This work describes the development of a microfluidic platform that can be used to study suspension stability and crystallization with in droplets as a function of time and concentration. Techniques for monodisperse droplet formation, droplet trapping and storage, and droplet dehydration are developed and used to design a microfluidic platform that can be adapted for the applications of interest. A geometric model is developed to predict the droplet shape and emulsion structure generated by microfluidic nozzles. However, droplet volume and structure spacing cannot be independently controlled using microfluidic nozzles, and a design consisting of an array of traps is considered to achieve the desired structure for stable, extended droplet observation. The dehydration of aqueous droplets stored in the array is characterized as a function of relative humidity, and is shown to be reasonably estimated as a species diffusing from a sphere into an infinite medium. The microfluidic platform for droplet dehydration is combined with particle tracking to show that the stability of particle suspensions can be probed as a function of salt concentration. The flocculation behavior observed in the trapped droplets agrees well with corresponding macroscale measurements as well as with previously published studies. The platform is also used to generate substantial sample sizes to measure nucleation statistics and crystal growth rates of glycine as a function of initial concentration, environmental conditions, and the presence of additives. These applications show proof of concept that the microfluidic platform is a useful tool for the analysis of the behavior observed during particle aggregation and crystallization.

Nanofluids, a new class of fluids engineered by suspending nanometer-sized particles in a host liquid, are offered as a new strategy in order to improve heat and mass transfer efficiency. My research was motivated by previous exciting studies on enhanced mass diffusion and the possibility of tailoring mass transport by direct manipulation of molecular diffusion. Therefore, a microfluidic approach capable of directly probing tracer diffusion between nanoparticle-laden fluid streams was developed. Under conditions matching previously reported studies, strong complexation interactions between the dye and nanoparticles at the interface between fluid streams was observed. When the tracer dye and surfactant were carefully chosen to minimize the collective effects of the interactions, no significant change in tracer dye diffusivity was observed in the presence of nanoparticles. Next, adapting tracer dyes for studies involving colloidal nanomaterials was explored. Addition of these charged tracers poses a myriad of challenges because of their propensity to disrupt the delicate balance among physicochemical interactions governing suspension stability. Here it was shown how important it is to select the compatible combinations of dye, nanoparticle, and stabilizing surfactant to overcome these limitations in low volume fraction (< 1 vol%) aqueous suspensions of Al2O3 nanoparticles. A microfluidic system was applied as a stability probe that unexpectedly revealed how rapid aggregation could be readily triggered in the presence of local chemical gradients. Suspension stability was also assessed in conjunction with coordinated measurements of zeta potential, steady shear viscosity and bulk thermal conductivity. These studies also guided our efforts to prepare new refrigerant formulations containing dispersed nanomaterials, including graphene nanosheets, carbon nanotubes and metal oxide and nitride. The influence of key parameters such as particle type, size and volume fraction on the suspension's thermal conductivity was investigated using a standard protocol. Our findings showed that thermal conductivity values of carbon nanotube and graphene nanosheet suspensions were higher than TiO2 nanoparticles, despite some nanoparticles with large particle sizes provided noticeable thermal conductivity enhancements. Significantly, the graphene containing suspensions uniquely matched the thermal conductivity enhancements attained in nanotube suspensions without accompanying viscosity, thus making them an attractive new coolant for demanding applications such as electronics and reactor cooling.

No / A vehicle that deviates laterally from its intended path of travel when the brakes are applied is considered to demonstrate ‘instability’ in the form of an unexpected and undesirable response to the driver input. Even where the magnitude of lateral displacement of the vehicle is small (i.e. ‘drift’ rather than ‘pull’) such a condition would be considered unacceptable by manufacturers and customers. Steering ‘drift’ during braking can be caused by several factors, some of which relate to vehicle design and others to external influences such as road conditions. The study presented here examines the causes and effects of steering drift during straight-line braking. A comparative analysis is made between two types of vehicle model: one built with rigid suspension components and the other with flexible components. In both the cases, the vehicle behaviour is simulated during braking in a straight line, and responses including lateral acceleration, yaw rate, and lateral displacement of the vehicle are predicted and analysed under fixed steering control. Suspension/steering geometry characteristics, namely toe steer and caster angle, have been studied to understand how the effect of variations in these parameters differs in models with rigid or flexible components drift during straight-line braking. Results from both vehicle models show that differences between rigid and flexible components can affect the predicted steering drift propensity. The differences between the two models have emphasized the importance of using flexible (compliant) components in vehicle handling simulations to achieve better correlation between prediction and experiment.

Two vehicular optimal control problems are visited. The first relates to the minimum lap time problem, which is of interest in racing and the second the minimum fuel problem, which is of great importance in commercial road vehicles. Historically, minimum lap time problems were considered impractical due to their slow solution times compared with the quasi-steady static (QSS) simulations. However, with increasing computational power and advancement of numerical algorithms, such problems have become an invaluable tool for the racing teams. To keep the solution times reasonable, much attention still has to be paid to the problem formulation. The suspension of a Formula One car is modelled using classical mechanics and a meta-model is proposed to enable its incorporation in the optimal control problem. The interactions between the aerodynamics and the suspension are thereby studied and various related parameters are optimised. Aerodynamics plays a crucial role in the performance of Formula One cars. The influence of a locally applied perturbation to the aerodynamic balance is investigated to determine if a compromise made in design can actually lead to lap time improvements. Various issues related to minimum lap time calculations are then discussed. With the danger of climate change and the pressing need to reduce emissions, improvements in fuel consumption are presently needed more than ever. A methodology is developed for fuel performance optimisation of a hybrid vehicle equipped with an undersized engine, battery and a flywheel. Rather than using the widely used driving cycles, a three-dimensional route is chosen and the optimal driving and power management strategy is found with respect to a time of arrival constraint. The benefits of a multi-storage configuration are thereby demonstrated. Finally, the nonlinear stability of a vehicle model described by rational vector fields is investigated using region of attraction (RoA) analysis. With the aid of sum-of-squares programming techniques, Lyapunov functions are found whose level sets act as an under-approximation to the RoA. The influence of different vehicle parameters and driving conditions on the RoA is studied.