Flow and Heat Transfer of a Micro Jet Impinging on a Heated Chip: Part I—Micro Free and Impinging Jet Flow

Abstract

Microscale jet flow impinging on the wall of a thermal chip and the resulting heat transfer along the wall are explored in a systematic fashion. The current article presents flow characteristics of the micro jet impinging on a wall and the accompanying paper [18] presents the resulting heat transfer. The jet is issued from a micro slot nozzle that has three different widths—that is, 50, 100, and 200 μm—and impinges normally on a small thermal chip (1.2 cm × 1.2 cm) that can be heated uniformly. Both the nozzle and the thermal chip are made using microfabrication technology. Flow visualization for the impinging jet along the wall of thermal chip was made. The wall jet flow structures along the small thermal chip were completely different from the case of a large-scale, macro jet impingement process. When the micro jet is impinging on the wall, either two spiral cells or the turbulent circulation flow are formed along the wall. The spiral cells grow in size when either the size of the nozzle, the nozzle-to-plate spacing, or the Reynolds number of the jet increases. The range of the Re and Ma numbers in the current experiments was 16–680 and 0.0146–0.146. Detailed discussions on the formation and growth of the spiral cells or the turbulent circulation flow along the wall are presented. In order to understand the peculiar phenomenon of the wall jet flows, special features of the micro free jet are further explored.

Keywords:

• micro impinging wall jets
• nozzle size effect
• spiral cells
• micro free jets