Abstract
Four types of KOH-etched silicon sonic nozzles with throat dimensions of around 90 μm are examined to unveil their discharging characteristics for 6×10 2< Re<8×10 3. With a specially designed clamping holder, the silicon nozzles are able to sustain an upstream pressure of at least 13.8×10 5 Pa. The critical back pressure ratio for choking is found to be insensitive to Re, and the largest of the four types is about 0.36. The silicon nozzle takes about 20 s to reach a stable Cd value, that is, a thermal equilibrium with sonic flow, after the flow starts. The discharge coefficients obtained in five days during two months have a scattering of only 0.02%, signifying good long-term stability.
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