Measured air flow rates through microorifices and flow prediction capability

Traditional orifice calculational formulas can be used to estimate air flow through openings, but they have not been validated for very small openings. Experiments performed in this study verified the applicability of classic flow relationships and calculational methodology for ''thin'' orifices 20 to 200 microns in diameter. The volumetric air flow through orifices was measured (downstream pressure approximately 760 mm Hg, ambient temperature) as the upstream pressure was increased by 1 psig increments from 1 to 5 psig, 10 psig increments from 10 to 100 psig, and 100 psig increments from 100 to 1000 psig. Above ''choked flow'' (upstream pressure approximately 13 psig) the air flow increased as a linear function of upstream pressure. Air flow rates on the same orifices exhibited a loss of flow as the temperature was increased by 2000 increments to 12000F. The upstream pressure was held at 15 psig, with the downstream pressure at 1 atmosphere and ambient temperature. The calculational methodology described is valid for predicting the flow of gases using the appropriate parameters for each gas