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Computational fluid dynamics (CFD) and heat transfer simulations are conducted for a novel heat exchanger. The heat exchanger consists of semi-circle cross-sectioned tubes that create narrow slots oriented in the streamwise direction. Numerical simulations are conducted for Reynolds numbers (Re) ranging from 700 to 30,000. Three-dimensional turbulent flows and heat transfer characteristics in the tube bank region are modeled by the k-e Reynolds-averaged Navier-Stokes (RANS) method. The flow structure predicted by the two-dimensional and three-dimensional simulations is compared against that observed by the particle image velocimetry (PIV) for Re of 1500 and 4000. The adequate agreement between the predicted and observed flow characteristics validates the numerical method and the turbulent model employed here. The three-dimensional and the twodimensional steady flow simulations are compared to determine the effects of the wall on the flow structure. The wall influences the spatial structure of the vortices formed in the wake of the tubes and near the exit of the slots. The heat transfer coefficient of the slotted tubes improved by more than 40% compare to the traditional nonslotted tubes.

Multi relaxation lattice Boltzmann method is implemented to study Rayleigh-Taylor instabilities. Two immiscible fluids (oil and water) are arrayed into three layers. D2Q9 lattice arrangement for two dimensional computational domains is employed. Density distribution functions for each fluid and distribution functions for the coloring step are determined. The evolution of the interface is identified with the coloring step. Buoyancy and other interaction forces, created by buoyancy, between phases are modeled. Two cases are studied one with periodic boundary condition instead of a side wall, and one bounded on all sides. The study is done with an aspect ratio of two and a density ratio of 1.2. The early and late stages of the instability are characterized. The early stage of both cases shows the initial periodic disturbance being amplified rapidly on the lower interface. The late stages show mushroom-like structures, with significant distortions occurring on the bounded case.

Gas-gas separation, to purify natural gas, is simulated using a membrane supported by a porous medium. Removing acidic gasses from the natural gas is gaining attention recently. Computational fluid dynamics simulations are conducted for asymmetric multi-component fluid flows in a channel. The flow system consists of a circular cross-section channel bounded by a porous layer which supports the membrane wall. The Navier-Stokes equations model the flow in the channel, while the flow in the porous medium is modeled by both the Darcy’s law and the extended Darcy’s law. Mass transport equations, including mass diffusion of mixtures of two gasses (CO2 and CH4), are employed to determine the concentration distribution. The membrane will be modeled as a functional surface; where the flux of each component will be determined based on the local partial pressure of each species, composition, and permeability and selectivity of the membrane. The effect of the porous medium on the membrane performance will be determined for a wide range of Reynolds number. The performance of the system will be measured by maximum mass separation with minimal frictional losses.

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