The heat transfer characteristics of 10% micro-encapsulated phase change material suspension(MEPCMS) and distilled water in the mini-tube of radius 1 mm and 2 mm were investigated. It appears that:for Reynolds number ranging from 400 to 1000

the local Nusselt number of MEPCMS and water in 1 mm tube is smaller than it in 2 mm tube. From the analysis of reason it is mainly because the thickness of 1 mm tube is larger than 2 mm tube resulting in stronger axial thermal conductivity. The distilled water joined in MEPCM in 1 mm tube can enhance the heat transfer between the fluid and tube wall and the local Nusselt number increase with Reynolds number increasing. While the 10% micro-encapsulated phase change material suspension in 2 mm shows weaker heat transfer characteristics than distilled water and the local Nusselt number decrease with Reynolds number increasing.