Convection Phenomena Research Articles

Micro-polar liquid flows with magnetohydrodynamic (MHD) mixed convection due to a nonlinear stretched sheet in a convective state

The topic of this study is the flow of a micro-polar liquid toward a nonlinear stretched surface using magnetohydrodynamics (MHDs). The analysis presents the effects of some important parameters on fluid flow. The mixed convection phenomena are used to examine the characteristics of heat transmission. By using the appropriate transformations, dimensional nonlinear equations can be transformed into dimensionless expressions. The governing dimensionless problems are solved using the modified Laplace decomposition approach by examining the effects of various boundary factors on flow and heat transfer.

Transport Features on Bidirectional Nanofluid Flow with Convective Heating and Variable Darcy Regime

The performance of Au and nanoparticles in Casson flow propelled by the rotational effect subject to convective heating and variable Darcy phenomenon is presented. As a means to contribute significantly to the biomedical industry for proper prediction and treatment of diseases like cancer, stenosis, et cetera, the Casson fluid model and magnetohydrodynamic effect are employed in this study to investigate the bidirectional-rotating boundary layer flow of blood since Casson rheology best describe the mammalian blood flow dynamics and that blood is electrically conducting in nature. The enormous performance of nanoparticles made them extremely useful; hence, they gained recognition over the conventional refrigerants and were widely used by scientists, modelers, and researchers for controlling and treating diseases via drug targeting (chemotherapy), etc. In the three-dimensional plane, the assumed electrically conducting fluid conveying nanoparticles is properly mixed through the Coriolis force, thus rotating with angular velocity across the variable porous medium. A numerical tool, Chebyshev Collocation Method (CCM) with pseudo-spectral approach, is deployed on the resulting transformed ODEs. Profile distributions of respective boundary layers to distinct responses of model parameters, including the Eckman, Darcy, and Biot numbers on Au and nanoparticles, are analyzed and discussed. The dominance of nanoparticles on both velocities is revealed, while Au nanoparticles demonstrated a higher thermal performance rate. A rise in the Darcy parameter has a diametrically opposed behavior on the primary and secondary velocities.

Nanofluid thermo-bio-convection in a horizontal porous wavy-walled annulus: Interaction of phototactic microorganisms and nanoparticles distribution

Transport phenomena related to thermo-bioconvection have recently emerged as an intriguing area of study because of their multi-physical applications such as bio-energy systems, food industries, solar collectors, pollutant dispersion in aquifers, biological wastes processing, chemical catalytic converters, geothermal energy usage, petroleum oil reservoirs, enhanced oil recovery, thermal energy storage, chemical processing equipment, fuel cell technology, medical application, microfluidic devices, and others. In this context, it is highly challenging to design and regulate a system with multi-physical transport in a complex geometry. The goal of the current study is to analyze the thermo-bioconvective heat transfer induced by a gradient of temperature and a motile of phototactic microorganisms with the presence of two types of nanoparticles inside a wavy-walled horizontal cylindrical porous annulus. The originality of this investigation is analyzing the influence of microorganisms, waviness parameters and hybrid nanofluid on thermo-convective instabilities. The effects of the wall waviness parameters, bioconvection Rayleigh number (Rab), thermal Rayleigh number (RaT), nanoparticles volume fraction ϕ and Lewis number (Le) on the flow structure, temperature, and isoconcentrations of microorganisms are investigated and explained in detail. The key findings showed that the Lewis number impacts the onset of thermo-convection and bioconvection and convection phenomena begins rapidly for small values of Lewis number. The nanoparticles enhance the heat transfer in case of thermo-bioconvective flow in a horizontal porous cylindrical system. The average Nusselt number Nu¯ decreases as the wall waviness parameters, amplitude λ, and undulation number η increase. It was also shown that thermo-convective instabilities may develop depending on thermal Rayleigh number, bioconvection Rayleigh number, nanoparticles volume fraction and wall waviness parameters.

Modeling and analysis of Bödewadt hybrid nanofluid flow triggered by a stretchable stationary disk under Hall current

In the recent era of science and technology scientists have influenced by the hybridization of nanofluids due to their advanced thermophysical features. Hybrid nanofluids have superior response to thermal conductivity than any other conventional nanofluids. Therefore, the present study investigates the Bödewadt flow of hybrid nanoliquid above a stretchable static disk located in the plane z=0. Bödewadt flow describes a stable and uniform angular rotation of liquid at a higher distance from the static disk. Such flow is characterized through pressure gradient in radial direction and is balanced with centrifugal forces. An incompressible homogeneous electrically conducting flow occupies its space at z≥0. Hybrid nanofluid is a mixture of nanoparticles Cu (copper) and TiO2 (titanium dioxide) with water considered as a base-fluid. Titanium dioxide reveals excellent photo catalytic attributes and hence is implemented in antibacterial/antiseptic compositions. Moreover, copper nano-ingredients metallic particles suggest suitable dye diminution and catalytic potential properties. Hall effect is encountered in the momentum equations to measure the magnetic field while radiation term is considered to address the energy analysis. The convective flow phenomenon is normalized by executing similarity functions. The reduced governing system is then solved in numerical manner using Runge-Kutta-Fehlberg (RKF-45) procedure. The flow phenomenon on velocity and thermal fields is discussed in graphical way. Three-dimensional flow visualization with two-dimensional contours and streamlines are portrayed as well. Moreover, the numeric data of local-Nusselt number shear stresses is computed against selected values of the physical parameters. The modification in Hall current magnifies the radial velocity field and reduces the velocity field along axial direction. The temperature field is enhanced by the increased variations in heat transfer Biot number. The influence of volume fractions results in modification of thermal profiles.

Single-Entity Electrochemistry in the Agarose Hydrogel: Observation of Enhanced Signal Uniformity and Signal-to-Noise Ratio.

For the first time, single-entity electrochemistry (SEE) was demonstrated in a hydrogel matrix. SEE involves the investigation of the electrochemical characteristics of individual nanoparticles (NPs) by observing the signal generated when a single NP, suspended in an aqueous solution, collides with an electrode and triggers catalytic reactions. Challenges associated with SEE in electrolyte-containing solutions such as signal variation due to NP aggregation and noise fluctuation caused by convection phenomena can be addressed by employing a hydrogel matrix. The polymeric hydrogel matrix acts as a molecular sieve, effectively filtering out unexpected signals generated by aggregated NPs, resulting in more uniform signal observations compared to the case in a solution. Additionally, the hydrogel environment can reduce the background current fluctuations caused by natural convection and other factors such as impurities, facilitating easier signal analysis. Specifically, we performed SEE of platinum (Pt) NPs for hydrazine oxidation within the agarose hydrogel to observe the electrocatalytic reaction at a single NP level. The consistent porous structure of the agarose hydrogel leads to differential diffusion rates between individual NPs and reactants, resulting in variations in signal magnitude, shape, and frequency. The changes in the signal were analyzed in response to gel concentration variations.

Numerical Analysis of Entropy Generation in a Double Stage Triangular Solar Still Using CNT-Nanofluid under Double-Diffusive Natural Convection

The analysis of entropy generation provides valuable information for the design and optimization of thermal systems. Solar stills are used for water desalination and purification. Using renewable energies, they provide a sustainable solution for drinking water supply in remote areas and off-grid situations. This work focuses on the 3D numerical study of entropy generation in a two-stage solar still subjected to the natural double diffusion convection phenomenon in the presence of CNT nanoparticles. The effects of Rayleigh number, buoyancy ratio, and nanofluid concentration on thermal, solutal, and viscous irreversibilities and flow structure were studied. The results show that increasing the buoyancy ratio leads to an increase in thermal and solutal entropy generation. The results of this study also show that total entropy is minimal for positive volume force ratios, N, at a nanoparticle volume fraction of around 3%, and for negative N ratios, at a volume fraction of around 4%.

Non-Newtonian Slippery Nanofluid Flow Due to a Stretching Sheet Through a Porous Medium with Heat Generation and Thermal Slip

The domains of engineering, electrical, and medicine all have a significant demand for nanofluids. Applications for nanofluid flow include electronic device storage, industrial cooling and heating frameworks, and associated medicinal management information systems. Nanofluids are utilized generally as coolants in heat exchangers such as thermostats, electronic cooling systems, and radiators due to their enhanced thermal characteristics. This study aims to explain the mixed convection phenomenon’s applications on the thermal impact of Maxwell nanofluid. The mass diffusivity is supposed to be a function of concentration, whereas the thermal conductivity and viscosity of Maxwell nanofluid are assumed to be functions of temperature. It is recommended to consider the additional thermal effects of thermal slip, magnetic fields, and heat generation phenomena. The fluid flow motion was caused by the vertically stretched sheet. The dimensionless formulation of the suggested physical model is shown by the suitable variables interacting. The shooting approach is used in the numerical simulations, and it is based on lowering higher-order nonlinear differential equations to first-order. The slip velocity and the magnetic parameters have a direct impact on the local skin friction coefficient and velocity, as indicated by the research findings. Also, the increase in values of the Maxwell parameter, porous parameter, and viscosity parameter leads to the enhancement of temperature distribution, while the decline in velocity distribution can be attributed to the same factors. A comparison is also made with the results described in the literature that is currently available, and a superb agreement is discovered.

Numerical investigation of convection–diffusion model by using the new upwind finite volume approach

In this study, we constructed a numerical technique for the simulation of the convection–diffusion problem under convection dominancy. Lagrange interpolation technique is applied to obtain new expressions for the approximation of variable at the interfaces of control volume. Moreover, based on these interface approximations new numerical scheme is developed to approximate convection–diffusion phenomena. The Crank–Nicolson approach is applied for the temporal approximation. This newly constructed numerical scheme is unconditionally stable with second-order accuracy in time and space both. Numerical tests are carried out for the justification of the new algorithm. A comparison of numerical results produced by proposed technique and some other numerical approaches is presented. This comparison indicates that for convection dominant phenomena, the numerical solution of conventional finite volume method contains with non-physical oscillations which analyze that proposed numerical technique results in a high accurate and stable solution.

Radiation absorption impact on the thermophysical properties of Cu- and TiO2-water nanofluids: Laplace transform technique

An electrically conducting time-dependent flow of water-based nanofluid comprised of Copper and Titanium oxide over a stationary plate embedding with a porous matrix is analyzed in this study. The novelty arises due to the interaction of both the thermal radiation as well as the radiation absorption that affect the heat transport phenomenon. In the single-phase flow, both the variation of particle concentration and the solutal concentration for the inclusion of chemical reaction are taken care of. Also, the influence of the free convection phenomena is explained significantly. The transformed dimensionless system of the governing equations is handled analytically by using the Laplace Transform method. The behavior of the characterizing parameters involved in the governing equations is presented via graphs and the simulation of the numerical results of the rate coefficients like shear rate and rate of heat and solutal transfer is deployed through the table. However, the physical significance of these parameters is deliberated briefly. Finally, the important outcomes are higher heavier species because of lesser solutal diffusivity which attenuates the fluid concentration throughout the domain. Further, radiation absorption causes a significant boost in the nanofluid temperature distribution.

Direct Numerical Simulation of Low and Unitary Prandtl Number Fluids in Reactor Downcomer Geometry

Mixed convection of low and unitary Prandtl fluids in a vertical passage is fundamental to passive heat removal in liquid metal and gas-cooled advanced reactor designs. Capturing the influence of buoyancy in flow and heat transfer in engineering analysis is hence a cornerstone to the safety of the next-generation reactor. However, accurate prediction of the mixed convection phenomenon has eluded current turbulence and heat transfer modeling approaches, yet further development and validation of modeling methods is limited by a scarcity of high-fidelity data pertaining to reactor heat transfer. In this work, a series of direct numerical simulations was conducted to investigate the influence of buoyancy on descending flow of liquid sodium, lead, and unitary Prandtl fluid in a differentially heated channel that represents the reactor downcomer region. From time-averaged statistics, flow-opposing/aiding buoyant plumes near the heated/cooled wall distort the mean velocity distribution, which gives rise to promotion/suppression of turbulence intensity and modification of turbulent shear stress and heat flux distribution. Frequency analysis of time series also suggests the existence of large-scale convective and thermal structures rising from the heated wall. As a general trend, fluids of lower Prandtl number were found to be more susceptible to the buoyancy effect due to stronger differential buoyancy across the channel. On the other hand, the effectiveness of convective heat transfer of the three studied fluids showed a distinct trend against the influence of buoyancy. Physical reasoning on observation of the Nusselt number trend is also discussed.

Heat and mass transfer effects on fluid past an exponentially accelerated vertical plate due to time‐fractional MHD‐free convection

AbstractThis article focuses on the study of heat and mass transfer (HMT) fluid flow over an exponentially accelerated vertical plate, which is subjected to an applied magnetic field and viscous dissipation. The research has applications in various manufacturing processes such as wire/fiber drawing, hot rolling, continuous casting, and hot extrusion, where heat transfer to the ambient medium and the hot moving material are of utmost importance. The findings could also be relevant to aerospace engineering applications. The study investigates the time‐fractional natural convection phenomenon and utilizes conservation laws to derive the flow guiding equations, which are then made nondimensional. Finite difference discretization is utilized to solve the dimensionless equations implicitly. Then the flow simulation results such as concentration, temperature, and velocity profiles are discussed based on the variation in parameters such as Prandtl number (), thermal/mass Grashof number (), Eckert number (), magnetic parameter (), time‐fractional order (), and Schmidt number . Also, the HMT rate is depicted using the Nusselt number and skin friction plots. It is noted that HMT increases when increases and decreases. The change in time‐fractional order affects the velocity profiles adjacent to the wall and is more significant in the case of lower values of the Prandtl number.

Radiative slip transport of magnetized gyrotactic micro-organisms submerged with nano fluid along a vertical stretching surface with suction/injection effects

Micro-organisms play an important role in numerous conditions such as toxin release, digestion and antibiotics. These remarkable features of motile organisms can lead to bio convection phenomena. Keeping in view, the present article is focused to study the collective impact of motile organisms and nanoparticles on flow past an elastic porous surface. Thermal radiation, viscous dissipation and prescribed surface slip condition is also imposed in order to acquire physically realistic analysis. The flow governing problem is modeled using fundamental laws of momentum and energy which afterward is transformed by utilizing a suitable scaling analysis. Role of emerging sundry parameters on quantities of physical interest are portrayed graphically and discussed in a physical manner. It is observed that fluid’s velocity and temperature rises for radiation parameter but concentration of fluid drops down. Local motile density slightly enhances with Dissipation, Suction and Radiation factor while it drops down with Slip factor. When injection of fluid raised then skin friction coefficient, Nusselt number, Sherwood number and motile microorganism density also raised.

Mixed convection of EG/NEPCM inside a lid-driven cavity with a rotating cylinder

Using the potential of nature's phenomena such as free convection phenomenon could help to cooling a piece, such as a moving hot plate in lid-driven problems. Moreover, adding modern nanostructures named nano-encapsulated phase change material (NEPCM) with ability of phase transition could greatly improve the heat transfer processes. In this study, the mixed convection of ethylene glycol (EG) and NEPCM was simulated inside a lid-driven cavity with a rotating cylinder to evaluate the contribution of Grashof number, cylinder speed, and concentration of NEPCM on the heat transfer characteristics. Hence, the findings of current numerical study indicated that the NEPCM with 6% concentration increased the mean Nusselt number by 41.7%. Moreover, the cylinder speed enhanced the mean Nusselt number by 38.7%. Finally, there was an optimum value for concentration occurred in 4% brought for Grashof number of 104.

Indirect urea electrooxidation by nickel(III) in alkaline medium: From kinetic and mechanism to reactor modeling

AbstractThis study consists in the determination of two kinetic laws of urea oxidation (UO) and electrooxidation (UEO) in alkaline media on nickel(III). Two kinds of active sites were examined, the first one derived from a Ni(OH)2 powder and the second from a massive nickel electrode. Partial orders of nickel(III) (two for UO and five UEO) enable to conclude about (i) the urea adsorption on two nickel(III) sites and (ii) that a multistep oxidation of urea occurs involving five nickel(III) site electroregenerations. A multipathway mechanism is also proposed to explain UEO facilitated by the nickel(III)/nickel(II) mediation system, and to predict the by‐products' formation previously identified (). At last, a model combining the UEO kinetic law previously established, with diffusive and convective transport phenomena was developed. A consistent correlation (maximum deviation of 6%) between laboratory electrolysis results with the model' predictions was obtained under different operating conditions, enabling the validation of this model.

Examination of effective strategies on changing the amount of heat transfer and entropy during non-Newtonian magneto-nanofluid mixed convection inside a semi-ellipsoidal cavity

Due to the application importance of convection flows under the impact of external fields such as magnetic field for non-Newtonian nanofluids, in cases such as nuclear processes, technologies related to lubrication, production and processing of food products, the modeling of these types of currents is very important. The existing research inquires the influence of heat production/absorption on the characteristics of non-Newtonian flow and entropy formation caused by convection heat transfer. For this purpose, the phenomenon of mixed convection inside the semi-elliptical chamber containing a power-law nanofluid is presumed in such a way that the Brownian motion of nanoparticles is considered. The curved and vertical walls of the enclosure are cold and under three different types of heating, respectively. The cold wall has no speed while the chamber vertical wall has a non-uniform velocity distribution (cosine) with a phase difference. The main goal of the research is to depict the impact of changing the position of applying the magnetic field and changing the phase difference of wall movement on the fluid flow. Flow modeling was accomplished via the utilization of lattice Boltzmann method and the accuracy of the findings was affirmed by comparing previous related studies. According to the research findings, enhancing the mean Nusselt number has a direct relationship with enhancing the phase difference. In addition, by enhancing the phase difference to 180, the mean Nusselt number up to 46% more is acquired, the influence of magnetic field applying becomes more conspicuous. In addition to the fact that the enhancing in Richardson number leads to increment of in the mean Nusselt number value and flow power, the effect of varying the phase difference becomes more noticeable with the enhancing in Richardson number. Enhancing in the Hartmann number, index of power-law and decreasing in the heat production/absorption coefficient lead to decrease in the entropy value and the average Nusselt number. By changing the position of applying the magnetic field, a current with various features can be acquired. Based on the results, it was demonstrated that changing the type of wall heating along with changing the heat absorption/production coefficient are very useful strategies in controlling the system thermal characteristics.

Construction and analysis of a HDG solution for the total-flux formulation of the convected Helmholtz equation

We introduce a hybridizable discontinuous Galerkin (HDG) method for the convected Helmholtz equation based on the total flux formulation, in which the vector unknown represents both diffusive and convective phenomena. This HDG method is constricted with the same interpolation degree for all the unknowns and a physically informed value for the penalization parameter is computed. A detailed analysis including local and global well-posedness as well as a super-convergence result is carried out. We then provide numerical experiments to illustrate the theoretical results.

Analysis of fluctuating heat and current density of mixed convection flow with viscosity and thermal conductivity effects along horizontal nonconducting cylinder

Due to excessive heating, various physical mechanisms are less interested in engineering and modern technologies. To reduce excessive heating, the aligned magnetic field acts like a coating material to insulate the heat which is a very important mechanism in modern technologies. To solve this problem, the primary goal of the current analysis is to utilize magnetization normal to the surface. Numerical simulations have been made of the magnetohydrodynamic convective heat-transfer phenomena of electrically conductive fluid flow down the horizontally non-magnetized heated cylinder. The associated non-linear PDEs that control fluid motion can be conveniently represented by using the finite-difference algorithm and primitive element substitution. The numerical outcomes are deduced in graphs and tabular form with the help of FORTRAN program. The distinct parameters in the flow model are affected by physical features such skin friction, heat transfer, and current density for velocity profile, magnetic field profile, and temperature profile together with their slopes. The current magnetohydrodynamics and thermal problem is very important in the fields of MRI resonance sequences, artificial heart wolves, internal heart cavities, and nanoburning technologies. Additionally, the increase in Prandtl Pr leads to a reduction in skin friction and heat transmission, which is physically consistent, due to frictional forces between viscous layers with lesser magnitude.

A novel high-dimensional and multi-physics modeling approach of proton exchange membrane fuel cell for real-time simulation

Fuel cell model provides state observation and quantitative analysis for Hardware-In-the-Loop (HIL) test platform. For a high-dimensional multi-physics model, the observed distribution of physical properties is meaningful for fuel cell stack optimization, manufacturing process and model-based control development. However, traditional modeling approach is difficult to consider both the calculation accuracy and efficiency. To solve this problem, this paper proposes a high-dimensional multi-physics real-time modeling approach for fuel cells based on partial differential equations (PDEs)-tridiagonal matrix equation transformation (TMET) and symmetric successive overrelaxation (SSOR) algorithm. In the proposed method, a generalized framework of TMET and a novel staggered grid technique is developed. In this case, both the convection and diffusion phenomena can be accurately described. For different fuel cells or parameters change, supplementary model modification or development is not required, only the global variables need to be re-assigned. Moreover, SSOR with bi-directional iteration mechanism is used to increase the probability of computational convergence and thus improve the calculation efficiency. Compared with commercial COMSOL model, by using the proposed modeling approach, the mean absolute percentage error (MAPE) of the simulated polarization output characteristics is 1.77%, the MAPE of different distribution characteristics can remain within 10%, and the calculation time can be shortened from hours even days to seconds.

Research on Spontaneous Diffusion and Fragmentation of Liquid Droplets Caused by Marangoni Effect

The Marangoni effect is important to drying silicon wafers, the fields of welding and improving engine liquid fuel efficiency. In this paper, we investigate the Marangoni flow caused by the evaporation of droplets of alcohol solution, which eventually causes the droplet "atomization" phenomenon. The Marangoni convection phenomenon was studied in terms of temperature and droplet concentration, and the changes of droplet diffusion and the degree of droplet "atomization" were investigated after droplets of different volume concentrations of Isopropyl Alcohol (IPA) were added to different solutions.

Mixed convection phenomena in tubes with wire coil inserts

A numerical investigation of the flow and heat transfer in a helical coil in laminar and transitional flow regime under mixed convection conditions is presented. The continuous separation and reattachment of the boundary layer caused by the wire coil, that interrupts the flow near the tube all, and the swirl induced by the helical shape of the insert, are identified as the mechanism for heat transfer enhancement. Simulations in the Reynolds number range 200<Re<1500 show the role of mixed convection on heat transfer, as the flow dynamics is sensitive to the buoyancy forced induced by the tube wall heating. The interaction of the secondary swirl flow with the buoyancy motion is investigated in this work, with the aim of clarifying the range where heat transfer could be worsened by the presence of the helical coil. The investigation has been undertaken considering a helical coil of geometrical characteristics e/D=0.071 and p/D=1.5 and water as working fluid. Validation with experimental results of friction factor and Nusselt number is also presented.