This study conducts a visual experimental investigation on low-pressure refrigerant R1233zd(E) in a parallel mini-channel heat sink. The evolution and distribution of flow patterns in parallel channels and the influence of flow patterns on heat-transfer characteristics were analyzed. Four flow patterns (bubbly flow

slug flow

churn flow

and wavy-annular flow) were observed in the channels when increasing the heat flux. At high heat flux levels

reverse flow occurs in some channels. In addition

it is observed that the distribution of flow patterns in different channels is slightly different. The variation trend of the local surface coefficient of the heat transfer can be divided into different stages based on the evolution of the flow pattern. Moreover

the middle and outlet local surface coefficients of the heat transfer exhibit different variation trends. When the vapor quality is less than 0.1

the surface coefficient of the heat transfer is almost independent of the mass flux. With an increase in vapor quality

the surface coefficient of the heat transfer is positively correlated with the mass flux.