A Unified Three-Dimensional Numerical Model for Boiling Curve in a Temperature Controlled Mode1

2018 ◽  
Vol 141 (1) ◽  
Author(s):  
Deepak Garg ◽  
V. K. Dhir
Keyword(s):  
Heat Flux ◽  
Numerical Model ◽  
Void Fraction ◽  
Three Dimensional ◽  
Nucleation Site ◽  
Boiling Curve ◽  
Increase With Increase ◽  
Wall Superheat ◽  
Uniform Wall ◽  
Temperature Controlled

In the present study, level set method is used to simulate the entire boiling curve in a temperature-controlled mode spanning all the three regimes viz., nucleate, transition, and film boiling with a unified numerical model supplemented with correlations specifying nucleation site density and waiting time between successive nucleations. In order to improve the performance of the code, parallel computing has also been implemented. Vapor evolution process along with temporal- and spatial-averaged wall heat flux and wall void fraction are computed for a uniform wall superheat case. Wall void fraction is found to increase with increase in wall superheat nonlinearly as different regimes of boiling were traversed. Energy partitioning from wall into liquid, interface, and microlayer has also been examined where it is found that as the wall void fraction increases, the percent energy going into liquid decreases while the microlayer contribution peaks around critical heat flux (CHF). Numerical simulations are carried out in 3D with water as test liquid and contact angle of 38 deg.

A Unified Three Dimensional Numerical Simulation of the Pool Boiling Curve

2017 ◽  
Author(s):  
Deepak Garg ◽  
Vijay K. Dhir
Keyword(s):  
Heat Flux ◽  
Contact Angle ◽  
Numerical Model ◽  
Critical Heat Flux ◽  
Void Fraction ◽  
Pool Boiling ◽  
Three Dimensional ◽  
Boiling Curve ◽  
Wall Superheat ◽  
Experimental Values

Three dimensional numerical simulations for pool boiling of saturated water at atmospheric pressure conditions are performed on a horizontal surface using finite difference method under the framework of parallel computing. Since heat conduction in the solid phase is not considered, in order to simulate realistic heating surface, dependence of bubble nucleation frequency and nucleation site density on wall superheat and contact angle are obtained from the correlations reported in the literature. Steady state boiling curve for all the three regimes viz. nucleate, transition and film boiling has been obtained with a unified numerical model by incrementing the wall superheat for a static contact angle of 38°. Evaporative heat flux from the microlayer is separately accounted for in the present study by sub grid modeling. Both the phases are considered as incompressible while the interface separating the phases is solved using level set method. The governing equations of mass, momentum and energy for both the liquid and the vapor phase are solved coupled with the jump conditions at the interface employing ghost fluid and cut cell method. Diffusion terms are treated implicitly while convection terms are treated using second order ENO scheme. Spatial and temporal averaged wall heat flux and wall void fraction are plotted and compared against correlations and experimental values previously reported. The nucleate boiling heat flux obtained from the present numerical model is under predicted in comparison to the Stephan and Abdelsalam correlation. Comparison of the computed wall void fraction against experimental values is done for the transition boiling region. At critical heat flux formation of long vapor column was seen while intermittent liquid surface contacts were seen in the transition boiling regime. The computed critical heat flux value is lower than that obtained from the correlation of Maracy and Winterton.

The Effect of Droplet Impingement on Pressure and Heat Flux Distributions on Molten Pool in GMAW-Based Rapid Forming

2014 ◽  
Vol 494-495 ◽  
pp. 391-394
Author(s):  
Feng Liang Yin ◽  
Sheng Zhu ◽  
Jian Liu ◽  
Xiao Ming Wang ◽  
Lei Guo
Keyword(s):  
Heat Flux ◽  
Numerical Model ◽  
Molten Pool ◽  
Flux Distribution ◽  
Three Dimensional ◽  
Heat Flux Distribution ◽  
Droplet Impingement ◽  
Dimensional Precision ◽  
Low Dimensional

A low dimensional precision is one of drawback for the GMAW-based rapid forming technique, which is related to pressure and heat flux on molten pool. To study pressure and heat flux on molten pool, the effect of droplet impinging process must been considered. A three-dimensional numerical model was built to analysis pressure and heat flux distribution on molten pool. Solving the model, it was found that pressure on the cathode by the arc decreases dramatically when the droplet is coming. As to heat flux, the appearance of droplet cuts down it within about 1.5 mm away from arc axial. Out of 1.5 mm away from arc axial, droplets effect on heat flux is not obvious.

Onset of Nucleate Boiling and Active Nucleation Site Density During Subcooled Flow Boiling

2002 ◽  
Vol 124 (4) ◽  
pp. 717-728 ◽  
Author(s):  
Nilanjana Basu ◽  
Gopinath R. Warrier ◽  
Vijay K. Dhir
Keyword(s):  
Heat Flux ◽  
Contact Angle ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Nucleation Site ◽  
Subcooled Flow Boiling ◽  
Site Density ◽  
Wall Superheat ◽  
Subcooled Flow ◽  
Nucleation Site Density

The partitioning of the heat flux supplied at the wall is one of the key issues that needs to be resolved if one is to model subcooled flow boiling accurately. The first step in studying wall heat flux partitioning is to account for the various heat transfer mechanisms involved and to know the location at which the onset of nucleate boiling (ONB) occurs. Active nucleation site density data is required to account for the energy carried away by the bubbles departing from the wall. Subcooled flow boiling experiments were conducted using a flat plate copper surface and a nine-rod (zircalloy-4) bundle. The location of ONB during the experiments was determined from visual observations as well as from the thermocouple output. From the data obtained it is found that the heat flux and wall superheat required for inception are dependent on flow rate, liquid subcooling, and contact angle. The existing correlations for ONB underpredict the wall superheat at ONB in most cases. A correlation for predicting the wall superheat and wall heat flux at ONB has been developed from the data obtained in this study and that reported in the literature. Experimental data are within ±30 percent of that predicted from the correlation. Active nucleation site density was determined by manually counting the individual sites in pictures obtained using a CCD camera. Correlations for nucleation site density, which are independent of flow rate and liquid subcooling, but dependent on contact angle have been developed for two ranges of wall superheat—one below 15°C and another above 15°C.

Heat Transfer Behavior on Small Horizontal Heaters During Pool Boiling of FC-72

1999 ◽  
Vol 121 (2) ◽  
pp. 386-393 ◽  
Author(s):  
T. D. Rule ◽  
J. Kim
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Time Resolved ◽  
Wall Superheat ◽  
Heated Area ◽  
Local Measurements ◽  
Transfer Behavior ◽  
Temperature Controlled

Detailed local measurements of wall heat flux during saturated pool boiling of FC-72 on a small heated area without sidewalls were made using an array of 96 temperature-controlled heaters. Data were obtained in the nucleate boiling, critical heat flux, and transition boiling regimes. The space and time resolved data were used to conditionally sample the heat flux according to whether or not boiling occurred on the surface, enabling the separation of the heat flux due to boiling from that due to natural convection or vapor contact. The heat transfer from the edge heaters was observed to be much higher than that for the inner heaters above the critical temperature. The heat transfer during liquid contact in transition boiling was constant for a given wall superheat for the inner heaters, and was observed to decrease with increasing wall superheat.

Pool Boiling Inversion on Surfaces With Separate Liquid-Vapor Pathways and Enhanced Macroconvection Mechanisms

2017 ◽  
Author(s):  
Arvind Jaikumar ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Flux ◽  
Pool Boiling ◽  
Boiling Curve ◽  
Analytical Models ◽  
Wall Superheat ◽  
Engineered Surfaces ◽  
Induced Flow ◽  
Nucleation Activity ◽  
Jet Characteristics ◽  
Liquid Vapor

A typical pool boiling curve relating the heat flux and wall superheat is often used to quantify the efficacy of the engineered surfaces. Surface enhancements promoting nucleation activity, wicking, roughness and microlayer partitioning have shown remarkable enhancements in CHF and HTC. The boiling curve for these surfaces show an increase in wall superheat with an increase in heat flux. However, recently developed surfaces using the concept of separate liquid-vapor pathways and enhanced macroconvection have shown a reverse trend where an increase in heat flux is accompanied by decreasing wall superheats. This counter intuitive trend in the boiling curve characteristics is called as boiling inversion in this work. The macroconvection heat transfer is identified as the contributing mechanism to the boiling inversion trend. The vapor-stream induced flow transition and the impinging liquid jet characteristics is quantitatively explained through analytical models available in literature. Furthermore, two surfaces exploiting this mechanism is also demonstrated in this work which sheds light on the interplay mechanisms.

Numerical Simulations of Bubble Pumps

2012 ◽  
Author(s):  
Soo W. Jo ◽  
S. A. Sherif ◽  
William E. Lear
Keyword(s):  
Heat Flux ◽  
Numerical Model ◽  
Numerical Simulations ◽  
Void Fraction ◽  
Uniform Heat Flux ◽  
Ammonia Vapor ◽  
Buoyant Force ◽  
Flow Parameters ◽  
Uniform Heat ◽  
Bubble Pump

A bubble pump is a key component for diffusion-absorption refrigeration systems operating at a single pressure. Nevertheless, research focusing on bubble pumps is not widely found in the literature. In this study, a bubble pump model with a shape of vertical tube subjected to a uniform heat flux from the tube outer surface is numerically simulated. A saturated ammonia-water solution enters the bubble pump inlet and receives heat from the pump wall along the entire pump length. During the process, most of the ammonia in the solution vaporizes, and the remaining solution is lifted by the buoyant force created by the ammonia vapor. A numerical model was implemented by employing a commercial CFD code. The applicability of the numerical model implemented in the code to the present numerical simulations was validated through a comparative study referring to experimental data of a boiling phase change flow of water in a vertical pipe being subjected to a uniform heat flux. To investigate the influence of the bubble pump’s geometrical dimension and the heat input on the operating status and performance, numerical simulations were performed for four bubble pumps with different diameters subjected to five amounts of heat flux. Simulation results are provided in terms of the flow parameters including void fraction, and vapor and liquid velocities. The simulated spatial distributions of the flow parameters were found to have steep gradients in the radial direction near the pump wall due to the heating from the pump wall. In addition, simulated flow parameters were compared to those in previous one-dimensional (1-D) work for the same problem. It was found that the void fraction profiles along the pump length simulated in this study seem to be similar to those in 1-D models, but somewhat different quantitatively. Based on the results, the present numerical simulation model of the bubble pump is considered to be useful for certain industrial applications.

Film Boiling Incipience at the Departure From Natural Convection on Flat, Smooth Surfaces

1998 ◽  
Vol 120 (2) ◽  
pp. 402-409 ◽  
Author(s):  
J. Y. Chang ◽  
S. M. You ◽  
A. Haji-Sheikh
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Natural Convection ◽  
Smooth Surface ◽  
Boiling Curve ◽  
Film Boiling ◽  
Smooth Surfaces ◽  
Wall Superheat ◽  
Boiling Incipience ◽  
Minimum Heat

The present research is an experimental study of pool boiling nucleation behavior using flat, smooth surfaces immersed in saturated highly wetting liquids, FC-72 and FC-87. A flush-mounted, copper surface of 10 mm × 10 mm is used as a heat transfer surface, simulating a microelectronic chip surface. At the nucleation incipient points of higher wall superheats with steady increase of heat flux, vapor film blankets the smooth surface and remains on the surface. To predict this film boiling incipience phenomenon from the smooth surface, an incipience map is developed over the boiling curve. When the incipient heat flux is higher than the minimum heat flux (MHF) and the incipient wall superheat value is higher than the transition boiling curve value at the incipient heat flux, the transition from single-phase natural convection to film boiling is observed at the incipient point. To prevent film boiling incipience, a microporous coating is applied over the smooth surface, which decreases incipient wall superheat and increases minimum heat flux. The film boiling incipience should be avoided to take advantage of highly efficient nucleate boiling heat transfer for the cooling of high-heat-flux applications.

Investigation on Variations of Void Fraction in a Subcooled Boiling Channel Under Vertical Forced Excitations

2021 ◽  
Vol 143 (6) ◽  
Author(s):  
Shao-Wen Chen ◽  
Wei-Cheng Lee ◽  
Yu-Hsien Chang ◽  
Ailing Ho ◽  
Jin-Der Lee ◽  
...  
Keyword(s):  
Heat Flux ◽  
Void Fraction ◽  
Experimental Tests ◽  
Dominant Frequency ◽  
Heat Fluxes ◽  
Fluid Temperature ◽  
Subcooled Boiling ◽  
Wall Superheat ◽  
Boiling Flow ◽  
Near Wall

Abstract Experimental tests were carried out to investigate the vertically forced excitation effects on the subcooled boiling flow. The heated circular channel with an inner diameter of 11.9 mm was operated with various heat fluxes (q″ ≈ 14.6–41.1 kW/m2) and inlet flow conditions (vin ≈ 0.21–0.42 m/s) under various vertical forced excitations (f ≈ 0–1.63 Hz), and the time variations of void fraction, near-wall fluid temperature and pressure were recorded during the tests. Fast Fourier transform (FFT) was applied to extract the dominant frequency from the transient signals, and the variations of averages and standard deviations of test data were obtained for analysis. Under lower heat flux, lower flow, and lower void conditions, the time-averaged void fraction may decrease under forced excitations, and the dominant frequencies of void variations were identical to those of forced excitations. However in higher heat flux and higher void conditions, the void fraction can slightly increase under forced excitations, but the excitation frequencies may not be clearly observed in the void FFT plots. In general, the transient and time-averaged void fraction can be affected by forced excitations, and the void variation trends are similar to those of near-wall fluid temperature, which implies the void variations may be related to the changes of thermal boundary layer thickness. Besides, the potential variations of void fraction were estimated by assuming changes of heat transfer coefficient and/or wall superheat, which appear similar trends to the observed void variations in the present tests.

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