Complex Flow Distribution Research Articles

Additive manufacturing of bipolar plates for hydrogen production in proton exchange membrane water electrolysis cells

Water electrolysis is a process that can produce hydrogen in a clean way when renewable energy sources are used. This allows managing large renewable surpluses and transferring this energy to other sectors, such as industry or transport. Among the electrolytic technologies to produce hydrogen, proton exchange membrane (PEM) electrolysis is a promising alternative. One of the main components of PEM electrolysis cells are the bipolar plates, which are machined with a series of flow distribution channels, largely responsible for their performance and durability. In this work, AISI 316L stainless steel bipolar plates have been built by additive manufacturing (AM), using laser powder bed fusion (PBF-L) technology. These bipolar plates were subjected to ex-situ corrosion tests and assembled in an electrolysis cell to evaluate the polarization curve. Furthermore, the obtained results were compared with bipolar plates manufactured by conventional machining processes (MEC). The obtained experimental results are very similar for both manufacturing methods. This demonstrates the viability of the PBF-L technology to produce metal bipolar plates for PEM electrolyzers and opens the possibilities to design new and more complex flow distribution channels and to test these designs in initial phases before scaling them to larger surfaces.

How Computational Modeling can Help to Predict Gas Transfer in Artificial Lungs Early in the Design Process.

Wearable extracorporeal membrane oxygenation (ECMO) circuits may soon become a viable alternative to conventional ECMO treatment. Common device-induced complications, however, such as blood trauma and oxygenator thrombosis, must first be addressed to improve long-term reliability, since ambulatory patients cannot be monitored as closely as intensive care patients. Additionally, an efficient use of the membrane surface can reduce the size of the devices, priming volume, and weight to achieve portability. Both challenges are linked to the hemodynamics in the fiber bundle. While experimental test methods can often only provide global and time-averaged information, computational fluid dynamics (CFD) can give insight into local flow dynamics and gas transfer before building the first laboratory prototype. In this study, we applied our previously introduced micro-scale CFD model to the full fiber bundle of a small oxygenator for gas transfer prediction. Three randomized geometries as well as a staggered and in-line configuration were modeled and simulated with Ansys CFX. Three small laboratory oxygenator prototypes were built by stacking fiber segments unidirectionally with spacers between consecutive segments. The devices were tested in vitro for gas transfer with porcine blood in accordance with ISO 7199. The error of the predicted averaged CFD oxygen saturations of the random 1, 2, and 3 configurations relative to the averaged in-vitro data (over all samples and devices) was 2.4%, 4.6%, 3.1%, and 3.0% for blood flow rates of 100, 200, 300, and 400 ml/min, respectively. While our micro-scale CFD model was successfully applied to a small oxygenator with unidirectional fibers, the application to clinically relevant oxygenators will remain challenging due to the complex flow distribution in the fiber bundle and high computational costs. However, we will outline our future research priorities and discuss how an extended mass transfer correlation model implemented into CFD might enable an a priori prediction of gas transfer in full size oxygenators.

CFD modeling of the OSU High Temperature Test Facility inlet plenum flow distribution during normal operation

This paper investigates the fundamental physical phenomena associated with internal coolant flow distribution in the upper plenum of a prismatic Very High Temperature Reactor (VHTR) during normal operation. Previous studies have revealed the importance of complex flow distribution in the inlet plenum with the potential to generate low velocity or stagnation zones that can subsequently lead to the formation of hot spots in the reactor core and hot streaks in the lower plenum. It is therefore of interest to ensure that coolant is evenly distributed when entering multiple reactor coolant channels. Non-uniformity in the flow distribution is assessed for the reference Oregon State University High Temperature Test Facility (HTTF) case. The HTTF is a reduced scale model (1:4 in height and diameter) of the Modular High Temperature Gas-Cooled Reactor (MHTGR). The developed CFD model reflects complete and detailed geometry of the HTTF upper plenum along with upcomer and metallic core support structure (MCSS). CFD results include parametric studies performed for circulator mass flow rate variation and mesh sensitivity analysis, generated using Siemens Starccm+ software. Outcomes also include variable pressure and temperature boundary conditions impact on the flow distribution.

Unidirectional Wetting Properties on Multi-Bioinspired Magnetocontrollable Slippery Microcilia.

Here, a smart fluid-controlled surface is designed, via the rational integration of the unique properties of three natural examples, i.e., the unidirectional wetting behaviors of butterfly's wing, liquid-infused "slippery" surface of the pitcher plant, and the motile microcilia of micro-organisms. Anisotropic wettability, lubricated surfaces, and magnetoresponsive microstructures are assembled into one unified system. The as-prepared surface covered by tilted microcilia achieves significant unidirectional droplet adhesion and sliding. Regulating by external magnet field, the directionality of ferromagnetic microcilia can be synergistically switched, which facilitates a continuous and omnidirectional-controllable water delivery. This work opens an avenue for applications of anisotropic wetting surfaces, such as complex-flow distribution and liquid delivery, and extend the design approach of multi-bioinspiration integration.

Coupling indoor airflow, HVAC, control and building envelope heat transfer in the Modelica Buildings library

This paper describes a coupled dynamic simulation of an indoor environment with heating, ventilation, and air conditioning (HVAC) systems, controls and building envelope heat transfer. The coupled simulation can be used for the design and control of ventilation systems with stratified air distributions. Those systems are commonly used to reduce building energy consumption while improving the indoor environment quality. The indoor environment was simulated using the fast fluid dynamics (FFD) simulation programme. The building fabric heat transfer, HVAC and control system were modelled using the Modelica Buildings library. After presenting the concept, the mathematical algorithm and the implementation of the coupled simulation were introduced. The coupled FFD–Modelica simulation was then evaluated using three examples of room ventilation with complex flow distributions with and without feedback control. Further research and development needs were also discussed.

Magnetic resonance measurement of fluid dynamics and transport in tube flow of a near-critical fluid

An ability to predict fluid dynamics and transport in supercritical fluids is essential for optimization of applications such as carbon sequestration, enhanced oil recovery, “green” solvents, and supercritical coolant systems. While much has been done to model supercritical velocity distributions, experimental characterization is sparse, owing in part to a high sensitivity to perturbation by measurement probes. Magnetic resonance (MR) techniques, however, detect signal noninvasively from the fluid molecules and thereby overcome this obstacle to measurement. MR velocity maps and propagators (i.e., probability density functions of displacement) were acquired of a flowing fluid in several regimes about the critical point, providing quantitative data on the transport and fluid dynamics in the system. Hexafluoroethane (C2F6) was pumped at 0.5 ml/min in a cylindrical tube through an MR system, and propagators as well as velocity maps were measured at temperatures and pressures below, near, and above the critical values. It was observed that flow of C2F6 with thermodynamic properties far above or below the critical point had the Poiseuille flow distribution of an incompressible Newtonian fluid. Flows with thermodynamic properties near the critical point exhibit complex flow distributions impacted by buoyancy and viscous forces. The approach to steady state was also observed and found to take the longest near the critical point, but once it was reached, the dynamics were stable and reproducible. These data provide insight into the interplay between the critical phase transition thermodynamics and the fluid dynamics, which control transport processes.

Numerical Simulation of Particle Trajectory in Electrostatic Precipitator

The performance of Electrostatic Precipitator (ESP) is significantly affected by complex flow distribution. Recent years, many numerical models have been developed to model the particle motion in the electrostatic precipitators. The computational fluid dynamics (CFD) code FLUENT is used in description of the turbulent gas flow and the particle motion under electrostatic forces. The gas flow are carried out by solving the Reynolds-averaged Navier-Stokes equations and turbulence is modeled by the k-ε turbulence model. The effect of electric field is described by a series equations, such as the electric field and charge transport equations, the charged particle equation, the charge conservation equation, the mass and momentum equations of gas, the mass and momentum equations of particle and so on. The particle phase is simulated by using Discrete Phase Model (DPM). The simulations showed that the particle trajectory inside the ESP is influenced by both the aerodynamic and electrostatic forces. The simulated results have been validated by the established data.

Heat Transfer Analysis of Exhaust Manifold with Water Jacket of a High Speed Gasoline Based on FSI

The fluid-structure interaction (FSI) method is employed to analyze heat transfer of a exhaust manifold with a water jacket. Three different turbulence models are valued to predict their spheres of application. The mutual effect on complex flow distribution and heat transfer with and without transition is also considered respectively. The results show that reasonable turbulence model and transition will contribute to a better numerical precision of temperature distribution. Considering transition will have a impact on the design of novel exhaust manifold of high speed gasoline engine. In addition, numerical results can be referred to improve the structure.

Determination of the effective radial mass diffusivity in tubular reactors under non-Newtonian laminar flow using residence time distribution data

Residence time distribution (RTD) plays an important role in the performance of a laminar flow reactor (LFR). The theoretical E-curve can be derived for the tube flow of a power law non-Newtonian fluid; however, in practice, the streamline flow can be disturbed by the use of corrugated tubes or coils or by the presence of mechanical vibration, high wall relative roughness, pipe fittings or curves. Moreover, stagnation or recirculation zones reduce the active volume of the reactor. The integration of the measured RTD with the process model for flow, heat transfer and reaction can be challenging. The approach proposed in this work is to introduce an effective radial mass diffusivity in the model to take into account the enhanced dispersion and to use the mean residence time as characteristic time. The LFR with radial diffusion was modeled and the simulation results showed the transition from ideal laminar flow to intense radial dispersion according to the modified Peclet number. The measured RTD of a tubular system with high wall relative roughness running with a Newtonian fluid and a pseudo-plastic fluid was compared with the simulated results in order to determine the effective radial diffusivity and the active volume. With these parameters, the LFR model would provide a more reliable prediction of the RTD, hence preventing the representation of complex flow distributions in the reactor.

Investigation of the three-dimensional flow over a 40° swept wing

AbstractThree-component laser Doppler anemometry (LDA) has been used to measure the complex flow distributions over the suction surface of a symmetrical 40°swept wing model at an angle of incidence of 9° and for the relatively low Reynolds number (based on the root chord) of 2·1 × 105. Emphasis was placed on the separation and reattachment of the boundary-layer flow, and the formation of vortical structures.The experimental programme now described utilised a large wind tunnel and several advanced measurement techniques to produce an unusually detailed collection of results. Thus, data are presented here for the behaviour of the three-dimensional boundary layer developing on the suction surface at positions from 30% to 90% semi-span. These results show the spatial variations of the time-averaged mean and fluctuating velocity components in three orthogonal directions, including the distributions of the normal and shear stress levels. Further analysis has enabled the time-averaged vortical structures to be identified and compared with the results of surface flow visualisation.Flow over a swept wing poses many challenges for the computational modeller. The underlying aim, here, therefore, was to produce a data archive for the validation of computer predictions. As will be shown, some of the experimental results have already been used in this way and the data base is available for use by other workers.

Autothermal hydrogen generation from methanol in a ceramic microchannel network

In this paper, the authors present the first demonstration of a new class of integrated ceramic microchannel reactors for all-in-one reforming of hydrocarbon fuels. The reactor concept employs precision-machined metal distributors capable of realizing complex flow distribution patterns with extruded ceramic microchannel networks for cost-effective thermal integration of multiple chemical processes. The presently reported reactor is comprised of five methanol steam reforming channels packed with CuO/γ-Al 2O 3, interspersed with four methanol combustion channels washcoated with Pt/γ-Al 2O 3, for autothermal hydrogen production (i.e., without external heating). Results demonstrate the capability of this new device for integrating combustion and steam reforming of methanol for autothermal production of hydrogen, owing to the axially self-insulating nature of distributor-packaged ceramic microchannels. In the absence of any external insulation, stable reforming of methanol to hydrogen at conversions >90% and hydrogen yields >70% was achieved at a maximum reactor temperature of 400 °C, while simultaneously maintaining a packaging temperature <50 °C.

4D flow for accurate assessment of complex flow distribution

4D flow for accurate assessment of complex flow distribution

Flow simulation in an electrostatic precipitator of a thermal power plant

The performance of electrostatic precipitator (ESP) is significantly affected by its complex flow distribution arising as a result of its complex inside geometry. In the present study the gas flow through an ESP used at a local thermal power plant is modeled numerically using computational fluid dynamics (CFD) technique to gain an insight into the flow behavior inside the ESP. CFD code FLUENT is used to carry out the computations. Numerical calculations for the gas flow are carried out by solving the Reynolds-averaged Navier–Stokes equations coupled with the k– ε turbulence model equations. The results of the simulation are discussed and compared with on-site measured data supplied by the power plant. The predicted results show a reasonable agreement with the measured data. The model developed is a novel tool for the thermal power plant to predict the effect of possible modifications made to the ESP design on the flow pattern.

Effect of fiber structure on dialysate flow profile and hollow-fiber hemodialyzer reliability: CT perfusion study

Uniform dialysate distributions in hollow-fiber hemodialyzers facilitate effective solute removal, and the fiber structure inside hemodialyzers plays a significant role in determining dialysate flow distribution and dialysis efficiency. The authors analyzed the effects of undulated fibers on dialysate flow profiles and hemodialyzer reliability using a perfusion CT technique. Using a multi-detector row CT unit, perfusion studies were performed on two different types of hemodialyzers: (A) straight fiber configuration; (B) undulated fiber configuration (wavy-shaped fibers). Deconvolution theory was used for image processing to derive dialysate flows, dialysate volumes, and mean transit time distributions. Three-dimensional perfusion maps for the two types of hemodialyzers were reconstructed using high resolution images and these parameters were compared at hemodialyzer midsections. Dialysate maldistributions were observed in both types of hemodialyzer. However, dialysate flow distributions were more uniform in the undulated-fiber hemodialyzer, whereas more complex flow distributions developed in straight-fiber hemodialyzer. Reliability as determined using intraclass correlation coefficients was markedly higher for the hemodialyzer containing undulated fiber (0.968 vs. 0.496 for type A and type B, respectively). The undulated-fiber type was found to have more uniform, consistent dialysate flow profiles. It is believed that this type of hemodialyzer will be found helpful for measurement and prescription of the delivered hemodialysis dose due to its better consistency.