Fully developed mixed convection of nanofluids in microtubes at constant wall temperature: Anomalous heat transfer rate and thermal performance

2017 ◽  
Vol 28 (3) ◽  
pp. 721-731 ◽  
Author(s):  
S.J. Hosseini ◽  
A. Malvandi ◽  
S.A. Moshizi ◽  
M. Zamani
Keyword(s):  
Heat Transfer ◽  
Mixed Convection ◽  
Heat Transfer Rate ◽  
Thermal Performance ◽  
Wall Temperature ◽  
Transfer Rate ◽  
Constant Wall Temperature ◽  
Anomalous Heat Transfer ◽  
Anomalous Heat

scholarly journals Premium jet cooling with two ribs over flat plate utilizing nanofluid mixed convection

2017 ◽  
Vol 21 (2) ◽  
pp. 963-976 ◽  
Author(s):  
Wael El-Maghlany ◽  
Mohamed Teamah ◽  
A.E. Kabeel ◽  
Ahmed Hanafy
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Mixed Convection ◽  
Flat Plate ◽  
Heat Transfer Rate ◽  
Thermal Performance ◽  
Transfer Rate ◽  
Richardson Number ◽  
Volume Fraction ◽  
Solid Volume Fraction

In this study, a numerical simulation of the thermal performance of two ribs mounted over a horizontal flat plate and cooled by Cu-water nanofluid is performed. The plate is heated and maintained at a constant temperature and cooled by mixed convection of laminar flow at a relatively low temperature. The top wall is considered as an adiabatic condition. The effects of related parameters such as Richardson number (0.01 ? Ri ? 10), the solid volume fraction (0.01 ? ? ? 0.06), the distance ratio between the two ribs (d/W = 5, 10, and 15), and the rib height ratio (b/W = 1, 2, and 3) on the ribs thermal performance are studied. The numerical simulation results indicate that the heat transfer rate is significantly affected by the distance and the rib height. The heat transfer rate is improved by increasing the nanoparticles volume fraction. The influence of the solid volume fraction with the increase of heat transfer is more noticeable for lower values of the Richardson number. The numerical results are summarized in the effect of pertinent parameters on the average Nusselt number with the assistance of both streamlines and isothermal ones. Throughout the study, the Grashof and Prandtl numbers, for pure water are kept constant at 103 and 6.2, respectively. The numerical work was displayed out using, an in-house computational fluid dynamic code written in FORTRAN, which discretizes non-dimensional forms of the governing equations using the finite volume method and solves the resulting system of equations using Gauss-Seidal method utilizing a tri diagonal matrix algorithm.

622 Heat transfer rate of gas flow through micro-tube with constant wall temperature

2015 ◽  
Vol 2015.68 (0) ◽  
pp. 253-254
Author(s):  
Taiki NAKAMURA ◽  
Seiryu MATSUSHITA ◽  
Chungpyo HONG ◽  
Yutaka ASAKO
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Rate ◽  
Wall Temperature ◽  
Transfer Rate ◽  
Gas Flow ◽  
Constant Wall Temperature ◽  
Flow Through

scholarly journals Heat Transmission Reinforcers Induced by MHD Hybrid Nanoparticles for Water/Water-EG Flowing over a Cylinder

Coatings ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 623
Author(s):  
Firas A. Alwawi ◽  
Mohammed Z. Swalmeh ◽  
Amjad S. Qazaq ◽  
Ruwaidiah Idris
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Volume Fraction ◽  
Liquid Velocity ◽  
Flow Characteristics ◽  
Hybrid Nanoparticles ◽  
Critical Parameters ◽  
Heat Transmission ◽  
Constant Wall Temperature

The assumptions that form our focus in this study are water or water-ethylene glycol flowing around a horizontal cylinder, containing hybrid nanoparticles, affected by a magnetic force, and under a constant wall temperature, in addition to considering free convection. The Tiwari–Das model is employed to highlight the influence of the nanoparticles volume fraction on the flow characteristics. A numerical approximate technique called the Keller box method is implemented to obtain a solution to the physical model. The effects of some critical parameters related to heat transmission are also graphically examined and analyzed. The increase in the nanoparticle volume fraction increases the heat transfer rate and liquid velocity; the strength of the magnetic field has an adverse effect on liquid velocity, heat transfer, and skin friction. We find that cobalt nanoparticles provide more efficient support for the heat transfer rate of aluminum oxide than aluminum nanoparticles.

Thermal Performance Assessment of Turbulent Flow Through Dimpled Tubes

2010 ◽  
Author(s):  
Pornchai Nivesrangsan ◽  
Somsak Pethkool ◽  
Kwanchai Nanan ◽  
Monsak Pimsarn ◽  
Smith Eiamsa-ard
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Friction Factor ◽  
Heat Transfer Rate ◽  
Thermal Performance ◽  
Transfer Rate ◽  
Staggered Arrangement ◽  
Plain Tube ◽  
Pitch Ratio ◽  
Surface Patterns

This paper presents the heat transfer augmentation and friction factor characteristics by means of dimpled tubes. The experiments were conducted using the dimpled tubes with two different dimpled-surface patterns including aligned arrangement (A-A) and staggered arrangement (S-A), each with two pitch ratios (PR = p/Di = 0.6 and 1.0), for Reynolds number ranging from 9800 to 67,000. The experimental results achieved from the dimpled tubes are compared with those obtained from the plain tube. Evidently, the dimpled tubes with both arrangements offer higher heat transfer rates compared to the plain tube and the dimpled tube with staggered arrangement shows an advantage on the basis of heat transfer enhancement over the dimpled tube with aligned arrangement. The increase in heat transfer rate with reducing pitch ratio is due to the higher turbulent intensity imparted to the flow between the dimple surfaces. The mean heat transfer rate offered by the dimpled tube with staggered arrangement (S-A) at the lowest pitch ratio (PR = 0.6), is higher than those provided by the plain tube and the dimpled tube with aligned arrangement (A-A) at the same PR by around 127% and 8%, respectively. The empirical correlations developed in terms of pitch ratio (PR), Prandtl number (Pr) and Reynolds number, are fitted the experimental data within ±8% and ±2% for Nusselt number (Nu) and friction factor (f), respectively. In addition, the thermal performance factors under an equal pumping power constraint of the dimple tubes for both dimpled-surface arrangements are also determined.

scholarly journals Improved Energy Efficiency of Mixed Convection Heating Process in Eccentric Annulus

2021 ◽  
Vol 13 (8) ◽  
pp. 168781402110391
Author(s):  
Ben Abdelmlek Khaoula ◽  
Ben Nejma Fayçal
Keyword(s):  
Heat Transfer ◽  
Energy Efficiency ◽  
Rayleigh Number ◽  
Mixed Convection ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Rotation Speed ◽  
Numerical Study ◽  
Heating Process ◽  
Eccentric Annulus

This paper deals with a numerical study of mixed convection heat transfer in horizontal eccentric annulus. The inner cylinder is supposed hot and rotating, however the outer one is kept cold and motionless. The numerical problem was solved using COMSOL Multiphysics® which is based on finite element method. The resolution of the partial differential equations was conducted through an implicit scheme with the use of the damped Newton’s method. The present numerical analysis concerns the effect of eccentricity, rotation speed and Rayleigh number on the flow patterns, heat transfer rate, and energy efficiency of the process. It was found that the heat transfer rate increases with the increase of Rayleigh number. In addition, the heat transfer rate drops with the increase of rotation speed. Finally, we have demonstrated that maximum energy efficiency is achieved not only with higher Rayleigh number but also it is maximum with small eccentricity.

A comprehensive review on mixed convection for various patterns of kinematically and thermally induced scenarios within cavities

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Leo Lukose ◽  
Tanmay Basak
Keyword(s):  
Heat Transfer ◽  
Mixed Convection ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Inertial Forces ◽  
Content Type ◽  
Flow Interaction ◽  
Experimental Works ◽  
Solid Obstacles ◽  
S Model

Purpose The purpose of this paper is to address various works on mixed convection and proposes 10 unified models (Models 1–10) based on various thermal and kinematic conditions of the boundary walls, thermal conditions and/ or kinematics of objects embedded in the cavities and kinematics of external flow field through the ventilation ports. Experimental works on mixed convection have also been addressed. Design/methodology/approach This review is based on 10 unified models on mixed convection within cavities. Models 1–5 involve mixed convection based on the movement of single or double walls subjected to various temperature boundary conditions. Model 6 elucidates mixed convection due to the movement of single or double walls of cavities containing discrete heaters at the stationary wall(s). Model 7A focuses mixed convection based on the movement of wall(s) for cavities containing stationary solid obstacles (hot or cold or adiabatic) whereas Model 7B elucidates mixed convection based on the rotation of solid cylinders (hot or conductive or adiabatic) within the cavities enclosed by stationary or moving wall(s). Model 8 is based on mixed convection due to the flow of air through ventilation ports of cavities (with or without adiabatic baffles) subjected to hot and adiabatic walls. Models 9 and 10 elucidate mixed convection due to flow of air through ventilation ports of cavities involving discrete heaters and/or solid obstacles (conductive or hot) at various locations within cavities. Findings Mixed convection plays an important role for various processes based on convection pattern and heat transfer rate. An important dimensionless number, Richardson number (Ri) identifies various convection regimes (forced, mixed and natural convection). Generalized models also depict the role of “aiding” and “opposing” flow and combination of both on mixed convection processes. Aiding flow (interaction of buoyancy and inertial forces in the same direction) may result in the augmentation of the heat transfer rate whereas opposing flow (interaction of buoyancy and inertial forces in the opposite directions) may result in decrease of the heat transfer rate. Works involving fluid media, porous media and nanofluids (with magnetohydrodynamics) have been highlighted. Various numerical and experimental works on mixed convection have been elucidated. Flow and thermal maps associated with the heat transfer rate for a few representative cases of unified models [Models 1–10] have been elucidated involving specific dimensionless numbers. Originality/value This review paper will provide guidelines for optimal design/operation involving mixed convection processing applications.

Numerical simulation of water/alumina nanofluid mixed convection in square lid-driven cavity

2019 ◽  
Vol 30 (5) ◽  
pp. 2781-2807
Author(s):  
Davood Toghraie ◽  
Ehsan Shirani
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Mixed Convection ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Richardson Number ◽  
Hartmann Number ◽  
Two Phase ◽  
Content Type ◽  
Driven Cavity

Purpose The purpose of this paper is to investigate the mixed convection of a two-phase water–aluminum oxide nanofluid in a cavity under a uniform magnetic field. Design/methodology/approach The upper wall of the cavity is cold and the lower wall is warm. The effects of different values of Richardson number, Hartmann number, cavitation length and solid nanoparticles concentration on the flow and temperature field and heat transfer rate were evaluated. In this paper, the heat flux was assumed to be constant of 10 (W/m2) and the Reynolds number was assumed to be constant of 300 and the Hartmann number and the volume fraction of solid nanoparticles varied from 0 to 60 and 0 to 0.06, respectively. The Richardson number was considered to be 0.1, 1 and 5. Aspect ratios were 1, 1.5 and 2. Findings Comparison of the results of this paper with the results of the numerical and experimental studies of other researchers showed a good correlation. The results were presented in the form of velocity and temperature profiles, stream and isotherm lines and Nusselt numbers. The results showed that by increasing the Hartmann number, the heat transfer rate decreases. An increase from 0 to 20 in Hartmann number results in a 20 per cent decrease in Nusselt numbers, and by increasing the Hartmann number from 20 to 40, a 16 per cent decrease is observed in Nusselt number. Accordingly, it is inferred that by increasing the Hartmann number, the reduction in the Nusselt number is decreased. As the Richardson number increased, the heat transfer rate and, consequently, the Nusselt number increased. Therefore, an increase in the Richardson number results in an increase of the Nusselt number, that is, an increase in Richardson number from 0.1 to 1 and from 1 to 5 results in 37 and 47 per cent increase in Nusselt number, respectively. Originality/value Even though there have been numerous investigations conducted on convection in cavities under various configurations and boundary conditions, relatively few studies are conducted for the case of nanofluid mixed convection in square lid-driven cavity under the effect of magnetic field using two-phase model.

scholarly journals Role of Rotating Cylinder toward Mixed Convection inside a Wavy Heated Cavity via Two-Phase Nanofluid Concept

Nanomaterials ◽  
2020 ◽  
Vol 10 (6) ◽  
pp. 1138 ◽  
Author(s):  
Ammar I. Alsabery ◽  
Mohammad Ghalambaz ◽  
Taher Armaghani ◽  
Ali Chamkha ◽  
Ishak Hashim ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Mixed Convection ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Volume Fraction ◽  
Rotating Cylinder ◽  
Alumina Nanoparticles ◽  
Optimum Number ◽  
Two Phase ◽  
Rotation Direction

The mixed convection two-phase flow and heat transfer of nanofluids were addressed within a wavy wall enclosure containing a solid rotating cylinder. The annulus area between the cylinder and the enclosure was filled with water-alumina nanofluid. Buongiorno’s model was applied to assess the local distribution of nanoparticles in the host fluid. The governing equations for the mass conservation of nanofluid, nanoparticles, and energy conservation in the nanofluid and the rotating cylinder were carried out and converted to a non-dimensional pattern. The finite element technique was utilized for solving the equations numerically. The influence of the undulations, Richardson number, the volume fraction of nanoparticles, rotation direction, and the size of the rotating cylinder were examined on the streamlines, heat transfer rate, and the distribution of nanoparticles. The Brownian motion and thermophoresis forces induced a notable distribution of nanoparticles in the enclosure. The best heat transfer rate was observed for 3% volume fraction of alumina nanoparticles. The optimum number of undulations for the best heat transfer rate depends on the rotation direction of the cylinder. In the case of counterclockwise rotation of the cylinder, a single undulation leads to the best heat transfer rate for nanoparticles volume fraction about 3%. The increase of undulations number traps more nanoparticles near the wavy surface.

Experimental Investigation on Thermal Performance of Heat Sink With Two Pairs of Embedded Heat Pipes

2007 ◽  
Author(s):  
Hsiang-Sheng Huang ◽  
Jung-Chang Wang ◽  
Sih-Li Chen
Keyword(s):  
Heat Transfer ◽  
Thermal Resistance ◽  
Heat Transfer Rate ◽  
Thermal Performance ◽  
Heat Sink ◽  
Transfer Rate ◽  
Heat Pipes ◽  
Total Heat ◽  
Heating Power ◽  
Total Heat Transfer

This article provides an experimental method to study the thermal performance of a heat sink with two pairs (outer and inner pair) of embedded heat pipes. The proposed method can determine the heat transfer rate of the heat pipes under various heating power of the heat source. A comprehensive thermal resistance network of the heat sink is also developed. The network estimates the thermal resistances of the heat sink by applying the thermal performance test result. The results show that the outer and inner pairs of heat pipes carries 21% and 27% of the total heat transfer rate respectively, while 52% of the heating power is dissipated from the base plate to the fins. The dominated thermal resistance of the heat sink is the base to heat pipes resistance which is strongly affected by the thermal performance of the heat pipes. The total thermal resistance of the heat sink shows the lowest value, 0.23°C/W, while the total heat transfer rate of the heat sink is 140W and the heat transfer rate of the outer and inner pairs of heat pipes is 30W and 38 W, respectively.

Sign in / Sign up

Export Citation Format

Share Document