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The main goal of this work is to explore exact analytical solutions for the transient hybrid nanofluid flow with heat transfer owing to a moving/exponentially accelerating infinite flat vertical plate with heat flux boundary conditions. Further, the uniqueness of this work is to investigate the impact of different types of hybrid nanofluids on heat transfer and unsteady flow features in the existence of thermal radiation and heat flux boundary conditions. For engineering variables like Nusselt number and skin friction coefficient, along with temperature and velocity profiles, graphs are used to reveal the results of the Laplace transform method. Increased heat transfer and friction values have been found for an exponentially accelerating plate. The findings can be utilized in heat exchangers as well as in electronics and chemical and biological reactors.

In the present work, coupled effects of forced convection, rotational conic surface and magnetic field on the phase change dynamics are numerically explored by using finite element method for a phase change material (PCM) filled 3D cylindrical reactor. The PCM filled region has a conic shape and it is rotating. The study is conducted for various values of rotational Re number (between 0 and 2500), magnetic field strength (Hartmann number between 0 and 30) and conic surface aspect ratio (between 1 and 2). It is observed that the coupled interactions between the rotational surface and magnetic field significantly affect the phase change process dynamics and convective heat transfer between different phases. Optimum value of rotational Reynolds number for minimum complete phase transition time is achieved at Rew = 1000. The magnetic field has a positive impact on the phase change process while it is impact is profound without surface rotation. There are 98% and 65% reductions in the complete phase transition times when configurations at Rew = 1000 are compared with motionless conic surface case in the absence and presence of magnetic field. The effects of rotation are profound when different aspect ratios of the PCM filled region is considered. The transition time is increased up to 553% without rotation while this value is only 86% when cases with lowest and highest aspect ratio are compared. A modal analysis with 30 mode is used to capture the phase change dynamics and coupled interactions between the rotational surface and magnetic field on the variation of liquid fraction.

Nanoliquid impingement heat transfer with a phase change material (PCM) installed radial system is considered. The study is performed by using the finite element method for various values of Reynolds numbers (100 ≤ Re ≤ 300), height of PCM (0.25H ≤ hpcm ≤ 0.75H), and plate spacing (0.15H ≤ hs ≤ 0.40H). Different configurations using water, nanoliquid, and nanoliquid + PCM are compared in terms of heat transfer improvement. Thermal performance is improved by using PCM, while best performance is achieved with nanoliquid and PCM-installed configuration. At Re = 100 and Re = 300, heat transfer improvements of 26% and 25.5% are achieved with the nanoliquid + PCM system as compared to water without PCM. The height of the PCM layer also influences the heat transfer dynamic behavior, while there is 12.6% variation in the spatial average heat transfer of the target surface with the lowest and highest PCM heights while discharging time increases by about 76.5%. As the spacing between the plates decreases, average heat transfer rises and there is 38% variation.

In this study, numerical analysis and optimization for the convective heat transfer and fluid flow over a facing step in the presence of an elliptic shaped porous object located downstream of the step are considered. The COBYLA optimization algorithm is used to find the optimum location and size of the porous object in order to maximize average Nu number. Air and nano-diamond/Fe3O4 hybrid nanofluid as the coolant in the thermo-fluid system. It is observed that the presence of the obstacle, varying its permeability, aspect ratio and location in the channel profoundly affect the fluid flow features and improvement amount in the heat transfer rate. The average Nu number is first reduced by about 14.7% and then increased by about 6.8% when the permeability of the object is increased. The optimum value of the Nu number is found as 2.037 while the optimum location and sizes are found as (Sx, Sy, r1, r2)=(0.538H,0.4509H,0.2138H, 0.348H) when air is used as heat transfer fluid. The average heat transfer rate is reduced with higher aspect ratio while the value of Nu number at the optimum point is 33% higher as compared to case with aspect ratio of 0.5. The average Nu number variation shows non-monotonic behavior for horizontal location of the object. When the object is closer to the top wall, the average Nu number becomes higher while the value at the optimum point is 19.8% higher in the parametric study. At the optimum operating point, hybrid nanoparticle addition in the fluid brings further enhancement of 28.4% in the average heat transfer.

Impacts of using double rotating cylinders and partly porous layers in the bifurcating channels on the hydro-thermal performance were numerically assessed. Hybrid nanoparticles were used in water and finite element method was selected as the solver. Effects of Reynolds number, rotational speeds of the cylinders and their locations in the bifurcating channels, porous layer sizes and nanoparticle solid volume fractions on the hydro-thermal performance features were explored. The contribution of different hot wall parts was changed with varying Reynolds number and rotational velocity of the cylinders. Depending upon the rotational direction of the cylinders, the vortex occurrence and size at the bifurcations change significantly. Heat transfer considering all hot walls rise with higher rotational speeds in both directions. The amount of improvement in the heat transfer rate becomes 25 % and 19 % with varying speeds of the cylinders as compared to motionless cylinders. The pressure coefficient reduces with increasing the second cylinder speed in clockwise direction and this is favorable for thermal performance since the heat transfer also increases. The overall impact of the varying horizontal locations of the cylinders on the heat transfer rate is slight. The separated zones at the branching depends on the porous layer sizes. The overall heat transfer behavior becomes opposite when varying the sizes of the porous layers in the horizontal and vertical channels. By using nanoparticles in the base fluid, 35.75 % improvement in the heat transfer rate is achieved for vertical wall at Re = 350 while pressure drop coefficient rises by about 8.5 % . The overall improvement in the heat transfer rate by using nanofluid is 26 % . Owing to diverse use of bifurcating channels in thermal engineering from fuel cells to electronic cooling, the proposed methods of heat transfer enhancement techniques can be considered simultaneously for effective control the thermal performance of those systems.

Heat and moisture transfer of two moving moist objects in a channel with convection of hot dry air is investigated numerically. A moving mesh approach is used for providing movement by means of the Arbitrary Lagrangian-Eulerian (ALE) framework. Governing equations for flow field and porous objects are solved by finite element discretization method for the 3D transient problem. Effects of drying air velocity and temperature are simulated by means of temperature, moisture content and heat transfer distributions. Results showed the importance of varying parameters on drying behavior. It was observed that the air velocity also has an increasing effect on evaporation and most reduction in moisture content is obtained at 0.8 m/s air velocity with 63.12% loss. Besides, there are insignificant differences between heat transfer values for fixed and moving objects, differences in average heat transfer values calculated between 6 and 13% for static bed and moving bed.

Development of modern electronic devices and heat exchangers is related to the energy transport intensity. For this purpose, it is possible to use the internal fins and nanofluids. The present study is devoted to mathematical simulation of free convective thermal transmission of alumina-water nanoliquid in a semi-open cavity with the complicated fin including the wall-mounted part and internal obstacle. Analysis has been carried out by means of the partial differential transport equations written on the basis of the non-dimensional, non-primitive variables. The special procedure has been developed for description of the stream function value at the body surface within the cavity. The developed code has been validated using the mesh sensitivity analysis and computational results of other researchers. Impacts of the Rayleigh number, internal obstacle position, and nano-sized particles concentration on nanoliquid flow and thermal transmission have been considered. It has been revealed that for the present formulation a growth of the solid particles concentration results in the heat transport degradation, while it is possible to find an optimal position of the inner body for the energy transport intensification.

Numerical investigation of laminar forced convection of pulsating flow in a 90-deg bifurcation was performed with the finite volume method. The inlet velocity varies sinusoidally with time while constant wall temperature is utilized. The working fluid is air with constant properties and the numerical work is conducted for a range of the Reynolds numbers (100–2000), dividing flowrates (0.3–0.7) and Strouhal numbers (0.1–10). It is observed that the amplitudes of oscillating heat transfer are damped as the value of the Strouhal number increases. The average value of Nu number rises for higher Reynolds number and the dividing flowrate for the downstream wall of the y-channel branch. As the value of the dividing flowrate increases from 0.3 to 0.7, heat transfer is less effective in the vicinity of the branch at the Reynolds number of 500. The effects of the Reynolds number on the average Nu number variation is more pronounced for the y-branch wall for different values of dividing flowrates. Resonant type behavior of average Nu number is obtained for the y-branch channel for diving flowrates of 0.3 and 0.5.

The main objective of this study is to design a low-grade heat driven ethanol-silica gel adsorption chiller. The low-grade waste heat is utilized in an adsorption chiller. For this purpose, an innovative bed heat exchanger including a condenser embedded inside the adsorbent bed is uniquely designed. The silica gel/ethanol pair is examined both analytically and numerically in this article. The cycles of the adsorption chiller are performed experimentally. The obtained isotherm for the silica gel/ethanol fitted to Type III isotherm behavior. The obtained equations of isotherm are also validated numerically. The new adsorption chiller design used in this study has reduced the desorption temperature for silica gel/ethanol pair to 37 °C which will widen the application area of adsorption chillers. The COMSOL Multiphysics program is used for 2-D numerical analysis of adsorbent bed. The mass transfer inside of the particle, the heat transfer in porous media, and Darcy law are used for analyzing the heat and mass transfer of the bed. Temperature and concentration distributions of adsorbent bed during the duration of adsorption and desorption processes are examined numerically. The specific cooling power and volumetric cooling power values of the system are found as 20.2 Wkg−1 and 4.5 kWm−3, respectively.

Heat transfer augmentation is a modern challenge in various engineering fields including heat exchangers, electronics, chemical and bio reactors, and others. Nanofluids as a new heat transfer liquids can be considered as effective media for increment of energy transport. Such gain is getting due to an increase in the effective thermal conductivity and change in the fluid flow dynamics. In the case of hybrid nanofluids when we can include two or several nanoadditives to the host liquid one can obtain more essential enhancement of transport processes. Therefore, this paper deals with the energy augmentation using hybrid nanofluids. The objective is to find exact analytical solutions to the unsteady hybrid nanofluid flow with heat transfer past an infinite flat vertical plate with a ramped temperature profile concerning time. The effects of various hybrid nanofluids on the unsteady flow and heat transfer features in the presence of the magnetic field, thermal radiation and a temperature-dependent heat source are explored. Results of radiation parameter, heat source parameter, magnetic parameter and nanoparticle volume fraction obtained by employing the Laplace transform technique for engineering variables such as skin friction coefficient and Nusselt number along with velocity and temperature profiles are analyzed using graphs. It has been found that a growth of the average Nusselt number occurs with the nanoparticle volume fraction, while this augmentation can be improved with use of hybrid nanofluid.

This work deals with the impact of magnetic field-dependent viscosity and magnetohydrodynamics on the natural convection heat transfer of Ag–MgO (50%–50%) water hybrid nanoliquid in a complicated enclosure. The considered cavity with concave or convex horizontal boundaries has been differentially heated and cooled by multiple heat sources and heat sinks. The governing equations (Navier–Stokes equations) constituting stream function (ψ)-vorticity (ζ) formulation with energy equation are solved by adopting a compact finite difference scheme. Meanwhile, the flow domain that is influenced by several factors including Hartmann number ( 0≤Ha≤60), hybrid nanoparticles volume fraction ( 0≤ϕhnp≤0.02), Rayleigh number ( 103≤Ra≤106), orientation angle of magnetic field ( 00≤γ≤900), magnetic number ( 0≤δ0≤1), different cases (Case-I to III), and internal heat generation or absorption ( −2≤Q≤2) is analyzed generously. Experimentally based correlations for thermal conductivity and dynamic viscosity have been used throughout the study. The outcomes show that the geometric parameters can be used as an excellent controller of the thermal performance inside the wavy chamber.

In the present work, performance assessment of a PCM filled three dimensional vertical cylinder is conducted under the combined effects of surface corrugation and presence of binary nanoparticles in the heat transfer fluid. The numerical simulation is performed by using finite element method with varying values of Reynolds number ( 100 ≤ Re ≤ 750 ), number ( 1 ≤ N ≤ 8 ) and height ( H / 10 ≤ h ≤ H / 2 ) of rectangular type corrugation form and volume fraction of particles ( 0 ≤ ϕ ≤ 0.02 ) in unsteady configuration. Thermal transport features are enhanced while charging time is reduced for higher values of Reynolds number, solid volume fraction of the binary mixture in the heat transfer fluid. Complete charging time is reduced by 57 % with increase of Reynolds number from 100 to 750 while it is reduced by 23 % when nanofluid at the highest solid volume fraction is used instead of water. However, the corrugation parameters have reverse effects on the charging process. A computational framework for reconstruction of heat transfer fluid and PCM temperatures for the unsteady parametric configuration in the computational domain is offered by utilizing proper orthogonal decomposition (POD) technique with 25 modes for heat transfer fluid and 75 modes for PCM.

The paper attempts to enhance the control of convective transport phenomena in magnetothermal devices applying a technique of multibanded magnetic field. For this demonstration, a typical cavity-like thermal system is considered involving linear heating, porous substance, hybrid nanofluid, and magnetic field. Four identical bands of magnetic fields are applied horizontally with uniform inactive zones between the bands. The transport equations of the coupled multiphysics evolving from the thermal buoyancy (due to linear heating at one sidewall and isothermal cooling at the opposite sidewall), filled porous medium, spatially intermittently active magnetic fields, and the engineered working fluid of Cu–Al2O3/water hybrid nanofluid are solved by an indigenously developed computing code. The study is conducted using the pertinent dimensionless parameters for the following ranges: Darcy–Rayleigh number (Ram = 1–104), Darcy number (Da = 10−5 − 10−1), Hartmann number (Ha = 0–70), and concentration of hybrid nanoparticles ϕ (= 0–2%). The convective phenomena are analyzed using the heatlines (for heat transport), streamlines (flow pattern), isotherms (static temperature), and the average Nusselt number (for heat transfer). The outcomes of this technique of multibanded magnetic field are rigorously compared with other established application methods of magnetic fields. It establishes different local behaviors along with an improved heat transfer. Heatline visualization reveals the definite portraits of heat flow paths depending upon parametric values. Furthermore, the presence of linear heating is in particular treated to explore the insight of linear heating (that featuring multiple heating and cooling zones along with the linear heater), utilizing the local Nusselt number and heatlines. One of the important advantages of this new technique is it is more energy-efficient particularly for the square or shallow cavity. The multibanded magnetic field shows a promising technique for the control of convective transport phenomena involving coupled multiphysics used during sophisticated applications (such as materials processing, biomedical applications, etc.).

In this study, a numerical study of MHD mixed convection nanofluid filled lid driven square enclosure was performed. The bottom wall of the cavity is heated and the top wall is kept at constant temperature lower than that of the heater. Other walls of the square enclosure and cylinder surface are assumed to be adiabatic. The governing equations are solved with finite element method. The influence of the Richardson number ( 0.001 ⩽ Ri ⩽ 10 ), Hartmann number ( 0 ⩽ Ha ⩽ 50 ), angular rotational speed of the cylinder ( - 10 ⩽ Ω ⩽ 10 ) and solid volume fraction of the nanoparticle ( 0 ⩽ ϕ ⩽ 0.05 ) on fluid flow and heat transfer are numerically investigated. It is observed that 17% of heat transfer enhancement is obtained for Ri = 10 when compared to flow at Ri = 1. Averaged heat heat transfer decreases with increasing Hartmann number and 14.2% of heat transfer enhancement is obtained for Ω = - 10 compared to motionless cylinder case at Ω = 0 . When the solid volume fraction of nanoparticle is increased, heat transfer increases.

In this study, numerical analysis of the heat transfer enhancement and fluid flow characteristics of a rotating cylinder under the influence of magnetic dipole in the backward facing step geometry is conducted. The governing equations are solved with a finite element based commercial solver. The effects of Reynolds number ( 10 ⩽ Re ⩽ 200 ), cylinder rotation angle ( - 75 ⩽ Ω ⩽ 75 ) and strength of the magnetic dipole ( 0 ⩽ γ ⩽ 16 ) on the heat transfer characteristics are studied for backward facing step flow. It is observed that the length and size of the recirculation zones can be controlled with magnetic dipole strength and cylinder rotation angles. As the Reynolds number increases, local Nusselt number increases and number of peaks in the presence of the magnetic field decreases. The effect of cylinder rotation on the local Nusselt number distribution is more pronounced at low Reynolds number.

Natural convection heat transfer in an inclined fin attached square enclosure is studied both experimentally and numerically. Bottom wall of enclosure has higher temperature than that of top wall while vertical walls are adiabatic. Inclined fin has also adiabatic boundary conditions. Numerical solutions have been done by writing a computer code in Fortran platform and results are compared with Fluent commercial code and experimental method. Governing parameters are Rayleigh numbers (8.105 ≤ Ra ≤ 4 × 106) and inclination angle (30° ≤ and ≤ 120°). The temperature measurements are done by using thermocouples distributed uniformly at the wall of the enclosure. Remarkably good agreement is obtained between the predicted results and experimental data. A correlation is also developed including all effective parameters on heat transfer and fluid flow. It was observed that heat transfer can be controlled by attaching an inclined fin onto wall.

Laminar mixed convection flow in the presence of magnetic field in a top sided lid-driven cavity heated by a corner heater was considered. The corner heater is under isothermal boundary conditions with different length in bottom and right vertical walls. Finite volume technique was used to solve governing equations. The temperature of the lid is lower than that of heater. The study is performed for different Grashof and Hartmann numbers at Re = 100. The obtained results showed some very interesting results.

The present work is aimed to study mixed convection heat transfer characteristics for a lid-driven air flow within a square enclosure having a circular body. Flows are driven by the left lid, which slides in its own plane constant velocity. This wall is isothermal and it moves up or down in y direction while the other walls remain stationary. The horizontal walls are adiabatic. The cavity is differentially heated and the left wall is maintained at a higher temperature than the right wall. Three different temperature boundary conditions were applied for the inner cylinder as adiabatic, isothermal or conductive. The computation is carried out for wide ranges of Richardson numbers, diameter of inner cylinder and center and location of the inner cylinder. It was found that the most effective parameter on flow field and temperature distribution is the orientation of the moving lid. The circular body can be a control parameter for heat and fluid flow. An interesting obtained result that the thermal conductivity becomes insignificant for small values of diameter of the circular body.

Effects of inclination angle on natural convection heat transfer and fluid flow in a two-dimensional enclosure filled with Cu-nanofluid has been analyzed numerically. The performance of nanofluids is tested inside an enclosure by taking into account the solid particle dispersion. The angle of inclination is used as a control parameter for flow and heat transfer. It was varied from = 0° to = 120°. The governing equations are solved with finite-volume technique for the range of Rayleigh numbers as 103 ⩽ Ra ⩽ 105. It is found that the effect of nanoparticles concentration on Nusselt number is more pronounced at low volume fraction than at high volume fraction. Inclination angle can be a control parameter for nanofluid filled enclosure. Percentage of heat transfer enhancement using nanoparticles decreases for higher Rayleigh numbers.

Heat transfer and fluid flow due to buoyancy forces in a partially heated enclosure using nanofluids is carried out using different types of nanoparticles. The flush mounted heater is located to the left vertical wall with a finite length. The temperature of the right vertical wall is lower than that of heater while other walls are insulated. The finite volume technique is used to solve the governing equations. Calculations were performed for Rayleigh number (103 ⩽ Ra ⩽ 5 × 105), height of heater (0.1 ⩽ h ⩽ 0.75), location of heater (0.25 ⩽ yp ⩽ 0.75), aspect ratio (0.5 ⩽ A ⩽ 2) and volume fraction of nanoparticles (0 ⩽ φ ⩽ 0.2). Different types of nanoparticles were tested. An increase in mean Nusselt number was found with the volume fraction of nanoparticles for the whole range of Rayleigh number. Heat transfer also increases with increasing of height of heater. It was found that the heater location affects the flow and temperature fields when using nanofluids. It was found that the heat transfer enhancement, using nanofluids, is more pronounced at low aspect ratio than at high aspect ratio.

A numerical analysis of MHD natural convection in a wavy open porous tall cavity filled with a Cu–water nanofluid in the presence of an isothermal corner heater has been carried out. The cavity is cooled from the left wavy wall and heated from the right bottom corner while the bottom wall is adiabatic. Uniform magnetic field affects the heat transfer and fluid flow with an inclination angle to the axis x ¯ . Mathematical model formulated using the single-phase nanofluid approach in dimensionless variables stream function, vorticity and temperature has been solved by finite difference method of the second order accuracy in a wide range of governing parameters: Rayleigh number (Ra = 100–1000), Hartmann number (Ha = 0–100), inclination angle of the magnetic field (γ = 0–π) and solid volume fraction parameter of nanoparticles (φ = 0.0–0.05). Main efforts have been focused on the effects of these parameters on the fluid flow and heat transfer inside the cavity. Numerical results have been presented in the form of streamlines, isotherms and average Nusselt numbers. It has been found heat transfer enhancement with Rayleigh number and heat transfer reduction with Hartmann number, while magnetic field inclination angle leads to non-monotonic changes of the heat transfer rate.

Heat transfer in a differentially heated, partitioned, square cavity containing heat generating fluid has been studied numerically. The vertical walls were isothermal, horizontal walls adiabatic and an isothermal partition at the reference temperature was attached to the bottom wall. Results have been obtained for various geometrical parameters specifying the height, thickness and position of the partition and for Rayleigh numbers characterizing internal and external heating from 103 to 106. Depending on the ratio of the internal and external Rayleigh numbers, two distinct regimes have been observed and studied with various geometrical parameters. Flow and temperature fields for these cases have been produced; average and local Nusselt numbers at hot and cold walls have been calculated. It is found that the flow field was modified considerably with partial dividers and heat transfer was generally reduced particularly when the ratio of internal and external Rayleigh numbers was from 101 to 102.

A numerical study has been carried out on inclined partially open square cavities, which are formed by adiabatic walls and a partial opening. The surface of the wall inside the cavity facing the partial opening is isothermal. Steady-state heat transfer by laminar natural convection in a two dimensional partially open cavity is studied by numerically solving equations of mass, momentum and energy. Streamlines and isotherms are produced, heat and mass transfer is calculated. A parametric study is carried out using following parameters: Rayleigh number from 103 to 106, dimensionless aperture size from 0.25 to 0.75, aperture position at high, center and low, and inclination of the opening from 0° (facing upward) to 120° (facing 30° downward). It is found that the volume flow rate and Nusselt number are an increasing function of Rayleigh number, aperture size and generally aperture position. Other parameters being constant, Nusselt number is a non-linear function of the inclination angle. Depending on the application, heat transfer can be maximized or minimized by selecting appropriate parameters, namely aperture size, aperture position and inclination angle at a given operation Rayleigh number.

Steady state two-dimensional mixed convection problem in a vertical two-sided lid-driven differentially heated square cavity is investigated numerically. The left and right moving walls are maintained at different constant temperatures while upper and bottom walls are thermally insulated. Three cases were considered depending on the direction of moving walls. Richardson number, Ri=Gr/Re2 emerges as a measure of relative importance of natural and forced convection modes on the heat transfer. Governing parameters were 0.01 1, the heat transfer is somewhat better due to formation of secondary cells on the walls and a counter rotating cell at the center.

Effects of a ceiling-mounted barrier on natural convection heat transfer in a square cavity with differentially heated wall are numerically investigated. A limit case, in which the partition has small thickness and low thermal conductivity, is studied. The study is performed for nine different locations of barrier on the ceiling, two different lengths of barrier as 15 and 50% of the side wall, and Rayleigh numbers from 103 to 106. The vorticity and streamfunction approach is used to obtain velocity distribution, and the energy equation is solved to determine temperature field in the cavity. The variations of the local Nusselt number on the hot and cold walls and the change of mean Nusselt number with the location of barrier in the cavities with different Rayleigh numbers are presented. The obtained results show that a wall-mounted barrier can be used to reduce heat transfer rate through the cavity; however, its effectiveness depends on length and location of barrier and Rayleigh number.