Numerical Study of an Evaporating Meniscus on a Moving Heated Surface

Volume 3 ◽  
2004 ◽  
Author(s):  
Abhijit Mukherjee ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Stokes Equations ◽  
Numerical Study ◽  
Heated Surface ◽  
Nucleate Boiling ◽  
Two Dimensions ◽  
Temperature Fields ◽  
Navier Stokes ◽  
Wall Heat Transfer ◽  
Parallel Plates

The present study is performed to numerically analyze an evaporating meniscus on a moving heated surface. This phenomenon is similar to the one observed at the base of a vapor bubble during nucleate boiling. The complete Navier-Stokes equations along with continuity and energy equations are solved. The liquid vapor interface is captured using the level set technique. A column of liquid is placed between two parallel plates with an inlet for water at the top to feed the meniscus. The location of water inlet at the top is kept fixed and the bottom wall is imparted with a velocity. Calculations are done in two-dimensions with a fixed distance between the plates. The main objective is to study the velocity and temperature fields inside the meniscus and calculate the wall heat transfer. The results show that the wall velocity creates a circulation near the meniscus base causing increased wall heat transfer as compared to a stationary meniscus. The local wall heat transfer is found to vary significantly along the meniscus base, the highest being near the advancing contact line.

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.

Effect of Contact Angle on the Heat Transfer to an Evaporating Meniscus on a Moving Heated Surface

2005 ◽  
Author(s):  
A. Mukherjee ◽  
S. G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Contact Angle ◽  
Stokes Equations ◽  
Contact Region ◽  
Heated Surface ◽  
Contact Angles ◽  
Navier Stokes ◽  
Wall Heat Transfer ◽  
Moving Wall ◽  
Liquid Circulation

Numerical simulation is carried out to study a 2D evaporating meniscus formed on a moving wall. The complete Navier-Stokes equations along with continuity and energy equations are solved. The liquid vapor interface is captured using the level set technique. The meniscus is fed with saturated water from the top whereas the bottom wall is maintained at a higher temperature and is also imparted with a velocity. The meniscus attains a steady shape when all the incoming liquid gets evaporated due to heat transfer from the wall. The advancing and receding contact region of the meniscus are provided with different contact angles. Results indicate that the average heat flux at the meniscus base increases with increase in contact angle. The primary reason for heat transfer from the wall is attributed to the liquid circulation inside the meniscus and the corresponding transient conduction from the wall. As the meniscus contact angle increases the liquid circulation is found to disturb the thermal boundary layer more effectively thereby resulting in increased wall heat transfer. The effect of contact angle on wall heat transfer to the moving and evaporating meniscus is compared to partial nucleate pool boiling.

Natural convection in an enclosure having a vertical sidewall with time-varying temperature

1996 ◽  
Vol 329 ◽  
pp. 65-88 ◽  
Author(s):  
Ho Sang Kwak ◽  
Jae Min Hyun
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Numerical Solutions ◽  
Stokes Equations ◽  
Numerical Study ◽  
Temperature Fields ◽  
Navier Stokes ◽  
Time Varying ◽  
Vertical Sidewall ◽  
Boussinesq Fluid

A numerical study is performed for time-varying natural convection of an incompressible Boussinesq fluid in a sidewall-heated square cavity. The temperature at the cold sidewall Tc is constant, but at the hot sidewall a time-varying temperature condition is prescribed, $ T_H = \overline{T_H} + \Delta T^{\prime} \sin ft $. Comprehensive numerical solutions are found for the time-dependent Navier–Stokes equations. The numerical results are analysed in detail to show the existence of resonance, which is characterized by maximal amplification of the fluctuations of heat transfer in the interior. Plots of the dependence of the amplification of heat transfer fluctuations on the non-dimensional forcing frequency ω are presented. The failure of Kazmierczak & Chinoda (1992) to identify resonance is shown to be attributable to the limitations of the parameter values they used. The present results illustrate that resonance becomes more distinctive for large Ra and Pr ∼ 0(1). The physical mechanism of resonance is delineated by examining the evolution of oscillating components of flow and temperature fields. Specific comparisons are conducted for the resonance frequency ωr between the present results and several other previous predictions based on the scaling arguments.

Numerical Study of the Effect of Surface Tension on Vapor Bubble Growth During Flow Boiling in Microchannels

2006 ◽  
Author(s):  
Abhijit Mukherjee ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Surface Tension ◽  
Vapor Bubble ◽  
Bubble Growth ◽  
Stokes Equations ◽  
Numerical Study ◽  
Flow Boiling ◽  
Navier Stokes ◽  
Wall Heat Transfer ◽  
Effect Of Surface

Microchannel heat sinks typically consist of parallel channels connected through a common header. During flow boiling random temporal and spatial formation of vapor bubbles may lead to reversed flow in certain channels which causing an early CHF condition. Inside the microchannels the liquid surface tension forces is expected to play an important role and impact the vapor bubble growth and corresponding wall heat transfer. In the present study growth of a vapor bubble inside a microchannel during flow boiling is numerically studied by varying the surface tension but keeping the value of contact angle constant. 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 fluid properties used are of water but the surface tension value is varied systematically. The effect of surface tension on bubble growth rate and wall heat transfer is quantified. The results indicate that for the range of parameters investigated surface tension has little influence on bubble growth and wall heat transfer.

Effect of wall-mounted V-baffle position in a turbulent flow through a channel

2019 ◽  
Vol 29 (10) ◽  
pp. 3908-3937 ◽  
Author(s):  
Younes Menni ◽  
Ahmed Azzi ◽  
Ali J. Chamkha ◽  
Souad Harmand
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Stokes Equations ◽  
Numerical Study ◽  
Rectangular Channel ◽  
Simple Algorithm ◽  
Two Dimensions ◽  
Large Reynolds Number ◽  
Constant Property ◽  
Content Type

Purpose The purpose of this paper is to carry out a numerical study on the dynamic and thermal behavior of a fluid with a constant property and flowing turbulently through a two-dimensional horizontal rectangular channel. The upper surface was put in a constant temperature condition, while the lower one was thermally insulated. Two transverse, solid-type obstacles, having different shapes, i.e. flat rectangular and V-shaped, were inserted into the channel and fixed to the top and bottom walls of the channel, in a periodically staggered manner to force vortices to improve the mixing, and consequently the heat transfer. The flat rectangular obstacle was put in the first position and was placed on the hot top wall of the channel. However, the second V-shaped obstacle was placed on the insulated bottom wall, at an attack angle of 45°; its position was varied to find the optimum configuration for optimal heat transfer. Design/methodology/approach The fluid is considered Newtonian, incompressible with constant properties. The Reynolds averaged Navier–Stokes equations, along with the standard k-epsilon turbulence model and the energy equation, are used to control the channel flow model. The finite volume method is used to integrate all the equations in two-dimensions; the commercial CFD software FLUENT along with the SIMPLE-algorithm is used for pressure-velocity coupling. Various values of the Reynolds number and obstacle spacing were selected to perform the numerical runs, using air as the working medium. Findings The channel containing the flat fin and the 45° V-shaped baffle with a large Reynolds number gave higher heat transfer and friction loss than the one with a smaller Reynolds number. Also, short separation distances between obstacles provided higher values of the ratios Nu/Nu0 and f/f0 and a larger thermal enhancement factor (TEF) than do larger distances. Originality/value This is an original work, as it uses a novel method for the improvement of heat transfer in completely new flow geometry.

A Numerical Study of the Hydrodynamics of Reversing Flows Around a Cylinder

1994 ◽  
Vol 116 (4) ◽  
pp. 202-208 ◽  
Author(s):  
K. Nakajima ◽  
Y. Kallinderis ◽  
I. Sibetheros ◽  
R. W. Miksad ◽  
K. Lambrakos
Keyword(s):  
Experimental Data ◽  
Finite Element Method ◽  
Stokes Equations ◽  
Numerical Study ◽  
Offshore Structures ◽  
Two Dimensions ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Random Behavior ◽  
Marching Scheme

A numerical study of the nonlinear and random behavior of flow-induced forces on offshore structures and experimental verification of the results are presented. The numerical study is based on a finite-element method for the unsteady incompressible Navier-Stokes equations in two dimensions. The momentum equations combined with a pressure correction equation are solved employing fourth-order artificial dissipation with a nonstaggered grid, instead of the more commonly used staggered meshes. The solution is advanced in time with a combined explicit and implicit marching scheme. Emphasis is placed on study of reversing flows around a cylinder. Comparisons with experimental data evaluate accuracy and robustness of the method.

Numerical Simulation of the Cooling Process of Cubic Shells

2011 ◽  
Author(s):  
Manabu Okura ◽  
Kiyoaki Ono
Keyword(s):  
Heat Transfer ◽  
Stokes Equations ◽  
Temperature Fields ◽  
Numerical Code ◽  
Navier Stokes ◽  
Cooling Process ◽  
Air Velocity ◽  
Navier Stokes Equations ◽  
The Difference ◽  
The Heat Transfer Coefficient

In order to keep the environment in an air-conditioned room comfortable, it is important to anticipate the air velocity and temperature fields precisely. The numerical code, solving simultaneously the Navier-Stokes equations governing flow field inside and outside the room and the heat conduction equation applying to walls, are developed. The assumption that the heat transfer coefficient between the fluid and the surface of solids is not used. This code is applied to investigate the cooling process of a cubic shell. The computational results agree with the experimental results. We also investigated the same process of the cubic shells whose walls are internally or externally insulated. The difference of the amount of heat transfer will be discussed.

Numerical Analysis of Vapor Bubble Growth and Wall Heat Transfer During Flow Boiling of Water in a Microchannel

2005 ◽  
Author(s):  
Abhijit Mukherjee ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Cross Section ◽  
Vapor Bubble ◽  
Bubble Growth ◽  
Stokes Equations ◽  
Flow Boiling ◽  
Navier Stokes ◽  
Channel Cross Section ◽  
Wall Heat Transfer ◽  
Wall Superheat

The present study is performed to analyze the wall heat transfer mechanisms during growth of a vapor bubble inside a microchannel. The microchannel is of 200 μm square cross section and a vapor bubble begins to grow at one of the walls, with liquid coming in through the channel inlet. 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 bubble grows rapidly due to heat transfer from the walls and soon turns into a plug filling the entire channel cross section. The average wall heat transfer at the channel walls is studied for different values of wall superheat and incoming liquid mass flux. The results show that the wall heat transfer increases with wall superheat but is almost unaffected by the liquid flow rate. The bubble growth is found to be the primary mechanism of increasing wall heat transfer as it pushes the liquid against the walls thereby influencing the thermal boundary layer development.

Developing Fluid Flow and Heat Transfer in a Semi-Porous Square Channel

2003 ◽  
Author(s):  
Tien-Chien Jen ◽  
Tuan-Zhou Yan ◽  
S. H. Chan
Keyword(s):  
Heat Transfer ◽  
Porous Media ◽  
Fluid Flow ◽  
Stokes Equations ◽  
Temperature Fields ◽  
Porous Channel ◽  
Navier Stokes ◽  
Axial Position ◽  
Navier Stokes Equations ◽  
Flow And Heat Transfer

A three-dimensional computational model is developed to analyze fluid flow in a semi-porous channel. In order to understand the developing fluid flow and heat transfer process inside the semi-porous channels, the conventional Navier-Stokes equations for gas channel, and volume-averaged Navier-Stokes equations for porous media layer are adopted individually in this study. Conservation of mass, momentum and energy equations are solved numerically in a coupled gas and porous media domain in a channel using the vorticity-velocity method with power law scheme. Detailed development of axial velocity, secondary flow and temperature fields at various axial positions in the entrance region are presented. The friction factor and Nusselt number are presented as a function of axial position, and the effects of the size of porous media inside semi-porous channel are also analyzed in the present study.

COMPARATIVE STUDY OF THERMAL FLOWS WITH DIFFERENT FINITE VOLUME AND LATTICE BOLTZMANN SCHEMES

2004 ◽  
Vol 15 (02) ◽  
pp. 307-319 ◽  
Author(s):  
AHMAD AL-ZOUBI ◽  
GUNTHER BRENNER
Keyword(s):  
Heat Transfer ◽  
Comparative Study ◽  
Finite Volume ◽  
Lattice Boltzmann ◽  
Numerical Solutions ◽  
Stokes Equations ◽  
Hybrid Approach ◽  
Navier Stokes ◽  
Steady Flows ◽  
Parallel Plates

In the present paper, a comparative study of numerical solutions for steady flows with heat transfer based on the finite volume method (FVM) and the relatively new lattice Boltzmann method (LBM) is presented. In the last years, the LB methods have challenged the classical FV methods to solve the Navier–Stokes equations and have proven to be superior in accuracy and efficiency for certain applications. Most of these studies were related to the transport of mass and momentum. In the meantime, significant effort has been invested in the application of the LBM to simulate flows including heat transfer. The studies in the present paper are the analysis of performance and accuracy aspects of LBM applied to the prediction of these flows. For a fully developed laminar flow between parallel plates, analytical solutions for the heat transfer in fully developed thermal boundary layers are available and may be compared with the respective numerical results. Finally, a hybrid approach is proposed to circumvent numerical problems of the thermal LB methods.

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