Laminar Convection Heat Research Articles

Magnetic mixed convection confined two-sided wavy enclosures having two-sided lid-driven walls containing obstacles with thermal radiation

The present research provides numerical handling of a laminar flow mixed-radiation interaction convection heat transfer within two-sided wavy enclosures containing adiabatic obstacles. The convection process is due to the movements of the enclosure side walls together with the difference in temperature and density. Two designs of the flow domain are recognized, namely, a wavy enclosure containing a square obstacle (D1) or including a cylindrical obstacle (D2). Both the flow domain and the magnetic field are inclined with different angles and impacts of the thermal radiation and heat absorption(generation) are conducted. The Galerkin Finite Element Method associated with the Characteristic-Based Split approach is utilized to solve the governing system. The prime outcomes detected that the growth of the radiation and heat generation parameters enhances the convective process. Also, the increase in the magnetic parameter causes a dominance of the nanofluid friction irreversibility compared to the heat transfer one.

Oseen's Correction to Stokes Drag in the Perspective of Newtonian and Micro-polar Fluid: A Technical Note

This study presents numerical investigations for a laminar steady combined convection heat transfer inside a lid driven cavity filled with different types of nanofluids (CuO-water nanofluid and Al2O3-water nanofluid) under different boundary conditions. The effect of two types of temperature distribution applied at the bottom wall of the cavity is studied.

Experimental investigation of substrate board orientation effect on the optimal distribution of IC chips under forced convection

ABSTRACT Steady-state experiments are conducted under the laminar forced convection heat transfer mode for the cooling of seven asymmetric IC chips (heat sources) mounted at different positions on the substrate board. The board is oriented at different angles, i.e., at 0° (horizontal), 30°, 60°, and 90° (vertical) to study its effect on the cooling of the IC chips. The goal is to determine the optimum configuration (arrangement of these seven IC chips on the board) leading to minimize their maximum temperature. The optimal configuration is determined by employing a hybrid optimization strategy that combines the Artificial neural network (ANN) with Genetic algorithm (GA) which is further validated with suitable experiments. Different correlations are proposed to study the effect of the substrate board orientation on the Nusselt number (cooling rate) and temperature of the IC chips. The results suggest that the temperature of the IC chips is a strong function of their size, positioning on the substrate board, input heat flux, and the substrate board orientation. The temperature of the IC chips is least for the 30° oriented board, as for this case, the maximum surface area of the board is in contact with the flowing air. This helps in cooling the chips effectively in lowering their temperature. The surface area available to dissipate the heat from the IC chips keeps on decreasing after the 30°. For the vertical orientation, the air entering the inlet section of the substrate board hits perpendicular to it. Hence, the temperature of the IC chips is maximum for the vertical substrate board. Air velocity is also crucial for the cooling of the IC chips. There is a temperature drop of 1.42–17.33% for the higher velocity (8 m/s) as compared to the lower one (4.5 m/s).

Heat Transfer Augmentation

This article presents a brief review of various methodologies applied for heat transfer enhancement in laminar flow convection regime. Experimental setup for laminar flow convection heat transfer enhancement using insertions has been explained along with the associated results. Nusselt’s number is found to be a key parameter for investigatigation in order to perceive the enhancement in heat transfer. Similarly, the magnetohydrodynamic mixed convection heat transfer enhancement technique has also been explored. The results of isotherms and fluid flow parameters are discussed which directly affect the heat transfer coefficient. This review article complements the literature in related field and thus will be helpful in order to carry out further experiments in heat transfer enhancement in future.

Heat Transfer Augmentation

This article presents a brief review of various methodologies applied for heat transfer enhancement in laminar flow convection regime. Experimental setup for laminar flow convection heat transfer enhancement using insertions has been explained along with the associated results. Nusselt’s number is found to be a key parameter for investigatigation in order to perceive the enhancement in heat transfer. Similarly, the magnetohydrodynamic mixed convection heat transfer enhancement technique has also been explored. The results of isotherms and fluid flow parameters are discussed which directly affect the heat transfer coefficient. This review article complements the literature in related field and thus will be helpful in order to carry out further experiments in heat transfer enhancement in future.

Laminar entry region mixed convection heat transfer from an inclined rectangular fin array

Purpose The paper aims to investigate the influence of the angle of inclination on mixed convection heat transfer from rectangular plated shrouded fin array computationally. This study has got applications in the various thermal field such as cooling, solar thermal and so on. Design/methodology/approach A computational study is made to evaluate the thermal performance in an inclined channel. Findings Increase in clearance from 0.01 to 0.25 results in an increase of local Nusselt number by is as high as 15% near the exit. At a higher value of Gr with an increase in C* from 0.10, Nu is found to increase by 5.5%. Increase in Gr by 1.37 times results in enhancement of Nu by a maximum of 25-30%. Around 10% increase in overall Nu value is observed with an increase in inclination (i.e. from 30° to 60°). Practical implications This study has got applications in the various thermal field such as cooling, solar thermal and so on. Originality/value Entry region mixed convection in a shrouded inclined finned channel is performed.

3D-printed tubes with complex internal fins for heat transfer enhancement—CFD analysis and performance evaluation

Additive manufacturing (AM), also known as 3D printing technology, is applied to fabricate complex fin structures for heat transfer enhancement at inner surface of tubes, which conventional manufacturing technology cannot make. This work considered rectangular fins, scale fins, and delta fins with staggered alignment at the inner wall of heat transfer tubes for heat transfer enhancement of internal flows. Laminar flow convective heat transfer at 500 < Re < 2000 has been numerically studied, and heat transfer performance of the tubes with 3D-printed interrupted fins has been compared to that with conventional straight continuous fins and smooth tubes. The benefit from heat transfer enhancement and the loss due to increased pumping pressure is evaluated using the total entropy generation rate in the control volume of heat transfer tube. The heat transfer coefficient in tubes with interrupted fins in staggered arrangement can have 2.6 times of that of smooth tube and 1.4 times of that with conventional continuous straight fins. The entropy generation in the tubes with interrupted fins in staggered arrangement only has 30–50% of that of smooth tube or tube with traditional continuous straight fins. The benefit of using interrupted fins in staggered arrangement is significant.

Convection in vertical annular gap formed by stationary heated inner cylinder and rotating unheated outer cylinder

A combined experimental and numerical study was conducted to understand the effect of rotation of outer cylinder on heat transfer from a vertical heated inner cylinder. The dimensionless analysis carried out for this problem underlines that the non dimensional heat transfer depends on the rotation parameter, radius ratio and aspect ratio. Experiments were conducted for the rotational parameter ranging from 0 ≤ ζ ≤ 526 at different heat loads, keeping the aspect ratio and radius ratio unchanged. Numerical simulations have been performed (for a wide range of rotation parameter 0 ≤ ζ ≤ 526 and fixed radius ratio) using a commercial computational fluid dynamics package ANSYS CFX 14. The heat transfer was found to increase progressively with increasing rotational parameter until a certain value of rotational parameter was reached, thereafter a sharp decay in heat transfer resulting from destabilization of flow field was observed. Three laminar heat convection modes, namely; natural, mixed and forced convection dominant, have been observed during the increasing phase of Nusselt number with rotation parameter. The transport mechanism under different heat transfer regimes was explored and discussed with the aid of numerically simulated flow and thermal fields.

Natural Convective Heat Transfer From the Horizontal Isothermal Surface of Polygons of Octagonal and Hexagonal Shapes

Heat transfer often occurs effectively from horizontal elements of relatively complex shapes in natural convective cooling of electronic and electrical devices used in industrial applications. The effect of complex surface shapes on laminar natural convective heat transfer from horizontal isothermal polygons of hexagonal and octagonal flat surfaces facing upward and downward of different aspect ratios has been numerically investigated. The polygons’ surface is embedded in a large surrounding plane adiabatic surface, where the adiabatic surface is in the same plane as the surface of the heated element. For the Boussinesq approach used in this work, the density of the fluid varies with temperature, which causes the buoyancy force, while other fluid properties are assumed constants. The numerical solution of the full three-dimensional form of governing equations is obtained by using the finite volume method-based computational fluid dynamics (CFD) code, FLUENT14.5. The solution parameters include surface shape, dimensionless surface width, different characteristic lengths, the Rayleigh number, and the Prandtl number. These parameters are considered as follows: the Prandtl number is 0.7, the Rayleigh numbers are between 103 and 108, and for various surface shapes the width-to-height ratios are between 0 and 1. The effect of different characteristic lengths has been investigated in defining the Nusselt and Rayleigh numbers for such complex shapes. The effect of these parameters on the mean Nusselt number has been studied, and correlation equations for the mean heat transfer rate have been derived.

Numerical Investigation of Mixed Convection Heat Transfer in Steady Flow Past a Row of Three Square Cylinders

In this paper, the numerical simulations of laminar mixed convection heat transfer from row of three isothermal square cylinders placed in side-by-side arrangement are carried out to understand the behavior of fluid flow around those cylinders under gradual effect of thermal buoyancy and its effect on the evacuation of heat energy. The numerical results are presented and discussed for the range of these conditions: Re = 10 to 40, Ri = 0 to 2 at fixed value of Prandtl number of Pr = 1 and at fixed geometrical configuration. In order to analyze the effect of thermal buoyancy on fluid flow and heat transfer characteristics the main results are illustrated in terms of streamline and isotherm contours. The total drag coefficient as well as average Nusselt number of each cylinder are also computed to determine exactly the effect of buoyancy strength on hydrodynamic force and heat transfer evacuation of each cylinder.

Numerical study of the effects of surface roughness on the mixed convection heat transfer of a laminar flow inside a horizontal curved dimpled tube

The effects of surface roughness on the hydro-thermal performance of laminar mixed convection heat transfer of water have been investigated numerically. The geometry was a semicircular curved horizontal dimples tube with a fixed dimensionless radius of curvature (2R/D = 6.62) and dimensionless roughness height of e/D = 0.1. Under low values of Re (100,200,400) and Gr numbers (20,000.100000,400,000), a constant heat flux was imposed on the tube walls. The three-dimensional governing equations were discretized, using a finite volume method. Dimensionless temperature, convective heat transfer coefficient, axial dimensionless velocity contours, secondary flow vectors, and surface friction coefficient are presented and discussed. The results showed that for identical conditions, the dimpled tube has better thermal performance compared to a smooth tube, especially in low Re values. So that in the low Re values, the dimpled tube has 58.2% higher heat transfer coefficient in comparison with the smooth ones. However, this predominance in thermal characteristics is mitigated by increasing Re number. Additionally, it has been shown that the skin friction coefficient of a curved dimpled tube is less than that of a smooth one in low Reynolds values. Using Colburn j factor and friction coefficient (f), and presenting j/f versus Re shows that the dimpled tube is more efficient at Re < 200.

Heat transfer correlation of viscoplastic fluid flow between two parallel plates and in a circular pipe with viscous dissipation

The present paper investigates the laminar forced convection heat transfer for a generalized Casson fluid flow through a horizontal circular pipe and between two parallel plates maintained at a uniform wall temperature. This study focuses on the effect of yield stress and flow index as well as Peclet number on thermal transport characteristics for both the entrance and the fully developed regions. Because of the viscous character of this kind of fluids, viscous dissipation is taken into account. The regularized Papanastasiou model is considered to avoid the discontinuous-viscosity behavior of the fluid. The governing equations are discretized by means of the finite volume method using the power law scheme. The numerical simulations are conducted using a source code based on the FORTRAN language. The results show that the increase in the Peclet number leads to the increase in the heat transfer rate at the inlet. Furthermore, the Nusselt number decreases when the flow index increases and increases downstream when the Casson number increases. Heat transfer is also significantly improved when viscous dissipation is taken into account. A correlation is proposed at the end of the study; it gives the asymptotic Nusselt number over a wide range of the Casson number (0 ≤ Ca ≤ 20), when viscous dissipation is neglected and taken into account. The comparison between both geometrical configurations shows that, from a thermal point of view, it is more interesting to use parallel plates than a pipe.

Numerical Analysis of Natural Convection and Radiation for Tube Solar Receiver With Glass Window

Conjugate laminar natural convection heat transfer and air flow with radiation of tube solar receiver with glass window were numerically investigated. The discrete ordinate method was used to solve the radiative transfer equation. And the three-dimensional steady-state continuity, Navier–Stokes, and energy equations were solved. The temperature difference based on environment and high temperature surface of receiver is varied from 100 K to 1000 K. The influence of the surface emissivity, heating temperature, convective coefficient, and convective temperature of environment on the heat transfer from the receiver with glass window has also been investigated. The numerical results indicated that the highest temperature of glass window increases and the high temperature area becomes wide, with the temperature of heating wall and surface emissivity increasing. Adopting higher convective coefficient of glass window can reduce the peak magnitude of temperature distribution on glass window of tube receiver up to 45%.

Momentum and heat transfer characteristics of a thin circular disk in Bingham plastic fluids

ABSTRACTThe laminar forced convection momentum and heat transfer aspects of a circular disk oriented normal to the flow and maintained at a constant flux or a constant temperature condition in a stream of a Bingham plastic fluid are studied over wide ranges of parameters as follows: Reynolds number, Re ≤ 150; Prandtl number, 1 ≤Pr ≤ 100; Bingham number, Bn ≤ 100, and thickness-to-diameter ratio, 0.01 ≤ (t/d) ≤ 0.075. The new results on hydrodynamics are analyzed in terms of streamline plots, recirculation length, morphology of yielded/unyielded regions, and drag coefficient, and on heat transfer aspects in terms of isotherm contours, local and average Nusselt number. The flow domain is spanned by the simultaneous existence of the yielded and unyielded sub-regions, depending upon the relative strengths of the fluid inertia (Re) and yield stress (Bn). All else being equal, the rate of heat transfer is higher for an isothermal disk than that for the isoflux condition. Both the drag and average Nusselt number bear a positive dependence on the Bingham number. The drag is influenced only slightly (∼5%) by thickness (t/d); however, the heat transfer can increase on this count by up to 15% under appropriate conditions. Finally, the present numerical results on drag and Nusselt number (in terms of jH-factor) have been correlated via simple empirical equations using the modified definitions of the Reynolds (Re*) and Prandtl number (Pr*), thereby enabling a priori estimation of drag and heat transfer in a new application.

Laminar free convection heat transfer and separated flow structure in a vertical channel with isothermal walls and two adiabatic opposing fins

Results of numerical study of laminar free convection and heat transfer in a vertical plane-parallel channel with two thin adiabatic fins on its walls are presented. The channel has the open inlet and outlet, and its surfaces are maintained at the same temperature. The channel height is unchanged with elongation parameter A = L/w = 10, and the fins are located in the middle of the channel toward each other. Fin height l/w = 0 ÷ 0.4 and Rayleigh number Ra = 102 ÷ 105 are varied in calculations. The effect of these parameters on the flow structure, temperature field, local and integral heat transfer, and gas flow caused by gravitational forces are analyzed in detail. Numerical analysis is based on solving the full Navier–Stokes and energy equations in twodimensional statement and Boussinesq approximation. To determine the dynamic and thermal parameters at the inlet and outlet, the calculation is carried out with two large volumes attached to the inlet and outlet. The features of the flow and heat transfer at separated flow around the channel fins are studied in detail in this work.

The Investigation of the Mixed Convection from a Confined Rotating Circular Cylinder

In this paper, a numerical study on the two-dimensional laminar mixed convective flow and heat transfer from an rotating circular horizontal and isothermal cylinder confined in a horizontal channel. The blockage ratio and the Prandtl number are fixed at 0.05 and 0.7 respectively. The continuity, momentum and energy equations are solved via the finite-volume method. Our results are in very good agreement with those resulting from preceding studies to Ri=0 and a=0, which makes it possible to validate on important extension of present work. The mixed convective flow and heat transfer is simulated by the Reynolds number is studied in the range 1 &lt;Re &lt;40, the Richardson number (Ri) demonstrating the influence of thermal buoyancy ranges from 0 to 1 and for rotational rate from α=0 to α=4. Major emphasis is given to the effect of rotating a circular cylinder on the mixed convection and also on the measurements of the local and average Nusselt numbers are also obtained. Furthermore, the representative streamlines and isotherm patterns are presented and discussed.

Combined Effect of Mixed Convection and Surface Radiation Heat Transfer for Thermally Developing Flow in Vertical Channels

ABSTRACTCombined effect of laminar flow mixed convection and surface radiation heat transfer for thermally developing airflow in a vertical channel heated from a side has been experimentally examined with different thermal and geometric parameters. The channel boundary is made of two isothermal walls and two adiabatic walls, the isothermal parallel wall is heated uniformly and the opposite cold wall temperature is maintained equal to the inlet conditions. The heated wall temperature ranged from 55 to 100°C, Reynolds number ranged from 800 to 2900 and the heat flux was varied from 250 to 870 W/m2. To cover the wide range of Reynolds numbers, two aspect ratios of square and rectangular section were used. Surface radiation from the internal walls is considered through two emissivities i.e. 0.05 and 0.85, to represent weak and strong radiation effects, respectively. From the experiments, surface temperature and Nusselt number distributions of convection and radiation heat transfer are obtained for different heat flux values. Flow structure inside the channel is visualized to observe the flow pattern. The results show the combined effect of laminar flow mixed convection and surface radiation on the total heat transfer rate within the channel. The accumulating buoyancy force and airflow moves together vertically in the upward direction to give significant heat transfer enhancement in the vertical orientation of the channel.

A numerical study of laminar natural convective heat transfer inside a closed cavity with different aspect ratio

Two-dimensional steady-state laminar natural convection was studied numerically for differentially heated air-filled closed cavity with adiabatic top and bottom walls. The temperature of the left heated wall and cooled right wall was assumed to be constant. The governing equations were iteratively solved using the control volume approach. In this paper, the effects of the Rayleigh number and the aspect ratio were examined. Flow and thermal fields were exhibited by means of streamlines and isotherms, respectively.Variations of the maximum stream function and the average heat transfer coefficient were also shown. The average Nusselt number and was correlated to the Rayleigh number based on curve fitting for each aspect ratio. The investigation covered the range 104 ≤ RA ≤ 107 and is done at Prandtl number equal to 0.693. The result shows the average Nusselt number is the increasing function of Rayleigh number. As the aspect ratio increases, Nusselt number decreases along the hot wall of the cavity. As Rayleigh number increases, Nusselt number increases. Result indicates that at constant aspect ratio, with increase in Rayleigh number the heat transfer rate increases.

Influence of Non-linear Thermal Radiation on MHD Double-Diffusive Convection Heat and Mass Transfer of a Non-Newtonian Fluid in a Porous Medium

The present paper deals with the problem of steady, magnetohydrodynamic laminar double-diffusive convection heat and mass transfer of a micropolar fluid over a vertical permeable semi-infinite plate embedded in a uniform porous medium in the presence of non-linear thermal radiation. In addition, the present model allows the influence of heat generation/absorption and first-order chemical reaction. The governing equations are solved efficiently by Runge–Kutta–Fehlberg method with shooting technique. The effects of thermal buoyancy ratio, Schmidt number, chemical reaction parameter, heat generation/absorption and surface suction/injection on the fluid velocity, microrotation, temperature and solute concentration are analyzed. It is found that increase in the inverse Darcy number results in decrease in the velocity and microrotation distributions whereas reverse effects are seen on the temperature and concentration distributions. Also, it is observed that with increase in the magnetic parameter there is decrease in the velocity and microrotation gradient whereas reverse effects are noticed on the temperature and concentration distributions.

Effect of Fluid Yield Stress on Natural Convection From Horizontal Cylinders in a Square Enclosure

ABSTRACTIn this study, laminar natural convection heat transfer to Bingham plastic fluids from two differentially heated isothermal cylinders confined in a square enclosure (with isothermal walls) has been investigated numerically. The governing partial differential equations have been solved over the ranges of the dimensionless parameters, namely, Rayleigh number, 102 to 106, Prandtl number, 10 to 100, and Bingham number, 0.01 to 100, for seven locations of inner cylinders as ±0.25, ±0.2, ±0.1 and 0. These values correspond to the range of Grashof number varying from 10 to 105. The detailed flow and temperature fields are visualized in terms of the streamlines and isotherm contours. Further insights are developed by examining the iso-shear rate contours and the yield surfaces delineating the fluid-like and solid-like regions. The corresponding heat transfer results are analyzed in terms of the distribution of the local Nusselt number along the cylinder surface together with its surface averaged value as functions of the Rayleigh number, Prandtl number, Bingham number, and positions of the cylinders. It is found that the average Nusselt number increases with the increasing values of the Rayleigh number and decreases with the increasing Bingham number. For sufficiently large values of the Bingham number, the average Nusselt number reaches its asymptotic value wherein heat transfer takes place solely by conduction. Based on the present numerical results, simple correlations for the prediction of the average Nusselt number and the limiting Bingham number have been developed. Also, a dimensionless criterion denoting the cessation of convection regime is outlined for this configuration.