A Visual Experiment of Single Bubble Growth Processes in a Vertical Rectangular Channel

Single bubble growth processes under subcooled boiling condition in a vertical rectangular channel with a gap of 2.8 mm have been visually studied. A high-speed camera was used to observe and record the bubble growth processes at a rate of 6000 frames per second. Four kinds of bubbles with different equivalent radius change trends near the ONB (Onset of Nucleate Boiling) point were observed. The bubble equivalent radius change trends were fitted by traditional empirical formula R(t) = k · tⁿ and found that the value of empirical parameter n was in the range of 0.11 to 0.53 which was smaller than that in literatures, and the value of empirical parameter k had a positive correlation with Ja number. The bubbles generated at the same nucleation point under different heating powers, inlet fluid temperatures and mass flow rates were compared and found that within the experimental range the changes of heating power and inlet fluid temperature had a significant effect on bubble growth rectangular channel which may be used in research nuclear reactor and engineering test reactor. Due to the shape and azimuth of the channel, the bubble behaviors in vertical rectangular channel may be different from those in conventional large-size circular channel or horizontal channel. The investigations reported in the literature generally involved multiple bubbles with complex interactions between the bubbles, and the bubble parameters were usually obtained by averaging the parameters of bubbles generated at different nucleation sites. However, even under the same working condition, bubbles generated by two adjacent nucleation sites may also have big differences. In this experiment, the steady single bubble growth processes in vertical rectangular channel with deionized water as the working fluid were visually investigated. Four kinds of bubbles with different bubble growth curves were observed and the equivalent bubble radius change trends at different heating powers, inlet fluid temperatures and mass flow rates were compared.