ROLE OF EASY-TO-ACTIVATE NUCLEATION SITES IN POOL BOILING

2018 ◽  
Author(s):  
Yi Liu ◽  
Ming-Chang Lu ◽  
Dongyan Xu
Keyword(s):  
Pool Boiling ◽  
Nucleation Sites

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.

Role of macrolayer evaporation in pool boiling at high heat flux

1986 ◽  
Vol 29 (12) ◽  
pp. 1953-1961 ◽  
Author(s):  
A.M. Bhat ◽  
J.S. Saini ◽  
R. Prakash
Keyword(s):  
Heat Flux ◽  
Pool Boiling ◽  
High Heat ◽  
High Heat Flux

scholarly journals Effect of Uniformly and Nonuniformly Coated Al2O3 Nanoparticles over Glass Tube Heater on Pool Boiling

2016 ◽  
Vol 2016 ◽  
pp. 1-6 ◽  
Author(s):  
Nitin Doifode ◽  
Sameer Gajghate ◽  
Abdul Najim ◽  
Anil Acharya ◽  
Ashok Pise
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
High Speed ◽  
Pool Boiling ◽  
Glass Tube ◽  
Al2o3 Nanoparticles ◽  
High Speed Camera ◽  
Coated Nanoparticles ◽  
Nucleation Sites ◽  
Coated Surface

Effect of uniformly and nonuniformly coated Al2O3 nanoparticles over plain glass tube heater on pool boiling heat transfer was studied experimentally. A borosilicate glass tube coated with Al2O3 nanoparticle was used as test heater. The boiling behaviour was studied by using high speed camera. Result obtained for pool boiling shows enhancement in heat transfer for nanoparticle coated surface heater and compared with plain glass tube heater. Also heat transfer coefficient for nonuniformly coated nanoparticles was studied and compared with uniformly coated and plain glass tube. Coating effect of nanoparticles over glass tube increases its surface roughness and thereby creates more nucleation sites.

Shear Cavitation

2005 ◽  
Author(s):  
P. A. Kottke ◽  
S. Bair ◽  
W. O. Winer
Keyword(s):  
Normal Stress ◽  
Hydrodynamic Pressure ◽  
Local Flow ◽  
Flowing Liquid ◽  
Principal Normal Stress ◽  
State Of Stress ◽  
Nucleation Sites ◽  
Theoretical Foundations ◽  
Viscous Stresses

The importance of cavitation in lubrication hydrodynamics is well recognized. Cavitation can also act as a source of experimental error in rheological measurements. Therefore, the ability to understand and predict cavitation is important for tribology. Nearly all models for cavitation prediction are based on the local hydrodynamic pressure. The appropriateness of this approach when viscous stresses are of the order of the hydrodynamic pressure is questionable. One cavitation model that considers the state of stress in a flowing liquid is the principal normal stress cavitation criterion (PNSCC), which proposes that cavitation will occur when the most tensile principal normal stress exceeds some critical value. Although this hypothesis can accommodate many experimental observations, its theoretical foundations are weak. In particular, it fails to account for the tensile strength of liquids and resulting need for nucleation sites; it neglects the role of transport of dissolved gases; and it does not consider the effect of a growing bubble on the local flow, and hence local state of stress. We demonstrate cavitation in low Reynolds number Couette flow, and present a model for cavitation in shear in the limit of creeping (Stokes) flow, which corrects for the theoretical failures of the PNSCC. We use numerical simulation to analyze cavitation onset, and obtain a more general cavitation criteria from which the PNSCC is recovered under certain conditions.

Evolution of Twin-Related Variants of α Phase in a Ti-V-Cu Alloy

2011 ◽  
Vol 172-174 ◽  
pp. 481-486 ◽  
Author(s):  
Hoi Pang Ng ◽  
Colleen J. Bettles ◽  
Barry C. Muddle
Keyword(s):  
Electron Microscopy ◽  
Early Stage ◽  
Twin Plane ◽  
System A ◽  
Cu Alloy ◽  
Α Phase ◽  
Transmission Electron ◽  
Nucleation Sites ◽  
Isothermal Ageing

The precipitation of a-phase has been investigated in a concentrated b-alloy of the Ti-V-Cu system. a-precipitates in geometrically coupled forms were developed in the alloy when subject to isothermal ageing at 500°C. High-resolution transmission electron microscopy (HRTEM) revealed that a-phase embryos tend to nucleate in a symmetrical manner directly from an early-stage solute-partitioned diffusional product. The a-precipitates so developed constitute twin-related variants characterized by a twin plane lying on one of the {0111}a planes. The results are discussed with respect to the role of Cu on the formation of heterogeneous nucleation sites for a-phase.

scholarly journals Structural Mutants of the Spindle Pole Body Cause Distinct Alteration of Cytoplasmic Microtubules and Nuclear Dynamics in Multinucleated Hyphae

2010 ◽  
Vol 21 (5) ◽  
pp. 753-766 ◽  
Author(s):  
Claudia Lang ◽  
Sandrine Grava ◽  
Mark Finlayson ◽  
Rhonda Trimble ◽  
Peter Philippsen ◽  
...  
Keyword(s):  
Spindle Pole Body ◽  
Spindle Pole ◽  
Wild Type ◽  
Nuclear Dynamics ◽  
Pole Body ◽  
Nucleation Sites ◽  
Bridge Structures ◽  
Cytoplasmic Microtubules ◽  
Tangential Directions

In the multinucleate fungus Ashbya gossypii, cytoplasmic microtubules (cMTs) emerge from the spindle pole body outer plaque (OP) in perpendicular and tangential directions. To elucidate the role of cMTs in forward/backward movements (oscillations) and bypassing of nuclei, we constructed mutants potentially affecting cMT nucleation or stability. Hyphae lacking the OP components AgSpc72, AgNud1, AgCnm67, or the microtubule-stabilizing factor AgStu2 grew like wild- type but showed substantial alterations in the number, length, and/or nucleation sites of cMTs. These mutants differently influenced nuclear oscillation and bypassing. In Agspc72Δ, only long cMTs were observed, which emanate tangentially from reduced OPs; nuclei mainly moved with the cytoplasmic stream but some performed rapid bypassing. Agnud1Δ and Agcnm67Δ lack OPs; short and long cMTs emerged from the spindle pole body bridge/half-bridge structures, explaining nuclear oscillation and bypassing in these mutants. In Agstu2Δ only very short cMTs emanated from structurally intact OPs; all nuclei moved with the cytoplasmic stream. Therefore, long tangential cMTs promote nuclear bypassing and short cMTs are important for nuclear oscillation. Our electron microscopy ultrastructural analysis also indicated that assembly of the OP occurs in a stepwise manner, starting with AgCnm67, followed by AgNud1 and lastly AgSpc72.

Effect of Thermophysical Properties of the Heater Substrate on Critical Heat Flux in Pool Boiling

2017 ◽  
Vol 139 (11) ◽  
Author(s):  
Pruthvik A. Raghupathi ◽  
Satish G. Kandlikar
Keyword(s):  
Thermal Conductivity ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Pool Boiling ◽  
Temperature Fluctuations ◽  
Operating Conditions ◽  
Force Balance ◽  
Heater Surface ◽  
Monel 400

While the role of the liquid properties, surface morphology, and operating conditions on critical heat flux (CHF) in pool boiling is well investigated, the effect of the properties of the heater material is not well understood. Previous studies indicate that the heater thickness plays an important role on the CHF phenomenon. However, beyond a certain thickness, called the asymptotic thickness, the local temperature fluctuations on the heater surface caused by the periodic bubble ebullition cycle are evened out, and the CHF is not influenced by further increasing the thickness. In the present work, data from literature and pool boiling experiments conducted in this study with seven substrates—aluminum, brass, copper, carbon steel, Monel 400, silver, and silicon—are used to determine the effect of the thermophysical property of the material on CHF for thick heaters that are used in industrial pool boiling applications. The results indicate that the product of density (ρ) and specific heat (cp) represents an important substrate property group that affects the CHF, and that the thermal conductivity is not an important parameter. A well-established force-balance-based CHF model (Kandlikar model) is modified to account for the thermal properties of the substrate. The predicted CHF values are within 15% of the experimental results.

Effects of Dissolved Gas Content on Pool Boiling of a Highly Wetting Fluid

1995 ◽  
Vol 117 (3) ◽  
pp. 687-692 ◽  
Author(s):  
S. M. You ◽  
T. W. Simon ◽  
A. Bar-Cohen ◽  
Y. S. Hong
Keyword(s):  
Heat Transfer ◽  
Pool Boiling ◽  
Electronics Cooling ◽  
Horizontal Cylinder ◽  
Gas Content ◽  
Free Fluid ◽  
Dissolved Gas ◽  
Boiling Incipience ◽  
Wetting Fluid

Experimental results on pool boiling heat transfer from a horizontal cylinder in an electronic cooling fluid (FC-72) are presented. The effects on the boiling curve of having air dissolved in the fluid are documented, showing that fluid in the vicinity of the heating element is apparently liberated of dissolved gas during boiling. Dissolved gas was found to influence boiling incipience only with high gas concentrations (>0.005 moles/mole). For low-to-moderate concentrations, a larger superheat is required to initiate boiling and a hysteresis is observed between boiling curves taken with increasing and decreasing heat flux steps. Boiling, a very effective mode of heat transfer, is attractive for electronics cooling. The present experiment provides further documentation of the role of dissolved gas on the incipience process and shows similarities with subcooled boiling of a gas-free fluid.

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