Effect Of Convective Flow Research Articles

Second law analysis on Hall effect of natural convection flow through vertical channel in the presence of uniform heat source/sink

Purpose Microfluidics is one of the extensive elaborated technologies in thermal and engineering fields due to its wide range of applications, such as micro heat exchangers, micro mixture and microchannel heat sinks, which is used to develop a large number of microscopic devices and systems. Enhancement of thermal energy using verity of nanoliquids is one of the challenges in these applications of microfluidics. Therefore, using single wall carbon nanotubes for enhancement of thermal energy in microchannel is the main purpose of this study. Hall effect of natural convection flow in a vertical channel with slip and temperature jump condition is considered. The impacts of radiative heat flux, uniform heat source/sink, viscous dissipation and joule heating are also taken into account. Design/methodology/approach Suitable non-dimension variables are applied to the governing equations to reduce the system into ordinary differential equations. The reduced nonlinear system is then solved numerically using Runge–Kutta–Fehlberg fourth–fifth-order method along with shooting technique. The impact of different pertinent parameters on numerical solutions of primary velocity, secondary velocity, temperature, entropy generation and Bejan number is comprehensively discussed in detail. Also, the obtained numerical results are compared with existing one which perfectly found to be in good agreement. Findings It is established that, with the aspects of Joule heating, viscous dissipation, radiative heat flux and uniform heat source/sink, the production in the entropy can be improved. Further, it is found that the increasing ratio of wall ambient temperature difference and nanoparticle volume fraction leads to enhance the entropy generation. The same effect reverses with increasing values of fluid wall interaction parameter (FWIP) and rare faction. The irreversibility ratio enhances with larger values of nanoparticle volume fraction and decelerates with increment values of FWIP. Originality/value The impact of single wall carbon nanoliquid in a vertical channel flow by using radiative heat flux, heat source/sink, joule heating and viscous dissipation is first time investigated. Further, the influence of Hall current is explored in detail.

Integrated studies of convection and ice layer formation during cooling of the bottom of a rectangular cavity

Experimental studies of the processes of crystallization of water as a liquid — simulator of melts with an inverse dependence of the density of melts on temperature — were carried out on two flat models. With the rapid cooling of the bottom of the cavity, substantial undercooling of the bottom layer of the liquid can be observed. The hydrodynamics in the process of growth of the ice layer at the bottom of the cavity was investigated. The effect of convective flow on the rate of crystallization and on the forms of the crystallization front has been studied. The evolution of the temperature field in the process of crystallization of water at the lower cooled boundary of the cavity is studied. It is shown that the evolution of temperature fields tracks the development stages of instability of the bottom layer of a liquid and the development of Rayleigh-Benard convection observed in a hydrodynamic experiment.

Investigations of Soret, Joule and Hall effects on MHD rotating mixed convective flow past an infinite vertical porous plate

We made an elaborate scrutiny on the Soret and Joule effects of MHD mixed convective flow of an incompressible and electrically conducting viscous fluid past an infinite vertical porous plate taking Hall effects into account. Perturbation technique is used to solve the non-dimensional equations. The effects of the various non-dimensional parameters on velocity, temperature and concentration within the boundary layer are examined. Besides that, computational deliberations or discussions are also undertaken on the effects of the pertinent or significant parameters on the skin-friction coefficient and rates of heat and mass transfer in terms of the Nusselt and Sherwood numbers respectively. The concentration distribution increases with increase in Soret effect and decrease with increase in chemical reaction parameter. An increase in Prandtl number results to decrease the temperature distribution. Both the primary and secondary velocity components and temperature increases with increasing heat source parameter. Skin friction coefficient decreases with an increase in permeability parameter, whereas it shows reverse effect for thermal and mass Grashof numbers. Nusselt number increases with an increase in Prandtl number. Sherwood number reduces with increasing Soret number.

Three-dimensional mesoscopic modeling of equiaxed dendritic solidification in a thin sample: effect of convection flow

A 3D mesoscopic envelope model is used to numerically simulate the experimental X-ray observations of the equiaxed dendritic isothermal solidification of a thin sample of Al-20 wt%Cu alloy including the natural convection flow. Several four-grain simulations are run to investigate the effect of the convection, of the grain position, and of the grain rotation on the tip growth kinetics of one of the grains. We show that the effect of convection flow – consequence of the presence of gravity parallel to the sample thickness direction, z – on the growth kinetics of the reference grain depends significantly on the position of the grain along the sample thickness.

Soret and Dufour Effect of Unsteady MHD Free Convective Flow of Kuvshinski Fluid with Heat and Mass Transfer

Soret and Dufour Effect of Unsteady MHD Free Convective Flow of Kuvshinski Fluid with Heat and Mass Transfer

Diffusion and Flow of CO2 in Carbon Anode for Aluminium Smelting

Using a well-made carbon anode with the right porosity characteristics is essential to the successful operation of a Hall–Heroult cell. Bubble generation at this carbon anode and its contribution to the overall voltage drop in aluminum production holds significant potential for reducing overpotential and improving energy savings. This voltage drop is believed to be greatly influenced by the gas diffusion in the anode carbon, for which there are a limited number of measurements to correlate with the carbon anode properties. In the present study, the CO2 gas diffusion characteristics were first investigated via measuring anode porosity using mercury intrusion porosimetry (MIP) for different samples with different permeability. Second, diffusion experiments were conducted by flowing CO2 gas into the anode sample at elevated temperatures (up to 960 °C). The impact of temperature, average pore size, and permeability on the diffusion coefficient was investigated. The diffusion coefficient was consequently calculated by curve fitting using diffusion theories. The value obtained varied from 1.38 × 10−6 to 7.89 × 10−6 m2/s. A high diffusion coefficient was measured in the carbon sample with larger average pore size and higher permeability. It was found that anomalous diffusion behavior in the temperature range 600 °C to 960 °C was caused by convective flow effects, different diffusion mechanisms, and the Boudouard reaction for these carbon anode samples. Furthermore, by plotting the measured diffusion coefficient against average pore size and permeability, an increasing trend of diffusivity with an increase in pore size and permeability was observed.

Numerical investigation of convective dropwise condensation flow by a hybrid thermal lattice Boltzmann method

The present paper, convective dropwise condensation flow over a cold spot is numerically investigated using a 2D hybrid thermal lattice Boltzmann (LB) model with vapor-liquid phase change. After validating the present LB model, dropwise condensation on a cold spot as the nucleation region is simulated so as to study the nucleation and growth of the isolated droplet. The well-known power law for the growth of a single condensing droplet is demonstrated. And then, both simulations of dropwise condensation and convective dropwise condensation are carried out to study the effect of forced convective flow on dropwise condensation. Aiming to consider the effect of contact angle, the droplet is growing in the constant contact radius (CCR) mode. The results indicate that the forced convectional flow complicates the internal flow of the droplet and the vapor flow. The detouring flow (including the lee-side vortex) around the droplet in an isothermal system is replaced by the suction flow owing to condensation. The interaction between the dragging force of the vapor flow and the surface tension gradient changes the size of two symmetric vortices within the droplet in dropwise condensation. The size of these two vortices inside the droplet depends on the velocity and direction of convective flow. By comparison, the heat transfer enhancement of the superimposed flow is not worth mentioning in spite of different flow mode. Not affected by the vapor flow, the heat transfer is weakened by increasing of the contact angle owing to the change of conduction resistance. The present study illustrates the mechanisms of convective dropwise condensation flow in detail.

A numerical and experimental analysis of the methodology of thermal conductivity measurements in fluids by concentric cylinders

A study of thermal conductivity measurements of fluids, using the technique of steady-state heat transfer in concentric cylinders, is presented. In order to evaluate the effect of convective flow on the measured value of conductivity, numerical results, which were obtained using computational fluid dynamics (CFD) in three dimensions, are compared with experimental data and analytical results of temperature profiles. This latter was obtained considering the hypothesis of heat transfer mechanism being entirely diffusive and solely in the radial direction. An experimental design was proposed aiming to analyze the effects of glycerol mass fraction (0%, 50 and 100%), annuli size (2.525, 4.525 and 6.525 mm) and heat rate (5, 10 and 15 W) in the formation of convective streamlines. The ratio between effective and absolute conductivities (kef/k) was used as a response to evaluate the convection intensity. The results were compared with empirical equations that correlate the ratio kef/k with the dimensionless numbers of Prandtl and Rayleigh, which are in the rate 4.37 ≤ Pr ≤ 3.8 × 103 and 9.0 ≤ Ra ≤ 4.4 × 104. An evaluation of the accuracy in measuring kef is showed based on the simulated data of temperature profiles in the axial, radial and angular directions.

Numerical modeling of flow film boiling in cryogenic chilldown process using the AIAD framework

Flow film boiling plays a dominant role in cryogenic chilldown process, which involves complicated heat transfer and flow regime transition. Nevertheless, existing researches about flow film boiling with cryogenic fluids are relatively limited. In this study, a Computational Fluid Dynamics (CFD) model based on a wall heat flux partition algorithm is built. The AIAD framework implemented in the two-fluid model is employed to appropriately calculate the drag force on the liquid-vapor interfaces. The CFD model is validated by the satisfactory coincidence between the simulated heat fluxes and experimental data in literature. Accordingly, the two-phase interaction on the flow regime and heat transfer is further investigated. The results reveal that the vapor film beneath the bulk liquid becomes thinner due to the drag force on the liquid-vapor interface. In addition, FFT analysis on the pressure drop shows that dominant frequency of the interfacial waves in the tube mainly locates around 2.8 Hz. The normalized intensity indicates that fluctuation becomes more violent with the increase of superheat and inlet liquid flow rate. Finally, comparison between correlations and experimental data indicates that a correlation of heat transfer coefficient considering both film boiling effect and forced convective flow effect needs to be proposed.

Numerical study of the effect of forced convective flow on dropwise condensation by thermal LBM simulation

The enhancement mechanism of forced convective flow on dropwise condensation over a cold spot is numerically investigated by two-dimensional hybrid thermal lattice Boltzmann (LB) model based on the Shan-Chen pseudopotential LB model. After validating the present LB model, dropwise condensation over a cold spot as the nucleation region is simulated. The well-known power law for the growth of a single condensing droplet is demonstrated. Finally, the simulation of dropwise condensation considering the convection flow or not is carried out in the constant contact radius (CCR) mode. Using the CCR model, the effect of contact angle can be also investigated. The result of streamline field indicates that the forced convectional flow complicates the internal flow of droplet and main flow. The dragging force from main flow changes the size of two symmetric vortices inside the droplet. And the channel flow is also strongly influenced by the suction effect caused by condensation at the three phase contact line. By comparison, the heat transfer enhancement of the superimposed flow is not worth mentioning. The present study illustrates the mechanisms of dropwise condensation under forced convectional flow.

Transient melting of an impure paraffin wax in a double-pipe heat exchanger: Effect of forced convective flow of the heat transfer fluid

A transient 2-D numerical study is carried out on the melting (energy storage) of an impure phase change material (paraffin wax) embedded in the annular gap formed by an outer equilateral pipe and an inner tube carrying the heat transfer fluid. A non-orthogonal curvilinear coordinate method is used to account correctly for the irregular boundaries of the annular domain. A set of parametric studies is performed by varying the bulk temperature and mass flow rate of the heat transfer fluid (HTF). Besides, numerical simulations are also made to ascertain the effects of the various cross-sectional shapes and positions of the inner tube as well as the initial state of the solid PCM on the melting process. The temporal velocity and temperature profiles are shown in addition to the cumulatively stored energy and total melt fraction as a function of the melting time. The results indicate that the bulk temperature of the HTF imposes a significant effect on the melting process compared to its mass flow rate. The lower eccentric position of the inner circular tube provides the maximum energy storage capacity compared to its concentric position. The concentrically placed circular inner tube provides the maximum energy storage in the annulus relative to the other two cross-sectional inner tubes namely prolate- and oblate-shaped elliptical tubes.

Effect of partial slip and chemical reaction on convection of a viscoelastic fluid over a stretching surface with Cattaneo-Christov heat flux model

This article explores the effect of homogeneous-heterogeneous chemical reaction and partial slipon convective flow of a viscoelastic fluid with Cattaneo-Christov heat flux modelin the presence of suction/injection and convective boundary condition. The governing system of non-linear partial differential equations arereformed into ordinary differential equations with the help of similarity variables and then they are solved using homotopy analysis method. It is found that the surface heat transfer rate enhances on increasing the thermal relaxation time parameter and the surface mass transfer rate improved by increasing the slip parameter and homogeneous chemical reaction parameter.

MHD Natural Convection Flow of CuO/Water Nanofluid in a Differentially Heated Hexagonal Enclosure with a Tilted Square Block

A numerical investigation has been performed to analyze the effect of magnetohydrodynamic natural convection flow in a differentially heated hexagonal enclosure having a tilted square block filled with CuO/water nanofluid. The horizontal walls of the cavity and tilted walls of the obstacle are uniformly heated of temperature $$\hbox {T}_\mathrm{h}$$ while the inclined walls are kept at constant temperature $$\hbox {T}_\mathrm{c}$$ . The governing conservation equations of the physical problem have been solved using finite element method based on Galerkin weighted residual technique and obtained numerical results are presented graphically in terms of streamlines, isotherms, average Nusselt numbers, mid height horizontal and vertical velocities, average temperature and average velocity of nanofluid for a range of Rayleigh number ( $$10^{3} \le { Ra} \le 10^{6}$$ ), Hartmann number ( $$0 \le { Ha} \le 70$$ ) and solid volume fraction ( $$0.1\% \le \phi \le 5\%$$ ) to show the flow structures and temperature characteristics. It is found that the flow fields and temperature distributions are influenced significantly for the effect of pertinent parameters. In addition, overall heat transfer rate enhanced due to higher values of Ra and $$\phi $$ along with lower value of Ha. Comparisons of the present results with the previously published results on the basis of special cases are performed and found to be in good agreement.

A Single-domain Approach to Simulate the Effect of Convective Flow on the Mushy-zone Structure in Czochralski Growth of Gadolinium Gallium Garnet Crystal

A numerical study was carried out to describe the effect of the melt hydrodynamics on the crystallization front shape in the Czochralski growth of a semitransparent oxide crystal. In the present model calculation, the enthalpy-porosity method was used to solve the phase change problem with the convection due to buoyant, thermocapillary and centrifugal forces. It was shown that the rotationally-driven flow protrudes into the mushy zone when the crystal rotation rate was increased to a certain critical value corresponding to Gr/Re2=0.89 as the ratio between the intensity of buoyancy and forced convection flow in the melt. The ratio between the vertical and horizontal temperature gradients beneath the mushy zone was found to be decreased by increasing the crystal rotation rate. It was shown that the shape of the zone deforms abruptly when the ratio between the axial and radial temperature gradients decreased to the values smaller than the unity. The Burger's number condition was found to be violated in the case Gr/Re2<0.89, at which the onset of geostrophic instability is expected.

Effects of Temperature Dependent Thermal Conductivity and Viscous Dissipation on Free Convective Flow along a Vertical Flat Plate with Asymptotic Solution

This paper reports us the surface temperature distribution effects of free convective flow along a vertical flat plate with temperature dependent thermal conductivity and viscous dissipation with asymptotic solution. The governing equations with associated boundary conditions reduce to local non-similarity boundary layer equations for this phenomenon are converted to dimensionless forms using a suitable transformation. The transformed non-linear equations are then solved using the implicit finite difference method together with Keller-box technique. Numerical results of the velocity and temperature profiles, skin friction and surface temperature profiles for different values of the thermal conductivity variation parameter, the Prandtl number and the viscous dissipation parameters are presented graphically. Also we considered the asymptotic solution for the effect of the thermal conductivity variation parameter, the Prandtl number and the viscous dissipation parameters in skin friction and surface temperature profiles. Detailed discussion is given for the aforementioned parameters. A good similarity is found in small and large value solution with all value solution for the thermal conductivity variation parameter, the Prandtl number and the viscous dissipation parameter for skin friction and surface temperature. Divergence is found near one (1).GANIT J. Bangladesh Math. Soc.Vol. 36 (2016) 33-46

Dendritic growth with the six-fold symmetry: Theoretical predictions and experimental verification

A free dendrite growing in a pure substance is considered with the interfacial effect of anisotropy and convective flow. A stable mode of dendritic growth with the six-fold crystal symmetry is studied using the solvability theory. We demonstrate that the obtained selection criterion for a stable mode of dendritic growth is a function of surface energy stiffness, arbitrary values of Péclet numbers and convective flow intensity. To predict the dendrite tip velocity V and its tip radius R a model of dendrite growth with the six-fold symmetry is formulated. We show that the model equations can be reduced to the growth kinetics with the low Péclet numbers, which exhibit the explicit relationships “tip velocity - undercooling”. The model predictions are compared with experimental data on ice dendrites grown from pure undercooled water on board of the International Space Station (under microgravitational conditions, μg) and on the Ground (under terrestrial conditions, 1g).

Temporal correlation between dyke swarms and crustal extension in the middle Palaeozoic Vilyui rift basin, Siberian platform

This paper presents results from new 40Ar/39Ar isotope dating of nine mafic dykes from three large dyke swarms (Vilyui–Markha, Kontai–Dzherba, and Chara–Sinsk) of the Yakutsk–Vilyui large igneous province (LIP), in addition to a reconstruction of the subsidence history of the middle Palaeozoic Vilyui paleorift basin (eastern Siberian platform). All previously published 40Ar/39Ar and U–Pb dates are summarized. Statistical analysis of the dyke ages reveals repeated magmatic events in the study area. Two major pulses of mafic magmatism are identified: one at the Frasnian–Famennian boundary, with a main peak at ca. 374.1Ma, and another in the latest Devonian with a peak at ca. 363.4Ma. The time of maximum intensity of dyke intrusion coincides (within uncertainty) with rapid subsidence in the Vilyui basin. The minimum total volume of middle Palaeozoic magmatism produced in the Yakutsk–Vilyui LIP is 100–215Kkm3, which is much less than earlier estimates. Most of the mafic material within the Yakutsk–Vilyui LIP is related to the Vilyui basin and associated dyke swarms. Backstripping analysis of sedimentation in depressions of the Vilyui basin was carried out. Estimates were obtained for the spatial distribution of the stretching factor of the crust and mantle lithosphere, averaging 1.17 and 1.44, respectively. The amount of extension due to dyke intrusion is estimated to be ~6%. Backstripping analysis of sedimentation in the Vilyui basin was used to assess the effect of both intraplate far-field forces and upwelling magma flows initiated by a mantle plume. A numerical thermomechanical model was developed to investigate the relations between two possible mechanisms by which the Vilyui rift was initiated: intraplate extension (passive rifting) and the ascent of a mantle magmatic diapir (active rifting). A model considering both of these mechanisms shows the contribution of the far-field extension forces and the effect of convective flows around the mantle plume, assuming a temperature of 1500°C for a heat source operating for ≥10Myr. The best-fit model predicts the formation of the Vilyui basin under extensional conditions with a depth-integrated horizontal driving force of 2.0×1013N/m, which corresponds to a lithostatic pressure of 0.73.

Determination of parameters of heat and mass transfer in evaporating drops

To compute parameters of heat and mass transfer in evaporating drops the emission-diffusion model is proposed. It is based on a dynamic balance between the vapor flow, obtained in the framework of the kinetic approach of Hertz-Knudsen, and diffusive flow of Maxwell. This approach allows taking into account characteristics of small droplet evaporation, where heat and mass transfer processes are not described by the regular diffusion model. The results of computations of the evaporation of free water droplets of different sizes according to regular diffusion and emission-diffusion models are compared. The effect of free convection flow and radiative heat transfer on droplets evaporation is determined. The suggested model is validated by comparison with experimental data obtained at the evaporation of water droplets suspended on polypropylene monofilaments. The form of droplet during evaporation is detected by microphotographing. The temperature of its surface is measured using infrared thermography. The numerical results and the experimental data show good agreement in time of evaporation and temperature of evaporating drops.

Assessment of Range of Olfactory Impact of Plant to Mechanical-biological Treatment of Municipal Waste

Plants (installations) to mechanical-biological treatment (MBT) of municipal solid waste belong to the object group being potential sources of odorants emission. One of the most important parameters of their characteristic is the range of the real olfactory impact. It depends on many factors, such as: the type of emitter (point or surficial) and its characteristics (among other things, height and surface, polluted air stream temperature), emission value and its variability in time, and also topography and land management method and local climatological and meteorological conditions. Assessment of range of olfactory impact of plants is the issue, which may be the subject of theoretical considerations. The search for answers for practical purposes is associated among other things with spatial planning (land use), decision-making on location and land management (improvement of the territory) around the MBT installation and resolving complaints and disputes arising from their nuisance for residents (inhabitants). In Poland, the range of onerous impact of waste management facilities has been, in the past, assessed mainly by the indicator method (based on the widths of the so-called protection zone), and currently is determined using mathematical modelling (especially for of planned undertakings) and direct olfactometric measurements (in the case of existing facilities).In the paper is presented a general outline of the methodology of assessment of a range of olfactory impact of fugitive emission from surficial sources. Theoretical considerations are illustrated on the example of the results of the examinations of large plant (installation) of the mechanical-biological treatment of waste. During the examinations, apart from usual odour emission and dispersion processes, the effect of the convective vertical flow of the odorant-polluted air effect was observed.The research program includes twelve series of direct olfactometric measurements (with field olfactometers) and odorimetric observations in measurement-observation (receptor) points, deployed in and around the MBT installation. In each series has been tagged the background of air polluted with odorants (on the windward side of MBT installation). The olfactometric examinations were carried out by method of identification and with characterizing the trail of the odour emitted from the explored source. The receptor points were determined mainly in the area, in which the odours were uniquely identifiable as to their origin. In addition, has been made one “intervention” series of odorimetric observations. During field examinations, olfactometric measurements were carried out with control of the current meteorological situation – measurements and observations of the weather conditions (wind, temperature and relative humidity of the air, the degree of cloudiness).

Macroinhomogeneity of the properties of semiconductor crystals due to the specifics of the melt’s behavior under microgravity conditions

The effect of convective flows caused by the changing direction of the residual gravitational vector relative to the solidification front on the radial inhomogeneity (macrosegregation) of the dopant distribution in semiconductor crystals is studied within the context of mathematical and physical simulation for terrestrial and space conditions. Theoretical calculations and experimental research are carried out by the example of the growth of Ge crystals and their heavy doping with Ga (1019 сm–3). The velocities of convective flows near the solidification front which lead to radial macroinhomogeneity in the grown crystals are theoretically calculated. The requirements to obtain homogeneous semiconductor crystals under real microgravity conditions are formulated.