The Onset of Flow Instability in Uniformly Heated Horizontal Microchannels

1999 ◽  
Vol 122 (1) ◽  
pp. 118-125 ◽  
Author(s):  
J. E. Kennedy ◽  
G. M. Roach, ◽  
M. F. Dowling ◽  
S. I. Abdel-Khalik ◽  
S. M. Ghiaasiaan ◽  
...  
Keyword(s):  
Heat Flux ◽  
Flow Instability ◽  
Experimental Parameter ◽  
Nucleate Boiling ◽  
Wall Heat Flux ◽  
Exit Pressure ◽  
Channel Exit ◽  
Demand Curves ◽  
Parameter Ranges ◽  
Heated Length

Onset of nucleate boiling and onset of flow instability in uniformly heated microchannels with subcooled water flow were experimentally investigated using 22-cm long tubular test sections, 1.17 mm and 1.45 mm in diameter, with a 16-cm long heated length. Important experimental parameter ranges were: 3.44 to 10.34 bar channel exit pressure; 800 to 4500 kg/m2s mass flux (1 to 5 m/s inlet velocity); 0 to 4.0 MW/m2 channel wall heat flux; and 7440–33,000 Peclet number at the onset of flow instability. Demand curves (pressure drop versus mass flow rate curves for fixed wall heat flux and channel exit pressure) were generated for the test sections, and were utilized for the specification of the onset of nucleate boiling and the onset of flow instability points. The obtained onset of nucleate boiling and onset of flow instability data are presented and compared with relevant widely used correlations. [S0022-1481(00)02101-0]

Empirical Correlation of Factors Influencing Departure From Nucleate Boiling in Steam-Water Mixtures Flowing in Vertical Round Tubes

1966 ◽  
Vol 88 (4) ◽  
pp. 367-373 ◽  
Author(s):  
D. Pasint ◽  
R. H. Pai
Keyword(s):  
Experimental Data ◽  
Heat Flux ◽  
Forced Convection ◽  
Mass Flow ◽  
Nucleate Boiling ◽  
Vertical Tube ◽  
Empirical Correlation ◽  
Factors Influencing ◽  
Vertical Tubes ◽  
Heated Length

An empirical correlation of forced convection DNB for steam-water mixtures between 500 and 3000 psia in uniformly heated vertical tubes is proposed. DNB quality is expressed in terms of pressure, mass flow, inlet enthalpy, heated length from inlet to DNB point, and tube dia. The experimental data of the authors at 2000–3000 psia, 250,000–1,000,000 lb/hr sq ft2 mass flow, and 40,000–180,000 Btu/hr sq ft heat flux, obtained from a 6 ft long, 3/4-in-ID electrically heated vertical tube, are correlated with other published results ranging from 500 to 2000 psia.

Flow Boiling in Minichannels of Copper, Brass, and Aluminum Round Tubes

2004 ◽  
Author(s):  
K. H. Bang ◽  
W. H. Choo
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Wall Heat Flux ◽  
Vapor Quality ◽  
Transfer Coefficients ◽  
Flow Boiling Heat Transfer

The past work on flow boiling heat transfer in minichannels ranging one to three millimeters of hydraulic diameter has indicated that the local heat transfer coefficients are largely independent of mass flux and vapor quality, but mainly a function of wall heat flux. The present work is a revisit of flow boiling in minichannels by conducting experiment using 1.67 mm inner diameter tubes of three different materials; aluminum, brass, and copper, to investigate an effect of the tube inner surface conditions with the focus on an effect on nucleate boiling. Tests were conducted for R-22, a fixed mass flux of 600 kg/m2s, 5∼30 kW/m2 of wall heat flux, 0.0∼0.9 of local vapor quality. The present experimental data confirmed that the flow boiling heat transfer coefficient in a minichannel varies only by heat flux, independent of mass flux and vapor quality. The effect of tube material was found small for the tubes used in the present work. The present data were well predicted by the correlation proposed by Tran et al. (1996).

Heat Transfer and Wall Heat Flux Partitioning During Subcooled Flow Nucleate Boiling—A Review

2006 ◽  
Vol 128 (12) ◽  
pp. 1243-1256 ◽  
Author(s):  
Gopinath R. Warrier ◽  
Vijay K. Dhir
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Flux ◽  
Nucleate Boiling ◽  
Wall Heat Flux ◽  
Forced Flow ◽  
Mechanistic Models ◽  
Subcooled Flow ◽  
Flux Partitioning ◽  
Empirical And Mechanistic Models

In this paper we provide a review of heat transfer and wall heat flux partitioning models/correlations applicable to subcooled forced flow nucleate boiling. Details of both empirical and mechanistic models that have been proposed in the literature are provided. A comparison of the experimental data with predictions from selected models is also included.

scholarly journals Computational fluid dynamics and population balance modelling of nucleate boiling of cryogenic liquids: Theoretical developments

2016 ◽  
Vol 8 (4) ◽  
pp. 178-200 ◽  
Author(s):  
Guan Heng Yeoh ◽  
Xiaobin Zhang
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Nucleate Boiling ◽  
Nucleation Site ◽  
Heat Transfer Process ◽  
Wall Heat Flux ◽  
Heated Wall ◽  
Balance Model ◽  
Bulk Liquid ◽  
Two Phase

The main focus in the analysis of pool or flow boiling in saturated or subcooled conditions is the basic understanding of the phase change process through the heat transfer and wall heat flux partitioning at the heated wall and the two-phase bubble behaviours in the bulk liquid as they migrate away from the heated wall. This paper reviews the work in this rapid developing area with special reference to modelling nucleate boiling of cryogenic liquids in the context of computational fluid dynamics and associated theoretical developments. The partitioning of the wall heat flux at the heated wall into three components – single-phase convection, transient conduction and evaporation – remains the most popular mechanistic approach in predicting the heat transfer process during boiling. Nevertheless, the respective wall heat flux components generally require the determination of the active nucleation site density, bubble departure diameter and nucleation frequency, which are crucial to the proper prediction of the heat transfer process. Numerous empirical correlations presented in this paper have been developed to ascertain these three important parameters with some degree of success. Albeit the simplicity of empirical correlations, they remain applicable to only a narrow range of flow conditions. In order to extend the wall heat flux partitioning approach to a wider range of flow conditions, the fractal model proposed for the active nucleation site density, force balance model for bubble departing from the cavity and bubble lifting off from the heated wall and evaluation of nucleation frequency based on fundamental theory depict the many enhancements that can improve the mechanistic model predictions. The macroscopic consideration of the two-phase boiling in the bulk liquid via the two-fluid model represents the most effective continuum approach in predicting the volume fraction and velocity distributions of each phase. Nevertheless, the interfacial mass, momentum and energy exchange terms that appear in the transport equations generally require the determination of the Sauter mean diameter or interfacial area concentration, which strongly governs the fluid flow and heat transfer in the bulk liquid. In order to accommodate the dynamically changing bubble sizes that are prevalent in the bulk liquid, the mechanistic approach based on the population balance model allows the appropriate prediction of local distributions of Sauter mean diameter or interfacial area concentration, which in turn can improve the predictions of the interfacial mass, momentum and energy exchanges that occur across the interface between the phases. Need for further developments are discussed.

Wall Heat Flux Partitioning During Subcooled Flow Boiling at Low Pressures

2003 ◽  
Author(s):  
Nilanjana Basu ◽  
Gopinath R. Warrier ◽  
Vijay K. Dhir
Keyword(s):  
Heat Flux ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Wall Heat Flux ◽  
Superheated Liquid ◽  
Pressure Data ◽  
Vapor Generation ◽  
Subcooled Flow Boiling ◽  
Wall Superheat ◽  
Subcooled Flow

In this work a mechanistic model for nucleate boiling heat flux as a function of wall superheat has been developed. The premise of the proposed model is that the entire energy from the wall is first transferred to the superheated liquid layer adjacent to the wall. A fraction of this energy is then utilized for vapor generation. Contribution of each of the heat transfer mechanisms — forced convection, transient conduction, and vapor generation, has been quantified in terms of nucleation site densities, bubble departure and lift off diameters, bubble release frequency, flow parameters like velocity, inlet subcooling, wall superheat, and fluid and surface properties including system pressures. To support the model development, subcooled flow boiling experiments were conducted at pressures of 1.03 to 3.2 bar for a wide range of mass fluxes (124 to 926 kg/m2s), heat fluxes (2.5 to 90 W/cm2) and for contact angles varying from 30° to 90°. Model validation has been carried out with low-pressure data obtained from present work and the wall heat flux predictions are within ± 30% of experimental values. Application of the model to high-pressure data available in literature also showed good agreement, signifying that the model can be extended to all pressures.

Enhancing Flow Boiling Heat Transfer in Microchannels Using Monolithically-Coated Silicon Nanowires

2011 ◽  
Author(s):  
Dan Li ◽  
Gensheng Wu ◽  
Wei Wang ◽  
Yunda Wang ◽  
Ronggui Yang
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Critical Heat Flux ◽  
Silicon Nanowires ◽  
Flow Instability ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Variable Cross

Flow boiling in microchannels has been attractive for cooling of high power electronics. However, the flow instability hinders the heat transfer performance such as the premature initiation of the critical heat flux (CHF) and could result in device burnout. Numerous methods have been implemented to suppress the instability of flow boiling, including integrating micro pin fins in the channels [1] and inlet restrictors [2], as well as fabricating microchannels with variable cross-sectional areas [3]. Recently, Li et al [4] and Chen et al [5] explored the pool boiling enhancement using nanowires, which shows much more uniform bubble generation and a higher heat transfer coefficient and critical heat flux compared to plain surfaces. The work presented here is the very first effort to explor the impacts of nanowire coating on the flow boiling performance in parallel microchannels. We present here a monolithic integration process to fabricate silicon micro-channels coated with silicon nanowires and the flow boiling characterization of the microchannels. By comparing the flow boiling curves in the microchannels with and without nanowire coating, we show significant performance enhancement for a nanowire-coated microchannel, such as earlier ONB (onset of nucleate boiling), delayed OFO (onset of flow oscillation), enhanced HTC (heat transfer coefficient) and suppressed flow instability.

Towards Mechanistic Wall Heat Flux Partitioning Model for Fully Developed Nucleate Boiling

2021 ◽  
Author(s):  
Muritala A Amidu
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Nucleate Boiling ◽  
Wall Heat Flux ◽  
Heated Wall ◽  
High Heat Flux ◽  
Mechanistic Models ◽  
Flux Partitioning ◽  
Evaporation Heat ◽  
Small Bubbles

Abstract Mechanistic models developed to predict partial nucleate boiling are not adequate for fully developed nucleate boiling due to differences in the prevailing heat transfer governing mechanisms. In place of the mechanistic model, several empirical correlations and semi-mechanistic models have been proposed over the years for the prediction of fully developed nucleate boiling as presented in this study but they are unsuitable for use in computational fluid dynamics (CFD) code. Recently, the simulation of fully developed nucleate boiling has become much more practical because of advancement in a computational method that involves the coupling of the interface capturing method (for slug bubbles) with the Eulerian multi-fluid model (for dispersed spherical bubbles). Nonetheless, there is a need for a mechanistic closure law for the fully developed nucleate boiling phenomenon that would complement this advancement in CFD. Towards this end, a mechanistic wall heat flux partitioning model for fully developed nucleate boiling is proposed in this study. This model is predicated on the hypothesis that a high heat flux nucleate boiling is distinguished by the existence of a liquid macro-layer between the heated wall and the slug or elongated bubbles and that the macro-layer is interspersed with numerous high frequency nucleate small bubbles. With this hypothesis, the heat flux generated on the heated wall is partitioned into two parts: conduction heat transfer across the macro-layer liquid film thickness and evaporation heat flux of the microlayer of the nucleating small bubbles. The proposed model is validated against experimental data.

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