In recent years, nanobubble technologies have drawn great attention due to their wide applications in many fields of science and technology. From previous studies, a kind of honeycomb structure for high efficiency nanobubble generation has been proposed. In this paper, the numerical simulations of bubbly flow in the honeycomb structure were performed by using a computational fluid dynamics–population balance model (CFD-PBM) coupled model. The numerical model was based on the Eulerian multiphase model and the population balance model (PBM) was used to calculate the bubble size distribution. The bubble size distributions in the honeycomb structure under different work conditions were predicted. Two different drag force models (Schiller-Naumann model and Tomiyama model) and two different aggregation models (Luo model and turbulent aggregation model) were investigated. Both two drag models gave similar prediction of bubble number density distribution at the outlet. The results obtained from Luo model had better reflection of the trend of number density distribution. The turbulence dissipation rate ε can be used to evaluate the nanobubble generating ability. The water tank was not included in the CFD model in this work. The bubbles in the water tank should be studied in the future.

In this study, tightening and untightening experiments were conducted for pitch difference nuts toward realizing good anti-loosening performance. By applying the three-dimensional FEM, the relationship between the tightening force F and the tightening torque T was clarified by varying the pitch difference α during the whole nut tightening/untightening process. The well-known F-T formula available for tightening the normal nut (α = 0) agrees with the FEM results and the F-T formula for untightening the normal nut (α = 0) was newly proposed. Then, the loosening resistance ability of the pitch difference nut was clarified focusing on the untightening in comparison with the normal nut.