Stagnation Region Research Articles

Thermal design of composite cold plates by topology optimization

Topology optimization has been extensively utilized to generate cold plates with efficient cooling performance. However, the design of composite cold plates remains challenging. This study presents a two-solid topology optimization method for conjugate heat transfer based on ordered SIMP (solid isotropic material with penalization). The proposed method aims to develop high-performance composite cold plates by leveraging the differences in thermal conductivity of various materials. The optimization results were investigated for four inlet and outlet combinations at various Reynolds numbers. The results indicate that using a staggered distribution of multiple inlets and outlets yields higher heat transfer than a single distribution. Furthermore, composite cold plates derived from the two-dimensional optimized models were numerically compared with rectangular flow channel and non-composite cold plates. The optimized channels exhibited superior hydrothermal performance over the rectangular flow channel, which was primarily attributed to the weakening of the velocity stagnation region. The average temperature (T¯) and root mean square temperature (RMST) of the heat source were reduced by a maximum of 2.53% and 57.67%, respectively. The friction factor decreased by up to 50.42%. Compared to non-composite cold plates, the decrease in RMST reached 16.24% without any additional increase in the pumping power. Composite cold plates further promote temperature uniformity by accelerating the heat transfer rate through their high thermal conductivity, thereby mitigating the occurrence of hotspots. Finally, the performance of the three test samples was experimentally compared to validate the numerical results. The optimized design enables the strategic allocation of highly thermally conductive material on a cold plate while employing more cost-effective alternatives in other areas. The proposed method is anticipated to expand the design possibilities for cold plates and provide insights into addressing concerns related to hotspots in equipment.

Design Impacts on Ram Air Vane Cooling in an Ultra-Compact Combustor

Abstract The ultra-compact combustor (UCC) aims to decrease the length of gas turbine combustors using a unique design geometry which wraps a combustion chamber around the central axial flow. This distinctive design enables an out of the box type of cooling scheme to be investigated for the turbine inlet vanes, termed the hybrid guide vane (HGV) in the UCC. The leading edge of the HGV experiences only compressor exit air as combustion products do not interact with the vane upstream of the 14% axial chord location. Previous studies were conducted which computationally evaluated the viability of taking in freestream flow through the HGV stagnation region for use as coolant. Based on these studies, a six vane HGV was manufactured which incorporated a solid vane and five hollow vanes. Each of these vanes incorporated different features to vary the size of the internal plug, trailing edge exit, and film cooling holes. In the present study, the cooled HGV was experimentally analyzed using pressure, thermocouple, and infrared (IR) thermography measurements to evaluate internal coolant flowrates and pressure loss along with cooling performance. Furthermore, the vanes were compared to isolate the impact of design differences on vane cooling. It was found that the location of the internal plug and incorporation of film cooling holes had a minor impact on coolant flow and cooling. Additionally, results showed exit area had the largest impact on surface temperature and coolant mass flow where the largest exit area allowed less restricted coolant flow resulting in the lowest average surface temperature. However, completely blocking the exit slot forced coolant to exit only through film cooling holes, stagnating the majority of the internal flow, resulting in surface temperatures higher than the uncooled, solid vane.

Area average heat transfer from a vertical flat plate impinged by circular inclined jet

ABSTRACT The inclined impinging jets owing to higher efficiency are widely used to disperse concentrated and transient heat loads. The temperature and heat transfer characteristics of jet cooling vertical hot plate at different inclinations are experimentally investigated. Experiments are performed to investigate the area average heat transfer over a flat surface of 600 × 300 mm2 placed at different location (z) of 3−20 d from the jet. The investigation is employed for Reynolds number based on hydraulic diameter of 11.5 mm ranging from 10,000 to 75,000. The orientation of the jet varies from 15° to 75°. The study aims to investigate the influence of jet orientation at different area locations on the surface from the point of impingement. The effect in stagnation region with different jet tilt is investigated. The area average temperature variation and characteristic temperature contours with increasing surface area and inclination is delineated. The characteristics of heat transfer on the surface’s periphery are studied. Heat transfer increases by 40% at lower tilt angle as the jet is displaced from 20 to 6 d, whereas the maximum average Nu occurs at higher inclination. The available Nusselt numbers in inclined jet are compared with present experimental results. A new empirical correlation is developed for a complete range of z/d, Re and large radial span.

3D Modeling and Numerical Investigation of Electrochemical CO2 Reduction in Microfluidic Flow Cells

Electrochemical reduction reaction is considered as a promising technical route for carbon‐neutral and mitigating greenhouse effect. concentration limitation hinders the performance of state‐of‐the‐art electrochemical reduction reaction. Increasing the mass transfer of reactants on the catalyst surface by flow cell design and porous electrode design has become the mainstream approach. Studying the distribution of mass in reaction region is important and beneficial to optimizing and designing efficient reactors. Herein, electrochemical reduction reaction reactors with micrometer and millimeter channels are simulated and systemically analyzed. The results reveal the microfluidic design can improve the mass transfer and reactant gas flow in the porous layer to reduce the concentration polarization and ensure uniform local potential of the reactor. A micrometer channel model requires only 10 sccm inlet gas supply to achieve the same current density compared to a millimeter flow channel with an inlet flow of 20 sccm. This study proposes a reasonable flow channel reactor to reduce gas stagnant region, which not only enhances the reduction performance effectively with evident potential dependence, but also guides the design for large‐scale reactors.

Heat transfer enhancement in a corrugated chamber filled with hybrid nanofluid under an influence of internal heated plate

PurposeThe purpose of this research is to scrutinize numerically the effect of internally equipped nonuniformly heated plate within wavy cavity on heat transfer enhancement in the case of hybrid nanofluid flow.Design/methodology/approachThe two-dimensional, steady, laminar, Newtonian and incompressible thermo-fluid flow phenomenon has been investigated numerically using Galerkin method. The considered parameters including number of waves (3–7), nondimensional length of heated plate (0.4–0.8), plate inclination angle (0º–90º), Rayleigh number (103–106) and concentration of nanoparticles (0.0–2.0) have been investigated in combination with involving hybrid nanofluid as a working fluid to augment thermal properties effectively. Two vertical wavy boundaries have low temperature whilst the other horizontal surfaces are adiabatic.FindingsThe Rayleigh number has a moderate impact on the values of Nusselt number, and skin friction parameter varied from 103 to 105 while it strongly affects them for Ra = 106, where Nu is roughly doubled (approximately 200%) in comparison with its value at Ra = 105 for all cases. Stream function is changed by the orientation of heated plate and Ra values, where its maximum value was 12.9 in horizontal position and 13.6 at vertical one. Results indicate a separation from the wavy walls at low Ra which tends to keep stagnation region at the deep parts of corrugated walls contrary the case at high Ra. The behavior of the isotherm contours tends to be distributed more evenly at lower values of Ra and angle of inclination lower than 45º. The resulting properties from mixing two materials for hybrid nanofluid into one base fluid show a good compromise between thermal capacity and heat conductivity, which is improved by 16% that leads to enhanced convective energy transport in the wavy chamber.Originality/valueThe originality of this work is the considered physical phenomenon where an influence of internal nonuniformly heated plate has been studied for the irregular geometry filled with a hybrid nanofluid. Such analysis allows defining the possible heat transfer enhancement for such an irregular cavity and inner heated plate.

CARD21: The Effect of Drainage Cannula Design and Tip Position on Thrombosis Risk During Venoarterial Extracorporeal Membrane Oxygenation: A Computational Analysis

Background: Venoarterial extracorporeal membrane oxygenation (VA ECMO) supports critically ill patients with refractory cardiopulmonary failure. Drainage cannulae remove venous blood from the patient, but variability in cannula selection and tip position may impact flow dynamics and thrombosis risk. Therefore, this study investigated the effect of tip position of single-stage (SS) and multi-stage (MS) VA ECMO drainage cannulae on the risk of thrombosis. Methods: Computational fluid dynamics was used to model flow dynamics within a patient-specific geometry of the venae cavae. The tip of the SS and MS cannulae was modelled in the superior vena cava (SVC), SVC-Right atrium (RA) junction, mid-RA, inferior vena cava (IVC)-RA junction, and IVC. Constant mass flow rates were applied at all major vein inlets reflecting normal physiological flows. Drainage flow rates of the cannula were set at a constant 4 L/min throughout all simulations. The risk of thrombosis was assessed by measuring blood residence time, stagnant volume, rate of blood washout, and high wall shear stress. Results: Changes in the tip position of the SS cannula resulted in variability of thrombosis risk, whereas the MS cannula showed similar thrombosis risk during all simulations. The SS cannula showed reduced thrombosis risk arising from stagnant regions when placed in the SVC or SVC-RA junction, whereas an MS cannula was predicted to create stagnant regions during all tip positions (Figure 1). Conversely, the risk of thrombosis was increased in all positions with the SS cannula arising from higher maximum wall shear stresses (Table 1). When positioned in the IVC-RA junction and IVC, the SS cannula exhibited higher risk of thrombosis arising due to both high and low shear, compared to the MS cannula. Conclusion: Tip position of the drainage cannula impacts cannula flow dynamics and, subsequently, the risk of thrombosis. The use of MS cannulae can reduce high shear-related thrombosis, but SS cannulae can eliminate stagnant regions when advanced into the SVC. Therefore, the choice of cannula design and tip position should be carefully considered during cannulation.Figure 1. Comparison of stagnation regions between the single-stage (a) and multi-stage (b) cannulae at varying tip positions.

P10: CFD Simulation Of Thrombosis In A Catheter Pump Inside The Left Ventricle

Study: Catheter pumps are small axial flow assist devices indicated for temporary use for a variety of indications. Uniquely positioned within the circulation, the pump impeller and motor are situated in the ascending aorta, and blood is pumped from the left ventricle (LV) via a long angled inlet cannula. The interplay of pulsatile LV blood dynamics with hemocompatibility performance of a catheter pump is not well characterized. The purpose of this study is to conduct computational fluid dynamics (CFD) simulation that includes multifactorial and synergistic models of blood damage to a catheter pump within a virtual in-vivo environment to analyze its hemodynamics. Methods: A generic catheter pump whose shape is inspired by the Impella 5.0 is situated within a static geometry consisting of a semi-realistic LV and aorta. We apply bloodDamageFoam, an OpenFOAM-based CFD code, to predict the hemodynamic flow and blood damage generated by the pump operating at 20 kRPM. The thrombosis model includes seven biochemical and biophysical agonists and accounts for the effects of high shear stress induced activation of von Willebrand factor. Results: CFD predicted 4.43 LPM blood flow rate from the LV delivered into the aorta. Moderate levels of hemolysis were predicted. The thrombosis model showed moderate degrees of platelet deposition on the cage of the inlet cannula and within the catheter pump chamber. Because the LV in this simulation was not beating, unrealistically large regions of flow stagnation and high platelet activation were observed in the LV. To address this, realistic pulsatility of a dilated LV is currently being modeled. Our latest progress will be presented at the meeting.

A significant study on radioactive cross fluid model with melting boundary near stagnation region

The current research endows the mathematical modeling for the stagnation point flow along with melting nonlinear radiative heat transfer for cross fluid. It has many applications such as synthesis of polymer solutions, plastic manufacturing, food processing, preparation of synthesis, adhesives, etc. A radially stretching sheet has started the flow keeping the assumption of rotational symmetry. Transformation approach is adopted to attain the nonlinear ordinary differential equations based on standard conservation laws of mass, linear momentum and also energy. Numerical solutions of the governing problem are computed via the shooting technique. Characteristics of the parameters appearing in modeling like the melting parameter, power–law index, local Weissenberg number, nonlinear radiation parameter, temperature ratio parameter and Prandtl number are comprehensively analyzed through graphical behavior. In addition, comparative analysis is presented for the cases when the value of free stream velocity overtops the stretching velocity and vice versa. Results are authenticated by taking special cases and excellent compatibility is achieved with the existing literature. The detailed analysis anticipates that the boundary layer structures could be strengthened by growing the melting parameter. Elevation in Weissenberg number caused velocity along with temperature profiles to demonstrate for [Formula: see text]. Further, the temperature behaves oppositely analogous to development in nonlinear radiation parameter besides the temperature ratio parameter.

Unraveling the Fate and Transport of DNAPLs in Heterogeneous Aquifer Systems—A Critical Review and Bibliometric Analysis

Dense nonaqueous phase liquid (DNAPL) in the subsurface environment beyond the permissible limit poses a threat to human health and a suite of ecological services. An accurate prediction of the concentration and mass fluxes of DNAPL at environmentally sensitive locations and their temporal variations can be obtained using robust and efficient fate and transport mathematical models. Thus, this study evaluated 412 articles published from 1990 to 2022 utilizing the Scopus® database to provide a quantitative overview of the present trends and future perspectives of the DNAPL transport research field, especially fate and transport models via bibliometric analysis. The major findings of the published literature based on the scale of the study and type of modeling framework, relationships of governing parameters with a scale of study, and recent developments in the mathematical models were discussed. The country-citation analysis revealed the USA and Canada as leading countries in DNAPL fate and transport research field. The findings of this study uncovered a need for studies considering low-permeability and stagnant regions, as well as the variable nature of the flow, transport, and reaction parameters to understand the complex plume evolution dynamics of DNAPLs under field-scale conditions. The nonlinear interactions between various flow and transport phenomena should be quantified during a model’s development by applying spatial- and time-varying global sensitivity analyses. The outcomes of the bibliometric survey, visual analysis, and concise review presented in this study can provide a wide range of references, emerging topics, and prospects to emphasize less focused on topics of DNAPL transport research.

Evaluation of Convective Heat Transfer and Natural Circulation in an Evacuated Tube Solar Collector

The evacuated tube solar collector ETC is studied intensively and extensively by experimental andtheoretical works, in order to investigate its performance and enhancement of heat transfer, for Baghdad climatefrom April 2011 till the end of March 2012. Experimental work is carried out on a well instrumented collectorconsists of 16 evacuated tubes of aspect ratio 38.6 and thermally insulated tank of volume 112L. The relationbetween convective heat transfer and natural circulation inside the tube is estimated, collector efficiency, effect oftube tilt angles, incidence angle modifier, The solar heating system is investigated under different loads pattern (i.eclosed and open flow) to evaluate the heat loss coefficient from tank and tubes, test the collector with variousaspect ratios (32.9 and 27.2). The enhancement in collector performance is studied by using two reflectors (FlatPlate and Curved Plate) and nanofluid (Water-AL2O3).Theoretical work is run by software (Fluent 6.3), to computethe velocity and temperature profiles within the tube, for different tube diameters, effect of tube junction angle andstagnant region in the bottom of the evacuated tube. The experimental results shows that the heat loss coefficientfor tube is W/m2.K and for tank is W/m2.K, the maximum collector temperature is 79°C in winter and99°C in summer, while that belong to nanofluid collector is 99°C in winter. The best tilted angle (optimum) ofevacuated tube is 41° annually. The collector efficiency increased when using nanofluid of (1, 0.6, 0.3)% volumefraction as(28.4, 6.8, 0.6)% respectively. The efficiency decreases as (33, 62)% when decreasing tube aspect ratiofrom 38.6% to 32.9% and 27.2% respectively. An increase of (16.9 and 7.08)% in collector efficiency is obtainedwhen using curved and flat plate reflectors respectively. From simulation the best junction angle of the tank is22.5°. The stagnant region is influenced with changing heat flux, tilted angle and aspect ratio.

Experimental investigation on time-averaged heat transfer characteristics of a row of pulsating jets

The heat transfer characteristics of a row of pulsating jets feeding by a cooling tube have been investigated for an active clearance control system. Experimental tests were performed to explore the effects of the frequency (rectangular signal, 5–30 Hz), Reynolds number (6000–20,000), jet-to-surface spacing ratio (6–10), and jet-to-jet spacing ratio (3–9) on the Nusselt number of the pulsating jets and the relative enhancement coefficient compared with the steady jets. Results show that the streamwise-averaged Nusselt number of the pulsating jets increases with the increase of frequency (5–25 Hz) and Re. Its distribution along the X/d is gentler with the increase of H/d and S/d. Heat transfer correlations are developed and two associated parameters SrRe0.911(H/S)0.348 and SrRe(H/d)0.540(S/d)-0.248 are obtained to effectively scale the enhancements. Maximum enhancements for the stagnation region and wall jet region are 29.3% and 26.8%, respectively. The heat transfer on the overall surface can be strengthened in a wider range of conditions compared with the stagnation region, which contributes to the heat transfer uniformity in certain conditions.

Local heat transfer characteristics of circular multiple air jet impinging on a semicircular concave surface

ABSTRACT The local heat transfer characteristics of circular multiple air jet impingement on semicircular concave surface were studied experimentally. For constant Reynolds number (Re = 9,000), the effect of jet to concave surface spacing (z/d = 1, 4.2, 6), ratio of curvature (D/d = 4.28, 6, 8.6), jet-to-jet spacing (s/d = 2.4, 4, 5.6), and number of jets were considered. The local heat transfer characteristics were determined by using infrared thermal camera and thin foil method. Lower curvature value ratio (D/d = 4.28) resulted higher average heat transfer coefficient due to broader spread of heat transfer distribution, whereas higher curvature ratio (D/d = 8.6) resulted in lower average heat transfer coefficient due to steeper heat transfer distribution in the stagnation area. At lower D/d, z/d, and s/d with seven jet configuration, the heat transfer coefficients were found effective as compared to other configurations due to broad heat transfer distribution and less interaction between the jets. At given D/d and s/d configuration, the stagnation Nu at θ = 0° do not coincide with jet hole center axis and this shift is more pronounced at higher z/d value. This could be due to additional push before jet impinging on concave surface. The secondary peaks were observed between two neighboring stagnation regions in Nu distribution along the center longitudinal line for lower z/d and higher s/d values. This resulted due to upwash that was obtained from jet interactions related to collisions with the wall jets. The correlations of stagnation line average Nu and overall average Nu were obtained. The coefficient of variance of local heat transfer coefficient for each configuration was determined, and correlation was proposed to analyze the degree of non-uniformity.

Three-dimensional characterisation of pore networks and fluid flow in segregated heaps in the presence of crushed ore and agglomerates

Due to the differences in ore feeds and stacking procedures, segregated pore networks are commonly observed in industrial heap leaching operations, which strongly affect the pore-scale fluid flow and the resulting metal leaching efficiency. Three segregated models, namely, the agglomeration model or AM with intra-particle pores, the crushed ore model or COM with inter-particle pores and the mixed segregated model or MSM with both intra- and inter-particle pores, are defined in this work. The segregated pore network in the MSM consists of agglomerates and crushed particles. The models were obtained by performing micro-computed tomography scanning experiments in packed beds followed by image processing algorithms. Several fluid flow-related parameters were quantified to understand the effects of segregated pore networks on fluid flow in heap leaching. The isolated and connected pores co-exist in porous ore heaps, and the latter determines heap hydrodynamics. The number of connected pores in the AM is higher than in the COM. However, the connected pores with too small pore throats are very slow in fluid transfer by capillarity, resulting in stagnant regions in ore beds. A smaller tortuosity value was also observed in the COM, resulting in fast-flowing preferential fluid flow paths. These are unfavourable to yield uniform fluid flow distributions in industrial heaps. The results of this work suggest the prerequisites for improving fluid flow distribution in heaps, including well-organised heap construction procedures, controlling the particle size distribution and large-scale studies coupled with non-invasive imaging and flow simulations.

Heat/mass transfer augmentation in a leading-edge channel with extended ribs

Gas turbine blade leading-edge cooling is critical due to a high thermal load in the stagnation region. It requires a significant portion of total cooling air supplied to the turbine blade. In order to meet the durability requirement, various cooling schemes are applied. One of the most commonly found in the leading-edge cooling passage is a rib-turbulator design. In this study, a novel rib-turbulator design is investigated for flow and heat transfer characteristics using numerical and experimental methods. The test section was designed to simulate a realistic internal passage, as a triangular channel with a rounded leading-edge. The rib turbulators are installed in a staggered manner. Numerical analyses were performed using a commercial CFD tool, ANSYS CFX. Naphthalene sublimation method was adopted to measure local convective heat/mass transfer distributions. The main geometrical parameter of interest was the extension length of the rib-turbulators (l/e = 0.0, 1.0, 1.5) in the leading-edge region. Based on the parametric study, the optimized case was found, and its heat transfer performance was compared to the baseline (conventional) case. The Reynolds number varied from 20,000 to 40,000. The optimized case showed a 12.7% better heat transfer performance in the leading-edge region than the baseline case at the Reynolds number 30,000 case.

Features of activation energy for a flow with microrotation near stagnation region and unbounded domain : a spectral simulation

This article is motivated to find the impact of various flow controlling parameters such as viscous dissipation, negative and positive values of activation energy on MHD stagnation point micropolar nanofluid flow over a surface. However, negative activation energy is scarce in practice, but the impact of negative values of activation energy could not be neglected as seen in chemical processes. The present mathematical model is solved with successive linearization method (a spectral technique). The velocity, angular velocity, temperature and concentration profiles are drawn by varying flow controlling parameters. The bar diagrams for skin friction, Nusselt number, Sherwood number and couple stress are also displayed. Results indicate that the activation energy boosts the concentration profile up. The negative values of activation energy have higher impact on concentration curves compared to positive values. Arrhenius function decays as activation energy enlarges. This eventually promotes the generative chemical reaction due to which concentration rises. By varying thermophoretic parameter from 0.1 to 0.3, 88.65% and 8.34% enhancement is captured in heat transfer and mass transfer respectively.

Pore-scale morphology effects on colloid deposition by trajectory tracking simulations

The migration and deposition of colloids in natural porous media is a phenomenon of high importance in hydrocarbon recovery, wastewater treatment and contaminant hydrogeology. Commonly described by colloid filtration theory (CFT), and using a single representative collector element, the theoretical framework is not accounting for morphological effects and heterogeneity of realistic porous media, including the local variations of balance of forces or presence of hydraulically stagnant regions in the vicinity of grain-to-grain contacts. So far developed numerical models of colloidal transport in porous media accounting for all major interactions and pore structure were applied to 2D systems. Known 3D simulations are limited to particulate flow with a reduced set of interactions.We propose a coupled colloid transport model combining computational fluid dynamics (CFD) and discrete element model (DEM) approaches, where the former provides the velocity field at a given time step, while the second calculates the updated colloid positions accounting for a set of forces acting on each colloid. Relationships between colloid retention and morphological characteristics, such as the pore coordination number and surface to volume ratio of a random sphere pack are investigated by pore partitioning of a digitized representation. The role of stagnation zones is quantified by expressing the capture probability of colloids as a function of distance to the nearest grain-to-grain contact measured along the curved surface.The analysis of pore space morphology of the collector and the simulated filtration process reveals a strong relation between colloid retention and pore connectivity. The simulations successfully mimic the expected effects of ionic strength of the carrier fluid, such as the increasing role of grain-to-grain contacts in colloid retention at low ionic strength.

Heat transfer investigation on under-expanded supersonic impinging jets

In this study, wall-resolved large-eddy simulations are performed to investigate the underpinning physics of impingement heat transfer in under-expanded supersonic impinging jets. The jet is generated with an infinite-lipped nozzle of diameter D, has a nozzle-to-wall distance of 5D, a nozzle pressure ratio (NPR) of 3.4 and a Reynolds number of 6×104 based on the ideally-expanded jet velocity. Two thermal boundary conditions of a heated isothermal wall and an adiabatic wall for the impingement plate are considered.Both impinging jets in the current study feature a strong stand-off shock, which oscillates periodically in front of the impingement plate at two dominant frequencies. These oscillations result in two local peaks of the mean heat transfer coefficients with the first peak located in the stagnation region but shifted away from the stagnation point (i.e. jet axis), whilst the second peak is located in the wall jet region. The instantaneous fields of pressure, vorticity and Nusselt number are first discussed to study qualitatively the connection between these two peaks of the mean heat transfer coefficient and the near-wall flow structures. The characteristics of these two peaks are then analysed using the near-wall statistics and spectra of the pressure, axial velocity and Nusselt number distribution.It is found that the first peak of the Nusselt number forms as a consequence of the jet impingement of the non-periodic turbulent structures, whilst the second peak is linked to the reattachment of the recirculation bubble in the wall jet. It is shown that the unsteady separation and reattachment processes are strongly related to the oscillatory motion of the stand-off shock at the dominant frequencies. Last but not the least, the first local minimum close to the stagnation point is also found to be associated with the strong oscillatory behaviour of the stand-off shock.

Numerical analysis of ternary hybrid nanofluid flow over a stagnation region of stretching/shrinking curved surface with suction and Lorentz force

In recent years, there has been a lot of interest in studying stagnation point flow. This is because stagnation point flow is used in many technological applications, such as cooling spinning machinery segments and nuclear reactors. This study analyzes the potential practical applications of the ternary (Cu-Fe3O4-SiO2/SA) hybrid nanofluid as it flows through a stagnation zone of a stretching or shrinking curved surface under the impact of suction and Lorentz force. To acquire numerical solutions, the governing PDEs are first altered into a system of ODEs and then entered into the MATHEMATICA program. We compare findings for validation purposes and illustrate the consequences of specific characteristics that will be planned for the physical quantities that are of interest. When magnetic field and suction are present, velocity improves, but the inverse is true for curvature and nanoparticle volume fraction for both stretching and shrinking surfaces. Temperature increases against nanoparticle volume fraction, magnetic field, and heat source/sink and decreases against suction and curvature parameters for both stretching and shrinking cases. When the values of the suction parameters were changed from 2.0 to 2.5, the heat transfer rates rose by an increase ranging from 34% to 39% may be determined. Improved velocity and temperature distributions may be attributed to the presence of ternary hybrid nanofluids. This research gives scientists and engineers a head start in adjusting the relevant parameters to get the best possible results in the associated practical applications.

Stability Analysis of Unsteady Mixed Convection Flow Near the Stagnation Point with Buoyancy Effect

This numerical study investigates the behaviour of the unsteady mixed convection flow and heat transfer near the stagnation region past a vertical plate in Al2O3-Cu/H2O hybrid nanofluids. By choosing an appropriate similarity transformation, an ordinary differential equations system is obtained, hence scrutinized via the bvp4c package embedded in the MATLAB program. The results show that as the nanoparticle volume fraction and unsteadiness parameter increase, the fluid's skin friction coefficient also increases. Also, an increase in the nanoparticle volume fraction and unsteadiness parameter has broadened the range of solutions hence, delayed the progress of boundary layer separation. In addition, the presence of the unsteadiness parameter provides a significant result in the thermal system. The first solution is declared stable by the stability analysis.

Study of thermophoresis and Brownian motion phenomena in radial stagnation flow over a twisting cylinder

This article deals with the analysis of nanofluid flow and its thermal energy transport in the stagnation region, impinged radially on a rotating circular cylinder with magnetohydrodynamic (MHD) effect. The swirling flow is driven by the rotational motion of a circular cylinder along the z -direction. A two-phase nanofluid model, namely the Buongiorno model is utilized to determine the thermal characteristics of nanoparticles, which highlights the influence of Brownian diffusion and thermophoresis on temperature and concentration distributions. Numerical outcomes are computed by applying the built-in program bvp5c in MATLAB. The focus of this manuscript is to determine the numerical interpretations of wall stresses with their asymptotic behavior, Nusselt number, and Sherwood number against relevant parameters. The axial and azimuthal wall stress parameters are obtained as a function of twist rate at various values of Reynolds number. Furthermore, the asymptotic behavior for small Reynolds number is compared with their corresponding numerical solutions. The comparison of our result as a special case for non-electrically conducting flow is found in exact agreement with the ones in the literature. It is noticed that wall stresses are greatly affected due to an increment in Reynolds number. The thermal and mass transport phenomena is reduced due to increment in the twisting rate of the cylinder. However, the momentum of the system is inclined, and consequently, an increase in the axial and azimuthal velocities is observed. Moreover, the numerical values of heat and mass transfer rates deteriorate because of thermophoresis; however, owing to the Brownian diffusion, the former declines, and the latter progress significantly.