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The swirl flow of Freon 12 in a tubular heat exchanger, indirectly heated by forced convection of water in an annular gap, is studied. Two identical situations are compared, with and without a twisted tape, to deduce the influence of the swirl flow in the particularly interesting boundary condition of indirect heating by another fluid (and not simply of uniform Joule heating). The heat transfer is greatly increased by the swirl flow, up to a factor of two at the burnout or dryout point.

Experimental research on highly dispersed, two-phase, turbulent flows was performed employing Freon 12 at different pressures up to the critical value. By means of visualization techniques it was possible to study the droplet size distribution, their spatial concentration, and the relationships among the deduced law of distribution and the main thermo-hydraulic parameters for different thermo-hydraulic conditions (pressure, mass velocity, and quality). Simple relations were developed which make it possible to determine, at least for some reference thermo-hydraulic situations, all of the characteristics of the liquid dispersed phase.