| The Ministry of Transport has put forward new requirements for promoting the construction of an eco-friendly transport system,strengthening environmental protection,and winning the battle against pollution.To achieve green material transportation,it is necessary to address the environmental pollution caused by the transportation of bulk materials and to realize intelligent,digital,and enclosed transportation of materials.Pneumatic conveying is a material handling technology that uses compressed air to transport bulk particles in pipelines,which is an effective measure for achieving green,safe,and convenient transportation of bulk materials.Predicting the pressure loss of a pneumatic conveying system is critical for its design and operation.In this study,the prediction model for pressure drop in pneumatic conveying was researched.Based on experimental research and numerical simulation methods such as additional pressure drop theory,computational fluid dynamics and discrete element coupling(CFD-DEM),the research aimed to investigate the variation law of pressure drop in gas-solid two-phase flow in pipelines,and carry out research on the modification of empirical formulas for pressure drop prediction models,gas-solid two-phase interaction laws,and pressure drop prediction modeling based on dimensionless numbers.Based on the Barth pressure drop theory,the pressure loss models for elbow pipes,horizontal pipes,accelerating pipes,and vertical pipes were analyzed to summarize the main factors affecting pressure loss.It was found that the pressure loss models for horizontal pipes and elbow pipes were the key points in studying the pressure loss of pneumatic conveying systems.In the Eulerian-Lagrangian coupling framework,the control equations for gas-solid two-phase were determined based on the continuity equation,momentum equation,and Newton’s second law.The Wen-Yu model,Saffman lift model,Magnus lift model,and soft sphere model were used to analyze the dynamic transfer of gassolid two-phase interactions and solid particle interactions.An experimental pneumatic conveying system was designed,and dimensional analysis was used to analyze the factors that affect the pressure drop of the pneumatic conveying system.This provides theoretical support and a methodological basis for studying the pressure drop characteristics of pneumatic conveying systems.In order to clarify the particle transport characteristics in horizontally and vertically curved pipes,on the basis of experimental verification,the coupled numerical simulation method of Computational Fluid Dynamics and Discrete Element Method(CFD-DEM)was used to study the transport patterns,velocity,mass flow rate,and the relationship between them and the change of gas phase pressure of 2.5mm diameter and 3.3mm height particles in horizontally and vertically curved pipes.The pneumatic conveying characteristics of curved pipes were analyzed from three perspectives: pressure and velocity distribution,and particle transport flow pattern.The study found that during the starting phase,the material plug in the curved pipe had an energy storage effect.Particles that were difficult to bend at one time would spontaneously form a morphologically stable material plug in the curved pipe,and continue to bend after the energy storage was completed.The sand dune flow had a small transport velocity and a high average mass flow rate,while the packed flow had a large transport velocity and a low average mass flow rate.In the stable transport phase,the pressure drop and the average particle velocity in the front and back sections of the curved pipe showed significant differences.The pressure drop in the front section was small with large fluctuations in the isobaric line,and the average particle velocity was fast.The pressure drop in the back section was large with small fluctuations in the isobaric line,and the average particle velocity was slow.The stable transport phase was not static but dynamic,and the particle velocity and mass flow rate exhibited regular fluctuations.Throughout the entire cycle of particle transport,the particle motion exhibited obvious regular changes.In the starting phase,the particles would stabilize into plugs in the middle of the curved pipe and the inlet area of the vertical pipe.As time progressed,the two material plugs would connect to form a particle accumulation zone,and the transport would enter a stable phase.In the stable transport phase,the particle flow pattern in the horizontal pipe was stable layered flow,and the particle flow pattern in the curved pipe was a stable fluctuating wave.The front section was a packed particle flow,and the back section was a particle accumulation layered flow.The particle flow pattern in the vertical pipe developed towards a suspended flow as the pipeline was extended.The experimental study of the pneumatic conveying process was carried out on a multi-functional pneumatic conveying system experimental bench built in-house,using the strategy of comparing experimental data with theoretical model calculations to investigate the pressure loss law before and after bending.It is found that: the stable conveying stage of the multifunctional pneumatic conveying experimental system can be analysed from two perspectives based on pressure signals,one direct observation method,direct observation of the pressure signal data information at the discharge port of the pneumatic conveying system,the pressure at the discharge port will reach a stable phase after the initial shock,and then smooth after another spike when the material is finished conveying,this analysis can be corroborated by the air flow data;secondly,it can be based on The second is that the stable conveying phase can be judged directly based on characteristic parameter modelling,which is a simpler method compared to the direct observation method,and can be used to classify the conveying state in more detail based on the different standard deviation data of different flow types.After the silo pump is discharged,the material needs to be stabilised by pressure and flow rate before entering the stable conveying stage;the bend pressure loss model is revised,and the revised bend pressure drop prediction model agrees well with the experimental values with an error within ±15.7%.The solid-phase friction coefficient is an important component of the pressure drop model in pneumatic conveying pipelines.Prediction models for solid-phase friction coefficient were constructed using the Froude number(Fr),solid-to-gas volume ratio(VLR),and solid-to-gas mass ratio(m*)in models 1 and 2,which were then used to predict pressure drop.Based on experimental data from a 16 m long pipeline conveying coal ash,regression analysis was used to obtain models 1 and 2 for solid-phase friction coefficient,which were then used in the pressure drop prediction model and validated in pipelines of lengths 123 m and 139 m.The study found that as Fr increased,the solid-phase friction coefficient decreased gradually,and the two were inversely proportional,with a good linear fit and an error far below 5%.As VLR increased,the solid-phase friction coefficient showed an overall increasing trend,and the effect of m* on solid-phase friction coefficient was similar to that of VLR.The system pressure drop model based on model 1 had high prediction accuracy for pipelines of lengths 16 m and 123 m,with average errors and standard errors of 6.61% and 16.22%,respectively.However,significant discrepancies were observed in the prediction of coal ash pressure drop in the 139 m long pipeline,where the prediction accuracy was high when the solid-to-gas mass ratio was below 90,with an average error of 16.85%,but the model showed significant errors in predicting pressure drop when the solid-to-gas mass ratio was above 90,with an average error of 46.8%.The pressure drop prediction results based on model 2 were similar to those of model 1,with average errors of 10.0%(123 m),16.02%(139 m,m*≤ 90),and 58.85%(139 m,m*> 90)for the above operating conditions. |
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