Flow and Heat Transfer of a Microjet Impinging on a Heated Chip: Part II Heat Transfer

This paper examines microscale heat transfer from a heated thermal chip due to jet impingement. The jet issues from a micro slot nozzle, which has three different widths including 50 m, 100 m, and 200 m, and impinges perpendicular to a small thermal chip (1.2 cmx1.2 cm) that is heated uniformly. Both the nozzle and the thermal chip are made by the standard microfabrication techniques. Arrays of temperature sensors and heaters are made along the thermal chip by depositing polysilicon films with varying concentrations of boron on the Si wafer. Local heat transfer along the thermal chip under different sizes of jet impingement slots are measured. The heat transfer processes along the small thermal chip differ significantly from the case of large-scale macro jet impingement and are related to the flow structures reported previously near the wall. The value of the Nusselt number can be well correlated if the nozzle-to-plate spacing ratio is normalized using the breakdown length of the impinging jet.