth of more than 4500 m (14,764 ft) in the Kuqa Depression of the Tarim Basin are rich in natural gas resources, categorized under the typical deep tight sandstone reservoirs. Based on the analysis of cores, borehole image logs, thin sections, and laboratory testing, this study comprehensively evaluated the effective fractures in deep tight sandstone reservoirs and illuminated the contribution of effective fractures to the properties of these reservoirs. Tectonic fractures are an important component in these reservoirs. More than 70% of these fractures are not filled by any minerals, and their apertures vary greatly, measured from a few to hundreds of microns. The influencing factors of the effective fractures in these reservoirs include tectonism, diagenesis, and in-situ stresses. The fractures that are formed at earlier tectonic movements are more susceptible to be filled with minerals. The diagenetic facies of strong cementation exhibit a higher abundance of mineral-filled fractures, while dissolution can cause fracture apertures to become larger and makes them more effective. The unfilled fractures, which are parallel to the maximum horizontal stress component, show larger apertures and therefore are more effective. Laboratory tests indicate that effective fractures contribute less to the reservoir storage space, with an average porosity contribution rate of 3.95%. However, the permeability of samples with microscopic effective fractures was found 1-2 orders of magnitude higher than those without such fractures, since these fractures are main pathways that can connect scattered pores to improve the effectiveness of storage space. Moreover, the macroscopic effective fractures with a smaller angle from the maximum horizontal stress component decide the dominant reservoir fluid flow direction. Consequently, effective fractures exhibit a leading contribution to the reservoir permeability.

Flow field simulation and stress analysis of a shell-tube heat exchanger with spiral bend tubes

The porous media model was improved to simulate the flow field of a shell-tube heat exchanger with spiral bend tubes. The improved porous medium model can be used to control the fluid flow direction. On the tube side, the streamline was along the spiral bend tubes. The fluid velocities and pressure drops on the tube and shell sides agree well with the experimental values. The fluid flow on the shell side is little affected by the spiral bend structure. The thermal stress of the spiral bend tubes was analyzed. The thermal stress of the spiral bend tubes is much smaller than the thermal stress of the straight tube. The thermal stress at the bend part decreases with the increase of bending angles.

Conjugate heat transfer study comprising the effect of thermal conductivity and irreversibility in a pipe filled with metallic foams

A parametric study is proposed in this paper to examine heat dissipation rate and entropy generation of a forced convection in a horizontal pipe which is filled with high porous metallic foams. The study quantifies the effect of thermal conductivity and pore density on entropy generation when the pipe is fully filled with copper, aluminium and nickel metallic foams of 0.6 m length in the fluid flow direction. To predict fluid flow and heat transfer features through these metallic foams the Darcy-extended Forchheimer (DEF) flow and the local thermal non-equilibrium (LTNE) models are employed. The characteristics of laminar, transition and turbulent in the non-foam region of the pipe are captured by considering the appropriate flow models. To affirm the methodology adopted in this work, the results of the present numerical solutions are validated with the available experimental results reported in the literature. Colburn j factor and thermal performance factor are the important factors that decide the performance and efficiency of any heat exchange device. Hence, these parameters are critically evaluated and are observed to increase with increasing pore densities of the metal foams and decrease with increasing flow rates of the fluid. Furthermore, the numerical analysis is extended to obtain the results of wall temperature, Nusselt number, heat transfer enhancement ratio, frictional irreversibility and Bejan number.

Design and Experimental Validation of a Novel High-Speed Omnidirectional Underwater Propulsion Mechanism

This article details the design, working principles, and testing of a novel position control mechanism for marine operations or inspection in extreme, hostile, or high-speed turbulent environments where unprecedented speed and agility are necessary. The omnidirectional mechanism consists of a set of counter-rotating blades operating at frequencies high enough to dampen vibrational effects on onboard sensors. Each rotor is individually powered to allow for roll control via relative motor effort and attached to a servo-swashplate mechanism, enabling quick and powerful manipulation of fluid flow direction in the hull's coordinate frame without the need to track rotor position. The mechanism inherently severs blade loads from servo torques, putting all load on the main motors and minimizing servo response time, while exploiting consistent blade momentum to minimize the corresponding force response time. A small-scale force-validating model is fabricated and tested for various force and moment commands. Kinematic and hydrodynamic analyses of the hull and surrounding fluid forces during various blade maneuvers are presented, followed by the mechanical design and kinematic analysis of each subsystem in a small scale model. Experimental results of the small-scale model are presented that verify the concepts presented for the larger-scale model. Finally, an open-loop controller is constructed with decoupled parameters for each degree of freedom.

Perturbation Analysis of Rivlin-Ericksen Fluid on Heat Transfer in the Presence of Heat Absorption

The problem of visco-elastic Rivlin-Ericksen fluid flow past a semi- infinite vertical plate embedded in a porous medium with variable temperature and suction in the presence of a uniform transverse magnetic field and thermal buoyancy effect is considered. The plate is assumed to move with a constant velocity in the direction of fluid flow while the free stream velocity is assumed to follow the exponentially increasing small perturbation law. Time-dependent wall suction is assumed to occur at the permeable surface. The dimensionless governing equations for this investigation are solved analytically using two-term harmonic and non-harmonic functions. Numerical evaluation of the analytical results is performed and some graphical results such as visco-elastic parameter Rm, heat absorption parameter Q, Grashof number Gr, Prandtl number Pr, time t, suction velocity parameter A, moving velocity parameter Up and an exponential parameter ε, for the velocity and temperature profiles within the boundary layer are presented. Skin-friction coefficient, Nusselt numbers are also discussed with the help of the tables.

Influence of Magnetic Field on Micropolar Fluid Flow in a Cylindrical Tube Enclosing an Impermeable Core Coated with Porous Layer

In this research work, we have investigated the Stokesian flow of a micropolar fluid in a cylindrical tube enclosing an impermeable core coated with porous layer in the presence of magnetic field. The axis of the cylinder is taken along the direction of fluid flow and the uniform magnetic field is applied in the direction perpendicular to the axis of the cylinder. Using appropriate boundary conditions, fluid velocities, microrotational velocities and stresses are evaluated for corresponding fluid flow regions. Expressions for volumetric flow rate through the annulus and the filtration velocity are obtained. Graphs of linear velocities, microrotational velocities and flow rate for various values of different parameters are plotted and discussed.

Cell biophysical stimuli in lobopodium formation: a computer based approach

Different cell migration modes have been identified in 3D environments, e.g., modes incorporating lamellopodia or blebs. Recently, a new type of cellular migration has been investigated: lobopodia-based migration, which appears only in three-dimensional matrices under certain conditions. The cell creates a protrusion through which the nucleus slips, dividing the cell into two parts (front and rear) with different hydrostatic pressures. In this work, we elucidate the mechanical conditions that favour this type of migration. One of the hypotheses about this type of migration is that it depends on the mechanical properties of the extracellular matrix. That is, lobopodia-based migration is dependent on whether the extracellular matrix is linearly elastic or non-linearly elastic. To determine whether the mechanical properties of the extracellular matrix are crucial in the choice of cell migration mode and which mechanotransduction mechanism the cell might use, we develop a finite element model. From our simulations, we identify two different possible mechanotransduction mechanisms that could regulate the cell to switch from a lobopodial to a lamellipodial migration mode. The first relies on a differential pressure increase inside the cytoplasm while the cell contracts, and the second relies on a change in the fluid flow direction in non-linearly elastic extracellular matrices but not in linearly elastic matrices. The biphasic nature of the cell has been determined to mediate this mechanism and the different behaviours of cells in linearly elastic and non-linearly elastic matrices.

Effect of Nozzle Clogging on the Fluid Flow Pattern in a Billet Mold with Particle Image Velocimetry Technology

The flow pattern of molten steel in a mold of continuous casting affects the temperature distribution and initially solidifies the shell thickness homogeneity, inclusion transport, and liquid slag entrapment. Alumina inclusions in Al-killed steel tend to adhere to the inner wall of the nozzle, which changes the nozzle geometry structures and affects the molten steel flow pattern in the mold. In this study, two different clog shapes—the hemispherical clog and tube clog—were identified based on the clogged straight-nozzle dissection results. The hydraulic straight-nozzle casting model with different clog situations was designed to investigate the effect of the clog status on the fluid flow in the mold using particle image velocimetry (PIV) technology. The results show that a tail stream with a length of 80 mm forms near the nozzle wall in the fluid flow direction when the hemispherical clog sticks to the nozzle and the jet stream deflects to the clogged side after the jet stream and tail stream mix. However, when the hemispherical clog sticks to the nozzle outlet, the jet stream deflects to the nonclogged side. The increase in the tube clog thickness causes an increase in the jet stream velocity magnitude near the nozzle outlet.

High-throughput laser fabrication of Ti-6Al-4V alloy: Part I. Numerical investigation of dynamic behavior in molten Pool

In the present work, an innovative high-throughput method was developed to fabricate a Ti-6Al-4V alloy via pulsed laser melting with water-cooled copper mold. Moreover, a three-dimensional transient model was established via numerical simulation to reveal the dynamic mechanism of heat transfer and fluid flow of the molten pool during high-throughput laser fabrication processes. Different laser powers, laser pulse durations and Marangoni coefficients were adopted to perform the numerical simulations, revealing the underlying physics of the heat transfer and fluid flow during the melting and solidification process. Special attention was paid to the cooling rate of the molten pool affected by cooling water velocity. Numerical results indicated that a “button” sample can be prepared in a short time of 200 ms by adjusting the processing parameters in this high-throughput preparation process. The maximum temperature of the molten pool was attained at the center underneath the laser beam and decreased radially outward. There was vigorous fluid flow mainly driven by thermal-capillary force in the molten pool. With increases in laser power and laser pulse duration, both the peak temperature and velocity of the molten pool increased. Accordingly, a high cooling rate was obtained under high cooling water velocity. Furthermore, the Marangoni effect fully changed the flow direction of the molten pool fluid, and the Marangoni convection flow influenced the temperature distribution of the molten pool. A new principle of the metallurgical dynamic behavior for the high-throughput laser fabrication process was established in this study and can provide technical guidance for high-throughput preparation experiments, such as laser parameter selection, structural control, and performance optimization.

Flutter prediction of cylindrical sandwich panels with saturated porous core under supersonic yawed flow

Supersonic flutter characteristics of cylindrical sandwich panels made of a saturated functionally graded porous (FGP) core and two homogeneous face sheets are studied in this paper based on the Biot’s poroelasticity theory. The third-order shear deformation theory (TSDT) is used to model the panel and the piston theory is hired to estimate the aerodynamic pressure create by the supersonic fluid flow. First, the set of the governing equations are solved numerically via generalized differential quadrature method (GDQM) and natural frequencies are calculated for various boundary conditions. Then, convergence of the solution is confirmed and its accuracy is demonstrated by comparing the results with those reported by other authors. Finally, the effects of geometrical parameters of the panel, thickness of the porous core, porosity distribution pattern, porosity parameter (size of pores), compressibility of pore fluid and yaw angle (fluid flow direction) on the flutter boundaries of FGP sandwich panels are investigated.

Numerical investigation of heat transfer and pressure drop characteristics in the micro-fin helically coiled tubes

The design of a compact heat exchangers is the challenging work in heat transfer research area. The enhancement of heat transfer can be achieved by increasing the surface area of the heat exchanger and changing the direction of fluid flow. Thus, in this study, the heat transfer and pressure drop characteristic in the micro-fin helically coiled tubes are investigated numerically by using ANSYS FlUENT 19.2. The realizable k − ε turbulence with enhanced wall treatment model was applied. These studies are carried out at different coil diameter from 100 mm to 200 mm, coil pitch of 25 mm to 45 mm and, Reynolds number varying from 10,000 to 25000. Effects of Reynolds number, fin number, coil diameter, and coil pitches on Nusselt number and pressure drop are discussed. At the same operating condition, the Nusselt number and pressure drop increase with an increase of fin number and Reynolds number. Compared to the smooth helical coiled tube, the micro-fin helical coiled tube having fin number Nf = 12 provides higher Nusselt number and pressure drop in the percentage of 39–51% and 22–36%, respectively. The coil pitches of helical tube have a small effect on Nusselt number. At the same Reynold number of 20000, the Nusselt number of smooth helical coiled tube with coil pitch 25 mm is about 0.86% and 1.71% higher than that of the tube with coil pitch of 35 mm and 45 mm, respectively. Moreover, the performance factor of micro-fin helical coiled tube with 8 fin declines from 1.08 to 0.96 with an increase of the coil diameter from 100 mm to 200 mm, respectively.

Basin inversion and structural architecture as constraints on fluid flow and Pb–Zn mineralization in the Paleo–Mesoproterozoic sedimentary sequences of northern Australia

Abstract. As host to several world-class sediment-hosted Pb–Zn deposits and unknown quantities of conventional and unconventional gas, the variably inverted 1730–1640 Ma Calvert and 1640–1575 Ma Isa superbasins of northern Australia have been the subject of numerous seismic reflection studies with a view to better understanding basin architecture and fluid migration pathways. These studies reveal a structural architecture common to inverted sedimentary basins the world over, including much younger examples known to be prospective for oil and gas in the North Sea and elsewhere, with which they might be usefully compared. Such comparisons lend themselves to suggestions that the mineral and petroleum systems in Paleo–Mesoproterozoic northern Australia may have spatially, if not temporally overlapped and shared a common tectonic driver, consistent with the observation that basinal sequences hosting Pb–Zn mineralization in northern Australia are bituminous or abnormally enriched in hydrocarbons. Sediment-hosted Pb–Zn mineralization coeval with basin inversion first occurred during the 1650–1640 Ma Riversleigh Tectonic Event towards the close of the Calvert Superbasin with further pulses taking place during and subsequent to the onset of the 1620–1580 Ma Isa Orogeny and final closure of the Isa Superbasin. Mineralization is typically hosted by the post-rift or syn-inversion fraction of basin fill, contrary to existing interpretations of Pb–Zn ore genesis where the ore-forming fluids are introduced during the rifting or syn-extensional phase of basin development. Mineralizing fluids were instead expelled upwards during times of crustal shortening into structural and/or chemical traps developing in the hangingwalls of inverted normal faults. Inverted normal faults predominantly strike NNW and ENE, giving rise to a complex architecture of compartmentalized sub-basins whose individual uplifted basement blocks and doubly plunging periclinal folds exerted a strong control not only on the distribution and preservation of potential trap rocks but the direction of fluid flow, culminating in the co-location and trapping of mineralizing and hydrocarbon fluids in the same carbonaceous rocks. An important case study is the 1575 Ma Century Pb–Zn deposit where the carbonaceous host rocks served as both a reductant and basin seal during the influx of more oxidized mineralizing fluids, forcing the latter to give up their Pb and Zn metal. A transpressive tectonic regime in which basin inversion and mineralization were paired to folding, uplift, and erosion during arc–continent or continent–continent collision, and accompanied by orogen-parallel extensional collapse and strike-slip faulting best accounts for the observed relationships.