Paper presented at the 7th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Turkey, 19-21 July, 2010.
An experimental investigation on the characteristics of two-phase boiling heat transfer of NH3, C3H8 and CO2 in horizontal small stainless steel tubes of 1.5 and 3.0 mm inner diameters are presented in this paper. Experimental data were obtained over a heat flux range of 5 to 70 kW/m2 mass flux range of 50 to 600 kg/m2s, saturation temperature range of 0 to 120C, and quality up to 1.0. The test section was heated uniformly by applying an electric current to the tubes directly. Nucleate boiling heat transfer was the main contribution, particularly at the low quality region. The heat transfer coefficient of the present working refrigerants was compared Laminar flow was observed in the small tubes. A new boiling heat transfer coefficient correlation based on the superposition model for refrigerants in small tubes was developed.