Two-phase flow patterns in spirally fluted tubes were investigated through visual observation. Both straight (horizontal) and coiled fluted tubes were studied using adiabatic flow of air and water in transparent castings. The same types of patterns which occur in smooth tubes (i.e. annular, stratified, wave, plug, slug, and bubble) were observed in both the straight and coiled fluted tubes. For these tubes, experimental data support the use of a flow regime map of the type proposed by Breber et al. (1980), which was developed for condensation in smooth tubes. Based on results of the testing of two straight and three coiled fluted tubes, a generalized, modified Breber-style map is proposed for the prediction of flow regimes in spirally fluted tubes.

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