Heat is a ubiquitous phenomenon and its spatial flow has wide reaching impact that spans industry, physiology and even meteorology through examples such as materials processing, thermotaxis and weather patterns. In fluids, spatial heat flow – temperature difference over a characteristic length scale – produces gradients in density and viscosity to generate convective currents which assuredly affects rheological properties and dynamics. The coupled effects between fluid flow and heat flow are phenomenologically explored. To achieve this, a custom-built apparatus capable of introducing, sustaining and measuring heat flux orthogonal to fluid flow was integrated into a stress-controlled rheometer to investigate the impact of steady state temperature gradients on rheological characteristics under steady shear. The novelty of this system is the capacity to independently control temperature of each rheometer plate (i.e. test surface) to establish discreet temperature gradients in the range of -16 K/mm to 30 K/mm, which also gives a window to any potential gravitational effects. Glycerol is used as a model Newtonian fluid to validate the system. Coupled dynamics is scaled by the Brinkman number and Richardson number and is found to have a linear relationship for glycerol. To expand on this knowledge, preliminary data on a more complex (non-Newtonian) system with relevance to heat transfer applications is presented. The rheological and heat flow data was presented using this approach for nanofluids of two weight fractions of Carbon Nanotubes (CNT) in glycerol in order to further understand the implications and opportunities that interrelationships between heat and fluid flow may present in a more complex system.

In chemical processing industries, heating, cooling and other thermal processing of viscous fluids are an integral part of the unit operations. Consequences of improper mixing include non-reproducible processing conditions and lowered product quality. Static mixers economically promote the mixing of flowing fluid streams. One typical static mixer, the helical static mixer, consists of left- and right-twisting helical elements placed at right angles to each other. The range of Reynolds numbers of practical flows for helical static mixers in industry is usually from very small values to not very large values (e.g., Re = 5,000). This thesis describes how static mixing processes of single-phase Newtonian and also non-Newtonian liquids can be simulated numerically and provides useful information that can be extracted from the simulation results. The Turbulent flow case is solved using the most common Reynolds Averaged Navier-Stocks (RANS) models as well as Large-Eddy Simulation (LES) turbulent flow model. The numerical simulation of the mixing in the helical static mixer has been performed via a two-step procedure. In the first step, the flow velocity (and the pressure) is computed. These values are then used as input to the next step. In the second step the particle trajectory in the flow field is calculated. At the entry of the pipe inlet, a large number of marker particles are uniformly distributed over half of the flow field. This represents a simplified model for diametrical feeding of the mixer with two liquids. Using different measurement tools, such as Residence Time Distribution (RTD) and Particles Distribution Uniformity (PDU), the performance of a six-element helical static mixer is studied. It is shown that the Reynolds number has a major impact on the performance of a static mixer. It is also shown that the performance of a helical static mixer is different for Newtonian and non-Newtonian fluids in non-creeping flows. Finally, heat transfer within a helical (open full item for complete abstract)

Bubble dynamics is an integral part of various industrial processes such as aeration, bubble column reactors, and has been a topic of active research for nearly eight decades. Significant progress has been made towards understanding the factors governing the departure bubble size and shape, in particular the effect of liquid physicochemical properties. Bubble dynamics plays an important role in industries such as cosmetics, pharmaceuticals, and paints where a large majority of the liquids being used are of non-Newtonian nature and undergo a change in their viscous properties under the effect of stress. The complex thermo-physical properties of non-Newtonian fluids play a huge role in dictating the bubble growth process and needs further investigation. The aim of this work is to gain a better understanding of the complex physics governing the growth of bubbles from capillary orifices submerged in liquid pools of aqueous solutions of polymers under constant gas flow rate through a combination of experimental and computational approaches. A comprehensive evaluation of existing computational techniques for studying single bubble growth is carried out and coupled level set VOF technique with modifications to the property estimation equation is suggested as a reliable technique to accurately model bubble growth in highly viscous fluids, with large capillary numbers greater than 1. Following this, a brief characterization of non-Newtonian fluids is made along with a comparison of most frequently used rheology models. Selecting the right model plays an important role in computational modeling as each model has its limitations and hence may only be applicable for certain concentrations of polymers. Rupesh Bhatia has shown in his work that the asymptotic forms of certain rheology models work better in characterizing the fluid and the importance of the Asymptotic Power Law (APL) model in the computational modeling of bubble growth in shear-thinning non-Newtonian fluids is esta (open full item for complete abstract)

Concentrated suspensions have been an area of research for years, with wide range of applications in industry and nature. One of the main issues encountered when handling such materials is the development of particle concentration inhomogeneities under shear, as a result of sedimentation and Shear Induced Migration (SIM). Experimental techniques to study the dynamics of suspension flows thus require high spatial and temporal resolutions to capture profiles of solid volume fraction in both transient and steady-state conditions. When optical access is possible, methods like particle tracking are employed due to their high temporal and spatial resolutions; however, optical access is limited in real systems and even in the majority of model suspensions. In these last cases, methods involving Nuclear Magnetic Resonance (NMR) are employed. These methods require the use of homemade devices, which makes them rare and expensive. Moreover, the time required for data acquisition is large, making them incapable of studying fast changes and monitoring volume fraction evolutions continuously. Available methods may thus not fully meet all the requirements to study most suspension flows. The objective of this thesis is to study SIM of particles in yield stress fluids. The contribution of this thesis comes into two parts. First, we introduce a new technique based on X-ray radiography with high temporal (O(0.1 sec)) and spatial (O(10 μm)) resolutions to overcome the above-mentioned limitations. This technique allows us to study the evolution of the solid volume fraction in fast suspension flows regardless of optical access. We benefit from the axial symmetry in our flow configuration, a wide gap Couette setup, to extract a 3D solid volume fraction field from a single X-ray projection image. We propose a mathematical algorithm based on the inversion of Abel transform in conjunction with H1 regularization and data denoising to measure the solid volume fraction field in suspensions i (open full item for complete abstract)

Blood is a complex fluid that consists of approximately 45% solid particulates by volume. These solid particulates, erythrocytes, cause the fluid to exhibit a non-Newtonian, shear thinning rheology under low shear rates (<200s-1) and Newtonian rheology otherwise. Many researchers employ Newtonian blood analogs to study the relationship between hemodynamics and morphogenesis when the predominant shear rates in the vessel are high. Non-biological, shear thinning fluids have been observed to transition from laminar to turbulent flow differently than Newtonian fluids. A discrepancy between the critical Reynolds number of blood and a Newtonian analog could result in erroneous predictions of hemodynamic forces. The goal of the present study was to compare velocity profiles near transition to turbulence of whole blood and a Newtonian blood analog downstream of a stenosis under steady flow conditions. Doppler ultrasound was used to measure velocity profiles of whole porcine blood and a Newtonian fluid in an in vitro experiment at 13 different Reynolds numbers ranging from 150 to 1200. Three samples of each fluid were examined and fluid rheology was measured before and after each experiment. Results show parabolic like velocity profiles for both whole blood and the Newtonian fluid at Reynolds numbers less than 250 (based on the viscosity at 400s-1). The Newtonian fluid had blunt velocity profiles with large velocity fluctuations (root mean square as high as 25%) starting at Reynolds numbers ~250 which indicated transition to turbulence. In contrast, whole blood did not transition to turbulence until a Reynolds number of ~300-600. All three blood samples were delayed compared to that of the Newtonian fluid, although there were variabilities between the critical Reynolds numbers. For Reynolds numbers larger than 700, the delay in transition resulted in differences in velocity profiles between the two fluids as high as 35%. A Newtonian assumption for blood at flow conditions (open full item for complete abstract)

The objective of this work is to gain information that could be used to design full scale mixing systems, and also could develop a design guide that can provide a reliable prediction of the power draw of different types of impellers. To achieve this goal, the power number behavior, including three operation regimes, the limits of the operation regimes, and the effect of baffling on power number, was compared across the full Reynolds number spectrum for Newtonian fluids in a laboratory-scale agitator. Six industrially significant impellers were tested, including three radial flow impellers: D-6, CD-6, and S-4, and also three axial flow impellers: P-4, SC-3, and HE-3. Results in laminar regime indicate that baffling has no effect on power number in this operation regime. There is an inversely proportional relationship between power number and Reynolds number. The upper limit for this operation regime should be lower than 10, the limit commonly noted in the literature. The product of power number and Reynolds number in this particular regime is approximately proportional to the number of blades for these six impellers; however, other shape factors that were not included in this study also contribute to it. In turbulent operation, baffling has a significant effect on power number: the power number for most impellers remains relatively constant in the baffled configuration while that for unbaffled configuration decreases with increasing Reynolds number. The impeller blade number is not the dominant factor that affects power number in this regime. Two hydrofoil impellers, SC-3 and HE-3, exhibit much lower power numbers when compared with the other impellers. Additionally, the impellers with higher power numbers in baffled tank tend to have lower ratios between unbaffled power number and average baffled power number when comparing at same Reynolds number. No difference between two configurations, baffled and unbaffled, exists at low Reynolds number end of transit (open full item for complete abstract)