Experiments and Universal Growth Relations for Vapor Bubbles With Microlayers

1978 ◽  
Vol 100 (1) ◽  
pp. 41-48 ◽  
Author(s):  
T. G. Theofanous ◽  
T. H. Bohrer ◽  
M. C. Chang ◽  
P. D. Patel
Keyword(s):  
Heat Transfer ◽  
Bubble Growth ◽  
A Priori ◽  
Theoretical Development ◽  
Rate Data ◽  
Vapor Bubbles ◽  
Generalized Coordinates ◽  
Wide Range ◽  
Extended Range ◽  
Microlayer Evaporation

Solutions for bubble growth rates including the effects of inertia, heat transfer, and microlayer evaporation were obtained in generalized coordinates. Experimental growth rate data, covering a wide range of superheats, were obtained under precisely controlled conditions. The theoretical development appears to provide a satisfactory a priori prediction of these data. In particular, the Γ-effect predicted earlier is fully corroborated by these data which are the first to cover an extended range of this parameter.

Near-Wall Microlayer Evaporation Analysis and Experimental Study of Nucleate Pool Boiling on Inclined Surfaces

1998 ◽  
Vol 120 (3) ◽  
pp. 641-653 ◽  
Author(s):  
G. F. Naterer ◽  
W. Hendradjit ◽  
K. J. Ahn ◽  
J. E. S. Venart
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heating Surface ◽  
Nucleate Boiling ◽  
Inclined Surfaces ◽  
Wide Range ◽  
Model Predictions ◽  
Microlayer Evaporation ◽  
Near Wall

Boiling heat transfer from inclined surfaces is examined and an analytical model of bubble growth and nucleate boiling is presented. The model predicts the average heat flux during nucleate boiling by considering alternating near-wall liquid and vapor periods. It expresses the heat flux in terms of the bubble departure diameter, frequency and duration of contact with the heating surface. Experiments were conducted over a wide range of upward and downward-facing surface orientations and the results were compared to model predictions. More active microlayer agitation and mixing along the surface as well as more frequent bubble sweeps along the heating surface provide the key reasons for more effective heat transfer with downward facing surfaces as compared to upward facing cases. Additional aspects of the role of surface inclination on boiling dynamics are quantified and discussed.

The Origin of the Dynamic Growth of Vapor Bubbles Related to Vapor Explosions

1998 ◽  
Vol 120 (1) ◽  
pp. 174-182 ◽  
Author(s):  
H. S. Lee ◽  
H. Merte
Keyword(s):  
Heat Transfer ◽  
Bubble Growth ◽  
Hydrodynamic Instability ◽  
Early Growth ◽  
Instability Mechanism ◽  
Vapor Bubbles ◽  
Vapor Interface ◽  
Vapor Explosions ◽  
Dynamic Growth ◽  
Classical Hydrodynamic

An explosive type of vapor bubble growth was observed during pool boiling experiments in microgravity using R-113. Photographs reveal that the liquid-vapor interface of the explosive bubbles are wrinkled and corrugated, leading to the conclusion that some type of instability mechanism is acting. The classical hydrodynamic instability theories of Landau and Rayleigh-Taylor do not consider the effect of heat transfer, at the interface, which is believed to be responsible for the observed instability of the evaporating surface. This was confirmed by the mechanisms proposed by Prosperetti and Plesset, combined with a model of the early growth of spherical vapor bubbles.

Numerical Modeling of Multidirectional Flow and Heat Transfer in Graphitic Foams

2009 ◽  
Vol 131 (5) ◽  
Author(s):  
S. A. Mohsen Karimian ◽  
Anthony G. Straatman
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Pore Structure ◽  
Linear Models ◽  
A Priori ◽  
Experimental Results ◽  
Transfer Model ◽  
Thermal Dispersion ◽  
Wide Range ◽  
Graphitic Foam

To investigate the feasibility of the use of foams with an interconnected spherical pore structure in heat transfer applications, models for heat transfer and pressure drop for this type of porous materials are developed. Numerical simulations are carried out for laminar multidirectional thermofluid flow in an idealized pore geometry of foams with a wide range of geometry parameters. Semiheuristic models for pressure drop and heat transfer are developed from the results of simulations. A simplified solid-body drag equation with an extended high inertia term is used to develop the hydraulic model. A heat transfer model with a nonzero asymptotic term for very low Reynolds numbers is also developed. To provide hydraulic and heat transfer models suitable for a wide range of porosity, only a general form of the length-scale as a function of pore structure is defined a priori, where the parameters of the function were determined as part of the modeling process. The proposed ideal models are compared to the available experimental results, and the source of differences between experimental results and the ideal models is recognized and then calibrated for real graphitic foam. The thermal model is used together with volume-averaged energy equations to calculate the thermal dispersion in graphitic foam. The results of the calculations show that the linear models for thermal dispersion available in literature are oversimplified for predicting thermal dispersion in this type of porous material.

Contribution of Microlayer Evaporation to Bubble Growth in Pool Saturated Boiling of Water

2013 ◽  
Author(s):  
Tomohide Yabuki ◽  
Takuya Saitoh ◽  
Osamu Nakabeppu
Keyword(s):  
Heat Transfer ◽  
Bubble Growth ◽  
Heated Surface ◽  
High Heat ◽  
High Heat Flux ◽  
Wall Heat Transfer ◽  
Heat Transfer Phenomenon ◽  
Microlayer Evaporation ◽  
Dry Out ◽  
Saturated Boiling

Heat transfer and formation characteristics of the microlayer are investigated by the surface temperature measurement with a MEMS thermal sensor and the wall heat transfer evaluation using an experimental data. The temperature data clearly indicated transition of heat transfer phenomenon on the heated surface from microlayer formation via dry-out of the microlayer to rewetting of the dry-out region. Microlayer evaporation transferred extremely high heat flux over 1 MW/m2 and was found to be the dominant heat transfer mechanism in the wall heat transfer during isolated bubble boiling of water. The contribution of microlayer evaporation to bubble growth was found to be 50% and not vary with wall superheat. Finally the spatial distribution of initial thickness of microlayer was calculated from the wall heat transfer.

scholarly journals A Systematic Review and Qualitative Synthesis Resulting in a Typology of Elementary Classroom Movement Integration Interventions

2020 ◽  
Vol 6 (1) ◽  
Author(s):  
Spyridoula Vazou ◽  
Collin A. Webster ◽  
Gregory Stewart ◽  
Priscila Candal ◽  
Cate A. Egan ◽  
...  
Keyword(s):  
Physical Activity ◽  
Teacher Collaboration ◽  
A Priori ◽  
Real Life ◽  
Dose Intensity ◽  
Routine Practice ◽  
Qualitative Synthesis ◽  
Wide Range ◽  
Meta Analyses ◽  
Movement Integration

Abstract Background/Objective Movement integration (MI) involves infusing physical activity into normal classroom time. A wide range of MI interventions have succeeded in increasing children’s participation in physical activity. However, no previous research has attempted to unpack the various MI intervention approaches. Therefore, this study aimed to systematically review, qualitatively analyze, and develop a typology of MI interventions conducted in primary/elementary school settings. Subjects/Methods Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were followed to identify published MI interventions. Irrelevant records were removed first by title, then by abstract, and finally by full texts of articles, resulting in 72 studies being retained for qualitative analysis. A deductive approach, using previous MI research as an a priori analytic framework, alongside inductive techniques were used to analyze the data. Results Four types of MI interventions were identified and labeled based on their design: student-driven, teacher-driven, researcher-teacher collaboration, and researcher-driven. Each type was further refined based on the MI strategies (movement breaks, active lessons, other: opening activity, transitions, reward, awareness), the level of intrapersonal and institutional support (training, resources), and the delivery (dose, intensity, type, fidelity). Nearly half of the interventions were researcher-driven, which may undermine the sustainability of MI as a routine practice by teachers in schools. An imbalance is evident on the MI strategies, with transitions, opening and awareness activities, and rewards being limitedly studied. Delivery should be further examined with a strong focus on reporting fidelity. Conclusions There are distinct approaches that are most often employed to promote the use of MI and these approaches may often lack a minimum standard for reporting MI intervention details. This typology may be useful to effectively translate the evidence into practice in real-life settings to better understand and study MI interventions.

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