A Simplified Force-Balance Model to Predict Bubble Departure Diameter in Horizontal Flow Boiling

2018 ◽  
Author(s):  
Jingyu Du ◽  
Chenru Zhao ◽  
Hanliang Bo ◽  
Yujia Zhou
Keyword(s):  
Reynolds Number ◽  
Flow Boiling ◽  
Heating Surface ◽  
Surface Tension Force ◽  
Nucleation Site ◽  
Force Balance ◽  
Horizontal Flow ◽  
Balance Model ◽  
Direction Parallel ◽  
Dimensionless Parameters

In this paper, a simplified force-balance model in horizontal flow boiling is proposed by introducing several dominant dimensionless parameters. Forces acting on a bubble attached in the direction parallel to the heating surface are analyzed completely, which include quasi-steady drag force, surface tension force and growth force in x-direction. When the force balance is broken in the x-direction before the y-direction, bubble will departure from the nucleation site immediately. Based on the force-balance analysis, bubble departure diameter is formulated to be a function of Jakob number, Reynolds number and Prandtl number. By analyzing the effects of dimensionless parameters, it is found higher Jakob number indicates larger bubble departure diameter, while the increase of Reynolds number will reduce the departure diameter. Besides, the simplified model is able to enlarge application of force-balance model under various dimensionless parameters and make the calculation of bubble departure diameter much easier. Finally, comparing with the experimental data reported in literature, the error between simplified force-balance model and experimental is about 25%.

Investigation of the Influence of Elevated Pressure on Subcooled Boiling Flow—Model Evaluation Toward Generic Approach

2017 ◽  
Vol 139 (7) ◽  
Author(s):  
Sara Vahaji ◽  
Sherman Chi Pok Cheung ◽  
Guan Heng Yeoh ◽  
Jiyuan Tu
Keyword(s):  
Mechanistic Model ◽  
Elevated Pressure ◽  
Nucleation Site ◽  
Empirical Models ◽  
Mechanistic Modeling ◽  
Force Balance ◽  
Balance Model ◽  
Subcooled Boiling ◽  
Flow Conditions ◽  
Wide Range

Modeling subcooled boiling flows in vertical channels has relied heavily on the utilization of empirical correlations for the active nucleation site density, bubble departure diameter, and bubble departure frequency. Following the development and application of mechanistic modeling at low pressures, the capability of the model to resolve flow conditions at elevated pressure up to 10 bar is thoroughly assessed and compared with selected empirical models. Predictions of the mechanistic and selected empirical models are validated against two experimental data at low to elevated pressures. The results demonstrate that the mechanistic model is capable of predicting the heat and mass transfer processes. In spite of some drawbacks of the currently adopted force balance model, the results still point to the great potential of the mechanistic model to predict a wide range of flow conditions in subcooled boiling flows.

A Scale Analysis Based Theoretical Force Balance Model for Critical Heat Flux (CHF) During Saturated Flow Boiling in Microchannels and Minichannels

2010 ◽  
Vol 132 (8) ◽  
Author(s):  
Satish G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Surface Tension ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Flow Boiling ◽  
Narrow Channel ◽  
Force Balance ◽  
Balance Model ◽  
Scale Analysis ◽  
Error Band

Accurate prediction of critical heat flux (CHF) in microchannels and minichannels is of great interest in estimating the safe operational limits of cooling systems employing flow boiling. Scale analysis is applied to identify the relevant forces leading to the CHF condition. Using these forces, a local parameter model is developed to predict the flow boiling CHF. The theoretical model is an extension of an earlier pool boiling CHF model and incorporates force balance among the evaporation momentum, surface tension, inertia, and viscous forces. Weber number, capillary number, and a new nondimensional group introduced earlier by Kandlikar (2004, “Heat Transfer Mechanisms During Flow Boiling in Microchannels,” ASME J. Heat Transfer, 126, pp. 8–16), K2, representing the ratio of evaporation momentum to surface tension forces, emerged as main groups in quantifying the narrow channel effects on CHF. The constants in the model were calculated from the available experimental data. The mean error with ten data sets is 19.7% with 76% data falling within ±30% error band and 93% within ±50% error band. The length to diameter ratio emerged as a parameter indicating a stepwise regime change. The success of the model indicates that flow boiling CHF can be modeled as a local phenomenon and the scale analysis is able to reveal important information regarding fundamental mechanisms leading to the CHF condition.

scholarly journals Predicting Critical Heat Flux With Multiphase CFD: 4 Years in the Making

2017 ◽  
Author(s):  
Emilio Baglietto ◽  
Etienne Demarly ◽  
Ravikishore Kommajosyula
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Bubble Dynamics ◽  
Flow Boiling ◽  
Heated Surface ◽  
Force Balance ◽  
Modeling Framework ◽  
Lift Off ◽  
Limiting Condition

Advancement in the experimental techniques have brought new insights into the microscale boiling phenomena, and provide the base for a new physical interpretation of flow boiling heat transfer. A new modeling framework in Computational Fluid Dynamics has been assembled at MIT, and aims at introducing all necessary mechanisms, and explicitly tracks: (1) the size and dynamics of the bubbles on the surface; (2) the amount of microlayer and dry area under each bubble; (3) the amount of surface area influenced by sliding bubbles; (4) the quenching of the boiling surface following a bubble departure and (5) the statistical bubble interaction on the surface. The preliminary assessment of the new framework is used to further extend the portability of the model through an improved formulation of the force balance models for bubble departure and lift-off. Starting from this improved representation at the wall, the work concentrates on the bubble dynamics and dry spot quantification on the heated surface, which governs the Critical Heat Flux (CHF) limit. A new proposition is brought forward, where Critical Heat Flux is a natural limiting condition for the heat flux partitioning on the boiling surface. The first principle based CHF is qualitatively demonstrated, and has the potential to deliver a radically new simulation technique to support the design of advanced heat transfer systems.

An onset of nucleate boiling criterion for horizontal flow boiling

2000 ◽  
Vol 39 (9-11) ◽  
pp. 909-918 ◽  
Author(s):  
Olivier Zürcher ◽  
John R. Thome ◽  
Daniel Favrat
Keyword(s):  
Flow Boiling ◽  
Nucleate Boiling ◽  
Horizontal Flow

A Perspective on Combustion-Driven Flows With Circulation

2001 ◽  
Author(s):  
Francine Battaglia ◽  
Ronald G. Rehm ◽  
Howard R. Baum ◽  
Mohamed I. Hassan ◽  
Kozo Saito
Keyword(s):  
Reynolds Number ◽  
Froude Number ◽  
Theoretical Studies ◽  
Swirl Number ◽  
Dimensionless Parameters ◽  
Parametric Investigation ◽  
Fire Whirl ◽  
Slender Column ◽  
Combustion Processes

Abstract Perhaps the most dramatic example of surprising behavior when circulation is imposed on a combustion-driven flow is the fire whirl, where the burning gases form a tall slender column. Relatively few studies have addressed the influence of circulation on the development of combustion-driven flows. Three dimensionless parameters characterize this interplay: the Froude number, the swirl number and the Reynolds number. It is surprising that for most studies, even with plausible assumptions concerning the experiments, not enough information is given to determine the values of these parameters. We will experimentally reconstruct these studies in an effort to characterize parametrically these interactions. Both buoyancy-driven and momentum-driven combustion processes will be investigated to determine the influence of circulation. Theoretical studies will occur in conjunction to provide the most complete parametric investigation.

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