FRICTION PRESSURE-DROP OF R-12 IN SMALL HYDRAULIC DIAMETER EXTRUDED ALUMINUM TUBES WITH AND WITHOUT MICRO-FINS

Adiabatic, single-phase liquid and two-phase Bow pressure drop were me asured for R-12 flowing in both rectangular plain and micro-fin tubes with hydraulic diameters 2.64 and 1.56 mm, respectively. The single-ph ase liquid friction factors for the plain and micro-fin tubes are unif ormly 14% and 36% higher, respectively, than that predicted by the Bla sius equation. For two-phase Bow, the pressure gradient increases with increasing mass velocity and vapor quality. The pressure gradient of the micro-Bn tube is higher than that of the plain tube at same mass v elocity and vapor quality; Predictive methods for the single-phase liq uid and two-phase friction factor were also developed. These data are not well correlated by the Chishohn correlation which uses the Lockhar t-Martinelli two-phase multiplier. However, the equivalent mass veloci ty concept proposed by Akers et al. provided a very good correlation o f the: present data. Both the plain and micro-Bn tube data are correla ted within +/-20% by a single curve. This work shows that the pressure drop is dominated by vapor shear in both the plain and micro-fin tube s. Vapor shear effects in micro-fin tube do not cause significant dist urbances in the two-phase Bow. This observation provides additional ev idence to support the conclusion in other work by Yang and Webb that t he distinctly steep condensation heat transfer curves at low mass velo city and high vapor quality are caused by surface tension drainage for ce.