Experimental Investigation of a Rising Bubble in Aqueous Gelatin Solution under Gelation Process

We have observed a progression of the shape and velocity of a bubble rising in aqueous gelatin solution under gelation process. Two experimental systems were designed to produce two different bubble sizes that were allowed to rise in test sections filled with aqueous gelatin solution. The physical gelling was allowed to proceed slowly in a temperature-controlled cooling system. The viscoelasticity of the aqueous gelatin solution was measured using a stress controlled rheometer under the same temperature history with the bubble rising observations. It was found that the change in bubble shape corresponds to the elastic behavior of solution due to the progress in gelation process. The gel point of the gelatin solution was conveniently determined by detecting the change in the shape of the rising bubble from a sphere shape to prolate and cuspidal shape. It was further observed that a small bubble is preferable during measurement because of its less impact on the gelation structure around the bubble. Subsequently, the measuring system designed in the present study is simple and convenient to install for offline process monitoring.