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Papers by abas ramiar

Proceedings of the Institution of Mechanical Engineers, Part E: Journal of Process Mechanical Engineering, 2019

This study deals with the launch time of main characteristic of NH3-H 2O absorption chiller under... more This study deals with the launch time of main characteristic of NH3-H 2O absorption chiller under different working condition. The aim of this work was about to scrutinize a lumped-parameter dynamic simulation of aqua-ammonia absorption chiller in addition to investigating the effect of subcooled liquid at condenser/absorber outlet on absorption chiller’s key parameters launch time. Also, the effect of ambient temperature on absorption chiller’s key parameters’ launch time is studied. In order to determine the thermodynamic properties of the working fluid, the Engineering Equation Solver software is applied. By making a link between Engineering Equation Solver and MATLAB software, the differential equations are solved in the MATLAB software environment by fourth-order Rung–Kutta method. According to the result, increase of the sub-cool liquid temperature at condenser outlet has no effect on absorption chiller’s key parameters’ launch time. Besides, 10 ℃-increase in subcooled liquid ...

International Journal of Thermal Sciences, 2021

Abstract Numerical studies are performed to investigate the condensation behavior of single and m... more Abstract Numerical studies are performed to investigate the condensation behavior of single and multiple bubbles in subcooled boiling flow. An open-source code is developed to model the dynamic behavior of the bubbles in real-time. The Newtonian flow is considered and relative equations are solved employing a coupled Level Set (LS) and Volume of Fluid (VOF) method known as CLSVOF model according to the Pressure Implicit with Splitting of Operators (PISO) algorithm. Initially, the numerical findings were compared and verified by available experimental data. The result of a single bubble condensation revealed that the initial bubble size, the subcooling of liquid, and the velocity of the flow not only significantly affect the bubble deformation behavior, but also the rate of condensation. For multiple bubbles, the results revealed that due to interaction between bubbles, bubbles' dynamic condensation behavior is more complex compared to a single one. Due to this interaction, it is found that the rate of bubble condemnation and condensation process vary. Furthermore, the effects of the gradient velocity, gradient temperature, and gap between multiple bubbles on the rate of mass transfer through the condensation are studied. A critical gap between multiple bubbles is introduced. It is found that when ( H ∗ = H / D ≥ 2 ) for different bubble diameters, the effect of bubbles interaction can be ignored. Here H ∗ is a dimensionless gap of center-to-center of bubbles.

Nowadays, the optimal use of energy, speed increase, fuel consumption reduction and environmental... more Nowadays, the optimal use of energy, speed increase, fuel consumption reduction and environmental pollution prevention are essential in the ship design and manufacturing discussion. So it is critical to be able to estimate ship's response to waves, since the resulting added resistance and increasing fuel consumption also increasing environmental pollution. In this study, the numerical solution of the Iran-Bushehr container ship model was determined to simulate the free surface flow around the hull and estimate the total resistance and investigate ship motions in 2 degree-of-freedom (heave and pitch) in regular head waves. Finally, the results of simulation in different conditions are presented and compared. KCS container ship used for validation. CFD codes in Star-CCM+ used to calculate three dimensional, incompressible, unsteady RANS equations.

Acta of bioengineering and biomechanics, 2017

PURPOSE Hemodynamic factors, such as Wall Shear Stress (WSS), play a substantial role in arterial... more PURPOSE Hemodynamic factors, such as Wall Shear Stress (WSS), play a substantial role in arterial diseases. In the larger arteries, such as the carotid artery, interaction between the vessel wall and blood flow affects the distribution of hemodynamic factors. The fluid is considered to be non-Newtonian, whose flow is governed by the equation of a second-grade viscoelastic fluid and the effects of viscoelastic on blood flow in carotid artery is investigated. METHODS Pulsatile flow studies were carried out in a 3D model of carotid artery. The governing equations were solved using finite volume C++ based on open source code, OpenFOAM. To describe blood flow, conservation of mass and momentum, a constitutive relation of simplified Phan-Thien-Tanner (sPTT), and appropriate relations were used to explain shear thinning behavior. RESULTS The first recirculation was observed at t = 0.2 s, in deceleration phase. In the acceleration phase from t = 0.3 s to t = 0.5 s, vortex and recirculation ...

One of the major drawbacks of material extrusion additive manufacturing (AM) is hot-end clogging.... more One of the major drawbacks of material extrusion additive manufacturing (AM) is hot-end clogging. This study aims to answer the question, “What thermal conditions lead to clogging during filament-based material extrusion?” Answering this question requires a clear understanding of temperature distribution inside the liquefier. However, this could not be achieved only through experimental measurements. Therefore, numerical simulations were also carried out by developing a 3D finite volume model of the hot-end. The results obtained from numerical simulations show good agreement with experimental measurements. They also give us a detailed picture of the temperature gradient near the nozzle. Moreover, a series of experiments were performed to determine when clogging occurs, and some criteria for avoiding clogging were presented. These results were also compared and combined with the numerical results to investigate the thermal condition leading to clogging. As the results show, overheati...

Advanced Powder Technology, 2021

Abstract In this paper, an Eulerian-Lagrangian simulation was conducted to achieve optimal Expand... more Abstract In this paper, an Eulerian-Lagrangian simulation was conducted to achieve optimal Expanded-Contracted Cavity Arrays microchannel. First, a new code was developed to solve the viscoelastic flow field, and then the particles were solved by adding appropriate forces to the OpenFOAM Lagrangian solver. This code was then validated for both Eulerian and Lagrangian models. Subsequently, the effect of different parameters such as flow rate, distance from the inlet, cavity depth and distance, and particle size were also studied to obtain the proper geometry for particle focusing. Finally, the selected channel was integrated with a straight channel to separate 4.8 and 13 μm particles. The results of current research can be used to find a proper design of an Expanded-Contracted Cavity Arrays channel to achieve precise focusing and efficient, continuous, and sheathless particle/cell separation, which is much worthy for applications such as high-speed cytometry, cell counting, sorting, and many biological applications.

Journal of Magnetism and Magnetic Materials, 2021

Abstract Although microfluidic devices are widely used for pathogen separation, they are highly s... more Abstract Although microfluidic devices are widely used for pathogen separation, they are highly sensitive to operating conditions which restricts its applications. Here, a magnetophoretic microfluidic device that benefits from characteristics of electroosmotic flow is described. The device is capable of separating magnetic particles (MPs) from human blood in considerably wide ranges of conditions with a perfect efficiency. The device includes two adjacent fluidic channels for the injection of blood containing particle-bonded pathogens and the buffer solution with a slit at the middle for shifting particles to the outlet. Integrating a conductive surface across the slit creates a manageable flow vortex that assists magnetic field to overcome drag force of particles and boosts their upward movement towards the slit. Obtained results indicate that by adjusting the strength of magnetic field and electric potential, a perfect on-chip separation is achievable for particles in the size range of 100 nm to 2.5 µm. Being significantly efficient in such a large range of operating conditions makes the device extremely versatile for targeting various particle-bonded pathogens.

Chemical Engineering and Processing - Process Intensification, 2021

Abstract Circulating tumor cells are malignant cells shed into the vasculature or lymphatics from... more Abstract Circulating tumor cells are malignant cells shed into the vasculature or lymphatics from a primary tumor and are carried around the body in the blood circulation. Separation of these cells can lead to early diagnosis and timely treatment. In this paper, numerical simulation is performed to introduce a novel design for high-throughput and efficient separation of three biological cell populations, including red blood cells (RBCs), white blood cells (WBCs), and MCF-7 breast cancer cells, by using Traveling Surface Acoustic Wave (TSAW) and Dielectrophoresis (DEP) simultaneously. The novel channel design consists of two units: focusing zone and separation zone. The injected cells are first focused on the focusing zone by TSAW force and then separated in the separation zone by a combination of TSAW and DEP forces. The effect of different operational and geometrical parameters on robust focusing and separation is also investigated. The results showed that by selecting the proper configuration, at the flow rate of 20 μl/min, a minimum acoustic voltage of 20 Vpp and a minimum electric potential of 5.25V and 12V are required to separate CTCs and WBCs from RBCs, respectively. This microfluidic channel design can be beneficial for integrating with lab-on-a-chip and clinical diagnosis applications.

SN Applied Sciences, 2020

The time that an absorption chiller needs to reach the designed working condition is called start... more The time that an absorption chiller needs to reach the designed working condition is called start-up. During this time, energy is consumed through the system while efficient refrigeration is not available. So, it's too important to consider the influencing parameters on this period of time so that reduction in energy consumption is achieved. Also, dynamic analysis is used to reduce the startup time and increase system performance in addition to strategic control purposes. Optimizing an absorption cycle during transient operations, such as start up or shut down is very important. The aim of this study is to investigate and compare the effect of employing refrigerant and solution heat exchangers (RHX and SHX) on dynamic performance of both NH 3-H 2 O and H 2 O-LiBr absorption chillers (ACs). Also, the effect of solution heat exchanger's efficiency on the start-up time of the key parameters of both ACs is investigated. To diminish the effect of approximate relations on the results, thermodynamic properties of NH 3-H 2 O and H 2 O-LiBr solutions are extracted from the EES software. By making a link between MATLAB and EES software, a set of differential equations is solved in MATLAB software. The fourth order Runge-Kutta method is employed to solve the differential equations system. This process is continued until convergence criteria are satisfied. The results show that removing SHX from the cycle increases the start-up time of both NH 3-H 2 O and H 2 O-LiBr AC's COPs by 11.76% and 45.16% respectively. The start-up time of the COP of H 2 O-LiBr absorption chiller is highly affected in comparison with the NH 3-H 2 O absorption cycle, by removing SHX or increasing the SHX efficiency. Also, utilizing the RHX does not affect the dynamic response of the key parameters of the both absorption chillers.

Journal of Biomechanics, 2020

Application of microfluidic systems for the study of cellular behaviors has been a flourishing ar... more Application of microfluidic systems for the study of cellular behaviors has been a flourishing area of research in the past decade. In the process of probing cell biomechanics the passage of a cell through a narrow microchannel or a small pore has attracted much attention during the recent years. And the study of cellular deformability and transportability using these systems with enhanced resolution and accuracy has opened a new paradigm for high-throughput characterization of both healthy and diseased cell populations. Here we use the level-set method to explore the relationship between the transit time and mechanical properties of normal white blood cells (WBCs) and breast cancer epithelial cells (MCF7) under different microenvironmental parameters (i.e., pressure difference, cell size, effective cell surface tension, constriction size and taper angle) in a 2-D computational domain by considering the cell as a viscous drop. The novel biomechanical relations are obtained for each cell type by the Response Surface Method (RSM), relating microenvironmental parameters to the dimensionless entry time of the normal and cancer cells. Our results revealed that MCF7 cells show a significantly different behavior (a bifurcating behavior when the pressure difference of inlet/outlet increases) in regards to the dimensionless entry time as a function of microchannel taper angle in comparison with the WBC. These results suggest that the microenvironmental parameters have a significant effect on the transportability of the cells and different cells have different behaviors in response to a specific microenvironmental parameter. Finally, it can be claimed that this method can be also utilized to distinguish between benign and cancerous cells or even to probe tumor heterogeneity toward high throughput cell cytometry.

Applied Thermal Engineering, 2021

Abstract Most important challenge in evacuated tube solar collector is lower performance in off-p... more Abstract Most important challenge in evacuated tube solar collector is lower performance in off-pick hours of sunlight which leads to utilizing thermal energy storage. In present study, thermal performance of evacuated tube solar collectors (because of its enormous application range) integrated with phase change material is evaluated, numerically. The corrugated tube is used instead of smooth tube. The proposed system which is an evacuated tube solar collector equipped with corrugated U-shaped tube and phase change material to store the additional thermal energy in pick hours of sunlight, is the innovation of present work. Numerical simulations were performed for both melting and solidification processes of phase change material. The influences of number of lobe, pitch and depth corrugated on thermal processes of proposed collector are analyzed. The results showed that although the collector outlet temperature in some cases were slight different, however, a significant enhancement in daily thermal efficiency is observed due to the longtime discharging process at night. The corrugated tube increases the collector efficiency by 21.55% compared to smooth tube. Furthermore, four-lobe corrugated tube retains the collector’s operation temperature up to 40 °C. Also, between investigated geometrical parameters, number of lobe has most impact on thermal performance.

Journal of Molecular Liquids, 2020

Abstract Separation of microparticles and cells from a heterogeneous mixture is critical in the f... more Abstract Separation of microparticles and cells from a heterogeneous mixture is critical in the fields of medicine, engineering, biology, and biotechnology. In this paper, a novel design for continuous separation of three particles/cells in a two-component fluid flow by dielectrophoresis, as the most efficient separation method, is discussed. A new solver is developed in OpenFOAM to simulate the separation of three polystyrene particles, which are only slightly different in size (2 μm, 3 μm, and 3.5 μm), in a circular channel containing a two-component fluid flow. Simulation results showed that for mean velocity U0 = 200 μm/s, electric potentials >25 V are required to separate particles efficiently. Then, separation of three biological cells including red blood cells, white blood cells, and MDA-MB-231 breast cancer cells is investigated. To achieve simultaneously two goals of separating the cells and preventing the two fluids to be mixed, it was found that the effective electric potential should be within the range of 9 V to 12 V.

Chemical Engineering and Processing - Process Intensification, 2020

Numerical investigation of the effect of the electrodes bed on the electrothermally induced fluid... more Numerical investigation of the effect of the electrodes bed on the electrothermally induced fluid flow velocity inside a microchannel,

Aerospace Science and Technology, 2018

In this work, numerical simulation of active flow control of high speed flows by means of unstead... more In this work, numerical simulation of active flow control of high speed flows by means of unsteady laser energy deposition was conducted. Supersonic flow over a sphere, cone and oblate spheroid was studied. The effect of single and multiple laser pulses on reduction of the drag force over these aerodynamic nose shapes were studied and compared. In addition, the effect of Mach number, location of energy deposition, number of laser pulses and the frequency of energy deposition were studied. A solver was developed for OpenFOAM to simulate the compressible flow at high Mach numbers. The shock capturing property of the solver was improved using AUSM+-up to calculate the pressure and velocity fluxes at the cell faces. For the validation purpose, simulation of the unsteady laser energy deposition in supersonic flow over a sphere was compared with experimental data. The results of single laser pulse deposition indicated that the interaction of the blast wave and bow shock leads to increase in the drag force. However, when the total laser energy was divided to smaller energy pulses and was applied at high frequency, the maximum drag force was decreased significantly and duration of drag reduction was increased. In addition, it was observed that by increasing the number of laser pulses and the distance between the energy deposition location and body, the duration of drag reduction was increased. In the end, energy saving efficiency for all the simulated cases was calculated. The energy saving efficiency was increased significantly by an increase in the free stream Mach number in spite of the decrease in the duration of drag reduction phase. For the conditions tested here, the maximum energy saving efficiency for supersonic flow over a cone was 65%, while it reached to as high as 750% and 460% for supersonic flow over a sphere and oblate spheroid.

Journal of Thermal Analysis and Calorimetry, 2019

In this paper, a numerical simulation of jet impingement quenching is provided. The VOF method in... more In this paper, a numerical simulation of jet impingement quenching is provided. The VOF method in the basic solver of the OpenFOAM CFD package is developed to simulate boiling and condensation phenomena. In simulations, surface tension and mass transfer between two phases were modeled with continuous surface force (CSF) model and Lee mass transfer model, respectively, and energy equation was solved in the solid region. Numerical simulation of jet impingement quenching process is validated by experimental data and a good agreement is observed. The effects of pulsating jet velocity and step jet velocity on quenching process are studied, and parameters such as temporal and spatial variation of solid part temperature and standard temperature uniformity index (STUI) are investigated. The effects of frequency and amplitude of sinusoidal single jet and also the period of two jets with step pulse are investigated. The results revealed that using two jets with step velocity profile leads to the best performance or least uniformity index (best temperature distribution) among the considered cases. Studying the maximum temperature difference inside the solid region indicated that for pulse flows this parameter is considerably lower than the continuous flows. Also, at a constant flow rate, 43% reduction in STUI is achieved by sinusoidal pulsating jet compared to the single continuous jet, while 66% STUI reduction was reached for two-jet cases. These substantial reductions in uniformity index present these methods as promising approaches for the quenching process in various industrial applications.

Chemical Engineering and Processing - Process Intensification, 2018

A phase-field method is used for simulation formation of viscous droplets by electric field in fl... more A phase-field method is used for simulation formation of viscous droplets by electric field in flow-focusing devices  A novel mathematical formulation is proposed for droplet size under several effective parameters  The influence of orifice diameter and flow rate under electric field are revealed for silicon oil droplets in aqueous solution

Heat and Mass Transfer, 2018

In this paper two-dimensional (2D), two-phase numerical model is proposed to investigate the effe... more In this paper two-dimensional (2D), two-phase numerical model is proposed to investigate the effect of water velocity in the channel on the two-phase flow regime in polymer electrolyte membrane (PEM) electrolyzer porous transport layer (PTL). To simulate the movement of gas-liquid interface finite element method has been used. The model includes a porous media as PTL and a water channel. The water and air is considered as incompressible. The results showed different water velocities although causing different paths of two-phase flow in the PTL have little effect on the type of two-phase flow regimes in the porous media. On the other hand, different water velocities cause different two-phase flows in the channel. For effective removal of airflow in the PTL, the range of water velocities in which the two-phase flow regime in the channel is a bubbly flow is recommended. Therefore, the minimum velocity is necessary for the bubbly flow in the channel.

Journal of the Brazilian Society of Mechanical Sciences and Engineering, 2018

In this article, heat transfer optimization of forced convection in a wavy channel with different... more In this article, heat transfer optimization of forced convection in a wavy channel with different phase shifts between the upper and lower wavy walls is represented. The flow is laminar in the range of (200 B Re B 800) and a uniform temperature of 350 K is considered in the wavy sections. The governing mass, momentum and energy equations are solved using the finite volume method. Different design parameters such as the channel height (h = 10, 15 and 20 mm), the amplitude of the wavy wall (A = 1.5, 2, 2.5 and 3 mm) and the phase shift of the upper wavy wall ð0 c 360 Þ are investigated. For optimization process, a recent method, named artificial bee colony (ABC) algorithm, is applied and compared with two other meta-heuristic algorithms, called particle swarm optimization (PSO) and differential evolution (DE). An ''in house'' code is developed which simultaneously uses the meta-heuristic algorithms and the computational fluid dynamics solver. The results indicate that ABC algorithm has higher accuracy and faster convergence rate than PSO and DE. The parameter considered for optimizing the average Nusselt number as the objective function was the phase shift. But, for optimizing the thermal performance factor, selected parameters were the wavy wall amplitude and the phase shift. The results showed that the maximum average Nusselt number is attained at c ¼ 250:2, A = 3 mm, h = 10 mm and Re = 800, in which the heat transfer rate has 96.6% enhancement rather than the parallel-plate channel. Also, it is found that c ¼ 283:3, A = 2.65 mm, h = 10 mm and Re = 800 are the optimized solutions to obtain the maximum thermal performance factor.