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Air and Abrasive Acceleration_6

Tham khảo tài liệu 'air and abrasive acceleration_6', kỹ thuật - công nghệ, điện - điện tử phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 100 3 Air and Abrasive Acceleration of steel particles dP 50-70 pm and aluminium particles dp 50-70 pm accelerated in convergent-divergent nozzles and they found excellent agreement between the measured velocities and the velocities calculated with their simulation method. The gain in using smaller abrasive particles was especially evident for short nozzles. If longer nozzles were utilised the influence of the abrasive particle diameter became less important. 3.6.4 Effects of Abrasive Particle Shape on Particle Velocity A very early statement on the effect of the abrasive particle shape on the particle velocity based on experimental results was due to Rosenberger 1939 The shape of the abrasive particles also influences the velocity. Spherical particles travel slower than angular particles other conditions being equal Shipway and Hutchings 1993a found experimentally that glass spheres achieved lower final velocities than irregular silica particles for a given air pressure for many nozzle types. They attributed this effect for two reasons. Firstly the irregularity of the silica shapes means that each particle with a given sieve diameter may have less mass than a sphere of this diameter and may also have a greater drag coefficient. Secondly the rebound behaviour of spheres and angular particles at the nozzle walls will differ. For a sphere the rebound angle tended to be equal to or larger than the approach angle. An angular particle can rotate on impact leading to a rebound angle which can be smaller than the approach angle. This may lead to higher acceleration along the nozzle and therefore a greater final velocity. Fokke 1999 applied a numerical procedure developed for spherical steel particles and compared the numerical results with experimental results obtained with irregular steel grit particles. He noted a 20 difference between numerical and experimental results. This 20 increase in abrasive particle velocity for grit particles is however a very preliminary .