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High Explosive Anti-Tank (HEAT) warheads and ammunitions are frequently produced by explosive casting inside an axis-symmetric mold with an inverted conical geometry in the basis. In order to prevent manufacturing defects, the solidification process must be controlled. In this study, a dimensionless solidification model has been proposed to investigate the heat transfer considering the natural convection inside the liquid explosive and the numerical simulations were performed by using COMSOL Multiphysics and Modeling Software, employing trinitrotoluene (TNT) thermophysical properties. The effect of three different boundary conditions on the top of the mold have been evaluated: convection, adiabatic and isothermal. It has been observed that solidification process was faster for convection case and slower for isothermal case, while an intermediary total solidification time value was found for adiabatic case. Moreover, liquid explosive was completely surrounded by solid explosive during the solidification process for convection case and also for adiabatic case through the end of the process. Otherwise, it was not observed for isothermal case. The natural convection effects promoted a vortex inside the liquid explosive, accelerating the heat transfer process. It has been concluded that isothermal mold top boundary condition should be preferred to prevent manufacturing defects, avoiding high thermal stress.

Understanding fluid flow, heat, and mass transfer over a stretching cylinder is essential in ascertaining the quality of wire coating and coper thinning. This study looks at the influence of the heat source, thermal radiation, chemical reaction, and natural convection of Carreau fluid flows over a vertical stretching cylinder immersed in a porous medium. Suitable similarity variables are applied to convert the partial governing equations arising in fluid flows, heat, and mass transfer into ordinary differential equations. The optimal homotopy analysis method is then utilized to solve the transformed highly nonlinear governing equations. The impacts of the relevant parameters such as the Weissenberg number, porosity, heat source parameter, radiative number, chemical reaction parameter, mixed convection parameter, and curvature parameter on the dimensionless velocity, temperature, and concentration distribution as well as for the skin friction, Nusselt number, and Sherwood number are discussed through graphs and tables. It is observed that the velocity shows an opposite behavior as compared to temperature, and concentration in shear-thinning, n 1 , and shear-thickening, n ≥ 1 , fluid for an increment of the Weissenberg number. Additionally, the thickness of the momentum, thermal, and concentration boundary layer is enhanced by the curvature of the cylinder.

Solid–liquid phase change has been widely used in practice, but most of the existing literature focuses on Newtonian phase change materials, and there are few studies on power-law phase change mate...

In this investigation, a comprehensive and accurate numerical analysis of the local thermal non-equilibrium effects on the natural convection characteristics in a horizontal elliptical porous annulus saturated with nanofluid has been carried out using finite volume technique. The internal surface is isothermally heated while the external one is fixed at uniform lower temperature. The nanofluid phase and the solid phase of the porous structure are hors local thermal equilibrium situation. The heat and the hydrodynamics equations in their dimensionless form under Darcy-Brinkman Forchheimer model were solved computationally by the finite volume technique using the standard SIMPLER algorithm. The results have been examined for various porous medium properties under the LTNE condition. The standard 0.05 significance level was used to identify the local thermal equilibrium within the system. According to the obtained results, the higher the Darcy number and the smaller the non-dimensional heat transfer coefficient for the solid/nanofluid interface, the modified thermal conductivity ratio and the media’s porosity, the higher are the LTNE effects. In addition, the spatial distribution contours of the LTNE sources within the porous annulus were schematized.

The thermophysical properties of the nanofluids override the physical properties of conventional fluids due to the high thermal conductivity of the nanoparticles. The applications of nanofluids have varied use in the era of bio-engineering and thermal sciences. Moreover, the nanoparticles attributed the significances in human blood arteries. Therefore, the present analysis manifests with the free convection of electrically conducting nanofluid embedding with resistive forces such that the magnetic field and permeability of the medium. The augmentation in the heat transfer properties is obtained because of the inclusion of radiative heat energy and absorption diffusion. Moreover, the nanoparticles volume fraction is focused with implementation of chemical reaction. Numerical treatment using the code in-build MATLAB code pdepeis employed for the transformed unsteady flow problem. The graphical computations against flow parameters are worked with justified physical importance. A declining change in nanoparticles is examined due to Prandtl number which is more progressive for steady case. The decreasing change in velocity is more dominant for nanoparticles as compared to pure fluid. The nanoparticles concentration reduces for effective variation of chemical reaction constant and Lewis number.

Numerical investigation on natural convection heat transfer of Tiwari - Das model nanofluid inside a square cavity with thermal radiation and magnetic field is carried out in this analysis. Ethylene Glycol E G is considered as base fluid and T i O 2 (Titanium Oxide) considered as nanoparticles for the present investigation. The side horizontal walls of cavity are assumed to be adiabatic and isothermal conditions on both sides walls are considered in this analysis. The finite difference method is implemented to solve the governing non-linear partial differential equations representing momentum and temperature equations. The sway of volume fraction parameter ( 0.01 ≤ ϕ ≤ 0.09 ) , magnetic field parameter ( 1.0 ≤ M ≤ 3.0 ) , Rayleigh number ( 100 ≤ R a ≤ 1000 ) , radiation parameter ( 0.1 ≤ R ≤ 0.9 ) , Reynolds number ( 0 . 1 ≤ R e ≤ 0 . 5 ) and Prandtl number ( 5.2 ≤ P r ≤ 7.2 ) on T i O 2 - E G nanofluid flow and heat transfer is illustrated through graphs. Furthermore, the codes of average Nusselt number with dissimilar values of pertinent parameters are also calculated and results are depicted through graphs. The result shows that, temperature of T i O 2 - E G nanofluid escalates inside the cavity with higher values of (M). Higher heat can be transferred from hot wall to cold wall when radiation parameter (R) intensifies.

Batch-type solar collector is a tilt-able water-heating solar-thermal system comprising an isosceles-trapezoidal enclosure housing a circular-cylinder absorber at the bottom wall, insulated side-walls, and flat-top glazing. Free convection of air inside such trapezoidal enclosure is studied numerically by varying the tilt angle of the whole enclosure from 0o-70o. The influence of tilt on the flow field has been demonstrated by plotting the streamlines and isotherms. The present study successfully identifies the importance of enclosure-tilt in quantifying heat-loss between absorber and glazing by developing a computational correlation between Nusselt and Rayleigh as a function of tilt. The correlation trend is non-monotonic over the range of angular Rayleigh numbers numerically experimented with having a peak around angular Rayleigh number 3×105 corresponding to the tilt-angle 30 degrees. The irregular-shaped cavity implies that the heat-transfer correlations already existing for regular-shaped cavities may not be used otherwise they will draw implausible conclusions and this argument identifies the novelty of the present study.

In this paper, we present a numerical study of turbulent natural convection in a square cavity differentially heated and filled with nanofluid and subjected to an inclined magnetic field. The standard k-e model was used as the turbulence model. The transport equations were discretized by the finite volume method using the SIMPLE algorithm. The influence of the Rayleigh number, the Hartmann number, the orientation angle of the applied magnetic field, the type of nanoparticles as well as the volume fraction of nanoparticles, on the hydrodynamic and thermal characteristics of the nanofluid was illustrated and discussed in terms of streamlines, isotherms and mean Nusselt number. The results obtained show that the heat transfer rate increases with increasing Rayleigh number and orientation angle of the magnetic field but it decreases with increasing Hartmann number. In addition, heat transfer improves with increasing volume fraction and with the use of Al2O3 nanoparticles.

The effect of nanoparticle shape on the natural convection heat transfer of Cu-Al2O3/water hybrid nanofluid inside a U-shaped enclosure is presented in this paper. The governing equations are transformed into the dimensionless form using dimensionless variables. A three-node triangular finite element method is used with the Newton-Raphson method to solve the problem numerically. The streamlines and isotherms as well as the local and average Nusselt numbers are presented for the fluid flow with Rayleigh number of 104 to 106.It is found that blade nanoparticle shape produces the highest heat transfer rate while sphere is the lowest.

The temperature rapid rise phenomenon often happens in the side-by-side frost-free refrigerators during the damper-off cycle, which leads to a decrease in damper-off duration and an increase in energy consumption. A three-dimensional transient model of natural convection during the damper-off cycle is established and experimentally validated to analyze the refrigerating compartment (RC) temperature rapid rise phenomenon. The results show that the violent natural convection airflow driven by the non-uniform temperature distribution will lead to the significant variation of RC temperature. The hot air rises from bottom into top layer along the three passages, which include the front gap (FG) between shelves and door boxes, the side gap (SG) between the right-side wall and door boxes and the rear gap (RG) between shelves and the rear wall. The air enthalpy along FG into the first layer is the dominant factor of the temperature rapid rise, accounting for almost 64.4% of the total inflow air enthalpy. The net air enthalpy flow along FG is larger than other passages in the first 15s and decreases rapidly as the temperature distribution becomes uniform.

We report the complex evaporation kinetics of saline sessile droplets on surfaces with elevated temperatures. Our previous studies show that on non-heated substrates, saline sessile droplets evaporate faster compared to the water counterparts. In the present study, we discover that on heated surfaces, the saline droplets evaporate slower than the water counterpart, thereby posing a counter-intuitive phenomenon. The reduction in the evaporation rates is directly dependent on the salt concentration and the surface wettability. Natural convection around the droplet and thermal modulation of surface tension is found to be inadequate to explain the mechanisms. Flow visualizations using particle image velocimetry (PIV) reveal that the morphed advection within the saline droplets is a probable reason behind the arrested evaporation. Infrared thermography is employed to map the thermal state of the droplets. A thermo-solutal Marangoni based scaling analysis is put forward and the major governing non-dimensional numbers have been accounted for in the analysis. It is observed that the Marangoni flow and internal advection borne of thermal and solutal gradients are competitive, thereby leading to the overall decay of internal circulation velocity compared to the equivalent pure water case, which reduces the evaporation rates. The theoretically proposed advection velocities conform to the experimental results. This study sheds rich insight on a novel species transport behaviour in saline droplets.

The unsteady natural-convection of Al2O3-water nanofluid form heated open T-pipe inside a cavity has been investigated by incompressible smoothed particle hydrodynamic (ISPH) method using non-homogenous two-phase Buongiorno?s model. Different lengths and heights of T-pipe shape are considered. The side walls of the cavity are kept at cool temperature Tc and the horizontal walls are thermally insulated. The Lagrangian description of the controlling governing equations is discretized and solved using improved ISPH method. In this study, ISPH method is improved using kernel renormalization function for boundary treatment plus modification in the source term of pressure Poisson equation. The source term of pressure Poisson equation contains the velocity divergence plus density invariance multiply by relaxation coefficient. The calculations are performed for variable lengths of T-open pipe (0.2 ? Lb ? 0.6), variable widths of T-open pipe (0.02 ? Wb ? 0.16), (0.02 ? Wt ? 0.16), and variable concentration of nanoparticles volume fraction (1% ? ?avg ? 10%). The obtained results showed that the maximum values of the stream function are reduced by 80.8% when ?avg is increased from 1-10%. Additionally, as lengths and widths of the T-pipe are raised, the average Nusselt numbers at the vertical walls are enhanced.

The thermophysical properties of bedrock are of primary importance when designing borehole thermal energy systems. We present a novel use of the Enhanced Thermal Response Test (ETRT) to determine bedrock thermal conductivity, natural convection, and drill hole thermal resistance as a function of depth in crystalline bedrock. Bedrock was heated with a 228-m-long hybrid cable containing copper wires and fiber optics for temperature monitoring. A reference fiber optic cable was installed along the whole length of the studied drill hole. For groundwater-filled boreholes, the ETRT offers a means to estimate the magnitude of buoyancy-driven natural convection. We estimated that the heating power in the ETRT should not exceed 20 Wm-1 for the thermal conductivities to be determined with sufficient accuracy. According our results, the accuracy of the ETRT can be significantly improved if the test is performed with a hybrid fiber optic cable combined with a reference fiber optic cable. Thermal resistance can be more accurately determined if a reference fiber optic cable is used. The most important achievement of this method is that compared to other measurement methods, the effective thermal conductivity of bedrock can be simultaneously determined along the entire length of the drill hole.

The paper addresses numerically a study on thermal management of a cavity-shaped thermal system providing localized heating at the bottom. For this fundamental study, different fluids namely air, water, ethylene glycol (EG), and nanofluid are considered in a square cavity from the application point of view. The upper halves of the sidewalls, and top wall act as the isothermal heat sink. The heater acts as an isothermal heat source. Four different configurations are studied in this work: (a) Case-1: central heating with one heater (b) Case-2: corner heating with one heater (c) Case-3: corner heating with two heaters of equal length (d) Case-4: central heating with two heaters of equal length. For all the configurations, the total length of heaters is fixed. The other walls are maintained in an adiabatic condition. The finite volume approach is employed to solve the governing differential equations numerically. The simulation is executed for a spectrum of Prandtl numbers covering the most commonly used working fluids, keeping the Rayleigh number and the volumetric concentration of nanoparticles fixed. The streamlines and isotherms are employed for the visualization of flow and thermal field. The transmission of heat by free convection is characterized by the Nusselt number. The irreversibility in the flow domain is studied using the contours of the entropy generation rate. The aim of this work is to find out the heater location and fluid for which the rate of heat transmission is maximum. The results reveal that the maximum heat removal rate occurs for central heating with a double heater (Case-4) and the minimum heat removal rate takes place for corner heating with a double heater (Case-3). It is noted that the heat transmission rate is maximum for nanofluid.

In this study, heat transfer utilizing non-Newtonian fluids with a power-law model in a rectangular enclosure containing a hot obstacle was verified experimentally. The impact of aspect proportion (AR) on fluid flow characteristics and heat transfer, obstacle shapes, and various amounts of carboxymethylcellulose was explored with distilled water which in turn controls the index of powers-law (n). The findings show that the increases in the Number of Rayleigh, lead to the greater the Number of Nusselt, and the greater the non-Newtonian behavior, increased the heat transfer. There is also a noticeable impact when changing the shape of an obstacle on heat transfer as the cylindrical shape enhances heat transfer greater than the cuboid shape. As for aspect proportion, it also affects heat transfer inversely.

This paper reports a numerical study of double-diffusive natural convection through an annular space delimited by a square cylinder on the outside and a cylindrical cylinder on the inside covered by a porous layer. The Darcy-Brinkmann-Forchheimer is used for modeling flow in both fluid and porous areas. The annular space is partially or completely filled with an isotropic porous medium. A finite volume method, using the Patankar-Spalding technique is used for solving the discretization of the dimensionless equations governing the problem. The effects of simultaneously applied thermal and solutal buoyancy forces on heat and mass transfer are shown in the results for a large range of buoyancy ratios N, Rayleigh number, and thermal conductivity. Streamlines, isotherms, and iso-concentrations are presented to analyze the flow structure transition from mass species dominated to thermal dominated flow. Results show that the buoyancy ratio can change the flow pattern and the increased thermal conductivity ratio can improve heat and mass transfer. A good agreement was obtained between the present results and those published were found.

This research presents an investigation of laminar two-dimensional double-diffusive free convection and entropy formation in an inclined enclosure under the influence of an inclined magnetic field. The performance of natural convective heat transfer can be improved by doing modifications in enclosure geometry that impact the flow structure. We have considered a dome-shaped enclosure to examine the heat and mass transfer performance. The enclosure is saturated with Cu-water nanofluid and the two sidewalls of the enclosure are maintained at constant temperature Tc(

Flow and heat transfer components of buoyancy driven convection in a hybrid nanofluid filled wavy-walled cavity are numerically investigated in this study. A cylindrical heat generating blockage is placed at the center of the cavity. The cavity is partially heated from its bottom wall and cooled from wavy-walls while the remaining walls are adiabatic. The cavity is permeated by a transverse magnetic field. Thermal conductivity model of hybrid nanofluid is developed comprising Brownian motions of different nanoparticles. The non dimensional governing equations are solved by implementing finite element method. Obtained results demonstrate the intensification of fluid flow circulation for increasing Rayleigh number and heater length. The heat transfer rate is expeditiously augmented for increase in Rayleigh number and hybrid nanoparticles volume fraction but reverse trend is observed for higher Hartmann number. The flow circulation and temperature distribution are influenced with the presence of heat generating cylinder and roughness of the cavity walls. In addition, strength of fluid motion becomes higher for wavy cavity containing heat generating obstacle compared to smooth cavity without blockage. Maximum heat transfer is ensured at lower heater length and radius of the heat generating cylinder. Heat transfer rate also increases with the roughness of the cavity.

This study aims to analyze the effect of fin geometry on the thermal performance of longitudinally finned-tube horizontal latent heat thermal energy storage (LHTES) systems. The longitudinal fins with different fin heights, thickness, and numbers were applied in the horizontal shell-and-tube LHTES system and the paraffin was packed in the annulus. The melting fronts, average temperature, and velocity profiles of Phase Change Material (PCM) were graphically illustrated and compared for charging processes. It was found that the incorporation of longitudinal fins in a small quantity (2.85% of total volume) could reduce the complete melting time by 34% in comparison to the bare-tube configuration. Melting characteristics were compared using average liquid fraction, average PCM temperature, and stored energy. It was recommended that the fin height should not exceed half of the annulus gap. The optimum fin volume was identified by comparing the enhancement ratio for examined configurations. Furthermore, for the same fin volume configurations, this study evaluated (i) whether a large number of short fins are beneficial or a smaller number of long fins and (ii) whether thick short fins are beneficial or thin long fins? Comparison results showed that a small number of long fins were more beneficial than that of more short fins and the melting characteristics of thin long fins were superior to that of the thick short fins. Finally, the optimum fin configuration was justified, and the priority sequence was suggested for the design of longitudinally finned-tube energy storage systems.

The PCM composited with metal foam (PCM-porous system) as heat sink to cool photovoltaic (PV) panel is a potential application. However, there has little attention on the differences in cooling effect of PCM-porous systems when PV panels install with different inclination angles. To fill this research gap, the charging processes of PCM-porous systems with different inclined angles (φ = 0°, 30°, 60°, 90°) have been investigated numerically and experimentally in the current work. Meanwhile, the influences of different Rayleigh numbers (Ra = 1.4568 × 106, 1.8210 × 108, 1.1654 × 1010) have been considered. Results show that the inclined angle has little impact on the PCM-porous system with small porosity (e = 85%, 90%), which is much different from the PCM-porous system with larger porosity (e = 95%). In the discussion, an interesting phenomenon has been found that the weak natural convection of liquid PCM in porous media induced by the inclined cavity plays a negative role in melting process, which is obvious in PCM-porous system with small porosity (e = 85%, 90%). But this negative effect is not necessarily a bad thing due to that it can extend the duration time to cool the PV panel. The maximum duration time of PCM-porous system with e = 85% or 90% is 2 times of system with e = 95% (φ≠0°).

This study aims to establish predictive formulas for the temperature dependence of impurity diffusion coefficient based on a hard-sphere (HS) model and the measurement results. The impurity diffusion coefficients of Sb, Bi, and In in liquid Sn were measured using the shear cell technique and stable density layering at 773 K and 973 K (500 °C and 700 °C, respectively) with suppression of natural convection. The temperature dependence of the impurity diffusion coefficient can be predicted by multiplying the ratio of the solvent to the solute of the following three factors by the self-diffusion coefficient of the solvent as the slope: (i) the square of mean atomic diameter, (ii) the first peak of the pair distribution function calculated by the HS model, and (iii) the square root of the converted atomic weight. If the ratio of the atomic diameter is close to one, the temperature dependence of the impurity diffusion coefficient can also be predicted with an accuracy similar to the abovementioned relationship by multiplying the following two factors by the self-diffusion coefficient of the solvent as the slope: (i) the atomic diameter ratio of the solvent to the solute and (ii) the thermodynamic factor. The predictive formulas based on the HS model showed an accuracy of approximately ±10 pct for the experimental values from 573 K to 973 K (300 °C to 700 °C).

The study of mass transfer in the non-Newtonian fluid is essential in understanding the engine lubrication, the cooling system of electronic devices, and the manufacturing process of the chemical industry. Optimal performance of the practical applications requires the appropriate conditions. The unsteady transient free convective flow of second-grade fluid with mass transfer and wall transpiration is concerned in the present communication. The behavior of the second-grade fluid under the influence of injection or suction is discussed. Suitable non-dimensional variables are utilized to transform the governing equations into non-dimensional governing equations. A Maple solver “pdsolve” that is using the centered implicit scheme of a finite difference method is utilized to solve the dimensionless governing equations numerically. The effects of wall injection or suction parameter, second-grade fluid viscoelastic parameter, Schmidt number, and modified Grashof number on the velocity and concentration profiles are graphically displayed and analyzed. The results show that with increasing wall suction, viscoelastic parameter, and Schmidt number, the velocity and concentration profiles decrease. Whereas, the velocity profiles show an opposite tendency in situations of wall injection. The wall suction has increased the skin friction and also the rate of mass diffusion in the second-grade fluid.

The prime objective of the current study is to examine the effects of third-grade hybrid nanofluid with natural convection utilizing the ferro-particle Fe 3 O 4 and titanium dioxide TiO 2 and sodium alginate (SA) as a host fluid, flowing through vertical parallel plates, under the fuzzy atmosphere. The dimensionless highly nonlinear coupled ordinary differential equations are computed adopting the bvp4c numerical approach. This is an extremely effective technique with a low computational cost. For validation, it is found that as the volume fraction of Fe 3 O 4 + TiO 2 hybrid nanoparticles rises, so does the heat transfer rate. The current and existing results with their comparisons are shown in the form of the tables. The present findings are in good agreement with their previous numerical and analytical results in a crisp atmosphere. The nanoparticles volume fraction of Fe 3 O 4 and TiO 2 is taken as uncertain parameters in terms of triangular fuzzy numbers (TFNs) [0, 0.05, 0.1]. The TFNs are controlled by α − cut and the variability of the uncertainty is studied through triangular membership function (MF).

A new type of nanofluids is nanoencapsulated phase change materials (NEPCMs), where nanoparticles are made of a shell and a core. In the current study, characteristics of free convection flow, entropy generation, and heat transfer of NEPCMs in an enclosure are investigated. The enclosure is an annulus between concentric horizontal circular and square cylinders with a porous medium. The governing equations (i.e., continuity, energy, and momentum) are written in the nondimensional form and then numerically solved by the control volume finite element method (CVFEM). The results of the validation are in good agreement with those of the literature. The effects of decision variables on the entropy generation number and the average Nusselt number are investigated. The outcomes discovered that there is a maximum for Nu ave and a minimum for N gen at θ f = 0.4 for each value of the Stefan number. Also, Nu ave and ECOP increase by 8.8% and 24.8%, respectively, while N gen decreases by 12.8% when ϕ increases from 0 (pure fluid) to 0.05 at θ f = 0.4 .

The present numerical work, based on the finite volume method, deals with the characterization of natural convective flow and thermal fields inside differentially vertical heated square cavities filled with a nanofluid as well as the quantification of the convective exchanges. The investigation is devoted to study the influence of the hybrid nanofluid (Al2O3-Cu / water) on the flow’s general structure with a particular attention to the Nusselt number. An exhaustive parametric study is conducted considering different combinations of Al2O3 and Cu nanoparticles (NPs) dispersed in water for a range of Rayleigh numbers (Ra) and total volume fractions An appropriate agreement with experimental data was observed for the estimation of the hybrid nanofluid thermal conductivity. From the results, it is observed that the heat transfer intensifies by increasing the Ra number and the nanoparticles volume fraction. The hybrid nanofluid seems to be the most efficient nanofluid in comparison with a base fluid and a single nanofluid. This heat transfer enhancement becomes more convincing with the increase of the Cu NPs content (% in volume).

In this paper, a modulated permanent helical magnetic field is imposed to improve segregation during directional solidification in a binary Sn–3.5 wt pct Pb alloy. The magnetic force created by this magnetic field significantly interferes with heat, mass and momentum transfer of molten metal during solidification. Our experimental results show that this magnetic field, with an appropriate modulation frequency, can not only promote columnar-to-equiaxed transition (CET) but also significantly reduce solute segregation otherwise caused by conventional helical magnetic fields. Our analysis demonstrates the advantages of this approach over natural convection and conventional electromagnetically forced convection.

Background The exploration of natural convection which is one the substantial types of convective heat transmission in various applications for instance heat exchangers and geothermal systems along with nanofluids (Nanofluids have greater thermal conductivity in comparison to the conventional fluids) engrossed all researchers’ attention. Methods This study is dedicated to the inspection of the free convection of nanofluid as well as entropy generation inside a porous cavity loaded with nano-encapsulated phase change materials (NEPCMs). The wavy bottom section of the enclosure may be subject to a constant heat flux due to the transmitted sunlight comes from a parabolic trough solar collector. The volumetric heat source/sink is comprised in the governing equation. The robust finite element method (FEM) is deployed to handle the transformed governing equations. Findings The numerical simulation of the streamlines and isotherms associated with velocity distribution for diverse factors are displayed. Further, the significant behavior of the contributing parameters on the Nusselt and Bejan numbers are represented. The results demonstrate that the various profiles of wavy bottom section could affect the heat transmission features as well as fluid flow remarkably. Furthermore, it is noteworthy that all the profiles of entropy enhance with increasing the amplitude with respect to the increasing undulation number for the existence of various Rayleigh number.

Background Free convection and second law scrutiny of nano-encapsulated phase change material (NEPCM) suspension along with entropy production inside a circular cold cylinder involving a wavy hot baffle is a significant thermal management aspect subject to various industrial applications. Phase change material (PCM) undergoes a solid-liquid phase mutation at a particular fusion temperature, and absorbs/releases an appreciable amount of energy because of the latent heat of phase mutation. Hence, NEPCMs would be prospective owing to their capability to enhance the working liquids’ performance, keeping the system at a particular cooling temperature. Methods In order to simulatethe free convection along with entropy generation of NEPCMs inside a circular cold cylinder entails a wavy hot baffle under CattaneoChristov heat flux model(Altered Fourier theory) and magnetic field, the finite element method (FEM) could be utilized to solve the governing equations. In this study, the amplitude of baffle could be changeable while its undulation number is fixed at 2. Findings Amplifying Raylegh number intensifies streamlines, isotherms, horizontal and vertical velocities, total entropy generation whittles down local Bejan number. Higher magnetic field strength is responsible for slow movement of NEPCMs and augments local Bejan number. Growth of baffle size yields squeezes the streamlines, horizontal and vertical velocities and intensified tilted isotherms.

Recent advancements in nanotechnology research have introduced hybrid nanofluids which are sophisticated classes of fluids with enhanced thermal properties that outperform conventional nanofluids. The objective of current communication is to illustrate the comparative mathematical model of MHD hybrid nanofluid and mono-nanofluid flows with heat flux condition through a stretching sheet. Impact of melting phenomenon, heat generation/absorption and natural convection is considered. The thermal radiation, viscous dissipation and temperature-dependent viscosity are also considered. In current model, two different nanoparticles namely zinc oxide ( ZnO ) and zirconium dioxide ( ZrO 2 ) are dispersed in kerosene oil ( C 10 H 22 ) base fluid to form a hybrid nanofluid. Similarity transformations are utilized to renovate the governing PDEs structure system into ordinary ones. The numerical computations of current mathematical model are computed through bvp4c built-in function in MATLAB with shooting scheme. The fluctuations of velocity and temperature distributions are analyzed with physical impacts for different flow parameters. It is visualized that the growing amount of convection parameter corresponds to increment in velocity profile. The velocity of hybrid nanofluid reduces as the magnetic parameter increases. It is analyzed that the thermal field of hybrid nanofluid is an increasing function of thermal radiation parameter. Furthermore, the thermal profile is a reducing function of melting and Prandtl numbers.

Experimentally determined vitamin degradation kinetic parameters are vital input for process optimization, e.g., of nutrient rich beverages such as milk and fruit juices. The standard method of obtaining these parameters is to subject a test-tube of the nutrient (in its food matrix) to a water bath at elevated temperatures and measure remaining concentration as a function of time. It is well known that accurate kinetic fitting requires measuring the temperature inside the test tube as a function of time (due to lag it is not identical to the water-bath temperature), and this is included in contemporary studies. However, the importance of axial temperature gradients for valid kinetic parameter estimations has not been discussed to the same extent. This contribution combines experiments and physical modelling to show how an axial temperature gradient evolves in a test tube (R = 13 mm, Z = 75 mm), due to free convection currents (T∞ – T0 = 57–71 °C). Consequently, the test tube temperature is not uniform in such an experiment. Thus, the positioning of the thermocouple in a test-tube-in-water bath experiment is essential for ensuring a valid estimation of the kinetic parameters. Simulations suggest that positioning it half-way between top and bottom is a suitable best practice.

In this paper, numerical study on natural convection heat transfer for confined thermo-dependent power-law fluids is conducted. The geometry of interest is a fluid-filled square enclosure where a uniform flux heating element embedded on its lower wall is cooled from the vertical walls while the remaining parts of the cavity are insulated, without slipping conditions at all the solid boundaries. The governing partial differential equations written in terms of non-dimensional velocities, pressure and temperature formulation with the corresponding boundary conditions are discretized using a finite volume method in a staggered grid system. Coupled equations of conservation are solved through iterative Semi Implicit Method for Pressure Linked Equation (SIMPLE) algorithm. The effects of pertinent parameters, which are Rayleigh number (103 ≤ Ra ≤ 106), power-law index (0.6 ≤ n ≤ 1.4), Pearson number (0 ≤ m ≤ 20) and length of the heat source (0.2 ≤ W ≤ 0.8) on the cooling performance are investigated. The results indicate that the cooling performance of the enclosure is improved with increasing Pearson and Rayleigh numbers as well as with decreasing power-law index and heat source length.

In this paper, the natural convective heat transfer from a stretching sheet oriented vertically involving surface mass transfer is of primary focus. A similarity solution in three dimensions is described for energy and momentum. The transformed equations are answered by using MATLAB in-built numerical programmer solver bvp4c. For a range of Prandtl numbers and surface mass transfer rates, friction factor and Nusselt numbers are tabulated. The heat transfer mechanism is observed to influence surface mass transfer. Heat transfer rate increases and thermal boundary layer thickness decreases with an increase of Prandtl values. In addition, the current results are compared with the previously published results and initiate to be a successful agreement.In this paper, the natural convective heat transfer from a stretching sheet oriented vertically involving surface mass transfer is of primary focus. A similarity solution in three dimensions is described for energy and momentum. The transformed equations are answered by using MATLAB in-built numerical programmer solver bvp4c. For a range of Prandtl numbers and surface mass transfer rates, friction factor and Nusselt numbers are tabulated. The heat transfer mechanism is observed to influence surface mass transfer. Heat transfer rate increases and thermal boundary layer thickness decreases with an increase of Prandtl values. In addition, the current results are compared with the previously published results and initiate to be a successful agreement.

An exhaustive numerical investigation is carried out to analyze the role of an isothermal heated thin fin on fluid flow and temperature distribution visualization in an enclosure. Natural convection within square enclosures finds remarkable pragmatic applications. In the present study, a finite difference approach is performed on two-dimensional laminar flow inside an enclosure with cold side walls and adiabatic horizontal walls. The fluid flow equations are reconstructed into vorticity - stream function formulation and these equations are employed utilizing the finite-difference strategy with incremental time steps. The parametric study includes a wide scope of Rayleigh number, Ra, and inclination angle ϴ of the thin fin. The effect of different Rayleigh numbers ranging Ra = 104-106 with Pr=0.71 for all the inclination angles from 0°-360° with uniform rotational length of angle 450 of an inclined heated fin on fluid flow and heat transfer have been investigated. The heat transfer rate within the enclosure is measured by means of local and average Nusselt numbers. Regardless of inclination angles of the thin fin, a slight enhancement in the average Nusselt number is observed when Rayleigh number increased for both the cases of the horizontal and vertical position of the thin fin. When the fin has inclined no change in average Nusselt number is noticed for distinct Rayleigh numbers.

Purpose The purpose of this study is the identification of the best method to apply the body force in the lattice Boltzmann method (LBM). In the simulation of mixed convection, especially for large Richardson number flows in a square cavity. Design/methodology/approach First, three methods for applying the body force were compared to each other in the LBM. Then, an LBM-based code was written in the FORTRAN language using these three methods. Next, that code was used to simulate natural/mixed convection in a two-dimensional cavity to evaluate the methods for applying the body force. Finally, the optimum way for applying the body force was used for the simulation of free convection heat transfer in a concentric annulus with Rayleigh number in a range of 1,000 to 50,000, and mixed convection heat transfer in a concentric annulus with Rayleigh number in a range of 10,000 to 50,000 and Reynolds number in a range of 100 to 400. Findings Mixed convection heat transfer was simulated in a two-dimensional cavity with Richardson number in a range of 0.0001 to 100. The results which were obtained in low Richardson number flows have shown good adaptation to the available data. However, the results of large Richardson number flows, for example, Ri = 100, have shown a significant difference to the available data. Investigations revealed that this difference was due to the method of applying the body force. Therefore, the choice of the best way to apply the body force was investigated. Finally, for the large Richardson number flows, the best method to apply the body force has been identified among the several techniques. Originality/value To the authors’ knowledge, the effects of methods for applying the body force were not investigated in the cavities mixed convection, even though there are numerous investigations conducted on mixed convection with the LBM. In this study, the effects of techniques to apply the body force were investigated in large Richardson number flows. Finally, the best method to apply the body force is distinguished between several techniques for the large Richardson number mixed convection flows.

The onset of natural convection in a fluid-saturated anisotropic porous layer, which rotates about the vertical axis, under the hypothesis of local thermal non-equilibrium, is analysed. Since the porosity of the medium is assumed to be high, the more suitable Darcy-Brinkman model is adopted. Linear instability analysis of the conduction solution is carried out. Nonlinear stability with respect to $$L^2$$ L 2 -norm is performed in order to prove the coincidence between the linear instability and the global nonlinear stability thresholds. The effect of both rotation and thermal and mechanical anisotropies on the critical Rayleigh number for the onset of instability is discussed.

The present article analyzes the effect of viscous dissipations on natural convection heat transfer. The power law model for non-Newtonian fluid with heat generation or absorption effect along a sinusoidal wavy surface with isothermal boundary condition is investigated. A simple coordinate transform is employed to map the wavy surface into a flat surface, and also, the fully implicit finite difference method is incorporated for the numerical solution. The findings of this study can help better understand the effect of parameters such as the Brinkman number, heat generation/absorption, wave amplitude magnitude, and generalized Prandtl number on convective heat transfer in dilatant and pseudoplastic non-Newtonian. Results show that as the Brinkman number increases, the amount of heat transfer decreases. This is physically justifiable considering that the fluid becomes warmer due to the viscous dissipation, decreasing its temperature difference with the constant temperature surface. Also, the effect of the power law viscosity index is surveyed. It is demonstrated that the magnitude of the local Nusselt number in the plane leading edge has the smallest quantity for pseudoplastic fluids compared to dilatant Newtonian fluids. Additionally, as the distance from the plane leading edge increases, the heat transfer declines.

Purpose The purpose of this paper is to examine numerically the magnetohydrodynamic (MHD) free convection and thermal radiation heat transfer of single walled carbon nanotubes-water nanofluid within T-inverted shaped corrugated cavity comprising porous media including uniform heat source/sink for solar energy power plants applications. Design/methodology/approach The two-dimensional numerical simulation is performed by drawing on Comsol Multiphysics program, based on the finite element process. Findings The important results obtained show that increasing numbers of Rayleigh and Darcy and the parameter of radiation enhance the flow of convection heat. Furthermore, by increasing the corrugation height, the convection flow increases, but it decreases with the multiplication of the corrugation height. The use of a flat cavity provides better output than a corrugated cavity. Originality/value The role of surface corrugation parameters on the efficiency of free convection and heat transfer of thermal radiation within the porous media containing the T-inverted corrugated cavity including uniform heat source/sink under the impact of Lorentz forces has never been explored. A contrast is also established between a flat cavity and a corrugated one.

This study aims to demonstrate a condition for suppressing natural convection for self-diffusion measurement in liquid metal by stable density layering of isotopic concentration. The self-diffusion coefficients (DPb) of 204Pb, 206Pb, 207Pb, and 208Pb were measured using the shear cell technique at 773 K (500 °C). Simultaneously, the impurity diffusion coefficient (DAg) of Ag, which is a marker to compare DAg with the reference data of suppressing natural convection, was measured. From the concentration profiles of Pb isotopes, density distributions were calculated using an approximation of the linear relationship between the density and isotopic concentration; in addition, density gradients, which were defined as the inner product between gravity vector and density gradient calculated from the density distribution, were obtained. The results suggest that DAg was in good agreement with the relative error in the reference data (within 0.47 pct), which can be attributed to the suppression of natural convection by predicted stable conditions. In contrast, natural convection was confirmed as DAg was three times larger than the reference data in predicted unstable conditions. From the density distribution obtained after the diffusion process, when the density gradient with the largest absolute value was greater than zero, the suppression of natural convection was confirmed in the self-diffusion measurements.

An investigative approach on study of a laminar natural heat convection on different geometric annuluses under impact of a constant magnetic field, using Ferro-Nano has been carried out. The three ...

The application of combined electric and magnetic fields is proposed for better heat transfer enhancement in a porous fin system. An inverse estimation technique is established to simultaneously de...