Iranian Journal of Science and Technology-Transactions of Mechanical Engineering最新文献

In the process of strip rolling, mill vibration induces vertical and horizontal displacements in the rolls and rolled parts, affecting the accuracy of the rolling analysis model. Constant changes occurred in the rolling zone between the upper and lower working rolls due to mill vibration, resulting in slight vertical and horizontal displacements of the rolled pieces. These displacements, subsequently, affected the precision and accuracy of the rolling analysis model. A dynamic rolling force optimization model was established in this paper based on the Karman differential equation, metal flow equation, and mixed lubrication friction model. This model took into account the small displacements in both vertical and horizontal directions of the rolled parts, effectively addressing the issue of rolling area variation. A vertical–horizontal coupling vibration model for the cold rolling mill was developed, employing the dynamic rolling force model and lumped mass method. The accuracy of the dynamic rolling force model was validated, and a comprehensive examination of the vibration mechanism of the rolling mill, including exploration of suppression methods, was conducted. The amplitude-frequency response of the coupled vibration system was determined using the multiple scales method, and the effects of external excitation and mill structure parameters on the coupled vibration characteristics were analyzed. The results indicated that the dynamic rolling force optimization model had considered the variations in rolling parameters and could explore the complex vibration patterns of the rolling mill itself from the perspective of varying rolling parameters, effectively addressing the issue of rolling region changes. Furthermore, it exhibited high precision in analyzing vertical and horizontal coupling vibrations in the rolling mill. The simulation results indicated that the primary cause of distance vibrations between the rollers was internal resonance triggered by similar external excitation frequencies and derived frequencies coupled in both vertical and horizontal directions. This was subsequently followed by the movement displacement of the hydraulic cylinder piston and changes in coupling parameters, which had a significant impact on the amplitude and resonance region of the vibration system.

The substantial rise in atmospheric pollutants attributed to the use of fossil fuels has driven the development of renewable energy sources as a burgeoning industry. Subsequently, amidst the ongoing quest for sustainable energy sources, wind energy has emerged as a reliable alternative. This has resulted in the development of various types of wind turbines. One of the most common types of vertical axis wind turbines is Savonius VAWTs. Despite possessing advantages, these turbines are less efficient compared to others. However, this shortcoming can be remedied by enhancing the aerodynamic performance of the turbines. This two-dimensional study examined the impact of placing an external object as a control rod at the rotor upstream or on the suction side by computational fluid dynamic methods. The rod was designed with circular, oval, dimpled, and bumpy cross-sections. The study evaluated different stagger angles for various diameter and distance ratios. The results showed that using a circular cross-section at a stagger angle = 30°, S/D = 1.5 and D/d = 2 increased efficiency by 40%. Implementing an oval cross-sectional design with stagger angle = 60° and S/D = 1 enhanced the rotor's efficiency to 90%. Using a bumpy cross-section yielded a jump in efficiency and expanded the operating range of the Savonius VAWT up to a tip speed ratio of 0.8.

With the continuous development of the economic society, there is a growing demand for higher power density in motors, which has made motor heat dissipation issues increasingly prominent. Excessive motor temperature can lead to various problems such as geometric deformation, increased losses, insulation aging, and demagnetization of permanent magnets, all of which severely impact the performance and safety of the motor. Developing efficient and reliable thermal management technologies for motors is crucial for improving motor efficiency, durability, and safety. Building on previous research, this paper provides a comprehensive summary and analysis of the current state of thermal management technologies for motors, going beyond specific types of motors. Firstly, it outlines commonly used thermal analysis methods such as lumped parameter thermal network, finite element method, and computational fluid dynamics. The challenges encountered during the thermal analysis process are also discussed. During thermal analysis, the accuracy of the winding equivalent methods, the convective heat transfer coefficient and the contact resistance directly and greatly affect the precision of the thermal analysis. Therefore, it is crucial to prioritize in-depth discussions regarding these factors to ensure accurate thermal analysis. Based on this foundation, the development and research status of motor thermal technology including air cooling, water cooling, oil cooling, and evaporative cooling is further explored. Oil possesses good insulation performance and corrosion resistance, enabling direct contact with heat sources. Consequently, oil cooling exhibits superior heat dissipation efficiency, addressing the thermal management challenges in high-power density motors. Special emphasis is given to summarizing and analyzing oil cooling technology. Additionally, the influence of phase change materials, encapsulation materials, and heat conduction plates on motor cooling efficiency is discussed. In conclusion, it is hoped that the contents of this paper will provide valuable guidance and reference for future research in thermal management technologies for motors.

To address the issue of incompatible nodal parameters between finite elements of different dimensions, this paper introduces a new interpolation formula, named “trial-correction” displacement interpolation, utilizing trilinear and cubic interpolations. This interpolation method is applied to construct an 8-node hexahedral solid element (Solid-H8-TC) with rotational degrees of freedom, featuring 6 nodal parameters including 3 translational and 3 rotational displacements. The element successfully passed the patch test and demonstrated convergence. Subsequent numerical examples show that the Solid-H8-TC element achieves a numerical accuracy of over 99% as the mesh is refined. Furthermore, the Solid-H8-TC element can be directly combined with shell elements, effectively resolving the compatibility issues of nodal parameters between finite elements of different dimensions. Lastly, the trial-correction displacement interpolation method employed in this study exhibits excellent scalability and provides a new theoretical basis for finite element analysis of plane, beam, and shell structures.

In the process of gas granulation of blast furnace slag, a cyclone separator serves to cool slag particles and separate them from hot air. This study focuses on modelling the cooling of slag particles in a cyclone separator. Simulations revealed the airflow field, temperature field and particle trajectory distribution within the cyclone separator. Key parameters such as particle size, flow rate, and air velocity were examined for their influence on operational parameters. The findings indicate that air and particles in the cyclone move around the wall, with lower air velocities and temperatures in the central region and higher values near the wall. In the range of inlet air velocity of 15–20 m/s, particle size of 1–5 mm, and particle flow rate of 1–9 kg/s, increasing the inlet air velocity, reducing the particle size, and decreasing the particle flow rate prolongs the particle residence time in the separator by about 3 s, reducing the exit temperature and enhancing the waste heat recovery efficiency. The overall waste heat recovery efficiency of the particle population can reach more than 60%. An orthogonal parameter table was employed to analyse the influence of these factors. The hierarchy of effect on temperature reduction was found to be particle size > slag flow rate > inlet airflow velocity > initial temperature of the slag particles. Finally, the equation correlating the waste heat recovery efficiency with the dimensionless number was derived, with a maximum deviation of 5.41% from the simulation results.

Abstract

This study focuses on exploring the natural convection heat transfer within water-alumina nanofluids and its practical applications in immersion cooling. The aim is to improve the efficiency of this cooling method by utilizing fluids with improved thermal properties. The selected geometry is a vertical cylinder, which is of great significance in engineering applications and academic research. The used nanofluid consists of ({{text{Al}}}_{2}{{text{O}}}_{3}-{text{water}}) nanofluid, with varying volume fractions (0.1, 0.2, and 0.5%). Experimental assessments were carried out using a steady-state methodology. Numerical simulations employ the single-phase and two-phase mixture approaches. The results of this research reveal the impressive accuracy of the mixture method in simulating external natural convection when compared to concurrently obtained experimental data. Furthermore, in the present paper, the single-phase method has yielded results deemed acceptable and closely aligned with the outcomes from the two-phase method. This alignment was achieved through the utilization of appropriate relationships, ensuring the accurate estimation of thermophysical properties. Notably, it becomes evident that established correlations for the Nusselt number correlation of natural convection designed for conventional fluids and the mere incorporation of the thermophysical properties of nanofluids are insufficient for the accurate prediction of the Nusselt number for nanofluids. In response to this challenge, a novel Nusselt correlation is introduced, comprehensively considering the thermophysical properties of ({{text{Al}}}_{2}{{text{O}}}_{3}-{text{water}}) nanofluids, nanoparticle transport mechanisms, geometric attributes of the studied object, and nanoparticle volume fraction. Comparative assessments with previous correlations emphasize the enhanced predictive accuracy of the proposed innovative correlation.

In this paper, a set of generalized nonlinear equations of motion for spinning Timoshenko shafts is derived using the concept of a geometrically exact approach. In order to investigate the primary resonance of the shaft, the multiple scale method is applied to the discrete equations of motion. In this study, the effects of shear deformation, rotary inertia, gyroscopic terms, and linear damping were considered. To show the advantages of the Timoshenko models, a comparison is made between the results of Timoshenko and classical models. As a result, it can be seen that in the Timoshenko model, the amplitude of the vibration is directly related to the slenderness ratio of the shaft. Also, linear and nonlinear shear terms can affect the primary resonance of spinning shafts and their effects are more noticeable in higher vibrational modes.

This study investigates the impact of memory on anisotropic visco-thermoelastic media using a novel three-phase-lag (3PHL) model. The Fourier–Laplace transform is applied to obtain the characteristic equations for phase velocity, specific loss, attenuation coefficient, and penetration depth of viscous waves. The validity of the proposed model is evaluated by comparing it with previously published results. The outputs show the coupling between phase velocity, specific loss, attenuation coefficient, and penetration depth changes with time delay parameters, illustrating the effect of memory in this 3PH model. A thorough analysis of the linear kernel function was also conducted. Additionally, the presence of several kernel functions reveals significant differences in this visco-thermoelastic medium. Numerical calculations were performed on poly-methyl material due to its high thermal conductivity, low thermal expansion coefficient, high glass transition temperature, and good creep resistance. Mathematica software is used to generate two-dimensional and three-dimensional graphical results. The author believes that this study will be useful for wave-based technologies such as ultrasonic devices and energy harvesting technologies to design more efficient models.

This experimental study investigates the effects of TiO₂ nano-particles on the cooling and tribological performance of a vapor compression refrigeration system running on R134a as refrigerant and polyolester oil (POE) as lubricant. Dynamic light scattering analysis was conducted to observe the dispersion of the nano-particles. The heat transfer rate in the evaporator and condenser was taken into consideration to observe the cooling performance of the system charged with combination of 0.1 vol% and 0.5 vol% TiO₂ incorporated nano-refrigerants (R0.1 & R0.5) and 0.1 vol% and 0.5 vol% TiO₂ incorporated POE nano-lubricants (P0.1 & P0.5). Coefficient of friction and wear rate analyses were also performed on the piston ring of the compressor by immersing the samples in two different lubricants (P0.1 & P0.5). The compressor’s suction-discharge characteristics were assessed to determine the impact of the nano-fluid combinations. Scanning electron microscopy was used to examine the morphology of the nano-particles and worn surfaces. Atomic force microscopy was utilized to observe the structure of the worn substrates. The chemical composition of the worn surfaces was analyzed using energy-dispersive X-ray and the thermal stability of the nano-additives was ascertained via thermogravimetric analysis and differential scanning calorimeter. The best cooling and tribological performance results were obtained when the system was run on a combination of R0.5 + P0.1. Compared to standard conditions (R134a + POE), the highest increase in COP was 35.86% for R0.5 + P0.1. With the same combination, the cooling time was reduced by 22.25% and the highest decrease in the average coefficient of friction was 8.02% for 0.1 vol% of TiO₂ incorporated POE lubricant (P0.1).

This paper presents a method to establish a mathematical model of non-circular gear tooth surface, which can avoid the issues of low accuracy and low efficiency in extracting tooth surface of previous non-circular gear tooth surface design methods. A new tooth envelope method is proposed, where the gear inserting knife rotates only on a fixed axis, while the non-circular gear rotates and translates in the horizontal plane. By utilizing the conjugate theory and coordinate transformation theory, the coordinate system, meshing equation, and tooth surface equation of the non-circular gear are obtained, and the 3D point cloud of the tooth surface is programmed. Finally, the mathematical model of the tooth surface proposed in this paper is used to establish multiple pairs of non-circular gears with different orders, and the correctness and generality of the method are verified by comparing the simulated and experimental transmission ratio with the theoretical transmission ratio in the test.