Channel Walls Research Articles

Numerical investigation of thermal and entropy generation characteristics in a sinusoidal corrugated channel under the influence of sinusoidal wall temperature

The corrugated channels play a vital role in many engineering applications, such as electronic cooling and heat exchanger devices; thus, forced convection heat transfer and entropy generation within the corrugated channels are important subjects to investigate. This study numerically investigated the laminar forced convection heat transfer and entropy generation of water flow within a sinusoidal corrugated channel. The channel walls were subjected to sinusoidal wall temperature heating while varying the wave parameters. The finite element method had been employed to solve the governing equation, and the simulation results were conducted for Reynolds number 5 ≤ Re ≤ 500, dimensionless wall temperature wavelength 0.25 ≤ λth ≤ 2.25, and Prandtl number Pr = 6.93. The main findings were depicted in terms of Nusselt number, skin friction coefficient, heat transfer effectiveness, total entropy generation, and Bejan number contours, as well as the results being compared with the results of uniform heating. In addition, the results demonstrated that sinusoidal heating significantly improved heat transfer compared to uniform heating for λth < 1.75 and all ranges of Reynolds number, while a critical Reynolds number was found, where the uniform heating showed a higher heat rate compared to non-uniform heating at λth ≥ 1.75 . Besides that, it is found that the sinusoidal wall temperature has lower entropy generation than uniform heating, except with λth = 0.25. This investigation recommends that sinusoidal wall temperature heating is more effective in heat transfer than uniform heating by 7.5, 2.78, 1.9, 1.52, and 1.34 factors at λth = 0.25, 0.75, 1.25, 1.75 and 2.25, respectively.

Field tuning study and RF electromagnetic design of a continuous-wave RFQ with ramped inter-vane voltage for AB-BNCT

A compact radio frequency quadrupole (RFQ) linac for accelerator-based boron neutron capture therapy is being developed at Xi'an Jiaotong University. By adopting a ramped inter-vane voltage in the beam dynamics design, the RFQ could accelerate a continuous wave proton beam to 2.6 MeV over a length of 4 m, effectively decreasing costs and saving space. To meet the beam-dynamics requirements, both the vane width and undercut were optimized during the electromagnetic design. In addition, π-mode stabilization loops were included to increase the mode separation, and fixed tuners with varying diameters were installed to obtain close frequency-tuning sensitivity. It was established that the field unflatness can be controlled within ±1.5% when all tuners remain at their nominal insertion depth. Optimized cooling-channel design was completed, and multi-physics analysis was conducted. The water tuning coefficients of the vane and wall channels were analyzed to establish the ability to fine tune the RFQ during operation.

Built‐in Electric Fields in Heterostructured Lamellar Membranes Enable Highly Efficient Rejection of Charged Mass

Separation membranes with homogeneous charge channels are the mainstream to reject charged mass by forming electrical double layer (EDL). However, the EDL often compresses effective solvent transport space and weakens channel‐ion interaction. Here, built‐in electric fields (BIEFs) are constructed in lamellar membranes by assembling the heterostructured nanosheets, which contain alternate positively‐charged nanodomains and negatively‐charged nanodomains. We demonstrate that the BIEFs are perpendicular to horizontal channel and the direction switches alternately, significantly weakening the EDL effect and forces ions to repeatedly collide with channel walls. Thus, highly efficient rejection for charged mass (salts, dyes, and organic acids/bases) and ultrafast water transport are achieved. Moreover, for desalination on four‐stage filtration option, salt rejection reaches 99.9% and water permeance reaches 19.2 L m‐2 h‐1 bar‐1. Such mass transport behavior is quite different from that in homogeneous charge channels. Furthermore, the ion transport behavior in nanochannels is elucidated by validating horizontal projectile motion model.

Analysis of the Effect of Peristaltic Transport Flux on Channel Wall: Bingham Fluid as A Model

This study is concerned with analyzing the peristaltic flow of Bingham fluid through an irregular tube with a short wavelength “relative to channel width” and using the governing equations of Bingham fluid in the Navier-Stokes equations in the Cartesian coordinate system. Significant results of the problem were obtained and analyzed using the Wolfram-Mathematica Computational Notebook.

MHD Flow of Jeffery Nanofluid Through Symmetric Ciliated Channel with Porous Medium: Biological Application

This paper emphasizes on examining the impact of a magnetic field, and porous medium on the non-Newtonian Jeffery nanofluid flows due to metachronal waves induced by ciliated structures that covering the inner walls of the symmetric channel. The governing equations namely continuity, motion, energy and nanoparticles concentration are formulated with suitable boundary conditions and simplified depending on the assumption of long wavelength and low Reynolds number. The simplified equations are solved by using Mathematica program. Further, these analytical solutions for velocity profile, temperature, concentration profiles and streamlines are graphically elucidated and discussed in detail. we concluded that the Hartman number and permeability parameter have opposite effect on the flow characteristics. Moreover, the Jeffery parameter has an increasing impact on the velocity profile whereas the dimensionless eccentricity of ellipse parameter decreases the velocity profile of the fluid.

Transient simulation of conjugate heat transfer of kerosene with thermal oxidative and surface coking reactions at a supercritical pressure

The regenerative cooling technology in aerospace applications often involves supercritical-pressure heat transfer of a hydrocarbon fuel, in which thermal oxidative reactions of the fuel would lead to surface coke accumulation on the cooling channel wall. In this paper, the long-term transient conjugate heat transfer of kerosene has been numerically investigated in a circular mini tube at a supercritical pressure of 3 MPa. The modified chemical mechanism and kinetics of thermal oxidative and surface coking reactions of kerosene are proposed, which, with an additional surface reaction, are capable of treating large coke deposition in regions with sharp temperature gradients. Transient surface coke accumulation and its effect on heat transfer are handled by a dynamic mesh technique. A series of numerical studies are conducted to elucidate the influences of surface heat flux, dissolved oxygen mass fraction, inlet fuel mass flow rate, and coke layer thermal conductivity on the supercritical-pressure heat transfer and thermal oxidative reactions. The effects of different reaction pathways on surface coke accumulation are analyzed comprehensively, and it is revealed that the oxygen-consuming surface coke deposition is initiated only at the high fuel temperature at around 590 K. The present numerical results would enhance fundamental understanding of the long-term transient heat transfer process of a hydrocarbon fuel at supercritical pressures in the regenerative cooling applications.

Evaluation of heat transfer performance of a channel mounted with square-wing perforated V-type baffles

ABSTRACT The current study examines the aerothermal performance behaviors of a rectangular-channel with square-wing perforated V-type baffles (SW-PVBs). The SW-PVBs were attached to lower channel walls at five attack angles, θ = 0° (solid V-type baffle), 22.5°, 45°, 67.5° and 90°. The heat transfer and pressure drop results of a channel without SW-PVBs were performed to normalize the results of the SW-PVBs and evaluate thermal performance factors (TPFs). It can be observed that as the attack angles decreased, the heat transfer and pressure loss rose. Among the SW-PVBs that were tested, those characterized by θ = 22.5° exhibited the most significant improvement in heat transfer, whereas SW-PVBs with θ = 45° gave the highest thermal performance factors. Additionally, the SW-PVBs with θ = 45° offered the highest TPF, as high as 1.93.

Flexural-Gravity Waves in a Channel with a Compressed Ice Cover

The characteristics of linear hydroelastic waves propagating in a channel covered with compressed ice are investigated. The channel has a rectangular cross-section and is assumed to be infinite in length. The fluid in the channel is non-viscous and incompressible; its flow is potential. The ice cover is modelled by an elastic plate of constant thickness frozen to the channel walls. Principal attention is paid to the investigation of the influence of ice compression on the parameters of hydroelastic waves. The problem is solved in a coupled hydroelastic formulation. The profiles of propagating waves in the channel are sought in the form of series on the normal modes of a dry plate. The modes are defined analytically through trigonometric and hyperbolic functions. It is shown that compression in the longitudinal and transverse directions has different effects on the dispersion relations of these hydroelastic waves, their shape and phase, as well as on the critical velocities and strains distribution.

Thermal performance of mixed convective radiative peristaltic flow of Bingham nanofluid

The significance of peristaltic phenomena has generated substantial interest within the fields of biological and biomedical engineering. Therefore, the present study deals with magnetohydrodynamics (MHD) peristaltic flow of Bingham nanofluid in a channel. Here the channel walls are symmetric and elastic in nature. Velocity slip, heat and mass convective conditions are enforced on channel walls. The aspects of dissipation, Joule heating and mixed convection is analyzed. Thermal transport included the features of thermal radiation, Brownian and thermophoresis motion. Analysis and modelling are investigated in the presence of the phenomenon heat generation and absorption. The analysis has been wrapped up under the assumptions of a long wavelength and a low Reynolds number. Numerical techniques are implemented for finding the solutions of governing differential system. Results for velocity, concentration, thermal field, rate of heat transfer, skin friction coefficient, Nusselt number and Sherwood number are analyzed subject to pertinent parameters. The study reveals that velocity is enhanced via both thermal Grashof number and velocity slip parameter. Temperature shows opposite behavior against radiation and Brinkman number. Rate of heat transfer enhances for larger values Brownian motion and Hartman parameters. This study's practical applications include the use of peristaltic pumps for drug delivery in the pharmaceutical and chemical industries.

Experimental investigation of local boron concentration in a 2 × 2 rod bundle channel under subcooled boiling flow

During the operation of pressured water reactors (PWRs), subcooled boiling occurring at the upper-span region of the fuel assembly causes migration of the boron concentration in the coolant. The distribution of boron concentration in the coolant is essential to predict the boron hideout within the Corrosion Related Unidentified Deposition (CRUD) and crud-induced power shift (CIPS). However, experimental data on local boron concentration of rod bundle geometries in subcooled boiling conditions are not available. In this paper, a vertical test channel is constructed to determine the distribution of the local boron concentration of a 2 × 2 rod bundle channel under subcooled boiling conditions. The bubble-boron concentration simultaneous measurement device is developed and calibrated to measure the local two-phase flow parameters and boron concentrations under the subcooled boiling conditions. The experimental results indicate that the boron concentration is highest near the narrowest gap and decreases toward the subchannel center or subchannel wall. The boron concentration increases linearly with void fraction in the central subchannel, while the boron concentration first increases rapidly and then slowly in the wall channel. The underlying mechanism for the boron concentration distribution is revealed by considering the boron enrichment on the bubble–liquid interface, diffusion of the boron concentration, boron mixing induced by bubble wake, and boron dilution caused by bubble condensation. On the basis of that, a boron equilibrium model considering the evaporation and condensation of bubbles is developed. The experimental data is used to support the development and validation of the boron equilibrium model. The comparison results show that the boron equilibrium model can predict the performance of the boron concentration in the rod bundle channel with an accuracy of 20 %.

Expansion-flow-modulated 3D printing of vertically aligned graphene photofuel cell

Channel-aligned regulation of photoelectrode within the bulk structure to generate eminent light absorbance and high-level pollutant adsorption is pivotal but challenging for realizing high-performance photofuel cell (PFC) system. Herein, we demonstrated an effective and scalable expansion-flow-modulated direct ink writing (DIW) 3D printing strategy for controllably constructing microlattice photoelectrode, with multiscale well-interconnected oriented channels built by layer-by-layer highly-regular assembly of filaments and vertical alignment of graphene nanosheets within filaments as well as uniform coupling of abundant photoactive nanoparticles to highly ordered channel walls. The unique architectural features enabled high-speed and effective diffusion/trapping of wastewater pollutants throughout the entire photoelectrode, and meanwhile facilitated ready spreading of incident light into the photoelectrode interior to yield high light absorption. As a result, an integrated 3D-printed vertically-aligned PFC (3DP VAPFC) assembled with as-fabricated photoelectrode exhibited its powerful capability for efficiently converting wastewater pollutants into electric energy under sunlight, with remarkable cycling stability and maximum power density of 0.11 mW cm−2. This work opens a promising route for architecting advanced photoelectrode toward PFC devices with highly efficient degradation and electricity generation of pollutants.

Investigations of Solid Particle Erosion on the Flow Channel Walls of a Radial Turbine for Diesel Engine Applications

Investigations of Solid Particle Erosion on the Flow Channel Walls of a Radial Turbine for Diesel Engine Applications

Label-free separation of peripheral blood mononuclear cells from whole blood by gradient acoustic focusing

Efficient techniques for separating target cells from undiluted blood are necessary for various diagnostic and research applications. This paper presents acoustic focusing in dense media containing iodixanol to purify peripheral blood mononuclear cells (PBMCs) from whole blood in a label-free and flow-through format. If the blood is laminated or mixed with iodixanol solutions while passing through the resonant microchannel, all the components (fluids and cells) rearrange according to their acoustic impedances. Red blood cells (RBCs) have higher effective acoustic impedance than PBMCs. Therefore, they relocate to the pressure node despite the dense medium, while PBMCs stay near the channel walls due to their negative contrast factor relative to their surrounding medium. By modifying the medium and thus tuning the contrast factor of the cells, we enriched PBMCs relative to RBCs by a factor of 3600 to 11,000 and with a separation efficiency of 85%. That level of RBC depletion is higher than most other microfluidic methods and similar to that of density gradient centrifugation. The current acoustophoretic chip runs up to 20 µl/min undiluted whole blood and can be integrated with downstream analysis.

Exact solutions of hydromagnetic convective flow in a microchannel with superhydrophobic slip and temperature jump: Microfluidics applications

AbstractThe researchers explored the free convective flow of a hybrid nanofluid in a vertical microchannel with a rectangular cross‐section. Notably, both channel walls were heated alternately, and a transverse magnetic field was applied across the channel. The channel walls had unique properties, one of which was nonslip and the other was exceedingly hydrophobic. The major purpose was to investigate the effects of magnetism and superhydrophobicity on important flow parameters. The differential equations in the investigation were solved, producing accurate results. The study yielded some significant discoveries. First, when heated, the magnetic parameter reduced skin friction on both sides. Second, in both heating conditions, the magnetic field reduced flow rate and velocity. The flow rates in the two reported situations were similar at a crucial temperature jump coefficient. Furthermore, for low‐temperature jump coefficients, heating the superhydrophobic side reduced the Nusselt number whereas heating the nonslip side had no magnetic effect. The percentage change in the value of Nusselt number and velocity decreases continuously with increase in nonlinear density variation with temperature (NDT) parameter and magnetic parameter. The percentage increases in the value of skin friction with increase in temperature jump and slip length but decrease in the percentage of skin friction for the effect of magnetic term and NDT parameter. As the NDT parameter increases, the velocity percentage rises to 50.59% when the superhydrophobic surface is heated and to 84.30% when the nonslip surface is heated. The temperature jump is statistically significant for the value of the Nusselt number and skin friction for the no‐slip surface condition. These discoveries have practical consequences for the design and management of both tiny and large‐scale systems, with possible applications in microfluidics, microelectronics, nanoscience, and nanotechnology.

Comparison of current collector architectures for Flow-electrode Capacitive Deionization

Flow-electrode Capacitive Deionization (FCDI) is a relatively young technology that allows energy-efficient desalination and salt concentration. FCDI employs flow electrodes, suspensions of conductive particles capable of storing ions in the electric double layer at their surface upon charging. To facilitate charging, the flow electrode particles must be electrically contacted using current collectors. Current collectors must guide the flow electrode along a membrane surface, provide a surface area for electrical contact with the particles, and be inert at high salt concentrations. In this study, we compare different current collector architectures for FCDI. Graphite plates and membrane-electrode assemblies made of carbon fiber fabric are two architectures described in the recent literature. We introduce a new current collector architecture based on a bipolar plate made of expanded graphite. These novel current collectors show up to 55 % higher salt transfer than graphite plates, rendering them a valuable new architecture for FCDI modules. Comparative analysis of different current collector architectures shows that the side walls of a flow channel are more effective at charge transport than the bottom wall. Furthermore, surface roughness impacts charge transport, with smoother surfaces leading to higher salt removal rates.

Flow across a circular cylinder in an inclined channel stabilized by buoyancy

In this study, flow across a circular cylinder confined in an inclined channel is considered, with account taken of mixed convection. Cases with opposing or aiding buoyancy that is not in alignment with the incoming flow are considered, and it is found that the flow around and in the wake of the cylinder is affected. The effects of inclination and buoyancy on the flow and heat transfer patterns are investigated, with a focus on the stabilization and destabilization of flow by these two factors. Simulation results are analyzed with regard to the flow field, lift and drag forces, heat transfer, the deviation of separation and through-flow in the channel, and the temperatures on the channel walls. The flow is more strongly destabilized by an opposing buoyancy, but can be fully stabilized by an aiding buoyancy in an inclined channel. The drag on the cylinder is minimized around a critical Richardson number Ricr. The inclination of the channel has significant effects on the local heat transfer on the cylinder and on the characteristics of the through-flow. The pattern of the wake flow, i.e., whether it is steady or unsteady, affects the heating of the channel walls.

Unraveling metachronal wave effects on heat and mass transfer in Non-Newtonian fluid

Non-Newtonian fluids flow generated by “cilia” are critical in medicine and bio-medical engineering. Such investigations are created by the back-and-forth movement of a microscopic hair-like structure connected to the walls, which causes a metachronal wave to form and drive biological fluids. Motivated by a wide range of biological applications, this study aims to explain the incompressible flow of Ellis fluid caused by the propagation of an infinite metachronal wave train traveling along channel walls owing to constantly beating cilia. The problem is simplified by low Reynolds number and long wavelength assumption. The mathematical model is solved with the aid of symbolic computational software Mathematica 13 version. The consequences of emerging parameters are then shown in graphical form and discussed comprehensively. From the study, it is worth mentioning that velocity declines with increasing material constants. Temperature distribution is also improved in the core sector of the channel and reduced at the walls. It is predicted that this approach will make an essential contribution to the progress and enhancement of various types of drug delivery systems in the biomedical industry and biomechanics.

Entropy production in the flow of Bingham-Papanastasiou fluid having temperature and shear rate-dependent viscosity

This article comprehensively examines entropy production in a peristaltic flow of Bingham-Papanastasiou fluid in an asymmetric wavy wall channel. The viscosity of the fluid is selected to depend on the temperature in addition to the shear rate. Furthermore, viscous dissipation is considered. The equations governing momentum and energy are adjusted to incorporate the existence of a nonlinear correlation between stress and strain rate. The energy dissipation caused by viscosity in the energy equation exhibits variation between Newtonian and non-Newtonian fluids due to their distinct rheological behaviors and response to shear forces. Newton’s law of viscosity states that the viscous dissipation term for Newtonian fluids follows a simple linear relationship between shear stress and shear rate. In contrast, non-Newtonian fluids exhibit more complex rheological behaviors, with the correlation between shear stress and shear rate described by various constitutive equations, depending on the specific type of non-Newtonian behavior. Consequently, the energy equation for non-Newtonian fluid flow problems becomes more intricate and nonlinear compared to the energy equation for Newtonian fluids, resulting in a more challenging analysis. Modeling of the equations is traditionally obtained using all steps involved in analyzing peristaltic flow. Using MATLAB's bvp5c solver, the obtained coupled set of differential equations is numerically solved. The research explores how the Bingham number and stress growth exponent parameters affect different dimensionless variables, including velocity, streamlines, temperature, axial pressure gradient, entropy production, and the Bejan number.

Effect of magnetic field on viscous flow through porous wavy channel using boundary element method

AbstractThe study aims to investigate the effect of uniform inclined magnetic field on two‐dimensional flow of a steady, viscous incompressible fluid at low Reynolds number through a porous wavy channel. We consider a channel having sinusoidal walls filled with a fully saturated porous medium. The porous regime is assumed to be homogenous and isotropic. The viscous flow through a porous regime is governed by Brinkman equation, where the viscous forces are dominant. This allows us to assume the no‐slip boundary conditions at the walls of the wavy channel. Boundary element method (BEM) based on non‐primitive variables namely, stream function‐vorticity variables is used to solve the Brinkman equation. Further, we consider a very small magnetic Reynolds number to eliminate the magnetic‐induced equation. We analyzed that an increase in Hartman number, porosity, and reduction in inclination angle of magnetic field, wave amplitude, and Darcy number led to a reduction in horizontal velocity, whereas an increase in Hartman number, porosity, wave amplitude, and decrease in Darcy number and angle of inclination of magnetic field led to an increase in vertical velocity. Moreover, the flow reversal phenomena occur in the vicinity of the crest regime of the porous wavy channel for high wave amplitude and low Hartman number. The proposed investigation has widespread applications, such as drug delivery systems to target the drug precisely, magneto‐hydrodynamic pumps to regulate the blood flow in artificial hearts to reduce the risk of blood clotting, and so forth.

Thermal enhancement of couple stress fluid flow through anisotropic porous media

This study examines forced convective heat transfer via an anisotropic porous channel in a couple stress flow. The flow field is assumed to be fully developed and governed by the Darcy Brinkman Forchheimer equation. The thermal field is assumed to be developing. The channel walls are subjected to constant heat flux. Since the momentum equation is non-linear and the thermal energy equation is linear, coupled equations are solved numerically using the finite difference method. The variation in the bulk mean temperature is linear with the axial distance for all values of the couple stress parameter and Darcy number. In the absence of axial conduction and heat sources or sinks in the flow field, it is easy to see that the energy gained by the fluid up to an axial distance is twice the axial distance. The parameters, anisotropic permeability ratio, and anisotropic angle enhance the heat transfer. The couple stress parameter lessens the enhancement in heat transfer. Anisotropy is critical in heat transmission for Darcy number, DaH≤0.8. The heat transfer rate decreases by more than 40% due to couple stress fluid and anisotropic effects in the channel, as opposed to the Newtonian isotropic situation. This investigation's findings have been compared with previous experimental and numerical research.