Bubble generation in liquid rope coiling
We present an experimental study of liquid rope coiling in order to explore different possibilities of air bubble generation in a viscous fluid. A column of viscous fluid falling on a smooth solid surface exhibits different behaviours, e.g., axisymmetric stagnation flow, coiling, rotatory folding, supercoiling, etc. These states provide ample opportunity for air to get trapped inside the body of a fluid. We investigate bubble generation mechanisms by studying the instability of a falling fluid rope and the characteristics of the observed bubbles. Our experiments show that a viscous rope undergoing supercoiling on the impact surface can, at times, produce a four-branched spiral pattern of bubbles. Finally, we provide a phase diagram illustrating the bubble properties relevant to the flow rate and fall height of the viscous jet. Our study provides a very simple method for the generation of mono/bi-dispersed bubbles in viscous fluids at high rates with an ability to tune the bubble size.