RESUMO

The aim of this study is to experimentally investigate the effect of inlet surface roughness, texture, and nozzle material on internal flow. Study results show that inlet surface roughness can affect the occurrence of cavitation much more than it affects hydraulic flip. Also, dimensionless driving pressures ranging from 1.28 to 1.48, correspond to the occurrence of cavitation, and ranges of 1.48 to 1.97, correspond to the occurrence of hydraulic flip in an acrylic nozzle. The variation of dimensionless driving pressures corresponding to the occurrence of cavitation caused by changing surface roughness is much greater than that of hydraulic flip, unless the roughness/hole diameter ratio rises to 0.0047. In an acrylic nozzle with a roughness/hole diameter ratio of 0.0115, the phenomenon of hydraulic flip becomes negligible. Increasing the diameter of the nozzle hole can reduce the effect of roughness on cavitation and the occurrence of hydraulic flip. The more adhesion between the wall of the nozzle and water molecules, the less likely is the occurrence of hydraulic flip, and there is a critical value of the dimensionless of the contact angle for the occurrence of hydraulic flip between 1.19 and 1.24 when the ratio of the roughness-to-hole diameter is ∼ 0.005. Burrs on the inside wall of the nozzle will eliminate hydraulic flip, even though cavitation exists within the nozzle. Cavitation is not only affected by coupling the ratio of the roughness-to-hole diameter and competition for the contractive and adhesive forces represented, it can also be affected by the surface texture of the nozzle, such as the occurrence of burrs.