Heat Transfer Characteristics of Turbulent Flames in Three-Dimensional Furnaces

2002 ◽  
Author(s):  
Essam E. Khalil
Keyword(s):  
Heat Transfer ◽  
Flow Pattern ◽  
Air Flow ◽  
Three Dimensional ◽  
Flow Regimes ◽  
Turbulent Flames ◽  
Shear Stresses ◽  
Governing Equations ◽  
Combustion Chambers ◽  
Local Flow

The recent advances in numerical methods and the vast development of computers have directed the designers to better development and modifications to air-flow pattern and heat transfer in combustion chambers. Extensive efforts are exerted to adequately predict the air velocity and turbulence intensity distributions in the combustor zones, and to reduce the air pollution and noise abatement to ultimately produce quite and energy efficient combustor systems. The present work utilizes mathematical modeling techniques to primarily predict what happens in three-dimensional combustion chambers simulating boiler furnaces, and areo engines in terms of flow regimes and interactions. The present work also demonstrates the effect of chamber design and operational parameters on performance, wall shear stresses, and vorticity under various operating parameters. The governing equations of mass, momentum and energy are commonly expressed in a preset form with source terms to represent pressure radients, turbulence and viscous action. The physical and chemical characteristics of the air and fuel are obtained from tabulated data in the literature. The flow regimes and heat transfer plays an important role in the efficiency and utilization of energy. The behavior was found to be strongly dependent on turbulent shear, mixing, blockage, wall conditions and location of fuel and air inlets. Eddies can be strong enough to have higher velocities typically near reactants supply openings. Excessive transverse flow velocities cause extra macromixing; the air flow regimes are complex and of three-dimensional nature; with the advance of computational techniques it is possible to accurately simulate three-dimensional flows. The results reported in this work were obtained with the aid of the three-dimensional program 3DCOMB; applied to axisymmetrical and three-dimensional complex geometry with and without swirl. The present numerical grid comprises, typically, 144000-grid node covering the combustion chamber volume in the X, R or Y and Z coordinates directions. The numerical residual in the governing equations typically less than 0.001%. A modified grid generation formula was proposed and incorporated in the present work. Examples of large industrial furnaces are shown and were in good agreement with available measurements in the open literature. One may conclude that flow patterns, turbulence and heat transfer in combustors are strongly affected by the inlet swirl, inlet momentum ratios, combustor geometry; both micro and macro mixing levels are influential. Greater tangential velocities and turbulence characteristics are demonstrated in situations with higher swirl intensities. The present modeling capabilities can adequately predict the local flow pattern and turbulence kinetic energy levels in complex combustors.

On the Mathematical Modeling of Heat Transfer Characteristics of Turbulent Flames in Industrial Furnaces

2002 ◽  
Author(s):  
Essam E. Khalil
Keyword(s):  
Mathematical Modeling ◽  
Heat Transfer ◽  
Flow Pattern ◽  
Three Dimensional ◽  
Flow Regimes ◽  
Wall Heat Transfer ◽  
Governing Equations ◽  
Heat Transfer Characteristics ◽  
Combustion Chambers ◽  
Transfer Characteristics

The recent advances in numerical methods and the vast development of computers had directed the designers to better development and modifications to air flow pattern and heat transfer in combustion chambers. Extensive efforts are exerted to adequately predict the air velocity and turbulence intensity distributions in the combustor zones and to reduce the emitted pollution and noise abatement to ultimately produce quite and energy efficient combustor systems. The present work fosters mathematical modeling techniques to primarily predict what happens in three-dimensional combustion chambers simulating boiler furnaces, areo engines in terms of flow regimes and interactions. The present work also demonstrates the effect of chamber design and operational parameters on performance, wall heat transfer under various operating parameters. The governing equations of mass, momentum and energy are commonly expressed in a preset form with source terms to represent pressure gradients, turbulence and viscous action. The physical and chemical characteristics of the air and fuel are obtained from tabulated data in the literature. The flow regimes and heat transfer play an important role in the efficiency and utilization of energy. The results are obtained in this work with the aid of the three-dimensional program 3DCOMB; applied to axisymmetrical and three-dimensional complex geometry with and without swirl with liquid or gaseous fuels. The present numerical grid arrangements cover the combustion chamber in the X, R or Y and Z coordinates directions. The numerical residual in the governing equations is typically less than 0.001%. The obtained results include velocity vectors, turbulence intensities and wall heat transfer distributions in combusors. Examples of large industrial furnaces are shown and are in good agreement with available measurements in the open literature. One may conclude that flow patterns, turbulence and heat transfer in combustors are strongly affected by the inlet swirl, inlet momentum ratios, combustor geometry. Both micro and macro mixing levels are influential. The present modeling capabilities can adequately predict the local flow pattern and heat transfer characteristics in Complex combustors. Proper representation of the heat transfer and radiation flux is important in adequate predictions of large furnace performance.

Heat Transfer Characteristics in Cylindrical Furnaces and Combustors

2003 ◽  
Author(s):  
Essam E. Khalil
Keyword(s):  
Heat Transfer ◽  
Complex Geometry ◽  
Three Dimensional ◽  
Heat Transfer Fluid ◽  
Operational Parameters ◽  
Governing Equations ◽  
Heat Transfer Characteristics ◽  
Combustion Chambers ◽  
Local Flow ◽  
Transfer Characteristics

The recent advances in numerical methods and the vast development of computers had directed the designers to better development and modifications to airflow pattern and heat transfer in combustion chambers. Extensive efforts are exerted to adequately predict the heat transfer characteristics in the combustor zones and to reduce the emitted pollution and noise abatement to ultimately produce quite and energy efficient combustor systems. The Present paper fosters mathematical modeling techniques to primarily predict what happens in cylindrical and three-dimensional combustion chambers simulating boiler and industrial furnaces in terms of heat transfer characteristics and interactions. The present work also demonstrates the effect of chamber design and operational parameters on performance under various operating parameters. The governing equations of mass, momentum and energy are commonly expressed in a preset form with source terms to represent effects of pressure gradients, turbulence and heat transfer. Fluid flow and heat transfer characteristics in combustors play an important role in the efficiency, thermal balance and performance. The present paper discusses the various combustion modeling assumptions and those of the heat transfer in furnaces. The results are obtained in this work with the aid of the three-dimensional program 3DCOMB; applied to axisymmetrical and three-dimensional complex geometry with and without swirl. The numerical grid comprises, typically, 288000-grid node covering the combustion chamber volume in the X, R or Y and Z coordinates directions. The numerical residual in the governing equations typically less than 0.001%. Examples of large industrial furnaces are shown and are in good agreement with available measurements in the open literature. One may conclude that heat transfer characteristics in combustors are strongly affected by the inlet swirl, inlet momentum ratios, combustor geometry; both micro and macro mixing levels are influential. Higher tangential velocities and turbulence characteristics are demonstrated in situations with higher swirl intensities. The present modeling capabilities can adequately predict the local flow pattern and turbulence kinetic energy levels in complex combustors.

Flow Past a Spinning Sphere With Surface Blowing and Heat Transfer

2005 ◽  
Vol 127 (1) ◽  
pp. 163-171 ◽  
Author(s):  
H. Niazmand ◽  
M. Renksizbulut
Keyword(s):  
Heat Transfer ◽  
Three Dimensional ◽  
Flow Regimes ◽  
Solid Sphere ◽  
Temporal Variations ◽  
Transfer Coefficients ◽  
Transfer Rates ◽  
Particle Spin ◽  
Flow Past ◽  
Angular Velocities

Computations are performed to determine the transient three-dimensional heat transfer rates and fluid forces acting on a stream-wise spinning sphere for Reynolds numbers in the range 10⩽Re⩽300 and angular velocities Ωx⩽2. In this Re range, classical flow past a solid sphere develops four different flow regimes, and the effects of particle spin are studied in each regime. Furthermore, the combined effects of particle spin and surface blowing are examined. Sphere spin increases drag in all flow regimes, while lift shows a nonmonotonic behavior. Heat transfer rates are not influenced by spin up to a certain Ωx but increase monotonically thereafter. An interesting feature associated with sphere spin is the development of a special wake regime such that the wake simply spins without temporal variations in its shape. For this flow condition, the magnitudes of the lift, drag, and heat transfer coefficients remain constant in time. Correlations are provided for drag and heat transfer.

scholarly journals Heat Transfer Enhancement by Coupling of Carbon Nanotubes and SiO2 Nanofluids: A Numerical Approach

Processes ◽  
2019 ◽  
Vol 7 (12) ◽  
pp. 937 ◽  
Author(s):  
Fitnat Saba ◽  
Saima Noor ◽  
Naveed Ahmed ◽  
Umar Khan ◽  
Syed Tauseef Mohyud-Din ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Carbon Nanotubes ◽  
Three Dimensional ◽  
Numerical Approach ◽  
Skin Friction Coefficient ◽  
Squeezing Flow ◽  
Hybrid Nanofluid ◽  
Governing Equations ◽  
Similarity Transformations ◽  
Rotating Channel

This article comprises the study of three-dimensional squeezing flow of (CNT-SiO2/H2O) hybrid nanofluid. The flow is confined inside a rotating channel whose lower wall is stretchable as well as permeable. Heat transfer with viscous dissipation is a main subject of interest. We have analyzed mathematically the benefits of hybridizing SiO 2 -based nanofluid with carbon nanotubes ( CNTs ) nanoparticles. To describe the effective thermal conductivity of the CNTs -based nanofluid, a renovated Hamilton–Crosser model (RHCM) has been employed. This model is an extension of Hamilton and Crosser’s model because it also incorporates the effect of the interfacial layer. For the present flow scenario, the governing equations (after the implementation of similarity transformations) results in a set of ordinary differential equations (ODEs). We have solved that system of ODEs, coupled with suitable boundary conditions (BCs), by implementing a newly proposed modified Hermite wavelet method (MHWM). The credibility of the proposed algorithm has been ensured by comparing the procured results with the result obtained by the Runge-Kutta-Fehlberg solution. Moreover, graphical assistance has also been provided to inspect the significance of various embedded parameters on the temperature and velocity profile. The expression for the local Nusselt number and the skin friction coefficient were also derived, and their influential behavior has been briefly discussed.

A Numerical Study of Three-Dimensional Convective Heat Transfer From a Window Covered by a Simple Partially-Open Plane Blind

2008 ◽  
Author(s):  
Patrick H. Oosthuizen ◽  
Murat Basarir ◽  
David Naylor
Keyword(s):  
Heat Transfer ◽  
Numerical Study ◽  
Three Dimensional ◽  
Side Surface ◽  
Governing Equations ◽  
Three Dimensional Flow ◽  
Buoyancy Forces ◽  
Fluid Properties ◽  
Higher Temperature ◽  
Open Plane

Heat transfer from the room-side surface of a window covered by a plane blind to the surrounding room has been considered. The window is at a higher temperature than the air in the room. There is an open gap between the blind system and the window at the top of the window and the effect of the size of this gap on the window-to-air heat transfer rate has been numerically examined. Three-dimensional flow has been considered. The flow has been assumed to be steady and laminar and it has been assumed that the fluid properties are constant except for the density change with temperature which gives rise to the buoyancy forces, this having been treated by using the Boussinesq approach. It has also been assumed that the flow is symmetrical about the vertical centre-plane of the window. The solution has been obtained by numerically solving the full three-dimensional form of the governing equations, these equations being written in terms of dimensionless variables. Results have only been obtained for a Prandtl number of 0.7. The effects of the other dimensionless parameters on the window Nusselt number have been numerically determined.

Numerical Computations of Flow Regimes in Enclosed Spaces

2012 ◽  
Author(s):  
Ahmed E. A. El Degwy ◽  
Sami M. Morkos ◽  
Ashraf S. Sabry ◽  
Essam E. Khalil
Keyword(s):  
Three Dimensional ◽  
Numerical Data ◽  
Flow Regimes ◽  
Efficient Design ◽  
Governing Equations ◽  
Healthcare Facilities ◽  
Energy Efficiency Improvement ◽  
Optimum Energy ◽  
Inlet Conditions ◽  
Modelling Assumptions

This paper is devoted to critically analyse the simulation validity of flow regimes in large rooms and enclosed spaces using commercially available computational fluid dynamics code. This assessment is carried out through detailed comparisons between previous experimental and numerical data as well as present numerical data. Governing equations of mass, momentum, energy and species are solved numerically to predict the air flow patterns and thermal behaviour in rooms and healthcare facilities. The present paper is divided to several sections that review the previous research in open literature and briefly describe the governing equations, boundary and inlet conditions, as well as modelling assumptions. The turbulence characteristics of the flow is represented through the two equation turbulence model that solves the transport equations for the kinetic energy of turbulence k and its dissipation rate ε in full three dimensional domain under steady state conditions. Energy efficiency improvement in air-conditioned buildings applications was found to depend mainly on the design configurations and operating parameters. The room airside design is one of the essential factors that strongly influence the HVAC airflow pattern and consequently the air quality and comfort inside special rooms. After comparing measured and predicted flow regimes in different spaces, a brief summary of conclusions with some recommendations to facilitate the development of optimum energy efficient design are presented.

Heat Transfer Characteristics of a Swirling Laminar Impinging Jet

2009 ◽  
Vol 132 (1) ◽  
Author(s):  
Koichi Ichimiya ◽  
Koji Tsukamoto
Keyword(s):  
Heat Transfer ◽  
Three Dimensional ◽  
Local Heat Transfer ◽  
Impinging Jet ◽  
Local Heat ◽  
Experimental Results ◽  
Governing Equations ◽  
Constant Wall Temperature ◽  
Numerical Heat Transfer ◽  
Narrow Space

This paper describes the characteristics of the heat transfer and flow of a swirling laminar impinging jet in a comparatively narrow space with a confined wall. Air is impinged on a flat surface with constant wall temperature. The heat transfer and flow field were analyzed numerically by solving three-dimensional governing equations. Heat transfer experiment and flow visualization were also performed. Numerical heat transfer was compared with experimental results. Temperature distribution and velocity vectors in the space were obtained for various swirl numbers at Reynolds number Re=2000. The numerical and experimental results show that the swirling jet enhances or depresses the local heat transfer, and the average Nusselt number ratio with and without swirl takes a peak at a certain swirl number.

scholarly journals Numerical Study of Fluid Flow and Heat Transfer Characteristics in Solid and Perforated Finned Heat Sinks Utilizing a Piezoelectric Fan

2019 ◽  
Vol 25 (7) ◽  
pp. 83-103
Author(s):  
Ayser Shamil Salman ◽  
Mohammed A. Nima
Keyword(s):  
Heat Transfer ◽  
Stokes Equations ◽  
Numerical Study ◽  
Air Flow ◽  
Experimental Studies ◽  
Three Dimensional ◽  
Heat Sinks ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Flow Generator

Numerical study is adapted to combine between piezoelectric fan as a turbulent air flow generator and perforated finned heat sinks. A single piezoelectric fan with different tip amplitudes placed eccentrically at the duct entrance. The problem of solid and perforated finned heat sinks is solved and analyzed numerically by using Ansys 17.2 fluent, and solving three dimensional energy and Navier–Stokes equations that set with RNG based k−ε scalable wall function turbulent model. Finite volume algorithm is used to solve both phases of solid and fluid. Calculations are done for three values of piezoelectric fan amplitudes 25 mm, 30 mm, and 40 mm, respectively. Results of this numerical study are compared with previous both numerical and experimental studies and give a good agreement. Numerical solution is invoked to explain the behavior of air flow and temperature distribution for two types of circular axial and lateral perforations. For each type, all the results are compared with an identical solid finned heat sink. Perforations show a remarkable enhanced in the heat transfer characteristics. The results achieved enhancement in the heat transfer coefficient about 12% in axial perforation and 25% in the lateral perforation at the maximum fan amplitude.  

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