Journal of Computational and Applied Research in Mechanical Engineering
Volume:13 Issue: 1, Summer-Autumn 2023

In this article, an extracorporeal membrane oxygenator (ECMO) is simulated in 2D geometry using computational fluid dynamics (CFD). Momentum and mass transport equations were solved for the laminar flow regime (30 < Re < 130 for the blood channel) using the finite element method. In this study, the software COMSOL was used as the solver. To this end, the main problem of ECMO devices is the pressure drop and the risk of thrombus formation due to blood stagnation, so to solve this problem, the oxygen transfer rate to the blood should be increased. Therefore, in the present study, to optimize the oxygen transfer rate of the blood, three basic parameters were examined: blood flow velocity, oxygen velocity, and membrane thickness. Blood flow was considered at five different velocities (0.2, 0.4, 0.5, 0.6, and 0.8 mm/s). Results showed that increased blood flow velocity adversely affected oxygen permeability, increasing oxygen permeability from about 60% at 0.2 mm/s to about 24% at 0.9 mm/s. In addition, five different membrane thicknesses (0.04, 0.06, 0.08, 0.2, and 0.3 mm) were investigated, and, as expected, better oxygen exchange occurred as the membrane thickness decreased. We also found that the diffusion rate is about 40% for the 0.4 mm/s thin films and about 25% for the same inlet velocity and larger film thickness. Furthermore, the oxygen diffusivity increases from 28% to 38% as the oxygen gas velocity increases. However, oxygen velocities above 0.8 mm/s should not be used, as the range of oxygen diffusivity variation decreases with higher oxygen gas velocities.

Arterial embolism is one of the major causes of brain infarction. Investigating the hemodynamic factors of this phenomenon can help us to get a better understanding of this complication. The carotid artery is one of the primary tracts that emboli can go toward the brain through it. In this study, we used a 3D model of the carotid bifurcation, and two geometries, elliptical and spherical, were considered for the clots. Hyperelastic and visco-hyperelastic models were used for the mechanical properties of clots. The governing equations of the fluid are Navier-Stokes and continuity equations and have been solved in an Arbitrary Lagrangian-Eulerian (ALE) formulation through the fluid-structure interaction method. The hemodynamic parameters of fluid and shear stress on the wall of the carotid artery were calculated. Besides, by using ADINA software, the effective stress (Von Mises stress) of the clots and the shear stress created on them were evaluated as well. Results revealed that the elliptical clot has more effects on the hemodynamic parameters of the fluid, and the mechanical property of clots has significant effects on the amount of stress created on the clots. Also, clot fracture will not occur due to the point that the maximum effective stress in this study was 1819 Pa but the creation of crack in clots is more probable, and this probability is more for the elliptical clot.

This research proposes a general formula for implementing in the control system of a dry-jet wet spinning machine to achieve a specific diameter size for Polysulfone hollow fibers. By employing Taguchi method, the effect of the operation parameters on the fiber geometry is investigated. The findings emphasize the significance of various fabrication parameters in determining the inner diameter (ID) and outer diameter (OD) of the hollow fibers. To mathematically predict the ID and OD, a first-order equation is developed using the least squares method. The accuracy of the proposed equation is validated through a series of experiments, where the ID and OD of the produced hollow fibers are determined using cross-sectional images by a scanning electron microscope. The results demonstrate a strong agreement between the proposed equation and the experimental data, with a maximum error of less than 7%. This research offers a valuable tool for optimizing hollow-fiber spinning plants and holds promise for improving their overall performance.

The reliability of manufacturing systems modeling and analysis is a complex process. Usually, their behavior is similar to multi-state systems. The configurations of such systems, possibly with load sharing and other structural dependencies, are designed to provide high reliability/availability. Consequently, this scheme can help companies to improve efficiency and reduce operating costs. Maintenance and part replacement are implemented during operation and utilization to keep their performance. Decision-making about spare ordering is difficult because of the interconnection between spare parts inventory and maintenance strategy. In this paper, the characteristic parameters of spare parts inventory management and maintenance policies are jointly considered for multi-machine systems (manufacturing systems) with different types of dependencies among them (economic, load-sharing, and multi-state configuration). Two maintenance policies are considered: condition-based and preventive maintenance. The interactions between maintenance policies and spare parts management are considered for determining a manufacturing system’s cost and availability. The influence of these factors is investigated. Load sharing factor and ordering time are more important, and their influence is higher than others.

This study focuses on the flow and pressure fluctuations of a fixed displacement radial piston pump with a valve plate with silencing grooves, and the effect of the number of pistons (5, 6, and 7) is investigated. Over the manifolds of the pump, valve plate silencing grooves are regarded as Top Dead Center and Bottom Dead Center. The mathematical modeling is run in MATLAB Simulink. Analyzing the flow characteristics and volumetric efficiency of the pump with and without silencing groove valve plate configuration of the pump is done. The opening and closing area pattern of the kidney port is also analyzed. The percentage reduction of flow and pressure fluctuation with the silencing groove is 19% and 16.16%, respectively, for Z = 7, as compared to the model without silencing groove valve plate. The volumetric efficiency of the model with silencing groove valve plate is improved from 1% to 2% as compared to the model without silencing groove valve plate. The lower the flow and pressure fluctuation coefficients, the higher the flow rate and volumetric efficiency of the pump for the model with silencing groove valve plate.

In the present study, the effect of the heating pipe profile on natural convection in a two-phase fluid inside a cavity has been investigated. This geometry has been simulated with the LB Method based on the D2Q9 model for analyzing stream lines, dimensionless velocity field of fluid flow, solid particles volume fraction, temperature arrangement, and Nusselt number. These parameters have been studied in three different cases of the cavity. The results are signified by changing the geometry from a horizontal ellipse to a circular one and a vertical ellipse;the maximum particle volume fraction is decreased. Also, by changing the geometry from a horizontal ellipse to a circular and vertical ellipse, larger velocity vectors have been formed around the geometry. The Nusselt number variations of circular and  vertical ellipse geometries are from 90⁰ to 270⁰. The Nusselt number variation of horizontal ellipse geometry is negligible from 90⁰ to 270⁰.  Also, the Nusselt number of the circular geometry is larger than the other geometries from 270⁰ to 90⁰. The highest average Nusselt number belongs to circular, vertical and horizontal ellipse geometries, respectively.

A thermodynamic evaluation is conducted on a combined heat and power system integrating a gas turbine (GT), a heat exchanger (HX1), and an organic Rankine cycle (ORC). Traditionally, ORC bottoming GT cycle is limited to mechanical power production. The novelty of this study is to recover wasted heat from the GT cycle in multistage, which is used for the simultaneous production of mechanical power and hot water supply. In the first stage, the HX1 recovers heat from the GT cycle compressed air to heat the water stream. In the second stage, the ORC cycle recovers thermal energy from the GT turbine exhaust stream to produce extra mechanical power with the remaining latent heat used to heat the water. Two models are proposed for comparison using ASPEN Plus software linked with the RAFPROP database. The modelled GT, in this study, is adopted from an actual machine. The steady-state results show that the combined system achieves 51.55% thermal efficiency compared with a standalone GT efficiency, which is only 21%. The thermal efficiency is divided into 24% mechanical power and 27.55% thermal load. The output hot water temperature is 65 oC. The outcomes of increasing the GT pressure ratio (12-25) are higher combined cycle net power output by up to 16% with a 9.5% reduction in the thermal energy rejected to the environment. Also, the GT efficiency increases from 20% to 22.5%; however, the final water temperature declines from 67 oC to 60 oC, which is still appropriate for various heating applications.

Microbubbles are used in ultrasound imaging, targeted drug delivery, destruction of cancerous tissues, etc. On the other hand, the demographic behaviors of small bubbles under the influence of Ultrasound have not been fully detected or studied. This study investigates the effect of the radial distribution of Sonazoid microbubbles on frequency response.  It is shown that the optimal subharmonic response is possible by controlling the size distribution. For this reason, the numerical simulation of the dynamic behavior of a coated microbubble is performed using MATLAB coding and the modified Rayleigh-Plesset equation. The Gaussian distribution is then applied, and the frequency response is investigated. It was shown that at a constant excitation pressure of 0.4 MPa and a standard deviation of 0.2, with increasing mean radius, the fundamental response increases. The subharmonic response increases reaches a peak value and decreases. This peak value occurs for frequencies of 4,6, and 8 MHz in the mean radius of 0.8, 1 and 1.6 μm. By increasing the frequency of excitation, it is transferred to a smaller mean radius. It is also observed that the fundamental and subharmonic responses are amplified by increasing the excitation pressure. Studies show that the optimal subharmonic response can be achieved for various applications by controlling the size distribution of microbubbles.

The theory of superposition of waves has been widely deployed in many engineering applications such as medical imaging, engineering measurements, and wave propagation in structures. However, these applications are prone to the interference of unwanted waves. The root cause of the weakness could be ascribable to the wave propagation pattern, which is not actively controlled. A new concept of imposing a time-lagging effect on the source of the wave as an active wave emission strategy is introduced and discussed in this paper. A numerical solver has been developed based on the finite volume Euler explicit method to investigate the wave propagation pattern when there is a time-lagged effect and frequency difference at the source of the wave. Our results reveal that time-lagged wave propagation will be more immune to the disturbance of other waves. The larger the time lag, the more resilient the wave is to resist the interference of other waves, even at a higher frequency. Time-lagged waves can be regarded as a promising active wave emission method that has many potential and robust engineering applications to be explored in the future.

As the smart materials, ionic polymer-metal composites (IPMCs), have a layered structure consisting of a polymeric membrane based on perfluorinated alkene, which is sandwiched between two noble metal-based electrodes, such as gold and platinum, and they can be bent significantly under applying a low-range of voltage. IPMCs are used in many applications, such as robotics, biomechanics, and medical purposes. In order to improve the performance of IPMC, in this article, three different anisotropic surface roughening methods with new and optimized fabrication instructions are used, and samples are compared. The experiments are applied to measure three main factors of IPMCs: displacement, blocking force, and lifetime. The results obtained from plasma samples show that the maximum displacement is 36.23 mm, the blocking force is 4.08 etching, 18 percent higher lifetime than micro sandblasting, and sandpaper under applying a voltage range between 1-7 V; as a result, the plasma etched IPMC sample has the most efficiency.