Mixing Uniformity And Fluid-solid Coupling Heat Transfer Performance Of Material In A Continuous Regeneration Drum With Differential Velocity

In the process of road construction and maintenance,the waste asphalt mixture produced by asphalt pavement is bound to pollute the environment and aggravate the resource pressure.Therefore,the recycling asphalt pavement(RAP)material needs to be solved urgently.The continuous regeneration technology,which has advantages in energy conservation,emission reduction and cost,has not yet been popularized.The fundamental reason is that the quality of finished materials produced by existing continuous regeneration equipment is poor.The quality of mixture is reflected in the uniformity on the one hand,and the temperature on the other hand.As the core part of the continuous recycling equipment,the recycling drum is the key to improve the mixture production quality.However,it has problems such as inefficient mixing and low mixing strength due to the structural defects of the existing recycling drum.To solve these problems,the relevant research on the regenerative drum is carried out.The research work has important theoretical significance and practical application value for improving the independent innovation ability and R&D ability of the equipment.The main research contents are as follows:According to the characteristics of continuous feeding and discharging of a continuous regeneration drum,a regeneration drum with differential velocity(DBDV)is proposed based on the existing regeneration drum(DB),which can not only prolong the mixing time of materials but also increase the movement frequency of materials.Taking DBDV as the research object,firstly,the mixing mechanism is described in detail by means of theoretical analysis,and the parameters affecting material movement in DBDV(i.e.installation parameters of the drum,geometric parameters of the mixing device,motion parameters and using parameters)are obtained.Based on the theoretical analysis of these parameters,their value range is obtained(i.e.the drum inclination is 1.68°～6.28°,the mixing blade installation angle is 33.22°～45.64°,the maximum linear speed is 16.39r/min,and the differential ratio is 2).The structural design of the differences between DB and DBDV is carried out by the theoretical analysis.Based on the previous research results,the mixing uniformity of DBDV is studied by discrete element simulation(DEM).To improve the simulation efficiency,the geometric model and motion parameters are established by the similarity theory,and the feasibility of the scaling model is verified.To ensure the reliability of the simulation results,the contact parameters used in the simulation are verified by drop test,sliding test,rolling test,double pendulum test and angle of repose test.To solve the influence of different uniformity evaluation parameters on the evaluation results,a comprehensive evaluation model based on gradation stability,mixing efficiency and dispersion is proposed,and the mixing effect of DBDV is compared with DB.The results show that the mixing uniformity of DBDV is better than that of DB.To obtain the best matching value of the research parameters when the mixing uniformity of DBDV is best,the parameter of DBDV are optimized.The parameters characterizing the mixing uniformity(gradation stability,mixing time and particle dispersion)are selected as the response values,the linear speed,drum inclination and mixing blade installation angle are selected as independent variables.The three-factor and three-level test scheme are designed by the box Behnken method,the mathematical model between response and independent variables are established by DEM and response surface method,and the reliability of the mathematical model is evaluated by analysis of variance,Then the influence of the coupling effect of independent variables on the response is analyzed.Based on the mathematical model,the multiresponse optimization method(i.e.satisfaction function)is used to optimize the parameters,and he conditions under which the mixing uniformity of DBDV is optimal,namely,the optimal parameter values(i.e.the linear speed is 0.9m/s,the drum inclination is 3.2°,the mixing blade installation angle is 45°),are obtained.And the mixing uniformity of DB and DBDV under the optimal parameters is compared.The results show that the mixing uniformity of DBDV is 13.55%higher than that of DB when the grading stability,mixing time,and dispersion of particles of different sizes in the mixture are comprehensively considered.On the premise of ensuring the optimal mixing uniformity of DBDV,the mixed heat transfer of materials in DBDV is studied.The heat transfer process of materials is theoretically analyzed.and the heat transfer of particles in DBDV is carried out by using fluid-solid coupling simulation technology(CFD-DEM).To improve the efficiency of coupling simulation,the similarity theory of fluid flow and heat transfer is analyzed,and the feasibility of the fluid similarity ratio is verified.The motion parameters and model of fluid are established by using this similarity theory.Analyze the change of temperature field under the coupling effect of particles and fluid,analyze the influence of fluid speed,RAP material proportion and aggregate temperature on particle heating temperature.It is obtained that the formula between the material temperature and regeneration ratio and the regeneration rate of DBDV(i.e.38.91%～51.72%)are obtained,which provides a basis for whether the material temperature produced by DBDV meets the engineering requirements.Finally,a prototype was made based on the designed DBDV,and an experimental platform is built.The experiments of mixing uniformity and material heat transfer in DBDV are carried out to provide strong support for the reliability of simulation.Then,the temperature data of finished materials produced by intermittent regeneration equipment are collected through field experiments,and the temperature of the material produced by DBDV and intermittent regeneration equipment is compared.It was obtained that the heating the aggregate to a lower temperature in DBDV can achieve the material temperature equivalent to that of the intermittent regeneration equipment,so as to lay a foundation for the development of continuous regeneration equipment.