Axial Pressure Drop Research Articles

Numerical assessment of using various outlet boundary conditions on the hemodynamics of an idealized left coronary artery model.

Vascular diseases are greatly influenced by the hemodynamic parameters and the accuracy of determining these parameters depends on the use of correct boundary conditions. The present work carries out a two-way fluid-structure interaction (FSI) simulation to investigate the effects of outlet pressure boundary conditions on the hemodynamics through the left coronary artery bifurcation with moderate stenosis (50%) in the left anterior descending (LAD) branch. The Carreau viscosity model is employed to characterise the shear-thinning behaviour of blood. The results of the study reveal that the employment of zero pressure at the outlet boundaries significantly overestimates the values of hemodynamic variables like wall shear stress (WSS), and time-averaged wall shear stress (TAWSS) compared with human healthy and pulsatile pressure outlet conditions. However, the difference between these variables is marginally low for human healthy and pulsatile pressure outlets. The oscillatory shear index (OSI) remains the same across all scenarios, indicating independence from the outlet boundary condition. Furthermore, the magnitude of negative axial velocity and pressure drop across the plaque are found to be higher at the zero pressure outlet boundary condition.

CFD—ANN study on axial dispersion in helical and serpentine millimetric coils

CFD simulations are reported to compare hydrodynamic/axial dispersion in a classical helical-shaped and planar serpentine-shaped tubular reactor at a millimetric scale (1-5 mm) for the first time. A two-step simulation approach is validated against experimental data on residence time distribution in serpentine coils. The method is then used for parametric analysis to explore the impact of geometric parameters on the coiling factor and axial dispersion coefficient. Dean vortices in the coiling region are visualized. The findings from the parametric analysis are utilized to develop empirical correlations and Artificial Neural Network (ANN) models for estimating coiling factors and axial dispersion coefficients in both serpentine and helical coils. The absolute average relative error (AERR) in predicting the coiling factor is 3.5% for helical coils and 4.6% for serpentine coils. The AERR of the ANN model for predicting the axial dispersion coefficient is 14% for helical coils and 10% for serpentine coils. The study reveals that both axial dispersion coefficient and pressure drop are higher in serpentine coils compared to helical coils. Axial dispersion is found to be relatively unaffected by pitch (helical) or bend diameter (serpentine) and tube diameter but shows significant reduction with a decrease in pitch circle diameter (helical) or gap between bends (serpentine). The developed correlations and ANN models can aid in the precise sizing of tubular reactors designed as helical or serpentine coils. This is exemplified through a case study involving the synthesis of an ionic liquid, where the helical configuration demonstrated a performance advantage of approximately 6% over the serpentine configuration.

Study on spray characteristics of a compact pressure swirl nozzle integrating tangential inlet flow channel and swirl chamber

Pressure swirl nozzles are widely applied in various heat and mass transfer applications due to advantages of reliable performance, simple structure, and easy processing. However, the complex design of the nozzle structure makes it difficult to miniaturize the pressure swirl nozzle, which restricts its use in limited spaces. In this study, a compact pressure swirl nozzle is proposed by merging a swirl chamber with the tangential inlet flow channel, addressing the issue of liquid atomization in limited spaces. The key geometric parameters are determined based on the internal flow properties by swirl chamber simulation. A spray test bench utilizing a phase Doppler particle analyzer and a high-speed camera was built to study the effect of pressure drop, geometric size, and nozzle inlet shape on spray characteristics. The simulation results show that the nozzle diameter and inlet shape are the main factors affecting flow in the swirl chamber. The experimental results further demonstrate that increasing nozzle diameter increases flow rate and spray cone angle, causing the droplets to move to the spray edge. The spray characteristics are affected by the inlet shape of the nozzle hole: radial velocity and particle size show a wider range of change with a funnel-shaped inlet. Axial velocity and pressure drop are obviously affected by a cylindrical-shaped inlet. This study provided a new design approach for pressure swirl nozzles and achieved flow rate of 5–35 l/h and Sauter mean diameter below 40 μm with an overall weight of 12 g. This compact nozzle construction is a reference for the design of atomizing nozzles in limited spaces.

Co-current filtrate flow in TFF perfusion processes: Decoupling transmembrane pressure from crossflow to improve product sieving.

Hollow fiber-based membrane filtration has emerged as the dominant technology for cell retention in perfusion processes yet significant challenges in alleviating filter fouling remain unsolved. In this work, the benefits of co-current filtrate flow applied to a tangential flow filtration (TFF) module to reduce or even completely remove Starling recirculation caused by the axial pressure drop within the module was studied by pressure characterization experiments and perfusion cell culture runs. Additionally, a novel concept to achieve alternating Starling flow within unidirectional TFF was investigated. Pressure profiles demonstrated that precise flow control can be achieved with both lab-scale and manufacturing-scale filters. TFF systems with co-current flow showed up to 40% higher product sieving compared to standard TFF. The decoupling of transmembrane pressure from crossflow velocity and filter characteristics in co-current TFF alleviates common challenges for hollow fiber-based systems such as limited crossflow rates and relatively short filter module lengths, both of which are currently used to avoid extensive pressure drop along the filtration module. Therefore, co-current filtrate flow in unidirectional TFF systems represents an interesting and scalable alternative to standard TFF or alternating TFF operation with additional possibilities to control Starling recirculation flow.

Increasing Performance of Spiral-Wound Modules (SWMs) by Improving Stability against Axial Pressure Drop and Utilising Pulsed Flow.

Spacer-induced flow shadows and limited mechanical stability due to module construction and geometry are the main obstacles to improving the filtration performance and cleanability of microfiltration spiral-wound membranes (SWMs), applied to milk protein fractionation in this study. The goal of this study was first to improve filtration performance and cleanability by utilising pulsed flow in a modified pilot-scale filtration plant. The second goal was to enhance membrane stability against module deformation by flow-induced friction in the axial direction ("membrane telescoping"). This was accomplished by stabilising membrane layers, including spacers, at the membrane inlet by glue connections. Pulsed flow characteristics similar to those reported in previous lab-scale studies could be achieved by establishing an on/off bypass around the membrane module, thus enabling a high-frequency flow variation. Pulsed flow significantly increased filtration performance (target protein mass flow into the permeate increased by 26%) and cleaning success (protein removal increased by 28%). Furthermore, adding feed-side glue connections increased the mechanical membrane stability in terms of allowed volume throughput by ≥100% compared to unmodified modules, thus allowing operation with higher axial pressure drops, flow velocities and pulsation amplitudes.

Experimental study on the flow characteristics of 7-pin hexagonal bundle assembly with grid spacers

Lead-cooled Fast Reactors (LFRs) are of great significance for future nuclear power systems. With the advantages of great neutronic properties and high passive safety, LFR has been selected as the reactor of China initiative Accelerator Driven System (CiADS), which has the potential to transmute long-lived nuclear waste into short-lived ones and enhance the utilization of nuclear fuel. The hexagonal bundle with grid spacers has been identified as a promising design of the CiADS fuel assembly. The new design of grid spacers has the advantages of reliable fixation, small flow resistance, and not easy to cause blockage. Flow characteristics in this fuel assembly model were revealed by the particle image velocimetry (PIV) method. The results showed the presence of cross-flow and high axial velocity areas around the grid spacers. The strongest cross-flow mixing was observed downstream of the grid spacers at a distance of approximately z/Dh = 7.5 (axial height/hydraulic diameter). Although the influence of the grid spacers was weak, it was still detectable downstream at a distance of z/Dh = 32. The axial velocity loss rates were obtained and they increased with Reynolds number. The highest axial velocity loss rate was in the edge subchannel. Measurements of axial pressure drop uncovered the pressure loss characteristics of grid spacers and a new correlation was proposed. This work contributes to the understanding of the flow and pressure drop characteristics of the CiADS fuel assembly and can facilitate the design of more efficient nuclear reactors.

Geometry optimization of axial cyclone for high performance and low acoustic noise

Axial flow cyclones are widely used to separate gas-particle mixtures in many industrial applications. This study aims to optimize the axial cyclone pressure drop, removal rate, and sound levels. Single and multi-objective optimizations using a surrogate model were used to minimize the Euler number, Stokes number, and overall sound pressure level (OASPL). A radial basis function artificial neural network approach was also applied to generate more reliable data. The performed three single-objective genetic algorithms optimization studies led to the minimized Euler, Stokes, and OASPL numbers values of 5.082, 0.333, and 3.607, respectively. Then, the multi-objective NSGA-II optimization technique was used to generate a Pareto front that decision-makers can use for optimal performance. It was found that the concave guide vane, the guide vane revolution, and swirler geometry significantly affect the performance of axial cyclones. The low values of acoustic noise were recorded at low tangential and axial velocities values.

An Improved Design for Flow Conditioning in Waste Water Pipes

In practical applications, waste water piping includes elbows and bends which give unrepeatable, asymmetric and swirling flow profiles, which result in flow meter inaccuracy. Flow conditioners can be inserted into the pipe network to remove these flow patterns prior to a flow meter, to improve the accuracy of the measurement and to reduce the length of straight-run which would otherwise be required. In this investigation, a new design of flow conditioner is considered in two configurations, with and without vanes. The performance of the conditioner is considered by exposing it to a swirling flow that was disturbed by two 90° bends. The flow downstream of the conditioner was simulated using CFD software STAR-CCM+ 12 to find the downstream axial velocity profile, swirl angle and pressure drop. The vane-less conditioner provided a suitable axial profile for flow measurement 2D downstream, at which point the swirl was removed. This illustrated the improved performance compared to other conditioners in the literature, but came at the price of a somewhat higher pressure drop. The addition of vanes improved the performance slightly in terms of regulating the flow and removing swirl, while at the same time increasing the pressure drop further.

Effect of nonheated rod arrangements on void fraction distribution in a rod bundle in high-pressure boiling flow

In boiling water reactors (BWRs), the fuel assembly incorporates nonuniform elements such as part-length fuel rods and water rods capable of modifying the moderator density distribution and axial pressure drop in order to improve the economic efficiency and the thermal margin. This study focuses on the void fraction distribution in a rod bundle with different nonheated rod arrangements in order to evaluate the effect of water rods as a nonheated section on the boiling flow dynamics in the rod bundle. A boiling flow experiment was conducted using the test facility for 3D thermal hydraulics in light water reactors (SIRIUS-3D) and a linear accelerator-driven high-energy X-ray computed tomography (CT) system under BWR rated pressure conditions. The test section was a 5 × 5 rod bundle of heated length 3708 mm that simulated a BWR rod bundle. The void fraction distribution in the 5 × 5 rod bundle was acquired at six heights via X-ray CT imaging. The experimental results show the effect of nonheated rod arrangements on the local void fraction and the evolution of boiling flow in the rod bundle.

Verification and validation of CFD and its application in PWR fuel assembly

Fuel assembly is one of the most important components in Pressurized Water Reactor (PWR). Mixing Vane Spacer Grid (MVG) provides support for the fuel bundle. However, the most important role for MVG is to mix the coolant and decrease the temperature gradient, ultimately enhance the heat transfer and improve Critical Heat Flux (CHF). Hence the performance of MVG are directly related to the safety and economics of PWR. Due to the complexity of MVG and the broad range of thermal hydraulic conditions involved, full scale, time consuming and costly full length rod bundle experiments (usually 5 × 5 or 4 × 4 or 6 × 6) were performed to study the complicated thermal hydraulic phenomenon. Recently, with the development of computer technology, Computational Fluid Dynamics (CFD) has become one of the most popular tools to simulate the flow field of the fuel assembly. In this paper, the method based on CFD to study the MVG performance is reviewed. The main process for CFD in simulating flow field of MVG is divided into two parts. The first part is the verification and validation of CFD codes under single phase-and two-phase flow. The second is the application of CFD for exploring the MVG performance. For the verification of single phase flow CFD simulation, mesh sensitivity, turbulent model effects were examined, the validation including axial pressure drop, lateral temperature distribution, and lateral velocity distribution. For two phase flow verification and validation, the sensitivities of different drag and non-drag forces on void fraction distribution were tested. The experimental data with a tube and an annual flow fields under two phase boiling were chosen to validate the two phase flow simulation and to cover different aspects of internal and external wall boiling effects. The verified and validated CFD codes were then used to study the performance of MVG. Considering the complexity of MVG, a separated effect study approach is presented to evaluate the performance of MVG. Another systematic approach from simple geometry to 5 × 5 MVG model to study the effect of different components, including vane, dimple, and spring were proposed for the simulation of two phase flow. Some indexes were reviewed and used to evaluate the performance of MVG.

Experimental measurements of gas-particle flows in large-scale strippers

Measurements of gas–solid particle flow in a large-scale stripper unit are reported. The experiments target industrial (pilot) scale measurements of gas-particle flow that can be used to validate numerical methods for modeling multiphase flows, such as computational fluid dynamics coupled to the discrete element method (CFD-DEM). Specifically, experiments were performed with Geldart Group B (533 µm) glass beads in a stripper unit. In general, previous CFD-DEM validation datasets were performed in benchtop experimental systems and limited to O(105) particles. Here, the number of particles in the isolated section of the stripper is O(107) for all tests. Measurements are reported for a ∼2 m tall section of the ∼1 m diameter stripper. Radial mass flux profiles measured at five axial positions and three axial pressure drop measurements are reported for six operating conditions.

New designs of turbulence promoters to use in saltwater purification processes

This paper describes a two-dimensional computational fluid dynamics (CFD) model of flow with mass transfer to simulate a membrane separation system. The fluid domain comprises two reverse osmosis (RO) membranes and is fitted with different wavy inserts that act as turbulence promoters. Four types of insert designs were evaluated in terms of salt deposition on the membranes, permeate flux, axial pressure drop in the channel, and plots of the Sherwood number against the Power number. According to numerical simulations, under the operating conditions of this investigation, the proposed designs generate better results than commercial designs. The gain in pure water flux achieves up to 2%, and salt deposition on the membrane surface is reduced by ~5% than the commercial Zigzag spacer arrangement.

Hydrodynamics of a bubble-induced inverse fluidized bed reactor with a nanobubble tray

This paper reports on the hydrodynamics of a bubble-induced inverse fluidized bed reactor, using a nanobubble tray gas distributor, where solid particles are fluidized only by an upward gas flow. Increasing the gas velocity, the fixed layer of particles initially packed at the top of the liquid starts to move downwards, due to the rise of bubbles in this system, and then gradually expands downwards until fully suspended. The axial local pressure drops and standard deviation were examined to delineate the flow regime comprehensively under different superficial gas velocities. Four flow regimes (fixed bed regime, initial fluidization regime, expanded regime, and post-homogeneous regime) were observed and three transitional gas velocities (the initial fluidization velocity, minimum fluidization velocity, and homogeneous fluidization velocity) were identified to demarcate the flow regime. Three correlations were developed for the three transitional velocities. As the fine bubbles generated from the nanobubble tray gas distributor are well distributed in the entire column, the bed expansion process of the particles is relatively steady.

Measurement of high-water-content oil-water two-phase flow by electromagnetic flowmeter and differential pressure based on phase-isolation

When the oil field has been exploited by long-term water-flooding, it will be in high water-content stage of production. However, it is a great challenge for high-water-content measurement due to oil droplets extremely dispersed in the water. In this paper, we developed a phase-isolation based method for high-water-content oil-water two-phase flow measurement. Phase-isolation was realized by axial-flow swirler to concentrate scattered and random oil droplets into the pipe center and change the inlet flow pattern into a particular annular flow before measuring. Owing to the axisymmetric velocity and phase distribution, the electromagnetic flow meter avoided the effect of random distribution of insulating phase, and then had a good measurement performance for total volume flow rate. Furthermore, we respectively studied using axial pressure drop, radial pressure drop and the ratio of the two pressure drops to measure water content. The results showed that the ratio of the two pressure drops not only improves the resolution of oil and water, but also effectively reduces the impact of error transfer. In the dual-parameter measurement experiment, the relative errors of total volume flow rate and water content were almost within ±5%.

A dynamic cluster structure-dependent drag coefficient model applied to the riser in high density circulating fluidized bed

A dynamic cluster structure dependent (DCSD) drag model based on energy dissipation minimization using the two-fluid model (TFM) and the kinetic theory of granular flow (KTGF) is applied to the riser in high density circulating fluidized bed (HDCFB). The characteristics of gas and solid are predicted by means of the DCSD drag model with the convective and local accelerations. The law of granular collision energy dissipation and drag energy dissipation are compared and the influence of granular collision energy dissipation to agglomerate structure is researched. The study shows that granular collision energy dissipation has great influence on heterogeneous structure of riser. Simulated solid volume fraction, axial pressure drop and solid mass flux are compared to experimental measurements, numerical analysis suggests that the temporal-spatial heterogeneous structure characteristics and particle collision affect the flow of the riser in the literature.

Theoretical investigation on submicron particle penetration through circular tubes inside a porous medium

The analytical infinite series solution of submicron particle transport in a circular tube bounded by a porous wall, such as a pinhole, is determined under the slip velocity boundary condition, and the solution is verified by using the experimental data in the previous studies for the specific cases. The results show that particle penetration rate increases with the increase of the porous parameter, the axial pressure drop, and the pinhole radius, whereas it decreases with increasing the pinhole length. The penetration rate of nano-particles are more sensitive to the variation of these parameters. However, the differences between the penetrations of particles ranging from 0.3 μm to 1 μm are not evident because the diffusion becomes weak gradually in this size range. In addition, a further comparison is performed between the analytical solution and the existing studies, and approximate expressions are presented for accurate calculation of particle penetration rate through pinholes appearing in porous materials including filter devices and masks.

Experimental Investigation of the Subchannel Axial Pressure Drop and Hydraulic Characteristics of a 61-Pin Wire Wrapped Rod Bundle

Abstract Wire-wrapped hexagonal fuel bundles have been extensively investigated due to their enhanced heat transfer and flow characteristics. Experimental measurements are important to study the thermal-hydraulic behavior of such assemblies and to validate and improve the predictive capabilities of specialized correlations and computational tools. Presently, very limited experimental data is available on the local subchannel pressure drop. Experimental measurements of subchannel pressure drop were conducted in a 61-pin wire-wrapped rod bundle replica, for Reynolds numbers between 190 and 22,000. Specialized instrumented rods were utilized to measure the local pressure drop and estimate the subchannels' friction factor. Three interior subchannels, one edge subchannel, and one corner subchannel were selected to study the effects of location and flow regimes on the friction factor and hydraulic behavior. The transition boundaries from laminar to transitions regimes, and from transition to turbulent regimes were estimated for the subchannels analyzed. The results were found to be in agreement with the predictions of the upgraded Cheng and Todreas detailed correlation (UCTD). The results of the experimental campaign provided a better understanding of the hydraulic behavior of the subchannels of wire-wrapped bundles, in relation to its geometrical features.

Microchannel zeolite 13X adsorbent with high CO2 separation performance

• Microchanneled zeolite monoliths for removal of CO 2 through phase separation. • CO 2 dynamic uptake of 3.4 mmol g −1 was obtained for 13X monoliths. • The monoliths present markedly low pressure drop under fast flow rate. • Mass transfer resistance in monolith significantly lower than those for beads. • Ultra high mechanical strength and thermal conductivity for zeolite adsorbent. Uniform 13X films with thicknesses of 3 and 11 µm were grown on supports in the form of steel monoliths with a cell density of 1600 cpsi and microchannels width of 0.5 mm. Sharp breakthrough fronts and a dynamic uptake of 3.4 mmol CO 2 g −1 zeolite were observed in the forwarding step of breakthrough experiments for a feed of 10% CO 2 in N 2 with a high flow rate at 293 K and 1 bar. Numerical modeling showed that the adsorption process was very fast and that the transport of CO 2 in the thin zeolite layer was the rate-limiting step, the mass transfer resistance for the 11 µm film is 2.2 times lower than zeolite 13X pellets and 100 times lower than zeolite 4A beads. Axial dispersion, pressure drop, and gas film resistance were shown to be negligible. The steel monolith support provides good mechanical strength and excellent thermal conductivity for the 13X films. The combination of properties makes this adsorbent a good performer when compared with other types of structured zeolite adsorbents in reported literatures. This microchannel adsorbent is a promising alternative to traditional adsorbents in processes of fast CO 2 separation with short cycle times.

Experimental investigation of axial pressure drop analysis on the additively manufactured porous regenerator

Regenerators are used in cryogenics for nitrogen and helium liquefaction through reversed Stirling cycle to achieve a low operating temperature of 40 K. An ideal regenerator has critical properties such as low thermal conductivity, optimum porosity, high heat transfer, and specific heat. In general, the matrix of the porous materials is in the form of wire mesh, fibrous wool, granules, or foams. The recent technological development in additive manufacturing (AM) allows it to extend its application to porous structure-based energy exchanging devices. Direct metal laser sintering (DMLS) is one of the AM processes used to fabricate complex geometry with uniform porosity, of considerably low cost compared with the conventional processes. This paper presents the development of an experimental setup to investigate the steady axial pressure drop analysis through various types of regenerators. These regenerators have been tested for multiple working fluids such as Argon and Helium gas at room temperature. The axial pressure drop results of the additive regenerator have been compared with the woven wire mesh and copper wool type of regenerators. The additively manufactured regenerator has a lower pressure drop of 9% and 14% than the copper wool and woven wire mesh type regenerators.

Coupled model of dual differential pressure (DDP) for two-phase flow measurement based on phase-isolation method

Phase-isolation is a novel ever-increasing multiphase separation technology, which can facilitate the multiphase fluid flowing concurrently with a substantially clear interface between two phases, and the phenomenon is promisingly employed for the separation and measurement of multiphase flows. Phase-isolation can be implemented by different kinds of lateral forces, of which the centrifugal force induced by the swirlers is the most convenient method. The radial pressure drop between pipe wall and pipe center, and the axial pressure drop along the pipe wall occurs at the downstream of the swirler. In the paper, the coupling model of dual differential pressure (DDP) including the radial-axial differential pressure and radial-radial differential pressure was built employing centrifugal phase-isolation for oil-water two-phase flow, and the theoretical measurement models were validated by our experimental data. At certain cross sections downstream of the swirler, the deviations between theoretical and experimental result of the volumetric oil fraction λo and mass flowrate Qm were below ±7.16% and ±1.14% respectively when the radial-axial differential pressure was adopted, while the deviations between theoretical and experimental result of λo and Qm were below ±6.91% and ±1.13% respectively using the radial-radial differential pressure. The acceptable deviation indicates that the DDP model can be the reference for the analysis and application of two-phase flow in the academic research and practical engineering.