A model based on an additive mechanism of heat transfer is proposed for pool boiling of single component systems. The contributing modes of heat transfer are: (i) the heat transferred as latent heat to the evaporating microlayer, (ii) the heat transferred by transient conduction during re-formation of the thermal boundary layer and (iii) the heat transferred by turbulent natural convection from the heating surface not influenced by the bubbles. The heat flux due to the evaporating microlayer is estimated from the instantaneous microlayer thickness during the bubble growth period. An estimate of the nucleation site density is obtained from a literature correlation that includes the boiling surface characteristics. Experimental data from the literature and the present study show very good agreement with the model, validating the postulated mechanism. Copyright © 1996 Elsevier Science Ltd.

R. J. Benjamin

Arcot R. Balakrishnan

Boundary layers

BUBBLE FORMATION

Heat conduction

Heat flux

Mathematical models

Natural convection

Nucleate boiling

INSTANTANEOUS MICROLAYER THICKNESS

Latent heat

THERMAL BOUNDARY LAYER REFORMATION

Heat transfer

Boiling

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Nucleate pool boiling heat transfer of pure liquids at low to moderate heat fluxes

International Journal of Heat and Mass Transfer

The initial size of the embryo, which is formed at the inception of boiling, plays a vital role in the accurate prediction of component scale wall boiling phenomenon. Embryo size predictions are typically calculated using the classical theory of nucleation. However, in recent times, the predictive capability of this theory was found to have limitations. Hence, there is need for a more fundamental and mechanistic model to overcome some of the drawbacks. In this paper, we propose a ‘work of formation’ based model for the embryo formation. This model is mechanistic and includes a Van der Waals based real gas treatment for the vapour. It also incorporates Lewins surface tension model that is a function of the boiling-nucleus size. The present model also accounts for the boiling occurrence in the presence of undissolved nanobubbles on the surface. The embryo formation model has been extensively tested for both low and high pressures, horizontal and vertical test section orientation, and for different surfaces and fluids. The energy required for the embryo formation was found to be higher, when the initial gas bubble is intact compared to when the gas bubble diffuses into the embryo. Some of the contradictory claims on the suitability of classical theory of nucleation to nanosurfaces have been tested. From the present embryo formation model, the physics of nucleation such as, the effect of pressure fluctuations and energy dissipation mechanisms involved in the formation is explained. © 2017 Elsevier Ltd

A mechanistic model for embryo size prediction at boiling incipience: ‘Work of formation’ based approach

Introduction to nanofluids--their properties, synthesis, characterization, and applications Nanofluids are attracting a great deal of interest with their enormous potential to provide enhanced performance properties, particularly with respect to heat transfer. In response, this text takes you on a complete journey into the science and technology of nanofluids. The authors cover both the chemical and physical methods for synthesizing nanofluids, explaining the techniques for creating a stable suspension of nanoparticles. You get an overview of the existing models and experimental techniques used in studying nanofluids, alongside discussions of the challenges and problems associated with some of these models. Next, the authors set forth and explain the heat transfer applications of nanofluids, including microelectronics, fuel cells, and hybrid-powered engines. You also get an introduction to possible future applications in large-scale cooling and biomedicine. This book is the work of leading pioneers in the field, one of whom holds the first U.S. patent for nanofluids. They have combined their own first-hand knowledge with a thorough review of theliterature. Among the key topics are: Synthesis of nanofluids, including dispersion techniques and characterization methods Thermal conductivity and thermo-physical properties Theoretical models and experimental techniques Heat transfer applications in microelectronics, fuel cells, and vehicle engines This text is written for researchers in any branch of science and technology, without any prerequisite.It therefore includes some basic information describing conduction, convection, and boiling of nanofluids for those readers who may not have adequate background in these areas. Regardless of your background, you'll learn to develop nanofluids not only as coolants, but also for a host ofnew applications on the horizon. © 2008 John Wiley & Sons, Inc.

Nanofluids: Science and Technology

Pool boiling on surfaces where sliding bubble mechanism plays an important role has been studied. The heat transfer phenomenon for such cases has been analysed. The model considers different mechanisms such as latent heat transfer due to microlayer evaporation, transient conduction due to thermal boundary layer reformation, natural convection and heat transfer due to the sliding bubbles. Both microlayer evaporation and transient conduction take place during the sliding of bubbles, which occurs in geometries such as inclined surfaces and horizontal tubes. The model has been validated against experimental results from literature for water, refrigerant R134a and propane. The model was found to agree well for these fluids over a wide range of pressures. The model shows the importance of the contributions of the different mechanisms for different fluids, wall superheats and pressures. © 2004 Elsevier Ltd. All rights reserved.

Analysis of pool boiling heat transfer: Effect of bubbles sliding on the heating surface

Steady state pool boiling heat transfer coefficients have been obtained experimentally for acetone-isopropanol-water and acetone-MEK (methyl ethyl ketone)-water ternary systems. The data show that, for a given heat flux, the heat transfer coefficients of mixtures are lower than those obtained for pure components constituting the mixture. The measured heat transfer coefficients were compared with predictions from literature correlations for pool boiling of multicomponent mixtures. In all the cases, overestimation or underestimation of the data was observed. The literature correlations incorporate an 'ideal' heat transfer coefficient and a correction term for the presence of other liquids. Part of the uncertainty associated with the literature correlations on comparison with the present data appears to be due to the uncertainty in estimating the ideal heat transfer coefficient. The methods suggested by the earlier authors found to be not applicable for the present heating surface-liquid combinations. Therefore, in the present study, two different correlations were tried for the ideal heat transfer coefficient and it was found that the performance of the literature correlations improved considerably. However, the methods reported in the literature and the correlations tried in the present study to estimate ideal heat transfer coefficient did not consider heating surface-liquid interaction and the effect of heating surface micro-roughness in boiling. Therefore, a correlation to estimate the ideal heat transfer coefficient has been proposed taking into account surface-liquid interaction parameter and surface roughness group. A new correlation to estimate mixture heat transfer coefficients has been proposed in the present study in terms of an ideal heat transfer coefficient and a correction term. In general, the correction term in binary mixtures is obtained by incorporating the binary diffusivity of the mixture. In multicomponent systems, the multicomponent diffusion coefficients have to be incorporated in the expression for the correction term. The mixture heat transfer coefficient correlation along with the correlation for ideal heat transfer coefficient proposed in the present study predicts the present experimental data as well as literature data satisfactorily. The heat transfer coefficient was found to be a function of the difference between the equilibrium vapor and liquid concentration of the light component(s) and the minimum heat transfer coefficient occurs at the maximum of this value. © 2004 Elsevier Inc. All rights reserved.

Experimental Thermal and Fluid Science

Heat transfer in nucleate pool boiling of multicomponent mixtures

Common fluids with particles of the order of nanometers in size are termed as 'nano-fluids' which have created considerable interest in recent times for their improved heat transfer capabilities. With very small volume fraction of such particles the thermal conductivity and convective heat transfer capability of these suspensions are significantly enhanced without the problems encountered in common slurries such as clogging, erosion, sedimentation and increase in pressure drop. This naturally brings out the question whether such fluids can be used for two phase applications or in other words phase change in such suspensions will be assistant or detrimental to the process of heat transfer. The present paper investigates into this question through experimental study of pool boiling in water-Al2O3 nano-fluids. The results indicate that the nano-particles have pronounced and significant influence on the boiling process deteriorating the boiling characteristics of the fluid. It has been observed that with increasing particle concentration, the degradation in boiling performance takes place which increases the heating surface temperature. This indicates that the role of transient conduction in pool boiling is overshadowed by some other effect. Since the particles under consideration are one to two orders of magnitude smaller than the surface roughness it was concluded that the change of surface characteristics during boiling due to trapped particles on the surface is the cause for the shift of the boiling characteristics in the negative direction. The results serve as a guidance for the design of cooling systems with nano-fluids where an overheating may occur if saturation temperature is attained. It also indicates the possibility of such engineered fluids to be used in material processing or heat treatment applications where a higher pre-assigned surface temperature is required to be maintained without changing the fluid temperature. © 2002 Elsevier Science Ltd. All rights reserved.

Pool boiling characteristics of nano-fluids

The nucleation site density (N/A) during pool boiling of binary mixtures has been experimentally examined in terms of the heating surface physical properties, the liquid physical properties, the vapour liquid equilibria and the surface micro-roughness. The liquid mixtures used were acetone - carbon tetrachloride and n-hexane - carbon tetrachloride. A parameter Ra, to characterize the micro-roughness of the heating surface was defined as the average value of the peaks and valleys on the surface. The study shows that while at low Ra values the physical properties of the liquid and the binary composition are not as important as the surface roughness; at higher Ra values the liquid properties and composition are also important. A correlation based on the present data has been proposed.

Canadian Journal of Chemical Engineering

Nucleation Site Density in Pool Boiling of Binary Mixtures: Effect of Surface Micro-roughness and Surface and Liquid Physical Properties

Proceeding of International Heat Transfer Conference 3

PHOTOGRAPHICAL STUDY FOR BOILING HEAT TRANSFER MECHANISM

Who's Who

Levin, David Saul, (born 28 Jan. 1962), Chief Executive, McGraw-Hill Education, New York, since 2014

Heat Transfer in Condensation and Boiling International Series in Heat and Mass Transfer

Drop Condensation of Stagnant Vapors

Journal of Heat Transfer

A Comprehensive Model for Nucleate Pool Boiling Heat Transfer Including Microlayer Evaporation

Journal	Data powered by TypesetInternational Journal of Heat and Mass Transfer
Publisher	Data powered by TypesetElsevier Ltd
ISSN	00179310
Open Access	No