Browsing by Author "Alba, Kamran"
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Item Bioimaging of Flow Dynamics in BTB(2017) Raghunandan, Santhanakrishnan; Alba, Kamran; Ganapathy, SivakumarGloriosa superba is a well-known source of the bioactive colchicine. It is one of the primary sources of treatment for gout and under drug development for cancer as well as cardiovascular diseases. The balloon type bubble bioreactor (BTBR) has been successfully used for the production of biopharmaceuticals. The biomanufacturing of colchicine can be increased by understanding the flow dynamics, mixing intensity inside the BTBR. The preliminary results illustrate the homogenous and heterogeneous flow patterns, the direction of flow inside the reactor at low and high gas injection rates. We will present the mean bubble diameter, the maximum and the minimum vorticity, density of the fluid, viscosity, and surface tension bioimaging as well as quantitative data, which could provide better understanding of the fluid dynamics for the biomanufacturing of biorhizome for therapeutic colchicine production.Item Biorheology (Part I) & Numerical Investigation of Flow-Induced Vibration (Part II)(2020-05) Mitra, Harsa; Ostilla-Mónico, Rodolfo; Alba, Kamran; Metcalfe, Ralph W.; Koeck, FrankThis Master’s thesis work is composed of two research categories. The first part seeks to develop a better understanding of the rheological properties of platelet-rich plasma (PRP), a blood-derived product used as a therapy for osteoarthritis and tendon injuries and the second part aims at evaluation of the flow-induced vibration (FIV) within a subsea choke valve. Blood-derived products, particularly PRP, have received increased attention in the past several years due to their great potential as a therapy for osteoarthritis and tendon injuries. Therefore, characterizing the mechanical properties of PRP becomes important to better understand its therapeutic efficacy. Rheological characterization of PRP provides further insight into its mechanism of action. Flow-sweep, Small Amplitude Oscillatory Shear (SAOS), Large Amplitude Oscillatory Shear (LAOS), and thixotropy tests have been performed at room and physiological temperatures to characterize the non-Newtonian properties of PRP samples. Flow-sweep tests reveal shear-thinning behavior (also observed in LAOS experiments), with higher apparent viscosity observed at temperature. Rheological models such as Carreau, Casson, power-law, and Herschel-Bulkley have been fitted to the flow-sweep data with the latter showing the closest agreement. The calculated boundaries of low/high-shear rates in flow-sweep tests as well as minimum-torque, sample-inertia, and instrument-inertia limits in SAOS frequency-sweep experiments are correspondingly provided for accurate interpretation of the results. Although, the window of interpretable SAOS results is found to be narrow. Furthermore, the non-linear and transient viscoelasticity is quantified with the help of the LAOS tests. The thixotropic behavior of PRP solutions is further quantified through the peak-hold test, and further compared against the results of whole blood previously published in the literature. Part two of the thesis investigates a wellhead choke valve, a type of control valve, which is mostly used to control the flow and pressure of fluids from a reservoir in an oil and gas production. A numerical study is performed using STAR-CCM+ software to study and visualize the complex physics of the compressible flow in question. Our study is carried out on a subsea choke valve model obtained from Master Flo Valve (USA) Inc., FIV investigation on dominant frequency modes within the flow has been conducted using fast-Fourier transform (FFT). The dominant frequency is then compared against the experimental natural frequency of vibration of the valve assembly to assess the risk of resonance and mechanical failure. To complement the FFT analysis, the Mach number, pressure, and temperature contours have been presented on three orthogonal planes within the valve.Item Buoyancy-driven Particle-laden Exchange Flows in Inclined Conduits(2018-05) Mirzaeian, Nima; Alba, Kamran; El Nahas, Medhat; Singh, Navdeep; Conrad, Jacinta C.As an extension to the previously investigated buoyancy-driven exchange flow of pure fluids in inclined ducts, we propose an experimental and theoretical approach to practically study the effect of solid particles within the flow. The flow problem starts in a density-unstable lock-exchange configuration with heavy suspension being on top of a light pure fluid in a long narrow pipe or channel. Suspension is a mixture of negatively-buoyant solid particles in a Newtonian pure fluid. The density difference between the heavy and light phases is small enough to neglect the inertia (Boussinesq approximation). Flow is firstly studied through an experimental framework. Various sedimentary, transitionary, and mixing regimes are observed based on the pipe inclination angle, [Greek small letter beta], and initial volume fraction of particles, [Greek small letter phi][subscript 0] . The results are mapped on dimensionless diagrams suitable for industrial design and environmental planning. Effects of particle size and fluid’s viscosity are further discussed. The sedimentary behavior is diminished by reducing particle size, whereas remains unchanged with fluid’s viscosity. The advancement frontal speed of the heavy suspension layer into the light pure fluid, V[subscript f] , is measured over full range of experiments. It is found that V[subscript f] becomes larger as the pipe is titled away from the horizontal direction. An intermediate range of particle volume fraction, [Greek small letter phi][subscript 0], is interestingly discovered to lead to maximal V[subscript 0] . A non-dimensional scale for frontal velocity is successfully proposed constituting various flow and geometrical parameters. For strictly vertical duct, a lubrication model is developed to theoretically investigate the flow in this simplified configuration. Novel particle-rich zones inside the suspension are further discovered in the vicinity of the advancing heavy and light fronts. It was further revealed that the geometry confinement plays a significant role in exchange flow dynamics through formation of interfacial patterns and particle-enrichment behavior. The fundamental findings of this thesis help understand the dynamics of important flows observed in nature within oceanographic and geophysical contexts as well as in industry through discharge, transport and dispersion of slurries, mine tailings, pastes, pharmaceuticals, paper pulp, drill cuttings, sludge, effluents and sewage, manufacture of cement clinker in inclined kilns, mineral processing in hydrocyclones, and inclined fluidized beds.Item Controlling Secondary Flows in Turbulent Taylor-Couette Flow Using Surface Heterogeneity(2022-12-13) Jeganathan, Vignesh; Ostilla-Mónico, Rodolfo; Alba, Kamran; Liu, Dong; Floryan, Daniel; Chen, GuoningTurbulent shear flows are abundant in geophysical and astrophysical systems and in engineering-technology applications. They are often riddled with large-scale secondary flows that drastically modify the characteristics of the primary stream, preventing or enhancing mixing, mass, and heat transfer. In this thesis, we study the possibility of modifying these secondary flows by using stress reducing surfaces including free-slip and superhydrophobic surface treatments that reduce the local shear. We focus on the canonical problem of Taylor-Couette flow, the flow between two coaxial and independently-rotating cylinders, which has robust pinned secondary structures called Taylor rolls that persist even at significant levels of turbulence. It is shown through experiments and simulations that stress reducing surfaces arranged in a spanwise manner destructively interfere with Taylor rolls by inducing additional secondary flows through surface heterogeneity, as long as the structure size can be fixed. Simulations also find that slanted free-slip surfaces, when applied at certain angles and wavelengths, induce a velocity that causes the large-scale structures to move when the domain is periodic. The minimum slip-lengths of the treatment required for this flow control to work are determined and rationalized, and their effectiveness beyond the Reynolds numbers studied here is also discussed. We also explore a novel framework for understanding the origins of Taylor rolls through a two-way coupling between velocities caused by Coriolis forces, and apply it to other flows finding that the framework is not valid.Item Creating Instrumentation to Test Opto-Mechanical Properties of Hydrogel for Use in Cataract Surgery(2023-04-13) Mathew, AllenCataract surgery is the most common procedure in the US, with over three million operations conducted annually. A cataract surgery typically involves emulsifying and draining the cataractous lens. The lens cavity is then repopulated using a semi-rigid plastic intra-ocular lens (IOL). Distant and close viewing is achieved in the eye by zonules that stretch and release the lens to adjust focus, a function known as accommodation. The higher rigidity of the IOL causes a weakened accommodation, requiring the patient to wear glasses. There are additional drawbacks to the IOL, such as the need for large incision area (6mm diameter), opacification, and cost (average of $9,600 per operation). A poly-ethylene glycol (PEG) hydrogel promises to be a more effective replacement for the natural lens, compared to the IOL. The hydrogel promises mechanical properties that more closely matches the natural lens, resulting in minimal loss of accommodation. Other potential benefits include a smaller incision size, lower toxicity, and lower cost. The aim of the project is to design and construct an eight-armed robot capable of stretching and releasing the hydrogel sample while producing a force v. time graph.Item Density-Stable Displacement Flow of Immiscible Fluids in Incline Pipes(2018-12) Oladosu, Olamide; Alba, Kamran; Olshanskii, Maxim A.; Jukes, Paul; Koeck, FrankWe experimentally study the iso-viscous displacement flow of two immiscible Newtonian fluids in an inclined pipe and the displacement flow of a viscoplastic fluid by a Newtonian fluid in an inclined pipe. The less dense displacing fluid is placed above the more dense displaced fluid in a density-stable configuration. In the Newtonian flow, the displacing and displaced solutions are oil and water-based respectively. The former exhibits non-wetting behavior in the vicinity of the pipe wall whereas the latter is wetting. The pipe has a small diameter-to-length ratio. The mixing and interpenetration of two fluids is observed over a wide range of controlling parameters, revealing remarkable results. A major contribution of the work is that compared to the previously studied miscible limit, there is novel behavior observed at the interface between the two fluids: the displaced fluid stays "pinned" to the lower wall of the pipe upon pumping the displacing one. This phenomenon, which is observed over all ranges of flow rate, inclination angle, and density difference, is associated with the wetting characteristic of the displacing liquid and is also present when light and heavy viscosity mineral oils are used as the displacing fluid. Ultrasonic Doppler Velocimetry (UDV) revealed a segmented velocity profile at the interface of the immiscible fluids. Due to pinning in the Newtonian case, the efficiency of the removal of displaced fluid in the immiscible limit can be lowered by 14% compared to the miscible case. Within the family of Newtonian immiscible fluids, the maximum efficiency is achieved at close-to-vertical inclination angle, large density difference, and counter-intuitively low imposed flow rate, which is of great importance in industrial design. In the immiscible viscoplastic flow, the displacing solution is a light oil while the displaced solution is a carbopol gel which is densified by glycerol. "Difficult" displacements (Bingham number >> 1), are studied, revealing center-type displacements similar to those in previous studies, in which the displacing oil leaves a ring of carbopol gel behind in the pipe. Displacement efficiency as measured by the dimensionless displaced fluid area α is discussed, as is fracturing of the gel layer due to high shear.Item Design of Chassis, Impact Attenuator, Suspension and Aerodynamic Systems of a Formula SAE Car(2019-05) Paul, Tittu; Ambler, Anthony P.; Basaran, Burak; Singh, Navdeep; Alba, KamranDesigning the first car for a Formula SAE team can be very challenging and confusing due to close interconnection between the design process of different subsystems. Once the working car is built, it is comparatively easy for the teams to build next year cars by testing and improving the already existing model. This thesis documents an attempt made to design the chassis, impact attenuator, aerodynamics and suspension systems of the first UH College of Technology Formula SAE car. A systematic design methodology was adopted to tackle the challenge of having many unavailable inputs while designing each subsystem. The effectiveness of various parameters selected during designing each subsystem where validated through testing. Chassis was designed according to the FSAE competition rules with the aim of achieving a specific target torsional stiffness. A standard impact attenuator was analyzed using SOLIDWORKS drop test simulation with different impact absorbing materials for its crashworthiness. An optimized double wishbone suspension was designed at front and rear which was found to be the best option available for Formula SAE cars. For the aerodynamic system, optimized multi element wings were designed as front, rear and side devices using ANSYS FLUENT. An undertray diffuser design was compared to the downforce generation capabilities of a side wing, both within the available space limits, and the side wing was found to be generating more downforce. Loads acting on suspension links were found out by calculating the load transfer expected to happen while cornering, braking and accelerating. Finally, FEA was conducted on the suspension links to determine the minimum tube size requirements for the components.Item Direct Numerical Simulations of Normal Vortex Blade Interaction(2022-05-10) Soriano, Steven Angel; Ostilla-Mónico, Rodolfo; Floryan, Daniel; Alba, KamranThe three-dimensional interaction between a vortex and a body-oriented normally is complex due to the interaction of inviscid and viscous mechanisms. The current thesis uses a direct numerical simulation (DNS) approach to simulate the Navier-Stokes equations in order to further understand the dynamics of the three-dimensional vortex-body interaction. The problem is modeled using a thin cylinder that travels towards and impacts a columnar vortex, cutting through it. The thesis focus on the process of boundary layer separation during the initial stages of the interaction, the evolution of secondary vorticity that is shed from the body's boundary layer and its subsequent interaction with the primary vortex, and the resulting external force affecting the body during the interaction. The interplay between inviscid and viscous mechanisms during the interaction categorizes the interaction into different interaction regimes (the weak and strong vortex regime) governed by the impact parameter--which is the ratio of free-stream velocity to the maximum vortex swirl velocity. Additionally, although the is no explicit regime that takes distinction based on the Reynolds number, the Reynolds number is critical to the time scale associated with the entertainment of boundary layer fluid into the primary vortex during and after the interaction. Simulations of the vortex-cylinder interaction were conducted by careful a variation of the impact parameter and Reynolds number. It was found that variation of the impact parameter revealed a gradual transition of the degree of inviscid interaction. Results from simulations done with a low impact parameter reveal an interaction dominated by ejection and inviscid interaction of secondary vorticity from the cylinder's boundary layer with the primary vortex. Simulations conducted with a high impact parameter revealed an interaction dominated by the viscous interaction of the cylinder surface and its boundary layer with the primary vortex. Flow topology around the cylinder is significantly different between impact parameter cases leading to distinct hydrodynamic force curves that contain unique peak structures. These peak structures are indicative of boundary layer fluid being pulled away from the cylinder and impingement of external flow against the cylinder's surface. Variations of the Reynolds number in both the high and low impact parameter cases identified that the Reynolds number has direct control of the unsteadiness present in the cylinder's boundary layer leading to the increase of secondary vorticity and subsequent turbulent structures that are developed during the interaction. Additionally, it is found that variations in the Reynolds number result in the formation of additional unique peak structures in the cylinder's hydrodynamic force curve.Item Double Diffusive Effects in Buoyancy Driven Exchange Flow of Miscible Fluids in Inclined Pipes(2016-12) Shariatnia, Shadi; Ghasemi, Hadi; Metcalfe, Ralph W.; Alba, KamranWe study double diffusion buoyancy-driven exchange flow of two miscible Newtonian fluids in an inclined pipe experimentally. Experiments have been carried in an adiabatic small-aspect-ratio pipe and the fluids involved are isoviscous. Inclined configuration has been studied for the first time in this research. There has also been observed a novel asymmetric behavior in the flow which has never been observed before in the isothermal limit in which the cold finger appears to advance faster than the hot one. complementary experiments have been done to clarify this asymmetric behavior is associated with the wall contact and the formation of a warm less-viscous film of the fluid lubricating the cold moreviscous finger along the pipe. On the other side of the pipe, a cool more-viscous film forms decelerating the hot less-viscous finger. The asymmetric behavior of the flow is finally quantified over the full range of experiments carried.Item Flow Instabilities in Flute-like Instruments(2020-05) Janjua, Ahmed Nawaz Nawaz; Ostilla-Mónico, Rodolfo; Yang, Di; Alba, KamranFlute-like instruments have a common working mechanism that consists of blowing across one end of a resonating tube to produce a jet of air that is directed at a sharp edge producing sound. Analysis of operation of flutes involves numerous research fields including fluid dynamics, physics, and aero-acoustics. In this study, an effort has been made to investigate more about the flow of air in flutes using 2D Direct Numerical Simulation. An analysis of the response of the jet of air by varying the jet width, profile, offset, and Reynolds number, and the flute labium angle in a 2D domain is the main focus of this study. We find that oscillations are sustained in the Reynolds number range 1000-2000, with lower Reynolds numbers producing no oscillations, and large Reynolds numbers developing a chaotic flow. These ranges also slightly differ for different parameters. We quantify the oscillation period and find heavy dependence on all parameters. These results lay out a framework to continue investigating instabilities in flute-like instruments.Item Fluids Viscosity Effect on Non-Isothermal Buoyancy-Driven Exchange Flow in Inclined Pipes(2019-12) Ravichandran, Gaarthick; Alba, Kamran; Singh, Navdeep; El Nahas, MedhatBuoyancy-driven exchange flow is studied experimentally for different Atwood numbers, inclination angles and fluid pairs. The density difference drives the flow, that is achieved through added salinity for isothermal case and temperature difference for the non-isothermal case. Detailed benchmarking experiments were run for isothermal and non-isothermal cases. The degree of flow instability and mixing was found to increase as the inclination angle moves towards vertical, in both isothermal and non-isothermal experiments. The influence of temperature in the non-isothermal experiments caused a significant increase in the flow instability and diffusion. The rate of fluids interpenetration was measured showing an asymmetry from the observed non-isothermal results. The heavy cold finger advances at a faster rate compared to the light hot fluid finger. This phenomenon was quantified for the full range of inclination angles and Atwood numbers. The effect of temperature-viscosity relation on the dynamics of the flow was studied experimentally. Each fluid phase was viscosified separately, maintaining the same density difference. The viscosities were varied by adding Xanthan gum. The effect of viscosity ratio was quantified by measuring the front velocity of the fluid fingers over the full range of inclination angles. Same density difference was maintained in both isothermal and non-isothermal experiments. The fluids interpenetration rate was maximum for intermediate inclination angles and was observed in both isothermal and non-isothermal (without Xanthan gum) cases. The overall observed asymmetry for visosified experiments was found to be less compared to the non-isothermal experiments (without Xanthan gum) at any given Atwood number.Item Investigating the Effects of Helical-shaped Blades on the Wake Characteristics and Performance of Vertical Axis Wind Turbines using Large Eddy Simulations(2023-08) Gharaati, Masoumeh; Yang, Di; Liu, Dong; Alba, Kamran; Floryan, Daniel; Xu, BenTurbulent wake flows behind helical- and straight-bladed vertical-axis wind tur bines (VAWTs) are studied numerically using the large eddy simulation method com bined with the actuator line model. The effects of blade geometry on turbine wake characteristics are explored at both lab- and field-scale VAWTs differed by their oper ational tip-speed ratios (TSRs). For the lab-scale VAWT, a small-size 5-blade VAWT design is considered, which operates at relatively low TSRs of 0.4-0.6 at the wind speed of 13m/s. For the field-scale VAWT, a commercial 3-blade VAWT is consid ered, which operates at a higher TSR of 1.19 at the wind speed of about 11 − 12m/s. In both cases, the wake flows behind straight- and helical-bladed VAWTs were sim ulated, and the flow characteristics were quantified and compared. At low TSRs, the simulation results show that the wake behind the straight-bladed VAWT expands considerably in the spanwise direction due to the quasi-2D vortex shedding effect from the straight blades. In contrast, the helical-bladed VAWT generates highly 3D wake flow structures to produce a relatively narrow wake with faster decay of turbulent intensity. At high TSRs, the helical-bladed VAWTs generate a screwdriver effect to induce mean vertical flow motions at the spanwise edges of the wake flow, which are balanced by a mean vertical counter-flow (i.e., with reversed direction) near the center of the wake. As a result, the wake flows behind helical VAWTs exhibit vertical tilting that affects the turbulent intensity and the Reynolds transport of momentum in the shear layers around the VAWT wake region, leading to faster wind speed recovery than the wake behind straight-bladed VAWTs. Suppose the different VAWT designs are used in wind farm applications. In that case, the field-scale helical-bladed VAWTs may improve the mean power production rate for the fully developed region of the wind farm by up to about 7.33% compared with the corresponding straight-bladed VAWT. Using the helical-bladed VAWTs also reduces the fatigue load on the structure by significantly reducing the spanwise bending moment (relative to the bottom base), which may improve the longevity of the VAWT system to reduce the long-term maintenance cost.Item Linear Theory of Particulate Rayleigh-Bénard Stability(2020-12) Prakhar, Suryansh; Prosperetti, Andrea; Ostilla-Mónico, Rodolfo; Alba, KamranThe stability threshold of the Rayleigh-Bénard problem is studied for a two-phase situation in which particles are introduced uniformly at the upper plate with a prescribed temperature and velocity. The particles exert a drag force on the fluid and exchange energy with it. These processes have the effect of enhancing the stability of the of the system. In other words, the critical Rayleigh number for the onset of convection increases in order that buoyancy can overcome the drag force imposed by the particles on the fluid. The critical Rayleigh number for the onset of convection is calculated numerically by solving the mass, momentum and energy equations for the fluid and the particulate phase under the point-particle approximation. The effect of the particles is explored by varying the number density, the mechanical and thermal Stokes numbers and ratio of the particle to fluid densities and heat capacities. Although the principle of exchange of stability is not applicable in this case, the numerical evidence shows that, at onset, the eigenvalue with the largest real part is purely real. This circumstance permits a simplified analytical solution based on a Fourier series expansion which is found to be close to the numerical results.Item Modeling Lubrication in Three Dimensional Wavy Elastomeric Seals(2022-12-13) Katchi, Saiprabhath; Metcalfe, Ralph W.; Alba, Kamran; Yang, Di; Floryan, Daniel; Liu, DongSkewed or wavy elastomeric seals are used for rotary sealing applications in the intermediate pressure range(1 - 10MPa). They provide the advantage of low friction and maintenance and virtually wear-free life. It is achieved by maintaining a thick lubricant film through the hydrodynamic action. Pressure-driven leakage is an important design parameter that defines the quality of a seal. Leakage depends on the thickness of the film, which is difficult to measure experimentally. Therefore, to design these sealing systems, it is necessary to have a robust numerical application to predict the behavior of these seals. Two fully coupled numerical approaches have been proposed in this thesis to address this problem. A Full system coupling model, where no simplifications are made to the solid model, and a Reduced system coupling model, where the solid model is reduced to a linear coupling operator. A penalty method has been implemented in the first model to address film rupture in the lubrication domain. The iterative block method has been extended to the soft EHL regime to track the cavitation boundary in the second model. A line contact study is carried out for simple O-ring cases to validate the models with the published literature. The Sine-O-ring seal, a wavy elastomeric seal, is studied using the second model for the hydrodynamic pressure and film thickness.Item Multiphase Fluid Mechanics in Biomanufacturing(2018-12) Raghunandan, Santhanakrishnan; Ganapathy, Sivakumar; Alba, Kamran; Iyer, Rupa; Balan, Venkatesh; Shireen, Wajiha; Zouridakis, GeorgeThe aim of this fluid mechanics work was to study the fundamental hydrodynamics mechanism in a balloon type bubble bioreactor (BTBB), which could provide a key guidance to improve biomanufacturing of biopharmaceuticals. A multiphase (liquid and air) computational fluid dynamics was performed with particle tracking velocimetry to observe flow patterns inside BTBB. The control experiment was investigated in 5 and 20L BTBB with water observed an increase in the bubble diameter (0.15 to 0.24 cm for 2L working volume in 5L; 0.27 to 0.36 cm for 16L working volume in 20L) with increasing volumetric flow rate (1 cc/min to 5.5 cc/min) and working volume (2L, 4L, 8L and 16L). However, the bubble diameter reduced with increasing interface forces such as viscosity, density and surface tension when compared with water (0.14 cm at 5.5 cc/min in salt solution; while it was 0.24 cm in water). The decrease in density and viscous fluid could be due to low detachment time and increasing density of the bubble or prevention of bubble coalescence. The reduction in surface tension (30 dynes/cm) resulted in the activation of sparger pores leading to the formation of numerous small bubbles. A homogeneous or laminar flow was observed in higher flow rates (3 cc/min) with increasing viscosity (5 mPa.s) and the flow was turbulent or heterogeneous with flow rates higher than 3 cc/min (4, 5, 5.5 cc/min). Moreover, the dual effect of increasing viscosity and density decreased the bubble sizes in case of CO2 and had laminar flow for higher flow rates (3 cc/min) when compared with the individual effect of density and viscosity. The flow data shows that the differential fluid mechanics pattern in non-uniform geometry BTBB, which can be used to design a flow sensor that could accurately controlling the mixing rate or mass transfer in large-scale biomanufacturing.Item Non-Isothermal Buoyancy Driven Exchange Flow of Miscible Fluids in Inclined Pipes(2016-12) Eslami, Bahareh; Ghasemi, Hadi; Metcalfe, Ralph W.; Alba, KamranThis thesis studies non-isothermal buoyancy-driven exchange flow of two miscible Newtonian fluids in an inclined pipe experimentally. The cold heavy fluid is released into the hot light one in an adiabatic small-aspect-ratio pipe in the Boussinesq limit. The maximal rate of interpenetration of the fluids in non-isothermal case is similar to the isothermal limit, maximal rate occurs at an intermediate angle. There has also been observed a novel asymmetric behavior in the flow never observed before in the isothermal limit in which the cold finger appears to advance faster than the hot one. Backed by meticulously-designed supplementary experiments, this asymmetric behavior is hypothetically associated with the wall contact and the formation of a warm less-viscous film of the fluid lubricating the cold more-viscous finger along the pipe. The asymmetric behavior of the flow is finally quantified over the full range of non-isothermal experiments carried.Item PERFORMANCE ANALYSIS AND THE EFFECTS OF KEY PARAMETERS IN SOLID PARTICLE BEDS(2021-12) Hossain, Nazmul; Metcalfe, Ralph W.; Ostilla-Mónico, Rodolfo; Ehlig-Economides, Christine; Alba, Kamran; Yang, DiFluid-solid particle beds have a broad range of industrial applications as packed and fluidized beds. The particle-particle collision, particle-wall interaction, and virtual mass force which initiates from particle motion influencing neighboring particles make it very difficult to analyze the problem experimentally and numerically. This work is focused on assessing the performance of the existing numerical models for determining minimum fluidization velocity (u_mf), the effects of the key parameters in bed optimization, the turbulence-like behavior initiating from three-dimensionality, quantification of bed performance, and jet-like patterns in uniform inflow. The Eulerian 2D model overestimates pressure drop near fluidization, and thus the U_mf from pressure drop slope cannot be determined accurately. We investigated the 2D TFM (Two-Fluid Model) abnormal pressure drop near minimum fluidization and proposed an Euler number as a more accurate alternative determining u_mf. From our research, the Kinetic Theory of Granular Flow (KTGF) model for particle interaction is more impactful near fluidization, and the drag model is more influential at velocities above u_mf. Our simulations have shown that wall effects on the particle bed including frictional losses and wall-particle collision are the dominant reasons for abnormal pressure drop near minimum fluidization. In an annular fluidized bed, 3D TFM showed that particle size is the most dominant factor in u_mf, followed by the particle bed height or overburden. Bed thickness does not influence u_mf for this type of fluidized bed. Our CFD-DEM simulations showed that there is an increase in recirculation zones for increasing bed thickness to particle ratio. An approach to quantifying the effectiveness of solid particle beds has been proposed with heat transfer between fluid and particles using the CFD-DEM approach. A more efficient capped fluidized bed design has been proposed, and the numerical results show the significant advantage of capped beds over packed, and fluidized beds. We also observed repeating cellular patterns in particle motion for very small size particles in large elongated fluidized beds, and jet-like patterns for uniform inflow under periodic boundary conditions. This will help us in understanding chaotic particle motion and in optimizing bed heat transfer in the future.Item Phase Behavior and Rheology of Colloids with Polymer-Mediated Attractions(2019-05) Park, Na Young; Conrad, Jacinta C.; Palmer, Jeremy C.; Robertson, Megan L.; Hu, Yandi; Alba, KamranMixtures of colloids and polymers are used in many industrial and commercial applications such as paints, consumer products, and drilling fluids. Addition of polymers to colloidal suspensions can cause attractions between the particles, such as depletion and bridging attractions. These attractions produce complex phase behavior and rheology of the final suspension. In addition to the attractions that arise, the properties of the polymer additives themselves – size, dispersity, charge/interaction with particle – likely also affect the final suspension behavior. In this work, we investigated the effects of these properties of the polymer additives to the phase behavior and rheology of the resulting suspensions. First, we explored the effect of polymer dispersity on the phase behavior of depletion mixtures by using unary and binary mixtures of uniform, small polymers as the depletant in a model colloidal suspension. We found that the phase behavior could be mostly collapsed, irrespective of polymer dispersity, if the polymer concentration was represented as a weighted sum of the two polymers' concentrations in a binary mixture. Then, a new model depletion mixture was developed for measuring stress-dependent rheological properties: shear thickening and first normal stress difference N1. Using this system, we measured the effects of polymer depletant size and dispersity on the rheology of a shear-thickening suspension. The presence of large polymers enhanced the shear thickening of the suspensions and changed the sign of N1 from negative to positive, compared to the nearly hard-sphere suspension. Finally, we explored the effect of polymer adsorption strength on the surface of the particles on the cluster formation and rheology of a model bridging mixture, based on the same model colloidal suspension as the depletion studies. This bridging mixture is a promising model system for future systematic comparisons of the effects of depletion and bridging attractions. The results of this work confirm the importance of studying the effects of the properties of the polymer additives themselves on the final behavior of model colloids with polymer-mediated attractions, and they suggest that this understanding can be used to tune properties of the resulting suspensions.Item Vortex Ring Collision with Free-Slip and No-Slip Wall(2019-05) Mishra, Aakash; Ostilla-Mónico, Rodolfo; Metcalfe, Ralph W.; Alba, KamranVortex ring collision on wall explains azimuthal instability, stretching, vorticity and wall turbulence in a simplified way, required in many applications. Present study performs high Reynolds number (2500 and 4000) simulations of vortex rings approaching no-slip and free-slip walls for different radius ratio (0.1, 0.2, 0.3, and 0.4). Structural and dynamic information, statistics on energy transfer and vortex stretching obtained using the simulations. Three-dimensional simulations helped to understand the mechanism of the formation of azimuthal instabilities and their dependence on Reynolds number and radius ratio, and verified that these instabilities influence the ejection velocity of the new ring, and the generation of small-scale turbulence. Interaction between a ring and a wall compared from that of a vortex pair collision. Axisymmetric simulations performed to help to verify whether the generation of small scales of the new vortex ring is due to azimuthal instabilities or other phenomena.