Search

For many centuries, researchers have investigated the complex interactions between a solid surface and a fluid in motion relative to the surface. For many cases, the classical no slip boundary condition holds true. However, there are a subset of situations where this assumption is not valid, and slip between the surface and fluid must be considered. One such example is a micropatterned, superhydrophobic surface, which has been shown to enable slip resulting in a decrease in drag and pressure loss for both laminar and turbulent flow. The hydrodynamic effects of these surfaces have been studied in depth, but the effects on heat transfer are largely unknown. The primary goal of this research effort was to explore the effects of slip flow on laminar convective heat transfer resulting from micropatterned, superhydrophobic surfaces. The first step toward achieving the research goal was to develop a model to study first order effects, predict the effect of slip flow on heat transfer, and design the experimental setup. The general momentum equation for Poiseuille flow was solved using modified boundary conditions consistent with slip flow, and the resulting velocity profile was input into the thermal balance equation which was numerically solved. The model assumed hydrodynamic slip but not thermal slip nor a temperature jump at the boundary, and as a result, it predicted a net increase in heat transfer performance. For the experimental portion of the study, laminar Poiseuille flow in a parallel plate configuration with a constant temperature boundary condition at 273 K using an ice bath was studied. Four sets of copper sample plates measuring 15 cm by 3.8 cm were fabricated with different surface condition: 1) uncoated smooth, 2) hydrophobic coated smooth, 3) uncoated micropatterned, and 4) hydrophobic coated micropatterned. The micropattern was a laser machined array of 25 \uf06dm x 25 \uf06dm microridges oriented in the streamwise direction. Contact angle measurements wer

The work contained herein describes the use of various magnetic fields to control the structure and dynamics of magnetic particle suspensions, with the practical aim of enhancing momentum, heat, and mass transport. The magnetic fields are often multiaxial and can consist of up to three orthogonal components that may be either static (dc), time-dependent (ac), or some combination thereof. The magnetic particles are composed of a ferromagnetic material—such as iron, nickel, cobalt, or Permalloy—and can exist in a variety of shapes, including spheres, platelets, and rods. The shape of the particles is particularly important, as this can determine the type of behavior the suspension exhibits and can strongly affect the efficacy of various transport properties. The continuous phase can be almost any fluid so long as it possesses a viscosity that allows the particles to orient and aggregate in response to the applied field. Additionally, if the liquid is polymerizable (e.g., an epoxy system), then composite materials with particular, field-directed particle assemblies can be created. Given the many combinations of various particles, suspending fluids, and magnetic fields, a vast array of behavior is possible: the formation of anisotropic particle structures for directed heat transport for use as advanced thermal interface materials; the stimulation of emergent dynamics in platelet suspensions, which give rise to field-controllable flow lattices; and the creation of vortex fluids that possess a uniform torque density, enabling such strange behaviors as active wetting, a negative viscosity and striking biomimetic dynamics. Because the applied fields used to produce many of these phenomena are uniform and modest in strength, such adaptive fluids open up the possibility of tuning the degree of mixing or heat/mass transfer for specific operating conditions in a number of processes, ranging from the microscale to the industrial scale. Moreover, the very nature of ma

For many centuries, researchers have investigated the complex interactions between a solid surface and a fluid in motion relative to the surface. For many cases, the classical no slip boundary condition holds true. However, there are a subset of situations where this assumption is not valid, and slip between the surface and fluid must be considered. One such example is a micropatterned, superhydrophobic surface, which has been shown to enable slip resulting in a decrease in drag and pressure loss for both laminar and turbulent flow. The hydrodynamic effects of these surfaces have been studied in depth, but the effects on heat transfer are largely unknown. The primary goal of this research effort was to explore the effects of slip flow on laminar convective heat transfer resulting from micropatterned, superhydrophobic surfaces. The first step toward achieving the research goal was to develop a model to study first order effects, predict the effect of slip flow on heat transfer, and design the experimental setup. The general momentum equation for Poiseuille flow was solved using modified boundary conditions consistent with slip flow, and the resulting velocity profile was input into the thermal balance equation which was numerically solved. The model assumed hydrodynamic slip but not thermal slip nor a temperature jump at the boundary, and as a result, it predicted a net increase in heat transfer performance. For the experimental portion of the study, laminar Poiseuille flow in a parallel plate configuration with a constant temperature boundary condition at 273 K using an ice bath was studied. Four sets of copper sample plates measuring 15 cm by 3.8 cm were fabricated with different surface condition: 1) uncoated smooth, 2) hydrophobic coated smooth, 3) uncoated micropatterned, and 4) hydrophobic coated micropatterned. The micropattern was a laser machined array of 25 \uf06dm x 25 \uf06dm microridges oriented in the streamwise direction. Contact angle measurements wer

Electrostatic properties of uidic nanoscale systems are of fundamental interest and play an important role in many engineering applications. Due to the large surface area to volume ratios of these systems, interfacial phenomena are of key importance to understanding their behavior. We present several studies of uidic nanoscale systems using the Poisson{Boltzmann equation which treats the uid as a continuum, and density functional theory of uids which uses a statistical mechanical treatment of the uid that includes nite-size e ects. Chemical equilibria at the interface is accounted for by coupling these methods with charge regulating theory. The e ects of charge regulation lead to several novel predictions about uidic nanoscale systems including pH dependent conductivities, reduced stability of doped colloidal dispersions, and a dependence of the surface charge on the solvent structure.

The investigation of aspect-ratio-dependent diffusion and equilibrium partitioning of semiconductor nanocrystals in rectangular nanochannels has been undertaken. The nanocrystals are terminated with hydrocarbon ligands and suspended in toluene, considered an aprotic solvent. Time-dependent concentration profiles are measured as a function of distance from the channel entrance by the calibrated fluorescence intensity of the nanocrystals. Both the forward diffusion of the nanocrystals and their reverse diffusion are characterized. Nanocrystals are first allowed to diffuse forward from a reservoir into the nanochannels over a long period (\u2265 3 days) until the inlet concentration reaches a steady state. Subsequently, these nanocrystals are allowed to diffuse out, in reverse, from the nanochannels back into the reservoir that is filled with neat toluene. The experimentally observed concentration profiles during forward diffusion are compared to the profiles resulting from a continuum transport model accounting for diffusion and wall-adsorption of nanocrystals. The transport model provides estimates on the diffusion constant, equilibrium coefficients, and the adsorption/desorption rate constants. For the aspect ratios ranging from 1 to 6, the observed concentration within the nanochannels is significantly higher (\u2265 x4) than the initial bulk concentration within the reservoir, indicating wall adsorption of nanocrystals. Despite the significant level of fluorescence intensity originating from the wall adsorbed NCs, the fractional surface coverage of nanocrystals remains below 1 monolayer. Using a two-site adsorption model, the diffusion constants from the forward diffusion profiles range from 10^-8 to 10^-9 cm^2 s^-1, while the adsorption rate coefficients range from 0.36 to 1.60 (x10^-15 cm^2 s^-1). In general, we observe an attractive van der Waals force between the NCs and the channel walls that allows for a reversible wall adsorption that strongly affects the a

Selective oxidation chemistry is a topic of intense interest worldwide, in particular when using molecular oxygen (O2) directly as the oxidizing species. The primary reason for using O2 rather than other oxidants is to take advantage of the inexpensive nature of oxygen; however, the radical ground state of O2 leads to non-selective reactions with organic substrates. As such, basic knowledge and understanding involving the fundamental reactions of O2 with organometallic species will be required in order to overcome this lack of selectivity. The work presented in this dissertation has two main research goals to help address this issue. First, we have synthesized and characterized a number of various pincer-carbene containing Ni and Pd hydrides. We have postulated that these species might function as homogeneous catalysts to deliver O atoms to various organic or inorganic substrates. Second, we are interested in demonstrating the reactions of these carbene complexes with O2. As both the precursors and O2 reaction products of carbene-pincer complexes have been studied only briefly previously, we anticipated that our studies would add to the fundamental understanding of these complexes. Specifically, syntheses and characterization of novel pincer carbene Pd-H complexes was achieved. The pincer carbene Pd-H complex proved reactive with O2; however, the isolation of a discrete Pd-OOH species was unsuccessful. Investigation of the oxygen transfer ability of these complexes was done through in situ reaction of Pd-H species, O2 and organic substrates. However, there was no evidence indicating oxygen transfer to the organic substrates. New pincer carbene Pd and Ni complexes were prepared and characterized through alternative routes to M-H or M-OOH. Although none of these routes led to isolation of M-OOH species, MeCCC-Pd-OTf reacted with H2O2/H2O to form MeCCC-Pd-OH. Further investigation on this reaction suggested that the desired Pd-OOH species may initially be formed which

Novel platinum nanostructures were synthesized by templating the growth of platinum on treated polymer surfaces and within disk-like aqueous bicellar assemblies. The growth mechanisms of all structures were examined in detail. Platinum hollow nanospheres with uniform shell thickness were prepared by the seeded growth of platinum on the surface of latex beads with an adsorbed porphyrin photocatalyst followed by core removal. Templating bicelles of a high yield were synthesized for the first time and verified by electron microscopy. Dendritic platinum nanowheels were obtained as a result of confined growth within the bicellar interior. Sintering experiments revealed an unusual stability of the nanowheels prompting further examination of their catalytic properties. The nanowheels have similar catalytic performance to a commercial catalyst but provide an improvement in stability. These platinum nanostructures have advantages over bulk catalyst as a result of improved surface to volume ratios leading to reduced costs in catalytic applications.