The high-speed imaging technique was used to observe the evaporation and nucleation process of the droplets of deionized water after impacting the surface of the micro-pillar structure. The results show that the evaporation time of droplet decreased with the increase of wall temperature. Compared with smooth surface

the heat transfer coefficient (HTC) of micro-pillar surface can be only enhanced under certain conditions. In this paper the temperature is 50

60

70

80 and 120℃

and the strengthening effect is best at 120℃. The evaporation of droplet can be divided into two stages. In the first stage

the diameter of the droplets is constant

and the height changes. In the second stage

the thickness of the droplet is close to the height of micro-pillar structure and the droplet dry in a very short time. As the wall temperature increases

the period of the first stage decreases obviously

and the nucleation density and the bubble diameter increase accordingly. It is worth to note that nucleation bubbles show a radial distribution on the micro-pillar surface because of the structure of array micro-pillars and the impact of dropping down.