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Influence of substrate material on flow in freezing water droplets—an experimental study
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.ORCID iD: 0000-0003-0684-6907
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.ORCID iD: 0000-0001-8235-9639
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.ORCID iD: 0000-0001-5310-9761
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
2021 (English)In: Water, E-ISSN 2073-4441, Vol. 13, no 12, article id 1628Article in journal (Refereed) Published
Abstract [en]

Freezing water droplets are a natural phenomenon that occurs regularly in the Arctic climate. It affects areas such as aircrafts, wind turbine blades and roads, where it can be a safety issue. To further scrutinize the freezing process, the main objective of this paper is to experimentally examine the influence of substrate material on the internal flow of a water droplet. The secondary goal is to reduce uncertainties in the freezing process by decreasing the randomness of the droplet size and form by introducing a groove in the substrate material. Copper, aluminium and steel was chosen due to their differences in thermal conductivities. Measurements were performed with Particle Image Velociometry (PIV) to be able to analyse the velocity field inside the droplet during the freezing process. During the investigation for the secondary goal, it could be seen that by introducing a groove in the substrate material, the contact radius could be controlled with a standard deviation of 0.85%. For the main objective, the velocity profile was investigated during different stages of the freezing process. Five points along the symmetry line of the droplet were compared and copper, which also has the highest thermal conductivity, showed the highest internal velocity. The difference between aluminium and steel was in their turn more difficult to distinguish, since the maximum velocity switched between the two materials along the symmetry line.

Place, publisher, year, edition, pages
MDPI, 2021. Vol. 13, no 12, article id 1628
Keywords [en]
Freezing, Internal flow, Marangoni flow, PIV, Water droplet
National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
URN: urn:nbn:se:ltu:diva-86286DOI: 10.3390/w13121628ISI: 000667373500001Scopus ID: 2-s2.0-85108428603OAI: oai:DiVA.org:ltu-86286DiVA, id: diva2:1578250
Note

Validerad;2021;Nivå 2;2021-07-06 (beamah)

Available from: 2021-07-06 Created: 2021-07-06 Last updated: 2023-09-04Bibliographically approved
In thesis
1. Influence of the Substrate on the Internal Flow in Freezing Water Droplets
Open this publication in new window or tab >>Influence of the Substrate on the Internal Flow in Freezing Water Droplets
2022 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

A water droplet that impacts on a cold surface will start to freeze and in time ice will accumulate. To exemplify, effects of ice accretion is important in areas such as power generation e.g. wind power and vehicles located in a cold climate e.g. aircraft, cars, and boats. The common denominator for these examples is that ice accumulation can lead to a loss of efficiency and in some cases danger.

Most studies have so far focused on investigating freezing water droplets visually in experiments or numerically in regards to how the freezing process behaves in terms of shape or freezing time for either a sessile or impacting droplet. It has been observed that the surface material and structures of the substrate is of importance. One part of the freezing process that has been less investigated is the internal flow and how it affects the freezing process.

In this thesis, the internal flow in a freezing water droplet has been investigated experimentally. The internal flow inside a droplet is calculated by using Particle Image Velocimetry. A metal plate with a groove filled with ice was used to generate an area for the nucleation to start and to be able to control the shape of the droplet. 

Previous work indicate that the substrate is of importance for the freezing process. The influence of the substrate material on the internal flow for similar shaped droplets is therefore investigated in Paper A, for a substrate temperature of -8°C. The results show that the substrate material, here in terms of metals such as aluminum, copper and steel, affect the magnitude of the internal velocity. In paper B it is investigated how the contact angle influence the internal flow. The vector field is examined at 9% of the total freezing time for water droplets at five different contact angles. A droplet with a higher contact angle will have a higher internal velocity in the center. A lower contact angle will barely show any movement in the center, however a higher velocity magnitude is observed close to the free surface compared to a droplet with a higher contact angle. Paper C studies the time until the directional change of the internal flow in a water droplet. Experiments at -8°C as in Paper B are used as well as experiments at -12°C for the five different contact angles. The time until the directional change is similar in time for both -8°C and -12°C while the total freezing time and also the time of the directional change varies with contact angles. A droplet with a lower contact angle will have a shorter time until the directional change occure while an increase in contact angle prolongs both freezing time and the time until the directional change.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2022
Series
Licentiate thesis / Luleå University of Technology, ISSN 1402-1757
Keywords
Internal Flow, Freezing, Water Droplets, Particle Image Velociometry
National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-90369 (URN)978-91-8048-085-7 (ISBN)978-91-8048-086-4 (ISBN)
Presentation
2022-06-17, E632, Luleå tekniska universitet, Luleå, 13:00 (English)
Opponent
Supervisors
Available from: 2022-04-22 Created: 2022-04-22 Last updated: 2022-05-27Bibliographically approved

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Fagerström, ErikLjung, Anna-LenaKarlsson, LinnLycksam, Henrik

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