Convective Heat Research Articles

Numerical study on the forced convective flow and heat transfer mechanism with macro-patterned hydrophilic-hydrophobic hybrid surfaces

Hydrophilic-hydrophobic hybrid surfaces can be used to harmonize the drag and heat transfer. However, the hybrid surfaces are almost microscopic scale and hardly used for forced convection at present. In this study, six macro-patterned hydrophilic-hydrophobic hybrid surfaces (square, diamond, circle, ellipse, triangle, and sector) and a no-slip surface are built. The performances are studied with the k-ε turbulent model by COMSOL, and the mechanism of performance change is analyzed with large eddy simulation (LES). The results show that macro-patterned hybrid surfaces can all reduce the flow drag but have different influences on heat transfer. With the increasing Reynolds number, the drag reduction rate (DR) declines. The largest DRs are 14.57% with the ellipse-patterned at lower Reynolds numbers, and 13.18% with the triangle-patterned at higher Reynolds numbers. For heat transfer capability, although adding hydrophobic parts, the square-patterned and diamond-patterned hybrid surfaces can raise Nusselt numbers. Combined above, the largest goodness factor (φ) enlarged rates are 16.43% (square-patterned) and 16.35% (diamond-patterned). Meanwhile, the influencing mechanism with the macro-patterned hybrid surface concludes four factors: the velocity slip, thermal resistance increases of air cavities, eddies of hydrophilic-hydrophobic interfaces, and the guiding effect of hydrophobic patterns' edges.

Computational investigation of transportation and thermal characteristics in a bi-modal slurry flow through a horizontally placed pipe bend

In this study, we develop a three-dimensional computational model to explore the transportation and thermal characteristics of a bi-modal slurry flowing through a horizontally placed 90° pipe bend. The slurry comprises silica sand (SS) and fly ash (FA) granular, with varying combinations (65:35, 75:25, 85:15, 95:05, and 100:0). The computational investigation has been carried out for different carrier fluid's characteristics, including Prandtl number, and flow velocity (5 m/s), for efflux concentrations of Cw = 40–60% for each mixture. Validated with experimental data, the computational approach employs a two-phase Eulerian-Eulerian RNG k-ε turbulence model and the kinetic theory of granular flow. Results reveal that the 65:35 combination exhibits minimal pressure drop, and the 100:0 combination shows maximum heat transfer characteristics, particularly with low-viscosity fluid (Pr = 2.88) and high particle efflux concentration (Cw = 60%). The study also examines bend loss coefficients (Kt), concentration distribution, convective heat transfer coefficient (h), and Nusselt number (Nu) across different Prandtl fluids and efflux concentrations.

The effect of anti-agglomerant tween on the thermal and rheological properties of TBAF semi-clathrate hydrate slurry used for cold storage systems

Hydrate, as a phase change cold storage material, can form the slurry with certain fluidity, enabling convective heat transfer during both the heat absorption and heat release stages (cold storage or refrigeration), with high heat transfer efficiency. However, high viscosity and significant flow pressure losses are the principal challenges limiting its advancement. The paper selected four non-ionic surfactants as hydrate anti-agglomerants (Tween 20, 40, 60, 80) and utilized DSC to examine their effects on the thermal properties of TBAF semi-clathrate hydrate slurry at three theoretical hydrate concentrations (with mass fraction of 0.60, 0.70, and 0.80). Additionally, it measured the viscosity variation during the endothermic dissociation stage of the TBAF hydrate slurry and calculated the flow pressure losses in hydrate slurries within various pipe diameters. The results revealed that the presence of Tween increased the hydrate growth within the slurry, resulting in a higher available phase change enthalpy. Tween 80 demonstrated the most significant increase in enthalpy increasing effect, with an available phase change enthalpy ranging from 128.08 to 170.03 kJ/(kg·slurry) and an increase in enthalpy of 52.14 % to 91.62 %. For TBAF hydrate slurries with the theoretical hydrate mass fraction of 0.60, the addition of Tween 20 or Tween 80 significantly reduced viscosity, dropping to between 57.6 mPa·s and 116 mPa·s, and reducing viscosity by 43.4 % to 71.9 %. Furthermore, most flows with anti-agglomerants were in the laminar regime. The addition of Tween 20 and Tween 80 achieved the maximum reduction in flow pressure loss per unit length, with the highest reduction being 80.2 % (0.11 kPa/m) and 71.1 % (0.15 kPa/m), respectively. Both the phase change enthalpy of the hydrate and the viscosity of the hydrate slurry impacted the flow pressure drop within pipes. Increasing phase change enthalpy and reducing viscosity are effective strategies for mitigating flow pressure drop.

The influence of heterogeneous catalytic processes on the heat flux to the surface and the chemical composition of the shock layer at high-speed flow around blunt bodies

Numerical modeling of the high-speed flow of a multicomponent dissociated gas around a blunt body was carried out for the flow regime corresponding to the thermally stressed point of the gliding trajectory of entry into the Earth's atmosphere in the surface temperature range of 800–2000 K. As boundary conditions, a stage-by-stage model of heterogeneous catalysis of the interaction of dissociated air with the thermal protection material SiO2 was used, previously developed by the authors on the basis of transition state theory and quantum mechanical calculations. The dependence of the modes of heterogeneous chemical reactions on the surface temperature and the density of surface adsorption centers and their influence on the chemical composition of the shock layer and the convective heat flux to the streamlined surface are analyzed. The contributions of individual mechanisms of heterogeneous recombination to the total rate of formation of molecules on the surface are estimated. The possibility of using the density of adsorption sites as an effective parameter when setting boundary conditions on a real thermal protection surface in flow problems is shown.

Investigation of the single-phase immersion cold plate amid PAO-4 and Noah@3000A – An experimental approach and its numerical verification

This study investigates improving traditional immersion cooling systems by employing cold plates in single-phase immersion cooling with dielectric fluids (Noah@3000 A and PAO-4). Experimental and CFD methods explore various cold plate structures in a 1 U server with a TTV heat source. Flow rates range from 1 to 3 LPM, and configurations include side-open, fully enclosed, and dual-open designs. Results show that incorporating cold plates reduces fluid bypass, enhancing thermal performance. High-viscosity dielectric oil as a coolant yields substantial improvements (36.1% and 41.6% at low and high flow rates) compared to traditional systems. Thermal resistance decreases with higher flow rates, more notably for Noah@3000A. Immersing the cold plate in liquid enhances convective heat transfer, reducing thermal resistances by 7.2% and 9.4% for Noah@3000A and PAO-4 at low flow rates. Smaller fin pitch consistently lowers resistance by eliminating bypass. Outlet configuration significantly influences thermal resistance, with Enclosed cold plates showing the least performance for PAO-4 and dual-open cold plate yields the worst performance with Noah@3000A. Differences in heat transfer behavior between PAO-4 and Noah@3000A are linked to laminar and turbulent flow characteristics. These findings offer insights into optimizing immersion cooling systems, emphasizing the impact of fluid choice and cold plate design on thermal performance.

Heat and mass transfer analysis of Casson-based hybrid nanofluid flow in the presence of an aligned magnetic field: An application toward mechanical engineering

This examination explores the flow of a hybridized nanofluid (HyNf) containing silica and tin oxide nanoparticles mixed with engine oil (EO/SnO2-SiO2). The flowing occurs via a permeable material constrained by a semi-infinite flat plate. The study takes into account various factors such as convective heat and mass transference, chemical reactions, the Dufour effect, the Lorentz force, thermal radiative fluxing, and radiative absorbing. The research involves converting the managing formulas of the flowing model into a dimensionless form and applying the regular perturbation procedure to find solutions for the rate of fluid flow, temperature, and species diffusion. The surface frictional factor, Nusselt quantity, and Sherwood quantity reflect the shearing stress, rates of heat transference, and rates of mass transport at the plate, respectively. An analysis is conducted on the impact of several factors, including the suction variable, magnetic variable, radiation-absorbing factor, Casson parameter, and Dufour number, on the flow and related quantities. This analysis is based on an examination of graphs and tables. The findings suggest that the heat transference rate in the Casson hybridized nanofluid is better than that in the mono nanofluid. It is exposed that the temperature reduces at the plate having improved frequency of oscillation and also fluid velocity declines for improving values of aligned magnetized field [Formula: see text], but it shows the reverse phenomenon with Gr1 and Gc1.

Magneto-Micropolar Nanofluid Flow Over a Convectively Heated Sheet with Nonlinear Radiation, Chemical Reaction, and Viscous Dissipation

A mathematical model is presented for analyzing the flow of magneto-micropolar nanofluid above a convectively heated permeable stretching sheet with nonlinear radiation, chemical reaction, and viscous dissipation. Similarity transformation is utilized to change the governing partial differential equations to the system of nonlinear ordinary differential equations (ODEs). The resulting system of ODEs is sorted out mathematically by utilizing the shooting method with the Adams-Moulton method of fourth order, and the obtained mathematical outcomes are compared with published results. The obtained numerical results reflect very good agreement with those from open literature. Numerical values of physical quantities like skin friction coefficient, Sherwood number, and Nusselt number for emerging parameters such as Pr , Nb , Nt , Le , etc. are also computed and discussed in this work. The impact of pertinent flow parameters on nondimensional velocity, temperature, and concentration profiles is illustrated via tables and graphs.

Target temperature-based simulation method for predicting performance and designing aircraft thermal anti-icing systems

The prevention of ice build-up on aircraft surfaces is crucial for safe operations. Thermal ice protection systems, particularly electro-thermal systems, are commonly employed to mitigate ice formation. However, the weight of electric batteries used in these systems significantly impacts aircraft performance, necessitating the minimization of power load during design. Despite this requirement, effective anti-icing operation mandates a sufficient heat flux to maintain surface temperature above the freezing point and evaporate any runback water film. Previous research has utilized numerical simulation analysis to predict the performance of electro-thermal anti-icing systems. The conjugate heat transfer method has been commonly employed to predict temperature distribution on the protected surface. However, non-isothermal surfaces exhibit distinct local convective heat transfer coefficients that influence local thermal balance, unlike isothermal surfaces that adopt the loosely-coupled method for computational efficiency. In this study, we present a novel target temperature-based anti-icing simulation method that predicts the required heat flux for thermal ice protection systems without employing the conjugate heat transfer method. Our objective was to calculate the necessary heat flux to achieve the desired non-isothermal surface temperature for effective anti-icing. By eliminating the excessive iteration process associated with the coupling method for conjugate heat transfer, we have streamlined the simulation procedure. Through validation, target temperature-based anti-icing simulation method, when compared to the tight coupling method, demonstrated the ability to predict the same surface water flow rates while reducing computation time by up to 90 %. Furthermore, when applied to design problems, our method achieved approximately a 10 % reduction in the required heat capacity for anti-icing compared to experimental values. As a result, target temperature-based anti-icing simulation method offers a more efficient alternative to traditional conjugate heat transfer methods, providing valuable insights for both predicting anti-icing system performance and optimizing aircraft design.

Analysis of Soret and Dufour effects on radiative heat transfer in hybrid bioconvective flow of carbon nanotubes

Numerous heat transfer applications, such as heat exchangers, solar trough collectors, and fields including food processing, material research, and aerospace engineering, utilize hybrid nanofluids. Compared to conventional fluids, hybrid nanofluids exhibit significantly enhanced thermal conductivity. The aim of this work is to explore flow and heat transmission features under of magneto-hydrodynamic bioconvective flow of carbon nanotubes over the stretched surface with Dufour and Soret effects. Additionally, comparative dynamics of the carbon nanotubes (SWCMT − MWCNT/C2H6O2 with SWCMT − MWCNT/C2H6O2 − H2O) flow using the Prandtl fluid model in the presence of thermal radiation and motile microorganisms has been investigated. Novel feature Additionally, the focus is also to examine the presence of microorganisms in mixture base hybrid nanofluid. To examine heat transfer features of Prandtl hybrid nanofluid over the stretched surface convective heating is taken into consideration while modeling the boundary conditions. Suitable similarity transform has been employed to convert dimensional flow governing equations into dimensionless equations and solution of the problem has been obtained using effective, accurate and time saving bvp-4c technique in MATLAB. Velocity, temperature, concentration and microorganisms profiles have been demonstrated graphically under varying impact of various dimensionless parameters such as inclined magnetization, mixed convection, Dufour effect, Soret effect, thermal radiation effect, and bioconvection lewis number. It has been observed that raising values of magnetization (0.5 ≤ M ≤ 4), mixed convection (0.01 ≤ λ ≤ 0.05) and inclination angle (0° ≤ α ≤ 180°) enhance fluid motion rapidly in Ethylene glycol based Prandtl hybrid nanofluid (SWCMT − MWCNT/C2H6O2) when compared with mixture base working fluid of carbon nanotubes SWCMT − MWCNT/C2H6O2 − H2O). Raising thermal radiation (0.1 ≤ Rd ≤ 1.7) and Dufour number (0.1 ≤ Du ≤ 0.19) values improves temperature profile. Moreover, a good agreement has been found between the current outcome and existing literature for skin friction outcomes.

Finite difference simulation of natural convection of two-phase hybrid nanofluid along a vertical heated wavy surface

This study employs finite difference modelling to investigate the natural convection of a two-phase hybrid nanofluid consisting of Al 2 O 3 and Cu nanoparticles dispersed in water along a vertically heated wavy surface. The hybrid nanofluid has unique features that influence convective heat transfer. Numerical solutions analyze fluid flow patterns and temperature distributions, providing insights into heat exchange and thermal management. The research highlights the importance of hybrid nanofluids, notably those containing Al 2 O 3 and Cu in a water base, in improving overall heat transfer efficiency. The mathematical model accounts for laminar and incompressible fluid flow with a Prandtl number of Pr = 6.2, Lewis number Le = 10, and maximum 10 % concentration of hybrid nanoparticles. After transforming the governing equations into a non-dimensional form, the implicit finite difference method is used to solve them. The solution employs the in-house FORTRAN 90 code and compares its outcomes with the benchmark results. Various parameters, such as the Schmidt number (Sc = 1 to 10), volume fraction of nanoparticles ( ϕ = 0.0 to 0.1), wavy amplitude (A = 0.0 to 0.3), and N BT = (0.05 to 0.2), are investigated regarding temperature, velocity, local skin friction coefficient ( C f ) , local Nusselt number (Nu), streamlines, and isotherms. Elevated volume fraction generally decreases skin friction, increases temperature, and may reduce velocity. Meanwhile, higher skin friction, temperature, velocity, and local Nusselt numbers often correlate with elevated Schmidt numbers. Changes in amplitude and N BT affect skin friction, temperature, velocity, and local Nusselt numbers, providing information on the dynamics of fluid systems. For example, when the volume fraction (ϕ) increases from 0 to 0.1 at Y = 2, the temperature rises by 75 % , while the velocity gradually decreases by 11.11 % . This is in contrast to findings according to when the N BT rises from 0.05 to 0.2 at Y = 1. In this case, the temperature drops by 18.75 % , followed by a 9.68 % fall in fluid velocity. Understanding these interactions enhances comprehension of heat transfer and fluid dynamics. By investigating these interactions, we not only improve our understanding of heat transfer and fluid dynamics, but also open the door to new strategies for improving thermal systems and manufacturing procedures.

Study on Thermal Metamaterial for Uniform Surface Temperature Distribution

Abstract This paper proposes a thermal metamaterial based on the theory of thermodynamics transformation, which can achieve uniform temperature distribution. The required anisotropic thermal conductivity is theoretically derived. This thermal metamaterial structure is achieved by alternating aluminum and polyimide of different lengths. The temperature distribution under the condition of different convective heat transfer coefficients was simulated and compared with pure aluminum. The simulation and experimental results show that the metamaterial significantly reduced the non-uniformity of the temperature distribution.

Experiment-Validated multiphysics modeling, generalizable deep learning and interpretable global sensitivity analyses for thermoelectric generators

Despite extensive studies on thermoelectric materials in a thermoelectric generator (TEG), the inverse design of TEG operating conditions remains challenging. Recent efforts in deep learning of TEGs using artificial neural network (ANN) lack global sensitivity analyses and interpretation of the connection-weights, leading to unknown coupling between input parameters and errors in importance ranking. This work reports a deep learning framework for TEGs using generalizable ANN, interpretable local (LSA) and global sensitivity analyses (GSA). Sensitivity analyses are applied to determine how energy conversion efficiency (η) under the practical Neumann and Robin thermal boundary conditions is affected by TEG operating conditions, including hot-side heat flux (qh), cold-side convective heat transfer coefficient (hf), temperature of the cooling medium (Ta), load resistance (RL), electric contact resistance (Rc), and thermal contact resistance (Kc). First, multiphysics TEG simulation results based on 3D finite element method (FEM) are validated by our experimental measurements using a self-built TEG performance evaluation system. The partial derivative-based LSA is done on a 1D theoretical TEG model to obtain the trend in sensitivity factors. Then, an ANN model is trained and validated based on the FEM simulation results and applied to the GSA process, aiming at reducing the computational load. Variance-based GSA is applied on the ANN model to determine the importance ranking and reflect the coupling between input parameters. The variance-based GSA ranks the importance as qh>hf>RL>Ta≈Rc≈Kc, and reflects the coupling between qh and hf. Finally, to interpret the ANN and the hidden deep learning process, a method combining the connection-weights algorithm and neural interpretation diagram (NID) is proposed to extract the hidden information in the connection weights. The ANN model is proven generalizable towards larger ranges of operating conditions. This work provides a framework to design TEG operating conditions towards higher energy conversion efficiencies.

Magnetohydrodynamic bioconvective flow past an elongated surface with convective heat transport, and velocity slip in a non‐Darcian porous regime

AbstractIn recent times, bioconvection has numerous uses, like, biological and biotechnological problems. The present study describes the magnetic bioconvective Buongiorno's flow model with microorganisms in a stretchable area with convective heat transfer and second‐order velocity slip in a non‐Darcian porous regime. Here, the influence of variable viscosity, viscous dissipation, Joule heating, and heat source/sink are considered in the occurrence of higher‐order chemical reactions. Employing proper similarity transformations leading equations are transformed to dimension‐free form. The transformed equations are solved via MATLAB bvp4c problem solver. This study's main objective is to graphically analyze the effects of different pertinent factors on the density of motile microorganisms, velocity, concentration, temperature, number of motile microorganisms' density, skin friction, mass transport rate, and heat transport rate. The main findings drawn from this study are viscosity and magnetic parameter lowers the fluid velocity. Biot number increases fluid temperature, but reduces heat transport rates and skin friction. Schmidt and Eckert numbers reduce the fluid concentration. A rise of 0.3 in bioconvective Rayleigh number and 0.2 in buoyancy ratio number causes a percentage drop in velocities of 8.79% and 3.91% (approximately), respectively, in the neighborhood of the sheet. Furthermore, the increase in Peclet number by 0.2 lowers the density number of microorganisms by 28%. Additionally, the profile of motile microorganisms is improved by thermophoresis impact, while it is diminished by chemical reaction.

Integrated Thermal Management System Concept with Combined Jet Plate, High Porosity Aluminum Foam and Target Plate for Enhanced Heat Transfer

Abstract An experimental investigation was carried out on high porosity metal foams subjected to array jet impingement with an objective to develop enhanced heat transfer configurations. In this study, we propose an integrated thermal management system aimed towards leveraging the conjugate heat transfer capabilities of target plate, metal foam, and the jet plate - all made from aluminum and assembled such that a proper contact between them can be established. Steady-state heat transfer experiments were carried out for 10 and 20 pores per inch (PPI) aluminum foams of 0.93 porosity. Both metal foams were 12.7 mm thick. The normalized jet-to-jet spacing was varied from 2 to 12 times the jet diameter, while the jet diameter was fixed. The ratio of the jet plate thickness and jet diameter (nozzle aspect ratio) was 6.35, which ensured proper development of jets inside the nozzles. Experiments were conducted over a wide range of Reynolds number (based on jet diameter) varied from 100 to 5,000. The obtained convective heat transfer coefficient for different configuration was evaluated in context with pressure drop. The analysis of experimental results reveal that large open area ratio jets combined with high porosity metal foams provide highly efficient and high-performance cooling for the investigated range of Reynolds numbers.

Numerical simulation and entropy optimization of hybrid nanofluid flow in an inclined wavy enclosure subjected to thermal radiation

The current study investigates two-dimensional natural convective heat transference and entropy production in a tilted wavy-walled enclosure under the magnetic field and thermal radiation effect. The enclosure is filled with Cu–Al2O3/H2O hybrid nanofluid and subjected to a non-uniformly heated curved left wall, constant cold right curved side, uniformly heated bottom side, and insulated upper side. The regulating formulas in the non-dimensional form are reduced to streaming function-velocity expression and are numerically solved based on the Bi-CGStab method. The simulations are behaved with diverse Rayleigh amounts, Hartmann numbers, an incline angle of the enclosure, radiation parameters, diverse amplitude of the curved wall, and volume fraction of hybrid nanoparticles. Numerical code validation with other published results agrees well with the present outcomes. Heat and entropy generation were improved with the change in dimensionless parameters, and the findings have been clarified through discussion. The observations indicate that the Rayleigh numbers, nanoparticle fractional size, amplitude, and radiation parameter influence the convective effect and entropy production inside the enclosure. In contrast, the Hartmann number detracts from the convective effect. The findings suggest that a rise in the cavity angle may result in a corresponding boost or decline in heat transference. The minimum Nusselt numbers is obtained at [Formula: see text], as the angle of incline of the enclosure restraints the fluid rapidity and diminishes the heat transference rates. To design heat exchangers, this particular study may serve as a guide.

Free convective heat transfer induced inside a vented duct having two aligned hot and cold cylinders: An experimental study

AbstractFree convective heat transfer created from two aligned cylinders immersed inside a vented air duct is experimentally investigated. The experiments include the measurements of cylinders temperature and the air temperature inside the enclosure under steady, turbulent, and incompressible flow properties by using steady‐state heat equations. The studied parameters include Rayleigh number (), opening sizes at lower and upper enclosure surfaces (), and space size between cylinders () with the constant ratio of enclosure width to cylinder diameter equal to 6. The findings displayed that the average air temperature inside the enclosure for the low values of S and O is low, and it rises as S is raised. The behaviors of Nu differ with changing Ra values. An interaction between hot cylinder and cold cylinder inside the enclosure is observed that depends on O and S values, and hence, they have a large impact on fluid temperature. The data indicated that rises with the for all and values. The value of for each cylinder depends on the values of and . The maximum value has been obtained when and with maximum enhancement between 30% and 50% depending on Ra values as compared with and , whereas the minimum average has been indicated when and . The profiles of reveal that , , and have a considerable influence on heat transfer.

Numerical Solution of Natural Convection Problems Using Radial Point Interpolation Meshless (RPIM) Method Combined with Artificial-Compressibility Model

A numerical method is used to solve the thermal analysis of natural convection in enclosures. This paper proposes the use of an implicit artificial-compressibility model in conjunction with the Radial Point Interpolation Meshless (RPIM) method to mimic laminar natural convective heat transport. The technique couples the pressure with the velocity components using an artificial compressibility model. The RPIM is used to discretize the spatial terms of the governing equation. We solve the semi-algebraic system implicitly in backward Euler pseudo-time. The proposed method solves two test problems—natural convection in the annulus of concentric circular cylinders and trapezoidal cavity. Additionally, the results are validated using experimental and numerical data available in the literature. Excellent agreement was seen between the numerical results acquired with the suggested method and those obtained through the standard techniques found in the literature.

Enhancing heat transfer in rectangular solar air heater channels: a numerical exploration of multiple Boomerang-shaped roughness elements with variable gaps

ABSTRACT In the current study, numerical investigations are carried out to enhance the convective heat transfer rate in a solar air heater embedded with multiple boomerang-shaped roughness. The boomerang roughness is attached to the absorber plate which is supplied with uniform heat flux. The boomerang roughness geometry is defined by the ratios of height to hydraulic diameter (e/Dh) at 0.09, pitch space to height (P/e) of 10.5 to 18, and the gap between the multiple boomerang arm (g) at 8.5 to 13.1 mm. These parameters are examined for turbulent flow conditions having Reynolds number (Re) ranging from 4000 to 22,000. Heat transfer and friction characteristics in the present work are defined and examined by nondimensional parameters Nusselt number (Nu) and friction factor (fr), respectively. The study compared Nusselt number and friction factor readings to measurements of a smooth channel under similar flow conditions. It compared friction and the Nusselt number coefficient to a smooth rectangular channel and a rough, purposely rough channel. The aim was to determine better heat transfer and reduced friction. The study found that the average Nusselt number (Nu/Nus) and convective heat movement were 3.39 times higher at g = 8.5 mm (θ = 90º) compared to g = 10.9 mm (θ = 80º) and 13.1 mm (θ = 70º) at p = 71. mm and Re = 22,000. The lowest Nu/Nus was 1.75 times for g = 13.1 mm and p = 71.3 mm at Re = 4000. Thinner boundary layers increased the average Nusselt number and convective heat transfer coefficients in systems with smaller gaps. The design model has a maximum THPP = 1.93 at a pitch space between roughness (p = 71.3 and P/e = 15.5, where e = 4.6 mm), gap (g = 8.5), and Re = 22,000.

Numerical analysis of electrothermoconvection of a dielectric nanofluid in a heated cavity

A numerical analysis of electrohydrodynamic (EHD) flow and heat transfer of nanofluid in a heated rectangular cavity is presented. A two-dimensional (2D) rectangular cavity heated from the bottom is considered. An electric potential difference is applied vertically, with the bottom wall acting as a high-voltage electrode, and the top wall is grounded. TiO2-25 # transformer oil nanofluid with nanoparticle volume fraction ranging from 0–5% is considered. The numerical model for EHD flow and heat transfer of nanofluid is implemented in the finite-volume method (FVM) based numerical framework of OpenFOAM. A single-phase approach based on the effective properties is adopted to model the nanofluids. A two-way coupled EHD flow model is employed to consider mutual interactions of flow and electric field variables. The flow and heat transfer behavior of nanofluids in the presence of an electric field is quantified with reference to the key parameters, electric Rayleigh number (T), and the nanoparticle volume fraction ϕ. The addition of nanoparticles increased the viscosity and marginally reduced the natural convective flow and heat transfer. However, EHD flow induced by the electric field aided in overcoming the weak natural convection flow in nanofluids. Results confirm that nanofluids’ net effective heat transfer rates are notably increased in the presence of the electric field. For the parameters under consideration, combining electric fields with nanofluids led to a significant heat transfer enhancement of up to 32.3%. The present study showcases the feasibility of combining passive heat transfer enhancement using nanoparticles and active heat transfer enhancement using EHD flow.

Nanoparticle aggregation and electro-osmotic propulsion in peristaltic transport of third-grade nanofluids through porous tube

In the modern era, the utilization of electro-kinetic-driven microfluidic pumping procedures spans various biomedical and physiological domains. The present study introduces a mathematical framework for characterizing the hemodynamics of peristaltic blood flow within a porous tube infused with ZrO2 nanoparticles. This model delves into the interactions between buoyancy, electro-osmotic forces, and aggregated nanoparticles to discern their influence on blood flow. We employ a third-grade fluid model to elucidate the rheological behavior of the pseudoplastic fluid which refers to its response to applied shear stress, specifically the relationship between shear rate and viscosity. The collective influence of accommodating heat convection, joule heating and aggregated nanoparticles contributes to the thermal behavior of fluids. The distribution of electric potential within the electric double layer (EDL) is predicted by solving the Poisson–Boltzmann equation. The rescaled equations are simplified using the lubrication and Debye-Hückel models as the underlying frameworks. The novel homotopy perturbation method is employed to obtain solutions for the finalized non-linear partial differential equation. Theoretical assessment of hemodynamic impacts involves plotting graphical configurations for various emerging parameters. As electro-osmotic parameter increase, the bloodstream encounters greater impedance, thereby enhancing the effectiveness of electro-osmotic assistance. Concurrently, elevated convective heat markedly reduces the rate of heat transfer, potentially resulting in a drop in blood temperature. It is important to note that maximum shear stress occurs when the artery is positioned horizontally, underscoring the significant impact of arterial alignment on wall shear stress. Skin friction intensifies with the increasing wall permeability as aggregated nanofluids pass through the arterial conduit. Therefore, aggregation of nanoparticles into the bloodstream yields a broader spectrum of distinctive physiological features. In summary, these findings enable more effective tool and device designs for addressing medication administration challenges and electro-therapies.