Analysis Of Mixing Performance Of Concrete Distributor Based On Solid-liquid Two-phase Flow

In the prefabricated construction industry,the concrete distributor is the key equipment for quantitative pouring and production of prefabricated components in the concrete forming process.The concrete distributor is equipped with a mixing device,its function is to prevent the initial setting and segregation of the concrete,and to keep the concrete with good homogeneity and fluidity.This subject originated from the "13th Five-Year Plan" National Key R&D Project-the development of technology and equipment for the digital intelligent and precise distribution of complex precast concrete components(2017YFC0704003),Through the use of computational fluid dynamics numerical simulation and experimental methods to study the mixing performance of the concrete distributor,it lays the foundation for the subsequent digital intelligent and accurate distribution.The subject studied the trajectory,speed and direction of the aggregate during the mixing process of the concrete distributor,and proposed and designed the factors that affect the mixing performance(concrete homogeneity,mixing energy consumption).A solid-liquid two-phase flow model was established to better describe the homogeneity and flow behavior of concrete in the distributor.At the same time,the rheological parameters(plastic viscosity,yield stress)in the model were calibrated by the parameter calibration experiment of concrete model and the accuracy of the parameters was verified.The characterization index of concrete mixing performance is proposed and used to study the influence of mixing process factors(mixing speed,mixing time),mixing rod structure design and concrete time-varying properties on mixing homogeneity and energy consumption performance.The influence of the rotation direction of the distributor mixing rod and the height of the concrete accumulation on the mixing performance is studied,and the reasonable and optimal mixing strategy is proposed based on the comparison of the mixing performance results.The specific research content is as follows:(1)The research background and significance of the subject are explained,and summarize the research status of mixers,the research status of fresh concrete theoretical models and the research status of evaluating material homogeneity on the basis of consulting domestic and foreign related literature research.The detailed structure and composition of the concrete distributor are introduced.The simulation method is used to track the movement trajectory of the aggregate during the mixing process of the distributor to obtain the effective and inefficient areas of mixing.The factors affecting the mixing performance(concrete homogeneity,mixing energy consumption)are proposed based on the state of the mixed concrete and the homogeneity of the aggregate,and the influencing factors are designed.(2)Based on computational fluid dynamics numerical simulation and experimental methods,the theoretical model of fresh concrete is studied.First of all,a theoretical model of mortar and aggregate was established according to the composition and working performance of the fresh concrete.Then,The rheological parameters(plastic viscosity,yield stress)of the concrete model were calibrated by V-shaped funnel,L-shaped box and slump test,and verify the accuracy of the parameters.Finally,the rheological parameters of freshly mixed concrete under the influence of time-varying were analyzed.(3)The index to characterize the mixing performance of concrete distributors,namely mixing homogeneity and energy consumption,was proposed.The theoretical model based on the concrete distributor predicts the homogeneity of the concrete and the mixing power value of the mixing rod at different speeds.At the same time,the concrete distributor experimental platform was used to measure the homogeneity of concrete and the mixing power under the same working conditions to verify the accuracy of the theoretical model.Based on the verified simulation model of the concrete distributor,the mixing process factors(mixing speed,mixing time),the design of the mixing rod structure and the influence of the time-varying concrete on the mixing performance are discussed.(4)The mixing strategy of changing the rotation direction of the mixing rod and the height of the concrete accumulation in the distributor is proposed.Through the proposed mixing strategy,the law of concrete homogeneity and energy consumption changing with time under different mixing modes of the concrete distributor under the same working conditions is analyzed.By comparing the mixing performance results of different mixing strategies,the evaluation method of mixing strategy is proposed and a reasonable and optimal concrete mixing strategy is given.