Influence of nozzle submergence depth on the ice melting dynamics and heat transfer characteristics in controlled underwater bubbly flows

Air injection into the water beneath ice generates bubbles that entrain warm water to impact the ice, which is a simple and effective method of de-icing. The submergence depth of the nozzle used to release the bubbles affects the ice melting process. Experiments are carried out in the range of submergence depths from 7.5 to 18 cm to analyze the ice morphology, bubble behavior, and heat transfer characteristics. The results show that the increase of the submergence depth causes the bottom ice-water interface profile to become flat and wide from tall and narrow. The melting rate in the height direction increases by 15.4 % when the submergence depth increases from 7.5 to 18 cm. A larger submergence depth yields a larger radial range of ice-water interface depression, which results in a larger maximum bubble contact area with ice during melting. The heat transfer coefficient increases with the increase of the submergence depth due to the decreasing gas holdup and the increasing flow rate of entrained water. A correction method to predict the heat transfer coefficients at different submergence depths is proposed, and the calculated data match well with the experimental data, with a deviation of less than 5 %. The results of this study are expected to be helpful for a more in-depth understanding of the ice melting process under a bubbly flow and provide a reference for the practical engineering application of bubble ice melting technology.