microchannel, flow pattern, refrigerant, evaporation, visualization
This paper presents visualization results of two-phase flow of R134a, R1234yf, and R1234ze(E) in microchannel tube with hydraulic diameter of 0.643 mm. Visualization section has been made to record the flow in the microchannel to study the flow characteristic. Flow pattern maps of R134a, R1234ze(E), R1234yf are reported in this paper. Flow pattern maps are presented in two ways: mass flux-quality as coordinates, and superficial velocities as coordinates. The quality range of experiment is from 0 to 1 thermally. Mass flux varies from 50 to 250 kgm-2s-1. Flow patterns are classified as: plug/slug flow, transitional flow, and annular flow. The quality of boundary between two flow patterns is lower when mass flux is higher. At low vapor superficial velocity, the flow is in plug/slug. The vapor fraction and the interface velocity in plug/slug flow agrees well to the homogeneous prediction. As the vapor velocity increases, the flow becomes transitional flow. At higher vapor velocity and high liquid-to-vapor velocity ratio, the flow becomes annular.