Pérez Pérez, Juan R.

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    Analysis of individual forces in force-balance model for bubble departure diameter prediction
    (2023-05-12) Pérez Pérez, Juan R.; Cancelos Mancini, Silvina; College of Engineering; Gutiérrez, Jorge G.; Rodriguez Abudo, Sylvia; Department of Mechanical Engineering; Baigés Valentín, Iván J.
    Understanding two-phase flow is key to the safety and efficiency analysis of Light Water Nuclear reactors (LWR). Because of inaccuracies, LWRs operate below the maximum point of output power to ensure safety. Computational Fluid Dynamics (CFD) methods use heat partitioning models for a better understanding of flow boiling with a special focus on the critical heat flux. In the heat partitioning models the bubble departure diameter is a term that highly influences the prediction of the heat flux. This work seeks an analysis of individual forces contained in a force-balance approach for bubble departure diameter prediction by using high speed photography. To analyze force expressions individually, two scenarios with different operating conditions are proposed. From the first scenario of a static bubble attached to a surface the contact pressure force F_cp and surface tension force F_s were validated to follow the physics of the problem. Then, the second scenario where a rapid growing bubble is analyzed allowed the computation of an experimental growth force based on the force-balance. A comparison was made between the experimental growth force and the growth force estimated from existing models. Comparing the Rayleigh-Plesset model growth force values with the experimental growth force gave a %difference of 833%. While the Added Mass model gave a %difference of 351%. From the comparison between the experimental growth force and the growth force estimated by the models a correction coefficient was proposed for the Rayleigh-Plesset model C=0.02 which made the average %difference 75% and an added mass coefficient was derived C_AM=0.09 for the Added Mass model which made possible an average %difference of 73%. By contributing to an improvement in the prediction of the bubble departure diameter LWRs can operate safely closer to their maximum operating point, thus allowing an increase in efficiency, lower operating cost or less fuel consumption.