On the onset of quench during spray cooling: The significance of oxide layers
| Autor: | Yasuyuki Takata, Masamichi Kohno, Shinya Inoue, Sumitomo Hidaka, Hiroyuki Fukuda, Takafumi Hamanosono, Satoshi Ueoka, Kengo Tsukamoto, Yutaku Kita |
|---|---|
| Rok vydání: | 2020 |
| Předmět: |
Quenching
Materials science Spray cooling 020209 energy Oxide Energy Engineering and Power Technology 02 engineering and technology Thermal conduction Industrial and Manufacturing Engineering Physics::Fluid Dynamics chemistry.chemical_compound 020401 chemical engineering chemistry 0202 electrical engineering electronic engineering information engineering Deposition (phase transition) Wetting 0204 chemical engineering Composite material Layer (electronics) Thermal effusivity |
| Zdroj: | Applied Thermal Engineering. 179:115682 |
| ISSN: | 1359-4311 |
| DOI: | 10.1016/j.applthermaleng.2020.115682 |
| Popis: | The effect of thermally-insulating layer, particularly oxide layer as found in metallurgical applications, on the water spray-cooling process was discussed. Such layers have been found to increase the quenching temperature at which the sprayed liquid begins to contact the hot surface, greatly increasing the cooling rate. The conventional, thermal-resistance based model can predict the shift of the quenching point qualitatively, albeit significant deviations remain due to the lack of fundamental understanding of the onset of liquid-solid contact. In the present paper, we conducted two sets of experiments in an attempt to shed light on the quench mechanism and the effect of oxide layer. First, we compared temperature histories during spray cooling of a stainless-steel plate with various oxide layers. The quench temperatures varied depending both on the composition and the thickness of the oxide layer. Additionally, quench was observed at temperatures as high as 350 °C, exceeding the thermodynamic wetting limit. Then, we moved on to single droplet impingement experiments to investigate the change of droplet behavior with respect to the surface temperature in detail. High-speed imaging allowed us to identify the transition of droplet impact behavior i.e. deposition and bouncing, which also occurred at different wall temperatures depending on the composition of oxide layer. Subsequently, we calculated the contact surface temperature assuming the transient heat conduction for a contact between two semi-finite bodies. As a consequence, the onset of droplet behavior transition was always found at the contact surface temperature of ca. 250 °C regardless of the composition and thickness of the oxide layer. The difference between the contact surface temperature and the wall temperature increased as the thermal effusivity of the oxide layer decreased, which was a direct cause of the inconsistent “apparent” quenching temperature. |
| Databáze: | OpenAIRE |
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