Research On Heating Eefficiency And Temperature Field Prediction Of Hot Air Heating For Asphalt Pavement

The technology and equipment for hot in-place recycling of asphalt pavement originated in Europe and the United States in the 1970 s,and its application in China began in the 1990 s.At the beginning of this century,the practice of hot in-place recycling projects has been carried out throughout the country.With the continuous in-depth research on hot in-place recycling technology and equipment,it has been more and more widely used in recent years due to its100% recycling of old asphalt pavement materials,less damage to aggregates,low construction costs,and little impact on traffic.At present,hot in-place recycling heating technology of infrared heating accounts for 20%,hot air heating 70%,microwave and others 10%.Hot air heating has become the mainstream of the hot in-place recycling equipment at home and abroad and is the preferred way of the hot in-place recycling technology.How to improve the heating efficiency of the hot air heating equipment,reduce fuel consumption and reduce construction costs has become the focus of domestic and foreign scholars.In this dissertation,the heating wall of in-situ hot air heater is taken as the research object,the hot air heating efficiency of asphalt pavement was studied based on jet impingement heat transfer model,analyzed the influence of the structural parameters of the hot air heating plate and heating parameters on the temperature field distribution and heating efficiency,and the sensitivity of the parameters,and optimized the parameters.The prediction model of asphalt pavement temperature field was established,and the accuracy of the model was verified by field tests.The main research contents and achievements are as follows:A heat transfer model of hot air jet impingement on asphalt pavement was established.The flow characteristics of hot air heating array jet impingement and the influence of convection heat transfer on asphalt pavement heat transfer were analyzed.The coupling interface is used as the internal calculation area to solve the problem that the traditional asphalt pavement heat transfer model equates the role of heating mode with the model heat flow boundary,which leads to the inaccurate description of hot air flow and heat transfer dynamic changes in the asphalt pavement heating process.The correctness of the model was verified through experiments.Based on the three-dimensional model of asphalt pavement heating by hot air,the influence of the structural parameters of hot air heating plate on asphalt pavement heating uniformity and heating speed and the sensitivity of each parameter were studied.Under the same heating power and environmental conditions,the heating uniformity index decreases first and then increases with the increase of the opening ratio and the nozzle diameter.The heating speed increases with the increase of the nozzle diameter,and decreases with the increase of the opening ratio,and the sensitivity of the nozzle diameter is the largest.The evaluation method of hot air heating speed and heating uniformity of asphalt pavement was proposed,and the structural parameters of hot air heating plate were optimized.The research results provide a basis for the design and manufacture of hot air heating equipment.The heating efficiency model of asphalt pavement with hot air was established based on the response surface method,and the influence law of hot air heating parameters and their coupling conditions on the heating efficiency was studied.The hot air heating parameters were optimized by using the desirability function method and improved genetic algorithm.The decrease of hot air temperature and velocity and the increase of the height of the heating plate from the ground are conducive to reducing the effective energy,and the hot air temperature and velocity have a coupling effect on the effective energy.At a higher hot air temperature,the effective energy is more sensitive to the height of the heating plate from the ground.The increase of the hot air temperature is conducive to improving the energy utilization rate,and the increase of the hot air velocity and the height of the heating plate from the ground will reduce the energy utilization rate,and the two parameters have a strengthening effect.When the height of the heating plate from the ground is small,the energy utilization rate is more sensitive to the hot air velocity.The research results provide a basis for setting the heating parameters of the hot air heater.A prediction model of temperature field of asphalt pavement heated by hot air based on the proper orthogonal decomposition(POD)method was constructed.The high-order temperature field sample library under different working conditions was established by numerical simulation method.The POD basis function of the temperature field was extracted by singular value decomposition,and the coefficients of the POD basis were obtained by radial basis function interpolation method to complete the establishment of asphalt pavement temperature field prediction model.The prediction time is only 11.23% of the numerical calculation time,and the calculation efficiency is greatly improved.Under the condition of variable power heating by hot air heater,the relative error between POD prediction solution and numerical simulation result of asphalt pavement temperature field is 8.96%.The accuracy of the jet impingement heat transfer model and the asphalt pavement temperature field prediction model in the hot in-place recycling was verified through the onsite experiment of asphalt pavement hot air heating.The engineering application example shows that the heating efficiency of the optimized hot air heater is significantly improved.Compared with the original hot air heater,the fuel consumption per unit area of the optimized hot air heater is reduced by 10.53%.The research results provide an important reference for the design of hot air heating equipment and on-site construction of hot in-place recycling.