On Correlating the Peak and Minimum Boiling Heat Fluxes With Pressure and Heater Configuration

1966 ◽  
Vol 88 (1) ◽  
pp. 94-99 ◽  
Author(s):  
John H. Lienhard ◽  
Kiyokazu Watanabe
Keyword(s):  
Heat Flux ◽  
Pressure Range ◽  
Pool Boiling ◽  
Three Dimensional ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Reduced Pressure ◽  
Minimum Heat ◽  
Dimensional Surface ◽  
Horizontal Wire

The peak nucleate boiling heat flux has been observed for five fluids during saturated pool boiling on horizontal wire heaters, ranging in radius from 0.0025 in. to 0.0254 in., over a reduced pressure range from 0.0010 to 0.0197. A scheme for correlating the peak and minimum heat fluxes is developed heuristically and successfully applied to these data. The result is a single three-dimensional surface which represents all of the data. The surface can be represented as the product of a function of geometric scale, and a function of pressure. The function of pressure appears to be the same in any configuration.

The Mechanism of and Stability Criterion for Nucleate Pool Boiling of Sodium

1969 ◽  
Vol 91 (3) ◽  
pp. 315-328 ◽  
Author(s):  
I. Shai ◽  
W. M. Rohsenow
Keyword(s):  
Heat Flux ◽  
Liquid Metals ◽  
Bubble Formation ◽  
Pool Boiling ◽  
Heat Fluxes ◽  
Nucleate Pool Boiling ◽  
Thermal Layer ◽  
Minimum Heat ◽  
Bubble Growth And Departure ◽  
Recorded Temperature

Experimental data for sodium boiling on horizontal surfaces containing artificial cavities at heat fluxes of 20,000 to 300,000 Btu/ft2 hr and pressures between 40 to 106 mm Hg were obtained. Observations are made for stable boiling, unstable boiling and “bumping.” Some recorded temperature variations in the solid close to the nucleating cavity are presented. It is suggested that for liquid metals the time for bubble growth and departure is a very small fraction of the total bubble cycle, hence the delay time during which a thermal layer grows is the most significant part of the process. On this basis the transient conduction heat transfer is solved for a periodic process, and the period time is found to be a function of the degree of superheat, the heat flux and the liquid thermal properties. A simplified model for stability of nucleate pool boiling of liquid metals is postulated from which the minimum heat flux for stable boiling can be found as a function of liquid-solid properties, liquid pressure, the degree of superheat, and the cavity radius and depth. At relatively low heat fluxes, convection currents have significant effects on the period time of bubble formation. An empirical correlation is proposed, which takes into account the convection effects, to match the experimental results.

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.

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

Pressure influence on saturated boiling of R141b over Cu and Si-coated surfaces

2021 ◽  
pp. 095440892110452
Author(s):  
Abhishek Swarnkar ◽  
Vikas J. Lakhera
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Flux ◽  
Pressure Range ◽  
Pool Boiling ◽  
Heat Fluxes ◽  
Working Fluid ◽  
Operating Pressure ◽  
Coated Surface ◽  
Coated Surfaces

Pool boiling has been a research topic of great interest over the decades due to its inherent capabilities of large heat transfer rates with narrow temperature gaps and it advocates its suitability in a large number of industrial applications. The present paper describes the effect of operating pressure on pool boiling of R141b over a plain Cu surface as well as Si-coated surface prepared by a direct current (DC) sputtering technique. The working fluid R141b undergoes saturated pool boiling under pressure ranging from −20 kPa(g) to + 30 kPa(g) with the acquired experimental data and trends compared with the existing correlations and theories. Within the pressure range considered, the surface superheat variation was insignificant at lower heat fluxes; however, at higher heat fluxes, the maximum reduction was found to be by 9.5°C and 14.8°C for the plain Cu surface and Si-coated surface, respectively, regarding the corresponding values of −20 kPa(g) pressure. With respect to the results under atmospheric conditions, at the pressure of + 30 kPa(g), a corresponding increase in heat transfer coefficient of 12.1% for the plain Cu surface and of 17.8% for a Si-coated surface was observed at a heat flux of 225 kW/m2 and 272 kW/m2, respectively. In comparison to the results under atmospheric pressure conditions, the accompanying augmentation in the critical heat flux was observed as 13.3% for the plain Cu and 21.2% for the Si-coated surfaces at a pressure of + 30 kPa(g). Based on the experimental data, a correlation is developed for predicting heat transfer coefficients within the given pressure range.

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.

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.

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.

Nucleate boiling heat transfer coefficients of halogenated refrigerants up to critical heat fluxes

2009 ◽  
Vol 223 (6) ◽  
pp. 1415-1424 ◽  
Author(s):  
K-J Park ◽  
D Jung ◽  
S E Shim
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Nucleate Pool Boiling ◽  
Transfer Coefficients ◽  
Average Deviation ◽  
Heat Transfer Coefficients

In this work, nucleate pool boiling heat transfer coefficients (HTCs) of five refrigerants of differing vapour pressures are measured on a horizontal, smooth copper surface of 9.53×9.53 mm. The tested refrigerants are R123, R152a, R134a, R22, and R32 and HTCs are taken from 10 kW/m2 to the critical heat flux (CHF) of each refrigerant. Wall and fluid temperatures are measured directly by thermocouples located underneath the test surface and in the liquid pool, respectively. Test results show that nucleate pool boiling HTCs of halogenated refrigerants increase as the heat flux and vapour pressure increase. This typical trend is maintained even at high heat fluxes above 200 kW/m2. Zuber's prediction equation for CHF is quite accurate showing a maximum deviation of 21 per cent for all refrigerants tested. For all refrigerants, Stephan and Abdelsalam's well-known correlation underpredicted nucleate boiling HTC data up to the CHF with an average deviation of 21.3 per cent, while Cooper's correlation overpredicted the data with an average deviation of 14.2 per cent. On the other hand, Gorenflo's and Jung et al.'s correlations showed 5.8 and 6.4 per cent deviations, respectively, in the entire nucleate boiling range up to the CHF.

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.

Framework for a Unified Model for Nucleate and Transition Pool Boiling

1989 ◽  
Vol 111 (3) ◽  
pp. 739-746 ◽  
Author(s):  
V. K. Dhir ◽  
S. P. Liaw
Keyword(s):  
Transfer Rate ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Heater Surface ◽  
Maximum Heat ◽  
Void Fractions ◽  
Thermal Layer ◽  
Averaged Model ◽  
Minimum Heat

An area and time-averaged model for saturated pool boiling heat fluxes has been developed. In the model, which is valid in the upper end of nucleate boiling and in transition boiling, the existence of stationary vapor stems at the wall is assumed. The energy from the wall is conducted into the liquid macro/micro thermal layer surrounding the stems and is utilized in evaporation at the stationary liquid–vapor interface. The heat transfer rate into the thermal layer and the temperature distribution in it are determined by solving a two-dimensional steady-state conduction equation. The evaporation rate is given by the kinetic theory. The heater surface area over which the vapor stems exist is taken to be dry. Employing experimentally observed void fractions, not only the nucleate and transition boiling heat fluxes but also the maximum and minimum heat fluxes are predicted from the model. The maximum heat fluxes obtained from the model are valid only for surfaces that are not well wetted and includes the contact angle as one of the parameters.

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