Investigations On Non-uniform Flow Characteristics Of Ice Slurry In A 90° Horizontal Elbow Pipe

Ice slurry usually refers to a solid-liquid phase slurry containing a large amount of ice crystal particles.It has lots of advantages including high cold storage density and good flow characteristics.The steady and safety of the transportation of the ice slurry make crucial function on the application of ice slurry.The components such as fittings and elbow pipes are the high occurrence places of ice blockage in the process of ice slurry transportation.The study on flow characteristics of ice slurry is significant for the safety of the ice slurry transportation and the precaution of the ice blockage.Therefore,the ice slurry is taken as the study object,and the method of experimental and numerical simulation are used to study the flow characteristics of ice slurry in a 90° horizontal elbow pipe as components of a transportation system.Firstly,the computational fluid dynamics-population balance coupling model(CFD-PBM)including multiphase flow model,particle dynamics model,interphase force model and turbulence model was developed.And the dynamic processes of ice crystal agglomeration and fragmentation were used to describe the he particle size and evolution law of ice crystal particles.At the same time,the 90° horizontal elbow pipe physical model was developed,and the 90° elbow pipe is divided into three parts: the inlet end,the elbow end and the outlet end.The grid convergence index(GCI)method was used to verify the grid independence.Then,the experimental platforms for the preparation,control and test of ice slurry was used to study the pressure drop of ice slurry with different flow velocity and ice packing factor(IPF).And the reliability of the CFD-PBM coupling model is verified by comparing the experimental data with the simulation data under the same conditions.Finally,this essay simulated the flow characteristics of ice slurry in the 90° horizontal elbow pipe.The pressure drop of ice slurry flow,the flow velocity,the ice volume fraction and the mean size of ice particles at the inlet,elbow and outlet of the elbow were analyzed in detail.The results show that:(1)The influence of the inlet velocity of the ice slurry on the pressure of ice slurry flow is much more than that of IPF at inlet.In addition,during the entire flow process of ice slurry in the 90° elbow pipe,the ice volume fraction in the upper half of the elbow is larger than that in the lower half.The mean size of ice particles was also higher in the upper part of the elbow,and the maximum of the mean size of ice particles appeared in the upper part of the elbow.(2)After the ice slurry flows into the elbow,it will produce a hoop velocity and gradually form a secondary flow.At the same time,the hoop velocity of the ice slurry will gradually form two obvious vortices.Therefore,the ice slurry in the mainstream area flows toward the outer wall of the elbow,and the ice slurry near the upper and lower wall surfaces is replenished to the inner wall of the elbow to maintain the continuity of the flow.(3)On the one hand,turbulence disturbance caused by secondary flow can make the distribution of the ice volume fraction more uniform,on the other hand,it can also enhance the fragmentation effect of larger ice crystal particles and the aggregation effect between smaller ice crystal particles.Therefore,after the ice slurry flows through the 90° elbow,the distribution of the ice volume fraction will be more uniform,and the mean size of the ice crystal particles will increase overall.(4)The combined action of centrifugal force and secondary flow,making the ice volume fraction and the mean size of ice particles increase,will lead to the ice blockage.Thus,there will be many adverse effects on the transport process of the ice slurry.In addition,the increase of the inlet velocity and IPF will increase the possibility of ice blockage.