Ammonia single-phase and two-phase frictional pressure losses in horizontal smooth and straight inner-grooved tubes

Abstract

The experimental study of single-phase and two-phase frictional pressure losses has been performed with ammonia flow in stainless steel smooth tubes (internal diameter of 5.5 mm and 8.5 mm) and six straight inner-grooved aluminium tubes with different nominal diameters (7.15 to 13.3 mm), length (0.45 to 2.0 mm) and thickness (0.35 to 0.8) of fins. Single-phase test boundary conditions correspond to Reynolds numbers of 1000 to 20,000. Two-phase tests have been carried out at saturation temperature of 45 to 65 °C, mass velocity of 50 to 210 kg·m−2s−1 and vapour quality of 0.1 to 0.9. Comparison of obtained test data with the existing frictional losses approaches shows that the Blasius model is appropriate to single-phase flows in smooth tubes, and Müller-Steinhagen and Heck's (1986) model is most accurate in predictions of two-phase frictional losses in smooth tubes. Existing approaches of single-phase frictional pressure loss predictions in the pipes and channels with longitudinal fins (Carnavos, 1980; Edwards and Jensen, 1994) are not adequately suited to the ammonia test points obtained in the considered straight inner-grooved tubes. A new semi-empirical model has been proposed, based on generalisation around the revealed geometric dimensionless factor, which accurately describes friction pressure losses in the considered inner-finned profiles. The simplest homogeneous model for defining two-phase friction pressure losses, using McAdams et al.'s (1942) recommendation for mixture dynamic viscosity definition and a new model of single-phase friction factor, best fit both quantitatively and qualitatively to ammonia two-phase test points in most of the considered straight inner-grooved tubes.