Prosthetic cardiac valve surgery is a well-established technique, but the search continues for engineering materials with sup..e rior mechanical characteristics in order to extend the service life of the implant. The introduction of pyrolytic carbon was seen as a breakthrough in the development of wear resistant, non-thrombogenic materials for such applications. However, thrombo-embolic phenomena and the need for anticoagulation treatment following valve insertion remain the main problems associated with artificial materials in this application. The work carried out in this research has studied the haemocompatibility of a commercially available, wear resistant TiffiN/TiCfDLC multilayer structure, and a second TiN coating deposited by RF reactive sputtering of a titanium target in a ArIN2 environment, as candidate materials for a heart valve prosthesis. The structure of the RF deposited tiN coating was assessed as a function of deposition conditions, and was seen to develop a particular preferred crystallographic orientation. The nature of this texture was influenced by the condition of the underlying substrate. The effect of substrate condition on the biocompatibility of the tiN coating was studied by assessment of fibroblast attachment and spreading, and by haemolytic analysis of released haemoglobin. The results showed that the initial attachment and orientation of fibroblast cells was influenced by the substrate condition, but no influence on the degree of spreading and haemolytic nature was observed. Characterisation of the TiN coating and the components of the multilayer structure was carried out by Atomic Force Microscopy (AFM), X-ray Photoelectron Spectroscopy (XPS), stylus profilometry and contact angle measurement. Haemocompatibility was studied by the interaction of the surfaces with plasma proteins, blood platelets and red blood ceUs. Cytotoxicity was studied using the MTT test. The degree of platelet activation on the surfaces correlated with their surface energy. The greatest degree of platelet spreading was observed on the more hydrophilic coatings. The lack of platelet activation seen on the DLC coating is attributed to its smooth surface and hydrophobic nature, resulting in higher levels of adsorption of anticoagulation proteins. The RF sputtered TiN coating caused significant levels of haemolysis and fibroblast cell death. None of the components of the multilayer structure caused such effects, although thrombus formation was observed to a degree on the Ti, TiN and TiC components of this structure. The toxic nature of the RF deposited TiN coating was not attributed to surface chemistry or roughness, but rather to a combination of the hydrophilic nature and the defect state of the surface.

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In this thesis, some fundamentals and possible applications of high-pressure microfluidics have been explored. Furthermore, handling fluids at high pressures has been addressed, specifically by creating and characterizing strong microvalves and pumps. A variety of microstructuring techniques was used to realize these microfluidic devices, e.g., etching, lithography, and bonding. To be able to handle high pressures, the valves and pumps need to be strong. This necessitates a strong actuator material. In this thesis, the material of choice is paraffin wax. A new way of latching paraffin-actuated microvalves into either closed or open position has been developed, using the low thermal conductivity of paraffin to create large thermal gradients within a microactuator. This allows for long open and closed times without power consumption. In addition, three types of paraffin-actuated pumps are presented: A peristaltic high-pressure pump with integrated temperature control, a microdispensing pump with high repeatability, and a pump system with two pumps working with an offset to reduce flow irregularities. Furthermore, the fundamental behavior of paraffin as a microactuator material has been explored by finite element modeling. One possibility that arises with high-pressure microfluidics, is the utilization of supercritical fluids for different applications. The unique combination of material properties found in supercritical fluids yields them interesting applications in, e.g., extraction and cleaning. In an attempt to understand the microfluidic behavior of supercritical carbon dioxide, the two-phase flow, with liquid water as the second phase, in a microchannel has been studied and mapped with respect to both flow regime and droplet behavior at a bi-furcating outlet.

Valvular heart disease (VHD) continues to have significant effects on many people’s lives, with numbers expected to grow tremendously over the next few years. Individuals suffering from severe valvular heart disease usually require a heart valve transplant in order to restore the native valve’s vital unidirectional flow regulation. Therefore, artificial heart valve (AHV) research is of very high importance. Previous research studies have provided substantial input in the realm of AHV design relative to durability, thrombotic and hemolytic potential, and overall functionality. However, modifications continue to be warranted due to limitations in the accuracy and time efficiency of the in vitro physiological flow replication process. The objective of this investigation is to develop and analyze a method of AHV performance evaluation using a novel test chamber within an automated mock circulatory loop. The constructed mock loop was designed to maintain consistency of current industrial and academic research systems while providing innovative loop component control that allows for run-time changes and performance screening to various physiological conditions. Pressure sensors, ultrasonic flow meter, process controls and mechanical feedback sensors are managed via Labview in order to provide sufficient real-time performance analysis during system operation. In addition, a unique mechanical heart valve (MHV) test chamber was constructed to incorporate the test AHV in the mock loop flow path. This research exposes a test tilting disk MHV to a series of 12 heart rate and stroke volume combinations so as to evaluate the system’s effectiveness in pathological condition replication with respect to AHV design research. A Particle Image Velocimetry (PIV) system was utilized to illuminate particles in the flow field and obtain representative vector plots. Results of this study validate the combined experimental test chamber and automated mock circulatory loop as a viable MHV performance evaluation system by using real-time pressure and flow data to analyze system fluid dynamics at the MHV test site. Consequently, the use of this arrangement in MHV performance analysis greatly improves upon time restraints and accuracy concerns associated with currently used manually controlled setups.

Previous research on new novel substrates for giant magnoresistance structures has indicated that a net increase in the effect is present. The substrates studied were V-grooved or stepped, however research presented in this thesis used an embossed surface manufactured from alumina oxide which consisted of regular hexagonal arrays with spacing of 110 nm and pore diameter of 60 nm. The physical properties measurements unveiled a net enhancement of the giant magnetoresistance effect thru the whole range of the copper spacer thicknesses deposited with direct current magnetron sputter. The maximum net increase appeared for a spacer thickness of 4.0 nm where the flat silicon substrate yielded a 3 % increase but the embossed surface substrate generated a 12% increase with an overall effect of a 4-fold net enhancement of the effect. Both the aluminum oxide substrates and the thin films structures can be manufactured inexpensively and can be also mass-produced, which are welcoming advantages for the technology sector of magnetic sensing.

Proton Exchange Membrane (PEM) fuel cells are becoming an increasingly important alternative to combustion engines as the fossil fuel reserves are depleted. Several papers have presented steady state analyses of the system, but few are known to present dynamic analysis of the flow and control of the hydrogen delivery process. This thesis presents the dynamic analysis of hydrogen delivery to a PEM fuel cell system. The hydrogen is delivered to the anode with use of an ejector for passive recirculation. The system to be studied consists of the manifolds, ejector, and pressure control valve. Models describing the elements of the anode delivery systems are formulated. The governing nonlinear equations are solved analytically and numerically, and the regimes of stable hydrogen delivery process are established. The linearized models are used for performance analysis and optimization of the hydrogen delivery process. The nonlinear model is used to improve the simulation of the dynamics of the PEM fuel cell system and validate the parameters at optimal linearized stability. Experiments are conducted to find the parameters used in the model, as well as validate the results. Both the linear and nonlinear models are implemented in Simulink and tested against the laboratory data from the PEM fuel cell system. The analysis showed that the models have the same time constant and dynamic behavior as the PEM system. The optimal parameters for stability and a faster response with no oscillations in the output are obtained. The redesigned valve and resulting dynamics of the PEM fuel cell system provides improved system performance.

The rotary valve is a widely used mechanical device in many solids-handling industrial processes. However, it may also be responsible for most of the attrition effects occurring in a typical process. In this study, the attrition effects occurring in a rotary valve operating as a stand-alone device and as part of a pneumatic conveying system were investigated. In the former case granular attrition was carried out at three different rotary valve speeds and the experimental results obtained were found to be in good agreement with the Gwyn correlation. In the latter case three typical air flow rates were used in the pneumatic conveying system. The size distribution of the attrition product obtained at the lowest air flow rate used was not adequately described by the Gwyn correlation. The attrition process and mechanisms involved were analysed and the minimum size of the attrition product obtained from both modes of operations was found to be similar. / Singapore-MIT Alliance (SMA)

The mitral valve in the heart sometimes struggles with diseases and complications, and needs to be replaced. This problem becomes more frequent with the ageing of the population in developed countries. The most common practice consists of suturing a prosthetic valve into place. However, newer methods are being devised and tested to make the surgery faster and less invasive. In particular, various types of new sutureless heart valve systems exist on the market. However, there is still a need for a tool designed for the intracardiac delivery and anchoring of a prosthetic mitral valve, as addressed here. A number of criteria and specifications were set by researchers at the Robarts Research Institute (London, ON) who came up with the design task. To address their request, ten conceptual designs of a sutureless, virtual-reality guided, self-anchoring, intracardiac system were developed to hold a prosthetic mitral valve, deliver it safely, and quickly affix it in position. The winning concept adequately met the design criteria. Two prototypes were manufactured. The attachment of a prosthetic valve to a simulated mitral valve annulus was tested with the first prototype to verify feasibility and measure leakage. The second prototype was pressure tested in a dynamic surgical phantom reproducing the circulatory conditions during surgery. While the preliminary feasibility of the concept was established, recommendations were made to develop a less bulky design.

The survey from US Department of Energy showed that about one-third of energy consumption in US is due to air conditioning and refrigeration systems. This significant usage of electricity in the HVAC industry has prompted researchers to develop dynamic models for the HVAC components, which leads to implementation of better control and optimization techniques. In this research, efforts are made to model a multi-evaporator system. A novel dynamic modeling technique is proposed based on moving boundary method, which can be generalized for any number of evaporators in a vapor compression cycle. The models were validated experimentally on a commercial supermarket refrigeration unit. Simulation results showed that the models capture the major dynamics of the system in both the steady state and transient external disturbances. Furthermore the use of MEMS (microelectromechanical) based Silicon Expansion Valves (SEVs) have reportedly shown power savings as compared to the Thermal Expansion Valves (TEVs). Experimental tests were conducted on a supermarket refrigeration unit fitted with the MEMS valves to explain the cause of these potential energy savings. In this study an advanced cascaded control algorithm was also designed to control the MEMS valves. The performance of the cascaded control architecture was compared with the standard Thermal Expansion Valves (TEVs) and a commercially available Microstaq (MS) Superheat Controller (SHC). The results reveal that the significant efficiency gains derived on the SEVs are due to better superheat regulation, tighter superheat control and superior cooling effects in shorter time period which reduces the total run-time of the compressor. It was also observed that the duty cycle was least for the cascaded control algorithm. The reduction in duty cycle indicates early shut-off for the compressor resulting in maximum power savings for the cascaded control, followed by the Microstaq controller and then the Thermal Expansion Valves.

Since water-use characteristics and the new technology of plumbing fixtures have changed, it is significant to educate a facility manager in the characteristics of these systems. Also, it is necessary to provide a better understanding of parameters that may determine the suitability of retrofitting plumbing fixtures. The 1992 Energy Policy Acts enforces 1.6-gallon per flush (gpf) for a toilet and 1.0 gpf for a urinal. In response to the regulation, the purpose of this research is to measure automatic flush valve performance (gpf) of fixtures in a mixed use classroom building at Texas A&M University. Water consumption (gpf) among three types of fixtures; low-consumption manual, old optic automatic and improved optic automatic systems are measured by using a magnetic water flow meter. The data in the study were analyzed to determine compliance with plumbing standards and to compare the average water volume per flush cycle of toilets in the men??s and women??s restrooms. Finally, the results of the data show that retrofitting the old optic automatic with the improved optic automatic system resulted in water savings of about 15.80% in toilets, and urinals.