Propagation of boiling fronts along horizontally arranged heated tubes

The behaviour of boiling fronts was studied experimentally, using pure liquids and their mixtures. The fronts are generated under isobaric conditions on the outer surface of a heated tube arranged horizontally in a liquid pool. The tube surface was covered with different metallic coatings. Depending on wall superheat, slow or fast propagating fronts were observed. Slow fronts, having velocities up to 1 ms −1 , were established at low superheats. Their movement depends on liquid superheat, pressure and properties of the heating surface. Fast propagating fronts form above a particular superheat, independent of the characteristic of the heating surface. Their propagation velocity ranges up to 15ms −1 . At the same superheat, boiling fronts are always slower in mixtures than in at least one of their components. Also, the minimum superheat required for generating fast fronts in mixtures is shifted towards higher values. Both effects are mainly associated with mass transfer during phase transition.