Falling film evaporation of R1234ze(E) and R245fa on a horizontal smooth tube

Falling film evaporation on a horizontal smooth tube with outer diameter of 19 nun was investigated using two refrigerants, R1234ze(E) and R245fa. The heat transfer coefficients were obtained at a film Reynolds number range of 100-1000, heat flux range of 2.5-40 kWm(-2), and saturation temperature range of 10-20 degrees C. The flow patterns of falling liquid film between tubes were observed under adiabatic and heating conditions. The effects of film Reynolds number, heat flux, saturation temperature, and refrigerant properties on the heat transfer were clarified. The heat transfer of falling film was characterized by nucleate boiling and convective heat transfer. Heat transfer was enhanced by increasing heat flux at high heat flux conditions, while heat flux at low heat flux condition had no significant influence. The measured heat transfer coefficients were compared with previous correlations, and a new prediction model that considers both nucleate boiling and convective heat transfer was developed for falling film evaporation.