Study on emptying-box problem with different inflow directions

•Theoretical predictions and experimental results on the transient stratified flow.•A modified theoretical model is proposed in this paper.•The new model is compared with the previous model, along with experimental results.•The new model has improved accuracy on estimating experimental evolution.

This study investigated the emptying-box problem with horizontal and vertical inflow directions. The salt-bath technique was used in simulation experiments with an acrylic reduced-scale model. The salt-bath technique uses salt water and fresh water to simulate the density difference between inside and outside fluids. The light-attenuation technique was used to analyze the experimental intensity data on the transient stratified flow. The experiments were categorized into two series based on the inflow direction: the horizontal inflow type emptying box EM(H) and the vertical inflow type emptying box EM(V). The emptying process of EM(H) was observed to only involve emptying the dense layer, similar to the classical displacement flow. The emptying process of EM(V) included emptying the dense layer and mixed layer. The results showed that the emptying times of EM(H) and EM(V) decreased when either the total effective opening area or initial reduced gravity was increased. The time to empty the dense layer in the EM(V) series was about 50–60% of that in the EM(H) series, and the total emptying time was much longer for the former series than for the latter series under the same conditions. Previous theoretical models were applied to both series and showed reasonable agreement with the experimental results. A new modified theoretical model for EM(V) was developed and compared with the previous model. The new model demonstrated improved accuracy with regard to estimating the experimental evolution.