Effect of Heat Flux on Bubble Coalescence Phenomena and Sound Signatures During Pool Boiling

2021 ◽  
Vol 143 (5) ◽  
Author(s):  
Akshat Negi ◽  
Aniket M. Rishi ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Flux ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Bubble Nucleation ◽  
Frequency Region ◽  
Heat Fluxes ◽  
Bubble Collapse ◽  
Fluid Temperature ◽  
Maximum Heat ◽  
Acoustic Signatures

Abstract Boiling heat transfer is extensively used in various industrial applications to efficiently dissipate a large amount of heat by maintaining low surface to fluid temperature differences. The maximum heat flux dissipated during boiling is limited by the critical heat flux (CHF). Difficulties in visualizing the boiling process and monitoring surface temperature make it difficult to identify the impending CHF condition. As a result, larger factors of safety are employed, and the equipment is operated at considerably lower heat fluxes. This study focuses on identifying acoustic signatures of different nucleate boiling regimes. The bubble nucleation and coalescence along with bubble collapse lead to variation in acoustic emission patterns during boiling. In this work, acoustic signatures representative of the impending CHF condition are identified during pool boiling of water over plain and enhanced copper substrates. It was observed that sound was dominant in two frequency regions (400–500 Hz dominant throughout the nucleate boiling, and 100–200 Hz dominant at heat fluxes > 100 W/cm2). However, just before CHF, a sudden drop in amplitude was observed in the high frequency region (400–500 Hz), while the amplitude in low frequency region (100–200 Hz) continued to rise. This combination of the amplitude trend has potential to predict the approaching CHF condition. This is the first study that correlates high-speed images with the acoustic trends at different stages of nucleate boiling and compares experimental frequency with Minnaert frequency for coalescing bubbles.

Effect of Heat Flux on Bubble Coalescence Phenomena and Sound Signatures During Pool Boiling

2020 ◽  
Author(s):  
Akshat Negi ◽  
Aniket M. Rishi ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Flux ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Bubble Nucleation ◽  
Frequency Region ◽  
Heat Fluxes ◽  
Working Fluid ◽  
Bubble Collapse ◽  
Maximum Heat ◽  
Acoustic Signatures

Abstract Boiling heat transfer is extensively used in various industrial applications to efficiently dissipate a large amount of heat by maintaining lower surface temperatures. The maximum heat flux dissipated during boiling is limited by the critical heat flux (CHF) and limited visualization of the boiling surface limits the identification of the impending CHF condition to rely on temperature monitoring alone. The study presented here focuses on developing a method for analyzing and identifying acoustic signatures throughout the nucleate boiling regimes that are indicative of the boiling state of the heater surface. The bubble nucleation and coalescence along with bubble collapse at the liquid-vapor interface leads to variation in acoustic emission patterns during boiling. These sound waves are studied and acoustic signatures that are representative of the impending CHF are identified over plain and enhanced copper substrates with water as the working fluid. During pool boiling study, it was observed that sound was dominant in two frequency regions (400–500 Hz dominant throughout nucleate boiling and 100–200 Hz dominant at heat fluxes > 100 W/cm2). However, just before CHF, a sudden drop in amplitude was observed in the high frequency region (400–500 Hz), while the amplitude in low frequency region (100–200 Hz) continued to rise. It was concluded that this acoustic study can be used as a tool to predict the approaching CHF condition.

Pool Boiling Using Thin Enhanced Structures Under Top-Confined Conditions

2006 ◽  
Vol 128 (12) ◽  
pp. 1302-1311 ◽  
Author(s):  
Camil-Daniel Ghiu ◽  
Yogendra K. Joshi
Keyword(s):  
Heat Flux ◽  
High Speed ◽  
Pool Boiling ◽  
Single Layer ◽  
Temperature Limit ◽  
Heat Fluxes ◽  
The Other ◽  
Vapor Flow ◽  
Maximum Heat ◽  
Maximum Heat Flux

An experimental study of pool boiling using enhanced structures under top-confined conditions was conducted with a dielectric fluorocarbon liquid (PF 5060). The single layer enhanced structures studied were fabricated in copper and quartz, had an overall size of 10×10mm2, and were 1mm thick. The parameters investigated in this study were the heat flux (0.8-34W∕cm2) and the top space S(0-13mm). High-speed visualizations were performed to elucidate the liquid/vapor flow in the space above the structure. The enhancement observed for plain surfaces in the low heat fluxes regime is not present for the present enhanced structure. On the other hand, the maximum heat flux for a prescribed 85°C surface temperature limit increased with the increase of the top spacing, similar to the plain surfaces case. Two characteristic regimes of pool boiling have been identified and described: isolated flattened bubbles regime and coalesced bubbles regime.

RELAP5-3D Sensitivity Studies of Incorporating Axial Boron Gradients Into a Heater Tube Experiment for Pool Boiling CHF Testing in TREAT

2020 ◽  
Author(s):  
Richard Hernandez ◽  
Nicholas R. Brown ◽  
Charles P. Folsom ◽  
Nicolas E. Woolstenhulme ◽  
Colby B. Jensen
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
National Laboratory ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Coupling Factor ◽  
Design Parameters ◽  
Coolant Temperature ◽  
Axial Region ◽  
Maximum Heat

Abstract Nuclear reactor designs are governed by postulated accident events that may occur during their operational lifetime. One type of incident is a reactivity-initiated accident (RIA), during which a sudden surge of power in the fuel components within the core may result in the latter exceeding its cooling capabilities. This could lead to a departure from nucleate boiling (DNB) event which results in a significant decrease in heat transfer capabilities. Preventing the occurrence of a DNB crisis requires a fundamental understanding of the cladding-to-coolant heat transfer under fast transient conditions, as well as the governing hydrodynamic and design parameters that influence when the critical heat flux (CHF) will be exceeded. Presently, large uncertainties in computer models used to predict CHF have led to conservative safety limits governing light-water reactor (LWR) designs. The Idaho National Laboratory (INL) is currently leading a combined effort that takes advantage of the restart of the Transient Reactor Test (TREAT) facility, to better understand the mechanism of CHF under in-pile pool boiling conditions. The goal of this laboratory directed project is to use the unique capabilities of TREAT coupled with a non-fueled nuclear heated borated stainless-steel 304 tube experiment within an experimental capsule. The borated tube will induce CHF in the surrounding coolant when subjected to a power pulse within the TREAT. The impacts of rapid surface heating effects as well as radiation-induced surface activation (RISA) will be experimentally investigated. This feature is a continuation to previous thermal hydraulics analysis that was conducted to inform on a test matrix for the design of the borated heater experiment. The borated tube was used in place of a solid rod so that the center axial region can be instrumented to allow for better experimental analysis. Therefore, it is desirable to design this rodlet so that the maximum heat flux occurs at the center of the axial length of the rod. The work presented here analyzes the potential to integrate axial boron gradients within this tube to shape its power curve. Several generic axial power shapes were initially considered. Natural boron concentrations between 0.1–2.0 wt.% were analyzed and a power coupling factor (PCF) was calculated for each. A self-shielding study was conducted to develop radial power profiles for several boron concentrations. These were then applied to three different power pulses to determine how these two parameters influence the chosen axial heat flux curve. Variations in the initial coolant temperature were investigated. Lastly, how the shape of the generic curve is affected following a DNB event was also studied. Two different CHF cases were included within the scope of this analyses; one during which CHF was exceeding along the entire axial region of the rod, and another where the former occurred at the center region only. The behavior of the curve overtime was investigated.

Pool Boiling in Saturated and Subcooled FC-72 Dielectric Fluid From a Porous Graphite Surface

2004 ◽  
Author(s):  
Mohamed S. El-Genk ◽  
Jack L. Parker
Keyword(s):  
Heat Flux ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Porous Coating ◽  
Dielectric Fluid ◽  
Subcooled Boiling ◽  
Porous Graphite ◽  
Rate Of Increase ◽  
Boiling Incipience

Experiments are conducted that investigated pool boiling of FC-72 liquid at saturation and 10, 20, and 30 K subcooling on porous graphite and smooth copper surfaces measuring 10 × 10 mm. The nucleate boiling heat flux, Critical Heat Flux (CHF), and surface superheats at boiling incipience are compared. Theses heat fluxes are also compared with those of other investigators for smooth copper and silicon, etched SiO2, surfaces and micro-porous coating. No temperature excursion at boiling incipience on the porous graphite that occurred at a surface superheats of < 1.0 K. Conversely, the temperature excursions of 24.0 K and 12.4–17.8 K are measured at incipient boiling in saturation and subcooled boiling on copper. Nucleate boiling heat fluxes on porous graphite are significantly higher and corresponding surface superheats are much smaller than on copper. CHF on porous graphite (27.3, 39.6, 49.0, and 57.1 W/cm2 in saturation and 10 K, 20 K, and 30 K subcooled boiling, respectively) are 61.5%–207% higher than those on copper (16.9, 19.5, 23.6, and 28.0 W/cm2, respectively). The surface superheats at CHF on the porous graphite of 11.5 K in saturation and 17–20 K in subcooled boiling are significantly lower that those on copper (25 K and 26–28 K, respectively). In addition, the rate of increase of CHF on porous graphite with increased subcooling is ~ 125% higher than that on copper.

Flow Boiling Dynamics of Water and Nanofluids in a Single Microchannel at Different Heat Fluxes

2013 ◽  
Author(s):  
Zachary Edel ◽  
Abhijit Mukherjee
Keyword(s):  
Heat Transfer ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Bubble Nucleation ◽  
Heat Fluxes ◽  
Forced Flow ◽  
Fluid Temperature ◽  
Nanofluid Flow ◽  
Nanoparticle Suspension ◽  
Nanoparticle Deposition

The preferable cooling solution to the problem of thermal management of modern electronics for increasing power dissipation could be micro heat exchangers based on forced flow boiling. Nanoparticle deposition can affect nucleate boiling heat transfer coefficient via alteration of surface thermal conductivity, roughness, capillary wicking, wettability, and nucleation site density. It can also affect heat transfer by changing bubble departure diameter, bubble departure frequency, and the evaporation of the micro and macrolayer beneath the growing bubbles. In this study, flow boiling was investigated using degassed, deionized water, and 0.001 vol% aluminum oxide nanofluids in a single rectangular brass microchannel for one inlet fluid temperature of 63°C, one flow rate of Re = 100, and two heat fluxes of 130 kW/m2 and 300 kW/m2. High speed images were taken periodically for water and after durations of 25, 75, and 125 minutes of nanofluid flow boiling. The change in regime timing revealed the effect of nanoparticle suspension and nanoparticle deposition on the Onset of Nucelate Boiling (ONB) and the Onset of Bubble Elongation (OBE). Single phase flows at the channel outlet were recorded and compared for different durations of nanofluid flow boiling. The addition of nanoparticles was found to stabilize bubble nucleation and growth and increase heat transfer in the thin film regions of the evaporating menisci.

Microporous Coatings to Maximize Pool Boiling Heat Transfer of Saturated R-123 and Water

2015 ◽  
Vol 137 (8) ◽  
Author(s):  
Joo Han Kim ◽  
Ajay Gurung ◽  
Miguel Amaya ◽  
Sang Muk Kwark ◽  
Seung M. You
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Transfer Coefficients ◽  
Maximum Heat ◽  
Microporous Coating ◽  
Plain Surface ◽  
Improved Performance

The present research is an experimental study for the enhancement of boiling heat transfer using microporous coatings. Two types of coatings are investigated: one that is bonded using epoxy and the other by soldering. Effects on pool boiling performance were investigated, of different metal particle sizes of the epoxy-based coating, on R-123 refrigerants, and on water. All boiling tests were performed with 1 cm × 1 cm test heaters in the horizontal, upward-facing orientation in saturated conditions at atmospheric pressure and under increasing heat flux. The surface enhanced by the epoxy-based microporous coatings significantly augmented both nucleate boiling heat transfer coefficients and critical heat flux (CHF) of R-123 relative to those of a plain surface. However, for water, with the same microporous coating, boiling performance did not improve as much, and thermal resistance of the epoxy component limited the maximum heat flux that could be applied. Therefore, for water, to seek improved performance, the solder-based microporous coating was applied. This thermally conductive microporous coating, TCMC, greatly enhanced the boiling performance of water relative to the plain surface, increasing the heat transfer coefficient up to ∼5.6 times, and doubling the CHF.

Investigation of the Dynamics of Nucleate Boiling in Subcooled Falling Liquid Films

2014 ◽  
Vol 9 (2) ◽  
pp. 145-155
Author(s):  
Vladimir Serdyukov ◽  
Anton Surtaev ◽  
Oleg Volodin
Keyword(s):  
Experimental Data ◽  
Heat Flux ◽  
Strong Dependence ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Liquid Films ◽  
Heat Fluxes ◽  
Nucleation Frequency ◽  
Water Films ◽  
Falling Liquid Films

This paper deals with the features of nucleation dynamics at boiling in falling water films at different subcooling, Reynolds number and heat fluxes. With the use of high-speed infrared and digital video the local parameters of nucleate boiling in falling liquid films such as: bubbles’ diameter before condensation, frequency of nucleation and temperature of onset of bubble appearance were received. Analysis of the experimental data showed that bubbles’ diameter before condensation has strong dependence on initial temperature and increases with the rise of heat flux. The main influence on nucleation frequency has the variation of heat flux density. At the same time the experimental data on nucleation frequency in falling water films are close to the frequency of nucleation at pool boiling. To identify the main features the comparison of received data on the local characteristics at boiling in subcooled falling liquid film with existing models for pool boiling was made

Experimental Study of Heat Transfer Enhancement in Pool Boiling by Using 2-Ethyl 1-Hexanol an Additive

2014 ◽  
Vol 592-594 ◽  
pp. 1601-1606 ◽  
Author(s):  
Sameer Sheshrao Gajghate ◽  
Anil R. Aacharya ◽  
Anil T. Pise ◽  
Ganesh S. Jadhav
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Boiling Heat Transfer ◽  
Bubble Dynamics ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Optimum Level ◽  
Transfer Coefficients ◽  
Nichrome Wire

The addition of additives to the water is known to enhance boiling heat transfer. In the present investigation, boiling heat transfer coefficients are measured for Nichrome wire, immersed in saturated water with & without additive. An additive used is 2-Ethyl 1-Hexanol with varying concentrations in the range of 10-10000 ppm. Extensive experimentation of pool boiling is carried out above the critical heat flux. Boiling behavior i.e. bubble dynamics are observed at higher heat flux for nucleate boiling of water over wide ranges of concentration of additive in water. Results are encouraging and show that a small amount of surface active additive makes the nucleate boiling heat transfer coefficient considerably higher, and that there is an optimum additive (500-1000ppm) concentration for higher heat fluxes. An optimum level of enhancement is observed up to a certain amount of additive 500-1000ppm in the tested range. Thereafter significant enhancement is not observed. This enhancement may be due to change in thermo-physical properties i.e. mainly due to a reduction in surface tension of water in the presence of additive.

Dynamics of Pool Boiling on Plain and Nanotube Coated Silicon Surfaces

2010 ◽  
Author(s):  
Vijaykumar Sathyamurthi ◽  
Debjyoti Banerjee
Keyword(s):  
Heat Flux ◽  
Surface Temperature ◽  
Chaotic Dynamics ◽  
Pool Boiling ◽  
Deterministic Chaos ◽  
Nucleate Boiling ◽  
High Heat ◽  
Heat Fluxes ◽  
Film Boiling ◽  
Test Fluid

Saturated pool boiling experiments are conducted over silicon substrates with and without Multi-walled Carbon Nanotubes (MWCNT) with PF-5060 as the test fluid. Micro-fabricated thin film thermocouples located on the substrate acquire surface temperature fluctuation data at 1 kHz frequency. The high frequency surface temperature data is analyzed for the presence of chaotic dynamics. The shareware code, TISEAN© is used in analysis of the temperature time-series. Results show the presence of low-dimensional deterministic chaos, near Critical Heat Flux (CHF) and in some parts of the Fully Developed Nucleate Boiling (FDNB) regime. Some evidence of chaotic dynamics is also obtained for the film boiling regimes. Singular value decomposition is employed to generate pseudo-phase plots of the attractor. In contrast to previous studies involving multiple nucleation sites, the pseudo-phase plots show the presence of multi-fractal structure at high heat fluxes and in the film boiling regime. An estimate of invariant quantities such as correlation dimensions and Lyapunov exponents reveals the change in attractor geometry with heat flux levels. No significant impact of surface texturing is visible in terms of the invariant quantities.

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