Effects of the half angle on the flow rectification of a microdiffuser

Abstract

This paper presents an experimental investigation of the influences of the half angle on the flow rectification of the microdiffuser pump and reports on flow visualization results to exhibit the flow separation characteristics in microdiffusers. The tested half angles vary from 5° to 55° with 5° increments, and constant pressures (290–550 Pa) are supplied to measure the volume flow rates in both expansion and contraction directions. The results show that the flow rate in the expansion direction is always larger than that in the contraction direction regardless of the half angle, indicating that the flow rectification tends to cause a net flow in the diffuser direction. For Re1 < 22, the maximum flow rectification is achieved at θ = 30°. For θ > 30°, a pair of symmetric recirculations is observed by the flow visualization technique. The effective area of the circulation grows with increasing half angle and driving pressure, suppressing the core flow and deteriorating the flow rectification consequently.