Theoretical and Experimental Investigation of Condensation Heat Transfer Enhancement on an Inclined Surface Coated with a Highly Conductive Porous Substrate PDF Download
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Author: Merid Aboye
Publisher:
ISBN:
Category : Condensation
Languages : en
Pages : 278
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Author: Merid Aboye
Publisher:
ISBN:
Category : Condensation
Languages : en
Pages : 278
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Author: American Institute of Chemical Engineers
Publisher:
ISBN:
Category : Chemical engineering
Languages : en
Pages : 432
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Author: David Milton Anderson
Publisher:
ISBN:
Category : Amphiphiles
Languages : en
Pages :
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Condensation of water vapor is an everyday phenomenon which plays an important role in power generation schemes, desalination applications and high-heat flux cooling of power electronic devices. Continuous dropwise condensation is a desirable mode of condensation in which small, highly-spherical droplets regularly form and shed off the surface before a thick liquid is formed, thereby minimizing the thermal resistance to heat transfer across the condensate layer. While difficult to induce and sustain, dropwise condensation has been shown to achieve heat and mass transfer coefficients over an order of magnitude higher than its filmwise counterpart. Superhydrophobic surfaces have been extensively studied to promote dropwise condensation with mixed results; often surfaces that are superhydrophobic to deposited droplets formed in the gas phase above the surface do not retain this behavior with condensed droplets nucleated and grown on the surface. Recently, nanostructured superhydrophobic surfaces have been developed that are robust to vapor condensation; however, these surfaces still are not ideal for condensation heat transfer due to the high thermal resistance of the vapor layer trapped underneath the droplets and the reduced footprint of direct contact between the highly-spherical droplets and the underlying substrate. This work has two main objectives. First, a comprehensive free energy based thermodynamic model is developed to better understand why traditional superhydrophobic surfaces often lose their properties when exposed to condensed droplets. The model is first validated using data from the existing literature and then extended to analyze the suitability of amphiphilic (e.g. part hydrophobic and part hydrophilic) nanostructured surfaces for condensation applications. Secondly, one of the promising amphiphilic surfaces identified by the thermodynamic model is fabricated and tested to observe condensation dynamic behavior. Two complementary visualization techniques, environmental scanning electron microscopy (ESEM) and optical (light) microscopy, are used to probe the condensation behavior and compare the performance to that of a traditional superhydrophobic surface. Observations from the condensation experiments are used to propose a new mechanism of coalescence that governs the temporal droplet size distribution on the amphiphilic nanostructured surface and continually generates fresh sites for the droplet nucleation and growth cycle that is most efficient at heat transfer.
Author: American Society of Mechanical Engineers. Winter Annual Meeting
Publisher: American Society of Civil Engineers
ISBN:
Category : Science
Languages : en
Pages : 80
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Author: Gregory L. Malchow
Publisher:
ISBN:
Category :
Languages : en
Pages : 114
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Author: Sameer Khandekar
Publisher: Springer Science & Business Media
ISBN: 1461484472
Category : Science
Languages : en
Pages : 155
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Book Description
Dropwise Condensation on Textured Surfaces presents a holistic framework for understanding dropwise condensation through mathematical modeling and meaningful experiments. The book presents a review of the subject required to build up models as well as to design experiments. Emphasis is placed on the effect of physical and chemical texturing and their effect on the bulk transport phenomena. Application of the model to metal vapor condensation is of special interest. The unique behavior of liquid metals, with their low Prandtl number and high surface tension, is also discussed. The model predicts instantaneous drop size distribution for a given level of substrate subcooling and derives local as well as spatio-temporally averaged heat transfer rates and wall shear stress.
Author: Ramana Saketh Vanga
Publisher:
ISBN:
Category : Condensation
Languages : en
Pages : 100
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Renewable energy systems operated by a thermal energy resource such as geothermal power plants and solar thermal power systems are demanding improvement in their condensation performance. While their energy resources are naturally obtained at almost no cost, heat rejecting components are relatively expensive to maintain and operate. In this research, a heterogeneous condensing surface is proposed to enhance the condensation heat transfer coefficient in vapor-to-liquid heat exchangers. Parallel stripes with hydrophobic feature and ones without it alternate on its surface. The effect of surface wettability variation that is generated by the heterogeneous surface on the dropwise condensation heat transfer of saturated steam on the flat plate copper surface is experimentally investigated. A vertical flat plate condenser is constructed to evaluate the performance of the heterogeneous condensing surface in comparison with a plain copper sample and a homogeneous hydrophobic-treated copper sample. Experimental results show that condensation heat transfer of steam on the homogeneous hydrophobic-treated sample is superior to that of the plain copper surface despite the fact that both the surfaces stably promote dropwise condensation. At the subcooling temperature of 3°C, the difference in the heat transfer coefficients between the plain copper sample and the hydrophobic-treated copper sample is almost twofold. The heat transfer coefficients for the heterogeneous surface at smaller subcooling temperatures, when its stripes situate horizontally, are as high as the heat transfer coefficients for the homogeneous hydrophobic-treated surface. The enhancement for the horizontal heterogeneous sample over the plain copper sample is approximately 100%. The heat transfer coefficient for the heterogeneous sample with its stripes being vertical at 4°C subcooling is 25% greater than that of the plain copper sample. Higher heat transfer coefficients are observed at smaller subcooling temperatures for all the samples. The results and observations of this project suggest that the heterogeneous surface has the potential to enhance the heat transfer coefficients.
Author: Samuel Steven Cruz
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Condensation is a phenomenon that is ubiquitous in nature and used to effectively transfer heat in many important industrial applications including thermal management of electronics, steam power generation, and natural gas processing. Industry relies mainly on filmwise condensation, where the condensate forms an insulating, thick liquid film on the condensation surface, posing a large thermal resistance. For almost a century, much work has explored developing surfaces that can promote the nucleation, growth, coalescence and effective shedding of mobile condensing droplets from surfaces, called dropwise condensation, which is known to enhance the heat transfer up to an order of magnitude. However, the requirement for ultra-thin coatings has hampered the wide adoption of this form of condensation as thin hydrophobic coatings degrade over time in various industrial applications. In this thesis, we model, fabricate, optimize, experimentally demonstrate a proof-of-concept for a novel condensation approach which we term capillary-driven condensation. The method consists of a hierarchical structure consisting of a hydrophobic porous membrane attached on top of a wicking structure that is firmly bonded to the condenser surface. The wicking structure and the membrane can be separately tailored to maximize the fluid flow in the wick and its effective thermal conductivity, as well as the maximum capillary pressure that the membrane can sustain to push fluid through a viscous pressure drop in the porous wick to an exit port. The geometry can be optimized to reduce the thermal resistance of the structure, as well as maximize the amount of condensate that can be removed passively by capillarity. To demonstrate the viability of this condensation method, we fabricated the proposed structure with highly-defined geometry utilizing silicon microfabrication technique s. The result is a surface which is able to constrain a thin film of condensate within a high thermal conductivity wicking structure while the top condensation surface appears dry despite sustaining condensation rates above those of filmwise condensation. The thickness of this layer and geometry of the membrane can be rationally designed to maximize the heat transfer coefficient even beyond dropwise condensation. Heat transfer measurements indicate a potential range of enhancement of ~~ 40% to ~~ 400% which is to be confirmed by more sensitive experiments that reduce error. The results from this thesis show a proof-of-concept and support the promise of capillary-driven condensation surfaces for various heat transfer applications.
Author: V. G. Rifert
Publisher: WIT Press (UK)
ISBN:
Category : Science
Languages : en
Pages : 402
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Book Description
In processes with condensation of steam-to-gas compositions or refrigerative agents an intensification of condensation is often required because thermal resistance on the condensation side can be greater than the thermal resistance of the heat transfer wall on the cooling side. In this work, a pair of researchers from the National Technical U. of Ukraine and the State Academy of Refrigeration (Ukraine) provide information about the enhancement of condensation, including research results from the former USSR they feel deserves wider dissemination as well as discussion of different theoretical models of the condensation process. The US office of WIT Press is Computational Mechanics. Annotation : 2004 Book News, Inc., Portland, OR (booknews.com).
Author:
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ISBN:
Category :
Languages : en
Pages :
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