The Significance of Grouping and Missed Bubbles on Interfacial Area Concentration and Void Fraction

摘要

The two-fluid model is used in nuclear reactor safety codes. Two of the important constitutive relations will be discussed in this study, the interfacial area concentration and void fraction. The Interfacial area concentration is directly affected by the number of bubbles and how these bubbles are categorized into groups. In this study, a new algorithm was implemented to account for trailing bubbles, bubbles with short response times, and the categorization of bubbles based upon diameter for all group 1 bubbles. The optical and conductivity probes were used to determine the void fraction and interfacial area concentration in a bubble column. The new algorithm was benchmarked against the previous algorithm. The data acquisition systems for both probes were set at 22 kHz. This is sufficient for the optical probe. However, due to the response time of the conductivity probe, the previous algorithm does not pick up all the bubbles at the 22 kHz sampling rate. There is an increase of up to 28% for the total interfacial area concentration when the trailing bubbles are collected, and bubble diameter is used instead of chord length for the optical probe. The conductivity probe for the 22k Hz sample rate in the new version, collects more bubbles than the previous version. The total void fraction for the conductivity probe is within 15% of the optical probe for the locations tested. The total interfacial area concentration is up to 80% higher than the optical probe. Additional testing should be completed at higher sampling rates to determine the overall accuracy when comparing the conductivity probe to the optical probe for the new algorithm. The higher sampling rate should increase the accuracy for determining the front and rear interface location for all bubbles in the system.