Dissertation•
Separate effects of surface roughness, wettability and porosity on boiling heat transfer and critical heat flux and optimization of boiling surfaces
01 Jan 2012-
TL;DR: Thesis (S.M.B.) as mentioned in this paper, Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering; and, S.M., M.B., and S.B.
Abstract: Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering; and, (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.
Citations
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01 Aug 1953
TL;DR: In this paper, a solution for the radius of the vapor bubble as a function of time is obtained which is valid for sufficiently large radius, since the radius at which it becomes valid is near the lower limit of experimental observation.
Abstract: The growth of a vapor bubble in a superheated liquid is controlled by three factors: the inertia of the liquid, the surface tension, and the vapor pressure. As the bubble grows, evaporation takes place at the bubble boundary, and the temperature and vapor pressure in the bubble are thereby decreased. The heat inflow requirement of evaporation, however, depends on the rate of bubble growth, so that the dynamic problem is linked with a heat diffusion problem. Since the heat diffusion problem has been solved, a quantitative formulation of the dynamic problem can be given. A solution for the radius of the vapor bubble as a function of time is obtained which is valid for sufficiently large radius. This asymptotic solution covers the range of physical interest since the radius at which it becomes valid is near the lower limit of experimental observation. It shows the strong effect of heat diffusion on the rate of bubble growth. Comparison of the predicted radius‐time behavior is made with experimental observations in superheated water, and very good agreement is found.
729 citations
TL;DR: In this article, the authors present an overview of the surface, thermal and material science to illustrate how new materials and designs can improve boiling and condensation, and focus on nanoengineered materials, with emphasis on further improving the heat-transfer performance and long-term robustness.
Abstract: Liquid–vapour phase change is a useful and efficient process to transfer energy in nature, as well as in numerous domestic and industrial applications. Relatively recent advances in altering surface chemistry, and in the formation of micro- and nanoscale features on surfaces, have led to exciting improvements in liquid–vapour phase-change performance and better understanding of the underlying science. In this Review, we present an overview of the surface, thermal and material science to illustrate how new materials and designs can improve boiling and condensation. There are many parallels between boiling and condensation, such as nucleation of a phase and its departure from a surface; however, the particular set of challenges associated with each phenomenon results in different material designs used in different manners. We also discuss alternative techniques, such as introducing heterogeneous surface chemistry or direct real-time manipulation of the phase-change process, which can offer further control of heat-transfer processes. Finally, long-term robustness is essential to ensure reliability and feasibility but remains a key challenge. Recent works in boiling and condensation have achieved unprecedented performance and revealed new mechanistic insights that will aid in material design. In this Review, we focus on nanoengineered materials, with emphasis on further improving the heat-transfer performance and long-term robustness.
373 citations
Cites methods from "Separate effects of surface roughne..."
...O’Hanley (2012)6 (RNHydrophilic) Epoxy micropillars (20 µm diameter, 500 µm spacing, 15 µm height) coated with 20 nm SiO2 layer (SPHydrophilic) Smooth sapphire substrate deposited with 2.5-µm thick layers of SiO2 particles (50 nm diameter) (RPHydrophilic) Epoxy micropillars (20 µm diameter, 500 µm…...
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TL;DR: In this article, the effects of surface wettability, porosity, and roughness on the critical heat flux (CHF) of water were examined using engineered surfaces and the results showed that porosity had little effect on the smooth non-porous surface CHF.
Abstract: The separate effects of surface wettability, porosity, and roughness on the critical heat flux (CHF) of water were examined using engineered surfaces. Values explored were 0, 5, 10, and 15 μm for Rz (roughness), 110° for static contact angle (wettability), and 0 and 50% for pore volume fraction. The porous hydrophilic surface enhanced CHF by 50%–60%, while the porous hydrophobic surface resulted in a reduction of CHF by 97%. Wettability had little effect on the smooth non-porous surface CHF. Surface roughness (Ra, Rq, Rz) had no effect on CHF within the limit of this database.
266 citations
TL;DR: In this paper, the authors presented the classification of micro/minichannels for single-phase flow and flow boiling and gave a general statement of heat transfer enhancement, and provided a state-of-the-art overview of the most recent enhancement techniques.
Abstract: With fast growing power consumption and device miniaturization, micro/minichannels are superior to macrochannels or conventional channels for high heat-flux dissipation due to their large surface area to volume ratios and high heat transfer coefficients. However, the associated large pressure drop penalty and flow boiling instability of micro/minichannels hinder their advancement in many practical applications. Therefore, enhancement techniques are required to stabilize the flow and further augment the heat transfer performance in micro/minichannels. This work first presents the classification of micro/minichannels for single-phase flow and flow boiling and gives a general statement of heat transfer enhancement. Then a state-of-the-art overview of the most recent enhancement techniques is specifically provided for further sing-phase flow and flow boiling enhancement in micro/minichannels. Two promising enhancement techniques, i.e., interrupted microfins and engineered fluids with additives are discussed for single-phase flow. For flow boiling, the focus is given on several selected enhancement approaches which can effectively mitigate flow boiling instability and another hot research topic, i.e., nanoscale surface modification. Besides, effects of wettability on bubble dynamics are presented, and a concept of flow-pattern based heat transfer enhancement is proposed. For both single-phase flow and flow boiling enhancement, a special emphasis is on those enhancement techniques with high thermal performance and relatively low pressure drop penalty.
108 citations
TL;DR: In this paper, an experimental study of flow boiling heat transfer and pressure drop was conducted using R245fa in stainless steel, brass and copper tubes of 1.1mm internal diameter.
40 citations
Cites background or methods from "Separate effects of surface roughne..."
...As previously discussed, O’Hanley [25] used the Ra and the Rz value to characterise if the surface is rough or smooth....
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...O’Hanley [25] conducted a study into the effects of surface characteristics in pool boiling, characterising the surface as rough or smooth based on the ‘‘ten point’’ Rz values and the Ra values....
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References
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01 Jan 2011
6,700 citations
Additional excerpts
...Zuber (1959) worked with the hydrodynamic instability model and predicts CHF as, [21],...
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2,532 citations
"Separate effects of surface roughne..." refers background in this paper
...[4] During this period, the bubble radius increases roughly linearly as predicted by Rayleigh (1917) [5]:...
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Book•
01 Jan 1994
TL;DR: In this paper, the basic models of two-phase flow are discussed and empirical treatments of two phase flow are provided. But the authors focus on convective boiling and condensing.
Abstract: Introduction 1. The basic models 2. Empirical treatments of two-phase flow 3. Introduction to convective boiling 4. Subcooled boiling heat transfer 5. Void fraction and pressure drop in subcooled boiling 6. Saturated boiling heat transfer 7. Critical heat flux in forced convective flow - 1. Vertical uniformly heated tubes 8. Critical heat flux in forced convective flow - 2. More complex situations 9. Condensation 10. Conditions influencing the performance of boiling and condensing systems 11. Multi-component boiling and condensation Appendix Index
2,426 citations
"Separate effects of surface roughne..." refers background in this paper
...[11] However, these correlations are an adequate starting point for bubble departure diameter analysis....
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...[11] Temporary dry spots begin to form on the surface, with the frequency and size of such dry spots increasing, until the critical heat flux (CHF) is reached (Point C in Figure 2-9)....
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01 Jan 1997
TL;DR: In this article, the analogy between heat and mass transfer is covered and applied in the analysis of heat transfer by conduction, convection and radiation, and the analysis is performed by using the handbook of numerical heat transfer.
Abstract: Handbook of Numerical Heat Transfer Free Full Download Links from Multiple Mirrors added by DL4W on 2015-04-10 02:13:35. Handbook of heat transfer / editors, W.M. Rohsenow, J.P. Hartnett. Y.I. Cho. m 3rd ed. p. cm. Includes bibliographical references and index. ISBN 0-07053555-8. Students investigate heat transfer by conduction, convection and radiation. The analogy between heat and mass transfer is covered and applied in the analysis.
1,644 citations
"Separate effects of surface roughne..." refers background or methods in this paper
...[2] Though in principle, it is possible for a single irreversible hot spot to form and grow to cover the entire surface, leading to CHF....
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...[2] As such, bubble frequency is also a function of a variety of surface and operating conditions....
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...[2] Heat transfer controlled growth occurs later, when the liquid superheat near the surface has been largely exhausted....
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...This process can best be understood through the following steps [2]:...
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...[2,6] Here, bubble radius varies with square root of time, as modeled by Plesset and Zwick (1954) [7]:...
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Book•
01 Jan 2003
TL;DR: In this paper, the authors introduce basic concepts of heat transfer, including thermal spreading and contact resistances, and forced convection and external flow. But they do not consider the effect of external flow on internal flow.
Abstract: Preface. Contributors. 1. Basic Concepts (Allan D. Kraus). 2. Thermophysical Properties of Fluids and Materials (R. T Jacobsen, E. W. Lemmon, S. G. Penoncello, Z. Shan, and N. T. Wright). 3. Conduction Heat Transfer (A. Aziz). 4. Thermal Spreading and Contact Resistances (M. M. Yovanovich and E. E. Marotta). 5. Forced Convection: Internal Flows (Adrian Bejan). 6. Forced Convection: External Flows (Yogendra Joshi and Wataru Nakayama). 7. Natural Convection (Yogesh Jaluria). 8. Thermal Radiation (Michael F. Modest). 9. Boiling (John R. Thome). 10. Condensation (M. A. Kedzierski, J. C. Chato, and T. J. Rabas). 11. Heat Exchangers (Allan D. Kraus). 12. Experimental Methods (Jose L. Lage). 13. Heat Transfer in Electronic Equipment (Avram Bar-Cohen, Abhay A. Watwe, and Ravi S. Prasher). 14. Heat Transfer Enhancement (R. M. Manglik). 15. Porous Media (Adrian Bejan). 16. Heat Pipes (Jay M. Ochterbeck). 17. Heat Transfer in Manufacturing and Materials Processing (Richard N. Smith, C. Haris Doumanidis, and Ranga Pitchumani). 18. Microscale Heat Transfer (Andrew N. Smith and Pamela M. Norris). 19. Direct Contact Heat Transfer (Robert F. Boehm). Author Index. Subject Index. About the CD-ROM.
1,368 citations
"Separate effects of surface roughne..." refers background in this paper
...[9] A dependence of boiling on surface wettability can be witnessed from this correlation, as presented in Figure 2-4....
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