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Article
Publication date: 27 May 2014

Shahzada Zaman Shuja and Bekir Yilbas

The heat transfer rates from the body to the working fluid can be improved through altering geometric configurations of the body and its arrangement in the flow system…

Abstract

Purpose

The heat transfer rates from the body to the working fluid can be improved through altering geometric configurations of the body and its arrangement in the flow system. One of the arrangements for this purpose is to locate the body at the channel inlet while the convection current opposes it. Since the flow field in the channel inlet influences the heat transfer rates, changing the aspect ratio and inclination of the body is expected to modify the flow field while enhancing the heat transfer rates. Consequently, investigation into the influence of the aspect ratios and tilting angles of the body on the heat transfer rates in the channel flow becomes essential. The paper aims to discuss these issues.

Design/methodology/approach

Numerical simulation of flow in a channel with the presence of solid block is carried out. The block aspect ratio is changed while keeping the area of the block constant for all aspect ratios. The tilting angle is also incorporated analysis to examine its effect on the Nusselt number.

Findings

The throttling effect of the block at channel inlet accelerates the flow between the channel wall and the block faces. This, in turn modifies the thermal boundary layer around the block. In this case, heat transfer rates increase considerably at the block faces where the flow acceleration suppresses the thermal boundary layer thickness. This is more pronounced for large block tilting angles. The Nusselt number attains low values for the block face opposing to the flow at the channel inlet and the back face of the block. This is attributed to the mixing of the thermal current emanating from the side faces of the block in the region close to the back surface. In this case, thermal boundary layer thickens and the heat transfer rates from the block reduce significantly. The Nusselt number improves with reducing the block aspect ratio, which is particularly true along the side faces of the block. In addition, the influence of the block tilting angle on the Nusselt number is considerable for the low block aspect ratios.

Research limitations/implications

The model study is validated with the previous studies for the drag coefficient. The study covers all the aspects of the flow situations and discusses the resulting fluid field and the heat transfer rates from the block.

Practical implications

It is an interesting work for cooling applications. The block aspect ratio and its tilting angle in the channel influence considerably the flow field and the Nusselt number variation around the block faces.

Social implications

The cooling technology may be improved through implementing the findings of the current work.

Originality/value

It is an original work and it has never been submitted to other journals.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 24 no. 5
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 23 March 2012

Esam M. Alawadhi and Raed I. Bourisliy

This paper presents the heat transfer enhancement from discrete heat sources using a wavy channel.

Abstract

Purpose

This paper presents the heat transfer enhancement from discrete heat sources using a wavy channel.

Design/methodology/approach

The finite element method is utilized to solve the hydrodynamic/thermal problem. The considered geometry consists of a channel formed by two wavy plates with six discrete heat sources placed on upper and lower walls. The global objective is to maximize the heat transfer from the heat sources. The wavy channel enhances heat transfer from the heat sources through the modification of the flow pattern in the channel. The effects of the Reynolds number, Prandtl number, waviness of the wavy wall, and the location of the heat sources on the thermal characteristics of the flow are investigated.

Findings

Results indicate that the wavy channel significantly enhances the heat flow out of the heat sources, with heat sources located at the minimum channel cross sections having the best performance. The Nusselt number increases with an increase in Reynolds number and waviness of the wavy channel. The higher Prandtl number has a positive effect on the heat flow out of the heat sources. The heat transfer enhancement can reaches as high as 120 percent for high Reynolds numbers and waviness of the channel.

Originality/value

The combination of wavy plates and optimum placement of heat sources can lead to better, less expensive thermal management of heat sources in electronic devices.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 22 no. 2
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 15 November 2021

Karthikeyan Paramanandam, Venkatachalapathy S. and Balamurugan Srinivasan

The purpose of this paper is to study the flow and heat transfer characteristics of microchannel heatsinks with ribs, cavities and secondary channels. The influence of…

Abstract

Purpose

The purpose of this paper is to study the flow and heat transfer characteristics of microchannel heatsinks with ribs, cavities and secondary channels. The influence of length and width of the ribs on heat transfer enhancement, secondary flows, flow distribution and temperature distribution are examined at different Reynolds numbers. The effectiveness of each heatsink is evaluated using the performance factor.

Design/methodology/approach

A three-dimensional solid-fluid conjugate heat transfer numerical model is used to study the flow and heat transfer characteristics in microchannels. One symmetrical channel is adopted for the simulation to reduce the computational cost and time. Flow inside the channels is assumed to be single-phase and laminar. The governing equations are solved using finite volume method.

Findings

The numerical results are analyzed in terms of average Nusselt number ratio, average base temperature, friction factor ratio, pressure variation inside the channel, temperature distribution, velocity distribution inside the channel, mass flow rate distribution inside the secondary channels and performance factor of each microchannels. Results indicate that impact of rib width is higher in enhancing the heat transfer when compared with its length but with a penalty on the pressure drop. The combined effects of secondary channels, ribs and cavities helps to lower the temperature of the microchannel heat sink and enhances the heat transfer rate.

Practical implications

The fabrication of microchannels are complex, but recent advancements in the additive manufacturing techniques makes the fabrication of the design considered in this numerical study feasible.

Originality/value

The proposed microchannel heatsink can be used in practical applications to reduce the thermal resistance, and it augments the heat transfer rate when compared with the baseline design.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 32 no. 7
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 4 December 2018

Younes Menni, Ahmed Azzi, Ali J. Chamkha and Souad Harmand

The purpose of this paper is to carry out a numerical study on the dynamic and thermal behavior of a fluid with a constant property and flowing turbulently through a…

Abstract

Purpose

The purpose of this paper is to carry out a numerical study on the dynamic and thermal behavior of a fluid with a constant property and flowing turbulently through a two-dimensional horizontal rectangular channel. The upper surface was put in a constant temperature condition, while the lower one was thermally insulated. Two transverse, solid-type obstacles, having different shapes, i.e. flat rectangular and V-shaped, were inserted into the channel and fixed to the top and bottom walls of the channel, in a periodically staggered manner to force vortices to improve the mixing, and consequently the heat transfer. The flat rectangular obstacle was put in the first position and was placed on the hot top wall of the channel. However, the second V-shaped obstacle was placed on the insulated bottom wall, at an attack angle of 45°; its position was varied to find the optimum configuration for optimal heat transfer.

Design/methodology/approach

The fluid is considered Newtonian, incompressible with constant properties. The Reynolds averaged Navier–Stokes equations, along with the standard k-epsilon turbulence model and the energy equation, are used to control the channel flow model. The finite volume method is used to integrate all the equations in two-dimensions; the commercial CFD software FLUENT along with the SIMPLE-algorithm is used for pressure-velocity coupling. Various values of the Reynolds number and obstacle spacing were selected to perform the numerical runs, using air as the working medium.

Findings

The channel containing the flat fin and the 45° V-shaped baffle with a large Reynolds number gave higher heat transfer and friction loss than the one with a smaller Reynolds number. Also, short separation distances between obstacles provided higher values of the ratios Nu/Nu0 and f/f0 and a larger thermal enhancement factor (TEF) than do larger distances.

Originality/value

This is an original work, as it uses a novel method for the improvement of heat transfer in completely new flow geometry.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 29 no. 10
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 1 August 1998

J.J. Hwang, T.Y. Lia and S.H. Chen

Turbulent fluid flow and heat transfer characteristics are analyzed numerically for fluids flowing through a rotating periodical two‐pass square channel. The smooth walls…

Abstract

Turbulent fluid flow and heat transfer characteristics are analyzed numerically for fluids flowing through a rotating periodical two‐pass square channel. The smooth walls of this two‐pass channel are subject to a constant heat flux. A two‐equation kε turbulence model with modified terms for Coriolis and rotational buoyancy is employed to resolve this elliptic problem. The duct through‐flow rate and rotating speed are fixed constantly; while the wall heat flux into the fluid is varied to examine the rotating buoyancy effect on the heat transfer and fluid flow characteristics. It is disclosed that the changes in local heat transfer due to the rotational buoyancy in the radially outward flow are more significant than those in the radially inward flow. However, the channel averaged heat transfer is altered slightly due to the rotational buoyancy in the both ducts. Whenever the buoyancy effects are sufficiently strong, the flow reversal appears over the leading face of the radially outward‐flow channel, and the radial distance for initiation of flow separation decreases with increasing the buoyancy parameter. A comparison of the present numerical results with the available experimental data by taking buoyancy into consideration is also presented.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 8 no. 5
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 3 April 2007

Shanglong Xu, Dichen Li, Bingheng Lu, Yiping Tang, Chaofeng Wang and Zhen Wang

The purpose of this paper is to adopt rapid prototyping (RP) technology to fabricate self‐hardening calcium phosphate composite (CPC) scaffolds with a controlled internal…

1463

Abstract

Purpose

The purpose of this paper is to adopt rapid prototyping (RP) technology to fabricate self‐hardening calcium phosphate composite (CPC) scaffolds with a controlled internal channel network to facilitate nutrient supplying and cell growth using RP technique and investigate their in vitro performance.

Design/methodology/approach

Porous scaffolds should possess branched channels to ensure uniform cell feeding and even flow of culture medium to promote uniform cell attachment and growth. A new three dimensional (3D) flow channel structure has been designed based on conversation of energy and flow. The CPC scaffold possessing such a channel network was made by indirect solid free form fabrication. Negative model of scaffold was designed by Pro/E software and its epoxy resin mold was fabricated on a sterolithography apparatus and the CPC slurry was filled in these molds. After CPC was self hardened, the mold was baked. The mold was removed by pyrolysis and then the designed scaffold was obtained.

Findings

The sizes of the fabricated scaffolds were consistent with the designed. The average compressive strength of the scaffold is approximately 6.0 MPa. Computational fluid dynamics and perfusion culture results showed that such a 3D flow channel arrangement would lead to a more uniform distribution of flow and cells and good transportation of nutrients.

Research limitations/implications

The size errors of fabricated scaffolds could not escape and perfusion methods were difficult to control.

Originality/value

The basic design concept presented showed great promise for use in bone tissue engineering and fabrication method enhanced the versatility of scaffold fabrication. The designed scaffold structure made it possible to keep integrality of the scaffold when direct observation cells inside the channel by scanning electron microscopy (SEM).

Details

Rapid Prototyping Journal, vol. 13 no. 2
Type: Research Article
ISSN: 1355-2546

Keywords

Article
Publication date: 20 April 2012

Weifeng Wu, Jian Li, Ting Li, Quanke Feng and Xiaoling Yu

The purpose of this paper is to find a solution of laminar liquid flow in asymmetric narrow channels. In many cases, an intuitive solution is much more useful and…

Abstract

Purpose

The purpose of this paper is to find a solution of laminar liquid flow in asymmetric narrow channels. In many cases, an intuitive solution is much more useful and necessary for engineering applications, although numerical solutions can be obtained.

Design/methodology/approach

The Navier‐Stokes equations of laminar liquid flow in asymmetric narrow channels are simplified based on geometric characteristics of narrow channels, physical characteristics of liquid and boundary conditions. The simplified Navier‐Stokes equations are solved theoretically. Verification of the obtained results is carried out based on comparing with the Jeffery‐Hamel flow, which is an exact solution of liquid flow in convergent or divergent channels proposed by Jeffery.

Findings

This paper proposed an intuitive solution of laminar liquid flow in asymmetric narrow channels. Obtained results show that the solution can provide a fairly precise flowrate, when a ratio between the width of the channel and the curvature of the boundary of the asymmetry channel is smaller than 0.2936/Re. Furthermore, the obtained solution of pressure distribution along the channel shows high enough accuracy, even though the Reynolds number reaches to higher than 105.

Research limitations/implications

Because the authors assumed the width of the channel is far smaller than the curvature of the boundary of the asymmetric channel, the obtained results could only fit finite cases. Because the Navier‐Stocks equations were finally simplified into one‐dimensional, it is impossible to forecast separation flows; so the obtained results will fail when the Re number is too big. However, experiments should be carried out further to verify these problems.

Originality/value

This paper proposes an intuitive solution of laminar liquid flow in asymmetric narrow channels, including the pressure distribution along the channel.

Details

Industrial Lubrication and Tribology, vol. 64 no. 3
Type: Research Article
ISSN: 0036-8792

Keywords

Article
Publication date: 26 August 2014

Sahin Ahmed and Ali J. Chamkha

The purpose of this paper is to develop and correct the problem studied by Makinde and Mhone (2005) to a rotating vertical porous channel immersed in a Darcian porous…

Abstract

Purpose

The purpose of this paper is to develop and correct the problem studied by Makinde and Mhone (2005) to a rotating vertical porous channel immersed in a Darcian porous regime in presence of a strong transverse magnetic filled and with the application of thermal radiation. In this investigation, the fluid is considered to be of viscous, electrically conducting, Newtonian and radiating and is optically thin with a relatively low density. Excellent agreement is obtained for exact solutions with those of previously published works.

Design/methodology/approach

In this investigation, a closed form analytical method based on the complex notations for the velocity, temperature and the pressure is developed to solve the governing coupled, non-linear partial differential equations. The accuracy and effectiveness of the method are demonstrated.

Findings

Interestingly observed that, the Lorentizian body force is not act as a drag force as in conventional MHD flows, but as an aiding body force and this will serve to accelerate the flow and boost the primary velocities. Due to the large rotation of the channel, the primary velocities are become flattered and shift towards the walls of the channel. With a rise in Darcian drag force, flow velocity and shear stress are found to reduce. Moreover, increasing thermal radiation and rotation of the channel strongly depress the shear stress, and maximum flow reversal, i.e. back flow is observed due to large Darcian resistance, thermal radiation and rotation.

Research limitations/implications

The analysis is valid for unsteady, two-dimensional laminar flow of an optically thick no-gray gas, electrically conducting, and Newtonian fluid past an isothermal vertical surface adjacent to the Darcian regime with variable surface temperature. An extension to three-dimensional flow case is left for future work.

Practical implications

Practical interest of such study includes applications in magnetic control of molten iron flow in the steel industry, liquid metal cooling in nuclear reactors, magnetic suppression of molten semi-conducting materials and meteorology and in many branches of engineering and science. It is well known that the effect of thermal radiation is important in space technology and high-temperature processes. Thermal radiation also plays an important role in controlling heat transfer process in polymer processing industry.

Originality/value

The paper presents useful conclusions with the help of graphical results obtained from studying exact solutions based on complex notations for Darcian drag force, rotation of the channel and conduction-radiation heat transfer interaction by unsteady rotational flow in a vertical porous channel embedded in a Darcian porous regime under the application hydromagnetic force. The results of this study may be of interest to engineers for heat transfer augmentation and drag reduction in heat exchangers as well as MHD boundary layer control of re-entry vehicles, etc.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 24 no. 7
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 15 June 2022

Abhijit Borah, Sumit Kumar Mehta and Sukumar Pati

The purpose of this paper is to analyze numerically forced convective conjugate heat transfer characteristics for laminar flow through a wavy minichannel.

Abstract

Purpose

The purpose of this paper is to analyze numerically forced convective conjugate heat transfer characteristics for laminar flow through a wavy minichannel.

Design/methodology/approach

The mass and momentum conservation equations for the flow of water in the fluidic domain and the coupled energy conservation equations in both the fluid and solid domain are solved numerically using the finite element method. The exteriors of both the walls are subjected to a uniform heat flux.

Findings

The results reveal that the theoretical model without consideration of the effect of wall thickness always predicts a lower value of average Nusselt number ( Nu¯) as compared to the case of conjugate analysis, although it varies with the thickness as well as material of the wall. For the low amplitude of the wall (α = 0.2), the performance factor (PF) becomes very high for Re in the regime of 5 (⩽) Re (⩽) 15. For any geometrical configurations, conjugate heat transfer analysis predicts higher PF as compared to that of nonconjugate analysis.

Practical implications

The present study finds relevance in several applications, such as solar collectors and heat exchangers used in chemical industries and heating-ventilation and air-conditioning, etc.

Originality/value

To the best of the authors’ knowledge, the analysis of combined influences of the thickness and the material of the wall of the channel together with the geometrical parameters of the channel, namely, amplitude and wavelength on the heat transfer and fluid flow characteristics for flow through wavy minichannel in the laminar regime is reported first time in the literature.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. ahead-of-print no. ahead-of-print
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 2 October 2007

Zhengying Wei, Yiping Tang, Wanhua Zhao and Bingheng Lu

The paper aims to summarize the design theory for labyrinth channels of water saving emitters.

1006

Abstract

Purpose

The paper aims to summarize the design theory for labyrinth channels of water saving emitters.

Design/methodology/approach

On the basis of extracting the structural parameters of labyrinth channels in water saving emitters, the hydraulic performance experiments on the integral emitters fabricated with higher resolution rapid prototyping technology are performed. Then, using multivariable linear regression, formulas of pressure versus flow rate and regression plots for different emitters are induced.

Findings

The formulas of flow rate versus structural parameters are summarized based on the trapezoid‐type channel unit, and verified through experiments. The relationships between flow rate, pressure and structural parameters of channels are established.

Research limitations/implications

The effect of emitter fabrication error on the flow rate is analyzed, which provides a basis for parameterized structural design and accuracy control in the fabrication of future emitters.

Practical implications

The QHn relationship equations are used to design emitters which have flow‐rate errors under both high‐ and low‐water pressure of less than 4 percent. So the QHn relationship equation of the emitter is well proven and accurate which can guide the design for the structure of emitters with trapezoid labyrinth channels.

Originality/value

In this paper, a new stereolithography system has been used to fabricate accurately a drip irrigation emitter with a complex microstructure, which cannot be obtained with conventional RP or other manufacturing processes. Compared to other manufacturing process, this new technique has higher manufacturing accuracy and can reduce the manufacturing cost and time. Furthermore, a design theory for labyrinth channels of water saving emitters is established.

Details

Rapid Prototyping Journal, vol. 13 no. 5
Type: Research Article
ISSN: 1355-2546

Keywords

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