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A mathematical model is developed to study the coupled heat and moisture transfer through a fabric system that consists of a single layer of fabric and an air gap. Properties of air and moisture are sensitive to temperature and hence are assumed to be functions of local temperature. Therefore the model is applicable to a broad range of boundary conditions. A numerical scheme is proposed to solve the distributions of temperature and moisture concentration throughout the layers, from which the thermal and evaporative resistances of the fabric system can be evaluated. Experiments are conducted for two particular fabrics using a sweating guarded hotplate, and the data show good agreement with the model predictions. Using this model, the effects of parameters in environmental conditions, air gap and material properties on the thermal and evaporative resistances are studied. This work provides fundamental basis for the optimization of garment fit and material properties to achieve good performance for the clothing system.

Water is a vital element of agriculture. Almost 75% of the world's water resources are used for farm irrigation. Using greenhouses in agriculture provides a good environment for plant growth and reduces water consumption. Desalination to obtain freshwater from seawater or brackish water has been used in the arid costal regions and areas that have encountered water shortages. Solar desalination systems integrated into greenhouses have been considered for fresh water production to satisfy their water demand. Two main types of greenhouse integrated desalination systems are used, namely, solar stills and greenhouse-integrated humidification-dehumidification type solar systems. The main objective of this project is to carry out a thermodynamic analysis and a comparison of solar stills and humidification-dehumidification type desalination units. The basic principles, components, types, advantages and disadvantages of solar stills and humidification-dehumidification type greenhouse integrated desalination systems were investigated in detail. A conventional single basin type solar still that includes a basin and a symmetrical tilted condensing cover (greenhouse roof), and a humidification- dehumidification desalination unit that consists of two evaporators and one condenser were selected for detailed analysis. In order to carry out the thermal analysis, some important data such as plant transpiration and evaporation, solar radiation and indoor conditions of the greenhouse were determined. The thermal analysis was based on tomato production. Typical year ambient air temperature, relative humidity, and wind velocity values were taken from TRNSYS 16 for Adelaide conditions. In order to provide a good environment for the tomato crops, the internal conditions of the greenhouse were selected in the range 15-29oC temperature and 60-80% relative humidity. Detailed mathematical thermal models of both conventional solar stills and the new humidification-dehumidification type systems were simulated and the fresh water production of both systems was evaluated by means of MATLAB 7.8. The results were compared with previous experimental results. The results demonstrated that even if the whole roof area is used, the required fresh water supply cannot be produced in the months of May, June and July by the simple solar still system, whereas adequate amounts of fresh water can be produced throughout the year by means of humidification-dehumidification type system. On the other hand, the annual water production of the simple solar still system and humidification-dehumidification type system were determined as 308.5 and 260 m3/year respectively. The thesis also considers the option of water storage for providing water requirement of the greenhouse plants. The parameters that affect the fresh water requirement of the both systems were also considered and their impact evaluated. The effects of the desalination system on the internal environment of the greenhouse were also considered. It was revealed from the results that the use of the solar still system during the period from April to October causes unsuitable greenhouse conditions for the greenhouse crops whilst appropriate conditions for the greenhouse crops were achieved throughout the year in the case of the humidification-dehumidification type system. On these and other grounds, the humidification-dehumidification type system was found more suitable for the given greenhouse and climatic conditions. / Thesis (MEng(MechanicalEngineering)--University of South Australia, 2010

Process intensification tools, such as the capillary reactor, offer several benefits to the chemical process industries due to the well-defined high specific interfacial area available for heat and mass transfer, which increases the transfer rates, and due to low inventories, they also enhance the safety of the process. This has provided motivation to investigate three such tools, namely the capillary microreactor, spinning disc and rotating tube reactors, in this study. / The gas-liquid slug flow capillary microreactor intensifies reactor performance through internal circulation caused by the shear between the continuous phase/wall surface and the slug axis, which enhances the diffusivity and consequently increases the reaction rates. However, integrating the complex hydrodynamics of this reactor with its chemical kinetics is a mathematically challenging task. Therefore, in this study, a simple-to-complex approach, using a set of state-of-the-art computational fluid dynamic tools, has been used. Firstly, simulations were performed without any chemical reaction to ascertain the extent of slug flow regime. The model also clearly captured the slug flow generation mechanism which can be used to structurally optimize the angle of entry in these reactors. Finally, the hydrodynamic model was also capable of estimating the pressure drop and slug lengths. After successfully simulating the hydrodynamics of the system, a reaction model was incorporated to study the chemical reaction kinetics. The results were compared with the published experimental work and were found to be in good agreement. / The spinning disc reactor utilizes the centrifugal and shear forces to generate thin liquid films characterized with intense interfering waves. This enables a very high heat transfer coefficients to be realized between the disc and liquid, as well as very high mass transfer between the liquid and the bulk gas phase. The waves formed also produce an intense local mixing with very little back mixing. This makes a spinning disc reactor an ideal contactor for multiphase processes. The focus of this study has been to elucidate the hydrodynamic behaviour of the liquid film flow over the horizontal spinning disc. Investigations were also performed to elaborate the local and overall hydrodynamic characteristics of a fully developed spinning disc reactor. Simulation results showed a continuous linear liquid film on the horizontal spinning disc and intense mixing performance in the annulus of the reactor around the disc surface. Finally, the film thickness data from the simulations were compared with the limited amount of data available for this novel process. / Rotating tube reactor also uses centrifugal forces to generate the liquid film and a high degree of mixing along with an improved control over the reactant retention times. In this work we have conducted a CFD analysis to understand the hydrodynamics of this new technology for future developments.

This Thesis develops a mathematical model for predicting the thermal response in the surgical drilling of bone. The model accounts for the bone, chip and drill bit interactions by providing a detailed account of events within a cylindrical control volume enveloping the drill, the cut bone chip within the drill bit flute and the solid bone. Lumped parameter approach divides the control volume into a number of cells and cells within the sub-volumes representing the drill solid, the bone chip and the bone solid are allowed to interact. The contact mechanics of rough surfaces is used to model chip-flute and chip-bone frictional interaction. In this way not only the quantification of friction due to sliding contact of chip-flute and chip-bone rough surface contact are treated, but also the contact thermal resistances between the rubbing surfaces are included in the model. A mixed combination of constant and adaptive mesh is employed to permit the simulation of the heat transfer as the drill bit penetrates deeper into the bone during a drilling process. Using the model the effect of various parameters on the temperature rise in bone, drill and the chip are investigated. It is found that maximum temperature within the bone occurs at the location adjacent to the corner of the drill-tip and drill body. The results of the model are found to agree favorably with the experimental measurements reported in the existing literature on surgical drilling.

The investigations presented in the thesis are theoretical studies of magnetohydrodynamic flows, heat and mass transfer in Newtonian/non-Newtonian cooling liquids, due to horizontal/vertical stretching sheet. The theoretical studies include the effect of magnetic field, uniform and non-uniform heat source/sink (flow and temperature dependent heat source/sink) effects. The considered problems include flow of viscous fluids in the presence of applied magnetic field and electric field with first order chemical reactions. The viscous incompressible Newtonian fluid flow in porous medium with Darcy-Forchheimmer model, electrically conducting fluid and nanofluid is studied. We introduce innovative techniques for finding solutions of highly nonlinear coupled boundary value problems such as Runge-Kutta method, Perturbation method and Differential Transform Method (DTM).   Chapter 1-2 gives a brief introduction. Chapter 3 focuses on Lie group analysis of MHD flow and heat transfer over a stretching sheet. The effects of viscous dissipation, uniform heat source/sink and MHD on heat transfer are addressed. In Chapter 4-6 we examined the laminar flow, thermocapillary flow of a nanoliquid thin film over an unsteady stretching sheet in presence of MHD and thermal Radiation in different situations. An effective medium theory (EMT) based model is used for the thermal conductivity of the nanoliquid.  Metal and metal oxide nanoparticles are considered in carboxymethyl cellulose (CMC) - water base liquid. In Chapter 7-9 we analyzed, heat and mass transfer in MHD, mixed convection, viscoelastic fluid flow, non-Darcian flow due to stretching sheet in presence of viscous dissipation, non-uniform heat source/sink and porous media have been investigated in different situations.  MHD and viscous dissipation have a significant influence on controlling of the dynamics.    In Chapter 10 the linear stability of Maxwell fluid-nanofluid flow in a saturated porous layer is examined theoretically when the walls of the porous layers are subjected to time-periodic temperature modulations. A modified Darcy-Maxwell model is used to describe the fluid motion, and the nanofluid model used includes the effects of the Brownian motion. The thermal conductivity and viscosity are considered to be dependent on the nanoparticle volume fraction. In Chapter 11 we studied MHD flow in a vertical double passage channel taking into account the presence of the first order chemical reactions. The governing equations are solved by using a regular perturbation technique valid for small values of the Brinkman number and a DTM valid for all values of the Brinkman number.

The objective of this PhD project is to develop novel membranes and desiccants that would help develop a second generation vacuum desiccant cooling (VDC) garment that is efficient, robust, durable and wearer-friendly. It was found that properly chosen support material could improve both mechanical strength and vapor flux for flat sheet polyvinylidene fluoride (PVDF), due to improved membrane structure and structure integrity that enhanced vapour mass transfer. Super solid desiccants were developed using a super absorbent polymer (SAP), which are sodium polyacrylate granules, as the host matrices to harbour LiCl. Furthermore, a novel desiccant based on loading LiCl in to hydrophobic hollow fibre membranes and therefore called membrane based desiccant fiber (MDF), was developed and demonstrated to be suitable for VDC. Heat and mass transfer for vapor absorption in MDF were analyzed. These membranes and desiccants, although developed for application in VDC, may also found applications in other fields such as water treatment, air conditioning, and natural gas dehumidification. Finally, based on the newly developed membranes and desiccants, three conceptual designs of second generation VDC garments are proposed.

With the world’s increasing usage of electronic devices such as mobile devices and batteries, improving the reliability and performance of these devices has become more and more important. Besides the common overheating issues, low-temperature environments can also cause performance degradation or failure to these devices. Research on thermal switches and thermal regulators aims to improve the thermal management of electronic devices across a range of operating conditions. However, continuous tuning of thermal transport with all-solid-state systems is still challenging. The primary purpose of this work is to propose and demonstrate compressible foams as novel variable thermal resistors and thermal regulators to control device temperature under various input heat flux and ambient temperature. The graphene/PDMS foam is first tested in this work to demonstrate promising performance as a thermal regulator, with continuous tuning capability and a system switching ratio over ~4. Then, the dependence of the thermal conductivity of polymer foams during compression is studied, where the thermal conductivity is measured using a customized system based on an infrared microscope. Unexpectedly, the thermal conductivity decreases slightly at a compression level of more than 10x, in contrast to common theories that the thermal conductivity would increase with the mass density. A simple “spring model” is proposed as a limit where the ligaments do not build contacts during compression. Our results now fall in between the “spring model” and other common theories and can be explained. To gain further insights, a molecular dynamic simulation is performed on a graphene random nanofoam on the nanoscale. The result also shows that the effective thermal conductivity along the compression direction is not sensitive to the mass density, consistent with our experimental data on the macroscopic scale. This work provides useful insights into dynamic thermal management of electronic devices.

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