Dynamics of a Water Droplet on the Heated Surface of Nano- and Micro-Structures

2012 ◽  
Author(s):  
Seol Ha Kim ◽  
Ho Seon Ahn ◽  
Joonwon Kim ◽  
Moo Hwan Kim
Keyword(s):  
Water Droplet ◽  
High Speed ◽  
Zirconium Alloy ◽  
Liquid Droplet ◽  
Heated Surface ◽  
Nucleate Boiling ◽  
High Speed Photography ◽  
Complete Wetting ◽  
Structured Surfaces ◽  
Bare Surface

In this study, we investigated the dynamic behavior of a water droplet near the Leidenfrost point (LFP) of bare and modified zirconium alloy surfaces with bundles of nanotubes (∼10–100 nm) or micro mountain-like structures using high-speed photography. A deionized water droplet (6 μL) was dropped onto the sample surfaces (20 × 25 × 0.7 mm) that were heated to temperatures ranging from 250°C to the LFP. The modified zirconium alloy surfaces showed complete wetting and well-spread features at room temperature due to strong liquid spreading by the structure. The meniscus of the liquid droplet on the structured surface experienced more vigorous dynamics with intensive nucleate boiling, compared with the clean, bare surface. The cutback phenomenon was observed on the bare surface; however, the structured surfaces showed a water droplet “burst”. We observed that the LFPs were 449°C, 522°C, and 570°C, corresponding to the bare, micro-, and nano-structures, respectively.

Experiments and Modeling of a Liquid Droplet Transported by a Gas Stream Impinging on a Heated Surface: Evaporative Regime

2009 ◽  
Author(s):  
Ryan P. Anderson ◽  
Alfonso Ortega
Keyword(s):  
Heat Transfer ◽  
High Speed ◽  
Single Phase ◽  
Heat Dissipation ◽  
Liquid Droplet ◽  
Heated Surface ◽  
Thin Liquid Film ◽  
Spray Cooling ◽  
High Speed Photography ◽  
Transfer Coefficients

Understanding the transport mechanisms involved in a single droplet impinging on a heated surface is imperative to the complete understanding of droplet and spray cooling. Evidence in the literature suggests that gas assisted sprays and mist flows are more efficient than sprays consisting only of liquid droplets. There has been few if any fundamental studies on gas-assisted droplets or spray cooling, in which a carrier gas or vapor stream propels the droplet to the target surface. The current work extends previous studies of a droplet impinging on a heated surface conducted by the same group from the single phase regime into the evaporative regime. For both regimes, understanding the transport physics due to the heat transfer from the heated surface to the droplet and then by convection and evaporation to the airflow is of fundamental importance. High-speed photography was used to capture the spreading process and yielded results that correlated well with previously published isothermal and single-phase results. The heat transfer was measured with a fitting approach by which the instantaneous temperature profile was matched to an analytic solution to determine the instantaneous value of the centerline heat transfer coefficient. A very large increase in the heat dissipation was observed when compared to previously published single-phase results. Heat transfer was optimized at Reynolds numbers that produced an optimally thin liquid film and high heat and mass transfer coefficients on the surface of the film.

Crevice Boiling in Steam Generators

1987 ◽  
Vol 109 (3) ◽  
pp. 761-767 ◽  
Author(s):  
S. Tieszen ◽  
H. Merte ◽  
V. S. Arpaci ◽  
S. Selamoglu
Keyword(s):  
Power Plants ◽  
Heated Surface ◽  
Nucleate Boiling ◽  
Forced Flow ◽  
High Speed Photography ◽  
Flow Conditions ◽  
Steam Generators ◽  
Pressurized Water ◽  
Support Plate ◽  
Primary Fluid

Experimental results are presented on the influence of confinement (normal to heated surface) on nucleate boiling in forced flow. The forced flow conditions and confinement geometry studied are similar to those found for boiling between a primary-fluid tube and a tube-support plate in steam generators of pressurized-water-reactor nuclear power plants. Visual observations of the boiling process within the confined region (crevice) between the tube and its support plate, obtained by high-speed photography, are related to simultaneous two-dimensional temperature maps of the hot primary-fluid-tube surface. The results demonstrate the existence of three confinement-dependent boiling regimes in forced flow conditions that are similar to those found in pool boiling conditions. These regimes are shown to be associated with the Weber number.

Multi-Jet Flows Underneath Small Bubble in Nucleate Boiling of Subcooled Self-Rewetting Fluid

2013 ◽  
Author(s):  
Leping Zhou ◽  
Yuanyuan Li ◽  
Longting Wei ◽  
Xiaoze Du
Keyword(s):  
High Speed ◽  
Marangoni Convection ◽  
Heated Surface ◽  
Ccd Camera ◽  
Jet Flow ◽  
Nucleate Boiling ◽  
Jet Flows ◽  
Wall Region ◽  
Heating Wire ◽  
Butanol Solution

Jet flow phenomenon is important in enhanced nucleate boiling heat transfer processes and applications. When heater sizes scale down, jet flow can be observed due to the Marangoni convection around bubbles staying on microscale heated surface. In this paper, two fluids were employed for comparing and demonstrating the effect of Marangoni convection on bubble behaviors on micro heating wire. One was ultrapure water and the other was aqueous n-butanol solution, a self-rewetting fluid. Bubble-top jet flow for water and multi-jet flows for n-butanol solution were observed around a platinum micro heating wire by high speed CCD camera. Corresponding numerical simulation proved that it is the Marangoni convection that attracts the sub-cooled water to flow from the super-heated microlayer at the bottom to the top of a stationary bubble. For n-butanol solution, however, the Marangoni convection can induce it to flow oppositely, which causes the subcooled solution to flow onto the heated surface. The simulation for the solution is in good agreement with the experiment where the subcooled liquid nears the bubble-top flow towards the bottom of bubble or the heated surface and hence the multi-jet flows occur. The multi-jet flows can sustain for a long period and cause transient chaos at the super-heated thin liquid layer near the heated surface. The temperature around the bubble presented sharp temperature gradient and the velocity in the near-wall region is almost vertical to the wall. The experimental and numerical studies on the effect of surface tension and thus Marangoni convection are crucial to the mechanisms of subcooled nucleate boiling of fluids.

Laser Interferometric Investigation of the Microlayer Evaporation Phenomenon

1975 ◽  
Vol 97 (1) ◽  
pp. 88-92 ◽  
Author(s):  
C. M. Voutsinos ◽  
R. L. Judd
Keyword(s):  
Heat Transfer ◽  
High Speed ◽  
Laser Interferometry ◽  
Nucleate Boiling ◽  
High Speed Photography ◽  
Heater Surface ◽  
Nucleate Boiling Heat Transfer ◽  
Interferometric Investigation ◽  
Microlayer Evaporation ◽  
Laser Interferometric

An experimental investigation is presented in which the growth and evaporation of the microlayer underlying a bubble forming on a glass heater surface has been studied using laser interferometry and high speed photography. The results presented for a single bubble indicate that the microlayer thickness is of the order of 5 μm. Subsequent analysis of these results confirms that the microlayer evaporation phenomenon is a significant heat transfer mechanism, representing approximately 25 percent of the total nucleate boiling heat transfer rate for the conditions investigated.

Inner Phase Change Behavior of Small Liquid Droplet on Heated Solid Surface

2011 ◽  
Author(s):  
Gui Lu ◽  
Yuan-Yuan Duan ◽  
Xiao-Dong Wang
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Bubble Dynamics ◽  
Liquid Droplet ◽  
Heated Surface ◽  
Nucleate Boiling ◽  
Boiling Regime ◽  
Change Behavior ◽  
Cyclical Process ◽  
Transient Boiling

An experimental investigation was conducted to visually observe the transient boiling in an individual water droplet on different heated solid surfaces, covering the free surface evaporation, nucleate, transition and spheroidal boiling regime. Diversified bubble dynamics, phase change and heat transfer behaviors for different boiling regimes of droplet were discussed in present work. In nucleate boiling regime, plenty nucleate bubbles with uniform diameters were confined within the bottom of the droplet, enhancing the heat transfer and cooling performance. The surface properties had great effects on the bubble dynamics in this regime. In the transition boiling regime, the phase change behaviors of a droplet displayed a cyclical process, restricted, sole-bubble and metastable cyclical styles were observed in the experiments. A vapor film between the droplet and surface exists in the spheroidal boiling regime, leading to the random movement of droplet above the heated surface and prolonging the lifetime of droplet significantly.

Flow Boiling on Micropin Fins Entrenched Inside a Microchannel—Flow Patterns and Bubble Departure Diameter and Bubble Frequency

2010 ◽  
Vol 132 (4) ◽  
Author(s):  
Santosh Krishnamurthy ◽  
Yoav Peles
Keyword(s):  
High Speed ◽  
Flow Boiling ◽  
Bubbly Flow ◽  
Nucleate Boiling ◽  
Flow Patterns ◽  
Heat Fluxes ◽  
High Speed Photography ◽  
Bubble Frequency ◽  
Pin Fins ◽  
Parallel Microchannels

Flow boiling of HFE 7000 in five parallel microchannels of 222 μm hydraulic diameter, each containing a single row of 24 in-line 100 μm pin fins, was investigated. High speed photography revealed the dominant flow patterns, namely, the bubbly flow, the multiple flow, and the wavy-annular flow. The interaction of the bubble with the pin fins during nucleate boiling from G=350 kg/m2 s to G=827 kg/m2 s and wall heat fluxes from 10 W/cm2 to 110 W/cm2 is detailed.

Time-dependent measurements of length and area of the contact line in contact-boiling regime

2021 ◽  
Vol 926 ◽  
Author(s):  
Mohammad Khavari ◽  
Tuan Tran
Keyword(s):  
Contact Line ◽  
Contact Area ◽  
High Speed ◽  
Liquid Droplet ◽  
Heated Surface ◽  
Bubble Nucleation ◽  
High Speed Imaging ◽  
Wide Range ◽  
Length And Area ◽  
The Impact

During the impact of a liquid droplet on a sufficiently heated surface, bubble nucleation reduces the contact area between the liquid and the solid surface. Using high-speed imaging combined with total internal reflection, we measure and report how the contact area decreases with time for a wide range of surface temperatures and impact velocities. We also reveal how formation of the observed fingering patterns contributes to a substantial increase in the total length of the contact line surrounding the contact area.

Subcooled Nucleate Boiling of Alumina Nanofluid With/Without n-Butanol as Surfactant

2013 ◽  
Author(s):  
Leping Zhou ◽  
Longting Wei ◽  
Xiaoze Du
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
High Speed ◽  
Heated Surface ◽  
Jet Flow ◽  
Nucleate Boiling ◽  
Wall Region ◽  
Al2o3 Nanoparticles ◽  
Nanoparticle Deposition ◽  
Alumina Nanofluid

Nucleate boiling process in nanofluids is important because of its potential in enhanced heat transfer. However, it is difficult to observe the boiling phenomenon due to the indistinct image. In this investigation, stable nanofluids was prepared by α-Al2O3 nanoparticles, 30 nm in diameter, and ultrapure water. The bubble behaviors in water were observed by high-speed CCD camera. Unique bubble sweeping phenomenon, existing in the upper and/or lower part of the heated wire, emerged due to the existence of nanoparticles. The experiment shows that the bubble-top jet flow phenomenon only exists when the small bubble returned to the heated surface, which demonstrates that it was the vertical Marangoni convection along the bubble interface that induced the jet flow. Meanwhile, flocculent clustering of nanoparticles can be observed to swirl at the bubble-bottom for low-concentration nanofluid, when the heat flux was relatively small. The SEM images of the nanoparticle deposition layers indicated increased thermocapillarity, but it seemed to delay the detachment of small bubbles from the heated surface. While n-butanol was included as surfactant, it promoted the nanoparticle deposition for low heat flux condition. The bubble behaviors were consistent with those of pure fluids and no bubble circling phenomenon was observed. The boiling curves were then depicted for alumina nanofluid with or without n-butanol. The boiling heat transfer in water was enhanced with increasing nanoparticle concentration. The boiling curves shifted right when increased the surfactant concentration in the nanofluid. It appeared that the surfactant-induced inhibited bubble growth and enhanced nanoparticle clustering in the near-wall region were the main reason for the shifting.

Dynamic Behavior of a Small Water Droplet Impact Onto a Heated Hydrophilic Surface

2016 ◽  
Vol 138 (4) ◽  
Author(s):  
El-Sayed R. Negeed ◽  
M. Albeirutty ◽  
Sharaf F. AL-Sharif ◽  
S. Hidaka ◽  
Y. Takata
Keyword(s):  
Dynamic Behavior ◽  
Water Droplet ◽  
High Speed ◽  
Heated Surface ◽  
Droplet Diameter ◽  
Video Camera ◽  
Surface Wettability ◽  
Hydrodynamic Characteristics ◽  
Small Water ◽  
Hot Surface

The aim of this study is to investigate the influence of the surface wettability on the dynamic behavior of a water droplet impacting onto a heated surface made of stainless steel grade 304 (Sus304). The surface wettability is controlled by exposing the surfaces to plasma irradiation for different time periods (namely, 0.0, 10, 60, and 120 s). The experimental runs were carried out by spraying water droplets on the heated surface where the droplet diameter and velocity were independently controlled. The droplet behavior during the collision with the hot surface has been recorded with a high-speed video camera. By analyzing the experimental results, the effects of surface wettability, contact angle between impacting droplet and the hot surface, droplet velocity, droplet size, and surface superheat on the dynamic behavior of the water droplet impacting on the hot surface were investigated. Empirical correlations are presented describing the hydrodynamic characteristics of an individual droplet impinging onto the heated hydrophilic surfaces and concealing the affecting parameters in such process.

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