On the Effect of Trapped Air in a Liquid Conduit on the Transient Flow Rate

Abstract

Trapped air in a liquid conduit has a great influence on the fluid transients. In this paper, especially its effect on the transient flow rate in a test pipeline is studied experimentally and analytically. Transient flow velocity, following quick opening of a valve attached at the downstream end, was measured. The experiments showed that the transient flow velocity often exceeds the final steady velocity. The numerical calculation by means of characteristics method showed a good agreement with the experiments. Maximum value of the transient flow velocity depends on the volume and the position of the trapped air, and the pressure loss of the pipeline and the valve, and the downstream pressure of the valve. Five dimensionless parameters, which represent above-mentioned factors respectively, are derived. And the relations between the maximum flow velocity and these five parameters are expressed graphically.