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Experimental study of the fundamental phenomena involved in pool boiling at low pressure

Abstract : Boiling is an efficient heat transfer mode used in numerous thermal or energy systems. In some systems boiling takes place at low pressure. The static head of the liquid column over the wall where bubbles nucleate is then not negligible against the saturation pressure at the free surface level. The pressure and the induced subcooling degree therefore cannot be considered as homogeneous around growing bubbles, resulting in non-homogeneous thermophysical properties in the fluid. The relative influence of the forces acting on a growing bubble differs from higher pressure conditions, yielding specific bubble dynamics features. Heat transfer is consequently also affected. The effect of the pressure on pool boiling was experimentally investigated during the isolated bubbles regime taking place from a single activated nucleation site. Experiments were first conducted with water for a wide range of subatmospheric pressures. Four distinct bubble dynamics behaviors were identified through high-speed camera visualizations. An adapted image processing of the recordings enabled the measurement of several bubble dynamics characteristics. In order to generalize the concept of pool boiling at "low pressure" and to get a better understanding of the related fundamental phenomena, new experiments were performed with a second fluid, cyclohexane, chosen from original thermodynamic similarity with water boiling at pressures lower than atmospheric. The comparison of fluids’ behaviors made possible the identification of parameters governing the specific phenomena occurring during boiling at low pressure. Besides, the experimental facility was improved to provide new functionalities. The high-speed measurement of the heat flux transferred under the growing bubble, its synchronization with the high-speed videos images and the study of boiling on enhanced surfaces are in particular made possible. Results are encouraging for a better understanding of the specific behaviors of low pressure boiling and for its future implementation in practical applications.
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Submitted on : Friday, November 30, 2018 - 3:59:09 PM
Last modification on : Wednesday, July 8, 2020 - 12:43:50 PM
Long-term archiving on: : Friday, March 1, 2019 - 3:08:49 PM

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  • HAL Id : tel-01940955, version 1

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Sandra Michaïe. Experimental study of the fundamental phenomena involved in pool boiling at low pressure. Thermics [physics.class-ph]. Université de Lyon, 2018. English. ⟨NNT : 2018LYSEI040⟩. ⟨tel-01940955⟩

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