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The vertical release of a lighter buoyant fluid, commonly referred to as a forced plume, into dense environment is a common occurrence in ocean and atmosphere. Such releases may have heterogeneity in them in form of particles with varied size, shape, and volume fraction. Normally in field conditions, the particle size ranges from a few microns to millimetres, and the volume fraction ranges from ϕv=0.1-10%. In this study, the effects of low values of ϕv (corresponding to a two-way coupled system) on the dynamics and structure of a plume umbrella cloud formed in a linearly stratified ambient were examined. Spherical particles with mean diameter dp=100μm, density, ρp=2500kgm-3, and ϕv=0-0.7% were injected along with the lighter plume fluid. Due to the phenomena of “particle fall-out” and “particle re-entrainment”, it was observed that a plume trough characterized by radius, Rc, and depth, Lp, forms below the neutral buoyant layer of an umbrella cloud. The plume trough formation is linked to the draw-down of the fluid from the neutral buoyant layer by the sedimenting particles. This trough either sustains or collapses depending on the plume conditions at the source, namely, the diameter d0, fluid buoyancy, g0′, vertical velocity, W0, and ϕv. In all the experiments, g0′ and d0 were kept constant while ϕv=0-0.7% and W0=0.2-0.65ms-1 were varied. The experiments revealed that the sustaining and collapsing trough regimes could be qualitatively demarcated based on a source effective Richardson number, Ri0∗, that accounts for the combined effect of ϕv and W0. It was found that when Ri0∗<0.018, the plume trough collapses, otherwise it is sustained. However, Ri0∗ failed to predict the variations in Rc and Lp and hence was unsuitable for quantifying the plume trough. Therefore, it was established that the characteristics of a plume trough (i.e. Rc and Lp) depend independently on the particle volume fraction (ϕv) and source Richardson number (Ri0), while the demarcation of the trough regimes could be done using Ri0∗. For a constant Ri0=-g0′d0W02, with an increase in ϕv the trough radius, Rc, was found to decrease. In contrast, Lp increases for a sustaining trough and decreases for a collapsing trough. For a constant ϕv, a decrease in Ri0 caused both Rc and Lp to increase irrespective of a sustaining or collapsing plume trough. Using equations of motion for sedimenting particles, an analytical expression for the trough radius, Rc, was formulated that accurately explains the experimental results. A relation for trough radius, Rc, that elucidates the dynamics of particle re-entrainment was also obtained. If a particle is within the value of Rc it is re-entrained into the plume, otherwise settles at the bottom. These results provide useful information needed for modeling particle-laden forced plumes.

Two approaches have traditionally been used to describe the widening rate of jets and plumes: the diffusion concept of Prandtl, and the entrainment principle of Morton, Taylor and Turner. The entrainment concept is based on depth-averaged flow scales, and was later applied to plane gravity currents on an incline by Ellison and Turner [ET]. The two parameterizations are compared here for free shear flows, and gravity currents. It is shown that the diffusion concept is suitable for supercritical gravity currents, and that both approaches agree for subcritical ones. Depth-averaged models are also used for open channel flows, but the depth and velocity scales for the two flows are different. Those of ET are derived from the velocity distribution, whereas the depth of an open channel flow is the vertical extent of the dense liquid phase, and the velocity is derived from its flux. To reconcile the two descriptions, we extended the mass-based flow scales of open channel flows to gravity currents in an earlier contribution. In the present study these scales are outlined, and extended further to axisymmetric and non-buoyant free shear flows. Ratios of the diffusion rates in terms of mass- and velocity-based flow scales, are obtained from available experimental data for free shear flows.

Effects of convection (forced and natural) on dendritic evolution of the Al-Cu alloy were investigated using a phase-field lattice-Boltzmann approach. The non-linear coupled equations were solved by applying a parallel and adaptive mesh refinement algorithm. Important physical aspects including dendritic fragmentation, splitting, and formation of solute plumes were simulated. Results showed that the dendritic growth patterns under convection exhibited remarkable difference from those without convection. The presence of flow led to variation of solute diffusion and upstream–downstream dendritic growth difference, which further influenced the development of dendritic arms and multi-dendritic competitive growth. When the convection intensity was magnified, the convection-induced anisotropy became dominated, and the growth patterns changed accordingly to accommodate the local thermodynamic variation.

Purpose The purpose of this study is to numerically and experimentally investigate the natural convection heat transfer in flat plates and plates with square, trapezoidal and triangular corrugations. Design/methodology/approach This work is an extension of the previous studies by Verderio et al. (2021a, 2021b, 2021c, 2021d, 2022a). An experimental apparatus was built to measure the plates’ temperatures during the natural convection cooling process. Several physical parameters were evaluated through the experimental methodology. Free and open-source computational tools were used to simulate the experimental conditions and to quantitatively and qualitatively evaluate the thermal plume characteristics over the plates. Findings The numerical results were experimentally validated with reasonable accuracy in the range of studied RaLP for the different plates. Empirical correlations of Nu¯LPexp=f(RaLP), h¯conv=f(RaLP) and Nu¯LPexp⋅(A/AP)=f(RaLP), with good accuracy and statistical representativeness, were obtained for the studied geometries. The convective thermal efficiency of corrugated plates (Δη), as a function of RaLP, was also experimentally studied quantitatively. In agreement with the findings of Oosthuizen and Garrett (2001), the experimental and numerical results proved that the increase in the heat exchange area of the corrugations has a greater influence on the convective exchange and the thermal efficiency than the disturbances caused in the flow (which reduce h¯conv). The plate with trapezoidal corrugations presented the highest convective thermal efficiency, followed by the plates with square and triangular corrugations. It was also proved that the thermal efficiency of corrugated plates increases with RaLP. Practical implications The results demonstrate that corrugated surfaces have greater thermal efficiency than flat plates in heating and/or cooling systems by natural convection. This way, corrugated plates can reduce the dependence on auxiliary forced convection systems, with application in technological areas and Industry 4.0. Originality/value The empirical correlations obtained for the corrected Nusselt number and thermal efficiency for the corrugated plate geometries studied are original and unpublished, as well as the experimental validation of the developed three-dimensional numerical code.

The aim of this work was to study, by remote sensing and numerical modeling, the thermal dispersion of a plume discharged into the sea by a nuclear power plant. The case study is the thermal discharge of the Laguna Verde nuclear power plant, located on the coast of the Gulf of Mexico. First, the thermal plume dispersion was characterized by applying remote sensing for different scenarios. Afterwards, Delft3D-FLOW numerical simulations were performed to expand the analysis of the thermal processes for a case in which the thermal plume tends towards the intake of the power plant. This thermal analysis was carried out by comparing the behavior of different dimensionless parameters. Moreover, the results of the numerical simulations were used to investigate the performance of the AEM and the k-L and k-ε turbulence models, available in the Delft3D-FLOW model. An LES turbulence model contribution was also analyzed. The results show that forced convection is predominant near the plume discharge area and at the vicinity of the intake structure. According to the metrics calculated, all turbulence models produced good agreement with the remote sensing data, except when the LES scheme was considered. Finally, the use of remote sensing and numerical simulations is helpful to better understand thermal plume dispersion.

AbstractExperiments reported here confirm experimentally the existence of the characteristic planar buoyant plumes that emerge as a consequence of the presence of a cylindrical heat source embedded in an homogeneous air-saturated and non-consolidated porous medium. The resultant buoyant plumes were visualized with IR thermography considering two important cases. First, under the action of natural convection and second, under the action of forced convection due to the passage of a constant air stream directed perpendicularly towards the horizontal cylindrical heat source buried in the porous medium. Such streams were induced at different tilt angles. For each case, the temperature distribution is shown and correspondence is found with the isotherms distribution predicted by the theoretical models reported in the literature. The use of infrared techniques appears as a helpful tool that allows us to witness all the process of rise and growth of the buoyant plumes until the phenomenon reaches steady state.Graphical abstract

Purpose – Unsteady simulation of forced convection of two heated horizontal cylinders confined in a 2D squared enclosure. The paper aims to discuss this issue. Design/methodology/approach – The finite-volume method is used to solve the transient heat transfer problem by employing quadrilateral mesh type. To solve the governing equations (conservations of mass, momentum and energy) on unstructured control volumes, a second-order quadratic upwind interpolation of convective kinematics scheme for the convection terms and the semi-implicit method for pressure-linked equations pressure correction algorithm were used. Findings – The results indicate that the variation of the area-averaged Nusselt number strongly depends on the Reynolds number. On the contrary, the effect of cylinders’ space on heat transfer was found to be nearly negligible for Re < 460. It is also observed that steady state flow and heat transfer shift to periodical oscillation, and ultimately chaotic oscillation in non-dimensional cylinders distance of 0.1; however the sequence of appearing this route is completely different for higher cylinder spaces. Research limitations/implications – Reynolds numbers between 380 and 550 and dimensionless horizontal distances of cylinders 0.1, 0.2 and 0.3. Originality/value – Comprehensive knowledge of the effect of tube arrays flow regime on each other and in turn, heat transfer among them. Better understanding of convective heat transfer around an array of horizontal cylinders compared with from those around a single cylinder because of the mutual interaction of the buoyant plumes generated by the cylinders. Time-dependent phenomena of the problem including periodical oscillation or chaotic features.

Using a fully coupled transient 3-dimensional numerical model, the effects of convection on the microstructural evolution of a thin sample of Ga-In25%wt. was predicted. The effects of natural convection, forced convection and thermoelectric magnetohydrodynamics were investigated numerically. A comparison of the numerical results is made to experimental results for natural convection and forced convection. In the case of natural convection, density variations within the liquid cause plumes of solute to be ejected into the bulk. When forced convection is applied observed effects include the suppression of solute plumes, preferential secondary arm growth and an increase in primary arm spacing. These effects were observed both numerically and experimentally. By applying an external magnetic field inter-dendritic flow is generated by thermoelectrically induced Lorentz forces, while bulk flow experiences an electromagnetic damping force. The former causes preferential secondary growth, while the latter slows the formation of solute plumes. This work highlights that the application of external forces can be a valuable tool for tailoring the microstructure and ultimately the macroscopic material properties.

The purpose of this communication is to present new results concerning velocity fields within the enclosure and close to the openings of a ventilated room with a buoyant turbulent 2D plume originating at its bottom. The enclosure is ventilated through lower and upper openings located on the two opposed vertical walls and separated by a vertical distance H. Depending on the enclosure geometry and forced plume characteristics, this situation can drive different kinds of flow regimes (blocked, intermediate and displacement) through the lower and upper openings. Three flow regimes are successively studied by adjusting a new densitometric Froude number related to the source flow rate, the densities inside and outside the enclosure and the area of the upper opening. When , buoyancy forces are larger than inertial forces and the displacement regime is then observed. In cases where inertial forces are larger than buoyancy forces then and the intermediate or blocked regimes are involved and forced convection dominates. Results of velocity fields measured by 2D PIV in the mid plane of the enclosure are presented for the three regimes. By using velocity and temperature measurements performed at the nozzle and at the lower and upper openings in seven x–y planes located at z/l=0, ±1/8, ±1/4, ±3/8, balance of mass flow rate is verified and heat loss by conduction through the walls is evaluated for the three studied regimes.

This paper discusses preliminary results of an analysis of SST variability in the coastal region of South America between 30 and 39° S that is largely influenced by the Rio de la Plata estuary's plume, and its relation with wind variability. Data are six years of daily ensembles of gridded satellite SST and sea surface winds with spatial resolutions of about 11 and 25 kilometers, respectively. At the central estuary most of the variance is explained by the annual cycle, whereas in coastal areas of the exterior estuary almost 10% is due to other processes. A principal components (Empirical Orthogonal Functions, EOF) analysis shows that the seasonal cycle can be explained in terms of two modes. The first one, characterizing fall-early winter/spring-early summer is related to the radiative cycle. The second mode, corresponding to late winter and late summer, displays warm/cold anomalies along the Uruguayan coast which are forced by the prevailing winds during those seasons that advect either the estuarine or oceanic water. An EOF analysis of the SST variability in sub-annual scale shows that a large portion of its variance is also related to zonal wind anomalies that force warm/cold SSTs along that coast, but in shorter time scales. Cold events observed in summer display anomalies of up to -5°C and occur under anomalously intense eastern winds (parallel to the coast) thus suggesting upwelling. Those events were very frequent during the observed period and showed large persistence, occurring up to one month. Given that the Río de la Plata estuary is a spawning and nursery ground for numerous coastal species, these factors might play an important role on biological activity so as in sediments transport.