Convective Heat Transfer Flow Research Articles

Laboratory investigations into convective heat transfer in road construction materials

This paper presents a laboratory investigation into natural air convection and the establishment of intrinsic permeability of road and railway construction materials. The laboratory investigations were performed using a heat transfer cell with an inner volume of 1 m3. The study shows the importance of natural air convection and a practical method for establishing the intrinsic permeability of coarse granular materials. Three different open-graded crushed rock materials and two lightweight aggregates were tested. All materials were tested for downward (conduction only) and upward (convection and conduction) heat flow conditions. The experimental results revealed that all three crushed rock materials are prone to developing natural air convection in thermal gradients of 4.5 to 11 °C/m, depending on the particle size distribution. Foam glass aggregates showed a convective heat transfer flow at the fairly low temperature gradient of 6.5 °C/m. No natural air convection was achieved in expanded clay aggregates within the temperature gradients imposed. Intrinsic permeability values were established based on the experimental results. The intrinsic permeability of crushed rock materials ranged from 1.1 to 2.2 × 10−6 m2 while that of foam glass materials was 0.9 × 10−6 m2.

Cooling of an isothermal surface having a cavity component by using CuO-water nano-jet

PurposeThe purpose of this study is to numerically analyze the convective heat transfer features for cooling of an isothermal surface with a cavity-like portion by using CuO-water nano jet. Jet impingement cooling of curved surfaces plays an important role in practical applications. As compared to flat surfaces, fluid flow and convective heat transfer features with jet impingement cooling of a curved surface becomes more complex with additional formation of the vortices and their interaction in the jet wall region. As flow separation and reattachment may appear in a wide range of thermal engineering applications such as electronic cooling, combustors and solar power, jet impingement cooling of a surface which has a geometry with potential separation regions is important from the practical point of view.Design/methodology/approachNumerical simulations were performed with a finite volume-based solver. The study was performed for various values of the Reynolds number (between 100 and 400), length of the cavity (between 5 w and 40 w), height of the cavity (between w and 5w) and solid nano-particle volume fraction (between 0 and 4 per cent). Artificial neural network modeling was used to obtain a correlation for the average Nusselt number, which can be used to obtain fast and accurate predictions.FindingsIt was observed that cavity geometrical parameters of the cooling surface can be adjusted to change the flow field and convective heat transfer features. When the cavity length is low, significant contribution of the inclined wall of the cavity on the average Nusselt number is achieved. As the cavity length and height increase, the average Nusselt number, respectively, reduce and slightly enhance. At the highest value of cavity height, significant changes in the convective flow features are obtained. By using nanofluids instead of water, enhancement of average heat transfer in the range of 35-46 per cent is obtained at the highest particle volume fraction.Originality/valueIn this study, jet impingement cooling of an isothermal surface which has a cavity-like portion was considered with nanofluids. Addition of this portion to the impingement surface has the potential to produce additional vortices which affects the fluid flow and convective features in the jet impingement heat transfer. This geometry has the forward-facing step for the wall jet region with flow separation reattachment in the region. Based on the above literature survey and to the best of the authors’ knowledge, jet impingement cooling for such a geometry has never been reported in the literature despite its importance in practical thermal engineering applications. The results of this study may be useful for design and optimization of such systems and to obtain best performance in terms of fluid flow and heat transfer characteristics.

CFD Simulation of Convective Heat Transfer on Vernacular Sustainable Architecture: Validation and Application of Methodology

The global background of energy shortages and climate deterioration demands bioclimatic sustainable buildings. Vernacular architecture can provide a useful resource of passive strategies and techniques for creating inner comfort conditions with minimum heating, ventilation, and air conditioning (HVAC) assistance. The identification and verification of such knowledge are essential for climate responsive or energy passive building design. Among the methods, computational fluid dynamics (CFD) is a useful tool for simulating convective heat transfer of vernacular architecture and predicting the convective heat transfer coefficient (CHTC) and flow field. Geometric complexity and diversity of building samples are crucial in the development of an effective simulation methodology in terms of computational cost and accuracy. Therefore, this paper presents high-resolution 3D steady Reynolds-averaged Navier–Stokes (RANS) CFD simulations of convective heat transfer on Japanese vernacular architecture, namely, “machiya.” A CFD validation study on the CHTC is performed based on wind-tunnel experiments on a cube heated by constant heat flux and placed in a turbulent channel flow with a Reynolds number of 3.3 × 104. Three steady RANS models and two boundary layer modeling approaches are compared and discussed. Results show that the SST k-ω model applied with low Reynolds number modeling approach is suitable for CHTC simulations on a simplified building model. The RNG k-ε model applied with wall functions is an appropriate choice for simulating flow field of a complicated building model. Overall, this study develops a methodology involving RANS model selection, boundary layer modeling, and target model fitting to predict the convective heat transfer on vernacular architecture.

Importance of convective heat transfer in flow of non-Newtonian nanofluid featuring Brownian and thermophoretic diffusions

Purpose This paper aims to address the flow of Sisko nanofluid by an unsteady curved surface. Non-uniform heat source/sink is considered for heat transfer analysis. Design/methodology/approach Numerical solutions are constructed using bvp4c procedure. Findings Pressure profile inside boundary region is increased when A and K are enhanced. Originality/value No such analysis is yet presented.

EXPERIMENTAL DETERMINATION OF CONVECTIVE HEAT TRANSFER COEFFICIENTS IN THERMAL BUOYACY VENTILATION SYSTEM

Objectives. The main goal of the article is to present the developed method for the experimental determination of convective heat transfer coefficients, suitable for studying the internal convection of models of complex configuration. Method. The study of free convection under the conditions of an internal problem was carried out by determining the conditional thickness of the boundary layer by a graphic method. The first was the selection of the calculated sections and planes for the experimental installation. The selection is carried out in such a way that the calculated planes are perpendicular to the heated walls of the channel in question. Installation of an experimental model is possible only in a room with low internal air mobility, as well as a stable temperature. In this room there should not be heating and heating devices that can create strong convective currents near the channel of the experimental installation. Result. The article presents the results of an experimental study to determine the temperature distribution of the air flow and average convective heat transfer coefficients over the height of the ventilation channel. A decrease in convective heat transfer coefficients at an altitude of 0.5 to 1 meter occurs less noticeably than at an altitude of 1 to 2 meters, which is associated with the restoration of flow after a vent removal. At the stabilization section, there is first a gradual decrease, and then an increase in axial velocity, which is caused by the merging of multidirectional air flows in this area. Conclusion. It was revealed that in the case of modeling free convection under the conditions of an internal problem in the presence of heat-removing boundaries within the limits of the calculated temperature difference, taking into account the flow turbulization has practically no effect on the final results.

Effect of a porous medium on flow and mixed convection heat transfer of nanofluids with variable properties in a trapezoidal enclosure

In the present study, the flow field and heat transfer of a water–copper nanofluid with variable properties in a trapezoidal enclosure saturated with porous media are studied. The governing equations are solved by finite volume method and the SIMPLER algorithm. The nanofluid flow is assumed to be laminar, steady and incompressible. Simulations are performed for sidewall (trapezoid legs) angles of 30°, 45° and 60° with respect to horizontal axis, Reynolds numbers from 10 to 1000, Darcy numbers of 10−2, 10−3, 10−4 and volume fractions of 0 to 0.04 of nanoparticles. Numerical results show that the average Nusselt number increases with increasing volume fraction of nanoparticles for all studied Darcy numbers. The convection and motion of the nanofluid decrease by reducing the Darcy number which leads to a reduction in the velocity and local Nusselt number. The average Nusselt number increases by increasing the Darcy number for all aspect ratios. Also, the average Nusselt number increases with increasing Reynolds number for all Darcy numbers, aspect ratios and volume fractions of nanoparticles.

Experimental study on heat transfer characteristics of annular flow between vertical concentric pipe

Concentric pipe heat exchangers have been utilized extensively in practical project, such as petroleum, chemical, geothermal energy utilization and other fields. The study of annular flow between vertical concentric pipes is dominated by boiling heat transfer, while the study of forced convection heat transfer for single-phase flow is scarce. In this paper, an experimental investigation is carried out to study of the flow and heat transfer characteristics of the annular flow between vertical concentric pipes. The annular in a vertical concentric pipe heat exchanger with 25mm ring gap is tested with different volume flow rates and different constant heat flow densities. The results show that the Nusselt number of annular flow between vertical concentric pipes increases with Reynolds number. The local convective heat transfer coefficients reduce with the distance from the top to the bottom, which lead to a gradually increased trend in the fluid temperature along the flow direction. Based on the experimental data, an empirical equation of the Nusselt number is obtained to evaluate the overall heat transfer performance of vertically concentric pipe heat exchangers.

A Theoretical Study of Steady MHD mixed convection heat transfer flow for a horizontal circular cylinder embedded in a micropolar Casson fluid with thermal radiation

In this study, an investigation is carried out for laminar steady mixed 2D magnetohydrodynamic (MHD) flow of micropolar Casson fluid with thermal radiation over a horizontal circular cylinder with constant surface temperature. In the present study, an investigation is carried out on the effects of physical parameters on Casson fluid non dimensional numbers. The governing nonlinear partial differential equations and the controlling boundary conditions are derived for this case study. Furthermore, these equations are solved numerically using finite difference technique known as Keller Box Method (KBM). The effects of non-dimensional governing parameters, namely Casson parameter, mixed convection parameter, magnetic parameter, radiation parameter on the Nusselt number and local friction coefficient, as well as temperature, velocity and angular velocity are discussed and shown graphically. It is noticed that the local skin friction and the local Nasselt number has decrement behaviors when increasing the values the Casson parameter. But the opposite happens when the mixed convection parameter λ increase. It is found that the results in this study are in good agreement with previous studies. This proves that calculations using KBM method and the chosen step size are accurate enough for this type of problems.

Effect of trapezoidal heater on natural convection heat transfer and fluid flow inside a cubical cavity

Purpose The purpose of this paper is to investigate natural convective heat transfer in a cubical cavity with the heat source of a trapezoidal form having a constant temperature. Design/methodology/approach The domain of interest is a cubical cavity with two isothermal opposite vertical walls, while other walls are adiabatic. A discrete heater of a trapezoidal shape is located at the bottom wall of the cavity. Governing equations formulated in dimensionless vector potential functions, vorticity vector and temperature with corresponding initial and boundary conditions have been solved numerically using a developed computational code based on the finite difference method. Findings The results show that the variation of geometric parameters, such as height, length and size of the local heater, significantly influences the evolution of a temperature field and fluid flow inside the enclosure. The effects of Rayleigh number and time on streamlines, isotherms and average Nusselt number have been studied. Originality/value The originality of this work is to explore three-dimensional (3D) natural convection in a cubical cavity with a local heat source of trapezoidal shape, to analyze the effects of heater geometric parameters and to compare obtained 3D data with two-dimensional results.

Flow and natural convection heat transfer characteristics of non-Newtonian nanofluid flow bounded by two infinite vertical flat plates in presence of magnetic field and thermal radiation using Galerkin method

The main goal of this paper is to investigate natural convective heat transfer and flow characteristics of non-Newtonian nanofluid streaming between two infinite vertical flat plates in the presence of magnetic field and thermal radiation. Initially, a similarity transformation is used to convert momentum and energy conservation equations in partial differential forms into non-linear ordinary differential equations (ODE) applying meaningful boundary conditions. In order to obtain the non-linear ODEs analytically, Galerkin method (GM) is employed. Subsequently, the ODEs are also solved by a reliable numerical solution. In order to test the accuracy, precision and reliability of the analytical method, results of the analytical analysis are compared with the numerical results. With respect to the comparisons, fairly good compatibilities with insignificant errors are observed. Eventually, the impacts of effective parameters including magnetic and radiation parameters and nanofluid volume fraction on the velocity, skin friction coefficient and Nusselt number distributions are comprehensively described. Based on the results, it is revealed that with increasing the role of magnetic force, velocity profile, skin friction coefficient and thermal performance descend. Radiation parameter has insignificant influence on velocity profile while it obviously has augmentative and decreasing effects on skin friction and Nusselt number, respectively.

Numerical analysis of natural convective heat transport of copper oxide-water nanofluid flow inside a quadrilateral vessel

Nanofluid based heat transfer approaches have a tremendous prospect to develop novel cost-effective cooling technologies. In response to this potential development, a problem of unsteady copper oxide-water nanofluid flow and natural convective heat transfer within a quadrilateral vessel with uniform heating of bottom wall using modified Buongiorno model are investigated. The sloping wall of the vessel is maintained at constant low temperature and the uniform thermal condition on the bottom heated wall is considered, whereas the upper horizontal wall is regarded as adiabatic. The governing equations along with boundary conditions are solved using the Galerkin finite element method. Partial differential equation solver COMSOL Multiphysics with Matlab interface is used in the simulation. The results of the present problem of a certain situation as a special case have been verified by the previously published standard numerical investigations. The flow, thermal and concentration fields, local and average Nusselt number for various pertinent parameters entered into the problem have been analyzed. The time evolutions for a steady-state solution are also examined. The results show that the adjustment factor with the optimal nanoparticle volume fraction and the thermal Rayleigh number controls the optimal heat transfer. The trapezoidal vessel having higher sloping angles with the vertical axis exhibits higher heat transfer. Heat transfer decreases rapidly in 1–10 nm size nanoparticles for a nanofluid solution.

Heat Transfer and Thermal Characteristics Effects on Moving Plate Impinging from Cu-Water Nanofluid Jet

The present article is focused on modelling of flow and heat transfer behaviour of Cu-water nanofluid in a confined slot jet impingement on hot moving plate. Different parameters such as various moving plate velocities, nanoparticles at various concentrations, variation in turbulent Reynolds number and jet nozzle to plate distance have been considered to study the flow field and convective heat transfer performance of the system. Results of distribution of local and average Nusselt number and skin friction coefficients at the plate surface are shown to elucidate the heat transfer and fluid flow process. Qualitative analysis of both stream function and isotherm contours are carried out to perceive the flow pattern and heat transfer mechanism due to moving plate. The results revealed that average Nusselt number significantly rises with plate velocity in addition with jet inlet Reynolds number. Correlations of the average Nusselt numbers are presented.

Effect of Hall Currents and Non-Linear Density Temperature Variation on Convective Heat and Mass Transfer Flow of a Viscous Fluid past a Stretching Sheet with Thermo-Diffusion, Chemical Reaction and Heat Source

Effect of Hall Currents and Non-Linear Density Temperature Variation on Convective Heat and Mass Transfer Flow of a Viscous Fluid past a Stretching Sheet with Thermo-Diffusion, Chemical Reaction and Heat Source

Unsteady MHD Convective Heat and Mass Transfer Flow in a Vertical Wavy Channel with Oscillatory Wall Temperature and Concentration

Unsteady MHD Convective Heat and Mass Transfer Flow in a Vertical Wavy Channel with Oscillatory Wall Temperature and Concentration

Mixed Convective Flow of Electrically Conducting Fluid in a Vertical Cylindrical Annulus With Moving Walls Adjacent to a Radial Magnetic Field Along With Transpiration

The steady, viscous flow and mixed convection heat transfer of an incompressible electrically conducting fluid within a vertical cylindrical annulus with moving walls are investigated. This annulus is under the influence of a radial magnetic field and the fluid is suctioned/injected through the cylinders' walls. An exact solution of the Navier–Stokes equations and energy equation is derived in this problem where heat is transferred from the hot cylinder walls with constant temperature to the cooler moving fluid. The role of the movement of the annulus walls is studied on the flow and heat transfer of the fluid within the annulus, for the first time. The effects of other parameters, including Prandtl number, Hartman number, mixed convection parameter, suction/injection parameter and ratio of the radius, on the behavior of the flow and heat transfer of the fluid is also considered. The results indicate that if, for example, the internal cylinder wall moves in the direction of z-axis and the external cylinder is stationary, the maximum and minimum heat transfer occur on the walls of internal and external cylinders, respectively. Moreover, the augmentation of the radius ratio between the two cylinders increases the rate of heat transfer and decreases the shear stress on the wall of the internal and external cylinders, however, the results on the wall of external cylinder are exactly the reverse. Consequently, by changing the effective parameters used in this paper, the flow of the fluid can be controlled and the heat transfer of the fluid can be improved.

Hall current and thermophoresis effects on magnetohydrodynamic mixed convective heat and mass transfer thin film flow

The combined influences of Hall current and thermophoresis on a magnetohydrodynamic mixed convective heat and mass transfer flow of a thin film second-grade fluid with viscous dissipation and thermal radiation past a stretching sheet are analyzed. An external strong and uniform magnetic field is applied transversely to the stretching sheet. The surface of the stretching sheet is taken to move with a linear velocity and subject to the constant reference temperature and concentration. Entropy generation is introduced to investigate the irreversibility associated with flow, heat and mass transfer. The basic governing equations for the velocities, temperature and concentration of the fluid motion have been modeled by employing appropriate similarity transformations which result in high nonlinear coupled differential equations with physical conditions. The solution of the transformed systems of equations has been achieved by employing Homotopy Analysis Method (HAM) which lead to detailed expressions for the velocities, temperature and concentration components. The obtained results are compared with the published results in the tables 3–5 demonstrating an excellent agreement and correlation. Graphs are discussed to elucidate the effects of various parameters.

Mixed convection in micropolar nanofluid flow through entrapped triangular enclosures and linear stability analysis considering magnetic effects and heat generation and absorption

In the present investigation, numerical computation for mixed convection heat transfer flow within entrapped triangular enclosures saturated with a micropolar nanofluid and linear stability analysi...

Thermal Diffusion (Soret Effect) on an Unsteady MHD Mixed Convective Heat and Mass Transfer Flow through Vertical Porous Medium with Chemical Reaction

A parametric study to investigate the effect of thermal diffusion (Soret effect) on an MHD mixed convective heat and mass transfer flow of an incompressible viscous electrically conducting fluid past a vertical porous plate. The magnetic reynolds number is assumed to be small that the induced magnetic field can be neglected as compared with the applied magnetic field. Sherwood number at the plate are demonstrated graphically for various values of the parameters involved in the problem

Mixed Convective Magnetohydrodynamic Heat Transfer Flow of Williamson Fluid Over a Porous Wedge

The present article examines the influence of thermal radiation on two-dimensional incompressible magnetohydrodynamic (MHD) mixed convective heat transfer flow of Williamson fluid flowing past a porous wedge. An adequate similarity transformation is adopted to reduce the fundamental boundary layer partial differential equations of Williamson fluid model in to a set of non-linear ordinary differential equations. The solutions of the resulting nonlinear system are obtained numerically using the fifth order numerical scheme the Runge-Kutta-Fehlberg method. The effects of different pertinent physical parameter such as magnetic parameter, Williamson parameter, radiation parameter and Prandtl number on temperature and velocity distributions are observed through graph.

Effects of the Form Factor and the Force of the Gravity on the Thermal Exchanges by Natural Convection in a Rectangular Cavity Filled with Nanofluid

Effects of the form factor on natural convection heat transfer and fluid flow in a two-dimensional cavity filled with Al2O3-nanofluid has been analyzed numerically. A model was developed to explain the behavior of nanofluids taking account of the volume fraction φ. The Navier-Stokes equations are solved numerically by alternating an implicit method (Method ADI) for various Rayleigh numbers varies as 103, 104 and 105. The nanofluid used is aluminum oxide with water Pr = 6.2; solid volume fraction φ is varied as 0%, 5% and 10%. Inclination angle Φ varies from 0° to 90° with a step the 15° and the form report varies as R = 0.25, 0.5, 1 and 4. The problem considered is a two-dimensional heat transfer enclosure. The vertical walls are differentially heated; the right is cold when the left is hot. The horizontal walls are assumed to be insulated. The nanofluid in the cavity is considered as incompressible, Newtonian and laminar flow. The nanoparticles are assumed to have a shape and a uniform size. However, it is supposed that the two fluid phases and nanoparticles are in a state of thermal equilibrium and they sink at the same speed. The thermophysical properties of nanofluids are assumed to be constant at the exception of the variation of density in the force of buoyancy, which is based on the approximation of Boussinesq values.