A Numerical Study of a Single Bubble Sliding on a Downward Facing Heating Surface

2005 ◽  
Author(s):  
Ding Li ◽  
Sathish Manickam ◽  
Vijay K. Dhir
Keyword(s):  
Heat Transfer ◽  
Numerical Study ◽  
Heating Surface ◽  
Single Bubble ◽  
Bubble Shape ◽  
Heater Surface ◽  
3D Numerical Simulation ◽  
Vapor Interface ◽  
Energy Equations ◽  
Sliding Distance

In this study, a complete 3D numerical simulation of single bubble sliding on a downward facing heater surface is carried out. The continuity, momentum and energy equations are solved using finite difference method and the level-set method is used to capture the liquid-vapor interface. The shape of sliding bubble changes from initially spheroids, to ellipsoids and finally to bubble-cap. The temperature gradient downstream the sliding bubble is much larger than that upstream the bubble. This indicates the sliding bubble enhances the heat transfer significantly. The bubble shape and sliding distance predicted from numerical analysis is compared with the experimental data.

Numerical Study of a Single Bubble Sliding on a Downward Facing Heated Surface

2006 ◽  
Vol 129 (7) ◽  
pp. 877-883 ◽  
Author(s):  
Ding Li ◽  
Vijay K. Dhir
Keyword(s):  
Numerical Study ◽  
Heated Surface ◽  
Three Dimensional ◽  
Single Bubble ◽  
Wall Heat Transfer ◽  
Heater Surface ◽  
Vapor Interface ◽  
Sliding Motion ◽  
Energy Equations ◽  
Sliding Distance

In this study, a complete three-dimensional numerical simulation of single bubble sliding on a downward facing heater surface is carried out. The continuity, momentum, and energy equations are solved using a finite-difference method. Level-set method is used to capture the liquid-vapor interface. The shape of the sliding bubble changes from a sphere, to an ellipsoid and finally to a bubble-cap. The wall heat flux downstream of the sliding bubble is much larger than that upstream of the bubble. This indicates that wall heat transfer is significantly enhanced by sliding motion of the bubble. The bubble shape and sliding distance predicted from numerical simulations is compared with data from experiments.

A Numerical Study of Single Bubble Dynamics During Flow Boiling

2004 ◽  
Author(s):  
Ding Li ◽  
Vijay K. Dhir
Keyword(s):  
Heat Transfer ◽  
Bubble Dynamics ◽  
Numerical Study ◽  
Flow Boiling ◽  
Forced Flow ◽  
Single Bubble ◽  
Horizontal Line ◽  
Vapor Interface ◽  
Single Bubble Dynamics ◽  
Liquid Vapor

Nucleate flow boiling is a liquid-vapor phase-change process associated with high heat transfer rates. A complete 3D numerical simulation of single bubble dynamics on surfaces inclined at 90°, 45° and 30° to the horizontal line and subjected to forced flow parallel to the surface is performed in this work. The continuity, momentum and energy equations are solved with finite difference method and the level-set method is used to capture the liquid-vapor interface. The heat transfer contribution of the micro-layer between the solid wall and evolving liquid-vapor interface is included in this numerical analysis. The effect of dynamic contact angle is also included. The numerical result of bubble growth and sliding distance have been compared with experimental data.

Flow Characteristics in a Three-Dimensional Rectangular Channel With a Pair of Ribs Placed Symmetrically at the Channel Walls

2000 ◽  
Author(s):  
M. Singh ◽  
P. K. Panigrahi ◽  
G. Biswas
Keyword(s):  
Heat Transfer ◽  
Large Scale ◽  
Numerical Study ◽  
Rectangular Channel ◽  
Turbine Blades ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Navier Stokes ◽  
Complex Flow ◽  
Energy Equations

Abstract A numerical study of rib augmented cooling of turbine blades is reported in this paper. The time-dependent velocity field around a pair of symmetrically placed ribs on the walls of a three-dimensional rectangular channel was studied by use of a modified version of Marker-And-Cell algorithm to solve the unsteady incompressible Navier-Stokes and energy equations. The flow structures are presented with the help of instantaneous velocity vector and vorticity fields, FFT and time averaged and rms values of components of velocity. The spanwise averaged Nusselt number is found to increase at the locations of reattachment. The numerical results are compared with available numerical and experimental results. The presence of ribs leads to complex flow fields with regions of flow separation before and after the ribs. Each interruption in the flow field due to the surface mounted rib enables the velocity distribution to be more homogeneous and a new boundary layer starts developing downstream of the rib. The heat transfer is primarily enhanced due to the decrease in the thermal resistance owing to the thinner boundary layers on the interrupted surfaces. Another reason for heat transfer enhancement can be attributed to the mixing induced by large-scale structures present downstream of the separation point.

NUMERICAL SIMULATION OF FLUID FLOW AND HEAT TRANSFER DURING THE INITIAL PHASE LEADING TO STEADY STATE SOLIDIFICATION IN D. C. CAST ALUMINUM ALLOYS

2010 ◽  
Vol 07 (02) ◽  
pp. 349-367 ◽  
Author(s):  
ABDEL ILLAH NABIL KORTI
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Steady State ◽  
Numerical Study ◽  
Direct Chill ◽  
Hot Tearing ◽  
Temperature Fields ◽  
Cast Aluminum ◽  
Surface Cracking ◽  
Energy Equations

In this paper, two dimensional unsteady flow and energy equations are employed for simulating the fluid flow, heat transfer and solidification during direct chill continuous casting of Al-Mg alloy billet. In these processes, the formation of some macro defects such as thermal cracking, hot tearing, surface cracking, etc, has been found to initiate during the starting phase of the operation. In this paper, a numerical study of these developing fluid flow and thermal phenomena from the beginning of casting operation to a steady-state is presented. The computations are based on an iterative deforming finite volume method and a single-domain enthalpy formulation to solve the growth of metal being solidified and the accompanying dynamic fluid flow and thermal behavior. The effect of phase change on convection is accounted for using a Darcy's law-type porous media treatment. The results indicate that the fluid flow and temperature fields change drastically at the initial stage but evolve slowly afterwards.

Numerical Study of Single Bubble Dynamics During Flow Boiling

2007 ◽  
Vol 129 (7) ◽  
pp. 864-876 ◽  
Author(s):  
Ding Li ◽  
Vijay K. Dhir
Keyword(s):  
Bubble Dynamics ◽  
Numerical Study ◽  
Flow Boiling ◽  
Three Dimensional ◽  
Horizontal Surface ◽  
Single Bubble ◽  
Bulk Liquid ◽  
Interface Heat Transfer ◽  
Single Bubble Dynamics ◽  
Energy Equations

Three-dimensional numerical simulation of single bubble dynamics during nucleate flow boiling is performed in this work. The range of bulk liquid velocities investigated is from 0.076to0.23m∕s. The surface orientations at earth normal gravity are varied from an upward facing horizontal surface to vertical through 30, 45, and 60deg. The gravity levels on an upward facing horizontal surface are varied from 1.0ge to 0.0001ge. Continuity, momentum, and energy equations are solved by finite difference method and the level set method is used to capture the liquid-vapor interface. Heat transfer within the liquid micro layer is included in this model. The numerical results have been compared with data from experiments. The results show that the bulk flow velocity, heater surface orientation, and gravity levels influence the bubble dynamics.

Numerical Study of Lateral Merger of Vapor Bubbles During Nucleate Pool Boiling

2003 ◽  
Author(s):  
Abhijit Mukherjee ◽  
Vijay K. Dhir
Keyword(s):  
Heat Transfer ◽  
Bubble Dynamics ◽  
Stokes Equations ◽  
Numerical Study ◽  
Heating Surface ◽  
Nucleate Boiling ◽  
Three Dimensions ◽  
Navier Stokes ◽  
Wall Heat Transfer ◽  
Simple Method

Nucleate boiling is one of the most efficient modes of heat transfer. At the start of nucleate boiling, isolated bubbles appear on the heating surface, the regime known as partial nucleate boiling. Transition from isolated bubbles to fully developed nucleate boiling occurs with increase in wall superheat, when bubbles begin to merge in vertical and lateral directions. The laterally merged bubbles form vapor mushrooms, which stay attached to the heater surface via numerous vapor stems. The present study is performed to numerically analyze the bubble dynamics and heat transfer associated with lateral bubble merger during transition from partial to fully developed nucleate boiling. The complete Navier-Stokes equations in three dimensions along with the continuity and energy equations are solved using the SIMPLE method. The liquid vapor interface is captured using the Level-Set technique. Calculations are carried out for multiple bubble-merger in a line and also in a plane and the bubble dynamics and wall heat transfer are compared to that for a single bubble. The results show that the merger process significantly increases the overall wall heat transfer. It is also found that the orientation of the bubbles strongly influences different heat transfer mechanisms.

Numerical Study of Fluid Flow and Heat Transfer for Al2O3-Water Nanofluid Impinging Jet

2009 ◽  
Author(s):  
Parisa Vaziei ◽  
Omid Abouali
Keyword(s):  
Heat Transfer ◽  
Numerical Study ◽  
Heat Removal ◽  
Turbulent Jets ◽  
Nano Particles ◽  
Working Fluid ◽  
Particle Volume ◽  
Hot Plate ◽  
Volume Fractions ◽  
Energy Equations

In this study a circular confined and submerged jet impinging on a horizontal hot plate is numerically simulated. Water and 36nm Al2O3-water nanofluid with various particle volume fractions are used as a working fluid for cooling the hot plate. Both laminar and turbulent impinging jets in various nozzle to plate distances and Reynolds numbers are considered. For laminar cases Navier-Stokes and energy equations and for turbulent cases RANS and time averaged energy equations were solved numerically to obtain the flowfield and temperature distribution. The turbulence effect was considered with a two equations model. The properties of nanofluid such as thermal conductivity, viscosity and density are modified using the appropriate models. The present study reports the Nusselt number on the hot plate for investigated cases. Temperature difference between the inlet fluid and the hot plate are obtained for different mass flow rates and particle volume fractions and are compared with experimental data for turbulent jets. The results show that using Al2O3 nano-particles in laminar jets enhances the heat transfer but for the turbulent jets Al2O3-water nanofluid has a lower performance for heat removal compared with clear fluid.

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.

Numerical study of the fin effect on mixed convection heat transfer in a lid-driven cavity

2010 ◽  
Vol 225 (2) ◽  
pp. 397-406 ◽  
Author(s):  
A A R Darzi ◽  
M Farhadi ◽  
K Sedighi
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Richardson Number ◽  
Numerical Study ◽  
Convection Heat Transfer ◽  
Thermal Conductivity Ratio ◽  
Driven Cavity ◽  
Ratio Change ◽  
Vertical Walls ◽  
Energy Equations

In this study, the mixed convective heat transfer in a lid-driven cavity was investigated numerically. The finite volume discritization method was used to solve the momentum and energy equations by using the classic Boussinesq incompressible approximation. The cavity vertical walls are insulated whereas the bottom (hot wall) and top (cold wall) surface are maintained at a uniform temperature and fins are located on bottom wall. The effect of fin numbers over the flow field and heat transfer was investigated at various Richardson numbers. Study was carried out for Richardson numbers ranging from 0.01 to 10, fin numbers between 1 and 7, fin height ratio change from 0.05 to 0.3, and thermal conductivity ratio (fin to fluid) from 10 to 104, respectively. The results are presented in the form of streamlines, temperature contours, and Nusselt number distributions. The results show that the Nusselt number increases when the number of fin and fin height decrease. In addition, in all cases an increasing Richardson number caused increasing the relative Nusselt number ( Nu / Nu0). The heat transfer enhancement was observed at low fin numbers (1 and 3) and high Richardson number in comparison with the cavity without fins.

Sign in / Sign up

Export Citation Format

Share Document