Effect of Outlet Position on Homogeneity of Two Layer Stratified Liquid

Abstract

In industry, there are several fields where density stratification occurs. It can happen when one batch of liquid is loaded on the top of another batch in the same storage tank. This phenomenon can cause trouble in operation and it can induce decadency of product quality, as well. In this paper, homogenisation of two stratified layer liquid was investigated. The homogenisation was achieved by an external pump. The experiments were carried out in a cylinder tank with 3.043 l active volume which is the scale-down of a ~100 m3 industrial tank. The residence time in the system was 3.48 h. The main goal of our research was to examine the effect of outlet position on mixing time. In our research, borax was used as stratified liquid. The density of the upper layer was 1.0022 g/cm3 and the lower layer was 1.0136 g/cm3density. The inlet was positioned above the liquid level. Two different experiments were carried out for three outlet positions. Firstly, we examined the mean residence time of the systems. For this, experiments were carried out in a constant, continuous tank filled with 1.0022 g/cm3borax solution meanwhile the inlet liquid density was 1.0136 g/cm3. Experiments were performed in the other way around, too (1.0136 g/cm3 tank solution, 1.0022 g/cm3 inlet). The flowrate of the outlet and the inlet was constant and identical. Secondly, mixing two-layer stratified liquid in circulated system using external pump was investigated, as well. Measuring apparatus was conductivity probe. Two probes were placed into the system. One of them was used for sampling the outlet and the other was situated in a fix position during all experiments. The data was evaluated by mean residence time where it was possible, and it was also analysed in accordance with the time request to achieve 95 % homogeneity. We examined the concentration differences between the sampling points in time.