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.