Sinha, Kumar Nishant Ranjan ; Schweikert, Kai ; Sielaff, Axel ; Stephan, Peter (2023)
On the nature of microlayer formation with Ethanol-water mixtures.
In: SSRN eLibrary
doi: 10.2139/ssrn.4614732
Artikel, Bibliographie
Kurzbeschreibung (Abstract)
The formation of liquid microlayers during the dewetting of a hot surface has significant effects on heat transfer in boiling and evaporation processes. Understanding the criteria for the formation of such microlayers is crucial for explaining the heat transfer characteristics, in particular the heat transfer coefficient (HTC). Research in this area has been almost exclusively concerned with the study of pure liquids, but not with the specific behavior of binary mixtures used in numerous boiling processes. As an example, we investigate the formation of microlayers in ethanol water mixtures, whose global boiling behavior has been widely studied. We conducted dewetting experiments during evaporation with pure ethanol as the reference case and with ethanol/water mixtures with ethanol fractions of 90% w/w and 70% w/w. Using high resolution infrared thermography, two evaporation regimes were identified depending on the process conditions and fluid composition: contact line evaporation (CLE) and microlayer evaporation (MLE). The transition from CLE to MLE in pure ethanol was observed at a critical dewetting velocity that depended on wall superheat. Interestingly, for an ethanol water mixture containing 90 wt% ethanol, MLE was observed at all wall superheats and dewetting velocities tested. This can be explained by two specific mixture effects: First, Marangoni convection leads to a flow toward the contact line, and second, the locally increased water concentration near the contact line reduces the evaporating mass flux, which favors film formation and thus MLE. However, with the further increase in water concentration, as with the 70% ethanol water mixture, MLE was observed only transiently for a few milliseconds, followed by a rapid shift to CLE at all wall superheats and dewetting velocities. These results provide valuable insight into the formation of microlayers in binary mixtures, and thus into the heat transfer characteristics observed in the nucleate boiling studies with binary mixtures.
| Typ des Eintrags: | Artikel |
|---|---|
| Erschienen: | 2023 |
| Autor(en): | Sinha, Kumar Nishant Ranjan ; Schweikert, Kai ; Sielaff, Axel ; Stephan, Peter |
| Art des Eintrags: | Bibliographie |
| Titel: | On the nature of microlayer formation with Ethanol-water mixtures |
| Sprache: | Englisch |
| Publikationsjahr: | 27 Oktober 2023 |
| Verlag: | Elsevier |
| Titel der Zeitschrift, Zeitung oder Schriftenreihe: | SSRN eLibrary |
| Kollation: | 18 Seiten |
| DOI: | 10.2139/ssrn.4614732 |
| Kurzbeschreibung (Abstract): | The formation of liquid microlayers during the dewetting of a hot surface has significant effects on heat transfer in boiling and evaporation processes. Understanding the criteria for the formation of such microlayers is crucial for explaining the heat transfer characteristics, in particular the heat transfer coefficient (HTC). Research in this area has been almost exclusively concerned with the study of pure liquids, but not with the specific behavior of binary mixtures used in numerous boiling processes. As an example, we investigate the formation of microlayers in ethanol water mixtures, whose global boiling behavior has been widely studied. We conducted dewetting experiments during evaporation with pure ethanol as the reference case and with ethanol/water mixtures with ethanol fractions of 90% w/w and 70% w/w. Using high resolution infrared thermography, two evaporation regimes were identified depending on the process conditions and fluid composition: contact line evaporation (CLE) and microlayer evaporation (MLE). The transition from CLE to MLE in pure ethanol was observed at a critical dewetting velocity that depended on wall superheat. Interestingly, for an ethanol water mixture containing 90 wt% ethanol, MLE was observed at all wall superheats and dewetting velocities tested. This can be explained by two specific mixture effects: First, Marangoni convection leads to a flow toward the contact line, and second, the locally increased water concentration near the contact line reduces the evaporating mass flux, which favors film formation and thus MLE. However, with the further increase in water concentration, as with the 70% ethanol water mixture, MLE was observed only transiently for a few milliseconds, followed by a rapid shift to CLE at all wall superheats and dewetting velocities. These results provide valuable insight into the formation of microlayers in binary mixtures, and thus into the heat transfer characteristics observed in the nucleate boiling studies with binary mixtures. |
| Zusätzliche Informationen: | Preprint |
| Fachbereich(e)/-gebiet(e): | 16 Fachbereich Maschinenbau 16 Fachbereich Maschinenbau > Fachgebiet für Technische Thermodynamik (TTD) DFG-Sonderforschungsbereiche (inkl. Transregio) DFG-Sonderforschungsbereiche (inkl. Transregio) > Sonderforschungsbereiche DFG-Sonderforschungsbereiche (inkl. Transregio) > Sonderforschungsbereiche > SFB 1194: Wechselseitige Beeinflussung von Transport- und Benetzungsvorgängen DFG-Sonderforschungsbereiche (inkl. Transregio) > Sonderforschungsbereiche > SFB 1194: Wechselseitige Beeinflussung von Transport- und Benetzungsvorgängen > Projektbereich A: Generische Experimente DFG-Sonderforschungsbereiche (inkl. Transregio) > Sonderforschungsbereiche > SFB 1194: Wechselseitige Beeinflussung von Transport- und Benetzungsvorgängen > Projektbereich A: Generische Experimente > A01: Erzwungene Be- und Entnetzung komplexer Oberflächen - Leitkonfiguaration Eintauchkörper |
| Hinterlegungsdatum: | 30 Nov 2023 10:45 |
| Letzte Änderung: | 15 Apr 2024 08:12 |
| PPN: | |
| Export: | |
| Suche nach Titel in: | TUfind oder in Google |
 |
Frage zum Eintrag |
Optionen (nur für Redakteure)
 |
Redaktionelle Details anzeigen |
Drucken
Impressum