Void fraction correlations analysis and their influence on heat transfer of helical double-pipe vertical evaporator

• 50 void fraction correlations were evaluated on heat transfer in vertical evaporators.
• Two-phase flow model based on control volume formulation was used.
• The drift flux parameter is common in all correlations with satisfactory results.

An analysis of 50 void fraction correlations available in the literature was performed to describe two-phase flow mechanism inside two helical double-pipe vertical evaporators. The evaporators considered water as working fluid connected in countercurrent so the change of phase was carried out into the internal tube. The discretized equations of continuity, momentum and energy in each flow were coupled using an implicit step by step method. The selection of the void fraction correlations for the mathematical model was based on inclusion of some theoretical limits. The results of this analysis were compared with the experimental data in steady state for two different evaporators, obtaining good agreement in the evaporation process for only 7 void fraction correlations. The Armand and Massena correlation had a mean percentage error (MPE)(MPE) of 3.08%, followed by Rouhanni and Axelsson I adquired MPE=3.16%MPE=3.16%, Chisholm and Armand obtained MPE=3.18%MPE=3.18%, Steiner as well as Rouhanni and Axelsson II with MPE=3.19%MPE=3.19%, Bestion reached MPE=3.20%MPE=3.20% and Flanigan presented MPE=3.21%MPE=3.21%. Furthermore, the experimental and simulated heat flux were acceptable (R2=0.939)(R2=0.939). Finally, the results showed that the drift flux parameter was important to evaluate the void fraction.