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Article
Publication date: 9 August 2011

Omar A. Melhem, Bekir S. Yilbas and S.Z. Shuja

The purpose of this paper is to investigate the heat transfer rates from the kerf surfaces and skin friction at the kerf wall due to the jet impingement in relation to…

Abstract

Purpose

The purpose of this paper is to investigate the heat transfer rates from the kerf surfaces and skin friction at the kerf wall due to the jet impingement in relation to laser cutting process.

Design/methodology/approach

Three‐dimensional modeling for the flow and heat transfer analysis is considered. The numerical scheme using the control volume approach is introduced to solve the governing equations of flow and heat transfer. The k‐w turbulence model is incorporated to account for the turbulence.

Findings

It is found that the Nusselt number and the skin friction remains high in the region next to the kerf inlet and it decreases towards the kerf exit for all kerf thicknesses considered. The flow acceleration in the kerf also results in the second peak of the Nusselt number and the skin friction.

Research limitations/implications

The melting at the kerf surface was omitted and the constant temperature boundary representing the melt surface is incorporated in the analysis. However, care was taken during the mesh generation to avoid grid dependent solutions.

Practical implications

The findings and discussions provide the useful information on the practical laser cutting process, in particular, physical insight into the effect of the kerf thickness on the heat transfer and skin friction.

Originality/value

No previous work has been carried out in three‐dimensional space to predict the heat transfer and skin friction, which are important for practical laser cutting applications. Therefore, the work reported is original.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 21 no. 6
Type: Research Article
ISSN: 0961-5539

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Article
Publication date: 26 October 2012

O. Momin, S.Z. Shuja and B.S. Yilbas

A model study of laser heating process including phase change and molten flow in the melt pool gives physical insight into the process and provides useful information on…

Abstract

Purpose

A model study of laser heating process including phase change and molten flow in the melt pool gives physical insight into the process and provides useful information on the influence of melting parameters. In addition, the predictions reduce the experimental cost and minimize the experimental time. Consequently, investigation into laser control melting of the titanium alloy becomes essential. The purpose of this paper is to do this.

Design/methodology/approach

Laser repetitive pulse heating of titanium surface is investigated and temperature field as well as Marangoni flow in the melt pool is predicted using finite volume approach. The influence of laser scanning speed and laser pulse parameter (defining the laser pulse intensity distribution at the workpiece surface) on temperature distribution and melt size is examined. The experiment is carried out to validate temperature predictions for two consecutive laser pulses.

Findings

The influence of laser scanning speed is significant on the melt pool geometry, which is more pronounced for the laser pulse parameter β=0. Temperature predictions agree with the thermocouple data obtained from the experiment.

Research limitations/implications

Although temperature dependent properties are used in the simulations, isotropy in properties may limit the simulations. The laser canning speed is limited to 0.3 m/s, which is good for surface treatment process, but it may slow for annealing treatments.

Practical implications

The results are very useful to capture insight into the melting process. In addition, the influence of laser scanning speed and laser pulse intensity distribution on the melt formation in the surface vicinity is well presented, which will be useful for those working on laser surface treatment process.

Originality/value

The work is original and findings are new, which demonstrate the influence of laser parameters on the melt pool formation and resulting Marangoni flow.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 22 no. 8
Type: Research Article
ISSN: 0961-5539

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Article
Publication date: 12 June 2009

S.Z. Shuja, B.S. Yilbas and S.M.A. Khan

The purpose of this paper is to consider flow over heat generating bodies in an open‐ends cavity, which finds applications in electronics cooling and industrial…

Abstract

Purpose

The purpose of this paper is to consider flow over heat generating bodies in an open‐ends cavity, which finds applications in electronics cooling and industrial processing. Heat transfer rates depend on the flow situation in the cavity, which is influenced by the cavity inlet and exit port locations, heat transferring body size and its orientation in the cavity, and the cavity size. Consequently, modeling of flow over heat transferring bodies in an open‐ends cavity and examination of the effect of the aspect ratio and orientation of the heat transferring bodies on the flow field and heat transfer rates becomes essential.

Design/methodology/approach

The flow over heat generating solid blocks situated in an open‐ends cavity is considered and the effects of blocks' orientations and aspect ratios on flow field as well as heat transfer rates are examined. A numerical scheme using a control volume approach is introduced to predict flow field in the cavity and heat transfer rates from the blocks.

Findings

It is found that complex flow structure is generated in the cavity due to the aspect ratios and orientations of the blocks. This, in turn, influences significantly heat transfer rates from the blocks in the cavity.

Research limitations/implications

Surface areas of blocks are kept the same and aspect ratio is varied such that the surface area of each block remains the same in the simulations. In addition, Steady flow situation is considered for governing equations of flow and heat transfer in the cavity. However, for the future study transient heating and flow situations can be considered while varying the surface araes of the blocks. This will provide useful information on the circulations in the cavity and the enhancement of heat transfer due to the complex flow structure.

Practical implications

In practice, cooling effectiveness can be improved through changing the aspects ratio of the heat generating bodies in the cavity.

Originality/value

The findings are original and will be useful for the scientists and the design engineers working the specific area of heat transfer and fluid flow.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 19 no. 5
Type: Research Article
ISSN: 0961-5539

Keywords

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Article
Publication date: 1 June 2005

S.Z. Shuja, B.S. Yilbas and M.O. Budair

To investigate the influence of conical and annular nozzle geometric configurations on the flow structure and heat transfer characteristics near the stagnation point of a…

Abstract

Purpose

To investigate the influence of conical and annular nozzle geometric configurations on the flow structure and heat transfer characteristics near the stagnation point of a flat plate with limited heated area.

Design/methodology/approach

The conical and annular conical nozzles were designed such that the exit area of both nozzles is the same and the mass flow rate passing through the nozzles is kept constant for both nozzles. The governing equations of flow and heat transfer are modeled numerically using a control volume approach. The grid independent solutions are secured and the predictions of flow and heat transfer characteristics are compared with the simple pipe flow with the same area and mass flow rate. The Reynolds stress turbulence model is employed to account for the turbulence. A flat plate with a limited heated area is accommodated to resemble the laser heating situations and air is used as assisting gas.

Findings

It is found that nozzle exiting velocity profiles differ considerably with changing the nozzle cone angle. Increasing nozzle cone angle enhances the radial flow and extends the stagnation zone away from the plate surface. The impinging jet with a fully developed velocity profile results in enhanced radial acceleration of the flow. Moreover, the flow structure changes considerably for annular conical and conical nozzles. The nozzle exiting velocity profile results in improved heat transfer coefficient at the flat plate surface. However, the achievement of fully developed pipe flow like velocity profile emanating from a nozzle is almost impossible for practical laser applications. Therefore, use of annular conical nozzles facilitates the high cooling rates from the surface during laser heating process

Research limitations/implications

The results are limited with theoretical predictions due to the difficulties arising in experimental studies.

Practical implications

The results can be used in laser machining applications to improve the end product quality. It also enables selection of the appropriate nozzle geometry for a particular machining application.

Originality/value

This paper provides information on the flow and heat transfer characteristics associated with the nozzle geometric configurations and offers practical help for the researchers and scientists working in the laser machining area.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 15 no. 4
Type: Research Article
ISSN: 0961-5539

Keywords

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Article
Publication date: 1 March 2002

S.Z. Shuja, B.S. Yilbas and M.O. Budair

The gas assisted Iaser heating of engineering surfaces finds wide application in industry. Numerical simulation of the heating process may considerably reduce the cost…

Abstract

The gas assisted Iaser heating of engineering surfaces finds wide application in industry. Numerical simulation of the heating process may considerably reduce the cost spent on experimentation. In the present study, 2‐dimensional axisymmetric flow and energy equations are solved numerically using a control volume approach for the case of a gas assisted laser heating of steel surfaces. Various turbulence models including standard kε, kε YAP, low Reynolds number kε and RSTM models are tested. The low Reynolds number kε model is selected to account for the turbulence. Variable properties of both solid and gas are taken into account during the simulation. Air is considered as an assisting gas impinging the workpiece surface coaxially with the laser beam. In order to validate the presently considered methodology, the study is extended to include comparison of present predictions with analytical solution for the case available in the literature. It is found that the assisting gas jet has some influence on the temperature profiles. This effect is minimum at the irradiated spot center and it amplifies considerably in the gas side. In addition, account for the variable properties results in lower surface temperatures as compared to the constant properties case.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 12 no. 2
Type: Research Article
ISSN: 0961-5539

Keywords

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Article
Publication date: 1 November 2002

B.S. Yilbas, S.Z. Shuja and M.O. Budair

Jet impingement onto surface finds wide application in industry. In laser processing an assisting gas jet is introduced either to shield the surface from oxidation…

Abstract

Jet impingement onto surface finds wide application in industry. In laser processing an assisting gas jet is introduced either to shield the surface from oxidation reactions or initiating exothermic reaction to increase energy in the region irradiated by a laser beam. When an impinging gas jet is used for a shielding purpose, the gas jet enhances the convective cooling of the cavity surface. The convective cooling of the laser formed cavity surface can be simulated through jet impingement onto a cavity with elevated wall temperatures. In the present study, gas impingement onto a slot is considered. The wall temperature of the cavity is kept at elevated temperature similar to the melting temperature of the substrate material. A control volume approach is used to simulate the flow and temperature fields. The Reynolds Stress Turbulence model (RSTM) is employed to account for the turbulence. To examine the effect of cavity depth on the heat transfer characteristics, the depth is varied while keeping the cavity width constant. It is found that impinging jet penetrates into a cavity, which in turn, results in a stagnation region extending into the cavity. An impinging gas jet has considerable effect on the Nusselt number along the side walls of the cavity while the Nusselt number monotonically changes with varying cavity depth.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 12 no. 7
Type: Research Article
ISSN: 0961-5539

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Article
Publication date: 1 May 2001

S.Z. Shuja and B.S. Yilbas

A laminar swirling jet impinging on to an adiabatic solid wall is investigated. The flow field is computed and entropy analysis is carried out for different flow…

Abstract

A laminar swirling jet impinging on to an adiabatic solid wall is investigated. The flow field is computed and entropy analysis is carried out for different flow configurations. The numerical scheme employing a control volume approach is introduced when solving the governing equations of flow and energy. In order to examine the effect of the nozzle exit velocity profile and the swirling velocity on the flow field and entropy generation rate, six nozzle exit velocity profiles and four swirl velocities are considered. It is found that the influence of swirl velocity on the flow field is more pronounced as the velocity profile number reduces. In this case, two circulation cells are generated in the flow field. The total entropy generation increases with increasing swirl velocity for low velocity profile numbers. The Merit number improves for low swirling velocity and high velocity profile numbers.

Details

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

Keywords

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Article
Publication date: 1 December 2002

S.Z. Shuja, B.S. Yilbas and M.O. Budair

The vortex shedding from a rectangular cylinder improves the heat transfer rates. Introducing a ground effect in such a flow system alters the shedding frequency, which in…

Abstract

The vortex shedding from a rectangular cylinder improves the heat transfer rates. Introducing a ground effect in such a flow system alters the shedding frequency, which in turn enables to vary the cooling rates of the cylinder. In the present study a laminar flow passing over a rectangular cylinder with a ground effect is considered. The flow and energy equations are solved numerically using a control volume approach. Strouhal and Stanton number variations due to gap height are computed and the influence of Strouhal number on Stanton number variation behind the cylinder is examined. The study is extended to include the predictions of entropy generation in the solution domain. It is found that shedding frequency increases as gap height reduces and further reduction in gap height results in diminishing of vortex shedding, in which case confined flow is developed in the gap. Heat transfer rates improve when Strouhal number is maximum. In the case of confined flow situation, heat transfer rates enhance substantially in the region close to the top corner of the cylinder, in which case, non‐uniform cooling of the surface is resulted.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 12 no. 8
Type: Research Article
ISSN: 0961-5539

Keywords

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Article
Publication date: 27 March 2009

B.S. Yilbas and S.Z. Shuja

The paper's aim is to provide information on heat transfer and flow characteristics for a jet emerging from a conical nozzle and impinging onto the cylindrical, which…

Abstract

Purpose

The paper's aim is to provide information on heat transfer and flow characteristics for a jet emerging from a conical nozzle and impinging onto the cylindrical, which resembles the laser heating process, for researchers and graduate students working in the laser processing area, which can help them to improve the understanding of the laser machining process.

Design/methodology/approach

A numerical scheme employing the control volume approach is introduced to model the flow and heating situations. The effect of jet velocity on the heat transfer rates and skin friction around the cylindrical cavity subjected to the jet impingement was investigated.

Findings

Increasing jet velocity at nozzle exit enhances the heat transfer rates from the cavity wall and modifies the skin friction at cavity wall, which is more pronounced as the cavity depth increases to 1 mm.

Research limitations/implications

The effects of nozzle cone angle on the flow structure and heat transfer characteristics were not examined, which perhaps limits the general usefulness of the findings.

Practical implications

Very useful information are provided for the laser gas assisted processing, which has a practical importance in machining industry.

Originality/value

This paper provides original information for the effects of the gas jet velocity on the cooling rates of the laser produced cavity.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 19 no. 2
Type: Research Article
ISSN: 0961-5539

Keywords

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Article
Publication date: 1 November 2002

S.Z. Shuja, B.S. Yilbas and M.O. Budair

A confined laminar swirling jet is an interesting research topic due to flow and temperature fields generated in and across the jet. In the present study, a confined…

Abstract

A confined laminar swirling jet is an interesting research topic due to flow and temperature fields generated in and across the jet. In the present study, a confined laminar swirling jet is studied, and flow and temperature fields are simulated numerically using a control volume approach. In order to investigate the influence of the jet exiting (exiting the nozzle and inleting to the control volume) velocity profiles on the flow and heat transfer characteristics, eight different velocity profiles are considered. To identify each velocity profile, a velocity profile number is introduced. Entropy analysis is carried out to determine the total entropy generation due to heat transfer and fluid friction. Merit number is computed for various swirling velocities and velocity profiles. It is found that swirling motion expands the jet in the radial direction and reduces the jet length in the axial direction. This, in turn, reduces the entropy generation rate and improves the Merit number. Increasing velocity profile number enhances the entropy production rate, but improves the Merit number.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 12 no. 7
Type: Research Article
ISSN: 0961-5539

Keywords

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