Numerical Investigation on Premixed Combustion Using a Fiber Mat Burner With a Boiler

2002 ◽  
Author(s):  
T. Golder ◽  
O. Kawaguchi
Keyword(s):  
Energy Equation ◽  
Solid Phase ◽  
Numerical Study ◽  
Radiant Energy ◽  
Radiative Properties ◽  
Local Thermal Equilibrium ◽  
Combustion Model ◽  
Non Local ◽  
Two Phases ◽  
Energy Equations

This paper presents a numerical study of combustion and multi mode heat transfer in inert porous media. In this case a sintered fiber mat is used. From this work it is understood that the premixed flame is stabilized on the downstream surface of the fiber mat burner. The influence of the flame location, the radiative properties of the porous material, the solid thermal conductivity, and stoichiometry on the flame speed and flame stability are determined using a one-dimensional conduction, convection, radiation, and combustion model. The fiber mat is allowed to emit, absorb, and scatter radiant energy. Non-local thermal equilibrium between the solid and gas was taken into account. Here, separate energy equations for the two phases are introduced, i.e. gas energy equation for the entire system and solid energy equation for the fiber mat. The results indicate that stable combustion can be maintained near the downstream surface of the fiber mat which is mostly controlled by solid-phase radiation.

An Engineering Estimate for Plug-Flow Convection in Porous Media Discarding Fluid Conduction

2009 ◽  
Vol 131 (3) ◽  
Author(s):  
Nihad Dukhan
Keyword(s):  
Porous Media ◽  
Solid Phase ◽  
Plug Flow ◽  
Convection Heat Transfer ◽  
Constant Heat Flux ◽  
Heated Wall ◽  
Local Thermal Equilibrium ◽  
Equilibrium Equations ◽  
Non Local ◽  
Flow Through

Metal and graphite foam are relatively new types of porous materials characterized by having high-solid phase conductivities. In many cooling applications of these materials, including high-power electronics, low-conductivity fluids flow through them, e.g., air. A simple approximate engineering solution for the convection heat transfer inside a two-dimensional rectangular porous media subjected to constant heat flux on one side is presented. The conduction in the fluid is set to zero, and for simplicity, a plug flow is considered. As a result, the non-local-thermal equilibrium equations are significantly simplified and solved. The solid and fluid temperatures decay in what looks like an exponential fashion as the distance from the heated wall increases. The results are in good agreement with one more complex analytical solution in the literature, in the region far from the heated wall only.

scholarly journals The effect of surface regression on the downward flame spread over a solid fuel in a quiescent ambient

2007 ◽  
Vol 11 (2) ◽  
pp. 67-86 ◽  
Author(s):  
Mohammad Ayani ◽  
Javad Esfahani ◽  
Antonio Sousa
Keyword(s):  
Solid Fuel ◽  
Flame Spread ◽  
Solid Phase ◽  
Numerical Study ◽  
Control Volume ◽  
Staggered Grid ◽  
Navier Stokes ◽  
Gas Temperature ◽  
Arrhenius Kinetics ◽  
Energy Equations

The present work is addressed to the numerical study of the transient laminar opposed-flow flame spread over a solid fuel in a quiescent ambient. The transient governing equations - full Navier-Stokes, energy, and species (oxygen and volatiles) for the gas phase, and continuity and energy equations for the solid phase (fuel) with primitive variables are discretized in a staggered grid by a control volume approach. The second-order Arrhenius kinetics law is used to determine the rate of consumption of volatiles due to combustion, and the zero-order Arrhenius kinetics law is used to determine the rate of degradation of solid fuel. The equations for the fluid and solid phases are solved simultaneously using a segregated technique. The physical and thermo-physical properties of the fluid (air) such as density, thermal conductivity, and viscosity vary with temperature. The surface regression of the solid fuel is modeled numerically using a discrete formulation, and the effect upon the results is analyzed. The surface regression of the solid fuel as shown affects on the fuel surface and gas temperature, mass flux and velocity of volatiles on the top surface of fuel, total energy transferred to the solid phase, etc. It seems the results to be realistic. .

Heat Transfer Characteristics of Porous Radiant Burners

1991 ◽  
Vol 113 (2) ◽  
pp. 423-428 ◽  
Author(s):  
T. W. Tong ◽  
S. B. Sathe
Keyword(s):  
Heat Transfer ◽  
Radiative Transfer ◽  
Heat Generation ◽  
Numerical Study ◽  
Radiant Energy ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
High Heat Transfer ◽  
Energy Equations ◽  
Radiant Burners

This paper reports a numerical study of the heat transfer characteristics of porous radiant burners, which have significant advantages over conventional burners. The heat transfer characteristics are investigated using a one-dimensional conduction, convection, and radiation model. The combustion phenomenon is modeled as spatially dependent heat generation. Nonlocal thermal equilibrium between the gas and solid phases is accounted for by using separate energy equations for the two phases. The solid matrix is assumed to emit, absorb, and scatter radiant energy. The spherical harmonics approximation is used to solve the radiative transfer equation. The coupled energy equations and the radiative transfer equations are solved using a numerical iterative procedure. The effects of the various factors on the performance of porous radiant burners are determined. It is revealed that for a given rate of heat generation, large optical thicknesses and high heat transfer coefficients between the solid and gas phases are desirable for maximizing radiant output. Also, low solid thermal conductivities, scattering albedos and flow velocities, and high inlet environment reflectivities produced high radiant output.

scholarly journals A numerical study of the solidification process of a retracting fluid filament

2021 ◽  
Author(s):  
Binh D. Pham ◽  
Truong V. Vu ◽  
Lien V. T. Nguyen ◽  
Cuong T. Nguyen ◽  
Hoe D. Nguyen ◽  
...  
Keyword(s):  
Aspect Ratio ◽  
Flat Surface ◽  
Numerical Study ◽  
Solidification Process ◽  
Navier Stokes ◽  
Front Tracking Method ◽  
Fluid Filament ◽  
Two Phases ◽  
Energy Equations ◽  
Eulerian Grid

In this study, the retraction and solidification of a fluid filament are studied by a front-tracking method/finite difference scheme. The interface between two phases is handled by connected points (Lagrangian grid), which move on a fixed grid domain (Eulerian grid). The Navier-Stokes and energy equations are solved to simulate the problem. Initially, the fluid filament has a shape as half of a cylindrical capsule contact with a cold flat surface. We consider the effect of the aspect ratio (Ar) on the solidification of the fluid filament. It is found that an increase in the aspect ratio (Ar) in the range of 2 – 14 causes the retraction length to increase. The rate of the solidification of a fluid filament decreases when the Ar ratio increases. The solidification time, the solidification height and the tip angle of the fluid filament under the influence of the aspect ratio are also considered. After complete solidification, a small protrusion on the top of the solidified fluid filament is found.

Solid Phase Contribution in the Two-Phase Turbulence Kinetic Energy Equation

1990 ◽  
Vol 112 (3) ◽  
pp. 351-361 ◽  
Author(s):  
T. W. Abou-Arab ◽  
M. C. Roco
Keyword(s):  
Kinetic Energy ◽  
Energy Equation ◽  
Solid Phase ◽  
Density Ratio ◽  
Turbulence Kinetic Energy ◽  
Time Averaging ◽  
Two Phase ◽  
Carrier Fluid ◽  
Double Time ◽  
Energy Equations

This paper presents a multiphase turbulence closure employing one transport equation, namely, the turbulence kinetic energy equation. The proposed form of this equation is different from the earlier formulations in some aspects. The power spectrum of the carrier fluid is divided into two regions, which interact in different ways and at different rates with the suspended particles as a function of the particle-eddy size ratio and density ratio. The length scale is described algebraically. A double-time averaging approach for the momentum and kinetic energy equations is adopted. The resulting turbulence correlations are modeled under less restrictive assumptions comparative to the previous work. The closures for the momentum and kinetic energy equations are given. Comparisons of the predictions with experimental results on liquid-solid jet and gas-solid pipe flow show satisfactory agreement.

A Numerical Study of Spark Ignition

2004 ◽  
Author(s):  
O. Ekici ◽  
V. K. Bokka ◽  
O. A. Ezekoye ◽  
R. D. Matthews
Keyword(s):  
Chemical Kinetics ◽  
Numerical Study ◽  
Control Volume ◽  
Theoretical Models ◽  
Spark Discharge ◽  
Physical Models ◽  
Local Thermal Equilibrium ◽  
Energy Equations ◽  
Volume Method ◽  
Kinetics Of

We present theoretical models to simulate spark discharge and ignition. Two models are presented. The first model considers simplified fluid mechanics with chemistry effects. The second model utilizes more sophisticated flow with no chemistry. The simplified model incorporates physical models of breakdown and chemical kinetics of combustion with species and energy equations solved using a control volume method. A three-step mechanism is used to simulate chemical kinetics for fuel combustion and nitrogen chemistry. Dissociation and ionization in the plasma are included by assuming local thermal equilibrium. The second model simulates a spark discharge in air with more complete physics of flow using a high order numerical method, which shows the evolution of the shock wave and a torus-like plasma kernel.

Numerical Performances Study of Curved Photovoltaic Panel Integrated with Phase Change Material

2020 ◽  
Vol 22 (4) ◽  
pp. 1439-1452
Author(s):  
Mohamed L. Benlekkam ◽  
Driss Nehari ◽  
Habib Y. Madani
Keyword(s):  
Phase Change ◽  
Phase Change Material ◽  
Numerical Study ◽  
Numerical Data ◽  
Navier Stokes ◽  
Photovoltaic Panel ◽  
Pv Panel ◽  
Energy Equations ◽  
Solid Liquid ◽  
Change Material

AbstractThe temperature rise of photovoltaic’s cells deteriorates its conversion efficiency. The use of a phase change material (PCM) layer linked to a curved photovoltaic PV panel so-called PV-mirror to control its temperature elevation has been numerically studied. This numerical study was carried out to explore the effect of inner fins length on the thermal and electrical improvement of curved PV panel. So a numerical model of heat transfer with solid-liquid phase change has been developed to solve the Navier–Stokes and energy equations. The predicted results are validated with an available experimental and numerical data. Results shows that the use of fins improve the thermal load distribution presented on the upper front of PV/PCM system and maintained it under 42°C compared with another without fins and enhance the PV cells efficiency by more than 2%.

Kinematic and Dynamic Parameters of a Liquid-Solid Pipe Flow Using DPIV∕Accelerometry

2007 ◽  
Vol 129 (11) ◽  
pp. 1415-1421 ◽  
Author(s):  
Joseph Borowsky ◽  
Timothy Wei
Keyword(s):  
Pipe Flow ◽  
Solid Phase ◽  
Fluid Phase ◽  
Central Moment ◽  
Steady Flows ◽  
Dynamic Parameters ◽  
Two Phase ◽  
Turbulence Structures ◽  
Two Phases ◽  
Flat Profile

An experimental investigation of a two-phase pipe flow was undertaken to study kinematic and dynamic parameters of the fluid and solid phases. To accomplish this, a two-color digital particle image velocimetry and accelerometry (DPIV∕DPIA) methodology was used to measure velocity and acceleration fields of the fluid phase and solid phase simultaneously. The simultaneous, two-color DPIV∕DPIA measurements provided information on the changing characteristics of two-phase flow kinematic and dynamic quantities. Analysis of kinematic terms indicated that turbulence was suppressed due to the presence of the solid phase. Dynamic considerations focused on the second and third central moments of temporal acceleration for both phases. For the condition studied, the distribution across the tube of the second central moment of acceleration indicated a higher value for the solid phase than the fluid phase; both phases had increased values near the wall. The third central moment statistic of acceleration showed a variation between the two phases with the fluid phase having an oscillatory-type profile across the tube and the solid phase having a fairly flat profile. The differences in second and third central moment profiles between the two phases are attributed to the inertia of each particle type and its response to turbulence structures. Analysis of acceleration statistics provides another approach to characterize flow fields and gives some insight into the flow structures, even for steady flows.

Numerical Study of the Effect of Inlet Constriction on Bubble Growth During Flow Boiling in Microchannels

2005 ◽  
Author(s):  
Abhijit Mukherjee ◽  
Satish G. Kandlikar
Keyword(s):  
Stokes Equations ◽  
Numerical Study ◽  
Flow Boiling ◽  
Navier Stokes ◽  
Channel Cross Section ◽  
Vapor Bubbles ◽  
Reversed Flow ◽  
Cross Sectional ◽  
Parallel Microchannels ◽  
Energy Equations

Flow boiling through microchannels is characterized by nucleation of vapor bubbles on the channel walls and their rapid growth as they fill the entire channel cross-section. In parallel microchannels connected through a common header, formation of vapor bubbles often results in flow maldistribution that leads to reversed flow in certain channels. The reversed flow is detrimental to the heat transfer and leads to early CHF condition. One way of eliminating the reversed flow is to incorporate flow restrictions at the channel inlet. In the present numerical study, a nucleating vapor bubble placed near the restricted end of a microchannel is numerically simulated. The complete Navier-Stokes equations along with continuity and energy equations are solved using the SIMPLER method. The liquid-vapor interface is captured using the level set technique. The results show that with no restriction the bubble moves towards the nearest channel outlet, whereas in the presence of a restriction, the bubble moves towards the distant but unrestricted end. It is proposed that channels with increasing cross-sectional area may be used to promote unidirectional growth of the vapor plugs and prevent reversed flow.

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