Pressure drop data and prediction method for enhanced external boiling tube bundles with R-134a and R-236fa

•Two of the latest enhanced boiling tubes have been studied under bundle boiling.•Refrigerants used were R-134a and R-236fa.•It was found that vapour quality and mass flux had the dominant effect on pressure drop.•A new phenomenological enhanced tube bundle boiling correlation was proposed.

The pressure drops of external flow over enhanced tube bundles were experimentally obtained at both adiabatic and diabatic conditions using R-134a and R-236fa as test fluids. The tests were carried out at saturation temperatures of 5 and 15 °C, mass fluxes from 4 to 40 kg m−2 s−1, heat fluxes from 15 to 70 kW m−2 and inlet vapour qualities ranging from 10% to 90%. The frictional pressure drop was found to be primarily a function of mass flux and vapour quality. After comparisons were made with prediction methods in literature a new pressure drop prediction method was proposed for adiabatic and diabatic conditions. The proposed method is based on local measurements (4 and 8 tube rows) and flow conditions (evaluated per tube pitch) and the prediction method is well adapted to local incremental implementation for flooded evaporator design.