Influence of Frictional Stress Models on Simulation Results of High-Pressure Dense-Phase Pneumatic Conveying in Horizontal Pipe

Based on the two-fluid model, a three-zone drag model was developed, and the kinetic theory of granular flows and the Schneiderbauer solids wall boundary model were modified to establish a new three-dimensional (3D) unsteady mathematical model for high-pressure dense-phase pneumatic conveying in horizontal pipe. With this mathematical model, the influence of the three frictional stress models, namely Dartevelle frictional stress model, Srivastava and Sundaresan frictional stress model, and the modified Berzi frictional stress model, on the simulation result was explored. The simulation results showed that the three frictional stress models accurately predicted the pressure drop and its variations with supplementary gas in the horizontal pipe, with relative errors ranging from −4.91% to +7.60%. Moreover, the predicted solids volume fraction distribution in the cross-section of the horizontal pipe using these frictional stress models exhibited good agreement with the electrical capacitance tomography (ECT) images. Notably, the influence of the three frictional stress models on the simulation results was predominantly observed in the transition region and deposited region. In the deposited region, stronger frictional stress resulting in lower solids volume fraction and a higher pressure drop in the horizontal pipe were observed. Among the three frictional stress models, the simulation results with the modified Berzi frictional stress model aligned better with the experimental data. Therefore, the modified Berzi frictional stress model is deemed more suitable for simulating high-pressure dense-phase pneumatic conveying in horizontal pipe

The short-term aging effect on the interface and surface wetting behavior of modified asphalt mixtures

In this study, the interface models and nanodroplets wetting models of base asphalt (BA), polyurethane modified asphalt (PU-MA) and polyurethane/graphene oxide composite modified asphalt (PU/GO-MA) with acidic and alkaline aggregates were constructed. The adhesion and debonding effects of modifiers on short-term aged asphalt mixtures were analyzed by molecular dynamics (MD) simulation. The moisture damage resistance of the mixture was evaluated by simulating the wetting characteristics of asphalt and water nanodroplets on the aggregate surface. The contact angle, adhesion work, debonding work and relative concentration distribution can effectively analyse the interface interaction behavior between asphalt and aggregate. The results show that the adsorption effect between aged asphalt and CaCO _3 was stronger, and short-term aging enhanced the interfacial adhesion of asphalt mixtures. Calcite was more hydrophilic, and its resistance to moisture damage was far less than quartz. The difference between the contact angle of water-aggregate and that of asphalt-aggregate can effectively analyze the water sensitivity of asphalt mixture. In addition, different components played different roles in the adsorption of asphalt and different aggregate surfaces. The synergistic analysis of the asphalt-aggregate interface and the asphalt nanodroplet-wetting aggregate surface can more comprehensively reveal the variation principle of asphalt parameters and nanoscale properties of asphalt mixtures