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

Abstract

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 approach, 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.

On air-entraining flow in pump's sump with a vertical suction pipe below critical submergence

“…When we define non-dimensional governing parameters, we can consider various options in the choice of characteristic scales. In the present study, we choose D and V i as length and velocity scales, respectively (see Hirata et al (2013) for the validity of these choices). In Table 1, we summarise the present values of experimental parameters.…”

“…The present experimental apparatus is similar with Hirata et al (2013). A turbo pump feeds working fluid (water) to a suction sump from a reservoir tank.…”

“…And unfortunately, we have not enough knowledge even for the flow in a slightly-complicated-geometry suction sump such as a simple vertical-wet-pit-pump-configuration one. Concerning the vertical-wet-pit-pump configuration, researchers have carried out experimental and numerical studies (Iversen, 1953;Denny, 1956;Tagomori, 1979;Tagomori,1980;Padmanabhan et al, 1984;Tagomori & Ueda, 1991;Okamoto et al, 1991;Oshima & Tagomori, 1992;Kuwakino, 1993;Iwano et al, 2002;Ansar, 2002;Li et al, 2004;Tang et al, 2011;Zhao & Nohmi, 2011;Kanemori & Pan 2015;Yamasaki et al, 2017) in addition to us (Funaki et al, 2008;Hirata et al, 2009;Hirata et al, 2013;Hirata et al, 2016). These studies suggest that we should know the flow and the air-entrainment mechanism more precisely, to prevent the air entrainment.…”

3D-PTV measurement verified by UVP for unsteady and three-dimensional flow inside a suction sump

“…In the main test of the present study, an experimental apparatus is substantially identical with Funaki et al (2008), Hirata et al (2009) and Hirata et al (2013a). A turbopump feeds working fluid (water) to a suction sump from a reservoir.…”

“…Our aim is to understand the complicated flow inside a suction sump in the vertical-wet-pit-pump configuration. Most of the flows appearing in various industrial and environmental problems like the present suction-sump flow become often complicated owing to both of their unsteadiness with poor periodicity and their fully-three-dimensionality (Funaki et al, 2008, Hirata et al, 2013a. So, in instantaneous and three-dimensional observations of such flows could give us useful and effective information.…”