Padilla-Viruet, Angel L.

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    An experimental study of bubble parameters in subcooled flow boiling in vertical channel to validate different heat flux partitioning models
    (2019-05-10) Padilla-Viruet, Angel L.; Cancelos, Silvina; College of Engineering; Torres-Nieves, Sheilla; Gutierrez, Gustavo; Department of Mechanical Engineering; Castillo, Paul
    Pressurized water reactors (PWR) are safely operating below maximum heat flux conditions because actual heat flux partitioning models fail to predict it accurately. Improving the heat flux models will lead to more efficient performance of PWRs and in turn increase energy output. In this work, two-phase flow is visualized in a scaled prototypical fuel element of a typical PWR. The test section is composed of a vertical square polycarbonate tube with a concentric cartridge heater resulting in a hydraulic diameter of 13.7 mm. Water is the working fluid at atmospheric pressure. This investigation intends to measure experimentally the bubble parameters that are required for heat flux partitioning calculations. The bubble parameters: (i) bubble departure diameter, (ii) lift-off diameter, (iii) growth time, (iv) wait time, (v) active nucleation site density and (vi) bubble release frequency; are measured experimentally using a high-speed camera. A MATLAB algorithm was developed to analyze 2500 images captured for each of the 15 test conditions conducted. Preliminary results have shown that isolated bubble regime can be achieved at the proposed test section. The classic heat flux partitioning model (Griffith, Clark, and Rohsenow 1958; Judd and Hwang 1976) and new (Basu 2003; Baglietto and Christon 2013) model are tested for mass flux between 250 kg⁄s-m^2 to 500 kg⁄s-m^2 and heat flux from 200 kW⁄m^2 to 300 kW⁄m^2 for 15℃ of subcooling. The average values obtained with their corresponding standard deviation are: a departure diameter of 0.348±0.036 mm, a lift-off diameter of 0.587±0.302 mm, a growth time of 0.935±0.062 ms, a wait time of 2.22±0.040 ms, a bubble release frequency of 317.5±5.6 Hz and an active nucleation site density of 1.15×106±9.29×10^4 sites⁄m^2.The average predicting error of the classic heat flux partitioning model was 35% ± 41% and in the new model was 41% ± 37%. Basu’s models for growth time show good predictions with 36% of error. On the other hand, Basu’s model for wait time (632% of prediction error) and release frequency (72% of prediction error) did not capture the experimental data.