The electrohydrodynamic (EHD) technique has recently been the subject of much research due to its ability to process a wide range of materials into monodispersed micro/nano-sized products. Recent developments in the technology allow this process to be portable and allow the incorporation of multiple layers in the final product which further increases the potential applications of this technique. This work explores a modular EHD needle design as a handheld and multineedle format for wound dressing and drug delivery applications respectively. The first part of this work investigates the effects of the electrode and collector positioning on the products generated by EHD processing. The electric field and flight times measured indirectly were found to affect particles and fibres differently. Once this was established, a mobile unit was constructed and assessed in its ability to generate fibrous wound dressings in situ. The device was able to direct fibre deposition with great accuracy and ease of use. The dressings were electrostatically attracted to the skin and adhered well due to electrostatic forces. An additional application of the multi-needle device is in the manufacturing of drug delivery products. Multi-needle devices were used to produce multi-layered capsules containing PLGA-chitosan-PLGA for potential anti-cancer therapy. This research demonstrates the potential of the modular needle device to produce products with real world biomedical applications. By incorporating the multi-needle device into the handheld format, this gives the potential of creating layered structures potentially incorporating multiple active agents on demand which can be directed towards a site of injury.

The superior oil sorption performance of electrospun polystyrene (PS)/PS-based fibres has rendered its use more competitive than the commercial melt blown polypropylene (PP) fibres. However, on a microscale level, the oil - sorbent interaction and its effect on the sorption behaviour is yet to be fully understood; considering PP polymer is known to have a lower surface energy than polystyrene. Furthermore, the commercialisation of electrospun PS sorbent has been hindered due to the poor mechanical strength of the fibre mats particularly after oil sorption. Therefore, the aim of this thesis is to (1) enhance the understanding of the oil sorption behaviour of electrospun PS fibres (single filament level) and (2) to explore ways to effectively enhance the mechanical properties of the PS fibre mat. The oil adherence potential of filaments of electrospun PS and subsequent comparison with filaments of the commercial melt blown PP sorbent was quantitatively evaluated using drop-on-fibre micro-sorption technique. This was preceded by a systematic optimisation of the electrospinning process, 20%w/w concentration of PS dissolved in DMF/THF (4:1) gave fibres with the best morphology for the micro-sorption test. Further experiments showed single filaments of electrospun PS to exhibit the strongest affinity to the two oils tested, with a mean adhesive energy of 18.0 x 10-13J and 26.2 x 10-13J for sunflower and motor oil respectively. This represents values 3 – 6 times higher than those recorded for single filaments of the PP counterparts. The superior oil adsorptivity of PS fibre was attributed to its chemical structure i.e. the presence of aromatic phenyl group in its structure. For the second aim of this thesis, a single step electrospinning method of blending PS and thermoplastic polyurethane PU polymers in different weight ratio of PSPU polymer blend was explored, using either a Flat Collector (FC) or a Drum Collector (DC) system. This was done in order to enhance the mechanical properties of PS fibres. The method is a simple, cost-effective engineering approach and exhibits great potential. The ultimate tensile strength (UTS) and elongation at UTS were seen to rise with increased PU content. Samples of PSPU ratio 6:4 fabricated using a DC system (PSPU_DC 6:4) and those fabricated using the FC system (PSPU_FC 6:4) recorded a 600% and 1000% increase in tensile strength respectively, in comparison to the pure PS mat. The oil sorption and retention capacities was seen to be dependent on several variables including the fibre collection system. Post treatment of the fibre mat using heat treatment around the polymer glass transition temperature (110oC) was seen to induce inter-fibre bonds, with the amount of bonds seen to rise with increase in treatment temperature. This causes a simultaneous increase in tensile strength. The work presented in this thesis has pioneered some key aspects that will take electrospinning of polymer fibres further. In terms of characterization, it is the first to quantitatively evaluate the oil adsorptivity of filaments of electrospun PS and melt blown polypropylene sorbents. This creates fundamental insight into the sorption mechanism at a micro-scale level to aid the design of future and improved electrospun sorbents. Also, the electrospinning of PS and PU presented in this thesis, is the first time polymer blend of both polymers is being electrospun for any application, with detailed characterisation of the bi-component fibres presented.

In this study, a novel K-junction microfluidic junction and a conventional cross-junction were investigated numerically and experimentally for microbubble generation and multiple fluids mixing. In the K-junction, liquid solutions were injected into the junction via three liquid inlet channels, along with inert nitrogen gas supplied via the gas inlet channel, to periodically generate microbubbles in a controlled manner at the outlet channel. Numerical simulations based on Finite Volume method and Volume of Fluid (VOF) technique and experiments of both the K-junction and the cross-junction were conducted. The effect of parameters such as contact angle, surface tension, viscosity, gas pressure and gas-liquid flow ratios on the microbubble size distribution was investigated. The process of microbubble generation, obtained through high speed camera imaging and the numerical simulation, has shown good agreement in both junctions as well as the influence of viscosity and gas-liquid flow ratios for the K-junction and cross-junction. It was indicated that parameters like solution viscosities, gas-to-liquid flow ratios, gas inlet pressure, and their combination have a significant influence on the microbubble diameter, which was found to be in the range of 70-240 μm when using micro capillaries of 100 μm inner diameter. The multiple fluids mixing study was investigated by using two or three different polymer solutions for the cross-junction and the K-junction respectively in simulations and experiments. It can be seen that the mixing process obtained from simulations agrees well with experimental results and chaotic mixing was found in the mixing area of the K-junction, with higher mixing efficiency than the cross junction. Fluorescent images of microbubbles generated by using polymer solutions with dyes inside have shown the devices’ potential of encapsulating fluorescent dyes and polymers on the shell of bubbles and could be adopted as a method to encapsulate active pharmaceutical ingredients for potential applications in drug delivery.

In our vessels, the endothelial glycocalyx is the first and foremost barrier directly exposed to the blood in the lumen. The functions of the normal endothelial glycocalyx under physiological conditions are widely accepted as a physical barrier to prevent the abnormal transportation of blood components (e.g. ions, proteins, albumin and etc.) and a mechanosensor and mechanotransducer to sense and transmit mechanical signals from the blood flow to cytoplasm. In this study, a series of large-scale molecular dynamics simulations were undertaken to study atomic events of the endothelial glycocalyx layers interacting with flow. This research is a pioneer study in which flow in the physiologically relevant range is accomplished based on an atomistic model of the glycocalyx with the to-date and detailed structural information. The coupled dynamics of flow and endothelial glycocalyx show that the glycocalyx constituents swing and swirl when the flow passes by. The active motion of the glycocalyx, as a result, disturbs the flow by modifying the velocity distributions. The glycocalyx also controls the emergence of strong shear stresses. Moreover, flow regime on complex surface was proposed based on results from a series of cases with varying surface configurations and flow velocities. Based on the dynamics of subdomains of the glycocalyx core protein, mechanism for mechanotransduction of the endothelial glycocalyx was established. The force from blood flow shear stress is transmitted via a scissor-like motion alongside the bending of the core protein with an order of magnitude of 10~ 100 pN. Finally, the mechanism of flow impact on ion transport was investigated and improved Starling principle was proposed. The flow modifies sugar chain conformations and transfers momentum to ions. The conformational changes of sugar chains then affect the Na+/sugar-chain interactions. The effects of flow velocity on the interactions are non-linear. An estimation in accordance to the improved Starling principle suggests that a physiological flow changes the osmotic part of Na+ transport by 8% compared with stationary transport.

This research explores the feasibility of the electrohydrodynamic processing using single and co-axial set-up as a single step processing tool for preparation of advanced drug delivery systems. A number of synthetic biodegradable and non-biodegradable polymers were used in order to prepare formulations incorporating drugs of different physicochemical characteristics. Based on the focus and the desired applications, the polymeric carrier and solvent system as well as the model drug of interest were selected to develop the drug delivery systems. Firstly, core-shell microparticles were prepared and optimized using co-axial electrohdrodynamic processing with precise control over the averaged particle size and size distribution. This was followed by integration of model drugs with different water-solubility. In this study, the release characteristics of the developed particles were investigated with single and simultaneous encapsulation of the drugs. Successful preparation of fixed dose combination formulation with high processing yield and encapsulation efficiency was reported. Secondly, single and co-axial electrohydrodynamic processing was utilized for preparation of smart drug delivery system for targeted release of prednisolone. Colon targeted drug delivery systems were developed using a pH-responsive polymer. Varying polymer drug ratio was applied to further enhance the release profiles and obtain an efficient delivery system whereby local delivery of prednisolone is made possible. Finally, microspheres were developed for co-encapsulation of anti-diabetic drugs with different water-solubility. The successfully developed sustained release formulations have the potential to overcome the existing limitations of conventional formulations by enhancing patient compliance and efficacy of the treatment of any chronic conditions.

The design of a Diesel injector is a key factor in achieving higher engine efficiency. The injector's fuel atomisation characteristics are also critical for minimising toxic emissions such as unburnt Hydrocarbons (HC). However, when developing injection systems, the small dimensions of the nozzle render optical experimental investigations very challenging under realistic engine conditions. For the present work, Computational Fluid Dynamics (CFD) was employed and transient, Volume Of Fluid (VOF), multiphase simulations of the flow inside and immediately downstream of a real-size multi-hole nozzle were performed, during and after the injection event with a small air chamber coupled to the injector downstream of the nozzle exit. A Reynolds Averaged Navier-Stokes (RANS) approach was used to account for turbulence. A moving mesh approach was followed for the movement of the needle. Models that can provide an accurate prediction of the liquid-gas interface and also capture the vapour-air mixing were used. Moreover, an evaporation model was developed. The code was validated against experimental data and data from the literature. 9 different injections were simulated for injection pressures equal to 400 bar and 900 bar, ambient pressure that varied from 60 bar to 1 bar and fuel temperature that varied from 300 K to 353 K. A high chamber temperature case and a high nozzle wall temperature case were also investigated. The results showed that the flow during the injection cannot be considered steady state and that hysteresis exists. After the end of injection, the state of the nozzle varied from being filled with liquid to being filled with air. Some form of dribble existed in all the injections while in one of them a late cycle mass expulsion was predicted. The effect of evaporation was found to be very small but it can contribute towards late cycle mass expulsion. In addition, the pressure drop due to the engine cycle could also have a similar effect.

The objective of the present work is to investigate and apply the fully Eulerian stochastic field method in conjunction with LES to an industrially-premixed turbulent reacting flows. This approach has shown promising results in recent studies and is of particular interest for complex geometry applications with flame configurations involving mixed modes of combustion. The relevant characteristics of the swirling flow in gas turbine applications are presented in the first part of the work. Following that, the numerical method is described and the relevant experimental dataset is discussed. The results are presented in two parts: isothermal and reacting flows. The test case of isothermal flows were studied at differing operating conditions. The influence of sub-grid turbulence models has been quantified in complex geometries. Dependencies of the Reynolds number on coherent structures has also been presented. In the reacting flows, the influence of the chemical mechanism and of the sub-grid pdf have been discussed. The formation of emissions inside the combustor chamber concludes the work and provides a contribution to the better understanding of industrial gas turbine combustion. The findings of this work strongly suggest, that the Eulerian stochastic field method is an effective and reliable tool to describe the combustion of complex flow configurations. The full scale case simulations are performed with the same set of model parameters, previously identified for simpler flames, which potentially eliminates the requirement of their adjustment.

Inorganic lamellar solid particles, for example molybdenum disulphide, have been used as solid additives in lubricants to improve their friction and wear properties. Recently, inorganic fullerene-like materials (IFLM) of metal dichalcogenides with a closed-cage structure have been synthesized. It has been shown that mechanical dispersion of IFLM nanoparticles in mineral and synthetic base oils gives benefits of low friction coefficient and wear and the benefits are superior to those of lamellar solids. The IFLMs positive effect on the oils performance was attributed to rolling mechanism and to their mechanical degradation. The aim of the thesis is to extend knowledge of inorganic tungsten disulphide (IFWS2) nanoparticles behaviour through study of their interactions with other additives in prepared oils. The investigation of the IF-WS2 lubrication efficiency had several major objectives. These were: to evaluate effect of various sliding-rolling ratios and temperatures, to classify the IF-WS2 from the point of view of additive groups and to evaluate the nature of interactions between specific additives and the nanoparticles. Lubrication efficiency of IF-WS2 nanoparticles dispersed in oils was evaluated on tribo-rigs with ball-on-disc configuration at a wide range of operating conditions. For the testing of oils with IF-WS2 Mini Traction Machine (MTM) and High-Frequency Reciprocating (HFRR) rigs were employed. Standard highly polished specimens made of AISI M52100 steel were used. In addition, Elastohydrodynamic (EHL) rig was utilised for film thickness measurements. One of the major outcomes of this work was establishing a positive effect of elevated temperature on IF-WS2 dispersion, friction and wear behaviour. Also, a certain sulphuric extreme pressure additive improved IF-WS2 dispersion properties, which was attributed to a synergistic reaction between these two additives. Moreover, the tribological performance of the nanosuspension was found to be improved by addition of stearic acid under moderate conditions, where nanoparticles show no contribution. Study of interactions between ZDDP and the nanoparticles has shown superior performance of the ZDDP solution compared to the nanosuspension under given conditions.

No description available.

A study of the thermal performance of an air-cooled micro-channel condenser using zeotropic refrigerant blend R-410A operating at high reduced pressure and at hot climate was conducted. The investigation of the condensation process at high ambient temperature is worth considering because the condensation saturation temperature should be high enough to be cooled by air at high ambient temperature. In this case a high operating pressure corresponding to the high condensation temperature is required; therefore, the condensation process of R-410A occurs at near-critical pressure and the vapour compression cycle operates in hot weather. In order to achieve a successful condensation process operating at hot climate, micro-channel tubes were suitable because of the high heat transfer coefficient associated with tubes of very small hydraulic diameter. The local heat transfer coefficient of R-410A was determined experimentally during the condensation process across the vapour-liquid dome at 0.7 and 0.8 reduced pressures and at 35 and 45°C ambient air temperatures, in two different rectangular tubes of Dₕ* =1.26 and 0.52 mm, over a mass flux range of 200≤G*≤800 kg/ m2s. Although, the temperature glide of the refrigerant R-410A was sufficiently small, the measurement of the mass flux and the heat transfer during condensation with other measuring parameters were always difficult to achieve with a high level of accuracy. The latest technology of the micro-foil heat flux sensor technique was used with a bespoke facility to accurately determine the heat duty of condensation along the micro-channel tubes. The behaviour of the heat transfer coefficient with the vapour quality was addressed. In addition, the behaviour of heat flux, vapour quality and wall temperature with the thermal length of the channel were intensively studied. The heat transfer coefficient was found to increase with the mass flux and the vapour quality and to decrease with the ambient temperature. Correlations by other researchers mostly disagreed with the present experimental data. Annular flow regime was adopted due to the cross section of tubes at these diameters. A new correlation in annular flow regime that accounted for the effect of near critical pressure of such refrigerant and the high temperature of the coolant air in the geometry of tubes under consideration was proposed to predict the heat transfer coefficient of condensation for which the available models are insubstantial. The resulting correlation successfully computed the experimental data. The physical comprehension and correlation resulting from this research contribute to enhance the existing knowledge for designing and optimising new equipment that utilise R-410A for air-conditioning and refrigeration applications, particularly in hot climates.