High Inlet Flow Rate Research Articles

Bionic leaf-inspired catalyst bed structure for solar membrane reactor aiming at efficient hydrogen production and separation

Membrane reactor technology permits efficient solar thermochemical conversion at low temperatures, but the performance is often limited by concentration polarization. To cope with the hydrogen (H2) concentration polarization in solar membrane reactors, this study proposes a bionic solar membrane reactor (BSMR) inspired by the excellent production-transport management ability of leaves. Designing the structural parameters of the bionic catalyst bed obtains the efficient BSMR, and mechanistically analyzes its reaction and separation performance enhancement. The results show that the BSMR achieves a synergistic reinforcement pattern of ordered H2 separation driving reaction and reaction providing H2 separation pressure at >90° pore block tilt angle, while large porosity differences and small pore block lengths can further amplify this synergy. Currently, the BSMR with pore blocks of 140° tilt angle, 20 mm length and 0.3 low porosity has the optimal performance, which improves methane conversion and hydrogen recovery by 13.4–99.0% and 13.7–99.0%, respectively, relative to the conventional solar membrane reactor under different operating conditions. Also, it is shown that optimal performance enhancement is achieved at high steam-to-methane ratios, low inlet temperatures and high inlet flow rates. In general, the design referring to leaves makes BSMR well inherit the consistently superior performance of leaves, providing new ideas for efficient hydrogen production and separation.

Shell and tube heat exchange comparison with gravitational water vortex flow configuration

As a recent addition to the heat exchanger family, gravitational water vortex heat exchangers may be considered a potential alternative to shell-and-tube heat exchangers in the process industry. Their shared reliance on the turbulent fluid flow for heat transfer and comparable sizes indicates the need to compare the two thermal systems in terms of input energy requirement, heat exchange effectiveness, temperature distribution, log-mean temperature difference and overall heat transfer coefficient. The present study reports an experimental comparison of the performance of a shell-and-tube heat exchanger with a gravitational water vortex heat exchanger for the same heat exchange area, mass flowrates and reference temperatures. The validation of the experiments is supported by the analytical results for both heat exchangers. The experimental findings highlight the importance of the presence of air core in the gravitational water vortex heat exchanger, which performs 40 % better than in the absence of air core. Moreover, the same air core provides support in outperforming the shell-and-tube configuration by a margin of 22 % and 24 % more heat transfer rate for the same hot-side inlet temperatures of 313 K and 323 K, respectively. The study concludes that the gravitational water vortex heat exchanger performs better than the shell-and-tube heat exchanger at high inlet flow rates, whereas the latter is more effective in terms of log-mean temperature difference with better heat loss counter measures.

Mixture formation characteristics and feasibility of methanol as an alternative fuel for gasoline in port fuel injection engines: Droplet evaporation and spray visualization

Under the background of energy saving and emission reduction, methanol is considered an ideal alternative fuel for gasoline because of its renewability, high combustion efficiency and low emissions, while an issue is the cold start of methanol port fuel injection engines. To comprehensively understand the underlying mechanisms and the feasibility of methanol as a substitute of gasoline, a suspension method was first used to investigate the evaporation characteristics of methanol and gasoline droplets at low temperatures. Then an optical intake port was constructed based on the outer contour modification strategy and an optical distortion correction algorithm was proposed. The effects of inlet temperature, inlet flow rate and injection pressure on spray characteristics of methanol and gasoline were comparatively investigated. In addition, the influence of valve temperature on the characteristics of spray impingement on a valve was studied. The results showed that the difference between the evaporation rates of methanol and gasoline was small at 60–90 °C. The difference became obvious when the temperature was below 60 °C or above 90 °C. Reducing the ambient humidity may reduce this difference and improve the cold start performance of methanol engines. A higher inlet temperature slightly increased the spray area. A higher inlet flow rate and injection pressure significantly increased the spray area, but also caused serious wet wall problem. From the point of view of spray in the port, methanol was a feasible substitute for gasoline in the presence of inlet flow and at low injection pressure of 6 bar. The valve temperature should exceed 200 and 230 °C for methanol and gasoline, respectively to form vapor films that prevent fuel adhesion onto the valve. However, methanol may not be a suitable alternative fuel for gasoline when spray directly impacted on the valve in port fuel injection engines due to its much smaller spray area.

The Double-Disk Diamond Window as Backup Broadband Window Solution for the DEMO Electron Cyclotron System

The second variant of the electron cyclotron heating and current drive system in DEMO considers the deployment of 2 MW power Gaussian microwave beams to the plasma by frequency steering. Broadband optical grade chemical vapor deposition diamond windows are thus required. The Brewster-angle window represents the primary choice. However, in the case of showstoppers, the double-disk window is the backup solution. This window concept was used at ASDEX Upgrade for injection of up to 1 MW at four frequencies between 105 and 140 GHz. This paper shows computational fluid dynamics conjugated heat transfer and structural analyses of such a circumferentially water-cooled window design aiming to check whether it might be used for DEMO microwave beam scenarios. This design was then characterized with respect to different parameters. Temperature and thermal stress results showed that it is a feasible window solution for DEMO, but safety margins against limits shall be increased by introducing design features able to make the fluid more turbulent. A first design change is proposed, showing that, in combination with a higher inlet flow rate, the maximum temperature in the disks can be reduced from 238 to 186 °C, leading, therefore, to lower thermal gradients and stresses in the window.

A pore-scale study for reactive transport processes in double-layer gradient electrode as negative side of a deep eutectic solvent electrolyte-based vanadium-iron redox flow battery

Porous electrodes are critical component of redox flow batteries (RFBs), that decide the fluid, species/charge transport and electrochemical reaction properties during the operation of RFBs. It is a potential way to elevate the performance of RFBs by applying the porous electrodes with gradient pore structures. However, it is still lack of a suitable numerical model to understand the reactive transport processes in the heterogeneous pore structures, thus to design and develop the optimal RFB electrodes. Using a lattice Boltzmann model, this work studies the pore-scale reactive transfer behaviors in a double-layer gradient electrode assembling as the negative side of deep eutectic solvents electrolyte-based vanadium-iron RFB, that consists of a graphite felt near the current collector side and a carbon paper near the membrane side. The numerical results reveal the galvanostatic discharging performance of double-layer electrode under the different electrolyte feeding modes and flow rates. Comparing with full flow-through feeding mode, the interdigitated flow feeding mode would give rise to serious inhomogeneity of electrolyte flowing at the low flow rate condition, thereby resulting in the sluggish convective mass transfer performance near the membrane side. Moreover, the total power loss of double-layer electrode is higher than that of the mono-layer carbon paper electrode within the low flow rate range. Conversely, the double-layer electrode with interdigitated flow mode can achieve the lowest total power loss than mono-layer electrodes at the high inlet flow rate. This work provides a new pathway to investigate the RFB power performance effected by the gradient porous structures of electrodes.

Fractional Flow Reserve (FFR) Estimation from OCT-Based CFD Simulations: Role of Side Branches.

The computational fluid dynamic method has been widely used to quantify the hemodynamic alterations in a diseased artery and investigate surgery outcomes. The artery model reconstructed based on optical coherence tomography (OCT) images generally does not include the side branches. However, the side branches may significantly affect the hemodynamic assessment in a clinical setting, i.e., the fractional flow reserve (FFR), defined as the ratio of mean distal coronary pressure to mean aortic pressure. In this work, the effect of the side branches on FFR estimation was inspected with both idealized and optical coherence tomography (OCT)-reconstructed coronary artery models. The electrical analogy of blood flow was further used to understand the impact of the side branches (diameter and location) on FFR estimation. Results have shown that the side branches decrease the total resistance of the vessel tree, resulting in a higher inlet flowrate. The side branches located at the downstream of the stenosis led to a lower FFR value, while the ones at the upstream had a minimal impact on the FFR estimation. Side branches with a diameter larger than one third of the main vessel diameter are suggested to be considered for a proper FFR estimation. The findings in this study could be extended to other coronary artery imaging modalities and facilitate treatment planning.

Characteristics of cavitation onset and development in a self-excited fluidic oscillator

Hydrodynamic cavitation has been widely employed in modern chemical technology. A high-speed camera experiment is conducted to reveal the characteristics of hydrodynamic cavitation generated in one self-excited fluidic oscillator. The images obtained from the high-speed camera system are employed to describe several development stages of the hydrodynamic cavitation. The gray intensity of the images which is the volume of bubbles formed is extracted to distinguish the cavitation bubbles from the water. It is found that three regions in the fluidic oscillator could be divided according to the distance from the entrance. The inception of cavitation occurs in the region nearest the entrance. For a relatively low inlet flow rate, the whole process of cavitation could complete within the region that is the second nearest the entrance as a low pressure area appears periodically in this region. For a high inlet flow rate, the vortexes in the region farthest from the entrance are able to generate sufficient low pressures to induce the generation of cavitation. In addition, the intensity of cavitation could be reflected by the cavitation number in a self-excited fluidic oscillator.

3D-Stacked Multistage Inertial Microfluidic Chip for High-Throughput Enrichment of Circulating Tumor Cells.

Whether for cancer diagnosis or single-cell analysis, it remains a major challenge to isolate the target sample cells from a large background cell for high-efficiency downstream detection and analysis in an integrated chip. Therefore, in this paper, we propose a 3D-stacked multistage inertial microfluidic sorting chip for high-throughput enrichment of circulating tumor cells (CTCs) and convenient downstream analysis. In this chip, the first stage is a spiral channel with a trapezoidal cross-section, which has better separation performance than a spiral channel with a rectangular cross-section. The second and third stages adopt symmetrical square serpentine channels with different rectangular cross-section widths for further separation and enrichment of sample cells reducing the outlet flow rate for easier downstream detection and analysis. The multistage channel can separate 5 μm and 15 μm particles with a separation efficiency of 92.37% and purity of 98.10% at a high inlet flow rate of 1.3 mL/min. Meanwhile, it can separate tumor cells (SW480, A549, and Caki-1) from massive red blood cells (RBCs) with a separation efficiency of >80%, separation purity of >90%, and a concentration fold of ~20. The proposed work is aimed at providing a high-throughput sample processing system that can be easily integrated with flowing sample detection methods for rapid CTC analysis.

Continuous citrate\u2010capped gold nanoparticle synthesis in a two\u2010phase flow reactor

A continuous manufacturing platform was developed for the synthesis of aqueous colloidal 10–20 nm gold nanoparticles (Au NPs) in a flow reactor using chloroauric acid, sodium citrate and citric acid at 95 oC and 2.3 bar(a) pressure. The use of a two-phase flow system – using heptane as the continuous phase – prevented fouling on the reactor walls, while improving the residence time distribution. Continuous syntheses for up to 2 h demonstrated its potential application for continuous manufacturing, while live quality control was established using online UV-Vis photospectrometry that monitored the particle size and process yield. The synthesis was stable and reproducible over time for gold precursor concentration above 0.23 mM (after mixing), resulting in average particle size between 12 and 15 nm. A hydrophobic membrane separator provided successful separation of the aqueous and organic phases and collection of colloidal Au NPs in flow. Process yield increased at higher inlet flow rates (from 70 % to almost 100 %), due to lower residence time of the colloidal solution in the separator resulting in less fouling in the PTFE membrane. This study addresses the challenges for the translation of the synthesis from batch to flow and provides tools for the development of a continuous manufacturing platform for gold nanoparticles.Graphical abstract

Numerical simulation of photocatalytic oxidation of gaseous pollutants using low Reynolds number turbulence models

Introduction: Photocatalytic oxidation of gaseous pollutants in differential reactors is simulated using computational fluid dynamics. Materials and methods: The momentum equation and pollutant transport are solved by using ANSYS Fluent. The SIMPLE algorithm is used to treat the pressure-velocity coupling. The laminar flow and low Reynolds k−ε models are used to describe turbulence. Results: Velocity field distribution and degradation efficiency of different models at various flow rates were obtained and compared with the experimental data. The simulation results of degradation efficiency under different models are basically consistent. Conclusion: Although low Reynolds k-ε models have better simulation results for high inlet flow rates, in terms of computation complexity, laminar flow is recommended for simulation.

Random pore structure and REV scale flow analysis of engine particulate filter based on LBM

Abstract In this article, lattice Boltzmann method (LBM) is used to simulate the multi-scale flow characteristics of the engine particulate filter at the pore scale and the representative elementary volume (REV) scale, respectively. Four kinds of random wall-pore structures are considered, which are circular random structure, square random structure, isotropic quartet structure generation set (QSGS), and anisotropic QSGS, with difference analysis done. In terms of the REV scale, the influence of different inlet flow velocities and wall permeabilities on the flow in single channel is analyzed. The result indicates that the internal seepage laws of random structures constructed in this article and single channel are in accordance with Darcy’s law. Circular random structure has better permeability than square random structure. Isotropic QSGS has better fluidity than anisotropic one. The flow in single channel is similar to Poiseuille flow. The flow lines in the channel are complicated and a large number of vortices appear at the ends of channel with high inlet flow rate. With the increase of inlet velocity, the static pressure in channel gradually increases along the axial direction as well as the seepage velocity. The temperature field in the channel becomes more uniform as the flow velocity increases, and the higher temperature distribution appears on the wall of the porous media.

Simulation Analysis of the Heat Transfer Performance of an N‐type Microchannel Heat Exchanger

AbstractA microchannel heat exchanger with a triangular wave and symmetrical triangular wave structure was proposed in this paper. In addition, a new N‐type microchannel heat exchanger was developed to balance the heat transfer performance and pressure drop. The relationship between different configurations of the N structure of the microchannel and the heat transfer performance was analyzed. The results showed that, at a high inlet flow rate, the symmetrical triangular wave microchannel had the best heat transfer performance, followed by the triangular wave microchannel and the straight channel. At the same flow rate, the degree of disturbance of the fluid was highest in the symmetrical N‐structure microchannel, and an excellent heat transfer effect was observed.

Thermohydraulic Behavior of the Liquid–Vapor Flow in the Receiver Tube of a Solar Parabolic Trough Collector

Abstract Liquid–vapor flows are present in many industrial applications. In particular, in the solar field, these flows are encountered in the new generations of solar parabolic trough collectors with direct steam generation (PTCs-DSG). In this technical brief, we compare the two-phase convective transfer and the pressure drop models in the PTC-DSG. The results show that the heat exchange coefficients estimated by Chen–Cooper, Shah, Gungor–Winterton, and Kandlikar models have same trend with difference between them. However, the models of Liu–Winterton and Steiner–Taborek seem inappropriate due to the decrease in the exchange coefficient for moderate and high steam qualities. In addition, a comparison of the models describing pressure drops with experimental data of literature was carried out. The results show that the pressure decreases as the steam quality increases and the differences between these models remain small. Friedel's model is the closest to the experiment for high inlet pressures and flow rates, while Chisholm's model gives the best prediction of the pressure drop for low inlet conditions. Effect analysis of inlet conditions shows that the increase in inlet water mass flow and decrease in pressure favor convective heat transfer. The variation of heat flux on tube wall does not affect the convective boiling heat coefficient evaluated by the Chen–Copper model, whereas it influences the calculating coefficient by Gungor–Winterton model for high heat flux and particularly for low steam qualities. Pressure drops are higher at high flow rates and low pressures.

CFD simulation of mass transfer in electrochemical reactor with mesh cathode for higher phenol degradation

Cathode, where electro-catalytic oxidation barely took place, could exert a significant influence on electro-catalytic efficiency, whereas little investigation has been focused on this effect. In this study, the effect of cathode configuration on electro-catalytic activities was investigated with phenol as model pollutant, and the mechanism was revealed from the perspective of mass transfer with computational fluid dynamics (CFD) simulation. Compared with the planar Ti cathode, the electro-catalytic reactor with mesh Ti exhibited 1.21–1.26 times faster phenol degradation rate under various testing inlet flow rates. CFD simulation revealed the higher velocity distribution both in the reactor and on anode surface when meshed Ti cathode was used, which benefited faster fluid flow so that the pollutant transfer was accelerate especially at higher inlet flow rate. Excellent agreement of mass transfer between CFD simulation and experimental analysis was achieved, the mass transfer coefficient with mesh Ti was 1.40–1.55 times of the case with planar cathode under various inlet flow rates. The enhanced mass transfer performance was mainly ascribed to the rhombic pores of mesh cathode where hydrogen bubbles generated on would escape timely and randomly at various directions, leading to the disturbance of fluid flow around the anode. This study highlighted mesh cathode played a key role in improving pollutant degradation, and CFD, as a versatile and convenient tool to analyze the hydrodynamic behavior of electro-catalytic reactor, showed a strong persuasion to guide the optimization of electrode configuration.

CFD investigation of the effect of manifold and microchannel ratio on the hydrodynamic performance of microchannel heat sink

Flow distribution of working fluid greatly affects the performance of microchannel heat sinks (MCHSs). Uniform flow distribution prevents the development of hot spots and dead zones. Major parameters that govern the flow distribution in MCHSs are manifold and microchannel geometry. Many studies involved complicated manifold designs or novel approaches which may not be easily incorporated. Also, many researchers have examined various microchannel geometrical parameters. However, simultaneous alterations of more than one parameter is scarce. The present study focuses on the effect of simple manifold layouts, namely rectangular manifold (Rect_MCHS), circular manifold (Circ_MCHS), and triangular manifold (Tria_MCHS), and microchannel geometry, defined by microchannel ratio, a ratio of microchannel width to microchannel spacing, on the hydrodynamic performance of MCHSs using three-dimensional computational fluid dynamic (CFD). The hydrodynamic performance of MCHSs was evaluated in terms of pressure drop, velocity distribution, and coefficient of flow nonuniformity. Results showed that higher inlet flow rates and smaller microchannel ratios produced better flow distribution performance in which the latter has a higher positive impact on the hydrodynamic performance of MCHSs. Smaller microchannel ratio designs have larger microchannel spacing which served as a barrier to create flow dispersion effect. This effect was further amplified at higher inlet flow rates. Generally, Rect_MCHSs produced the best hydrodynamic performance. Furthermore, variation in temperature showed negligible impact on the hydrodynamic performance of MCHSs, compared to inlet flow rate and microchannel ratio. This suggests that studies which concern with flow distribution performance could be conducted without the energy aspect to reduce computational time.

CFD and experimental analyses of flow distribution uniformity in minichannel reactors with a bifurcation structure manifold

This study investigated the flow distribution uniformity and pressure drop in minichannel reactors with a bifurcation structure inlet manifold and different type outlet manifolds. The numerical model was established and validated by experimental results. In order to analyze the effects of structural parameters on the flow distribution uniformity of the manifold, the bifurcation inlet manifold was first designed based on the principle of minimum entropy generation. The results showed that longer channel length of bifurcation in the inlet manifold allowed the flow to be fully developed and equally split into several flows. Then, with an identical bifurcation inlet manifold, the influences of outlet manifold with structures of bifurcation, triangle and rectangle, as well as the parallel minichannel length on the flow uniformity of minichannel reactors were also built and investigated. The results showed that the rectangular structure outlet manifold simplified the structure of minichannel reactors and reduced the parasitic power consumption. The flow uniformity of minichannel reactor increased as the parallel minchannel length increased and the impact was more significant at high inlet flow rate than at low inlet flow rate.

Numerical study of nanoencapsulated phase change material inside double pipe heat exchanger

AbstractNanoencapsulated phase change material (NPCM) slurry is a dispersion where the phase change material (PCM) is dispersed in fluid. Compared with fluid, these nanofluids have a higher heat capacity during the phase change and a possible enhancement, as a result of this phase change, in the heat transfer phenomenon. To appreciate the merits, in terms of energy, a numerical study has been carried out with fluid based on NPCM inside double pipe heat exchanger. The numerical simulation results have been validated using experimental heat transfer data. The Reynolds and Nusselt numbers have been determined using thermal conductivity and viscosity evaluated in the same conditions as those in numerical model. The results obtained show an improvement of this energetic criterion at low mass flow rate compared with the base fluid. Analysis of the numerical and analytical results reveal that higher inlet flow rate and NPCM concentration results in higher heat transfer rate. In addition, increasing NPCM slurry temperature decreases its performance due to fast melting of PCM inside the tube.

Study on Characteristics of Heat Transfer and Flow Resistance in Random Porous Foam Metal

Porous foam metal has great application prospects in the field of compact heat exchangers. The characteristics of heat transfer and resistance for foam metal with random structure and different porosities (30%, 50%, 70% and 90%) were studied by finite element method in this study. The generated foam structures can be considered as homogeneous model and has better heat exchange capacity at higher inlet flow rate, and the boundary layer can develop well along the flow direction. The open–cell foammetal structure has a uniform heat transfer perpendicular to the flow direction. The bottom plate temperature of the low–porosity structure is more uniform at low flow rates. The intermediate porosities (50% and 70%) at high flow rates has a higher uniformity. As the porosity decreases, the internal pressure increases significantly and the pressure loss also becomes significantly larger. The corresponding optimal porosity is 57%, 66% and 76% at inlet flow rates of 0.001 m/s, 0.01 m/s and 0.1 m/s, respectively.

CFD modelling of a membrane reactor for hydrogen production from ammonia

Despite the growing use of hydrogen (H2) as a transport fuel, one of the major barriers still remaining is efficient and inexpensive fuel distribution and storage. Current approaches, such as compression, liquefaction or metal hydride formation, incur a significant energy penalty. Ammonia (NH3) has long been considered a prospective H2 medium, exhibiting a higher volumetric H2 density than liquid H2, through liquid-phase storage at mild pressure. Decomposition of NH3 into H2 and N2 can be achieved via use of catalytic reactors and fuel-cell-grade H2 can be produced using metal membranes at H2 distribution sites.In this study, a 3-Dimensional (3D) Computational Fluid Dynamics (CFD) model has been developed to understand the performance of the H2 separation process in gas mixtures derived from an NH3-cracking reaction. The reactor consists of 19 tubular membrane tubes, each 470 mm long, inside a tubular shell with an inner diameter of 130 mm. Standard transport and energy equations governing a 3D, pressure-based, steady-state model were derived from the laws of conservation of mass, momentum and energy. The governing equations were solved using commercial CFD software ANSYS Fluent 18.0. Gas flow and mixing were modelled by the two-equation standard k-epsilon model for closure. Coupled solver was used for pressure-velocity coupling, enabling a pseudo-transient option with pseudo time steps of 0.01 s. To estimate H2 permeation through the metal membrane, a constant H2 permeability of 3.0E–07 mol.m−1 s−1 Pa−0.5 derived from series of experiments tested under a range of industrial conditions, was used. Model simulations were conducted for an adiabatic temperature of 300 °C, a feed-side pressure of 7.8 bara and a permeate side pressure of 0.1 bara. A parametric analysis was carried out to explore the effects of variation in total feed-gas flow and effects of changes in NH3-cracking efficiency on H2 production rates and H2 yields. The model estimated that 4.6–11.6 kg H2/day can be produced from a 30-70 L min−1 NH3 inlet flow with 80-90% NH3-cracking efficiency. At lower NH3 inlet flow rates, higher H2 yields can be obtained within a shorter distance of the membrane tubes due to relatively slower velocities and longer residence times. At high inlet flow rates, H2 yields were significantly lower due to their faster velocities and shorter resident times, but high yields (>95%) were still observed at the membrane reactor outlet. A sensitivity analysis of the model showed that even if metal membranes functioned at only 50% of the maximum permeability, a high H2 yield similar to that estimated using 100% permeability can still be achieved at the H2 outlets.

Effects of electrothermal vortices on insulator-based dielectrophoresis for circulating tumor cell separation.

Insulator-based dielectrophoresis (iDEP) is a powerful technique for separation and manipulation of bioparticles. In recent years, iDEP designs using arrays of insulating posts have shown promising results toward reaching high-efficiency bioparticle manipulation. Joule heating (JH) and electrothermal (ET) flows have been observed in iDEP microdevices and significantly affecting their performances. In this research, we utilize mathematical modeling to study, iDEP technique and the effects of JH and ET flow on device performance and propose a separation scenario for selective trapping of circulating tumor cells (CTCs). A robust numerical model is developed to calculate the distribution of electric and fluid flow fields in the presence of JH and ET flow, and predict the cells' trajectory inside the system. Our results indicate that JH not only induces temperature rise in the system, but also may alter the design iDEP separation scenario by inducing ET vortices that affect the cell's trajectory. To investigate the impact of JH-induced ET flow characteristics and vortex generation on separation efficiency, we introduce a dimensionless force ratio encompassing the effects of electrical field, drag forces, JH, and ET flow. Interestingly, it was found that ET flows can be used to significantly enhance the separation efficiency, even in higher inlet flow rates. Lastly, the effect of post geometry has been discussed.