Papers by Sasan Kheirandish
Journal of Fluids and Structures
Journal of Flow Chemistry, 2020
Mixing of high-viscosity liquids (e.g. glycerol–water solutions) is challenging and costly and of... more Mixing of high-viscosity liquids (e.g. glycerol–water solutions) is challenging and costly and often requires employing active mixing methods. Two-phase flow micromixers have attracted attention due to their low cost, simple structure, and high performance. In the present work, we investigate the mixing of similar fluids with viscosities equal to or higher than that of water in a two-phase (gas-liquid) slug-flow micromixer, as an economical passive design. Various cases are studied, in which the liquid samples to be mixed are either water or glycerol–water solution. The performance of the proposed slug-flow micromixer is compared with that of a single-phase micromixer with similar geometrical configuration. We demonstrate that mixing efficiencies higher than 90% are attainable for species with viscosities of about 54% higher than that of water (O(10 −3 ) kg m −1 s −1 ); a result that is not attainable in the corresponding single-phase micromixer. Moreover, a mixing efficiency of more than 80% is achieved at the outlet of the micromixer for solutions with viscosities of 160% higher than that of water.
Iranian Journal of Science and Technology, Transactions of Mechanical Engineering, 2018
It is known that atherosclerosis disease can lead to narrowing of human arteries over time. In th... more It is known that atherosclerosis disease can lead to narrowing of human arteries over time. In this research, the flow field in the left external carotid artery is studied numerically considering fluid–structure interactions and effect of different activities on the risk of atherosclerosis disease is evaluated. In this research, it is studied as to whether having physical exercise can reduce the risk of this disease to a great extent. The artery’s tissue is assumed homogeneous and isotropic hyperelastic in fluid–structure interaction simulations. The normal heart cycle (without physical activity) is considered 0.8 s (75 bpm), and the effects of normal and high activities (having physical exercise with heart rates of 100, 120 and 150 bpm) are studied on the artery’s parameters (one healthy subject is studied). It is shown that the results obtained by considering fluid–structure interaction are close to those of rigid wall consideration in low activity. However, when the person has very high activity (i.e., heart rates of 120 and 150 bpm), the differences become noticeable, and rigid wall assumption cannot be correct. Wall shear stress is one of the parameters that shows specific reaction to high exercise. Maximum difference between time average wall shear stress in normal activity and very high activity (150 bpm) is about 103.7% for FSI simulation. Wall shear stress also shows greater difference between fluid–structure interaction and rigid wall consideration with respect to the other parameters by 36.2% in very high activity.
IEEE Transactions on Components, Packaging and Manufacturing Technology, 2021
The present numerical study uses finite volume formulation to investigate the thermal performance... more The present numerical study uses finite volume formulation to investigate the thermal performance of cylindrical heat sinks with different minichannel profiles and working fluids, including nanofluid and pure water. The numerical simulations are carried out in the laminar flow regime. The considered minichannel profiles include straight, converging-diverging, zigzag, and wavy. First, the straight design and the nonstraight ones with equal amplitudes were compared based on their thermal performance, and it was observed that the wavy minichannel has an edge over the other profiles in the studied range of Reynolds numbers. Then, the wavy design was chosen and further investigated by changing the amplitude of the walls’ waveform for both working fluids. It was found that larger wave amplitudes raise the pressure drop and the heat transfer coefficient; however, the thermal performance parameter, which compares the relative importance of these two parameters, still follows an increasing trend. For the wavy minichannel heat sink, the thermal performance factor can increase up to 17% when the waviness is increased from 0.25 to 0.75 mm. Finally, after fitting the obtained numerical data, novel predictive correlations are derived based on different thermal and hydrodynamic parameters of the wavy heat sinks. This is achieved by the optimization of independent variables using a genetic algorithm.
Journal of Micromechanics and Microengineering
In today's complex Micro-Electro-Mechanical Systems (MEMS), investigation of flow through... more In today's complex Micro-Electro-Mechanical Systems (MEMS), investigation of flow through irregular micro/nanochannels, such as bended channels, variable cross-sectional area channels, and those with rough surfaces, can contribute considerably to efficient designing of the microdevices and to gain a better understanding of the flow structure in these geometries. The present paper reviews the prominent studies published in literature on rarefied gas flow through these types of complex geometries. The main focus of the study is to explore the physical aspects of the findings and the analyses provided in support of the results. Finally, the areas in which a gap exists in literature and could be subjects of future studies are introduced.
IEEE Transactions on Components, Packaging and Manufacturing Technology, 2021
The present numerical study uses finite-volume formulation to investigate the thermal performance... more The present numerical study uses finite-volume formulation to investigate the thermal performance of cylindrical heat sinks with different minichannel profiles and working fluids, including nanofluid and pure water. The numerical simulations are carried out in the laminar flow regime. The considered minichannel profiles include straight, converging-diverging, zigzag and wavy. Firstly, the straight design and the non-straight ones with equal amplitudes were compared based on their thermal performance, and it was observed that the wavy minichannel has an edge over the other profiles in the studied range of Reynolds numbers. Then, the wavy design was chosen and further investigated by changing the amplitude of the walls' wave-form for the both working fluids. It was found that larger wave amplitudes raise the pressure drop and the heat transfer coefficient; however, the thermal performance parameter, which compares the relative importance of these two parameters, still follows an increasing trend. For the wavy minichannel heat sink, the thermal performance factor can increase up to 17% when the waviness is increased from 0.25 to 0.75 mm. Finally, after fitting the obtained numerical data, novel predictive correlations are derived based on different thermal and hydrodynamic parameters of the wavy heat sinks. This is achieved by optimization of independent variables using genetic algorithm.
Iran J Sci Technol Trans Mech Eng, 2019
It is known that atherosclerosis disease can lead to narrowing of human arteries over time. In th... more It is known that atherosclerosis disease can lead to narrowing of human arteries over time. In this research, the flow field in the left external carotid artery is studied numerically considering fluid-structure interactions and effect of different activities on the risk of atherosclerosis disease is evaluated. In this research, it is studied as to whether having physical exercise can reduce the risk of this disease to a great extent. The artery's tissue is assumed homogeneous and isotropic hyperelastic in fluid-structure interaction simulations. The normal heart cycle (without physical activity) is considered 0.8 s (75 bpm), and the effects of normal and high activities (having physical exercise with heart rates of 100, 120 and 150 bpm) are studied on the artery's parameters (one healthy subject is studied). It is shown that the results obtained by considering fluid-structure interaction are close to those of rigid wall consideration in low activity. However, when the person has very high activity (i.e., heart rates of 120 and 150 bpm), the differences become noticeable, and rigid wall assumption cannot be correct. Wall shear stress is one of the parameters that shows specific reaction to high exercise. Maximum difference between time average wall shear stress in normal activity and very high activity (150 bpm) is about 103.7% for FSI simulation. Wall shear stress also shows greater difference between fluid-structure interaction and rigid wall consideration with respect to the other parameters by 36.2% in very high activity.
Journal of Flow Chemistry, 2020
Mixing of high-viscosity liquids (e.g. glycerol–water solutions) is challenging and costly and of... more Mixing of high-viscosity liquids (e.g. glycerol–water solutions) is challenging and costly and often requires employing active mixing methods. Two-phase flow micromixers have attracted attention due to their low cost, simple structure, and high performance. In the present work, we investigate the mixing of similar fluids with viscosities equal to or higher than that of water in a two-phase (gas-liquid) slug-flow micromixer, as an economical passive design. Various cases are studied, in which the liquid samples to be mixed are either water or glycerol–water solution. The performance of the proposed slug-flow micromixer is compared with that of a single-phase micromixer with similar geometrical configuration. We demonstrate that mixing efficiencies higher than 90% are attainable for species with viscosities of about 54% higher than that of water (O(10−3) kg m−1 s−1); a result that is not attainable in the corresponding single-phase micromixer. Moreover, a mixing efficiency of more than 80% is achieved at the outlet of the micromixer for solutions with viscosities of 160% higher than that of water.
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Papers by Sasan Kheirandish