scholarly journals NUMERICAL ANALYSIS OF NUCLEATE BOILING FLOW IN A PILOT-SCALE THERMOSIPHON

2020 ◽  
Author(s):  
Bruna Iten Bittelbrunn ◽  
Roberto Fischer Junior ◽  
Harlley Henrique Parno ◽  
Henry França Meier ◽  
Jaci Carlos Schramm Câmara Bastos
Keyword(s):  
Numerical Analysis ◽  
Nucleate Boiling ◽  
Pilot Scale ◽  
Boiling Flow

Comparison of Heat Transfer Rates Around Moving and Stationary Bubbles During Nucleate Boiling

2005 ◽  
Author(s):  
David M. Christopher ◽  
Hao Wang ◽  
Xiaofeng Peng
Keyword(s):  
Heat Transfer ◽  
Numerical Analysis ◽  
Nucleate Boiling ◽  
High Heat ◽  
Marangoni Flow ◽  
Transfer Rates ◽  
High Heat Transfer ◽  
Nucleate Boiling Heat Transfer ◽  
Bubble Movement ◽  
Transfer Mechanisms

Nucleate boiling is known to be a very efficient method for generating high heat transfer rates from solid surfaces into liquids; however, the fundamental physical mechanisms governing nucleate boiling heat transfer are not well understood. This paper describes a numerical analysis of the heat transfer mechanisms around stationary and moving bubbles on a very thin microwire. The numerical analysis accurately models the experimentally observed bubble movement and fluid velocities. The analytical model was then used to study the heat transfer mechanisms around the bubbles. The analysis shows that the primary heat transfer mechanism is not the direct heat transfer to the bubble, but rather the large amount of convection around the outside of the bubble induced by the Marangoni flow that transfers at least twice as much energy from the wire than the heat transfer directly under the bubble. The enhanced heat transfer due to the Marangoni flow was evident for both stationary and moving bubbles.

Nucleate Boiling Flow Simulation With Coupling of Eulerian and Lagrangian Methods

2005 ◽  
Author(s):  
Bosˇtjan Koncˇar ◽  
Ivo Kljenak ◽  
Borut Mavko
Keyword(s):  
Model Simulation ◽  
Fluid Model ◽  
Nucleate Boiling ◽  
Homogeneous Distribution ◽  
Lagrangian Simulation ◽  
Radial Profiles ◽  
Boiling Flow ◽  
Tracking Model ◽  
Two Fluid Model ◽  
Two Fluid

Subcooled boiling flow was simulated by combining the two-fluid model of the CFX-4.4 code and a Lagrangian bubble-tracking model. At present, both models are coupled “off-line” via the local bubble Sauter diameter. The two-fluid model simulation with the CFX-4.4 code provides local values of turbulent kinetic energy field of the liquid phase, which is used as an input for the bubble-tracking model. In the bubble-tracking model, vapour is distributed in the liquid in the form of individually tracked bubbles. The result of the Lagrangian simulation is a non-homogeneous distribution of local Sauter diameter, which is used in the two-fluid model to predict the interfacial forces and interfacial transfer rates of mass and heat transfer. The coupled approach requires a few iterations to obtain a converged solution. The results of the proposed approach were validated against boiling flow experiments from the literature. A good agreement between measured and calculated radial profiles of void fraction and bubble diameter was obtained.

Advanced Computational Modeling of Multiphase Boiling Flow and Heat Transfer

2010 ◽  
Author(s):  
Huiying Li ◽  
Sergio A. Vasquez ◽  
Peter Spicka
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Volume Fraction ◽  
Nucleate Boiling ◽  
General Purpose ◽  
Phase Changes ◽  
Pressurized Water ◽  
Flow And Heat Transfer ◽  
Boiling Flow

Numerical simulation of boiling flow and heat transfer presents a number of unique challenges in both theoretical modeling and developing robust numerical methodology. The major difficulty arises due to the heat transfer and phase changes between heated walls and fluid (liquid and vapor). Furthermore, modeling of the liquid-vapor interfacial transfers of momentum, heat and mass proves to be equally challenging. The multiphase boiling modeling approach described in this paper has been found to be capable of addressing these issues and is therefore suitable for inclusion in an advanced general purpose CFD solver. In the present approach, boiling flows are modeled within the framework of the Eulerian multifluid model. The governing equations solved are phase continuity, momentum and energy equations. Turbulence effects can be accounted for using mixture, dispersed or per-phase multiphase turbulence models. Wall boiling phenomena are modeled using the baseline mechanistic RPI model for nucleate boiling, and its extensions to non-equilibrium boiling and critical heat flux regime. A range of sub-models are considered to account for the interfacial momentum, mass and heat transfer, and flow regime transitions. An advanced numerical scheme has been developed for solving the model equations which can handle the heat partition between heated walls and fluid, provide for wall and interfacial mass transfer source terms in phase volume fraction equations, and address the coupling between the phase change rates and the pressure correction equation. The wall boiling models and numerical algorithm have been implemented in an advanced, general-purpose CFD code, FLUENT. Validations have been carried out for a range of 2D and 3D boiling flows, including pressurized water through a vertical pipe with heated walls, R-113 liquid in a vertical annulus with internal heated walls, a 3D BRW core channel geometry with vertical heated rods, and water in a vertical circular pipe under critical heat flux and post dry-out conditions. The results demonstrate that the wall boiling models are able to correctly predict the wall temperature and vapor volume fraction distribution. The predictions in all the cases are in reasonable good agreement with available experiments. Tests also indicate that the present implementation is fast and robust, as compared to previous approaches. All the cases are able to be simulated with the use of the FLUENT steady-state multiphase solver with reasonable numbers of iterations.

Subcooled Boiling Flow Heat Transfer From Plain and Enhanced Surfaces in Automotive Applications

2008 ◽  
Vol 130 (1) ◽  
Author(s):  
Franz Ramstorfer ◽  
Helfried Steiner ◽  
Günter Brenn ◽  
Claudius Kormann ◽  
Franz Rammer
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Nucleate Boiling ◽  
Heated Wall ◽  
Transfer Model ◽  
Subcooled Boiling ◽  
Cooling Systems ◽  
Porous Coatings ◽  
Transfer Rates ◽  
Boiling Flow

The requirement for the highest possible heat transfer rates in compact, efficient cooling systems can often only be met by providing for a transition to subcooled boiling flow in strongly heated wall regions. The significantly higher heat transfer rates achievable with boiling can help keep the temperatures of the structure on an acceptable level. It has been shown in many experimental studies that special surface finish or porous coatings on the heated surfaces can intensify the nucleate boiling process markedly. Most of those experiments were carried out with water or refrigerants. The present work investigates the potential of this method to enhance the subcooled boiling heat transfer in automotive cooling systems using a mixture of ethylene-glycol and de-ionized water as the coolant. Subcooled boiling flow experiments were carried out in a vertical test channel considering two different types of coated surfaces and one uncoated surface as a reference. The experimental results of the present work clearly demonstrate that the concept of enhancing boiling by modifying the microstructure of the heated surface can be successfully applied to automotive cooling systems. The observed increase in the heat transfer rates differ markedly for the two considered porous coatings, though. Based on the experimental data, a heat transfer model for subcooled boiling flow using a power-additive superposition approach is proposed. The model assumes the total wall heat flux as a nonlinear combination of a convective and a nucleate boiling contribution, both obtained from well-established semiempirical correlations. The wall heat fluxes predicted by the proposed model are in very good agreement with the experimental data for all considered flow conditions and surface types.

Dynamics and Heat Transfer Associated With a Single Bubble During Nucleate Boiling on a Horizontal Surface

1999 ◽  
Vol 121 (3) ◽  
pp. 623-631 ◽  
Author(s):  
G. Son ◽  
V. K. Dhir ◽  
N. Ramanujapu
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Numerical Analysis ◽  
Bubble Dynamics ◽  
Nucleate Boiling ◽  
Liquid Interface ◽  
Horizontal Surface ◽  
Wall Superheat ◽  
Static Contact ◽  
Vapor Liquid

In this study, a complete numerical simulation of a growing and departing bubble on a horizontal surface has been performed. A finite difference scheme is used to solve the equations governing conservation of mass, momentum, and energy in the vapor-liquid layers. The vapor-liquid interface is captured by a level set method which is modified to include the influence of phase change at the liquid-vapor interphase. The disjoining pressure effect is included in the numerical analysis to account for heat transfer through the liquid microlayer. From the numerical simulation, the location where the vapor-liquid interface contacts the wall is observed to expand and then retract as the bubble grows and departs. The effect of static contact angle and wall superheat on bubble dynamics has been quantified. The bubble growth predicted from numerical analysis has been found to compare well with the experimental data reported in the literature and that obtained in this work.

Advances in Modeling Critical Heat Flux in LWR Boiling Flows With the NEK-2P CFD Code

2018 ◽  
Author(s):  
Adrian Tentner ◽  
Prasad Vegendla ◽  
Ananias Tomboulides ◽  
Aleks Obabko ◽  
Elia Merzari ◽  
...  
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Vertical Channel ◽  
Nucleate Boiling ◽  
Heated Wall ◽  
Transfer Model ◽  
Axial Distribution ◽  
Two Phase ◽  
Wide Range ◽  
Boiling Flow

The paper focuses on the extension of the NEK-2P Wall Heat Transfer model, which was initially developed for the analysis of Critical Heat Flux (CHF) under Dryout (DO) conditions to the simulation of CHF under Departure from Nucleate Boiling (DNB) conditions. The paper presents results of recent NEK-2P analyses of several CHF experiments including both DO and DNB conditions. The CHF experiments analyzed have measured the axial distribution of wall temperatures in two-phase boiling flow in a vertical channel with a heated wall. The axial distribution of the calculated wall temperatures is compared with the corresponding experimental data. Reasonably good agreement with measured data is obtained in predicting the CHF location and post CHF wall temperature magnitudes illustrating the ability of the NEK-2P code and Extended Boiling Framework (EBF) models to simulate the CHF phenomena for a wide range of thermal-hydraulic conditions.

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