Thermofluid Systems Research Articles

Fluid‐Structure Interaction and Heat Transfer Characteristics of a Thin Flexible Heater Submersed in Non‐Newtonian Fluids Inside a Shear‐Driven Cavity

ABSTRACTThis study examines fluid‐structure interaction (FSI)–induced flow and heat transfer phenomena in a double‐sided shear‐driven, that is, lid‐driven cavity filled with non‐Newtonian power‐law fluids. A flexible thin heater positioned at the center of the cavity serves as the heat source, while the moving side walls maintained at constant low temperature perform as a heat sink. The numerical approach adopts the finite element Galerkin method, integrating the Arbitrary Lagrangian–Eulerian framework with moving mesh technique to solve the associated flow, thermal, and stress fields. The thermoelastodynamic system behavior is analyzed through streamline, isothermal, and heater deformation visualizations, along with an evaluation of heat transfer performance, namely, the average Nusselt number. FSI‐induced internal stress scenario in the heater is also studied in terms of maximum von Mises stress. Variation of system conditions necessarily includes mixed convection strength, shearing effect, fluid rheology, and flexibility of the heater manifested by four governing system parameters, namely, the Richardson number (0.1 ≤ Ri ≤ 10), Reynolds number (100 ≤ Re ≤ 300), power‐law index (0.6 ≤ n ≤ 1.4), and Cauchy number (10⁻⁴ ≤ Ca ≤ 10⁻⁸). The findings of this study reveal a significant improvement in heat transfer for shear‐thinning fluids, with the most notable enhancement occurring at the highest Richardson number (Ri), where the heat transfer rate shows an increase of up to 33.33% compared with Newtonian fluids. The insights of this study might be helpful in heat transfer enhancement of industrial process equipment, particularly in applications such as food processing, electronics cooling, and chemical engineering, where non‐Newtonian fluids are extensively used in reactors and related thermofluid systems.

Thermal management and power generation characteristics in a bifurcating channel by using a piezo-embedded inclined elastic fin assembly during turbulent forced convection of ternary nanofluid

Numerous engineering systems use piezoelectric energy harvesters (PE-EHs), which have several benefits including low cost, simplicity, better power density, and ease of installation. They can be used in different applications for energy harvesting and different external sources such as wind and vortex induced vibrations due to fluid–structure interaction can be utilized. This study uses a unique elastic fin PE/EH assembly for power generation, thermal management, and flow control in a bifurcating channel. Performance of the system is improved by using ternary nanofluid in the channel cooling system. Galerkin weighted residual FEM with ALE is used as the solution method. The convective heat transfer performance and power generation by the EH device are investigated in relation to the varying following parameters: Reynolds number (Re between 10000 and 30000), PE-EH inclination (γ between 0 and 60), fin horizontal location (xf between −H and H), and nanoparticle loading in the base fluid (ϕ between 0 and 0.03). The vortex size and distribution near the junction are significantly influenced by the fin inclination and horizontal location of the fin assembly within the bifurcating channel. When varying other parameters of interest, using nanofluid at the highest loading results in significant deflection of the fin assembly and power generation within the PE-EH. Enhancement factors (EFs) for power generation becomes 15.6 and 39.8 when cases of lowest and highest Re are compared with pure fluid and nanofluid while they are 2.93 and 3.38 for thermal performance improvements. Fin inclination of γ=30 is found as the optimum inclination for achieving the highest power from the assembly. Higher inclination of elastic fin/PE-EH assembly results in cooling performance deterioration while average Nu reduces by a factor of 2.94 by varying inclination from γ=30 to γ=60 with nanofluid. For power generation, effects of using nanofluid with varying inclination is significant and EF becomes 252 from γ=0 to γ=30. There are opposing tendencies for the device’s power generation and cooling performance enhancement when the fin’s horizontal placement is changed. EF for average Nu is 7.25 for varying fin location. As the loading of nanoparticle inside the base fluid increases, the average Nu and generated power exhibit non-linear rising characteristics. Polynomial type correlations are provided for the average Nu and power from the device by varying elastic fin assembly inclination and nanoparticle solid volume fraction. Potential of using hybrid nanofluid in PE-EH embedded thermo-fluid system is shown. The design, development, and optimization of self-sufficient power production systems that may be used to various thermo-fluid systems, such as electronic cooling and thermal control in a range of heat transfer devices, may benefit from the findings.

Canard explosions in turbulent thermo-fluid systems.

A sudden transition to a state of high-amplitude periodic oscillations is catastrophic in a thermo-fluid system. Conventionally, upon varying the control parameter, a sudden transition is observed as an abrupt jump in the amplitude of the fluctuations in these systems. In contrast, we present an experimental discovery of a canard explosion in a turbulent reactive flow system where we observe a continuous bifurcation with a rapid rise in the amplitude of the fluctuations within a narrow range of control parameters. The observed transition is facilitated via a state of bursting, consisting of the epochs of large amplitude periodic oscillations amidst the epochs of low-amplitude periodic oscillations. The amplitude of the bursts is higher than the amplitude of the bursts of an intermittency state in a conventional gradual transition, as reported in turbulent reactive flow systems. During the bursting state, we observe that temperature fluctuations of the exhaust gas vary at a slower time scale in correlation with the amplitude envelope of the bursts. We also present a phenomenological model for thermoacoustic systems to describe the observed canard explosion. Using the model, we explain that the large amplitude bursts occur due to the slow-fast dynamics at the bifurcation regime of the canard explosion.

Linear temporal stability of Jeffery–Hamel flow of nanofluids

Flow stability plays a key role in transition to turbulence in various systems. This transition initiates with disturbances appearing in the laminar base flow, potentially amplifying over time based on flow and fluid parameters. In response to these amplified disturbances, the flow undergoes successive stages of different laminar flows, ultimately transitioning to turbulence. One influential parameter affecting flow stability is the nanoparticle volume fraction (ϕ) in nanofluids, extensively employed in thermofluid systems like cooling devices to enhance fluid thermal conductivity and the heat transfer coefficient. Focusing on the impact of nanoparticles on Jeffery–Hamel flow stability, this study assumes fluid properties are temperature- and pressure-independent, exclusively examining the momentum transfer aspect. The analysis commences by deriving the base laminar flow solution. Subsequently, linear temporal stability analysis is employed, imposing infinitesimally-small perturbations on the base flow as a modified form of normal modes. A generalized Orr–Sommerfeld equation is derived and solved using a spectral method. Results indicate that, assuming nanofluid viscosity as μnf=μf/(1−ϕ)2.5, nanoparticle effects on momentum transfer and flow stability hinge on the ratio of nano-solid particle density to base fluid density (Rρ=ρs/ρf). For ϕ∈(0,0.1], flow stabilization occurs with ϕ when Rρ<3.5000, while destabilization is observed when Rρ>4.0135. Notably, nanoparticles exhibit a negligible impact on flow stability when 3.5000≤Rρ≤4.0135.

Synergistic Heat Transfer in Enclosures: A Hybrid Nanofluids Review

This review aims to comprehensively explore the concepts of heat transfer (HT) and entropy generation (Egen) within cavities containing hybrid nanofluids (HN). Additionally, the review encompasses various enclosure shapes, such as triangle, square, rectangle, wave, trapezoid, hexagon, octagon, semicircle, circle, cube, C-shaped, L-shaped, M-shaped, T-shaped, W-shaped, irregular shaped, and other types of cavity designs. Also, different types of hybrid nanoparticles such as silver-magnesium oxide, copper-aluminum oxide, multi-walled carbon nanotubes-iron oxide, copper-titanium dioxide, silver-copper, aluminum oxide-titanium dioxide, carbon nanotubes-aluminum oxide, multi-walled carbon nanotubes-magnesium oxide, carbon nanotubes-iron oxide, carbon nanotubes-copper, aluminum oxide-silicon dioxide, aluminum oxide-silver, nanodiamond-cobalt oxide, etc., and base fluids such as water, ethylene glycol, carboxymethyl cellulose, etc are presented in this research. In addition, a thorough analysis of the extensive literature underscores the significant influence of elements like blocks, obstacles, fins, or cylinders within cavities on both HT and Egen. These findings carry substantial practical implications for the study of thermofluid systems.

Optimization of Reynolds stress model coefficients at multiple discrete flow regions for three-dimensional realizations of fractal-generated turbulence

The quantification of global turbulence statistical moments generated by grid turbulators is crucial for the enhancement of conjugate heat transfer in industrial thermo-fluid systems. As such, there is a need for precise, low-cost alternatives to numerically model three-dimensional flow dynamics of fractal-generated turbulence (FGT) behind multilength-scale square fractal grids (SFGs), in contrast to previously-reported direct numerical simulations. In this study, a numerical framework consisting of multiple applications of the Reynolds stress model (RSM), each employing its own distinct set of optimized coefficient values, is developed by segregating an FGT flow domain into its production and decay regions with Nelder-Mead optimization on key coefficients then performed independently for each region. The flow fields predicted by such RSM framework achieved overall disparities below 3% and 13% w.r.t. reported experimental measurements of mean velocity and turbulence intensity, respectively, considering the evolution in the flow domain along the streamwise, vertical, and spanwise directions. This is therefore the first documentation of any RANS-turbulence model being validated for mean velocity and turbulence intensity predictions of FGT in all three-dimensions. Thereafter, this proposed RSM framework is generalized to predict industry-relevant turbulence statistical moments of four additional FGT flows. The predicted centerline-statistics are verified against reported experiments, and the findings potentially enable realizations of FGT induced by arbitrary SFGs without relying on a posteriori validation while eliminating further reliance on the Nelder-Mead optimization algorithm on a case-by-case basis. The findings indicate a potential to apply the model coefficients as continuous functions of space to simulate the entire FGT domain. Overall, the accurate and numerically sustainable realizations of FGT in 3D provide valuable insights to engineer potent fluid-solid heat transfer via passive turbulence management within HVAC systems.

Universality of oscillatory instabilities in fluid mechanical systems

Oscillatory instability emerges amidst turbulent states in experiments in various turbulent fluid and thermo-fluid systems such as aero-acoustic, thermoacoustic and aeroelastic systems. For the time series of the relevant dynamic variable at the onset of the oscillatory instability, universal scaling behaviors have been discovered in experiments via the Hurst exponent and certain spectral measures. By means of a center manifold reduction, the spatiotemporal dynamics of these real systems can be mapped to a complex Ginzburg–Landau equation with a linear global coupling. In this work, we show that this model is able to capture the universal behaviors of the route to oscillatory instability, elucidating it as a transition from defect to phase turbulence mediated by the global coupling.

External Stefan and Internal Marangoni Thermo-Fluid Dynamics for Evaporating Capillary Bridges.

We probe the evaporation mechanisms of wettability-moderated, confined capillary bridges and bulges. For the first time, we explore the internal Marangoni hydrodynamics and external Stefan advection dynamics in the surrounding gaseous domain due to evaporative effects. A transient simulation approach based on the level set (LS) method and the Arbitrary Lagrangian-Eulerian (ALE) framework was adopted to computationally model the capillary bridge profiles and evaporation phenomenon with generic contact line dynamics (both CCR and CCA modes). The governing equations corresponding to the transport processes in both the liquid and gaseous domains are simulated in a fully coupled manner with appropriate boundary conditions to precisely trace the liquid-vapor interface and the three-phase contact point during evaporation. The effect of the bridge confinement phenomenon, i.e., the extent of confined ambient surrounding the liquid-vapor interface between the solid surfaces, is explored. Also, the role of wetting state and contact line dynamics during CCR and CCA modes of evaporation were probed, and good agreement with experimental observations was noted. Results show that the evaporation rate is primarily dictated by the confinement phenomenon, and wettability effects play a marginal role. A higher confinement curtails the evaporation rate due to an increased local vapor concentration around the liquid bridges. However, the wetting state substantially affects the internal Marangoni effect dynamics and the Stefan advection dynamics due to its explicit influence on the nonuniform evaporative flux along the liquid-vapor interface. Between superhydrophobic confinements, the contact lines are confined in the wedge-shaped region, thereby locally augmenting the vapor concentration. As a result, the large evaporative flux near the bulge region develops a higher temperature gradient, thereby inducing upscaled thermal Marangoni flow compared to hydrophilic confinements. These findings may have significant implications for the efficient designing and development of thermofluidic systems involving thermal transport, mixing, and deposition of dissolved particles in liquid bridges.

Revisiting thermo-physical property models of Al2O3-Water nanofluid for natural convective flow

One of the comprehensive ways of heat transport performance augmentation of thermo-fluid systems is to use nanofluid over base fluid. This study mainly scrutinizes several existing models of thermal conduction coefficient and absolute viscosity of Al2O3-water nanofluid with the experimental data. A benchmark problem of natural convective flow is selected to test the performance of the available nanofluid models. The Rayleigh number varies between 103 and 109, while the solid-volume proportion (φ) changes from 0 to 4%. The governing mathematical model is numerically discretized via the Galerkin finite element procedure under appropriate auxiliary conditions. The results produced by the models are verified with the existing experimental findings based on the evaluation of the Prandtl number and average Nusselt number. It has been confirmed that the AH model (Azmi's viscosity and Ho's conductivity models) is suitable for lower nanoparticle concentration (φ = 0.01), the AM model (Azmi's viscosity and Maxwell's conductivity models) for moderate concentration (0.01 < φ < 0.04), and the NH model (Ngueyn's viscosity and Ho's conductivity models) for higher value of the solid-volume proportion (φ = 0.04).

Unveiling the Dynamics of Entropy Generation in Enclosures: A Systematic Review

This extensive review aims to provide a thorough understanding of entropy generation (Egen) in confined conduits, or enclosures, by examining a vast array of peer-reviewed research. The review covers various studies on Egen in enclosures with different geometric configurations and highlights the significant effects of thermo-physical dynamics, such as temperature gradient, viscous dissipation, frictional drag, and magnetic field strength, on Egen characterization. The review covers a broad range of studies that investigate Egen in enclosures with diverse geometric configurations and different types of fluids, including air, water, and various types of nanofluids. Furthermore, the review also includes different enclosure structures, such as I, L, C, U, semicircular, triangular, square, rectangular, rhombic, trapezoidal, polygonal, and channel types, as well as wavy wall configurations. Notably, the review also encompasses both 2D and 3D cases to present a complete comprehension of Egen in confined conduits. In addition, the review carefully evaluates the validity methods utilized in numerical investigations, incorporating a diverse array of mesh types and sizes utilized in research. A thorough examination of the vast literature demonstrates that enclosures with obstacles, such as single or multiple rotating cylinders, exhibit a noticeable increase in Egen. Also, the review highlights that the use of nanofluids significantly increases Egen. These findings have important practical implications in the analysis of thermofluid systems, including but not limited to heat exchangers, chip cooling, food storage, solar ponds, and nuclear reactor systems. Based on the comprehensive review conducted in this study, several future research directions have been proposed for the emerging field of Egen in enclosures. This study explores the intricate mechanisms of Egen in enclosures and highlights potential avenues for further investigation in this area. These insights will contribute to the advancement of the knowledge base and practical applications of thermofluid systems, including heat exchangers, chip cooling, food storage, solar ponds, and nuclear reactor systems.

Effect of Temperature Gradients and DC Electric Field on Electrothermal Convection in a Rotating Layer of Walter's-B Fluid Saturated Porous Media

Thermal convection in fluid-saturated porous media has diverse applications across geothermal energy utilisation, thermal insulation engineering, grain storage and understanding geodynamic processes. The thermal convection's physics is crucial for optimising the thermofluid system, improving energy efficiency, and enhancing our understanding of natural phenomena. The study examines how the initiation of electrothermal convection in a rotating viscoelastic fluid layer (Walter's B) is influenced by basic temperature gradients and a uniform vertical DC electric field, considering three different types of velocity boundary conditions: free-free, rigid-rigid, and lower rigid and upper free. By applying an electric field to a fluid, studying electrothermal convection helps engineers design effective cooling systems for electronics. The eigenvalue problem is solved by using the Galerkin technique. The Galerkin method is a widely used numerical technique for solving eigenvalue problems. The DC electric field effect exhibits a more stabilising effect for free-free boundaries than rigid and rigid-rigid boundaries. Moreover, the linear temperature profile exhibits a more stabilising effect than the parabolic temperature profile. The control of electrothermal convection on the system with the impact of other physical parameters is also discussed.

Second law analysis of a transient hexagonal cavity with a rotating modulator

PurposeThe main focus of this article is on analyzing the entropy generation characteristics of an air-filled hexagonal thermo-fluid system with an adiabatic clockwise rotating dynamic modulator through second law analysis. This modulator rotation creates striations that affect natural convection. This convection is generated by the thermal stratification between the top and bottom walls. To fully analyze the system, the study considers both conduction and convection heat transfer by introducing a uniformly thick top wall. Overall, the study looks at the behavior of a conjugate thermo-fluid system. ApproachThe system is solved numerically using non-dimensional Navier Stokes equations as a moving mesh problem by the Arbitrary Lagrangian Euler finite element method. The parameters whose effects have been conceptualized here are 102≤Re≤ 103, 104≤Ra≤ 107, and 103≤Bi≤ 104. Air is chosen to be the working fluid with Pr of 0.71. Effects of these parameters are visualized by spatially averaged total entropy generation, spatially averaged total exergy generation, spatially averaged Bejan's number, and fast Fourier transform analysis. FindingsThe present study indicates a 46.91 % rise in entropy generation for Re ranging from 500 to 1000. Moreover, for the same case, a decrement of 88.31 % is observed in exergy generation with the greatest amplitude in the case of the lowest heat transfer. This phenomenon is further supported by the amplitude of the fundamental frequency, where the thermodynamic configuration with the lowest heat transfer has the highest peak. OriginalityAs far as the authors are aware, no previous research has been conducted to analyze the entropy generation characteristics of a hexagonal conjugate transient system that involves a dynamic modulator stirring the flow. Therefore, this study represents a novel contribution to the existing literature on the subject. LimitationsPresent study focused on only a single type of blade irrespective of its aerodynamic design, size, or thickness. Moreover, the blade is also considered to be a rigid body that is not affected by the hoop stress generated from its own rotation.

The influence of energy and temperature distributions on EHD destabilization of an Oldroyd-B liquid jet

This work examines the impact of an unchanged longitudinal electric field and the ambient gas on the EHD instability of an Oldroyd-B fluid in a vertical cylinder, where the system is immersed in permeable media. In order to explore the possible subject uses in thermo-fluid systems, numerous experimental and theoretical types of research on the subject are conducted. The main factors influencing the dispersion and stability configurations are represented by the energy and concentration equations. The linear Boussinesq approximating framework is recommended for further convenience. A huge growth in numerous physical and technical implications is what motivated this study. Using the standard normal modes of examination, the characteristics of velocity fields, temperature, and concentration are analyzed. The conventional stability results in a non-dimensional convoluted transcendental dispersion connection between the non-dimensional growth rate and all other physical parameters. The Maranogoni phenomenon, in which temperature and concentration distributions affect surface tension, has been addressed. It is observed that the intense electric field, the Prandtl numeral, the Lewis numeral, and the Lewis numeral velocity ratio have a stabilizing influence. As opposed to the Weber numeral, the Ohnesorge numeral, and the density ratio have a destabilizing influence.

Impact of Reynolds number in modulating wall stresses in radial stagnation-point flow

Wall stresses play a critical role in fluid dynamics and understanding their impact can lead to significant improvements in system performance and efficiency. This article presents a study on the impact of the Reynolds number and magnetic number on wall stresses, energy transport, and thermodynamic irreversibility analysis in axisymmetric flow near the stagnation region. We consider a hybrid nanofluid flow containing titania and silica nanoparticles, using Yamada-Ota and Xue thermal conductivity models. The flow is driven by a cylinder rotating along the z-direction with solar radiation and a magnetic field. To formulate the problem, we use similarity transformation to obtain dimensionless ordinary differential equations and obtain numerical solutions with graphical illustrations by bvp5c in Matlab. The comparison between hybrid nanofluid models indicates a higher rate of heat transformation, with the Yamada-Ota hybrid nanofluid model demonstrating better and faster heat transport properties than the Xue model. This study underlines the importance of understanding the impact of controlled parameters on wall stresses to optimize fluid dynamics system performance and efficiency. Moreover, it highlights the potential of entropy generation analysis to identify changes in thermal processes and reduce the loss of available mechanical power in thermo-fluid systems and provides a foundation for exploring and developing advanced technologies and systems with improved heat transfer performance and energy efficiency.

Entropy Production Analysis in an Octagonal Cavity with an Inner Cold Cylinder: A Thermodynamic Aspect

Understanding fluid dynamics and heat transfer is crucial for designing and improving various engineering systems. This study examines the heat transfer characteristics of a buoyancy-driven natural convection flow that is laminar and incompressible. The investigation also considers entropy generation (Egen) within an octagonal cavity subject to a cold cylinder inside the cavity. The dimensionless version of the governing equations and their corresponding boundary conditions have been solved numerically using the finite element method, employing triangular mesh elements for discretization. The findings indicated that incorporating a cold cylinder inside the octagonal cavity resulted in a higher heat transfer (HT) rate than in the absence of a cold cylinder. Furthermore, using the heat flux condition led to a higher average Nusselt number (Nuavg) and a lower Bejan number (Be) than the isothermal boundary condition. The results also showed that HT and Egen were more significant in the Al2O3-H2O nanofluid than the basic fluids such as air and water, and HT increased as χ increased. The current research demonstrates that employing the heat flux condition and incorporating nanoparticles can enhance the rate of HT and Egen. Furthermore, the thermo-fluid system should be operated at low Ra to achieve greater HT effectiveness for nanofluid concerns.

Exergy Analysis for Combustible Third-Grade Fluid Flow through a Medium with Variable Electrical Conductivity and Porous Permeability

A mathematical investigation of a thermodynamical system linked with energy management and its impact on the environment, especially climate change, is presented in this study. In this regard, a numerical investigation of the flow and heat transfer of hydromagnetic third-grade liquid through a porous medium. The permeability of the medium and electrical conductivity of the fluid are assumed to be temperature functions. The appropriate mathematical formulations for momentum, energy, and entropy equations are presented in both dimensional and dimensionless forms. We obtained the numerical solutions using the spectral version of the Chebyshev collocation method and compared the result with the shooting Runge–Kutta method. Numerical results for velocity, temperature, entropy, and Bejan profiles are communicated through tables and graphs with adequate physical interpretation. The thermal stability of the thermo-fluid system that guarantees the prevention of spontaneous fluid heating that fuels climate change is also included in the analysis.

Cilia and electroosmosis induced double diffusive transport of hybrid nanofluids through microchannel and entropy analysis

Abstract A mathematical model is presented to analyze the double diffusive transport of hybrid nanofluids in microchannel. The hybrid nanofluids flow is driven by the cilia beating and electroosmosis in the presence of radiation effects and activation energy. Cu–CuO/blood hybrid nanofluids are considered for this analysis. Phase difference in the beatings of mimetic cilia arrays emerge symmetry breaking pump walls to control the fluid stream. Analytical solutions for the governing equations are derived under the assumptions of Debye–Hückel linearization, lubrication, and Rosseland approximation. Dimensional analysis has also been considered for applying the suitable approximations. Entropy analysis is also performed to examine the heat transfer irreversibility and Bejan number. Moreover, trapping phenomena are discussed based on the contour plots of the stream function. From the results, it is noted that an escalation in fluid velocity occurs with the rise in slippage effects near the wall surface. Entropy inside the pump can be eased with the provision of activation energy input or by the consideration of the radiated fluid in the presence of electroosmosis. The results of the present study can be applicable to develop the emerging thermofluidic systems which can further be utilized for the heat and mass transfer at micro level.

A PINN Surrogate Modeling Methodology for Steady-State Integrated Thermofluid Systems Modeling

Physics-informed neural networks (PINNs) were developed to overcome the limitations associated with the acquisition of large training data sets that are commonly encountered when using purely data-driven machine learning methods. This paper proposes a PINN surrogate modeling methodology for steady-state integrated thermofluid systems modeling based on the mass, energy, and momentum balance equations, combined with the relevant component characteristics and fluid property relationships. The methodology is applied to two thermofluid systems that encapsulate the important phenomena typically encountered, namely: (i) a heat exchanger network with two different fluid streams and components linked in series and parallel; and (ii) a recuperated closed Brayton cycle with various turbomachines and heat exchangers. The results generated with the PINN models were compared to benchmark solutions generated via conventional, physics-based thermofluid process models. The largest average relative errors are 0.17% and 0.93% for the heat exchanger network and Brayton cycle, respectively. It was shown that the use of a hybrid Adam-TNC optimizer requires between 180 and 690 fewer iterations during the training process, thus providing a significant computational advantage over a pure Adam optimization approach. The resulting PINN models can make predictions 75 to 88 times faster than their respective conventional process models. This highlights the potential for PINN surrogate models as a valuable engineering tool in component and system design and optimization, as well as in real-time simulation for anomaly detection, diagnosis, and forecasting.

Forced convection of nanofluid in double vented cavity system separated by perforated conductive plate under magnetic field

In this study, forced convection in a double vented cavity system separated by a perforated conductive partition plate is studied under magnetic field effects. Nanofluid is used while two phase modeling approach is adopted. The conjugate thermal system is studied for different values of Reynolds number (250–1000), Hartmann number (0–50), and conductivity ratio (0.01–100). Variations of the size and inner part of the conductive plate are also considered while solid volume fraction of nanoparticles is taken as 0.03. Thermal performance improvements are observed by increasing the Reynolds number and conductivity ratio. When nanofluid is used instead of pure fluid, the average Nusselt number (Nu) increment becomes 9% at the lowest and highest Reynolds number cases. When magnetic field is activated, the highest variation in the average Nu is seen for the left upper part while the amount becomes 14%. The Nu increments become 240% for the left upper part when lowest and highest conductivity cases are compared while this amount is 18% when all hot walls are considered. When full partition and perforated plate partitions are compared, less than 1.5% in the variation of thermal performance is achieved while 29.6% reduction in the volume of the partition is seen. Using perforated partitions is recommended as it results in the reduction of the material, cost and weight of the overall thermo-fluid system.

Hybrid Nano-Jet Impingement Cooling of Double Rotating Cylinders Immersed in Porous Medium

A cooling system with impinging jets is used extensively in diverse engineering applications, such as solar panels, electronic equipments, battery thermal management, textiles and drying applications. Over the years many methods have been offered to increase the effectiveness of the cooling system design by different techniques. In one of the available methods, nano-jets are used to achieve a higher local and average heat transfer coefficient. In this study, convective cooling of double rotating cylinders embedded in a porous medium is analyzed by using hybrid nano-jets. A finite element formulation of the thermo-fluid system is considered, while impacts of Reynolds number, rotational speed of the double cylinders, permeability of the porous medium and distance between the cylinders on the cooling performance are numerically assessed. Hybrid and pure fluid performances in the jet cooling system are compared. It is observed that the cooling performance improves when the rotating speed of the cylinder, permeability of the medium and jet Reynolds number are increased. The heat transfer behavior when varying the distance between the cylinders is different for the first and second cylinder. Higher thermal performances are achieved when hybrid nanofluid with higher nanoparticle loading is used. An optimization algorithm is used for finding the optimum distance and rotational speeds of the cylinders for obtaining an improved cooling performance, while results show higher effectiveness as compared to a parametric study. The outcomes of the present work are useful for the thermal design and optimization of the cooling system design for configurations encountered in electronic cooling, energy extraction and waste heat recovery.