Periodicity and bifurcations in capillary tube boiling with a concentric heating wire

Nucleate boiling from a vertical glass capillary in a pool of water is investigated here. Electrical heating is provided with a wire passing concentrically through the center of the capillary, and a fast-response thermocouple at the lip of the capillary records the instants of bubble departure. Different lengths and diameters of capillaries are used in the experiments. The average frequency of bubbling is seen to increase with applied heat flux, the relation being linear in the initial stages. With the heat flux used as a bifurcation parameter, one-dimensional return maps of the time interval between successive bubble emission events are used to study the transitions from the periodic state. The first bifurcation from the periodic to a two-period state is observed to be due to lateral instability of the liquid film adhering to the capillary wall. Further bifurcations to period two and then to period three bubbling are also observed. Simplified analysis of the different phases of the boiling process yields solutions which show close agreement with the experimental data.