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Boiling regimes of a single droplet impinging on a superheated surface: effect of the surrounding medium

Guggilla, Ganesh ; Sielaff, Axel ; Stephan, Peter (2024)
Boiling regimes of a single droplet impinging on a superheated surface: effect of the surrounding medium.
In: International Journal of Heat and Mass Transfer, 220
doi: 10.1016/j.ijheatmasstransfer.2023.124982
Article, Bibliographie

Abstract

Impinging droplets on a hot surface is a significant phenomenon in many industrial applications, such as spray cooling. Previous studies reported various morphological behaviours affecting the droplet's wetting, heat transfer, and evaporation characteristics. However, there is an ambiguity in understanding the influence of the surrounding medium on the resulting boiling regimes. The present work aims to study this aspect through an experimental investigation using high-speed photography and infrared thermography. During the experiments, the degassed FC-72 liquid droplets have impinged onto a heated chromium-plated calcium fluoride (CaF2) surface with a constant impact velocity. Three ambient conditions, such as saturated vapour (heated vapour), air at liquid saturation temperature (heated air), and air at room temperature (ambient air), are used. The surface temperature is varied in each ambience until the complete droplet dewetting, i.e., the Leidenfrost phenomenon has appeared. In this study, the stages of boiling are perceived as film evaporation, excessive and nominal bubbly boiling, transition, and Leidenfrost. With different surrounding media, the onset of a regime and its boiling morphology are distinct. During the film evaporation regime, the droplet heat transfer is high for the impact in ambient air, and the contact line evaporation is dominant in the vapour medium. In contrast, heat transfer is enhanced for the droplet impingement in a vapour medium during the bubbly boiling. It is attributed to increased nucleation sites and excessive bubbling compared to air media. Correlations from the literature are also revisited to understand the onset of bubbly boiling and the droplet breakup at the Leidenfrost point. An overall comparison of droplet heat transfer during the boiling regimes in surrounding media is discussed in this paper.

Item Type: Article
Erschienen: 2024
Creators: Guggilla, Ganesh ; Sielaff, Axel ; Stephan, Peter
Type of entry: Bibliographie
Title: Boiling regimes of a single droplet impinging on a superheated surface: effect of the surrounding medium
Language: English
Date: 2024
Place of Publication: Amsterdam
Publisher: Elsevier
Journal or Publication Title: International Journal of Heat and Mass Transfer
Volume of the journal: 220
DOI: 10.1016/j.ijheatmasstransfer.2023.124982
Abstract:

Impinging droplets on a hot surface is a significant phenomenon in many industrial applications, such as spray cooling. Previous studies reported various morphological behaviours affecting the droplet's wetting, heat transfer, and evaporation characteristics. However, there is an ambiguity in understanding the influence of the surrounding medium on the resulting boiling regimes. The present work aims to study this aspect through an experimental investigation using high-speed photography and infrared thermography. During the experiments, the degassed FC-72 liquid droplets have impinged onto a heated chromium-plated calcium fluoride (CaF2) surface with a constant impact velocity. Three ambient conditions, such as saturated vapour (heated vapour), air at liquid saturation temperature (heated air), and air at room temperature (ambient air), are used. The surface temperature is varied in each ambience until the complete droplet dewetting, i.e., the Leidenfrost phenomenon has appeared. In this study, the stages of boiling are perceived as film evaporation, excessive and nominal bubbly boiling, transition, and Leidenfrost. With different surrounding media, the onset of a regime and its boiling morphology are distinct. During the film evaporation regime, the droplet heat transfer is high for the impact in ambient air, and the contact line evaporation is dominant in the vapour medium. In contrast, heat transfer is enhanced for the droplet impingement in a vapour medium during the bubbly boiling. It is attributed to increased nucleation sites and excessive bubbling compared to air media. Correlations from the literature are also revisited to understand the onset of bubbly boiling and the droplet breakup at the Leidenfrost point. An overall comparison of droplet heat transfer during the boiling regimes in surrounding media is discussed in this paper.

Uncontrolled Keywords: Spreading dynamics, Heat transfer, Single droplet, Boiling, Surrounding media
Identification Number: Artikel-ID: 124982
Additional Information:

Preprint 2023 über SSRN veröffentlicht.

Divisions: 16 Department of Mechanical Engineering
16 Department of Mechanical Engineering > Institute for Technical Thermodynamics (TTD)
DFG-Collaborative Research Centres (incl. Transregio)
DFG-Collaborative Research Centres (incl. Transregio) > Transregios
DFG-Collaborative Research Centres (incl. Transregio) > Transregios > TRR 75 Droplet Dynamics Under Extreme Ambient Conditions
Date Deposited: 30 Nov 2023 07:04
Last Modified: 15 Apr 2024 08:12
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