Research On Flow-Field Characteristics Of Pneumatic Conveying System Of Sweeping And Suction Sweeper

The pollution caused by urbanization construction,natural factors and people's daily life is increasing rapidly,which makes it inevitable to clean the road with a road sweeper.The dust absorption performance of the sweeper is directly determined by the characteristics of the flow field in the pneumatic conveying system.So it was studied in this thesis.The main work are as follows:The physical characteristics and the mechanism of the dust particles'motion?starting,suspended and settling?in the pavement were introduced.Then the law of action between the dust particles and the air flow was further understood.The relationships between the starting velocity of dust particles,the speed of suspension,the velocity of settlement and the particle size of dust particles were deduced,which provided theoretical guidance and data support for subsequent simulation analysis.The modeling process of pneumatic conveying system was introduced,the expanding area was set up around the suction nozzle by considering that the boundary condition of suction port can't be determined.The structural parameters of the expanding area were discussed in order to ensure the effectiveness and the efficiency of computation,and finally the structural parameters were determined.The influence of the transition form of the transition region on the flow field in the pneumatic conveying system was compared and analyzed.The results showed that the structure of the circular transition structure can effectively suppress the eddy current in the transition zone and improve the distribution of the flow field in the suction nozzle.The influence of the fan power on the flow field characteristics of pneumatic conveying system was studied.Then the matching between fan power and pavement cleanliness and energy saving could be realized.The L₅₀?5⁷?orthogonal test simulation was determined after the determination of the seven design variables of the pneumatic conveying system.The simulation results showed that the relationship between design variables?the pipe diameter-D,the distance between two pipes-L1,the width of the core area of the suction nozzle-B1,the height of the transition region of the suction nozzle-H₁,the shoulder height of the core area of the suction nozzle-H₂,the oblique angle of the shoulder of the suction nozzle-?1 and the oblique angle of the middle part of the suction nozzle-?2?and target variables?the average velocity of air flow in the forward gas surface of the suction nozzle-Vf,the average velocity of near ground air flow in the core area of the suction nozzle-V₀,the deviation between the average velocity of air flow in the concentration area of the inlet of the suction nozzle and V₀-?,the average velocity of air flow at the inner section of the suction pipe-V₁,the pressure drop between the near ground surface of the core area of the suction nozzle and the section of the suction pipe-?P?were complex,so it was necessary to balance the influence of design variables on target variables in order to ensure the expected values of all the target variables.Approximate models of five target variables were established by three kinds of approximate model schemes.The results showed that only the approximate model established by the response surface model satisfied the precision requirement.The combined algorithm which was made up of multi-Island genetic algorithm and sequential two times planning algorithm was determined.Then the multi-objective optimization of pneumatic conveying system was carried out.The optimization results showed that the target variables of the optimized model were optimized compared with the original model,and the minimum optimization ratio is 4.789%,the maximum is63.131%.The distribution of air distribution at the key position is even more uniform.The optimized model can absorb the sand,whose density was 3000kg/m³ and particle diameter was 30mm.Simulation results indicated that the optimization model had high reliability.The optimal design method of pneumatic conveying system?model establishment,boundary condition determination,parametric modeling,approximate modeling,multi-objective optimization and multiphase flow validation?mentioned is this thesis,can be used to guide the R&D design of pneumatic conveying system.