A Three-Dimensional Numerical Modelling of Atmospheric Pool Boiling by the Coupled Map Lattice Method

2005 ◽  
Author(s):  
A. Gupta ◽  
P. S. Ghoshdastidar
Keyword(s):  
Thermal Diffusion ◽  
Heated Surface ◽  
Pool Boiling ◽  
Three Dimensional ◽  
Coupled Map Lattice ◽  
Lattice Method ◽  
Copper Strip ◽  
Basic Objective ◽  
Cml Model ◽  
Bubble Rising

In the present paper, the characteristic atmospheric pool boiling curve is qualitatively reproduced for water on a temperature controlled thin copper strip having comparable length and breadth by the coupled map lattice (CML) method using a three-dimensional boiling field model. The basic objective of the work is to improve the prediction of the critical heat flux (CHF) with respect to the 2D CML model of Ghoshdastidar et al. [10]. The work models saturated pool boiling of water at 1 bar on a large (much larger than the minimum wavelength of 2D Taylor waves) and thin horizontal copper strip. The pool height is 0.7 mm, indicating thin film boiling. In the present model, it is assumed that boiling is governed by (a) nucleation from cavities on a heated surface, (b) thermal diffusion, (c) bubble rising motion and associated convection, (d) phase change and (e) Taylor instability. The changes with respect to 2D model are primarily with respect to 3D modelling of thermal diffusion and 2D distribution of nucleating cavity sizes. The predicted CHF is 1.57 MW/m2 as compared to the actual value of 1.3 MW/m2 and 0.36 MW/m2 predicted by the 2D CML model of Ghoshdastidar et al. [10]. It can be said that for the first time a coupled map lattice method which is essentially qualitative in nature has been able to predict the CHF of saturated pool boiling of water at 1 bar very close to the actual value.

Numerical modelling of atmospheric pool boiling by the coupled map lattice method

2004 ◽  
Vol 218 (2) ◽  
pp. 195-205 ◽  
Author(s):  
P S Ghoshdastidar ◽  
S Kabelac ◽  
A Mohanty
Keyword(s):  
Enhancement Factor ◽  
Heated Surface ◽  
Pool Boiling ◽  
Coupled Map Lattice ◽  
Boiling Curve ◽  
Lattice Method ◽  
Copper Strip ◽  
Order Of Magnitude ◽  
Spatio Temporal ◽  
Bubble Rising

In the present paper, the characteristic atmospheric saturated pool boiling curve is qualitatively reproduced for water on a temperature-controlled long and thin copper strip using the coupled map lattice (CML) method known in non-linear spatio-temporal chaos dynamics. The pool height is 0.7 mm, indicating that the boiling is of the thin-film type. The work modifies the basic theoretical model proposed by Shoji in 1998 in terms of nucleation superheat distribution and mixing. The stirring action of the bubbles is modelled by increasing the fluid thermal diffusivity by an enhancement factor. It is assumed that boiling is governed by (a) nucleation from cavities on a heated surface, (b) thermal diffusion, (c) bubble rising motion and associated convection, (d) phase change and (e) Taylor instability. The effectiveness of the enhancement factor approach in the present model is clearly seen in its capability of reproducing the saturated pool boiling curve well and predicting the critical heat flux (CHF) in the same order of magnitude of the actual value.

Heat Flux Controlled Pool Boiling of Zirconia–Water and Silver–Water Nanofluids on a Flat Plate: A Coupled Map Lattice Simulation

2015 ◽  
Vol 137 (2) ◽  
Author(s):  
Sayan Sadhu ◽  
P. S. Ghoshdastidar
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Surface Roughness ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flat Plate ◽  
Pool Boiling ◽  
Coupled Map Lattice ◽  
Nanoparticle Concentration ◽  
Cml Model

In the present work, the characteristic atmospheric saturated heat flux controlled pool boiling curves for zirconia–water and silver–water nanofluids have been reproduced by the coupled map lattice (CML) method using a two-dimensional (2D) boiling field model. The heater is a long horizontal flat plate of thickness 0.44 mm. The pool height is 0.7 mm. The stirring action of the bubbles is modeled by increasing the fluid thermal diffusivity by an enhancement factor. The thermal conduction in the plate is also incorporated into the model. The basic advantage of CML is that individual bubbles are not tracked, and yet the effects of bubbles are reflected qualitatively in the final solution. In the simulation of atmospheric saturated pool boiling of water minimum cavity diameter taken is 0.8 μm based on which a random distribution of cavity sizes has been specified. In the boiling of ZrO2–water nanofluid there is a deposition of nanoparticles in the cavities on the heated surface resulting in reduction of surface roughness. This feature is taken care of by proportionate decrease in minimum cavity diameter. The CML model predicts decrease in heat transfer coefficient and increase in critical heat flux (CHF) with increase in zirconia nanoparticle concentration. In the case of Ag–water nanofluid no such deposition of nanoparticles has been reported; rather surface oxidation occurs which increases the surface roughness. This is simulated by proportionately increasing the minimum cavity diameter with weight fractions of nanoparticles. The present CML model predicts increase in the heat transfer coefficient and decrease in CHF with increase in silver nanoparticle concentration. Thus, the CML results for the boiling of the aforesaid two nanofluids match qualitatively with the published experimental works.

Numerical Study on Bubble Departing Behavior From Heated Surface in Subcooled Pool Boiling

2011 ◽  
Author(s):  
Yasuo Ose ◽  
Zensaku Kawara ◽  
Tomoaki Kunugi
Keyword(s):  
Numerical Simulations ◽  
High Speed ◽  
Numerical Study ◽  
Heated Surface ◽  
Pool Boiling ◽  
Three Dimensional ◽  
Condensation Model ◽  
Departure Behavior ◽  
Shape Changes ◽  
Good Agreement

In this study, in order to clarify the heat transfer characteristics of the subcooled pool boiling and to discuss its mechanism, the boiling and condensation model for numerical simulation on subcooled boiling phenomena has been developed. In this paper, the three dimensional numerical simulations based on the MARS (Multi-interface Advection and Reconstruction Solver) with the boiling and condensation model which consisted of the improved phase-change model and the relaxation time based on the quasi-thermal equilibrium hypothesis have been conducted for the subcooled pool boiling phenomena especially regarding to the bubble departure behavior from the heated surface. The results of the numerical simulations were compared with the experimental data obtained by the high-speed camera (Phantom 7.1) with the Cassegrain optical system, and then the influence of the degree of subcooling for the bubble departing behaviors including their shape changes from the heated surface were numerically predicted. As the results, the numerical results of the bubble departing behavior from the heated surface showed in good agreement with the experimental observations quantitatively.

Database of Sail Shapes vs. Sail Performance and Validation of Numerical Calculation for Upwind Condition

2007 ◽  
Author(s):  
Yutaka Masuyama ◽  
Yusuke Tahara ◽  
Toichi Fukasawa ◽  
Naotoshi Maeda
Keyword(s):  
Numerical Method ◽  
Vortex Lattice ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Numerical Calculations ◽  
Navier Stokes ◽  
Coupling Scheme ◽  
Aerodynamic Coefficients ◽  
Lattice Method ◽  
Cfd Method

Database of full-scale three-dimensional sail shapes are presented with the aerodynamic coefficients for the upwind condition of IMS type sails. Three-dimensional shape data are used for the input of numerical calculations and the results are compared with the measured sail performance. The sail shapes and performance are measured using a sail dynamometer boat Fujin. The Fujin is a 34-foot LOA boat, in which load cells and charge coupled devices (CCD) cameras are installed to measure the sail forces and shapes simultaneously. The sailing conditions of the boat, such as boat speed, heel angle, wind speed, wind angle, and so on, are also measured. The tested sail configurations are as follows: mainsail with 130% jib, mainsail with 75% jib and mainsail alone. Sail shapes are measured at several height positions. The measured shape parameters are chord length, maximum draft, maximum draft position, entry angle at the luff and exit angle at the leech. From these parameters three-dimensional coordinates of the sails are calculated by interpolation. These three-dimensional coordinates are tabulated with the aerodynamic coefficients. Numerical calculations are performed using the measured sail shapes. The calculation methods are of two types; Reynolds-averaged Navier-Stokes (RANS)-based CFD and vortex lattice methods (VLM). A multi-block RANS-based CFD method was developed by one of the authors and is capable of predicting viscous flows and aerodynamic forces for complicated sail configuration for upwind as well as downwind conditions. Important features of the numerical method are summarized as follows: a Finite- Analytic scheme to discretize transport equations, a PISO type velocity-pressure coupling scheme, multi-block domain decomposition capability, and several choices of turbulence models depending on flows of interest. An automatic grid generation scheme is also included. Another calculation method, the vortex lattice method is also adopted. In this case, step-by-step calculations are conducted to attain the steady state of the sail in steady wind. Wake vortices are generated step-by-step, which flow in the direction of the local velocity vector. These calculated sail forces are compared with the measured one, and the validity of the numerical method is studied. The sail shape database and comparison with numerical calculations will provide a good benchmark for the sail performance analysis of the upwind condition of IMS type sails.

Prediction of Steady Propeller Performance with a Nonlinear Slipstream and Boundary-Layer Effect

1995 ◽  
Vol 39 (04) ◽  
pp. 297-312
Author(s):  
You-Hua Liu
Keyword(s):  
Boundary Layer ◽  
Three Dimensional ◽  
Leading Edge ◽  
Viscous Drag ◽  
Viscous Effects ◽  
Lattice Method ◽  
Suction Force ◽  
Layer Effect ◽  
Dimensional Boundary ◽  
Propeller Performance

Both slipstream deformation and viscous effects are factors that affect the performance of a rotating marine propeller but neither of them has been properly treated in most of the current lifting-surface methods and surface panel theories. With the introduction of a partial roll-up wake model that is flexible to various cases of propeller geometry and loading condition, this paper presents a vortex-lattice method that can improve propeller performance prediction especially at heavy loading conditions. Some observations on the calculation of the blade leading-edge suction force and how to deduct it to account for the viscous drag increasing are given. The scale effect of propeller performance can be readily predicted by the quasi-three-dimensional boundary-layer calculation presented in this paper. Some patterns of the limiting streamlines on blade surfaces are also illustrated and compared with experimental results.

Steady-State Behavior of a Three-Dimensional Pool-Boiling System

2008 ◽  
Vol 130 (4) ◽  
Author(s):  
Michel Speetjens
Keyword(s):  
Steady State ◽  
Model Problem ◽  
Separation Of Variables ◽  
Pool Boiling ◽  
Three Dimensional ◽  
Electronics Cooling ◽  
Nucleate Boiling ◽  
Cooling Capacity ◽  
State Behavior ◽  
Steady State Behavior

Pool-boiling serves as the physical model problem for electronics cooling by means of phase-change heat-transfer. The key for optimal and reliable cooling capacity is better understanding of the conditions that determine the critical heat-flux (CHF). Exceeding CHF results in the transition from efficient nucleate-boiling to inefficient film-boiling. This transition is intimately related to the formation and stability of multiple (steady) states on the fluid-heater interface. To this end, the steady-state behavior of a three-dimensional pool-boiling system has been studied in terms of a representative mathematical model problem. This model problem involves only the temperature field within the heater and models the heat exchange with the boiling medium via a nonlinear boundary condition imposed on the fluid-heater interface. The steady-state behavior is investigated via a bifurcation analysis with a continuation algorithm based on the treatment of the model with the method of separation of variables and a Fourier-collocation method. This revealed that steady-state solutions with homogeneous interface temperatures may undergo bifurcations that result in multiple solutions with essentially heterogeneous interface temperatures. These heterogeneous states phenomenologically correspond with vapor patches (“dry spots”) on the interface that characterize transition conditions. The findings on the model problem are consistent with laboratory experiments.

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