Mohamed Alshehhi

Experimental Investigation of Advanced Microscale Reactors for Enhanced Carbon Capture and Natural Gas Sweetening Applications

There is an active need to develop compact mass transfer systems for high efficiency gas-liquid absorption applications, such as solvent-based carbon capture and natural gas sweetening processes. The present paper focuses on the absorption of carbon dioxide in aqueous diethanolamine using microreactors having hydraulic diameters of 762, 508 and 254 μm. The mass transfer phenomenon was studied and characterized with respect to absorption efficiency and mass transfer coefficient. Parametric studies were conducted varying the liquid and gas phase concentrations. Liquid-side volumetric mass transfer coefficients as high as 620 s−1 were achieved, which is between 2–3 orders of magnitude higher than that reported for most conventional gas-liquid absorption systems. High levels of absorption efficiency, close to 100%, were observed under certain operating conditions. The presently observed process intensification was attributed to an increase in the specific interfacial area with reduction in the channel diameter.Copyright

Enhanced Carbon Capture in a Multiport Microscale Absorber

Increasing concerns on the effects of global warming leading to climate change has necessitated the development of efficient technologies to separate acid gas components, such as carbon dioxide and hydrogen sulfide, from gaseous mixtures. Microscale technologies have the potential to substantially enhance gas-liquid absorption processes on account of their inherent high surface area to volume ratio. The present work reports the mass transfer characteristics during gas-liquid absorption in a multiport microscale absorber. The reactor was designed to comprise of 15 straight, parallel channels having a hydraulic diameter of 456 micrometer and square cross-sectional geometry. The absorption of CO2 mixed with N2 into aqueous diethanolamine was investigated. The performance of the absorber was characterized with respect to the absorption efficiency and mass transfer coefficient. Parametric studies investigating the effects of the gas and liquid phase superficial velocity were performed and discussed. Additionally, the effect of varying the liquid reactant concentration was investigated and discussed.Copyright

Experimental Investigation of Enhanced Absorption of Carbon Dioxide in Diethanolamine in a Microreactor

Natural gas in its originally extracted form comprises carbon dioxide and hydrogen sulfide as small, but non-negligible fractions of its dominant component, methane. Natural gas in the above form is typically subjected to a sweetening process that removes these acid gases. Microscale technologies have the potential to substantially enhance mass transport phenomena on account of their inherently high surface area to volume ratio. The present work reports the mass transfer characteristics during gas-liquid absorption in a microreactor. The absorption of CO2 mixed with N2 into aqueous diethanolamine was investigated in a single straight channel having a hydraulic diameter of 762 micrometer and circular cross-sectional geometry. The performance of the reactor was characterized with respect to the absorption efficiency and mass transfer coefficient. Close to 100% absorption efficiency was obtained under optimum operating conditions. Shorter channel lengths were observed to yield enhanced values of mass transfer coefficient on account of the improved utilization of the liquid reactants’ absorption capacity for a given reactor volume. In comparison to the 0.5 m long channel, the mass transfer coefficients with the 0.3 m and 0.1 m channels were higher on an average by 35.2% and 210%, respectively. Parametric studies investigating the effects of phase superficial velocity, liquid and gas phase concentration were performed. The mass transfer coefficients achieved using the present minichannel reactor were 1–3 orders of magnitude higher than that reported using conventional gas-liquid absorption systems.Copyright

Parametric Performance Analysis of an Electrostatic Wire-Cylinder Aerosol Separator in Laminar Flow Using a Numerical Modeling Approach

A numerical methodology based on the Lagrangian approach is outlined to study the performance of a select class of electrostatic aerosol separators. This modeling method is used to perform a parametric study on the efficiency of a wire-cylinder separator in separation of water aerosols from air. The geometry consists of an 80 µm diameter wire placed in the centerline of a 20 mm diameter cylinder. The work focuses on the effect of applied voltage (in the range of 4 to 8 kV), flow velocity (in the range of 0.3 to 1.5 m/s), flow temperature (in the range of 280 K to 320 K), and separator length (in the range of 0.05 to 0.15 m) on charging of water aerosols and on separator collection efficiency in laminar flow. The aerosols size ranges between 0.01–10 µm. The results of the study show that applied voltage, flow rate, and separator length affect the separation efficiency significantly, while the effect of flow temperature seems negligible.

Numerical Simulation of Solid-Phase Split at Junctions in Particle Laden Pipe Flow

The present study is a part of an industrial research project and consists in simulating a gas-particle flow through junctions under different geometrical and flow conditions. The purpose is to study the effects of the size of particles, the angles of the junction and the flow rate on the flow split. The particles are usually considered as products to transport, such as in pneumatic conveying, where phase split, if necessary, is done in symmetrical Y-junctions to avoid mal-distribution issues. Thus, asymmetrical junctions were, usually, avoided in transportation networks. However, it appeared that the particles can manifest within networks for transportation of gases as contaminants to be eliminated. A typical example is that of Black Powder in gas pipelines in the oil industry. In such piping networks, different types of junctions can be used and it is worth understanding the behavior of particles for unsymmetrical configurations as well. The numerical simulation combines the k-e and the Discrete Phase DPM turbulence and multiphase models, respectively. Relatively, good agreement in the results between the model and the experiments was obtained. The simulations were extended to Black Powder particles and the corresponding results showed interesting features for different Stokes numbers. The simulation results showed that, for Stokes numbers much smaller than unity (St≤0.2), the solids phase split can be considered to follow the air flow split closely. For intermediate Stokes numbers (St≈1), the particles gain some independence from the gaseous phase. For Stokes numbers slightly higher than unity (St≥5), the orientation plays an important role.Copyright

Numerical Analysis of Condensation of R134a in a Single Microchannel

The present work proposes a numerical, transient modeling approach for the simulation of condensation heat transfer in a single microchannel. The model was based on the volume of fluid approach, which governed the hydrodynamics of the two-phase flow. User-defined routines were implemented in order to simulate the effects of condensation, which included mass transfer at the liquid-vapor interface and the associated release of latent heat. A channel having hydraulic diameter of 100 micrometer was modeled using a two-dimensional computational domain. The working fluid was R134a and the vapor mass fluxes at the channel inlet ranged from 245 to 615 kg/m2s. The channel wall was maintained at a constant heat flux, ranging between 200 to 800 kW/m2. The predictive accuracy of the numerical model was assessed by comparing the two-phase frictional pressure drop and Nusselt number with the available empirical correlations in the literature. A reasonably good agreement was obtained for both parameters with mean absolute errors as low as ±7.5% for pressure drop and ±15.6% for Nusselt number. Further, a qualitative comparison of various flow patterns against experimental visualization data was performed. The predicted flow patterns were classified based on the relative dominance of surface tension and inertia forces, and the results were in close agreement with visualization data. On the whole, the newly developed approach was found to have a high predictive accuracy with respect to the simulation of condensation phenomena in microscale domains and was concluded to be a useful tool in support of the design and optimization of advanced microchannel-based heat exchangers.Copyright

Numerical simulation of FENE-P viscoelastic fluids flow and heat transfer in grooved channel with rectangular cavities

The forced convection heat transfer for non-Newtonian viscoelastic fluids obeying the FENE-P model in a parallel-plate channel with transverse rectangular cavities is carried out numerically using ANSYS-POLYFLOW code. The flow investigated is assumed to be two-dimensional, incompressible, laminar and steady. The flow behavior and temperature distribution influenced by the re-circulation caused by the variation of cross-section area along the stream wise direction have been studied. The constant heat flux condition has been applied and the effects of the different parameters, such as the aspect ratio of channel cavities (AR = 0.25, 0.5), the Reynolds number (Re = 25, 250, and 500), the fluid elasticity defined by the Weissenberg number (We), and the extensibility parameter of the model (L2), on heat transfer characteristics have been explored for channels of three successive cavities configuration. Different levels of heat transfer enhancement were obtained and discussed.

Flow Behavior of FENE-P Fluids in Grooved Parallel Plates With Transverse Cavities

Numerical investigation of the flow behavior for Newtonian and viscoelastic FENE-P fluids in a parallel-plate channel with transverse rectangular cavities is carried out using ANSYS-POLYFLOW code. A two-dimensional, laminar and steady flow is considered and the flow behavior influenced by the generated vortices at the transverse rectangular cavities has been studied. The effect of Reynolds number, fluid elasticity and the rheological parameters of the FENE-P model L2, on the flow field is examined. In all non-Newtonian considered cases, different flow field were observed which shows different behavior compared to the Newtonian case.Copyright

Phase-Doppler Anemometry Measurements in Water-Air Impinging Jet Flows

Flow visualization using high speed photography is used to study the structure of two liquid and one air impinging turbulent jets. The break up structure is discussed and the resulting spray angle at large air flow rates is obtained. The spray angle increases with the air flow rate except for the case when the water jet velocity is so small that the flow rate of air does not have significant effects on the spray angle. Phase Doppler Anemometry measurements of liquid droplet sizes and velocities are also given in terms of radial profiles at several axial locations from the point of impingement.Copyright

Heat-Transfer Analysis of Visco-Elastic Giesekus Fluid in a Duct Between Parallel Plates and in a Straight Pipe of a Circular Cross-Section

This work aims to conduct numerical simulation to investigate the convective heat transfer of viscoelastic fluids obeying Giesekus model flowing either along straight pipe of circular cross-section or within the space between parallel plates with constant heat flux thermal boundary condition and neglected viscous dissipation. The numerical technique used is based on finite element software (ANSYS Polyflow 14.0) and the obtained numerical solutions are compared against the analytical solution available in literature. The effect of the rheological parameters on the heat transfer enhancement is discussed.Copyright