Alireza Bordbar | Columbia University (original) (raw)

Papers by Alireza Bordbar

Chemical engineering journal, Jun 1, 2024

Zenodo (CERN European Organization for Nuclear Research), Jan 25, 2023

Aiche Journal, Sep 12, 2021

The mechanisms underlying homogeneous fluidization of Geldart A particles have long been debated.... more The mechanisms underlying homogeneous fluidization of Geldart A particles have long been debated. Recent experiments shed fresh insights that both a solid‐like and a fluid‐like state exist. Herein, 3D computational fluid dynamics‐discrete element method simulations with the incorporation of interparticle van der Waals forces were performed for five typical Geldart A particles to investigate the bed structure in the homogeneous fluidization regime. Simulation results reproduce the existence of the solid‐like and fluid‐like states, showing that in the solid‐like state, particles have enduring and strong interparticle van der Waals forces that stabilize the bed to keep the bed stationary; while in the fluid‐like state, the interparticle van der Waals forces are dominated by the drag force, and particles show global circulation. Both interparticle van der Waals forces and friction are found to be necessary for the existence of the solid‐like state, and increasing the former has an effect to widen the solid‐like state.

Journal of Industrial and Engineering Chemistry, Jun 1, 2018

This paper reviews the state-of-the-art numerical techniques employed in the literature for model... more This paper reviews the state-of-the-art numerical techniques employed in the literature for modelling slug flow in microchannels. The proposed solutions in literature for overcoming some of the drawbacks of the numerical methods are presented. Additionally, literature covering specific applications such as enhancement of heat transfer and mixing is reviewed to provide further insight into the transport mechanisms and their applications. Digital microfluidics, as a means of slug manipulation and control, is introduced in the following section of the paper. The application of thermocapillary, magnetic, electric, optical and acoustic forces is elaborated in particular.

Heat Transfer Engineering, May 15, 2019

Thermal performance enhancement of microchannel heat sinks for electronics cooling is becoming mo... more Thermal performance enhancement of microchannel heat sinks for electronics cooling is becoming more and more necessary. To this end, microchannels with non-circular cross-sections conveying immiscible droplets have been employed in the present study and geometric manipulations are applied to enhance fluid mixing and consequently achieve a higher rate of heat removal. Three-dimensional numerical simulations are performed using volume of fluid method for channels of 100 µm hydraulic diameter. Constant wall temperature is chosen as the boundary condition for heating section of the channels. Effects of parameters such as adding curvature to the side walls and varying the entering velocity of the base liquid on heat transfer rate are studied. A performance coefficient is used to evaluate the relative impact of increase in both the Nusselt number and pressure drop as a result of adding curvature to the channel walls. Results of the study showed that slug flow in curved channels is capable of improving the thermal performance in comparison with single liquid flow in straight channels and in best case, can improve the performance up to 50%.

Vacuum, May 1, 2018

Due to complexities of microfluidic devices, not all of the micro-ducts are straight. As a result... more Due to complexities of microfluidic devices, not all of the micro-ducts are straight. As a result, there is a need for utilizing geometric turns and serpentine microchannels. The main purpose of this study is to investigate the effect of applying sharp bends and curved corners to the microchannel geometry on the thermal and hydrodynamic behaviors of rarefied gas flow. In this regard Direct Simulation Monte Carlo method has been employed with pressure driven implicit boundary condition. Comparisons of mass flow rate, slip velocity, shear stress and heat transfer have been carried out between these cases. The obtained results depicted that the mass flow rate is increased by applying curvatures of various radii and the maximum enhancement in mass flow rate is for a radius-to-width ratio equal to 0.6.

Canadian Journal of Chemical Engineering, Feb 1, 2018

† This article has been accepted for publication and undergone full peer review but has not been ... more † This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as

Abstracts with programs, 2022

Journal of The Brazilian Society of Mechanical Sciences and Engineering, Jan 2, 2017

Industrial & Engineering Chemistry Research

Geological Society of America Abstracts with Programs

Journal of Geophysical Research: Solid Earth

The rheology of lavas and magmas exerts a strong control on the dynamics and hazards posed by vol... more The rheology of lavas and magmas exerts a strong control on the dynamics and hazards posed by volcanic eruptions. Magmas and lavas are complex mixtures of silicate melt, suspended crystals, and gas bubbles. To improve the understanding of the dynamics and effective rheology of magmas and lavas, we performed dam‐break flow experiments using suspensions of silicone oil, sesame seeds, and N2O bubbles. Experiments were run inside a magnetic resonance imaging (MRI) scanner to provide imaging of the flow interior. We varied the volume fraction of sesame seeds between 0 and 0.48, and of bubbles between 0 and 0.21. MRI phase‐contrast velocimetry was used to measure liquid velocity. We fit an effective viscosity to the velocity data by approximating the stress using lubrication theory and the imaged shape of the free surface. In experiments with both particles and bubbles (three‐phase suspensions), we observed shear banding in which particle‐poor regions deform with a lower effective viscosi...

Journal of Flow Chemistry

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.

Heat Transfer Engineering

Abstract Thermal performance enhancement of microchannel heat sinks for electronics cooling is be... more Abstract Thermal performance enhancement of microchannel heat sinks for electronics cooling is becoming more and more necessary. To this end, microchannels with noncircular cross-sections conveying immiscible droplets have been employed in this study and geometric manipulations are applied to enhance fluid mixing and consequently achieve a higher rate of heat removal. Three-dimensional numerical simulations are performed using volume of fluid method for channels of 100 µm hydraulic diameter. Constant wall temperature is chosen as the boundary condition for heating section of the channels. Effects of parameters such as adding curvature to the side walls and varying the entering velocity of the base liquid on heat transfer rate are studied. A performance coefficient is used to evaluate the relative impact of increase in both the Nusselt number and pressure drop as a result of adding curvature to the channel walls. Results of the study showed that slug flow in curved channels is capable of improving the thermal performance in comparison with single liquid flow in straight channels and in best case, can improve the performance up to 50%.

Vacuum

Abstract Due to complexities of microfluidic devices, not all of the micro-ducts are straight. As... more Abstract Due to complexities of microfluidic devices, not all of the micro-ducts are straight. As a result, there is a need for utilizing geometric turns and serpentine microchannels. The main purpose of this study is to investigate the effect of applying sharp bends and curved corners to the microchannel geometry on the thermal and hydrodynamic behaviors of rarefied gas flow. In this regard Direct Simulation Monte Carlo method has been employed with pressure driven implicit boundary condition. Comparisons of mass flow rate, slip velocity, shear stress and heat transfer have been carried out between these cases. The obtained results depicted that the mass flow rate is increased by applying curvatures of various radii and the maximum enhancement in mass flow rate is for a radius-to-width ratio equal to 0.6.

The Canadian Journal of Chemical Engineering

An optimized planar micromixer has been employed to study its performance in mixing liquids with ... more An optimized planar micromixer has been employed to study its performance in mixing liquids with various rheological behaviours. This design takes advantage of a number of passive techniques, including split-and-recombination of the channel, contraction of the channel, and embedding diamond-shaped obstacles in the main channels. Three-dimensional Navier-Stokes equations, along with an advection-diffusion model are solved by means of a finite-element scheme. Numerical simulations are performed for species with power law indexes ranging from 0.6-1.4, and the resulting mixing efficiencies are compared for different cases. Pressure drop is also evaluated and compared by taking into account the rheological behaviour of the fluids. The results revealed that in the studied range of Reynolds numbers, shear-thickening fluids present higher efficiencies in the diffusion-dominated regimes by 5 % at the best case. Shear-thinning flows have a better performance at higher Reynolds numbers and expedite the diffusion-advection transition point compared to other regimes. Transition occurs at a Reynolds number of 0.1 for the shear-thinning regime, while for Newtonian fluids this point is at a Reynolds number equal to 1. Moreover, it is found that the variation of mixing efficiency for shear-thickening flows with different fluid behaviour indexes is not significant in the studied Reynolds number range.

Langmuir : the ACS journal of surfaces and colloids, Jan 17, 2018

The spreading and rebound patterns of low-viscous droplets upon impacting spherical solid surface... more The spreading and rebound patterns of low-viscous droplets upon impacting spherical solid surfaces are investigated numerically. The studied cases consider a droplet impinging onto hydrophobic and superhydrophobic surfaces with various parameters varied throughout the study, and their effects on the postimpingement behavior are discussed. These parameters include impact Weber number (through varying the surface tension and impingement velocity), the size ratio of the droplet to the solid surface, and the surface contact angle. According to the findings, the maximum spreading diameter increases with the impact velocity, with an increase of the sphere diameter, with a lower surface wettability, and with a lower surface tension. Typical outcomes of the impact include (1) complete rebound, (2) splash, and (3) a final deposition stage after a series of spreading and recoiling phases. Finally, a novel, practical model is proposed, which can reasonably predict the maximum deformation of lo...

International Journal of Computational Fluid Dynamics

Journal of the Brazilian Society of Mechanical Sciences and Engineering, 2017

Journal of Industrial and Engineering Chemistry

Abstract This paper reviews the state-of-the-art numerical techniques employed in the literature ... more Abstract This paper reviews the state-of-the-art numerical techniques employed in the literature for modeling slug flow in microchannels. The proposed solutions in literature for overcoming some of the drawbacks of the numerical methods are presented. Additionally, literature covering specific applications such as enhancement of heat transfer and mixing is reviewed to provide further insight into the transport mechanisms and their applications. Digital microfluidics, as a means of slug manipulation and control, is introduced in the following section of the paper. The application of thermocapillary, magnetic, electric, optical and acoustic forces is elaborated in particular.