Distortion of a free surface during tank discharge

Abstract

During the process of withdrawing fluids from tanks, surface distortion and subsequent gas ingestion have been observed in situations where no liquid rotation was present. The distortion takes the form of a depression of the liquid surface over the outlet, which leads to ingestion of gas in the outlet line before all of the liquid has drained from the tank. This phenomenon becomes more important as the fluid flow rate is increased. The flow of fluids from tanks, under conditions that lead to gas ingestion, has been studied with emphasis on a theoretical solution, e.g., Abramson et al. and Saad and Oliver. However, no results applicable to the problem studied here have been obtained, and to the authors' knowledge, no comprehensive experimental study of the ingestion phenomenon has been undertaken prior to this work. This paper describes the results of such an investigation for flat-bottomed, right cylindric tanks with right cylindric outlets located on the tank centerline. The work discussed here deals primarily with the determination of the maximum height of the liquid surface when the surface distortion reaches the outlet. This distance is called the "gas ingestion" height, h. This note extends the experimental work and correlation of Ref. 3. A more complete description of the theoretical work is presented in Ref. 3.