Research On The Evolution And Influencing Factors Of Explosive Boiling In Vertical Vessel

Pressurized liquefied gas(such as liquefied petroleum gas,etc.)is widely used in the energy and chemical fields.Because of its high energy density,when the container containing the liquefied gas is subjected to external impact or cracks due to corrosion,the medium in the container is prone to overheating and boiling,in severe cases,it can cause boiling liquid expansion vapor explosion(BLEVE),causing injury to surrounding personnel and equipment.At present,the research on the bumping process mainly focuses on the single effect of the filling rate and the opening diameter of the container from the macroscopic level,and the understanding of the mechanism of the bumping process is not enough.In view of this,this paper explores the evolution law of bumping of superheated liquid in a vertical container and the coupling effect of container opening diameter and filling rate on the bumping process by combining visual experiments and numerical simulations.The main work and conclusions are as follows:(1)The experimental research is carried out based on the visualized superheated liquid bumping experimental system.A dynamic pressure sensor is installed on the top of the container to record the pressure response during the discharge and bumping process.Complete monitoring of the evolution of the bumping two-phase flow.(2)The evolution characteristics of the bumping two-phase flow in the vertical vessel are revealed through visual experimental research.Among them,in the first pressure rebound stage,a large number of bubbles are first generated near the liquid surface,and a mist-like two-phase flow is rapidly formed in the gas phase space.When the two-phase flow fills the container,the pressure reaches a peak value.It accelerates as the opening diameter increases;in the second pressure rebound stage,as the opening diameter increases,the slug effect of the two-phase flow limited by the opening weakens,and the upward flow characteristics of the bottom two-phase flow in the vertical direction change from intermittent expansion to continuous flow.(3)By summarizing the pressure response laws under different filling rates and opening diameters,three typical pressure curve shapes are proposed: gentle type(type I),transition type(type II)and steep rise type(type III).When the opening diameter is smaller,the pressure response mainly exhibits the characteristics of type I.With the increase of the opening diameter,the pressure response presents the characteristics of type II and type III in turn.the larger the opening diameter.Considering the coupling effect of opening diameter and filling rate,the depressurization coupling parameter ΔP×(1-F)is proposed,which can provide a basis for judging the pressure response type.(4)A numerical calculation model is established to describe the bumping process of superheated liquid,and the inner and outer spaces of the container are solved at the same time,which avoids the influence of the simplification of the boundary conditions at the opening of the container on the numerical simulation.By comparing with the experimental pressure curve,the reliability of the model is verified,and the pressure peak error is 12.6%.(5)The evolution mechanism of the bumping development process of the vertical container was further studied through numerical simulation.The simulation results showed that the boiling time and boiling intensity were jointly affected by the opening diameter and the filling rate.When the expansion velocity of the boiling two-phase flow was greater than the discharge velocity When the pressure starts to rebound;the filling rate has a significant effect on the migration height of the two-phase flow,which in turn affects the rebound pressure.(6)Based on experimental research and numerical simulation analysis,it is proposed that the main factors affecting the bumping strength of vertical vessels are initial superheat degree,opening diameter and unfilled rate.Based on this,an evaluation index of bumping strength is defined,which is convenient for evaluating the coupling effect of opening diameter and filling rate,and 9 sets of working conditions experiments under the conditions of 74 mm,104mm,147 mm opening diameter and 25%,50%,and 75% filling rate are carried out.The validity of the evaluation index of bumping intensity was verified,and the results were in good agreement.