An experimental study of evaporation heat transfer coefficients for single circular small tubes was conducted for the flow of C3H8, NH3, and CO2 under various flow conditions. The test matrix encompasses the entire quality range from 0.0 to 1.0, mass fluxes from 50 to 600kgm-2s-1, heat fluxes from 5 to 70kWm-2, and saturation temperatures from 0 to 10°C. The test section was made of circular stainless steel tubes with inner diameters of 1.5mm and 3.0mm, and a length of 2000mm in a horizontal orientation. The test section was uniformly heated by applying electric power directly to the tubes. The effects of mass flux, heat flux, saturation temperature, and inner tube diameter on the heat transfer coefficient are reported. Among the working refrigerants considered in this study, CO2 has the highest heat transfer coefficient. Laminar flow was observed in the evaporative small tubes, and was considered in the modification of boiling heat transfer coefficients and pressure drop correlations.
|Number of pages||8|
|Journal||International Journal of Multiphase Flow|
|Publication status||Published - Sep 2011|
- Heat transfer coefficient
- Natural refrigerant
- Small tube