Elevating Leidenfrost temperature by orderly droplet stream impingement boiling

Impinging high frequency microscale droplet stream on a high temperature substrate is an effective method to realize point heat sink. The boiling patterns and the heat transfer characteristics of droplet impingements were investigated based on the captured images and the measured heat transfer. In the experiments, six different hydrodynamic patterns could be identified, base on which the phase diagram was drawn. The boundaries of different boiling patterns varied with the flowrate as well as the frequency of the droplet stream. The substrate temperature threshold for the transition from the contact boiling regime to the levitation transition boiling regime was influenced by flowrate apparently, but it was independent of droplet frequency. However, both the hydrodynamic patterns and the heat transfer measurements showed that the Leidenfrost temperature was elevated by increasing the flowrate or the droplet frequency. Compared to the droplet stream with random size and spacing, the Leidenfrost temperature could be increased by impinging orderly droplet stream without using more coolant. The reason was inferred that periodical collisions of droplet train released vapor in an efficient manner.