Occurrence Condition of Air Entrainment into a Vertical Wet-Pit Pump

Katsuya HIRATA, Jiro FUNAKI, Yoshihiro KUBOTA, Katsuhisa INAGAKI, Miki TAOKA, Takuya SAIDA
2013 Journal of Fluid Science and Technology  
In the present study, we consider the air entrainment into a suction pipe which is vertically inserted down into a suction sump across a mean free-water surface. This configuration is often referred to as the "vertical wet-pit pump", and has many practical advantages in construction, maintenance and operation. In particular, we focus our concern upon the critical submergence depth S c , which is one of the prime and conventional indicators for the air-entrainment occurrence. By a systematic
more » ... oach, we experimentally investigate the influences of kinetic and geometric parameters upon S c . As the kinetic parameters, we consider the Reynolds number Re and the Weber number We, in addition to the Froude number Fr, on such a basis as Fr is not much larger than unity in many actual cases. As the geometric parameters, we consider back clearance X, sump breadth B and bottom clearance Z. Here, all parameters are non-dimensionalised by the outside diameter D and the intake velocity V i of the suction pipe. As a result, we reveal the effects of such six parameters upon S c . The We effect, namely, the surface-tension effect can be ignored at We > 12. And, the Re effect, namely, the viscous effect becomes negligibly small at Re > 3×10 4 . Under such conditions for We and Re, we could consider only the Fr effect, namely, the gravitational effect. Concerning the X/D and B/D effects, S c /D attains the maximum at a certain X/D or B/D. On the other hand, the Z/D effect is monotonic, and becomes small at Z/D > 2.5. Some aspects of these geometric effects can be evaluated by a local-Froude-number effect on the basis of the global relation between S c /D and Fr. And, the other aspects is necessarily considered to be related with the flow structure in the suction sump.
doi:10.1299/jfst.8.364 fatcat:wlzydzvqnve57kjstbcivwuh5y