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Droplet temperature measurement using a fiber Bragg grating

[Display omitted] •FBG sensor as non-invasive method for droplet temperature measurement.•Heat transfer at the liquid-gas interface is explained by a coefficient α.•Measurement based on vapor layer and enclosure temperatures, and α coefficient.•α is fiber-to-droplet distance-dependent and independen...

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Bibliographic Details
Published in:Applied thermal engineering 2024-10, Vol.254, p.123905, Article 123905
Main Authors: Stancalie, Andrei, Andrei, Ionut -Relu, Boni, Mihai, Staicu, Angela, Pascu, Mihail Lucian
Format: Article
Language:English
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Summary:[Display omitted] •FBG sensor as non-invasive method for droplet temperature measurement.•Heat transfer at the liquid-gas interface is explained by a coefficient α.•Measurement based on vapor layer and enclosure temperatures, and α coefficient.•α is fiber-to-droplet distance-dependent and independent of humidity and volume.•Temperature variation measurement with an accuracy of ±0.15 °C. The need to measure droplets temperature with high precision in moderate or extreme environments has driven the development of advanced methods. Here, we report, for the first time, the measurement of droplet temperature using optical fiber-based temperature sensors. Specifically, a fiber Bragg grating sensor was used as a non-invasive technique to determine the temperature behavior of single micro-volumetric pendant droplets. The fiber sensor method, which provides indirect measurements, was validated by experimental and simulation data from the literature, showing good agreement. The temperature measurements rely on monitoring the vapor layer temperature near the droplet at sub-millimeter fiber-to-droplet distances and on determining a coefficient that characterizes the temperature difference between the droplet and the surrounding vapor layer at the liquid–gas interface. We calibrated the method by conducting measurements under various relative humidities and fiber-droplet contact conditions. We found that the coefficient remains constant for a specific distance regardless of the relative humidity or the droplet volume. Furthermore, we observed the minor influences that the environmental relative humidity and droplet content has on the behavior of the recorded temperatures during the short period after droplet generation.
ISSN:1359-4311
DOI:10.1016/j.applthermaleng.2024.123905