The effects of contact angle on two-phase flow in capillary tubes

Abstract

A two-phase gas—liquid flow was studied in small diameter (1.6 mm i.d.) horizontal tubes. Adiabatic flow of air-water mixtures was tested over a range of flow rates, 1000:1 for air and 600:1 for water. Flow maps were established for four systems with different contact angles. Each system contained the same fluids (air and water) and had the same tube diameter, however, the tube material was different for each system. The four tube materials were pyrex, polyethylene, polyurethane and FEP, a fluoropolymer resin. Three of the contact angles, measured on a flat sample of each tube material, were partially wetting (34° 61° and 74°) and one was partially non-wetting (106°). The flow maps for the systems were very similar except for a region of rivulet flow. Rivulet flow is a new flow regime that replaces wavy flow when the contact angle becomes large. On the other hand, the transition boundaries for the non-wetting system, except for the plug—slug transition, were significantly changed.