Sharif Digital Repository

Particle capture at porous media in cross-flow microfiltration is studied to investigate permeability reduction as a function of membrane pore size and particle size distribution. A new model in pore scale and its pertinent mathematical expressions, which consider pore and particle size distribution, are provided. Permeability reduction of the membrane because of size exclusion during particulate suspension flow was predicted using the developed model. It is assumed that the size exclusion is the dominant mechanism of particle retention causes pore blocking and permeability reduction in the porous media.The exact analytical solution of the stochastic model for size exclusion is used to... 

Tapered circular cylinders are employed in a variety of ocean engineering applications. While being geometrically simple, this configuration creates a complex flow pattern in the near wake of the structure. Most previous experimental studies on tapered circular cylinders were dealing with stationary cylinders to explore the wake flow field and vortex shedding patterns past the cylinder. Few studies paid attentions to the vortex induced vibration of the tapered cylinders. This paper reports some results from in-water towing-tank experiments on the vortex-excited vibrations of tapered circular cylinders in a uniform flow. Cylinders with different mean diameters (28 and 78 mm), mass ratios (6.1... 

Wind tunnel experiments were conducted to evaluate surface pressure distribution over a semi span swept wing with a sweep angle of 33°. The wing section has a laminar flow airfoil similar to that of the NACA 6-series. The tests were conducted at speeds ranging from 50 to 70 m/s with and without surface roughness. Surface static pressure was measured on the wing upper surface at three different chordwise rows located at the inboard, middle, and outboard stations. The differences between pressure distributions on the three sections of the wing were studied and the experimental results showed that roughness elements do not influence the pressure distribution significantly, except at the inboard... 

Pressure transient analysis in vertically heterogeneous reservoirs is examined. The inclusion of a separate model for the free fluid flow in the wellbore is essential to allow for hydraulic communication and mixing of the fluid issuing from different reservoir layers. A two-dimensional model coupling Darcy flow in the reservoir with Navier-Stokes flow in the wellbore is developed and solved by the finite element technique. The coupled wellbore-reservoir flow model is used to analyze a layered reservoir with an abrupt change in permeability and a thick formation showing a gradual change in permeability with depth. Contrary to conventional reservoir models, this new model is able to capture... 

Particle capture at porous media in cross-flow microfiltration is studied to investigate permeability reduction as a function of membrane pore size and particle size distribution. A new model in pore scale and its pertinent mathematical expressions, which consider pore and particle size distribution, are provided. Permeability reduction of the membrane because of size exclusion during particulate suspension flow was predicted using the developed model. It is assumed that the size exclusion is the dominant mechanism of particle retention causes pore blocking and permeability reduction in the porous media.The exact analytical solution of the stochastic model for size exclusion is used to... 

Crossflow microfiltration of non-alcoholic beer is investigated numerically and it has been verified by experimental data. Due to the presence of particles with different sizes in feed suspension, a modified combination of three mechanisms of particle back-diffusion is developed to predict particle deposition and cake layer buildup during the process. The simulation results show that smaller particles (about 1μm) are the main contributor to the cake layer due to a minimum in back transport and are the main reason of the flux decline. On the other hand, larger particles (a p>20μm) are swept away along the membrane during the filtration process and move toward the membrane exit due to the... 

The flow hydrodynamic effects and film cooling effectiveness placing two small coolant ports just upstream the main jet (combined triple jets) were numerically investigated. Cross sections of all jets are rectangular and they are inclined normally into the hot cross-flow. The finite volume method and the SIMPLE algorithm on a multiblock nonuniform staggered grid were applied. The large-eddy simulation approach with three different subgrid scale models was used. The obtained results showed that this flow configuration reduces the mixing between the freestream and the coolant jets and hence provides considerable improvements in film cooling effectiveness (both centerline and spanwise averaged... 

In the present work, a thermal modeling is conducted for optimal design of compact heat exchangers in order to minimize cost and entropy generation. In this regard, an εNTU method is applied for estimation of the heat exchanger pressure drop, as well as effectiveness. Fin pitch, fin height, fin offset length, cold stream flow length, no-flow length, and hot stream flow length are considered as six decision variables. Fast and elitist nondominated sorting genetic algorithm (i.e., nondominated sorting genetic algorithm II) is applied to minimize the entropy generation units and the total annual cost (sum of initial investment and operating and maintenance costs) simultaneously. The results for... 

Effects of suppression devices on the vortex induced vibration (VIV) of inclined cylinders appear not to have received previous due attentions. The current paper reports the results of some towing tank experiments on the vortex induced cross-flow vibrations of bare and helically straked cylinders in vertical and inclined arrangements. Rigid test cylinders were mounted on a single degree of freedom elastic support. The inclination angles examined were θ=0°, ±20° and ±45°. The Reynolds number ranged from 4000 to 45. 000 and the reduced velocity from 1 to 16. With all tests the mass ratio and the mass-damping parameters were kept constant.Test results on "inclined bare" and "inclined helically... 

The flux behavior during the industrial cross-flow ultrafiltration of apple juice in a batch process was modeled using a combination of the fouling and concentration polarization models. It was observed that the major flux reduction was at the beginning and at the end of operation due to fouling and increasing solute concentration in the feed tank, respectively. The fouling phenomenon was analyzed by classical and empirical models and it was shown that the empirical one has the best correlation within less than 0.3% error for each experiment. The most significant advantage of this model is its ability to predict a steady flux, while other models predict zero flux at infinite time, which is... 

A series of experiments was performed to investigate the interaction of an under-expanded axisymmetric supersonic jet exhausted from a flat plate with a high subsonic crossflow. The goal was to study the effect of boundary layer thickness (δ) and jet to freestream dynamic pressure ratio (J) on flow field pressure distributions. The resulting measurements upstream of the jet showed that with increasing boundary layer thickness, the magnitude of the pressure coefficient decreases, whereas downstream of the jet, the recovery of the back-pressure moved closer to the nozzle exit. Flow field measurements indicated that with increasing boundary layer thickness, the jet plume dissipation rate... 

In this research, poly(vinyl alcohol) (PVA)/chitosan electrospun nanofibrous membrane (ENM) was prepared by electrospinning method in order to investigate its dye removal ability from colored wastewater. The morphology and average fiber diameter of the membranes were investigated by scanning electron microscopy (SEM), image analysis and atomic force microscopy (AFM). The chemical characterization was studied by Fourier transform infrared spectroscopy (FTIR). The permeability of the membranes was evaluated by measuring pure water flux (PWF). In order to investigate the performance of the prepared membranes they were used in the batch adsorption and membrane separation for dye removal from... 

Instability and breakup of a liquid jet under the influence of a gaseous crossflow in the presence of an electric field is investigated. A dispersion relation for disturbances on the jet surface is derived for the combined effects based on pioneer linear stability analysis for low speed limits. Effects of Weber, Bond and Ohnesorge numbers on the growth rate of disturbances are studied. The theoretical analysis developed for breakup length is used for comparisons with experimentally obtained breakup lengths. Measured breakup lengths were predicted satisfactorily by the linear theory in the region of low crossflow velocities (0–4 m/s) and electric field intensities (0–3×105 V/m). © 2017... 

Three dimensional responses of riser subjected to Vortex Induced Vibration (VIV) are investigated. Proportionality relations of stress and fatigue damage are mentioned. A computer code has been developed for time domain modeling of VIV of riser accounting for both Cross-Flow (CF) and In-Line (IL) vibration. The wake oscillator model is used to calculate the VIV of each strip. The wake oscillators are coupled to the dynamics of the long riser, while the Newmark-beta method is used for evaluating the structural dynamics of riser. The wake dynamics, including IL and CF vibrations, is represented using a pair of non-linear Van der Pol equations that solved using modified Euler method. The... 

An experimental investigation of primary breakup dynamics and spray characteristics of a rotary atomizer with high aspect ratio radial-axial discharge channel is described. A high-resolution shadow imaging technique with pulsed backlight illumination was used for spray visualization. For the rotary atomizer with high aspect ratio discharge channel and radial-axial orientation, visualization showed the occurrence of Centripetal–Coriolis-induced stream-mode injection for all operating conditions. In this mode of injection, a crescent liquid film forms in the channel exit and issues from the orifice as a liquid column or a thin liquid sheet depending on atomizer operating conditions. It was... 

This study investigates an ethanol liquid jet subjected to combination of an air crossflow and a normal electric field. The results on the liquid jet trajectory and subsequent droplets flight paths are presented. The liquid jet trajectory was found as a function of two non-dimensional quantities; the liquid jet to the crossflow momentum ratio and the electroinertial number. The electroinertial number is defined as the ratio between the liquid jet specific momentum and the electric force. A correlation is introduced for the jet trajectory in low crossflow speeds and electric field intensities. The same two quantities control the detached droplets flight paths. Satellite droplets flight angles...