Pressure drop characteristics of two-phase flow in a vertical channel with offset strip fins

Abstract

Flow visualization photographs and measured pressure drop data are presented for vertical two-phase flow in an adiabatic channel with offset strip fins. Pressure drop data were obtained for two-phase flow of R-113 at atmospheric pressure over ranges of mass flux and quality typically encountered in small refrigeration and air-conditioning systems. Values of the two-phase multiplier for flow in the offset strip fin matrix were found to be 40–50% higher than those for a round tube under the same flow conditions. Particularly large deviations were observed at high-quality conditions where the pressure drop due to fin form drag becomes more significant. A theoretical analysis of the pressure drop associated with two-phase flow in channels with offset strip fins is also presented. This model accounts for the individual contributions of wall shear and form drag to the overall pressure gradient. While this model represents the trends of the measured data rather well, it slightly underpredicts the two-phase multipliers over the range of conditions explored here. A semiempirical superposition model of the frictional component of pressure drop for two-phase flow in offset fin matrices is also developed. Two-phase multipliers predicted using this model are in good agreement with experimental measurements, with a mean deviation of 15%.