Identification and prediction of injection bubble shape in MLPS colloidal suspension

Abstract

Reliable identification and prediction of a bubble shape are important to the research of bubble dynamics. The transparent MLPS colloidal suspensions, representing the viscoelastic behavior, were employed in this paper and the bubble morphology was investigated by the gas injection method. Several influencing factors, such as the concentration, the sample height, the pinhole diameter, and the gas flow rate, were analyzed. The observed data show that the bubble was initially controlled by elasticity and then by viscoelasticity. The corresponding bubble shapes revealed ‘inverted carrot’ and ‘inverted teardrop’ respectively. The bubble shape parameters including the aspect ratio, the tail proportion, the equivalent diameter ratio, and the top curvature ratio were considered in the proposed identification method. Furthermore, a prediction equation was proposed to identify a detached bubble shape based on several influence parameters including the concentration, the sample height, the pinhole diameter, and the gas flow rate. The calculated results were in good agreement with the test results. Therefore, combined with the bubble shape criterion, a bubble shape at the detachment could be accurately identified with the provision of some pre-known parameters such as the material properties and the test conditions, without the information in the bubble growth process such as the growth rate, the observation time, etc.