Search results

1 – 10 of 906
Article
Publication date: 1 May 1995

M.A.I. El‐Shaarawi, M.A. Al‐Nimr and M.A. Hader

The paper presents a finite‐difference scheme to solve thetransient conjugated heat transfer problem in a concentricannulus with simultaneously developing hydrodynamic and…

Abstract

The paper presents a finite‐difference scheme to solve the transient conjugated heat transfer problem in a concentric annulus with simultaneously developing hydrodynamic and thermal boundary layers. The annular forced flow is laminar with constant physical properties. Thermal transient is initiated by a step change in the prescribed isothermal temperature of the inner surface of the inside tube wall while the outer surface of the external tube is kept adiabatic. The effects of solid‐fluid conductivity ratio and diffusivity ratio on the thermal behaviour of the flow have been investigated. Numerical results are presented for a fluid of Pr = 0.7 flowing in an annulus of radius ratio 0.5 with various values of inner and outer solid wall thicknesses.

Details

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

Keywords

Article
Publication date: 3 August 2015

Diego C. Knupp, Carolina Palma Naveira-Cotta, Adrian Renfer, Manish K. Tiwari, Renato M Cotta and Dimos Poulikakos

The purpose of this paper is to employ the Generalized Integral Transform Technique in the analysis of conjugated heat transfer in micro-heat exchangers, by combining this hybrid…

Abstract

Purpose

The purpose of this paper is to employ the Generalized Integral Transform Technique in the analysis of conjugated heat transfer in micro-heat exchangers, by combining this hybrid numerical-analytical approach with a reformulation strategy into a single domain that envelopes all of the physical and geometric sub-regions in the original problem. The solution methodology advanced is carefully validated against experimental results from non-intrusive techniques, namely, infrared thermography measurements of the substrate external surface temperatures, and fluid temperature measurements obtained through micro Laser Induced Fluorescence.

Design/methodology/approach

The methodology is applied in the hybrid numerical-analytical treatment of a multi-stream micro-heat exchanger application, involving a three-dimensional configuration with triangular cross-section micro-channels. Space variable coefficients and source terms with abrupt transitions among the various sub-regions interfaces are then defined and incorporated into this single domain representation for the governing convection-diffusion equations. The application here considered for analysis is a multi-stream micro-heat exchanger designed for waste heat recovery and built on a PMMA substrate to allow for flow visualization.

Findings

The methodology here advanced is carefully validated against experimental results from non-intrusive techniques, namely, infrared thermography measurements of the substrate external surface temperatures and fluid temperature measurements obtained through Laser Induced Fluorescence. A very good agreement among the proposed hybrid methodology predictions, a finite elements solution from the COMSOL code, and the experimental findings has been achieved. The proposed methodology has been demonstrated to be quite flexible, robust, and accurate.

Originality/value

The hybrid nature of the approach, providing analytical expressions in all but one independent variable, and requiring numerical treatment at most in one single independent variable, makes it particularly well suited for computationally intensive tasks such as in optimization, inverse problem analysis, and simulation under uncertainty.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 25 no. 6
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 5 May 2015

Jin Wang, Chunwei Gu and Bengt Ake Sunden

The purpose of this paper is to analyze the effect of thermal conductivity on gas turbine blades, and to investigate the contribution of different rib configurations to the heat

Abstract

Purpose

The purpose of this paper is to analyze the effect of thermal conductivity on gas turbine blades, and to investigate the contribution of different rib configurations to the heat flux and the film cooling effectiveness.

Design/methodology/approach

The Renormalization Group (RNG) model with enhanced wall treatment was used for the turbulence modeling, and the SIMPLE algorithm was used to handle the pressure-velocity coupling.

Findings

A flame-shape distribution on the internal wall provides high heat flux compared to a hawk-shape distribution; the film cooling effectiveness on the external wall is enhanced for the lateral film cooling effectiveness by heat conduction and film cooling (convection); by comparing the square-rib and pin-rib configurations, the circular-rib configuration offers a higher film cooling effectiveness on the Aluminum wall.

Research limitations/implications

In the present research, the combination of internal cooling and external cooling is used to predict cooling effectiveness on film-cooled flat plate; two kinds of different plate materials are used to obtain the influence of the thermal conductivity. The successful computational method should give guidelines for potential CFD users in engineering sciences.

Practical implications

The results of the paper are of engineering interest where film cooling and ribbed surfaces are applied. The successful computational method will also serve as guidelines for potential users of CFD in design as well as research and development work.

Originality/value

In the present research, the combination of internal cooling and external cooling is used to predict cooling effectiveness on film-cooled flat plate; two kinds of different plate materials are used to obtain the influence of the thermal conductivity.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 25 no. 4
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 1 June 1999

M.A.I. El‐Shaarawi, M.A. Al‐Nimr and M.M.K. Al Yah

Transient conjugated forced convection in the thermal entry region of a thick‐walled annulus, filled with a homogeneous and isotropic porous medium, has been numerically…

Abstract

Transient conjugated forced convection in the thermal entry region of a thick‐walled annulus, filled with a homogeneous and isotropic porous medium, has been numerically investigated using finite‐difference techniques. Non‐Darcian effects as well as axial conduction of heat have been considered. The flow is assumed to be hydrodynamically fully developed and steady but thermally developing and transient. The thermal transient is initiated by a step change in the prescribed isothermal temperature on the outer surface of the external tube of the annulus while the inner surface of the internal tube is kept adiabatic. A parametric study is carried out to explore the effects of the Darcy number, the inertia term, the Peclet number and the porous medium heat capacity ratio on the transient thermal behavior in a given annulus.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 9 no. 4
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 1 May 2001

M.A.I. El‐Shaarawi and S.A. Haider

Conjugate laminar forced convection heat transfer in the entry region of eccentric annuli is numerically investigated. Heat transfer parameters are presented for a fluid of Pr …

Abstract

Conjugate laminar forced convection heat transfer in the entry region of eccentric annuli is numerically investigated. Heat transfer parameters are presented for a fluid of Pr = 0.7 flowing in an annulus of radius ratio 0.5 for four values of dimensionless eccentricity ranging from 0.1 to 0.7. Solid‐fluid conductivity ratio (KR) is varied to cover the range for practical cases with commonly encountered inner and outer tube thickness. Boundary conditions applied are isothermal heating of the inner surface of the core tube, while the outer surface of the external tube is maintained at the inlet fluid temperature. Limits for KR above which the conjugation can be neglected are obtained.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 11 no. 3
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 9 January 2009

E. Vishnuvardhanarao and Manab Kumar Das

The purpose of this paper is to consider the conjugate heat transfer from a flat plate involving a turbulent plane wall jet. The bottom wall of the solid block is heated by a…

Abstract

Purpose

The purpose of this paper is to consider the conjugate heat transfer from a flat plate involving a turbulent plane wall jet. The bottom wall of the solid block is heated by a constant heat flux.

Design/methodology/approach

High Reynolds number two‐equation model (κϵ) has been used for turbulence modeling. The parameters considered are the conductivity ratio of solid and fluid, the solid slab thickness and the Prandtl number. The Reynolds number considered is 15,000 because the flow becomes fully turbulent and then is independent of the Reynolds number. The range of parameters considered are: conductivity ratio = 1‐1,000, solid slab thickness = 1‐10 and Prandtl number = 0.01‐100.

Findings

The non‐dimensional bottom surface temperature is high for high‐Prandtl number fluid and vice versa. As conductivity ratio increases, it decreases whereas it increases with the increase in slab thickness. Similar trend is observed for the distribution of the interface temperature. The Nusselt number computed based on the interface temperature increases with Prandtl number. It is observed that for the range of parameters considered, local Nusselt number distribution superimposes with each other. The average heat flux at the interface has been computed and found to be equal with average heat flux at the bottom which ensures the overall heat balance.

Originality/value

The study of conjugate heat transfer with a turbulent wall jet will be useful for cooling of heated body.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 19 no. 1
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. 33 no. 1
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 1 April 2005

Bassam A/K and Abu‐Hijleh

The aim of this work is to determine the optimal number and location of the fin(s) for maximum laminar forced convection heat transfer from a cylinder with multiple high…

Abstract

Purpose

The aim of this work is to determine the optimal number and location of the fin(s) for maximum laminar forced convection heat transfer from a cylinder with multiple high conductivity radial fins on its outer surface in cross‐flow, i.e. Nusselt number, over a range of Reynolds numbers.

Design/methodology/approach

The effect of several combinations of number of fins, fin height, and fin(s) tangential location on the average Nusselt number was studied over the range of Reynolds numbers (5‐150). The problem was investigated numerically using finite difference method over a stretched grid. The optimal number and placement of the fins, for maximum Nusselt number, was determined for several combinations of Reynolds number and fin height. The percentage improvement in heat transfer per fin(s) unit length, i.e. cost‐efficiency, was also studied.

Findings

The results indicate that the fin(s) combination with the highest normalised Nusselt number is not necessarily the combination that results in the highest fin cost‐efficiency.

Originality/value

The results of the study can be used to design highly efficient cross‐flow forced convection heat transfer configurations from a horizontal cylinder with minimum cost.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 15 no. 3
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 14 July 2020

Subhasree Dutta, Somnath Bhattacharyya and Ioan Pop

This study aims to numerically analyse the impact of an inclined magnetic field and Joule heating on the conjugate heat transfer because of the mixed convection of an Al2O3–water…

Abstract

Purpose

This study aims to numerically analyse the impact of an inclined magnetic field and Joule heating on the conjugate heat transfer because of the mixed convection of an Al2O3–water nanofluid in a thick wall enclosure.

Design/methodology/approach

A horizontal temperature gradient together with the shear-driven Flow creates the mixed convection inside the enclosure. The nonhomogeneous model, in which the nanoparticles have a slip velocity because of thermophoresis and Brownian diffusion, is adopted in the present study. The thermal performance is evaluated by determining the entropy generation, which includes the contribution because of magnetic field. A control volume method over a staggered grid arrangement is adopted to compute the governing equations.

Findings

The Lorentz force created by the applied magnetic field has an adverse effect on the flow and thermal field, and consequently, the heat transfer and entropy generation attenuate because of the presence of magnetic force. The Joule heating enhances the fluid temperature but attenuates the heat transfer. The impact of the magnetic field diminishes as the angle of inclination of the magnetic field is increased, and it manifests as the volume fraction of nanoparticles is increased. Addition of nanoparticles enhances both the heat transfer and entropy generation compared to the clear fluid with enhancement in entropy generation higher than the rate by which the heat transfer augments. The average Bejan number and mixing-cup temperature are evaluated to analyse the thermodynamic characteristics of the nanofluid.

Originality/value

This literature survey suggests that the impact of an inclined magnetic field and Joule heating on conjugate heat transfer based on a two-phase model has not been addressed before. The impact of the relative slip velocity of nanoparticles diminishes as the magnetic field becomes stronger.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 31 no. 1
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 28 October 2014

Majid Ashouri, Mohammad Behshad Shafii and Hossein Rajabi Kokande

The purpose of this paper is to study the influence of magnetic field on natural convection inside the enclosures partially filled with conducting square solid obstacles. Also…

Abstract

Purpose

The purpose of this paper is to study the influence of magnetic field on natural convection inside the enclosures partially filled with conducting square solid obstacles. Also, the effect of thermal conductivity ratio between the solid and fluid materials is investigated for different number of solid blocks.

Design/methodology/approach

The dimensionless governing equations are transformed into sets of algebraic equations using finite volume method and momentum equations are solved by the SIMPLE algorithm with the hybrid scheme. The validation of the numerical code was conducted by comparing the results of average Nusselt number with previously published works.

Findings

The results indicate that both the magnetic field and solid blocks can significantly affect the flow and temperature fields. It is shown that for a given Rayleigh number, variation of Nusselt number might be increasing or decreasing with change in solid-to-fluid thermal conductivity ratio depending on magnetic field strength and number of solid blocks.

Originality/value

No work has been reported previously on the effect of magnetic field on natural convection flow in a cavity partially filled with square solid blocks. The numerical analysis of conductivity ratio between the solid and fluid materials under the effect of magnetic field have been carried out for the first time.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 24 no. 8
Type: Research Article
ISSN: 0961-5539

Keywords

1 – 10 of 906