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A fundamental study of hierarchical metal surface texturing for enhanced dropwise condensation under flow conditions

Titel Englisch A fundamental study of hierarchical metal surface texturing for enhanced dropwise condensation under flow conditions
Gesuchsteller/in Rudolf von Rohr Philipp
Nummer 162847
Förderungsinstrument Projektförderung (Abt. I-III)
Forschungseinrichtung Institut für Verfahrenstechnik ETH Zürich
Hochschule ETH Zürich - ETHZ
Hauptdisziplin Maschineningenieurwesen
Beginn/Ende 01.01.2016 - 31.07.2018
Bewilligter Betrag 213'666.00
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Keywords (4)

dropwise condensation; heat transfer augmentation; surface structuring; hydrophobic

Lay Summary (Deutsch)

Lead
??Eine grundlegende Studie über hierarchische Metalloberflächenstrukturierung für eine verbesserte Tropfenkondensation unter StrömungsbedingungenDie Kondensation ist ein Prozess, welcher sehr oft in der Natur und Technologie auftritt, mit einer Reihe von wichtigen Anwendungen insbesondere bei der Stromerzeugung. Wasserdampf kondensiert auf einer Metalloberfläche in der Regel durch Bildung eines kontinuierlichen Kondensatfilms aufgrund der inhärenten Hydrophilie von vielen solcher Oberflächen. Diese Form der Kondensation wird als Film-Kondensation (FWC) bezeichnet. Wenn jedoch die Oberfläche hydrophob ist, kann das Kondensat die Oberfläche nicht benetzen und bildet Tropfen, die in regelmäßigen Abständen zu Tropfen heranwachsen. Diese Form der Kondensation wird als Tropfenkondensation (DWC) bezeichnet und ergibt wesentlich bessere Wärmeübertragungswerte. Im Vergleich zur Film-Kondensation sind diese Werte bis zu einer Größenordnung höher.
Lay summary
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Inhalt und Ziel des Forschungsprojekts
Wir entwerfen Oberflächenstrukturen zur Demonstration des optimalen Verhaltens der Kondensation unter Strömungsbedingungen. Die Substrate bestehen aus Materialien von ausgezeichneter chemischer und mechanischer Robustheit, z.B. Edelstahl. Kommerziell verfügbare Mikrofabrikationstechniken werden eingesetzt, um gezielt die Mikrorauhigkeit zu erzeugen. Diese rational gestalteten Oberflächen werden in Bezug auf die Wärmeübertragung, Tropfenablösung und Langlebigkeit bei Dampfdurchflussbedingungen experimentell untersucht und charakterisiert. 
 
Direktlink auf Lay Summary Letzte Aktualisierung: 25.10.2015

Verantw. Gesuchsteller/in und weitere Gesuchstellende

Mitarbeitende

Publikationen

Publikation
Rationally 3D-Textured Copper Surfaces for Laplace Pressure Imbalance-Induced Enhancement in Dropwise Condensation
Sharma Chander Shekhar, Stamatopoulos Christos, Suter Reto, von Rohr Philipp Rudolf, Poulikakos Dimos (2018), Rationally 3D-Textured Copper Surfaces for Laplace Pressure Imbalance-Induced Enhancement in Dropwise Condensation, in ACS Applied Materials & Interfaces, 10(34), 29127-29135.

Zusammenarbeit

Gruppe / Person Land
Formen der Zusammenarbeit
LTNT , Prof.D.Poulikakos Schweiz (Europa)
- vertiefter/weiterführender Austausch von Ansätzen, Methoden oder Resultaten
- Publikation
- Forschungsinfrastrukturen
- Austausch von Mitarbeitern

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Aktiver Beitrag

Titel Art des Beitrags Titel des Artikels oder Beitrages Datum Ort Beteiligte Personen
SCCER EIP Networking Meeting, 2017 Einzelvortrag Dropwise Condensation for improved Heat Transfer in Industrial Applications 04.09.2017 Luzern, Schweiz Poulikakos Dimos; Stamatopoulos Christos; Rudolf von Rohr Philipp; Sharma Chander Shekhar;
SCCER EIP Networking Meeting, 2016 Einzelvortrag Surface Engineering for Heat Transfer Enhancement of Convective Dropwise Condensation 16.09.2016 Zurich, Schweiz Sharma Chander Shekhar; Stamatopoulos Christos; Poulikakos Dimos; Rudolf von Rohr Philipp;


Abstract

Improving the efficiency of condensation heat transfer has been an active area of research in the last few decades, due to its widespread importance to applications such as power generation, water desalination, environmental control and thermal management. A significant body of research effort is being devoted to the design of novel metal surfaces to achieve and maintain dropwise condensation (DWC) due to its much higher heat transfer efficiency as compared to filmwise condensation (FWC). However, such surfaces are usually tested in relatively mild laboratory conditions involving low saturation pressures and temperatures and negligible vapor flow velocity. Sustenance of the DWC mode for long operational times, materials that are application relevant and under severe vapor flow conditions (flow condensation), despite its importance, has remained elusive so far. In this research, we propose a rational approach towards the design, fabrication and characterization of DWC surfaces with vapor flow over these surfaces aiming at overcoming mentioned thresholds in heat transfer and durability. Based on the extensive experience of the co-applicant labs (LTR and LTNT) on interfacial phenomena across a range of length scales, a novel pathway to design and fabricate surface textures for enhanced DWC heat transfer will be pursued. This involves the use of Direct Metal Laser Sintering (DMLS), a recent technique of additive manufacturing (3D printing) of complex metal geometries through the layer by layer localized melting and subsequent welding of particles in a metal powder. The nature of this process opens up opportunities for its exploitation towards controlled fabrication of well-defined surface micro-features outside cleanroom environments. Such micro-features will allow fundamental considerations on the surface wettability characteristics requisite for enhanced DWC heat transfer, which are not the same as for traditional superhydrophobic surfaces. We propose to use DMLS to realize enhanced DWC through a two-prong strategy. First, create a novel and rationally designed surface texture consisting of superhydrophobic diverging microcavities to induce capillarity driven condensate droplet self-ejection from its formation locations in the texture. Second, create a closed cell honeycomb-like microstructure on the surface and impregnate it with a lubricant to achieve a slippery surface for efficient condensate droplet shedding. We plan to characterize these surfaces under the effect of vapor flow across the surface. Most of the currently reported DWC measurements on designed surface textures in the literature are performed at convenient “pool” conditions, without any flow of vapor - as very common in applications. Vapor flow induces shear on condensate droplets and thus can aid DWC by reducing the droplet departure diameter. However, high temperature vapor shear also causes mechanical degradation of the surface. In our research, the surface characterization will be performed not only with respect to condensation heat transfer performance, but also with respect to surface durability with regards to sustainability of the DWC mode for long operational times. The condensation heat transfer will be investigated in an experimental setup that mimics demanding operating conditions of realistic condensers. This will involve detailed heat transfer measurements and observations of the condensate droplet dynamics for in depth analysis of condensate nucleation, droplet growth and shedding. The durability of the DWC mode on these surfaces will be investigated through accelerated endurance tests involving another experimental setup that allows flow condensation of steam at above-atmospheric saturation pressures and at various levels of vapor velocity. With the above-described new paradigms for surface fabrication and characterization, this work will be a significant improvement over the state of the art in the field of DWC heat transfer.
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