Wavy Channel Research Articles

Optimization Investigation on Wavy Channel Printed Circuit Heat Exchanger for Solar Energy Powered Brayton Cycle

The Printed Circuit Heat Exchanger(PCHE) has received widely attention for their high effectiveness and compact size and they appear promising to be employed as the heat exchanger in solar thermal system. In this research, the thermal and hydraulic performance of the wavy channels for solar energy were investigated detailed in different amplitudes, inclined angles and channel diameters. The three-dimensional numerical analysis was performed by computational fluid dynamics(CFD) tool and the model is validated by comparing with previous experimental data. Besides, it was difficult to get the universal correlations of Nusselt number and friction factor for various geometrical parameters. In this article, the Kriging response surface method is applied to predict the friction factor and j factor for PCHE wavy channels in different geometrical parameters based on the CFD simulation results. The thermal-hydraulic characters predicted by Kriging response surface showed overall good agreement with the CFD results. Moreover, one of the most popular multi-objective genetic algorithms NSGA-II was adopted in optimization. to maximize j factor, while minimize the fanning friction factor.

Heat transfer characteristics of sinusoidal wavy channel with secondary corrugations

Present study deals with three-dimensional numerical investigations on flow and heat transfer characteristics of sinusoidal wavy channel with secondary corrugations. Computations are carried out by using commercial software ANSYS Fluent 17.2 by considering different wave amplitudes and number of waves in streamwise as well as spanwise directions for fixed width and height of the channel. Flow and heat transfer characteristics of secondary corrugated channels are compared with channels having spanwise and streamwise corrugations alone. Flow characteristics are explained with the help of streamline plots. Volume weighted-average values of secondary flow intensity have been shown to demonstrate the strength of secondary flow generated in different corrugated channels. Effect of secondary flow on heat transfer characteristics has been explained with the help of field synergy principle.

Wavy channels triple-tube LHS unit with sinusoidal variable wavelength in charging/discharging mechanism

A novel wavy channels triple-tube latent heat storage (LHS) unit accompanied by variable wavelength is examined in charging/discharging mechanisms. The LHS triple-tube LHS unit is filled with phase change material (PCM) in the middle tube while water is passed in the inner and outer tubes as the heat transfer fluid (HTF) in opposite directions. Different wavy configurations with variable sinusoidal wavelength and wave amplitude are studied and compared with the smooth channels unit. The performance of the unit is assessed based on the charging/ discharging time and heat storage/recovery rate using different contour plots for the temperature and liquid fraction. The results show the significant effects of channel waviness on the performance of the system. For the best unit, the charging and discharging times reduce by almost 50% and 48%, respectively, compared with the smooth walls LHS system. Moreover, the rates of heat storage and recovery for the best configuration are increased by 100% and 99%, respectively, compared with the LHS unit with no wavy walls. This study also aims to develop the possibility of the practical application of high-performance LHS units using geometry modification.

Numerical modeling of particle motion and deposition in turbulent wavy channel flows

This work investigates the turbulent flow and particles deposition in wavy duct flows. The v2f turbulence model was used for simulating the turbulent flow through the wavy channel. The instantaneous turbulence fluctuating velocities were simulated using the Kraichnan Gaussian random field model. For tracking particles in the fluid flow, the particle equation of motion was solved numerically. The drag, Saffman lift, Brownian, and gravity forces acting on a suspended particle were included in the particle equation of motion. The effects of duct wave amplitude and wave length on deposition of particles of different sizes were studied. A range of waves with different amplitudes and wave lengths were simulated. The particle tracking approach was validated for turbulent flow in a flat horizontal channel where good agreement with previous studies was found. The presented results showed that the duct wavy walls significantly increase the particle deposition rate.

A numerical study on bubble dynamics in sinusoidal channels

In the present work, we investigate the dynamics of a bubble, rising inside a vertical sinusoidal wavy channel. We carry out a detailed numerical investigation using a dual grid level set method coupled with a finite volume based discretization of the Navier–Stokes equation. A detailed parametric investigation is carried out to identify the fate of the bubble as a function of Reynolds number, Bond number, and the amplitude of the channel wall and represented as a regime map. At a lower Reynolds number (high viscous force), we find negligible wobbling (path instability) in the dynamics of the bubble rise accompanied only with a change in shape of the bubble. However, at a higher Reynolds number, we observe an increase in the wobbling of the bubble due to the lowered viscous effects. Conversely, at a lower Bond number, we predict a stable rise of the bubble due to higher surface tension force. However, with a gradual increase in the Bond number, we predict a periodic oscillation which further tends to instigate the instability in the dynamics. With a further increase in the Bond number, a significant reduction in instability is found unlike a higher Reynolds number with only change in the shape of the bubble. At lower values of Reynolds numbers, Bond numbers, and channel wall amplitudes, the instability is discernible; however, with an increase in the channel wall amplitude, the bubble retains integrity due to higher surface tension force. At a higher Bond number and channel wall amplitude, a multiple breakup in the form of secondary bubbles is observed. We propose a correlation which manifests the average bubble rise velocity and the fluctuating velocity (due to channel waviness) as a function of Reynolds number, Bond number, and channel wall amplitude. Finally, we conclude that the bubble dynamics pertinent to the offset channels with varying amplitudes does not remain the same as that of the symmetric channel.

Influence of various shapes of CuO nanomaterial on nanofluid forced convection within a sinusoidal channel with obstacles

Heat transfer intensification is significant for enhancement of the performance of various industrial uses such as condensers. In addition, the presence of nanofluid considerably increases the thermal features of carrier fluid. In current paper, CuO nanoparticles involving different shapes have been employed for heat transfer augmentation in wavy channel with obstacles. This work tries to focus on the main flow pattern and indicate the highest operative terms on the heat rate. In order to do this, computational simulation was applied to simulate hydrothermal behavior. Significant parameter studies were performed to investigate the influences of wavelength and height ratios and velocity inlet. According to obtained results, suitable formula for Nusselt number is offered. Outputs show that Nu goes up with augment of height of obstacle due to increasing in strength of intensity. Also, thinner temperature boundary layer thickness can be seen for greater wavelength ratio. Our finding reveals that heat transfer rate increases more than 55% as the spherical nanoparticles is replace by platelet ones.

An oscillation effect on MHD radiative Casson fluid flows in an asymmetric channel through group theoretical analysis

The flow has been made by considering oscillation and radiation effects for the magnetohydrodynamic (MHD) Casson fluid model within an asymmetric wavy channel. Oscillation occurs during the flow by taking into account the pressure gradient across the ends of the channel. The governed mathematical statement is handled analytically by choosing the group theoretical method. The partial differential equations (PDEs) of the governed system are transformed into ordinary differential equations (ODEs) by calculating the symmetries. Further, the mathematical problem is concluded and the graphical results are shown for the following emerging parameters: Casson fluid parameter β, wavelength λ, oscillation parameter ω, Reynolds number Re, Hartmann number M, radiation parameter R, heat source–sink parameter Q, and Peclet number Pe. The magnitude of velocity profile f(η) increased with an increase in β, λ, Re, and K. With variations of H and ω, f(η) decreased. The temperature profile θ(η) increased when the values of Pe, Q, and R increased.

Thermal-hydraulic performance evaluation of gas-liquid multiphase flows in a vertical sinusoidal wavy channel in the presence/absence of phase change

Turbulent gas-liquid multiphase flows with and without phase change in a vertical wavy channel are addressed. The multiphase flow field is resolved using the volume of fluid method (VOF), and the flow equations are discretized and numerically solved by the well-known finite volume method. As a multiphase system without mass transfer, air/water flow is considered. It is shown that numerical simulation is well capable of predicting the various multiphase flow regimes ranging from slug to bubbly flows inside wavy channels. Moreover, accurate predictions of overall pressure drop are provided by numerical solutions for various air and water flow rates and the phase shift angle between wavy channel walls. Additionally, condensing flows of refrigerant R134a are simulated inside wavy channels. It is found that for almost all the cases considered in the present study, the convective heat transfer coefficient is higher in wavy channels in respect to straight channels. However, a significant pressure drop penalty is observed especially for high mass fluxes across wavy channels. Therefore, the use of the wavy channels for the enhancement of condensing heat transfer is only advisable for low mass fluxes with the phase shift angle of 180°.

Numerical Investigation and Thermal Transfer on a Wall Corrugated without and with Artificial Roughness

The objective of this study is to give the designer an appreciation of the heat transfer enhancement in turbulent flows through corrugated channels in a heat plate exchanger. Precisely, the influence of a new technic named the artificial roughness is probed on corrugated walls, with their variable wall amplitudes for assessing the effectiveness of the heat exchange. For that purpose, a numerical simulation approach is adopted. The rectangular, triangular, trapezoidal and sinusoidal corrugated wall and artificial roughness wall shapes are investigated, in order to determine the optimal wall profile resulting in significance increase in the heat exchange process with a minimum friction loss. The numerical results are presented in the form of isotherms, streamlines, contour, Nusselt number (Nu) and friction coefficient (Cf) using commercial software ANSYS- Fluent where the Reynolds number is in the range from 3 000 to 12 000. Our simulations reveal that the sinusoidal-corrugated channel has the highest heat transfer enhancement followed by rectangular, triangular and trapezoidal-corrugated channel. In addition, introduction of artificial roughness in the wavy channel induces stronger secondary flow which makes the flow three-dimensional and improve the heat transfer by a maximum 40% at a Reynolds number equal to 12 000. This may indicate benefits for designing heat plate compact exchangers capable of higher performances in the turbulent flow regimes.

Emerging Attractor in Wavy Poiseuille Flows Triggers Sorting of Biological Cells.

Microflows constitute an important instrument to control particle dynamics. A prominent example is the sorting of biological cells, which relies on the ability of deformable cells to move transversely to flow lines. A classic result is that soft microparticles migrate in flows through straight microchannels to an attractor at their center. Here, we show that flows through wavy channels fundamentally change the overall picture. They lead to the emergence of a second, coexisting attractor for soft particles. Its emergence and off-center location depends on the boundary modulation and the particle properties. The related cross-stream migration of soft particles is explained by analytical considerations, Stokesian dynamics simulations in unbounded flows, and Lattice-Boltzmann simulations in bounded flows. The novel off-center attractor can be used, for instance, in diagnostics, for separating cells of different size and elasticity, which is often an indicator of their health status.

Streamline segment statistics propagation in inhomogeneous turbulence

Streamline segment statistics are collected from tomographic particle image velocimetry and direct numerical simulation data of a turbulent wavy channel flow. The model equation for such statistics is adapted for inhomogeneous turbulence. The novel formulation is applied to explain the observations and identify the locally acting mechanisms.

Unsteady MHD Convective Heat and Mass Transfer Flow in a Vertical Wavy Channel with Oscillatory Wall Temperature and Concentration

Unsteady MHD Convective Heat and Mass Transfer Flow in a Vertical Wavy Channel with Oscillatory Wall Temperature and Concentration

Submicron Particle Focusing and Exosome Sorting by Wavy Microchannel Structures within Viscoelastic Fluids.

Exosomes, submicron membrane vesicles (30-200 nm) secreted by almost all cells, containing significant information such as proteins, microRNAs and DNAs, are closely associated with disease diagnostic and prognostic tests for liquid biopsy in clinical practice. However, their inherently small sizes lead to great challenges for isolating them from complex body fluids with high-throughput and high-purity. In this work, a reverse wavy channel structure using viscoelastic fluids with the addition of biocompatible polymer was presented for elasto-inertial focusing and sorting of submicron particles and exosomes. The microfluidic periodically reversed Dean secondary flow generated by repeated wavy channel structures could facilitate particle focusing compared with traditional straight channels. Four differently sized fluorescent submicron spheres (1 μm, 500 nm, 300 and 100 nm) were used to study the focusing behavior under various conditions. We have achieved simple, high-throughput, and label-free sorting of exosomes with purity higher than 92% and recovery higher than 81%. This developed elasto-inertial exosome sorting technique may provide a promising platform in various exosome-related biological research and pharmaceutical applications.

Effects of Radiative Electro-Magnetohydrodynamics Diminishing Internal Energy of Pressure-Driven Flow of Titanium Dioxide-Water Nanofluid due to Entropy Generation.

The internal average energy loss caused by entropy generation for steady mixed convective Poiseuille flow of a nanofluid, suspended with titanium dioxide (TiO2) particles in water, and passed through a wavy channel, was investigated. The models of thermal conductivity and viscosity of titanium dioxide of 21 nm size particles with a volume concentration of temperature ranging from 15 °C to 35 °C were utilized. The characteristics of the working fluid were dependent on electro-magnetohydrodynamics (EMHD) and thermal radiation. The governing equations were first modified by taking long wavelength approximations, which were then solved by a homotopy technique, whereas for numerical computation, the software package BVPh 2.0 was utilized. The results for the leading parameters, such as the electric field, the volume fraction of nanoparticles and radiation parameters for three different temperatures scenarios were examined graphically. The minimum energy loss at the center of the wavy channel due to the increase in the electric field parameter was noted. However, a rise in entropy was observed due to the change in the pressure gradient from low to high.

Detection and tracking of bubbles in two‐phase air water flow for non‐convergent sinusoidal channel

Bubble detection and tracking, which is essential for the enhancement of gas–liquid two-phase flow applications, is difficult due to optical noise surrounding bubble boundaries. Two-phase flow applications involving unconventional wavy channels further complicate these tasks by introducing non-linearity. In this work, the authors apply a path-based approach to transform a sinusoidal channel into a straightened horizontal channel for bubble detection and tracking. Segmented morphological operations are applied to the linear channel to identify each bubble as a single entity and to eliminate noise caused due to illumination conditions. The bubbles are detected through blob analysis and are associated across different frames based on motion, estimated by Kalman filter in both sinusoidal and path-based approach to the sinusoidal channel. The results show that the proposed path-based straightened channel gives more accurate results for the benchmark parameters of bubble count and bubble velocities than the sinusoidal channel with a percentage error reduction of 31.61% for bubble count and 27.36% for velocity.

Study of thermal and hydraulic performance of air cooled minichannel heatsink with novel geometries

Numerical and experimental study of minichannel heat sinks (MCHS), with air as a cooling medium, has been performed for straight channel heatsink (SC HS), wavy channel heatsink (WC HS) and branch wavy channel heatsink (BWC HS) to investigate thermal and hydraulic performances. After considering both the conduction and the convection as a mode of heat transfer, numerical computation of three-dimensional conjugated heat transfer between the heat sink and air flow has been performed by using full domain simulation in ANSYS Fluent. Laminar model is selected for the study of air flow and heat transfer as the Reynolds number varied from 300 to 1900 for a different range of air flow rates. Heating powers of 20 watt and 30 watt are applied at the base of the heat sink. Followed by detailed experimentation, the numerical results are also examined to get acquainted with the flow fields and their roles in the thermal performance of individual heat sinks. It has been found that the thermal-hydraulic performance factor of BWC HS exhibited superiority over SC HS and WC HS. It is also noticed that significant improvements in the junction temperature of BWC HS have been achieved. Experimental results have been validated with numerical results.

Production‐limited delayed detached eddy simulation of turbulent flow and heat transfer

AbstractA hybrid RANS/LES model based on the BSL k‐ω RANS model, termed the production‐limited delayed detached eddy simulation (PL‐DDES) model, was developed for simulating turbulent flow and heat transfer. The PL‐DDES model was obtained by limiting the production of turbulence kinetic energy with the proposed control resolution function. The PL‐DDES model was tested by simulating turbulent flow and heat transfer in a plane and a wavy channel with different thermal boundary conditions and different Reynolds numbers in this paper. The results of the plane channel flow show that the performance of the PL‐DDES model is better than that of the improved delayed detached eddy simulation (IDDES) model for alleviating the log‐law layer mismatch (LLM) issue. With a much coarser grid resolution, although the resolved turbulent scales decrease, the time‐averaged velocity and temperature are successfully predicted. The capability of predicting turbulent flow and heat transfer over a wavy wall manifests, and the PL‐DDES model has considerable potential in industrial and environmental applications.

A spatial Markov model for upscaling transport of adsorbing-desorbing solutes

The Spatial Markov Model (SMM) is an upscaled model with a strong track record in predicting upscaled behavior of conservative solute transport across hydrologic systems. Here we propose an SMM that can account for reactive linear adsorption and desorption processes and test it on a simple benchmark problem: flow and transport through an idealized periodic wavy channel. The methodology is built using trajectories that are obtained from a single high resolution random walk simulation of conservative transport across one periodic element. Our approach encodes information about where a particle starts at the inlet, where it leaves at the outlet, how long it takes to cross the domain and one additional piece of information, the number of times a particle strikes the boundary, with the objective of predicting large scale transport with arbitrary linear adsorption and desorption rates. Our benchmark problem demonstrates that predictions made with our proposed SMM agree favorably with results from direct numerical simulations, which resolve the full transport problem.

Experimental investigation of TiO2–water nanofluid flow and heat transfer inside wavy mini-channel heat sinks

The present study comprises experimental investigation on heat transfer and hydrodynamic characteristics of TiO2 nanofluid as coolant in wavy channel heat sinks having three different channel configurations. The performance of TiO2 nanofluids having concentrations of 0.006, 0.008, 0.01 and 0.012 vol% is compared with that of distilled water under laminar regime at heating powers of 25 W, 35 W and 45 W. Results indicated that for all heat sinks, nanofluids showed better heat transfer characteristics than distilled water. With an increase in heating power, TiO2 nanofluid thermal performance was decreased. Using 0.012% TiO2 nanofluids, minimum wall base temperature and maximum enhancement in Nusselt number are noted as 33.85 °C and 40.57%, respectively, for heat sink with wavelength of 5 mm and amplitude of 0.5 mm corresponding to Reynolds number of 894 at heating power of 25 W. Pumping power requirement is function of flow rate and pressure drop, and its maximum value of 0.0284 W is associated with heat sink with minimum wavelength. Moreover, variation in wavelength of channel is found to have dominating effect on heat transfer performance of heat sink as compared to the width of channel.

Time-dependent analysis of electroosmotic fluid flow in a microchannel

The present work models electroosmotic induced fluid flow in a microfluidic device. For theoretical analysis, the geometry of this device is considered as an asymmetric, narrow, wavy channel with charged surface. It is assumed that the length of the channel is finite and the characteristic wavelength is very large compared to the half width of the channel. The flow is assumed to be governed by Navier–Stokes equations augmented with electric body force. A transient two-dimensional flow analysis is presented by employing lubrication theory. Debye–Huckel linearization is adopted to obtain a general solution of Poisson–Boltzmann equation. The flow rate, velocity profile, pressure distribution, and wall shear stress are analyzed as functions of various parameters involved like zeta-potential ratio, Debye–Huckel parameter, etc. It is noted that the fluctuations in pressure and shear stress increase with the increasing zeta-potential ratio when the Helmholtz–Smoluchowski velocity is positive. The streamline pattern and the particle trajectories are analyzed to understand the trapping phenomenon and the retrograde motion. It is observed that the electroosmosis phenomenon drastically modulates the fluid flow in microchannels. Although the asymmetric nature of the wavy channel does not support active particle transport, the applied electric field enhances the particle motion favoring optimal conditions. It is observed that the extreme asymmetry of the wall motility reduces the net flow rate. Further, it is noticed that the asymmetry reduces the amplitudes of the pressure. This model can help toward designing artificial organs based on microfluidic devices which can also be applicable to analyze lumenal flow inside arteries and flow inside intrauterine system, and to implant the embryo at the best location in the uterus for human-assisted reproduction.