Analysis of the velocity and displacement of a condensing bubble in a liquid solution

The absorption of steam bubbles in a hot aqueous solution of Lithium Bromide is a key process that occurs in the absorber vessel of a heat transformer system. During the condensation process, their size and shape changes dynamically with time as they rise up through the column of liquid. An understanding of the factors that control the vertical upwards motion of the bubbles is necessary to enable proper design of such units. However, the exact vertical displacement of a bubble moving through a liquid is difficult to predict and becomes much more complex if the bubble is simultaneously collapsing. In this paper, the displacement of steam bubbles collapsing in a concentrated aqueous lithium bromide solution (LiBr-H2O) has been quantified experimentally. A simple kinetic model predicting the vertical displacement as a function of time was then developed from elementary force-balance considerations. A key feature of the system is the large variability in the motion of the bubbles arising from extreme fluctuations in their size and shape. Bubble dynamic morphology was modelled with stochastic techniques and the output from this was used in the kinetic model to predict dispersion in bubble displacement with time. While the uncertainty predicted by the stochastic model is shown to be less than that observed experimentally, it nonetheless highlights the importance of this random behaviour during the design of such an absorption column.