Performance test of KOH-etched silicon sonic nozzles

Discharge characteristics of small sonic nozzles in the shape of pyramidal convergent and conical divergent

“…2. KOH etching can result in good surface roughness, but the nozzle geometry is limited to a pyramidal shape [7][8][9]. Laser machining can achieve the desired nozzle geometry, but yields, so far, poor surface roughness.…”

“…: +886 7 6077296; fax: +886 7 6077000. Our previous studies [7,8] employed the technique of KOH anisotropic etching to fabricate small sonic nozzles from a silicon wafer. Owing to the nature of anisotropic etching, the nozzles achieved had pyramidal convergent and divergent sections.…”

“…Four types of nozzles were investigated for their discharge characteristics and size effect in Reynolds numbers ranging from 3 × 10 2 to 8 × 10 3 . From the results [7,8], the pyramidal silicon nozzles possess good properties including thermal response, maximum sustainable pressure, and long-term stability. However, the pyramidal sonic nozzles have a divergent angle of 35.3°, much larger than the ISO-suggested 4°-6°.…”

“…A higher CBPR signifies that the nozzle may be choked easily and can be operated at a higher back pressure ratio. Therefore, the fabrication methods employed here are slightly different from those in our previous studies [7,8]. The KOH anisotropic etching is utilized to fabricate the upstream convergent section of the nozzle.…”

“…2 shows a schematic illustration of the configuration. The conical diffuser features the major difference in geometry from the pyramidal sonic nozzles in [7,8] lengths were made to study how the configuration affects the pressure loss of the nozzle. Experiments were performed to find out the discharge coefficients (Cd) and CBPRs.…”