Flow regime transition criteria for upward two-phase cross-flow in horizontal tube bundles

In comparison with great success in the two-phase flow research for internal flows, relatively limited two-phase researches have been performed for external flows such as two-phase cross-flow in horizontal tube bundles. The recent demand of compact and efficient design of shell-tube type heat exchangers requires comprehensive understanding of void fraction, heat transfer, pressure drop, flow-induced vibration and flow regime in the shell side. The flow regimes are strongly related to the two-phase external-flow structure and affect the heat transfer performance in the heat exchangers. To this end, extensive literature survey has been performed to understand the flow regime appearing in the upward two-phase cross-flow in horizontal tube bundles. This study has classified the flow regime into 5 distinct flow regimes such as bubbly, cap bubbly, churn, finely dispersed bubbly and annular flows. A new model of the flow regime transition criteria has been proposed based on the analysis on the underlying physics of the upward two-phase cross-flow behavior in horizontal tube bundles. The newly developed flow regime transition criteria have been compared with 12 flow regime maps measured in horizontal tube bundles with normal square pitch array, normal triangular pitch array and parallel triangular pitch array. The test conditions of the 12 flow regime maps include the pitch/diameter ratio ranging from 1.17 to 1.5 and the tube diameter ranging from 0.00979 m to 0.020 m. The fluid systems are air-water, boiling iso-butane, boiling propane, boiling n-pentane, boiling R134a and R235fa. A fairly good agreement with some discrepancy has been obtained between the newly developed transition criteria and the measured flow regime maps.