Abstract: When the cold recycling machine sprays foamed asphalt, asphalt is easy to accumulate at the nozzle, and the flow of each nozzle is uneven. To solve the above problems, it is necessary to increase the pressure of foamed asphalt nozzle to reduce asphalt accumulation and balance the flow of each nozzle. This article first starts from the essence of asphalt foaming behavior, and based on the multiphase flow mixing theory, considered the changes in asphalt viscosity and water state during the asphalt foaming process. The viscosity temperature characteristic function of asphalt and the phase transition function of water were introduced into the calculation model to modify the fluid volume (VOF) model and establish a control model for asphalt foaming behavior. Secondly, numerical simulations were conducted to compare the nozzle pressure and flow rate during the asphalt foaming process with experiments, and it was found that the errors of the asphalt foaming behavior control model in terms of nozzle pressure and flow rate were 9.2% and 7.7%. Finally, based on the above asphalt foaming behavior model, the numerical simulation model of foamed asphalt spraying device was constructed. According to the designed experimental scheme, the spraying process of foamed asphalt was simulated numerically. Based on the simulation results, a Kriging surrogate model was constructed on the Isight platform, and a multi-objective optimization model was established with the goal of improving outlet pressure and reducing the mass flow rate of each nozzle. The multi-objective optimization model was solved by the NSGA-II algorithm. The Pareto solution set was obtained. The optimization results were obtained by analyzing the Pareto solution set. The results show that when the asphalt pipe diameter is 0.74a, the foaming pipe diameter is 0.58b, the foamed asphalt nozzle diameter is 0.6c, and the number of foamed asphalt nozzles is d, the performance of the foamed asphalt spraying device was optimal. Under the premise of considering the characteristics of asphalt foaming behavior, the performance of foamed asphalt spraying device is improved.

Key words: foamed asphalt, spraying device, multiphase flow, VOF model, multi-objective optimization