Liquid Jet Flow into Still Gas : Jet Flow by Circular Rough Tube

Abstract

Instead of using the nozzle in the previous report, rough tubes are used as a water jet source. Jet core-length is measured against tube wall roughness, tube diameter and temperature of water. The jet core-length saturates after it increases with the jet velocity. Saturated value of jet corelength of each rough tube is constant if the frictional coefficient of the tube is less than a critical value, but it decreases if the frictional coefficient is larger than this. The critical coefficient depends upon the stability number (=W_e/R_e), ratio of kinematic viscosity of water to air as well as upon Nikradse's equivalent sand roughness of the tube. It is confirmed that the relation between the frictional coefficient and Reynolds number of the jet just at which its core-length saturates is identified from the boundary of complete rough regime in Moody's diagram. The limit of roughness which has any effect on the jet core-length is found on this boudary, and the allowable finishing order of jet nozzle wall for hydraulic process can be estimated by applying this limit.