The Effects of Downcomer Diameter on an Air Entrainment of Vertical Plunging Water Jet on The Water Surface

The difficulty in finding clean water is issued to become Indonesia’s problem in 2025. Seawater processing to produce clean water for commonly used or called water desalination will be a promising solution to solve the problem of clean water scarcity. One of the seawater desalination processes is to utilize micro-bubbles generated from air entrainment. Air entrainment is a phenomenon where the surrounding air is trapped in the water and forms a bubble. Using the vertical plunging jet setup will lead to bubble formation as a result of the collision between the vertical water jet and the pond surface below it. This study determines the effect of downcomer diameter on the parameters that influence the parameter of air entrainment quality by using a vertical plunging jet configuration. Some set up tools that support research consists of pumps, nozzle, downcomer, airflow meter, anemometer, and water pond. Results of the research are in the form of qualitative data such as videos and photos, by using a high-speed camera with backlighting. The qualitative data obtained will be processed with an image processing program to acquire quantitative data. The results of the study revealed that the downcomer diameter affects the air entrainment rate. On the other hand, jet velocity affects the area of dispersion and depth of penetration.

Experimental Characterization of Air-Entrainment in a Plunging Water Jet System Using Particle Image Velocimetry (PIV)

This paper presents a detailed experimental study of a plunging jet on a free liquid surface. An experimental characterization facility is designed and constructed for generating a vertical round water jet impinging on a free surface of a pool. The experimental analysis focuses on the jet penetration depth, its relation to impact velocity Vj and free jet length Lj. Present results are compared with previous studies. The flowmap for four different regimes, in terms of impact jet velocity is obtained. The details of the two-dimensional velocity field below the pool liquid free surface under a no-entrainment regime, is obtained using Particle Image Velocimetry (PIV) and reveals the entrainment behavior of the impinging jet flow below the interface.