A study is performed on identification of the flow patterns and void fraction inside the vertical tube evaporator with flashing inside and heating from the outside of the tube wall using electrical probes and photographic method. The basic flow patterns identified from the output voltage itself and probability density function of the output voltage from electrical probes are Bubbly, Slug and Churn flow. However, Annular flow pattern does not appear in present experimental system due to the small evaporation rate. Also, the flow patterns are changing along the axial distance from the tube inlet with various system pressure.
Those results are compared with the flow pattern map proposed by Mishima and Ishii [4]. Certain differences come from the nonequilibrium phenomena inside the tube. The trend of flow pattern observed in present research is in agreement with the flow pattern map of Mishima and Ishii.
