Investigation of Pool Boiling Critical Heat Flux Enhancement on a Modified Surface Through the Dynamic Wetting of Water Droplets

2012 ◽  
Vol 134 (7) ◽  
Author(s):  
Ho Seon Ahn ◽  
Joonwon Kim ◽  
Moo Hwan Kim
Keyword(s):  
Surface Tension ◽  
Heat Flux ◽  
Contact Angle ◽  
Critical Heat Flux ◽  
Pool Boiling ◽  
Water Layer ◽  
Contact Angles ◽  
Water Droplets ◽  
Dynamic Wetting ◽  
Modified Surface

Dynamic wetting behaviors of water droplet on the modified surface were investigated experimentally. Dynamic contact angles were measured as a characterization method to explain the extraordinary pool boiling critical heat flux (CHF) enhancement on the zirconium surface by anodic oxidation modification. The sample surface is rectangular zirconium alloy plates (20 × 25 × 0.7 mm), and 12 μl of deionized water droplets were fallen from 40 mm of height over the surface. Dynamic wetting movement of water on the surface showed different characteristics depending on static contact angle (49.3 deg–0 deg) and surface temperature (120 °C–280 °C). Compared with bare surface, wettable and spreading surface had no-receding contact angle jump and seemed stable evaporating meniscus of liquid droplet in dynamic wetting condition on hot surface. This phenomenon could be explained by the interaction between the evaporation recoil and the surface tension forces. The surface tension force increased by micro/nanostructure of the modified zirconium surface suppresses the vapor recoil force by evaporation which makes the water layer unstable on the heated surface. Thus, such increased surface force could sustain the water layer stable in pool boiling CHF condition so that the extraordinary CHF enhancement could be possible.

On the Role of Marangoni Effects on the Critical Heat Flux for Pool Boiling of Binary Mixtures

1996 ◽  
Vol 118 (1) ◽  
pp. 103-109 ◽  
Author(s):  
W. R. McGillis ◽  
V. P. Carey
Keyword(s):  
Surface Tension ◽  
Heat Flux ◽  
Binary Mixtures ◽  
Critical Heat Flux ◽  
Full Range ◽  
Pool Boiling ◽  
Marangoni Effect ◽  
Restoring Force ◽  
Marangoni Effects

The Marangoni effect on the critical heat flux (CHF) condition in pool boiling of binary mixtures has been identified and its effect has been quantitatively estimated with a modified model derived from hydrodynamics. The physical process of CHF in binary mixtures, and models used to describe it, are examined in the light of recent experimental evidence, accurate mixture properties, and phase equilibrium revealing a correlation to surface tension gradients and volatility. A correlation is developed from a heuristic model including the additional liquid restoring force caused by surface tension gradients. The CHF condition was determined experimentally for saturated methanol/water, 2-propanol/water, and ethylene glycol/water mixtures, over the full range of concentrations, and compared to the model. The evidence in this study demonstrates that in a mixture with large differences in surface tension, there is an additional hydrodynamic restoring force affecting the CHF condition.

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.

Effects of Surface Orientation on the Pool Boiling Heat Transfer in Water/2-Propanol Mixtures

1999 ◽  
Vol 121 (1) ◽  
pp. 80-88 ◽  
Author(s):  
S. Ahmed ◽  
V. P. Carey
Keyword(s):  
Heat Transfer ◽  
Surface Tension ◽  
Heat Flux ◽  
Binary Mixtures ◽  
Critical Heat Flux ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Bulk Liquid ◽  
Heater Surface ◽  
Pool Boiling Heat Transfer

To explore the role of Marangoni effects in the pool boiling heat transfer of binary mixtures, experiments have been conducted with water/2-propanol mixtures at three different concentrations under normal gravity with different orientations of the heater surface. The system pressure was subatmospheric (∼5.5 kPa) and the bulk liquid temperature was near the saturation temperature of the fluids tested. The molar concentrations of2-propanol tested were 0.015, 0.025, and 0.1. These concentrations of 2-propanol are selected because their strong variation of surface tension with concentration gives rise to high surface tension gradients near the heater surface during nucleate boiling. Boiling curves were obtained both for an upward-facing and a downward-facing heater surface. For each concentration of 2-propanol, the critical heat flux has been reached in both orientations of the heater surface. Models of pool boiling heat transfer and the critical heat flux condition for binary mixtures are tested to correlate the data. Comparison of boiling curves and CHF obtained at different orientations of the heater surface indicates that there is strong gravity independent mechanism of boiling heat transfer in these mixtures.

INVESTIGATING THE RELATIONSHIP BETWEEN SURFACE WICKABILITY AND CRITICAL HEAT FLUX DURING POOL BOILING

2018 ◽  
Author(s):  
Youngsup Song ◽  
Yangying Zhu ◽  
Daniel J. Preston ◽  
H. Jeremy Cho ◽  
Zhengmao Lu ◽  
...  
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Pool Boiling ◽  
The Relationship

THE CRITICAL HEAT FLUX AT THE POOL BOILING OF SOME BINARY LIQUID MIXTURES

2019 ◽  
Author(s):  
Samson Semenovich Kutateladze ◽  
G.I. Bobrovich ◽  
I. I. Gogonin ◽  
N.N. Mamontova ◽  
V.N. Moskvicheva
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Pool Boiling ◽  
Liquid Mixtures ◽  
Binary Liquid Mixtures ◽  
Binary Liquid

Effects of Surface Coating on the Critical Heat Flux for Pool Boiling from a Downward Facing Surface

2004 ◽  
Vol 11 (2) ◽  
pp. 133-150 ◽  
Author(s):  
M. B. Dizon ◽  
J. Yang ◽  
F. B. Cheung ◽  
J. L. Rempe ◽  
K. Y. Suh ◽  
...  
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Surface Coating ◽  
Pool Boiling

scholarly journals Influence of moisture content on the contact angle and surface tension measured on birch wood surfaces

2021 ◽  
Author(s):  
Rami Benkreif ◽  
Fatima Zohra Brahmia ◽  
Csilla Csiha
Keyword(s):  
Surface Tension ◽  
Contact Angle ◽  
Moisture Content ◽  
Solid Wood ◽  
Contact Angles ◽  
Surface Moisture ◽  
Wood Coatings ◽  
The Relationship ◽  
Wood Surfaces

AbstractSurface tension of solid wood surfaces affects the wettability and thus the adhesion of various adhesives and wood coatings. By measuring the contact angle of the wood, the surface tension can be calculated based on the Young-Dupré equation. Several publications have reported on contact angle measured with different test liquids, under different conditions. Results can only be compared if the test conditions are similar. While the roles of the drop volume, image shooting time etc., are widely recognized, the role of the wood surface moisture content (MC) is not evaluated in detail. In this study, the effect of wood moisture content on contact angle values, measured with distilled water and diiodomethane, on sanded birch (Betula pendula) surfaces was investigated, in order to find the relationship between them. With increasing MC from approximately 6% to 30%, increasing contact angle (decreasing surface tension) values were measured according to a logarithmic function. The function makes possible the calculation of contact angles that correspond to different MCs.

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