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To improve the casting quality as well as the casting efficiency during the casting process, the effect of the interaction of process parameters and system structural parameters on the shrinkage volume and efficiency of the casting was investigated in this paper by using the response surface method for the simulation prediction of A356 alloy sand casting. The relationship between variables and response (shrinkage volume, solidification time) was established by Box-Behnken Design with pouring temperature (650–710 °C), mold preheating temperature (200–300 °C), width/thickness ratio of cross-section of sprue (1.2–1.5), width/thickness ratio of inner sprue section (2–4) and length/diameter ratio of straight sprue (1.5–2.5) as variables by the response surface method. The results are then optimized, and the optimal solution is selected by the NSGA-II algorithm and TOPSIS method. The results show that the changes in the cavities of the optimized and improved pouring system enhance the flow of the metal fluid and make the filling more complete. The gentle cooling of temperature is conducive to heat dissipation and layer-by-layer sequential solidification, which can effectively eliminate the casting's internal shrinkage loosening and shrinkage holes defects, thus forming a dense casting with good performance. After solving the optimized parameters and improving the pouring system, the solidification time (integrated solidification time) was reduced from 129.24 to 88.10s, and the shrinkage volume was reduced from 9.68 to 4.06 cm3. [ABSTRACT FROM AUTHOR]

To address the problem of low efficiency for manual detection in the defect detection field for metal shafts, we propose a deep learning defect detection method based on the improved YOLOv5 algorithm. First, we add a Convolutional Block Attention Module (CBAM) mechanism layer to the last layer of the backbone network to improve the feature extraction capability. Second, the neck network introduces the Bi-directional Feature Pyramid Network (BiFPN) module to replace the original Path-Aggregation Network (PAN) structure and enhance the multi-scale feature fusion. Finally, we use transfer learning to pre-train the model and improve the generalization ability of the model. The experimental results show that the method achieves an average accuracy of 93.6% mAP and a detection speed of 16.7 FPS for defect detection on the dataset, which can identify metal shaft surface defects quickly and accurately, and is of reference significance for practical industrial applications. [ABSTRACT FROM AUTHOR]

Pulsating heat pipes are widely used in cooling electronic devices, automotive radiators, refrigeration, and air conditioning systems. The addition of nanoparticles is one of the effective ways to improve the heat transfer characteristics of fluids. This paper, based on large eddy simulation (LES) numerical method and field synergy theory, investigates the heat transfer characteristics of Al2O3/Cu mixed nanofluid in a self-excited oscillating heat exchanger tube. Through multi-objective optimization of field synergy angles, field synergy factors, and structural parameters, the enhanced heat transfer mechanism of mixed nanofluids in a self-excited oscillating heat pipe is investigated. It is found that there is a significant negative correlation between the heat transfer coefficient h at the wall surface of the heat exchanger tube and the synergistic angle β. The incorporation of nanoparticles improves the synergistic properties between the velocity and temperature fields. The optimum structural parameters are L/D = 0.469931, α = 128.9904° and d2/d1 = 2.047937, and the optimization increases Nu by 1.92%, decreases f by 10.46%, and decreases the temperature synergy angle β by 2.24°. At the same time, the orthogonality or lack of orthogonality between isotherms and streamlines determines the extent of synergistic performance in the countercurrent vortex. [ABSTRACT FROM AUTHOR]

Electro-hydraulic power impulse water jets can convert the shock wave generated in the liquid by discharging into mechanical energy, and it has been widely used in material forming, surface cleaning, pipeline dirt cleaning and ore breaking process. Compared with the traditional high pressure water jets, the energy utilization of electro-hydraulic power impulse water jets is up to 80% while the water consumption is reduced by 40-55%. This paper has taken electro-hydraulic power impulse water jets as the research object, employed obtaining the maximum pressure of compression impulse matrix surface as the research goal, studied in depth the equivalent discharge circuit, characteristic equation and the relationship between the electrical parameters of the electro-hydraulic power impulse discharge circuit and built the calculation method of the voltage, the inductance, the capacitance and the electrode spacing parameter of electro-hydraulic power impulse water jets discharge circuit. So, it will provide important theoretical basis for further studies of electro-hydraulic power impulse technology and the existing water jets device. [ABSTRACT FROM AUTHOR]

To achieve efficient preparation of emulsion droplet, this paper uses a two-dimensional mathematical model coupled with the phase field model and the electrostatic field model to calculate the droplet formation in parallel flow focusing multichannel, and analyzed the effect of electric field strength on the droplet formation process. In addition, the effects of different capillary numbers and dispersed phase viscosity on droplet formation were also analyzed. The results show that the emulsion in the channel always generates droplet by dripping regime, and the droplet have the best monodispersity. Applying appropriate electric field strength can realize droplet formation frequency and size regulation. Increasing the dispersed phase viscosity increases the breakup thread of the dispersed phase fluid, and the droplet size obtained gradually decreases, the difference in droplet size can be slowed down by applying the electric field. Increasing the electrostatic force leads to a higher droplet deformation rate. The droplet shape classification is plotted using the capillary number (Ca) and electrostatic number (Ca E). It is found that the droplet flow pattern in the channel remains a circle only when Ca and Ca E are sufficiently small. [Display omitted] [ABSTRACT FROM AUTHOR]

• Numerical analysis of the performance of a new fishtail-type stirrer. • PIV experiments validate the correctness of the model. • Compared to the RT impellers, fishtail impeller reduce power consumption by 16.4 %. • Compared to the RT impeller, fishtail impellers are effective in reducing mixing times and increasing mixing efficiency. • The fishtail impeller increases the pumping flow by 13.5 % and the pumping efficiency by 27.66 % compared to the RT impeller. In this study, a new fishtail impeller was introduced to improve the mixing of fluids in the stirred tank. The validity of the numerical model was first demonstrated by PIV experiments. Secondly, the CFD technique was used to analyze and predict the flow field characteristics in the stirred tank. Also, the effect of blade inclination on the mixing effect is analyzed. Finally, a comparative Analysis with the whale tail impeller is carried out to demonstrate the superiority of this research work. The results show that The results of the study showed that the power number of the fishtail impeller was reduced by 16.4 % compared to the RT impeller. The pumping efficiency of the fishtail impeller was increased by 25.52 %. The results also show that increasing the blade inclination increases the turbulent kinetic energy in the stirred tank. Comparative analysis with the whale-tail impeller reveals that the power number of the fish-tail impeller is reduced by 17.2 % and the pumping efficiency is increased by 19.97 %. [Display omitted] [ABSTRACT FROM AUTHOR]

In this work, the self-excited oscillating pulsating circular pipe is the object of study. Based on the flow evolution characteristics of the boundary layer and vortex, the mechanism of enhanced heat transfer by self-excited oscillating pulsating flow is investigated. Moreover, a vital flow structure, the boundary vortex ring (BVR for short), is proposed. The study results show that the vortex evolution within the shear layer inside the self-excited oscillating pulsating chamber has an important influence on the formation of the downstream boundary vortex ring. Both have the same period but different phases. The boundary vortex group formed by the BVR is distributed at intervals in the pipe, and its role in promoting fluid flow increases first and then decreases. At the same time, the strength of the central mainstream area is gradually strengthened. The boundary vortex group's flow state determines the downstream pipe's heat transfer characteristics. The low-velocity zone on both sides determines the position of the heat transfer coefficient enhancement, and the central vorticity determines the amplitude of the enhancement. The boundary vortex group with a complete structure can effectively promote heat transfer, while the boundary vortex group with an incomplete structure can suppress heat transfer. The time-averaged boundary layer thickness increase ratio δ′ and the time-averaged equal diameter circular tube performance evaluation index ηT provide the fundamental indexes for designing and optimizing variable cross section heat transfer circular tubes. Furthermore, the heat transfer coefficient of the tube wall varies synchronously with the thickness of the boundary layer. [ABSTRACT FROM AUTHOR]