AUT Journal of Mechanical Engineering
Year:2024 | Volume:8 | Issue:2|Papers Count:7

This article presents a comprehensive approach to enhance heat transfer rates in a 3D channel using Ferrofluids. The study investigates the individual and combined impacts of rectangular winglet vortex generators and magnetic fields on flow characteristics, heat transfer enhancement, and entropy generation. Numerical solutions are derived for the governing partial differential equations using the finite volume technique and the SIMPLE algorithm. The investigation assesses the influence of key parameters, including the type of rectangular winglet vortex generator (simple, concave, and convex), Reynolds number, and magnetic field strength. Optimal operational conditions are identified based on thermodynamics' first and second laws. This study has been conducted in three steps, and the interaction of created vortices and their effect on heat transfer, pressure drop, and entropy production were investigated. In the first step, the effect of the vortex generator in different Reynolds has been investigated. In the next step, the impact of applying a magnetic field at different intensities by a current-carrying wire has been studied in a channel without vortex generators. Finally, the application of vortex generators and magnetic fields has been investigated simultaneously. The results showed that using the concave vortex generator in the absence of a magnetic field increased the heat transfer by 50% and pressure drop by 60%. Applying a magnetic field in the channel without vortex generators has increased heat transfer and pressure drop by 70% and 118%, respectively. Moreover, it is observed that the magnetic field induces a greater pressure drop penalty than the vortex generator for achieving the same heat transfer augmentation. The simultaneous application of magnetic field and vortex generator has also increased the heat transfer and pressure drop by 200% and 269%, respectively, for simple vortex generators.

In the present work, an experimental study of the thermal gradient effect on the reverse osmosis process is performed to evaluate pure water penetration and water production under the effect of the temperature gradients and the salt concentration. The experimental study uses a novel experimental setup designed and built for the present work. The Reverse Osmosis membrane was used in the experimental setup. The results showed that this process is dependent on salt concentration and temperature gradient between permeate-water and saline-water sides. It is observed that in 10. 8o C temperature difference between the permeate-water and the saline-water part for 1 gr/lit salt concentration at saline-water part, the Process time is 20 min, water flux is 0. 142 kg/(m2 s) and salt concentration in the saline-water part varies from 1. 04 gr/lit to 1. 22 gr/lit. In addition, for a 1. 5o C temperature difference between the permeate-water part and the saline-water part for 1 gr/lit salt concentration at the salinewater part, the Process time is 35 min, water flux is 0. 043kg/(m2 s) and salt concentration in the salinewater part varies from 1. 004 gr/lit to 1. 059 gr/lit. It can be concluded, that while the temperature gradient increases, the Process time decreases, and pure water penetration from saline-water to permeate-water part also increases. As a result, the salt concentration and electrical conductivity can increase in the saline-water part.

The small distance between two rotating shafts can disturb them, cause interference in their performance, and affect the system's efficiency. The application of the counter-rotating double shafts has some specific benefits. For example, these shafts can be used under the water to neutralize the driving torque effect, prevent the submarine's self-propulsion, and increase the submarine's power to move forward and maneuver. The aim of this study is designing an optimum viscoelastic vibration absorber for a Counter-Rotating Double Shaft to deal with the vibration. In order to overcome vibrations, Viscoelastic cylinders are modeled as distributed spring and damper which are considered between the two shafts, and their vibration equations are obtained. Optimal position and distributed stiffness and damping coefficients are determined using a particle swarm optimization algorithm. The objective function to be minimized is defined as the relative distance between shafts which is controlled by Equivalent stiffness and damping coefficients of considered viscoelastic vibration absorber. The present results show that applied viscoelastic polymer with the nearest features to the optimum values can drastically decrease the relative distance between shafts and absorb the vibration of rotating shafts.

This study investigates the evolution of bubble shape within a square area filled with blood. The accuracy of the numerical solution is validated using Laplace's problem and the free-rising of the bubble. The analysis is conducted in two dimensions and in a transient manner. The effects of ultrasound waves are applied as a function of pressure on the boundaries of the solution domain. Results show that applying a linearly increasing pressure on the computational domain boundaries causes a reduction in bubble radius. Furthermore, it is observed that assuming the air inside the bubble behaves as an ideal gas, leads to more pronounced changes in bubble radius compared to constant density assumptions. Oscillatory pressure distributions on the external boundaries result in corresponding oscillations in bubble radius. These fluctuations in bubble size could be utilized to exert tension on the walls of blood clots, ultimately aiding in their dissolution. The most intensive bubble size fluctuations occur in the frequency of 1 (MHz). Additionally, the disproportionate changes in bubble radius with pressure variations are attributed to the hysteresis phenomenon.

Applying heat sinks as extended surfaces plays a significant role in cooling various industrial equipment. This study investigates the impact of heat transfer parameters of fins, such as practical geometry, wall heat flux, coolant velocity, and the angle at which the coolant flow interacts with the fin. The geometry of the fins includes rectangular and triangular shapes, with a heat flux range of approximately 4. 6-18. 5 kW/m2, coolant velocities ranging from 1-2 m/s, and angles of 0º, 45º, and 90º between the fin position and cooling flow direction. Aluminum, known for its high conductivity, was chosen as the material for the fin structure, with air serving as the primary cooling flow. The study found that triangular fins exhibited a higher convective heat transfer rate than rectangular fins, approximately 47. 4% higher on average across all conditions. However, rectangular fins dissipated heat from the wall more effectively. Pressure drop was assessed by comparing cooling flow velocities associated with each fin in various positions. Results revealed that the sharp tip of triangular fins reduced the vorticity effect, increased average flow velocity, and decreased pressure drop. Additionally, rectangular fins were approximately 10. 4% more efficient on average than triangular fins. The study also concluded that the impact angle had a negligible effect on the efficiency of both rectangular and triangular fins.

The last stage blade rows of modern low-pressure gas turbines are subjected to high static and dynamic loads. The centrifugal forces primarily cause the static loads due to the gas turbine's rotational speed. Dynamic loads can be caused by stationary gas forces, for example. A primary goal in designing modern and robust blade rows is to prevent high cycle fatigue caused by dynamic loads due to synchronous or non-synchronous excitation mechanisms. Damping elements are one of the most common structures to alleviate excessive vibration amplitudes in turbomachinery applications. This paper deals with fracture investigations of the gas turbine blade of a 15 MW Gas injection station in the national Iranian South oil company in the southwest of Iran. Macroscopic and scanning electron microscopy images of the fracture section of the tube show two phenomena erosion and fatigue. Therefore, to more accurately identify the cause of the failure, stress and vibration analysis of the blade is performed individually and coupled with other blades by the connecting tube using ANSYS software. To validate finite element results, the modal test of a single blade and group of blades is done. According to the observation of fatigue at the section of the tube failure and the possibility of error in the design, the sensitivity measurement of the diameter and installation position of the tube is done.

In recent years, there has been a rise in the popularity of using data-driven artificial intelligence models for detecting faults in rotating machinery. The challenge lies in creating a model that can be used even when sensor data is not available and the operating conditions differ from those observed during development. This article addresses the issue of potential failures in gear, bearing, and shaft components and suggests two strategies-adjusting entry and cost functions-to address these challenges in developing a one-dimensional convolutional neural network model. These strategies enable the model to extract features from the input signal with minimal dependency on operating conditions. By analyzing the 2009 PHM (Prognostics and Health Management Society) challenge competition dataset, the model achieved its highest accuracy by using the frequency spectrum of velocity and acceleration from vibrational signals. The model’s average accuracy for signals recorded by any arbitrary sensor is 79. 6%, even if some operating speeds were not observed during training. Incorporating a suggested penalty function based on p-value into the cost function increased accuracy by up to 13. 6%. Consequently, implementing the proposed strategies in similar cases is highly recommended, as demonstrated by successful application in two industrial cases.