Convection Regime Research Articles

Experimental investigation of mixed mode ultraviolet tent house solar dryer under natural convection regime

A mixed mode natural convection ultraviolet (UV) tent house solar dryer is designed and installed at University Teaching Department, Chhattisgarh Swami Vivekanand Technical University, Bhilai, Chhattisgarh (21°27′N, 81°43′E) India for drying potato slices. This solar dryer is equipped with a solar flat plate collector (area 1.12 m2), covered with 5.0 mm thick glass and consists of two trays of the same size (0.57 m X 1.11 m) in a drying chamber on which equal quantities of potato slices were placed. The local atmospheric conditions including relative humidity, atmospheric temperatures, solar intensity, and wind velocity have been recorded for analyzing various parameters. The solar intensity and atmospheric temperature ranges from 134 to 993 W/m2 and 36.2 °C to 44.9 °C respectively. The initial moisture content value of 85.25% reaches 14.75% for 2.5 mm thick potato slices and for 5.0 mm thickness, the initial & final moisture content values are 85.10% & 14.90% respectively. The upper and lower tray temperature varies from 34.2 °C to 59.7 °C and 33.6 °C to 57.1 °C respectively. The open sun drying took 6 h longer than the solar natural convection drying. Moisture ratio for 2.5 mm thickness and 5.0 mm thickness lies 0.475–0.001 and 0.650–0.003 respectively. The maximum dryer efficiency is 26.62% and 21.61% for 2.5 mm and 5.0 mm thick potato slices respectively. All the drying kinetics is superior in the 2.5 mm thickness of the potato in process of drying using natural convection.

Numerical study of mixed and free convection heat transfer under ocean conditions

The mixed and free convection heat transfer of vertical upward flow under ocean conditions is studied numerically. The turbulent heat transfer in a smooth circular tube at low flow rates and the effects of ocean conditions are validated by experimental data. A CFD method based on the v2-f turbulence model and additional inertial force is established. The analysis indicates that the effects of ocean conditions on heat transfer depend on the Buoyancy parameter. In particular, for the mixed convection regime, the overall heat transfer increases, and the local heat transfer deterioration is aggravated. The mixed and free convection heat transfer under ocean conditions is dominated by the Coriolis force and gravity, so the influence of rolling radius is weak. As the rolling period increases, the heat transfer variation increases due to the inclination effects. However, as the rolling amplitude increases, the heat transfer behavior is non-monotonic and difficult to predict due to the combined action of Coriolis effects and buoyancy effects. The introduction of pulsating flow breaks the symmetry of heat transfer, and the hot spot only appears on one side. The overall heat transfer increases, but the local heat transfer deterioration is further aggravated.

Пассивная конвективная вентиляция в двойном воздушно-пористом слое с внутренним тепловыделением, зависящим от доли твердой фазы

The convective stability of a two-layered system consisting of a heat-generating porous region underlying an air region has been numerically studied. The linear dependence of the heat release on the solid volume fraction is taken into account in the porous region. The equal constant temperature values are fixed on the external impermeable boundaries of the system. The critical internal Rayleigh-Darcy number at which the convection is induced in the system in the form of two-dimensional roll patterns with a given wave number has been determined. The convective flow is possible due to the formation of unstable density stratification in the presence of internal heat release. Two types of stationary convection, namely, the local and the large-scale convection, have been studied. The local flow arises in the air sublayer and scarcely penetrates into the porous sublayer. The large-scale convection covers both sublayers. The change in the convective regime occurs with the growth of one or another parameter of the system and indicates the variation of the instability type. It is accompanied by an abrupt (by times and tens of times) change in the critical wave number of roll patterns. Numerical calculations show a decrease in the onset value for both types of convection with increasing solid volume fraction ϕ in the porous sublayer and increasing relative thickness d of the air sublayer. The growth of the Darcy number (the dimensionless per-meability of the porous sublayer) also causes destabilization of the air motionless state at the given ϕ and d. The variation of the convection regime from a large-scale flow to a local one occurs with increasing relative thickness of the air sublayer, whereas an opposite transition from the local to the large-scale convection regime is observed with increasing Darcy number.

Modelling of pool boiling on the structured surfaces using Lattice Boltzmann method

The process of boiling on spatially structured surfaces is simulated by a hybrid model based on Lattice Boltzmann Method and heat transfer equation. The model permits to study heat transfer at boiling in a wide range of surface superheats for different surface structural characteristics. The regimes of natural convection, nucleate boiling, and transition to film boiling are studied. The boiling curves for the surfaces with different structural and wetting properties are obtained. It was shown that the onset of nucleate boiling occurs at lower wall superheat on the structured surfaces than that on the smooth surface. However, at high wall superheats the heat flux and the critical heat flux at modified surfaces are lower. It was obtained that special modification of both structural and wetting properties of heat exchange surface permits to obtain higher removal heat flux as well as higher critical heat flux.

The diverse meteorology of Jezero crater over the first 250 sols of Perseverance on Mars

NASA’s Perseverance rover’s Mars Environmental Dynamics Analyzer is collecting data at Jezero crater, characterizing the physical processes in the lowest layer of the Martian atmosphere. Here we present measurements from the instrument’s first 250 sols of operation, revealing a spatially and temporally variable meteorology at Jezero. We find that temperature measurements at four heights capture the response of the atmospheric surface layer to multiple phenomena. We observe the transition from a stable night-time thermal inversion to a daytime, highly turbulent convective regime, with large vertical thermal gradients. Measurement of multiple daily optical depths suggests aerosol concentrations are higher in the morning than in the afternoon. Measured wind patterns are driven mainly by local topography, with a small contribution from regional winds. Daily and seasonal variability of relative humidity shows a complex hydrologic cycle. These observations suggest that changes in some local surface properties, such as surface albedo and thermal inertia, play an influential role. On a larger scale, surface pressure measurements show typical signatures of gravity waves and baroclinic eddies in a part of the seasonal cycle previously characterized as low wave activity. These observations, both combined and simultaneous, unveil the diversity of processes driving change on today’s Martian surface at Jezero crater.

Three-dimensional convection regimes in a two-layer system with evaporation for different types of thermal loads on a substrate

Three-dimensional convection regimes in a two-layer system with evaporation for different types of thermal loads on a substrate

On enhancing interfacial mass transport through microextraction in dispersed droplet systems

The physio-chemical hydrodynamics and the solute transport around a translating dispersed drop are often multicomponent and multiphase systems. When such a dispersed droplet system is out of the thermodynamic equilibrium, steep momentum and concentration gradients are developed around the interface leading to rapid flow and solute transport. In broader perspectives, the dispersed droplet system has direct/indirect relevance to addressing the technological challenges in the 21st century, namely, energy storage, hydrogen production, CO2 capture, biofuel production, chemical analysis, diagnosis extraction, and drug delivery. Environmental engineering challenges include flotation and separation technology, inkjet printing, coatings, and paints. The most challenging issue in such applications is enhancing the transport rate from the droplet to the bulk of the fluid. In this work, we have proposed a novel method to foster the transport of solute from the drop to the bulk fluid by altering the viscosity of the bulk fluid. We have exploited the shear-thinning behavior of the fluid in bulk to reduce the viscous losses and resistances to the mass transfer. A linear thermodynamic equilibrium relation at the fluid-fluid interface is considered. The scant prior experimental results were observed to agree with the present findings. Therefore, the extensive numerical findings are presented for the ranges of pertinent parameters such as Reynolds number, (1≤Re≤75) Peclet number, (10≤Pe≤103), internal to external fluid diffusivity ratio, (0.5≤dratio≤4), dispersed to continuous fluid viscosity ratio, (0.25≤μratio≤4) and power-law index, (0.4≤n≤1). The drag coefficient exhibits an increase of 180% with the increase in the μratio as well as with the n at the maximum convective regime. The Sherwood number exhibits a positive dependence on the Reynolds number, Peclet number, and the diffusivity ratio. On the contrary, the viscosity ratio lowers the transport of species from the droplet to the fluid due to the reduced internal circulations inside the droplet. Shear-thinning fluid behavior offers a higher extraction efficiency than the Newtonian fluid (upto 30% increase in at low Pe). Finally, simple predictive correlative equations have been proposed for the drag coefficient and the average Sherwood number over the conditions considered here.

Experimental adjustment of the turbulent Schmidt number to model the evaporation rate of swimming pools in CFD programmes

Water evaporation rate is among the most significant parameters to design and select air conditioning systems in buildings with indoor swimming pools. Experimental correlations are today widely used to estimate water evaporation rate, although discrepancies of up to 80% among existing correlations have been shown. An alternative to these empirical methods is the calculation of evaporation rate through computer fluid dynamics techniques. One of the most significant parameters to solve the mass transfer at the air-water interface in these models is the value of the turbulent Schmidt number. Although this value depends on air and water conditions (i.e., temperatures, velocities, and vapour pressure, among others), commercial computer fluid dynamics programmes set a fixed value by default. This study presents a new value through an experimental adjustment. A total of 40 experimental tests have been performed in a wind tunnel under typical conditions in indoor swimming pools. Afterwards, the adjustment was validated with data from 145 experimental tests reported in the scientific literature. The mean relative error in the evaporation rate using the turbulent Schmidt number was 7%, as against 25% using the value by default. The maximum error was reduced from 35% to 15% in forced convection regime.

Linking Large-Scale Double-ITCZ Bias to Local-Scale Drizzling Bias in Climate Models

Abstract Tropical precipitation in climate models presents significant biases in both the large-scale pattern (i.e., double intertropical convergence zone bias) and local-scale characteristics (i.e., drizzling bias with too frequent drizzle/convection and reduced occurrences of no and heavy precipitation). By untangling the coupled system and analyzing the biases in precipitation, cloud, and radiation, this study shows that local-scale drizzling bias in atmospheric models can lead to large-scale double-ITCZ bias in coupled models by inducing convective-regime-dependent biases in precipitation and cloud radiative effects (CRE). The double-ITCZ bias consists of a hemispherically asymmetric component that arises from the asymmetric SST bias and a nearly symmetric component that exists in atmospheric models without the SST bias. By increasing light rain but reducing heavy rain, local-scale drizzling bias induces positive (negative) precipitation bias in the moderate (strong) convective regime, leading to the nearly symmetric wet bias in atmospheric models. By affecting the cloud profile, local-scale drizzling bias induces positive (negative) CRE bias in the stratocumulus (convective) regime in atmospheric models. Because the stratocumulus (convective) region is climatologically more pronounced in the southern (northern) tropics, the CRE bias is deemed to be hemispherically asymmetric and drives warm and wet (cold and dry) biases in the southern (northern) tropics when coupled to ocean. Our results suggest that correcting local-scale drizzling bias is critical for fixing large-scale double-ITCZ bias. The drizzling and double-ITCZ biases are not alleviated in models with mesoscale (0.25°–0.5°) or even storm-resolving (∼3 km) resolution, implying that either large-eddy simulation or fundamental improvement in small-scale subgrid parameterizations is needed.

Voltammetric and electrodeposition study for the recovery of antimony from effluents generated in the copper electrorefining process

Antimony is a metalloid with limited availability as a primary resource, but it is commonly found as an impurity in effluents generated in the copper metallurgy. Thus, the development of clean and selective processes to recover antimony from these wastewaters would improve the sustainability of the copper production. In this work, an emulated effluent of the copper electrorefining industry that contains antimony and hydrochloric acid was characterized by means of voltammetric and electrodeposition tests using two different cell configurations: a static cell, and a dynamic cell with a rotating disk electrode (RDE). Voltammograms were obtained at varying hydrochloric acid and antimony concentrations, inversion potentials, scan rates and RDE rotation rates. Two main conclusions were drawn: (a) the deposition of antimony is a mass transfer-controlled process; and (b) an increase in hydrochloric acid concentration improves the deposition of antimony. The diffusion coefficient of antimony species was obtained applying the Randles-Ševčík and the Levich equations; both of them providing very similar values (5.29 ± 0.20 · 10−6 cm2 s−1). The effective electrodeposition of antimony from highly concentrated hydrochloric acid solutions was demonstrated. The surface examination of the electrodes revealed that compact and adherent deposits of antimony could be obtained under operating conditions that minimize the hydrogen evolution reaction in both potentiostatic and galvanostatic modes. Intensified convective regimes by using the RDE improve the supply of dissolved antimony towards the electrode surface, thus leading to a notorious increase in current density and, consequently, in the rate of antimony deposition.

A Bio-Thermal Convection in a Porous Medium Saturated by Nanofluid Containing Gyrotactic Microorganisms Under an External Magnetic Field

The study of thermal convection in porous media saturated by nanofluid and microorganisms is an important problem for many geophysical and engineering applications. The concept of a mixture of nanofluids and microorganisms has attracted the interest of many researchers due to its ability to improve thermal properties and, as a result, heat transfer rates. This property is actively used both in electronic cooling systems and biological applications. Thus, the purpose of this research is to study biothermal instability in a porous medium saturated by a water-based nanofluid containing gyrotactic microorganisms in the presence of a vertical magnetic field. Given the presence of an external magnetic field in both natural and technological situations, we were motivated to perform this theoretical research. Using the Darcy-Brinkman model, a linear analysis of the convective instability has been considered for both-free boundaries, taking into account the effects of Brownian diffusion and thermophoresis. The Galerkin method was used to perform this analytical study. We have established that heat transfer is accomplished by stationary convection without oscillatory movements. In stationary convection regimes, metal oxide nanofluids (Al2O3), metallic nanofluids (Cu, Ag), and semiconductor nanofluids (TiO2, SiO2) are analyzed. Increasing the Chandrasekhar and Darcy numbers improve system stability significantly, but increasing porosity and modified bioconvection Rayleigh-Darcy number speed up the beginning of instability. To determine the transient behavior of heat and mass transports, a non-linear theory based on the representation of the Fourier series method is applied. In small time intervals, the transitional Nusselt and Sherwood numbers exhibit an oscillatory character. The Sherwood numbers (mass transfer) in the time interval reach stationary values faster than the Nusselt numbers (heat transfer). This research might help with seawater convection in the oceanic crust as well as the construction of biosensors.

Determination of energy partition of a cucumber grown Venlo-type greenhouse in southeast China

Accurate determination of energy partition inside greenhouses is a key procedure in optimizing efficient water management. In this study, micro-meteorological data and energy fluxes of cucumber were measured during four planting seasons (2018–2021) in a Venlo-type greenhouse to analyze the energy manifestation in different growing stages. The results showed that the latent heat flux (λET) was the primary component of net radiation (Rn), accounting for 61.2–72.6 % of Rn during the whole growing seasons, followed by sensible heat flux (H, 19.8–24.3 % of Rn) and soil heat flux (G, 7.6–14.8 % of Rn). The λET increased while both H and G decreased as the crop grew. Especially, H was larger than λET at midday in the initial growing stage. Energy partition was intensely affected by the leaf area index (LAI). The λET/Rn increased linearly with the increase in LAI, while the H/Rn decreased linearly and G/Rn decreased exponentially until LAI reached 4 m2 m−2. Canopy conductance (Gc), Priestley-Taylor coefficient (α), and the decoupling coefficient (Ω) were calculated to evaluate the controlling factors over cucumber λET. The high values of the α (= 1.15 ± 0.05) and the Ω (= 0.65 ± 0.05) indicated that the cucumber λET was principally constrained by Rn. The Gc was calculated by inverting Penman-Monteith (PM) equation using aerodynamic conductance (Ga) values obtained by the heat transfer coefficient (hs) method based on accurate convection regimes. The Gc varied from 1.42 to 17.98 mm s−1 and high Gc values corresponded to high λET. The λET was estimated by the Ω model with the mean root mean square error (RMSE) and mean absolute error (MAE) equaled 32.65 and 25.73 W m−2, while the determination coefficient (R2) was 0.94. The H was reproduced by the Bulk Transfer (BT) model to validate Ga with the RMSE and MAE equaled 32.57 and 24.95 W m−2, the R2 was 0.86. The results also indicated that the simplified energy balance (EB) method was an optional approach to analyzing energy partition in greenhouses. Consequently, more energy could be saved by avoiding the excessive application of water and thus improving crop water use efficiency in greenhouses.

Winds at the Mars 2020 Landing Site: 1. Near‐Surface Wind Patterns at Jezero Crater

AbstractThis is the first part of a two‐part paper. NASA's Mars 2020 Perseverance rover measured winds on the Jezero crater floor close to the delta of an ancient river. A mostly repeatable diurnal cycle was observed and presented two regimes: (a) a convective regime, from dawn to sunset, with average easterly to southeasterly winds, during which maximum wind speeds were measured, and (b) a nighttime regime with westerly‐northwesterly winds followed by a relatively calm period with highly variable wind directions as a function of sol and time of night. The timing and magnitude of the observed regimes are consistent with primary control by regional and local slope flows. Data suggest that the surface circulation at Jezero region in northern spring and summer is highly unaffected by large‐scale circulation except during particular periods in the diurnal cycle or generally during dust storms, which is supported by MarsWRF model simulations. Consequently, the observed seasonal variability was weak. However, sol‐to‐sol and seasonal variability were measured, most of it during certain nighttime periods. Traveling waves consistent with baroclinic instability were clearly observed in surface winds at Ls ∼ 75°. The early MY36/2022A regional dust storm at Ls ∼ 153° disturbed the wind patterns with changes suggesting enhanced tidal flows. After sunset, the dust storm also produced detectable gravity wave activity, increasing the mixing in the nighttime planetary boundary layer during storm conditions. Inferred wind directions from dust devil movies strongly suggest that prevailing winds continued to be slope‐driven during the late summer, fall and early winter seasons.

Magneto laminar mixed convection and entropy generation analyses of an impinging slot jet of Al2O3-water and Novec-649

In this study, the cooling capability and heat transfer characteristics in the mixed convective regime of a hot surface by a confined impinging slot jet in the presence of a uniform magnetic field have been investigated numerically. Besides, the second law of thermodynamics is applied to analyze the entropy generation inside the simulation medium. The simulations are for a two-dimensional slot jet that is directed vertically downward and impinges on a hot isothermal surface at the bottom. The set of non-dimensional governing equations is solved using ANSYS Fluent, which employs a finite volume approach in combination with a non-dimensionalization scheme. Flow patterns, isotherms, and entropy generation rates were calculated for various fluids (Air, Water, Novec-649, Al2O3-Water (3 %) nanofluid), that cover a wide range of Prandtl number values (Pr = 0.71–12.64), in the presence of a uniform magnetic field with Hartmann number values ranging from 0 (no magnetic field) to 100 (strong magnetic field). We prove that the Prandtl number plays a key role in determining heat transfer efficiency and entropy generation. Fluids with a high Pr number are more efficient for surface cooling, although they generate more entropy than low Pr fluids. Nanofluid with a high-volume fraction can be a better choice rather than air and water. On the other hand, we show that applying the magnetic field result in a very efficient method to reduce entropy generation although they degrade heat transfer efficiency. It is interesting that at a higher magnetic field, a high Prandtl number plays a better role. The percentage of reduction of Nuave by applying magnetic field is 28.5 % for air (Pr = 0.71), 45.2 % for water (Pr = 6.2), 43.4 % for Al2O3-water nanofluid (Pr = 4.91) and 48.3 % for Novec-649 (Pr = 12.64).We postulate that applying magnetic fields combined with high Pr number fluids, could provide an excellent balance between heat transfer efficiency and exergy destruction, thus providing efficient control options for thermal management and heat transfer.

Numerical Investigation of Mixed Convective Heat Transfer of a Twisted Square Tube

Study of the heat transfer performance of twisted tubes have been limited to forced convective conditions (inertia-dominated flow) without studying the effect of different isothermal wall temperature (buoyancy force). Therefore, this work investigated the flow and heat transfer behavior of a twisted square tube of a varying pitch length at different mixed convective regimes. The model continuity, momentum, and energy equations were solved using the finite volume technique. The numerical model setup was validated using experimental results and a satisfactory result was achieved. The result shows that the twisted square tube performs better than the smooth tube subjected to the same conditions. The heat transfer rate and drag coefficient increase with decreasing twist pitch length. In addition, the result shows that increment of buoyancy force, while inertia force is kept constant leads to a high reduction of drag as compared to increasing inertia force, while buoyancy force is kept constant. Overall, a 15% increase (at Ri=1) is obtained in the drag coefficient and a 13% increase (at Ri=0.5) is obtained in the heat transfer rate in the 100 mm twist pitch length as compared to the 600 mm twist pitch length.

Conjugate mixed convection heat transfer with internal heat generation in a lid-driven enclosure with spinning solid cylinder

The current study investigates conjugate mixed convection heat transmission with internal heat generation in a square enclosure driven by a sliding lid and a solid cylinder with a heat-conducting surface at its center. The enclosure has a stationary bottom wall that is kept at a constant hot temperature and a cold upper wall that moves consistently. The solid cylinder rotates both clockwise and counterclockwise at different angular speeds. Two-dimensional steady continuity, momentum, thermal energy equations, and boundary and interface conditions are solved using a commercial CFD tool based on the finite element method. By choosing Reynolds, Grashof, and Richardson numbers, as well as varying the rotating cylinder's speed and direction under three different scenarios incorporating volumetric heat generation, parametric modeling of the mixed convection regime is carried out. The streamline and isotherm plots are used to illustrate qualitative findings. In contrast, the average Nusselt number, normalized Nusselt number, average drag coefficient, and average fluid temperature are used to assess quantitative thermal performance measures. This study reveals that the system's thermal performance is less dependent on the solid cylinder's rotational speed and direction. It successfully depicts the heat transfer enhancement with increasing Reynolds and Grashof numbers. A thorough study of the current facts can lead to the best choice of regulating parameters.

Regionalization of the summertime planetary boundary layer height in comparison with various reanalysis datasets over China

Knowledge about the regionalization of the planetary boundary layer (PBL) height (PBLH) remains unclear for such a huge country like China, largely to the limited observations. By using K-means clustering of summer radiosonde-derived PBLHs, combined with land surface related factors, we classified China into six regions, including Northeast China, North China, South China, Inner Mongolia, Tibet Plateau, and Northwest China. Overall, the PBLH in China generally reaches the minimum at 0800 Beijing time (BJT), as opposed to the peak at 1400 BJT when the convective PBL is well developed. Concerning the spatial distribution, the PBLH at 14 BJT exhibits a “northwest high-southeast low” pattern with the highest (2259 m) occurring in Inner Mongolia. Furthermore, the performances of several commonly used reanalysis products (ERA5, FNL, and CERA) are comprehensively compared against PBLH. Among all the three reanalysis datasets, The PBLHs from ERA5 present the strongest relationship with those from radiosounding observations across China, suggesting its robustness and suitability in estimating PBLHs. In terms of the performance of the reanalysis dataset in characterizing three PBL regimes such as convective, neutral and stable PBL, the PBLHs from ERA5 show significant positive correlations (R > 0.7) with the observed counterparts for both convective and neutral PBL regimes in most areas. However, all three reanalysis datasets tend to overestimate the PBLH under stable SBL. Our findings indicate that PBLH biases in reanalysis products are partly attributed to the misrepresentation of PBL thermal regimes, which is probably owing to the unsatisfactory simulations of cloud effects in weather models. Overall, this study presents the first regionalization of high-resolution radiosonde-derived PBLHs in China and quantitatively evaluates three popular reanalysis products, which have great implications for better application of datasets and improve the model parameterization of PBL.

Magnetohydrodynamic Natural Convection of Water in an L-Shaped Container Filled With an Aluminum Metal Foam

Abstract The current research employed computational simulation to assess magnetohydrodynamic (MHD) natural convection in an L-shaped container with a metal foam, which has a variety of engineering applications. The originality of this study is the use of numerical simulation combined with multi-objective optimization in terms of cooling rate enhancement and entropy generation reduction to investigate the optimal natural convection regimes. The influence of varied aspect ratios (AR), tilted angles of the container (θ), Hartmann number (Ha), and porosities (Φ) on the cooling rate with regard to the average Nusselt number (Nuave), Nusselt number enhancement (NNE), dimensionless surface temperature ([Ts]) and entropy generation (S) were evaluated. According to the findings of this study, little effect was found to be exerted by the MHD and θ on the Nuave, Ts, and S except for a porosity of 0.9. Furthermore, the Nuave and NNE enhance while the Ts and S reduce as the aspect ratio AR increases. In this case, the maximum increase in NNE was 8.78 times, with the greatest reductions in Ts and S as AR = 0.8, Φ = 0.1, θ = 0 deg, and Ha = 0 compared to the least favorable design. Thus, this optimum investigation of the CFD yields a novel approach and valuable recommendations for the optimum design of cooling in an L-shaped container.

Heat Transport in Rotating Annular Duct: A Short Review

Heat transport in rotating processes finds a wide range of application in which academic issues in the fluid mechanics and heat transfer areas are here reported. This paper discusses successive works from the seminal paper of Taylor (1923) to recent numerical results established from a broad range of methods such as DNS, LES, RANS or LB methods. The flow regimes identification is thus reported in Taylor–Couette geometry. The role of the axial flow rates in the apparition, stabilization and destruction of the large-scale of the turbulent structures is depicted in the case of Taylor–Couette–Poiseuille geometry. In a non-isothermal condition, a discussion is held on the various exponent values found in the scaling relationships relying on the Nusselt number as a function of the Rayleigh or Reynolds numbers according to the regimes of thermal convection.

Numerical simulation for nanofluid forced/free convection in a partially heated parallelogram enclosure: Effects of wall undulation and inclined Lorentz forces

AbstractThe present study possesses the mathematical computational analysis for mixed convection nanofluid (CuO–water) flow in a lid‐driven parallelogram enclosure with corrugated walls. A partially heated source is located at the bottom corrugated wall. The remaining portions of upper and lower corrugated boundaries are adiabatic. The verticals walls are kept cold. The flow dynamic established with wall undulation and inclined Lorentz forces generate complex mathematical formulation via partial differential equations. Finite element method is implemented to get numerical interpretation of these equations. The simulation is performed against various emerging parameters and the outcomes in terms of isotherms, streamlines and line graphs. The results are recorded against various Richardson numbers , Hartman number , nanoparticles volume fraction , and amplitude of the corrugated horizontal walls . It is observed that against smaller Richardson number streamlines indicate forced convection flow while at higher Richardson number flow divert toward free convection regime. Additionally, heat transportation is maximum when magnetic field is applied in perpendicular direction as well as at maximum amplitude of wall undulations.