Littérature scientifique sur le sujet « Condensation droplet jumping »
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Articles de revues sur le sujet "Condensation droplet jumping"
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Gao, Sihang, Fuqiang Chu, Xuan Zhang et Xiaomin Wu. « Behavior of condensed droplets growth and jumping on superhydrophobic surface ». E3S Web of Conferences 128 (2019) : 07003. http://dx.doi.org/10.1051/e3sconf/201912807003.
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Droplets on the superhydrophobic surface can fall off the surface spontaneously, which greatly promote dropwise condensation. This study considers a continuous droplet condensation process including droplet growth and droplet jumping. A droplet growth model considered NCG is developed and droplet jumping is simulated using VOF (Volume Of Fluid) model. Al–based superhydrophobic surfaces are prepared using chemical deposition and etching method. The Al-based superhydrophobic surface has a contact angle of 157°±1° and a rolling angle of 2°±1°. An observation experiment is designed to observe droplet jumping on superhydrophobic surface using a high– speed camera system. The result of droplet growth model shows a good match with experimental data in mid-term of droplet growth. Fordroplet jumping, simulation and experiment results show that droplet jumping of different diameter hasa universality in a non–dimensional form. The jumping process can be divided into 3 stages and droplet vibration is observed.
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Birbarah, Patrick, Shreyas Chavan et Nenad Miljkovic. « Numerical Simulation of Jumping Droplet Condensation ». Langmuir 35, no 32 (12 juillet 2019) : 10309–21. http://dx.doi.org/10.1021/acs.langmuir.9b01253.
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Chongyan, Zhao, Chen Feng, Yan Xiao, Yan He, Huang Zhiyong et Bo Hanliang. « SIMULATION OF DROPLET SIZE DISTRIBUTION DURING JUMPING-DROPLET CONDENSATION ». Proceedings of the International Conference on Nuclear Engineering (ICONE) 2019.27 (2019) : 1748. http://dx.doi.org/10.1299/jsmeicone.2019.27.1748.
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Zhang, Lenan, Zhenyuan Xu, Zhengmao Lu, Jianyi Du et Evelyn N. Wang. « Size distribution theory for jumping-droplet condensation ». Applied Physics Letters 114, no 16 (22 avril 2019) : 163701. http://dx.doi.org/10.1063/1.5081053.
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Mukherjee, Ranit, Austin S. Berrier, Kevin R. Murphy, Joshua R. Vieitez et Jonathan B. Boreyko. « How Surface Orientation Affects Jumping-Droplet Condensation ». Joule 3, no 5 (mai 2019) : 1360–76. http://dx.doi.org/10.1016/j.joule.2019.03.004.
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Birbarah, Patrick, et Nenad Miljkovic. « Internal convective jumping-droplet condensation in tubes ». International Journal of Heat and Mass Transfer 114 (novembre 2017) : 1025–36. http://dx.doi.org/10.1016/j.ijheatmasstransfer.2017.06.122.
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Nath, Saurabh, S. Farzad Ahmadi, Hope A. Gruszewski, Stuti Budhiraja, Caitlin E. Bisbano, Sunghwan Jung, David G. Schmale et Jonathan B. Boreyko. « ‘Sneezing’ plants : pathogen transport via jumping-droplet condensation ». Journal of The Royal Society Interface 16, no 155 (juin 2019) : 20190243. http://dx.doi.org/10.1098/rsif.2019.0243.
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We show that condensation growing on wheat leaves infected with the leaf rust fungus, Puccinia triticina , is capable of spontaneously launching urediniospores off the plant. This surprising liberation mechanism is enabled by the superhydrophobicity of wheat leaves, which promotes a jumping-droplet mode of condensation powered by the surface energy released from coalescence events. We found that urediniospores often adhere to the self-propelled condensate, resulting in liberation rates of approximately 10 cm −2 h −1 for leaves infected with rust. Urediniospores were catapulted up to 5 mm from the leaf’s surface, a distance sufficient to clear the laminar boundary layer for subsequent dispersal even in gentle winds.
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Mulroe, Megan D., Bernadeta R. Srijanto, S. Farzad Ahmadi, C. Patrick Collier et Jonathan B. Boreyko. « Tuning Superhydrophobic Nanostructures To Enhance Jumping-Droplet Condensation ». ACS Nano 11, no 8 (31 juillet 2017) : 8499–510. http://dx.doi.org/10.1021/acsnano.7b04481.
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Antao, Dion S., Kyle L. Wilke, Jean H. Sack, Zhenyuan Xu, Daniel J. Preston et Evelyn N. Wang. « Jumping droplet condensation in internal convective vapor flow ». International Journal of Heat and Mass Transfer 163 (décembre 2020) : 120398. http://dx.doi.org/10.1016/j.ijheatmasstransfer.2020.120398.
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Ashrafi-Habibabadi, Amir, et Ali Moosavi. « Droplet condensation and jumping on structured superhydrophobic surfaces ». International Journal of Heat and Mass Transfer 134 (mai 2019) : 680–93. http://dx.doi.org/10.1016/j.ijheatmasstransfer.2019.01.026.
Texte intégralThèses sur le sujet "Condensation droplet jumping"
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Queeney, John (John Keeler). « Evaporative cooling via jumping droplet condensation on superhydrophobic surfaces for localized car air conditioning ». Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/100886.
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Thesis: S.B., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 28).
Car air conditioning systems cool the entire cabin, which is inefficient, as only the air surrounding the passengers needs to be cooled to realize a similar effect. These air conditioning units draw large amounts of power, enough to be detrimental to fuel efficiency. This presents problems for cars with smaller engines and electric cars that lack the battery capacity to provide adequate cooling with traditional air conditioning technology. A novel solution to these problems uses evaporative cooling via jumping droplet condensation on superhydrophobic surfaces to provide localized cooling with 100 times less power input. Jumping droplet condensation takes place when microscale droplets coalesce on superhydrophobic surfaces and excess surface energy is converted to kinetic energy, resulting in droplets that jump perpendicularly off the surface. As these droplets fall through the air, they evaporate, cooling the surrounding air and providing localized cooling. To test this technology, a prototype device was designed, fabricated, and tested at different relative humidities in an environmental chamber. Cooling of up to 4.8°C relative to ambient was achieved at 80% relative humidity, 4 cm from the condensing surface. This result suggests an optimal humidity for the operation of these devices and prompts further lines of study for the optimization of this technology.
by John Queeney.
S.B.
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Mukherjee, Ranit. « Exploiting Interfacial Phenomena to Expel Matter from its Substrate ». Diss., Virginia Tech, 2021. http://hdl.handle.net/10919/104925.
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Spontaneous expulsion of various forms and types of matter from their solid substrates has always been an integral part of interfacial physics problems. A thorough understanding of such interactions between a solid surface and different soft materials not only expands our theoretical knowledge, but also has applications in self-cleaning, omniphobic surfaces and phase-change heat transfer. Although there is a renewed interest in the design of robust functional surfaces which can passively remove highly viscous liquids or dew, or retard ice accretion or frost formation, the physics of several dewetting and/or deicing mechanisms are yet to be fully understood. Even though we know how jumping-droplet condensation offers significantly better heat transfer performance than regular dropwise condensation and can liberate foreign particles, fundamental questions on the effect of surface orientation on jumping-droplet condensation or how it helps in large-scale fungal disease epidemic in plants are still unanswered. Thus, we first try to fill the knowledge gap in jumping-droplet condensation by characterizing their orientation-dependence and their role in a large-scale pathogenic rust disease dissemination among wheat. Unfortunately, understanding of such dewetting mechanisms does not necessarily translates to prevention or removal of ice and frost on subzero surfaces. Use of superhydrophobic structures or hygroscopic materials to retard the growth of frost was found to be limiting. Therefore the search for an efficient, inexpensive, and environmentally favorable anti-icing or de-icing mechanism is still underway. Here we give a framework for making a novel de-icing construct by analyzing a peculiar jumping frost phenomena where frost particles spontaneously jump off the surface when a polar liquid is brought above. Lastly, we demonstrate a simple and cost-effective technique to design a slippery liquid-infused surface from low-density hydrocarbon-based polymers, which is able to effectively remove a wide variety of soft materials. The main all-encompassing theme of this dissertation is to enhance our understanding of several dewetting phenomena, which might enable better design and/or mitigation strategies to control the expulsion of various forms of matter from a wide variety of surfaces.Doctor of Philosophy
A few years back, a laundry detergent company in India came up with a famous ad campaign; it showed kids coming home from school with dirt all over their clothes to face the wrath of their parents. Rather than casually disparaging their mischievousness, the ad would make us think with their tagline: "Agar daag (Lit. stain, Fig. mess) lagne se kuch achha hota hain, toh daag achhe hain na? (Fig. If something good comes out of a mess, is it a mess?)". While this presents to us an excellent philosophical conundrum, in reality, we always find ways to get rid of foreign materials from surfaces of everyday use. Using water or dirt-repellent coatings on our shoes/clothes/car windshields or in worst case, spending hours trying to clean frost off our cars is something we are all familiar with. Finding innovative ways to remove unwanted materials from surfaces is not limited to humans, but also exhibited by various natural organisms. The excellent water repellency of lotus leaves, antifogging abilities of mosquito eyes or cicada wings, and slipperiness of pitcher plants are just few examples of natural self-cleaning surfaces designed to keep foreign materials or dew droplets off the surface. Sometimes we take a leaf or two out of these natural designs to help our cause. Surfaces with extreme water repellency are called superhydrophobic (hydro: water, phobos: fear). For a long time, gravity was considered to be the only passive droplet removal mech- anism on these surfaces. About ten years ago, researchers found out that when two or more small dew droplets come together on these surfaces, they jump off the surface. Compared to the gravity removal, much smaller droplets can be removed via this method resulting in better anti-fogging qualities and heat transfer performance on the surface. As the jumping droplet event itself is independent of gravity, it was long assumed that the performance of these surfaces would not be dependent on their orientation. These jumped droplets can also take off with contaminating particles by partially or fully engulfing them. A recent study has brilliantly showed how rust spores are liberated from the superhydrophobic wheat leaves via jumping dew droplets. This fundamentally new mode of pathogen transport is yet to be fully understood at the same scale as we know wind or rain-induced fungal spore transport. In this work, we try to fill the knowledge gap by answering questions such as whether the surfaces with the abilities of gravity-independent jumping-induced droplet removal ironically fail to gravity and how far can spore(s) travel engulfed in a jumped droplet. But it is not just water droplets (or particles collected by water droplets) on a surface that we want to get rid off. The solid phase of water, i.e., ice or frost, when formed on regular surfaces, is actually harder to remove. The common ice-preventing surfaces are generally unable to stop complete frost formation and forces us to use salt or other moisture attracting chemicals to remove ice from a surface, knowing very well what is the economic and environmental cost of these chemicals. Here, we have introduced a novel de-icing mechanism by holding only a drop of water over a sheet of frost. The simplicity of our experimental setup may remind you the home physics experiments we all did in our childhood. We finish our discussion by designing a slippery surface from regular polymer films used in food packaging. Although the idea behind these slippery surfaces has been around since 2011, polyethylene films have never been used to make such surfaces before. Here, we show through extensive characterization that by choosing a suitable lubricating oil and a polyethylene-based film, we can finally get all of our ketchup to slide out of their packets, without struggle. If the future design of superhydrophobic condensers, de-icing constructs, or slippery surfaces benefit from the work reported here, may be I can finally say with certainty, "Daag Achhe Hain (Dirt is good.)."
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Di, Novo Nicolò Giuseppe. « Water self-ejection, frosting, harvesting and viruses viability on surfaces : modelling and fabrication ». Doctoral thesis, Università degli studi di Trento, 2022. https://hdl.handle.net/11572/355461.
Texte intégralRésumé :
The wettability and phase change phenomena of water are ubiquitous on biological and artificial surfaces. Properties like water repellency, self-cleaning, coalescence induced condensation jumping, anti-frosting, and dew harvesting arise on surfaces with particular structures and chemistry and are of particular interest for energy and water saving.
This thesis collects different studies of wettability and phase change on natural and artificial surfaces: growth and self-ejection of condensation droplets on micro and nanostructured surfaces we fabricated, their applications, the Sliding on Frost of condensation droplets observed on the Cotinus Coggygria leaf, the dew harvesting property of the Old Man of the Andes Cactus enhanced by distance coalescence through microgrooves and finally, a theoretical study of viruses viability in sessile droplets.
The first chapter introduces the theoretical framework of wettability and phase changes on surfaces.
In the second chapter, we present the self-ejection of condensation droplets from hydrophobic nanostructured microstructures. We modelled analytically the droplets jumping and fabricated surfaces to verify the predictions. The fabricated geometry was inspired by the modelling and the available fabrication techniques. We tested the surfaces in condensation conditions. Using a high frame rate camera coupled with a long working distance microscopy objective, we investigated the growth and ejection transient. We then compared the experimental self-ejection velocity for various structures geometry with our analytical models.
In Chapter 3, we investigated the applications of the fabricated surfaces reported in Chapter 2.
In Chapter 4, we explore the condensation frosting on the leaf of Cotinus Coggygria, native of our woods and with interesting hydrophobic properties. Covered by wax nanotubules, it exhibits coalescence-induced condensation jumpings that may be a useful cleaning tool. Furthermore, the frost is delayed but not only for the jumping. Surprisingly, at temperatures some degrees below zero, we observed what we called ‘droplet Sliding on Frost bridges’, that further delays frosting. We described the feasibility of this sliding in terms of dynamic contact angles of the surface and contact angles of supercooled water on ice. By capturing high temporal and spatial resolution videos we investigated the sliding on frost and droplet recalescence (fast dendrite growth that partially solidify the liquid). The responsible for the failure of sliding for temperatures from about -8 ° C down appears to be the advancing angle of water on ice that increases with the subcooling rather than the recalescence that blocks the drop in place. These results add a piece to the fundamental research on the supercooled water-ice-vapour interfaces.
As it often happens, biological surfaces offer a starting point for the study of fundamental mechanisms and the development of artificial surfaces with optimized properties. In the Chapter 5, the multifunctional roles of hairs and spines in Old Man of the Andes Cactus (Oreocereus trolli) are studied. We study the morphology of the appendages, the hairs wettability, mechanical properties of both, and the dew formation on spines. The longitudinal microgrooves on the spines cause a particular phenomenon of distant coalescence (DC), in which smaller droplets flow totally or partially into larger ones through the microgrooves, with consequent accumulation of water in a few large drops. An earlier study has shown artificial micro-grooved surfaces that exhibit DC are more efficient than flat ones at collecting and sliding dew, and thus these cactus spines could act as soil dew conveyors. The agreement between our analytical model and experimental data verifies that the flow is driven by the Laplace pressure difference between the drops. This allowed us to obtain a general criterion for predicting the total or partial emptying of the smaller drops as a function of the dynamic contact angles of a surface. Based on this criterion, an hydrophilic material with small contact angle hysteresis would allow a greater number of complete drops emptying.
The COVID-19 pandemic has raised the problem of contagion from airborne and deposited droplets. In the last chapter, we report the state of the art of experiments on the viability of viruses in deposited droplets. Up to date, it has been experimentally highlighted that the relative viability of some viruses (RV) depends on the material chemistry, temperature, and interestingly, on relative humidity (RH) with a U-shaped trend. One of the current hypotheses is that the cumulative dose of salt concentration (CD) affects RV. We model the RV of viruses in sessile droplets by inserting a RV-CD relation in a model of droplet evaporation. By considering a saline water droplet (one salt) as the simplest approximation of real solutions, we analytically simulate the time evolution of salt concentration, vapor pressure, and droplet volume varying contact angles, droplet sizes, and RH in the range 0–100%. The results elucidate some previously not yet well-understood dynamics, demonstrating how three main regimes—directly implicated in nontrivial experimental trends of virus RV—can be recognized as the function of RH. The proposed approach could suggest a chart of a virus fate by predicting its survival time at a given temperature as a function of RH and contact angle. We found a good agreement with experimental data for various enveloped viruses and predicted in particular for the Phi6 virus, a surrogate of coronavirus, the characteristic U-shaped dependence of RV on RH. Given the generality of the model, once experimental data are available that link the vulnerability of a certain virus (such as SARS-CoV-2) to the concentrations of salts or other substances in terms of CD, it is envisioned that this approach could be employed for antivirus strategies and protocols for the prediction/reduction of human health risks associated with SARS-CoV-2 and other viruses.
Actes de conférences sur le sujet "Condensation droplet jumping"
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Miljkovic, Nenad, Daniel J. Preston, Ryan Enright et Evelyn N. Wang. « Electric-Field-Enhanced Jumping-Droplet Condensation ». Dans The 15th International Heat Transfer Conference. Connecticut : Begellhouse, 2014. http://dx.doi.org/10.1615/ihtc15.cds.008896.
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Traipattanakul, B., C. Y. Tso et Christopher Y. H. Chao. « Study of Electrostatic-Induced Jumping Droplets on Superhydrophobic Surfaces ». Dans ASME 2017 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/imece2017-70311.
Texte intégralRésumé :
Condensation of water vapor is an important process utilized in energy/thermal/fluid systems. When droplets coalesce on the non-wetting surface, excess surface energy converts to kinetic energy leading to self-propelled jumping of merged droplets. This coalescing-jumping-droplet condensation can better enhance heat transfer compared to classical dropwise condensation and filmwise condensation. However, the resistance force can cause droplets to return to the surface. These returning droplets can either coalesce with neighboring droplets and jump again, or adhere to the surface. As time passes, these adhering droplets can become larger leading to progressive flooding on the surface, limiting heat transfer performance. However, an electric field is known to be one of the effective methods to prevent droplet return and to address the progressive flooding issue. Therefore, in this study, an experiment is set up to investigate the effects of applied electrical voltages between two parallel copper plates on the jumping height with respect to the droplet radius and to determine the average charge of coalescing-jumping-droplets. Moreover, the gravitational force, the drag force, the inertia force and the electrostatic force as a function of the droplet radius are also discussed. The gap width of 7.5 mm and the electrical voltages of 50 V, 100 V and 150 V are experimentally investigated. Droplet motions are captured with a high-speed camera and analyzed in sequential frames. The results of the study show that the applied electrical voltage between the two plates can reduce the resistance force due to the droplet’s inertia and can increase the effects of the electrostatic force. This results in greater jumping heights and the jumping phenomenon of some bigger-sized droplets. With the same droplet radius, the greater the applied electrical voltage, the higher the coalescing droplet can jump. This work can be utilized in several applications such as self-cleaning, thermal diodes, anti-icing and condensation heat transfer enhancement.
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Xu, Zhenyuan, Lenan Zhang, Kyle L. Wilke et Evelyn N. Wang. « MODELING OF JUMPING-DROPLET CONDENSATION WITH DYNAMIC DROPLET GROWTH ». Dans International Heat Transfer Conference 16. Connecticut : Begellhouse, 2018. http://dx.doi.org/10.1615/ihtc16.hte.023384.
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Aili, Abulimiti, Hongxia Li, Mohamed H. Alhosani et TieJun Zhang. « Characteristics of Jumping Droplet-Enhanced Condensation on Nanostructured Micromesh Surface ». Dans ASME 2016 5th International Conference on Micro/Nanoscale Heat and Mass Transfer. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/mnhmt2016-6382.
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Jumping-droplet enhanced condensation has recently attracted huge interest due to its remarkable potential of heat transfer performance enhancement, and studies have been done to design superhydrophobic surfaces with various surface morphologies. We fabricated a superhydrophobic micromesh-covered surface using a facile and scalable method. ESEM condensation experiment results show that droplets in pores formed by the mesh wires had faster growth rate in the upward direction than droplets on wires. This is mainly because of the confining role of the wires and higher heat transfer rate due to larger solid-liquid contact area. Also, these droplets always jumped at the size of pores (∼35 μm) when they coalesced with other droplets on wires. Moreover, droplets in pores were distorted by mesh wires, resulting in larger surface area. Theoretical predictions show, for a specific droplet radius, coalescence jumping of distorted droplets on the mesh-covered surface releases more excess surface free energy, and has larger jumping velocity than that of spherical droplets on the plate surface without mesh. This better performance was further validated by constant exposure of those two surfaces to electron beam during which work of adhesion was gradually increased. As expected, droplets on the mesh-covered surface coalesced and jumped while coalescing droplets on the plate surface could not as the exposure time increased. Our results offer new insights for designing hierarchical structured superhydrophobic surfaces to further enhance the performance of condensation heat transfer processes.
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Mukherjee, Ranit, Austin S. Berrier, Joshua R. Vieitez, Kevin R. Murphy et Jonathan B. Boreyko. « EFFECTS OF SURFACE ORIENTATION ON JUMPING-DROPLET CONDENSATION ». Dans International Heat Transfer Conference 16. Connecticut : Begellhouse, 2018. http://dx.doi.org/10.1615/ihtc16.cod.023745.
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Su, Junwei, Hamed Esmaeilzadeh, Chefu Su, Majid Charmchi, Marina Ruths et Hongwei Sun. « Characterization of Jumping-Droplet Condensation on Nanostructured Surfaces With Quartz Crystal Microbalance ». Dans ASME 2017 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/imece2017-72315.
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The spontaneously jumping motion of condensed droplets by coalescence on superhydrophobic surfaces has been an active area of research due to its great potential for enhancing the condensation efficiency. Despite a considerable amount of microscopic observations, the interfacial wetting characterization during jumping-droplet condensation is still notably lacking. This work focuses on applying a novel acoustic sensor - quartz crystal microbalance (QCM), to characterize the interfacial wetting on nanostructured surfaces during jumping-droplet condensation. Copper oxide nanostructures were generated on the surface of QCM with a chemical etching method. Based on the geometry of the nanostructures, we modified a theoretical model to reveal the relationship between the frequency shift of the QCM and the wetting states of the surfaces. It was found that the QCM is extremely sensitive to the penetrated liquid in the structured surfaces. Then, the QCM with nanostructured surface was tested on a customed flow condensation setup. The dynamic interfacial wetting characteristics were quantified by the normalized frequency shift of the QCM. Combined with microscopic observation of the corresponding drop motion, we demonstrated that partial wetting (PW) droplets with an about 25% penetrated area underwent spontaneously jumping by coalescence. However, the PW droplets no longer jumped when the penetrated area exceeds 50% due to the stronger adhesion between liquid and the surface. It shows that the characterization of the penetrated liquid in micro/nanostructures, which is very challenging for microscopic observation, can be easily carried out by this acoustic technique.
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Ho, Jin Yao, Kazi Fazle Rabbi, Soumyadip Sett, Teck Neng Wong, Kai Choong Leong et Nenad Miljkovic. « Nanostructuring of Metallic Additively Manufactured Surfaces for Enhanced Jumping Droplet Condensation ». Dans ASME 2021 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2021. http://dx.doi.org/10.1115/imece2021-70949.
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Abstract Vapor condensation on metallic surfaces is a phase-change phenomenon that has widespread applications in many processes. Jumping-droplet-enhanced condensation is an effective mode of dropwise condensation due to its higher droplet removal rate, enabling more efficient heat transfer. However, maintaining stable jumping-droplet condensation, requires surface structures to be suitably designed to prevent droplet pinning and surface flooding. In recent years, using metal additive manufacturing (AM) processes to create heat exchanger surfaces has received significant attention due to its design freedom and versatility in fabricating highly complex functional parts. Here, we present a highly scalable method of fabricating superhydrophobic (SHP) AM surfaces from aluminum alloy, AlSi10Mg, and an experimental investigation of their thermal performance during steam condensation. The test samples were fabricated by Selective Laser Melting (SLM), an AM technique for producing metallic parts. Through detailed material characterizations, we found that it is possible to achieve superior superhydrophobicity on AM surfaces, with unique cellular-like nanoscale surface features, by simple chemical etching and functionalization processes. To understand the droplet dynamics and obtain insights on the effects of AM nanostructures on the condensate droplet morphology and jumping, we carried out condensation experiments with an environmental scanning electron microscope (ESEM) at low supersaturation of ∼1.06. The important relations between the fabricated AM nanostructure morphology and droplet dynamics are established by characterizing the droplet departure diameter and droplet jumping frequency. To determine the anti-flooding and condensation heat transfer performances of the AM SHP surfaces, pure vapor condensation experiments under higher supersaturation conditions were carried out in a well-controlled environmental chamber. Together with the aid of high-resolution imaging and heat transfer measurements, we demonstrate significant reduction in droplet pinning sites due to the implementation of the AM cellular-like structure. This reduces the thermal barrier between the condensing surface and surrounding vapor, and hence, increases the condensation heat transfer. Our results show that excellent droplet jumping performance and better droplet mobility can be achieved by using AM SHP surfaces as compared to conventional SHP aluminum extruded tubing. These results underscore the potential of advancing AM structured surfaces for jumping-droplet-enhanced condensation under high heat flux conditions.
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Zhang, Tian-Yu, Lin-Wei Mou, Jia-Qi Li et Li-Wu Fan. « Enhanced Steam Condensation Heat Transfer on a Honeycomb-Like Microporous Superhydrophobic Surface Under Different Condensing Pressures ». Dans ASME 2020 Heat Transfer Summer Conference collocated with the ASME 2020 Fluids Engineering Division Summer Meeting and the ASME 2020 18th International Conference on Nanochannels, Microchannels, and Minichannels. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/ht2020-8938.
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Abstract Steam condensation heat transfer was studied over a honeycomb-like microporous superhydrophobic surface under various pressures, in order to elucidate the effects of pressure on the jumping-droplet condensation behaviors. The condensing pressure was varied from 4 kPa to 13 kPa, based on the typical operating conditions of condensers in power plants. Stable coalescence-induced droplet jumping was realized on the honeycomb-like superhydrophobic surface over this range of pressure, leading to a great enhancement on the condensation heat transfer as compared to that on the common hydrophobic surface, especially at small degrees of subcooling (e.g., < 10 K). The frequency and number of jumping droplets were observed to decrease at lower pressures because of the less amount of condensate produced, and at higher degrees of subcooling due to the occurrence of surface flooding. The increasing condensing pressure was found to lead to a later onset of surface flooding. The results indicated that the honeycomb-like superhydrophobic surface has a great potential for industrial condensation equipment operating at multiple pressures owing to its superior performance and facile fabrication.
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Orejon, Daniel, Yota Maeda, Fengyong Lv, Peng Zhang et Yasuyuki Takata. « Effect of Microstructures on Superhydrophobic and Slippery Lubricant-Infused Porous Surfaces During Condensation Phase-Change ». Dans ASME 2018 16th International Conference on Nanochannels, Microchannels, and Minichannels. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/icnmm2018-7640.
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Superhydrophobic surfaces (SHSs) and slippery lubricant-infused porous surfaces (SLIPSs) are receiving increasing attention for their excellent anti-icing, anti-fogging, self-cleaning and condensation heat transfer properties. The ability of such surfaces to passively shed and repel water is mainly due to the low-adhesion between the liquid and the solid surface, i.e., low contact angle hysteresis, when compared to hydrophilic or to hydrophobic surfaces. In this work we investigated the effect of surface structure on the condensation performance on SHSs and SLIPSs. Three different SHSs with structures varying from the micro- to the nano-scale were fabricated following easy and scalable etching and oxidation growth procedures. The condensation performance on such surfaces was evaluated by optical microscopy in a temperature and humidity controlled environmental chamber. On SHSs important differences on the size and on the number of the coalescing droplets required for the jump to ensue were found when varying the surface structure underneath the condensing droplets. A surface energy analysis is proposed to account for the suppression of the droplet-jumping performance in the presence of microstructures. On other hand, by impregnating the same SHSs with a low surface tension oil, i.e., SLIPSs, the adhesion between the condensate and the SLIPSs can be further reduced. On SLIPSs slight differences on the droplet density over time and shedding performance upon the inclusion of microstructures were observed. Droplets were found to shed faster and with smaller diameters on SLIPSs in the presence of microstructures when compared to solely nanostructured SLIPSs. We conclude that on SHSs the droplet-jumping performance of micrometer droplets is deteriorated in the presence of microstructures with the consequent decrease in the heat transfer performance, whereas on SLIPSs the droplet self-removal is actually improved in the presence of microstructures.
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Zhu, Y., C. Y. Tso, T. C. Ho et Christopher Y. H. Chao. « Study of Coalescence-Induced Jumping Droplets on Biphilic Nanostructured Surfaces for Thermal Diodes in Thermal Energy Storage Systems ». Dans ASME 2020 14th International Conference on Energy Sustainability. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/es2020-1703.
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Abstract Thermal energy can be better harvested and stored by integrating thermal diodes with thermal energy storage systems. Among different types of thermal diodes, jumping-droplet thermal diodes exploiting superhydrophilic and superhydrophobic surfaces yield greater thermal rectification performance (i.e. diodicity) due to high latent heat. However, the condensation heat transfer and coalescing-jumping droplets are restricted by the ability of water to nucleate on the superhydrophobic surface, leading to a limited maximum jumping height, finally resulting in degradation of diodicity of the thermal diode. To solve this problem, we propose coating hydrophilic bumps on the superhydrophobic surface which can provide preferable nucleation sites, forming a new type of nanostructured surface, called biphilic surface. This work aims to investigate coalescence-induced jumping droplets on biphilic surfaces to enhance diodicity of phase change thermal diodes. Our experimental results show that the jumping height and jumping volumetric flux of the coalescence-induced jumping droplets on a biphilic surface are enhanced by 42% and 254% compared to those on a superhydrophobic surface, respectively. Based on the jumping droplet results, a mathematical model for diodicity is built. 244% improvement can be achieved in the thermal diode with an optimized biphilic surface as compared to that with a superhydrophobic surface, which provides an effective strategy to improve the diodicity of a phase change thermal diode and an alternative approach to enhance the energy harvesting and storage capability in thermal energy storage systems.