Two-phase Pressure Drop during Flow Boiling of Hydrocarbon Fluids

The paper reports pressure drop data for hydrocarbon fluids boiling in vertical upflow in a 8.68 m long, 25.4 mm i.d. tube, heated by direct electrical heating. These data were recorded simultaneously with the boiling heat transfer measurements. The systematic trends of the measured pressure gradient with respect to vapour quality, mass flux and pressure are examined. This provides useful information in terms of the relative importance of the constituent parts of the twophase pressure gradients, namely, friction, gravity and acceleration components. The examination of the trends also confirms the internal consistency of the measured data. The two-phase pressure drop data under flow boiling conditions are then compared with the well regarded Chisholm correlation from the open literature and also with the HTFS correlation. The results of these comparisons are presented. It is noted that in the near zero vapour quality region the measured pressure gradient data may be lower than the predictions because of the effect of subcooled boiling. Subcooled boiling could, for example, result in higher actual vapour qualities than the calculated equilibrium values. This, in turn, would result in a lower than predicted gravitational component, affecting the overall two-phase pressure drop.