Evaporation of refrigerants in a smooth horizontal tube: prediction of R407C heat transfer coefficients and pressure drops

This paper presents experimental local heat transfer coefficient and pressure drop results obtained during the evaporation of the zeotropic mixture R407C (R32-R125-R134a, 23/25/52 % in weight). The test section was a smooth, horizontal, stainless steel tube (6 turn ID, 6 in length) uniformly heated by Joule effect. The effects of mass flux, heat flux and evaporating pressure on the heat transfer coefficients have been investigated. The experimental tests have been performed with a refrigerant mass flux of 200 and 355 kg/m(2)s varying the heat flux within the range 8.0-16.9 kW/m(2) and the evaporating pressure from 3.5 up to 10.0 bar.