Enhancement of Heat Transfer of Mixing Convection in a Vertical Channel by a Moving Block

2013 ◽  
Vol 29 (1) ◽  
pp. 95-107 ◽  
Author(s):  
W.-S. Fu ◽  
J.-C. Huang ◽  
Y.-Y. Wang ◽  
Y. Huang
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Rate ◽  
Channel Flow ◽  
Transfer Rate ◽  
Three Dimensional ◽  
Vertical Channel ◽  
Convection Flow ◽  
Enhancement Of Heat Transfer ◽  
Lower Velocity ◽  
Lower Magnitude

AbstractEnhancement of a heat transfer rate of mixed convection flow in a three-dimensional vertical channel with insertion of a moving slender block is investigated numerically. A slender block is installed along the direction of the channel flow, and the movement of the slender block is in periodic motion and transverse to the channel flow. The interaction between the moving block and the channel flow destroys and suppresses the velocity and thermal boundary layers on the heat surface periodically. Various ratios of the Richardson numbers (Gr/Re2) are simulated. The results show that under a higher velocity of the channel flow and a lower magnitude of Gr/Re2, the enhancement of heat transfer rate is better. Oppositely, under a lower velocity of the channel flow and a higher magnitude of Gr/Re2, the effect of natural convection driven by the buoyancy force is stronger and it is unfavorable to the heat transfer. A counter effect of the heat transfer rate is observed. These phenomena which are seldom analyzed before by numerical simulation are carried out in this study.

A Numerical Study of Three-Dimensional Natural Convective Heat Transfer From a Plate With a “Wavy” Surface

2001 ◽  
Author(s):  
Patrick H. Oosthuizen ◽  
Matt Garrett
Keyword(s):  
Heat Transfer ◽  
Prandtl Number ◽  
Surface Waves ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Three Dimensional ◽  
Wavy Surface ◽  
Surface Waviness ◽  
Dimensionless Amplitude ◽  
The Mean

Abstract Natural convective heat transfer from a wide isothermal plate which has a “wavy” surface, i.e., has a surface which periodically rises and falls, has been numerically studied. The surface waves run parallel to the direction of flow over the surface and have a relatively small amplitude. Two types of wavy surface have been considered here — saw-tooth and sinusoidal. Surfaces of the type considered are approximate models of situations that occur in certain window covering applications, for example, and are also sometimes used to try to enhance the heat transfer rate from the surface. The flow has been assumed to be laminar. Because the surface waves are parallel to the direction of flow, the flow over the surface will be three-dimensional. Fluid properties have been assumed constant except for the density change with temperature that gives rise to the buoyancy forces, this being treated by means of the Boussinesq type approximation. The governing equations have been written in dimensionless form, the height of the surface being used as the characteristic length scale and the temperature difference between the surface temperature and the temperature of the fluid far from the plate being used as the characteristic temperature. The dimensionless equations have been solved using a finite-element method. Although the flow is three-dimensional because the surface waves are all assumed to have the same shape, the flow over each surface thus being the same, and it was only necessary to solve for the flow over one of the surface waves. The solution has the following parameters: the Grashof number based on the height, the Prandtl number, the dimensionless amplitude of the surface waviness, the dimensionless pitch of the surface waviness, and the form of the surface waviness (saw-tooth or sinusoidal). Results have been obtained for a Prandtl number of 0.7 for Grashof numbers up to 106. The effects of Grashof number, dimensionless amplitude and dimensionless pitch on the mean heat transfer rate have been studied. It is convenient to introduce two mean heat transfer rates, one based on the total surface area and the other based on the projected frontal area of the surface. A comparison of the values of these quantities gives a measure of the effectiveness of the surface waviness in increasing the mean heat transfer rate. The results show that while surface waviness increases the heat transfer rate based on the frontal area, the modifications of the flow produced by the surface waves are such that the increase in heat transfer rate is less than the increase in surface area.

Pressure Drop and Heat Transfer Characteristics of Louvered Fin Heat Exchangers

2013 ◽  
Vol 465-466 ◽  
pp. 500-504 ◽  
Author(s):  
Shahrin Hisham Amirnordin ◽  
Hissein Didane Djamal ◽  
Mohd Norani Mansor ◽  
Amir Khalid ◽  
Md Seri Suzairin ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Heat Transfer Rate ◽  
Heat Exchangers ◽  
Transfer Rate ◽  
Three Dimensional ◽  
Considerable Effect ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Louvered Fin

This paper presents the effect of the changes in fin geometry on pressure drop and heat transfer characteristics of louvered fin heat exchanger numerically. Three dimensional simulation using ANSYS Fluent have been conducted for six different configurations at Reynolds number ranging from 200 to 1000 based on louver pitch. The performance of this system has been evaluated by calculating pressure drop and heat transfer coefficient. The result shows that, the fin pitch and the louver pitch have a very considerable effect on pressure drop as well as heat transfer rate. It is observed that increasing the fin pitch will relatively result in an increase in heat transfer rate but at the same time, the pressure drop will decrease. On the other hand, low pressure drop and low heat transfer rate will be obtained when the louver pitch is increased. Final result shows a good agreement between experimental and numerical results of the louvered fin which is about 12%. This indicates the capability of louvered fin in enhancing the performance of heat exchangers.

Effect of a Magnetic Field on the Heat Transfer Rate on Free Convection in a Rectangular Cavity

2005 ◽  
Author(s):  
Gustavo Gutierrez ◽  
Ezequiel Medici
Keyword(s):  
Magnetic Field ◽  
Heat Transfer ◽  
Natural Convection ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Stokes Equations ◽  
Rectangular Cavity ◽  
Convection Flow ◽  
Interesting Phenomenon ◽  
The Magnetic Field

The interaction between magnetic fields and convection is an interesting phenomenon because of its many important engineering applications. Due to natural convection motion the electric conductive fluid in a magnetic field experiences a Lorenz force and its effect is usually to reduce the flow velocities. A magnetic field can be used to control the flow field and increase or reduce the heat transfer rate. In this paper, the effect of a magnetic field in a natural convection flow of an electrically conducting fluid in a rectangular cavity is studied numerically. The two side walls of the cavity are maintained at two different constant temperatures while the upper wall and the lower wall are completely insulated. The coupling of the Navier-Stokes equations with the Maxwell equations is discussed with the assumptions and main simplifications assumed in typical problems of magnetohydrodynamics. The nonlinear Lorenz force generates a rich variety of flow patterns depending on the values of the Grashof and Hartmann numbers. Numerical simulations are carried out for different Grashof and Hartmann numbers. The effect of the magnetic field on the Nusselt number is discussed as well as how convection can be suppressed for certain values of the Hartmann number under appropriate direction of the magnetic field.

Investigation of the effects of geometrical parameters, eccentricity and perforated fins on natural convection heat transfer in a finned horizontal annulus using three dimensional lattice Boltzmann flux solver

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Mahyar Ashouri ◽  
Mohammad Mehdi Zarei ◽  
Ali Moosavi
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Heat Transfer Rate ◽  
Lattice Boltzmann ◽  
Transfer Rate ◽  
Three Dimensional ◽  
Maximum Heat ◽  
Content Type ◽  
Dimensional Lattice ◽  
Fin Spacing

Purpose The purpose of this paper is to investigate the effects of geometrical parameters, eccentricity and perforated fins on natural convection heat transfer in a finned horizontal annulus using three-dimensional lattice Boltzmann flux solver. Design/methodology/approach Three-dimensional lattice Boltzmann flux solver is used in the present study for simulating conjugate heat transfer within an annulus. D3Q15 and D3Q7 models are used to solve the fluid flow and temperature field, respectively. The finite volume method is used to discretize mass, momentum and energy equations. The Chapman–Enskog expansion analysis is used to establish the connection between the lattice Boltzmann equation local solution and macroscopic fluxes. To improve the accuracy of the lattice Boltzmann method for curved boundaries, lattice Boltzmann equation local solution at each cell interface is considered to be independent of each other. Findings It is found that the maximum heat transfer rate occurs at low fin spacing especially by increasing the fin height and decreasing the internal-cylindrical distance. The effect of inner cylinder eccentricity is not much considerable (up to 5.2% enhancement) while the impact of fin eccentricity is more remarkable. Negative fin eccentricity further enhances the heat transfer rate compared to a positive fin eccentricity and the maximum heat transfer enhancement of 91.7% is obtained. The influence of using perforated fins is more considerable at low fin spacing although some heat transfer enhancements are observed at higher fin spacing. Originality/value The originality of this paper is to study three-dimensional natural convection in a finned-horizontal annulus using three-dimensional lattice Boltzmann flux solver, as well as to apply symmetry and periodic boundary conditions and to analyze the effect of eccentric annular fins (for the first time for air) and perforated annular fins (for the first time so far) on the heat transfer rate.

scholarly journals Three-dimensional transient mathematical model to predict the heat transfer rate of a heat pipe

2015 ◽  
Vol 7 (2) ◽  
pp. 168781401456781 ◽  
Author(s):  
S Boothaisong ◽  
S Rittidech ◽  
T Chompookham ◽  
M Thongmoon ◽  
Y Ding ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Mathematical Model ◽  
Heat Pipe ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Three Dimensional

Heat Transfer Enhancement of Channel Flow via Vortex-Induced Vibration of Flexible Cylinder

2014 ◽  
Author(s):  
Junxiang Shi ◽  
Jingwen Hu ◽  
Steven R. Schafer ◽  
Chung-Lung (C. L. ) Chen
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Convective Heat Transfer ◽  
Heat Transfer Rate ◽  
Channel Flow ◽  
Convective Heat ◽  
Thermal Performance ◽  
Transfer Rate ◽  
Thermal Boundary Layer ◽  
Flexible Cylinder

Thermal diffusion in a developed thermal boundary layer is considered as an obstacle for improving the forced convective heat transfer rate of a channel flow. In this work, a novel, self-agitating method that takes advantage of vortex-induced vibration (VIV) is introduced to disrupt the thermal boundary layer and thereby enhance the thermal performance. A flexible cylinder is placed at the centerline of a rectangular channel. The vortex shedding due to the cylinder gives rise to a periodic vibration of the cylinder. Consequently, the flow-structure-interaction (FSI) strengthens the disruption of the thermal boundary layer by vortex interaction with the walls, and improves the mixing process. This new concept for enhancing the convective heat transfer rate is demonstrated by a three-dimensional modeling study at different Reynolds numbers (84∼168). The fluid dynamics and thermal performance are analyzed in terms of vortex dynamics, temperature fields, local and average Nusselt numbers, and pressure loss. The channel with the self-agitated cylinder is verified to significantly increase the convective heat transfer coefficient. When the Reynolds number is 168, the channel with the VIV improves the average Nu by 234.8% and 51.4% as opposed to the clean channel and the channel with a stationary cylinder, respectively.

scholarly journals A Numerical Research of Heat Transfer in Rectangular Fins with Different Perforations

2019 ◽  
Vol 8 (12S) ◽  
pp. 367-371
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Buoyancy Force ◽  
Temperature Drop ◽  
Density Variation ◽  
Transfer Enhancement ◽  
Enhancement Of Heat Transfer ◽  
Numerical Research

Heat Transfer enhancement needs buoyancy force. This is to be achieved by making perforations on fin surfaces. The present paper is a study on the enhancement of heat transfer in terms of density, velocity and temperature with three different perforation geometry (parallel square, inclined square and circular). CFD was used to carry out the study of density variation, velocity and temperature drop among different perforated fins. This type of perforated fin has an improvement in heat transfer rate over its dimensionally equivalent solid fin.

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