Peculiar phenomenon of micro-free-jet flow

This is the first time that free microjet flow dynamics is explored experimentally in the open literature. The microjet is issued from a microslot nozzle made by microelectromechanical system techniques. Three different sizes of slot nozzles that have the widths of 50, 100, and 200 mu m are fabricated. Careful flow visualization and instantaneous velocity measurements at different locations for these jet flows are made at different Reynolds numbers. The results indicate that the vortex formation and merging processes that occurred in the large-scale macrojet are completely absent in the microjet, and the microjet flow phenomenon is drastically different from that of the macrojet. A microjet can penetrate much deeper than a macrojet. A critical Reynolds number for the breakdown of the microjet is determined. Detailed discussion on the microjet dynamics will be presented in this paper.