Effect of curing conditions and harvesting stage of maturity on Ethiopian onion bulb drying properties

The study was conducted to investigate the impact of curing conditions and harvesting stageson the drying quality of onion bulbs. The onion bulbs (Bombay Red cultivar) were harvested at three harvesting stages (early, optimum, and late maturity) and cured at three different temperatures (30, 40 and 50 oC) and relative humidity (30, 50 and 70%). The results revealed that curing temperature, RH, and maturity stage had significant effects on all measuredattributesexcept total soluble solids

Dendritic growth velocities in an undercooled melt of pure nickel under static magnetic fields: A test of theory with convection

Dendritic growth velocities in an undercooled melt of pure nickel under static magnetic fields up to 6 T were measured using a high-speed camera. The growth velocities for undercoolings below 120 K are depressed under low magnetic fields, but are recovered progressively under high magnetic fields. This retrograde behavior arises from two competing kinds of magnetohydrodynamics in the melt and becomes indistinguishable for higher undercoolings. The measured data is used for testing of a recent theory of dendritic growth with convection. A reasonable agreement is attained by assuming magnetic field-dependent flow velocities. As is shown, the theory can also account for previous data of dendritic growth kinetics in pure succinonitrile under normal gravity and microgravity conditions. These tests demonstrate the efficiency of the theory which provides a realistic description of dendritic growth kinetics of pure substances with convection

Tools for developing continuous-flow micro-mixer : numerical simulation of transitional flow in micro geometries and a quantitative technique for extracting dynamic information from micro-bubble images

Recent advance in the microfluidics including its fabrication technologies has led to many novel applications in micro-scale flows. Among them is the continuous-flow micromixer that utilizes the advantages associated with turbulent flows for rapid mixing, achieving the detection of fast kinetic reaction as short as tens of microseconds. However, for developing a high performance continuous-flow micromixer there are certain fundamental issues need to be solved. One of them is an universal simulation approach capable of calculating the flow field across entire passage for entire regime from very low Reynolds number laminar flow through transition to fully turbulent flow. Though the direct numerical simulation is potentially possible solution but its extremely high computing time stops itself from practical applications. The second major issue is the inevitable occurrence of cavitation bubbles in this rapid flow apparatus. This phenomenon has opposite effects: (a) deteriorating performance and damaging the micromixer; (b) playing a catalyst role in enhancing mixing. A fully understanding of these micro bubbles will provide a sound theoretical base for guiding the design of micromixer in order to explore the advantage to maximum while minimizing its disadvantages. Therefore, the objectives of this PhD programme is to study the tools that will effectively advance our fundamental understandings on these key issues while in short term fulfil the requires from the joint experimental PhD programme held in the life science faculty for designing a prototype experimental device. During this PhD study, an existing numerical approach suitable for predicting the possibly entire flow regime including the turbulence transition is proposed for simulating the microscale flows in the microchannel and micromixer. The simulation results are validated against the transitional micro-channel experiments and this numerical method is then further applied for the micromixer simulation. This provides the researcher a realistic and feasible CFD tool to establish guidelines for designing high-efficiency and cost-effective micromixers by utilizing various possible measures which may cause very different flows simultaneously in micromixer. In order to study microscale cavitation bubbles and their effects on micromixers, an innovative experimental setup is purposely designed and constructed that can generate laser-induced micro-bubbles at desired position and size for testing. Experiments withvarious micro-scale bubbles have been performed successfully by using an ultra high-speed camera up to 1 million frame rate per second. A novel technique for tracking the contours of micro-scale cavitation bubble dynamically has been developed by using active contour method. By using this technique, for the first time, various geometric and dynamic data of cavitation bubble have been obtained to quantitatively analyze the global behaviours of bubbles thoroughly. This powerful tool will greatly benefit the study of bubble dynamics and similar demands in other fields for fast and accurate image treatments as well

Development of Imaging Paradigms for Drug Distribution and Fate in the Eye

Aging-associated vision loss is increasingly prevalent in our population and intravitreal injections are commonly used to administer ocular drugs to the posterior segment of the eye. This work aims to visualize and predict the delivery of ocular drugs by combining micro- computed tomography (micro-CT) imaging and computational fluid dynamics (CFD) modeling. Intravitreal injections were administered into ex vivo porcine eyes and imaged for an extended period of time to track the progression of the injected drug mimic. Non-invasive imaging allowed for precise determination of contrast agent concentration, flow patterns and fate. A computational model was developed that provided quantitative agreement with the concentration values found in the experimental study and allowed for easy manipulation of parameters. The ability to accurately model drug transport following an intravitreal injection provides vital information to better understand the specific concentration and time frame for the drug to reach the target sit

Development and validation of computational fluid dynamics models for the coupled simulation of heat transfer and fluid flow in the coral microenvironments

This thesis explored the temperature deviations between coral surface temperature and ambient seawater temperature that likely determines the microscale processes involved in coral bleaching. The work presented here applied Computational Fluid Dynamics (CFD) technique coupled with hydrodynamic modelling and ray-tracing to predict coral surface warming due to the effects of stressors. This thesis demonstrates that modelling microscale temperature could yield important insights into thermoregulation in corals, which may lead to a more effective reef management

Nanofluid Flow in Porous Media

Studies of fluid flow and heat transfer in a porous medium have been the subject of continuous interest for the past several decades because of the wide range of applications, such as geothermal systems, drying technologies, production of thermal isolators, control of pollutant spread in groundwater, insulation of buildings, solar power collectors, design of nuclear reactors, and compact heat exchangers, etc. There are several models for simulating porous media such as the Darcy model, Non-Darcy model, and non-equilibrium model. In porous media applications, such as the environmental impact of buried nuclear heat-generating waste, chemical reactors, thermal energy transport/storage systems, the cooling of electronic devices, etc., a temperature discrepancy between the solid matrix and the saturating fluid has been observed and recognized