DESIGN AND PERFORMANCE EVALUATION OF A PRESSURE-REDUCING DEVICE FOR AEROSOL SAMPLING FROM HIGH-PURITY GASES

Pressure-reducing devices are used to reduce the gas pressure from that existing in the high-purity compressed gas system to ambient conditions in order to measure the particulate contaminants. This study deals with the design and performance evaluation of a pressure reducing device. The pressure reducing device using an orifice plate geometry has been designed by calculating the design parameters taking into account low particle loss, compactness, and light weight. The pressure reducer is designed to operate at an upstream pressure up to 150 psig (1034.3 kPa) and for a variety of high purity gas types such as N2, O2, air, and Ar. For the University of Minnesota pressure reducer, the background was found to be < 0.02 particles/ft3 (0.706 particles/m3) over the pressure range from 15 to 100 psig. Particle penetration for particle sizes <2 mum was >80% and decreased for larger particle size with 50% penetration at approximately 3 mum and 10% penetration at 5 mum. The experimentally determined particle penetration data agreed well with calculated values. Lastly, a pressure reducer of the orifice plate design was found to be suitable for particle sampling in a high-purity N2 gas distribution system. The concentrations of particles > 0.02 mum and 0.5 mum in the high-purity nitrogen gas system were 0.61 and 0.18 particles/ft3, respectively.