The focus of this project is the storage of thermal energy in packed beds for bulk electricity storage applications. Packed beds are composed of pebbles through which a heat transfer fluid passes, and a thermodynamic model of the heat transfer processes within the store is described. The packed beds are investigated using second law analysis which reveals trade-offs between several heat transfer processes and the importance of various design parameters. Parametric studies of the reservoir behaviour informs the design process and leads to a set of design guidelines. Two innovative design features are proposed and investigated. These features are segmented packed beds and radial-flow packed beds respectively. Thermal reservoirs are an integral component in a storage system known as Pumped Thermal Energy Storage (PTES). To charge, PTES uses a heat pump to create a difference in internal energy between two thermal stores; one hot and one cold. The cycle reverses during discharge with PTES operating as a heat engine. The heat pumps/engines require compression and expansion devices, for which simple models are described and are integrated with the packed bed models. The PTES system behaviour is investigated with parametric studies, and alternative design configurations are explored. A multi-objective genetic algorithm is used to undertake thermo-economic optimisations of packed-bed thermal reservoirs and PTES systems. The algorithm generates a set of optimal designs that illustrate the trade-off between capital cost and round-trip efficiency. Segmentation is found to be particularly beneficial in cold stores, and can add up to 1% to the round-trip efficiency of a PTES system. On the basis of the assumptions made, PTES can achieve efficiencies and energy densities comparable with other bulk electricity storage systems. However, the round-trip efficiency is very sensitive to the efficiency of the compression–expansion system. For designs that utilised bespoke reciprocating compressors and expanders, PTES might be expected to achieve electricity-to-electricity efficiencies of 64%. However, using compression and expansion efficiencies typical of off-theshelf devices the round-trip efficiency is around 45%.

This research project has developed a computer-assisted methodology whereby the temporal and spatial distribution of temperature in thick film circuits fabricated on ceramic substrates may be predicted. The analogy between thermal and electrical systems is used to define a thermal structure in electrical format which is then simulated using ASTEC3 electronic analysis package. Procedures have been developed whereby the three heat transfer mechanisms namely conduction, convection and radiation may be modelled. Models have also been proposed which allow the more important sections of a thermal structure to be analysed in finer detail. These procedures have been used hi the solution of some standard heat flow problems whose solutions have also been obtained by other more conventional techniques for comparison. Programs have been developed which facilitate the presentation of the results in the form of contour-maps or 3-D temperature distribution plots. Software has also been developed which can generate the electrical equivalent description of a device in ASTEC3 syntax. Estimates of the computing times required to carry out electro-thermal simulations of hybrid and VLSI devices have been made. The predicted computation times are feasible. Confirmatory experiments have been carried out in large scale using partially heated samples prepared from printed circuit boards. These were heated electrically and temperature measurements were made using an infrared thermometer. These structures were modelled and simulated using ASTEC3 for comparison. It was found that for an accurate thermal analysis there was a need for reliable data for the thermal conductivity of the glass-fibre laminate and the heat transfer coefficients of convection. Experiments were designed to measure the thermal conductivity of the laminates tangential to the plane of the boards. A standard Lees' disc apparatus was also used to measure this parameter in a direction normal to the boards. A Schlieren optics apparatus was used to study the convection plumes over the surface of the plates in a horizontal position with the heated side facing upwards which provided a significant insight into the flow regime over such surfaces. Values were subsequently determined for the convection coefficients from the boards. Using the measured thermal conductivities of FR4 boards and the estimated convection coefficients, excellent agreement was achieved between the measured and simulated results. Temperature measurements were also conducted at reduced dimensional scale on especially designed thick film resistor samples. The samples were fabricated by R.S.R.E and temperature measurements were carried out using a thermal imaging equipment manufactured by AGEMA. Again the Schlieren apparatus was used to observe the convection plumes forming over the devices which led to a better understanding of the heat transfer mechanism from such devices. These observations were then used to estimate the natural convection coefficients from the surface of horizontally positioned resistor samples which were then included in the ASTEC3 model of the devices. The subsequent ASTEC3 thermal simulation showed an excellent agreement with the measured temperature profile.

Thesis (MTech (Chemistry))--Cape Peninsula University of Technology, 2012. / Crystal engineering is the synthesis of new crystalline materials with specific chemical and physical properties which allows the comprehensive understanding of the non covalent interactions that occur between molecules in the crystalline state. This has lead to extensive work being done in terms of host design. The study of non-covalent interactions formed by - these materials is crucial to understanding many biological processes. This study focuses on the inclusion compounds of 1, 4-bis (diphenylhydroxymethyl) benzene H, a host compound engineered by EWeber, that conforms to Weber's rules for host design as it is bulky, rigid, and has hydroxyl moieties that act as hydrogen-bonding donors. A Cambridge Structural Database (CSDversion 5.33) search has revealed that no research has been conducted on this host compound. Characterization of the compounds were conducted using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), hot stage microscopy (HS), gas chromatography (GC), powder X-ray diffraction(PXRD) and single X -ray diffraction. Host: guest ratios determined from TG analysis were correlated with structural analysis results. We have successfully prepared inclusion compounds with N, N- dimethylformamide(DMF) N, N- dimethylacetamide (DMA), N-methylformamide (NMF) and N-methylacetamide (NMA), 2-picoline, 3-picoline, 4-picoline, pyridine and morpholine. Following which a series of competition experiments were conducted to establish the selectivity profile of the host by dissolving the host in an excess of two guests pairs, between DMF: DMA, DMF: NMF, DMF: NMA, DMA: NMF, DMA: NMA and NMF: NMA. The results of the competition experiment showed that the host had high selectivity for DMF and the selectivity profile follows a trend as follows DMF>NMA>NMF>DMA. The results for the competition experiments between the picolines, pyridine and morpholine were inconclusive.

No description available.

M.Ing. / The steelmaking process is briefly described with regard to process parameters and products influencing the fume extraction function of the water-cooled ducting. The flow distribution in the complex tubular network was determined by developing a software program based on parallel pass connections. A heat transfer analysis was performed on the specific problematic section referred to as the fixed elbow, with boundary conditions simulating the actual maximum operating conditions in an electric arc furnace. The temperature distribution was incorporated in a thermal stress analysis and a total stress profile was obtained for the radial as well as circumferencial positions. Areas of maximum stress were identified and the theory of fatigue failure due to cyclic operation was applied to these maximum stress conditions. The ABAQUS finite element program was used to model the behaviour of the material under the operating conditions using the sequencially coupled heat transfer and stress analysis routine. The results obtained correlates well with the actual failure of water-cooled ducting sections in operation and provides a platform for designing and optimising similar equipment for industrial applications.

The research described in this thesis involves the development of a video coding scheme which provides lossless Region Of Interest (ROl) coding specifically targeted toward the compression of thermal video sequences. In particular the scheme is designed to provide lossless coding of critical temperature data contained in thermal video sequences used within firefighting applications. High coding efficiency is achieved by the use of Discrete Cosine Transform (DCT) based lossy coding for non-critical areas of the video sequence. The research is divided into three key sections; an investigation into thermal video, the practical development of a novel scheme for selective lossless compression of thermal video containing critical temperature data, and the presentation and analysis of test results which demonstrate the effectiveness of the scheme. The scheme's multi-pass encoder stores data which enables the recovery of the losses which occur within critical thermal data as a result of the lossy DCT coding stage. This error recovery data is stored as codewords where each individual codeword is used to represent the error data for up to two pixels within the ROI. Efficient entropy coding of the error recovery data is achieved through a combination of a new adaptive reordering scheme followed by Run Length Coding (RLC) and Variable Length Coding (VLC). By storing these error recovery codes within the normally unused colour channels of a compressed video sequence, the compressed thermal video sequence can be transmitted as an MPEG-1, MPEG-2 and MPEG4 compliant bitstream. This novel storage mechanism allows the error recovery codes to be spatially mapped to the ROl data, and hence the scheme can benefit from the motion compensation facilities provided within the MPEG compliant bitstream. Decoding of the lossy video sequence can be carried out using any MPEG compliant decoder. Lossless ROl decoding can be carried out using the special decoder described in, and provided with, the thesis.

As the worldwide energy demand continues to increase, scientists and engineers are faced with the increasingly difficult task of meeting these needs. Currently, the major energy sources, consisting of oil, coal, and natural gas, are non-renewable, contribute to climate change, and are rapidly depleting. Renewable technology research has become a major focus to provide energy alternatives which are environmentally-friendly and economically competitive to sustain the future worldwide needs. Thermal energy storage using adsorption is a promising technology which can provide energy for heating and cooling applications using solar and waste heat sources. The current work aims to improve adsorption systems to provide higher energy outputs and therefore, more economical systems. New adsorbents and operating conditions were tested with the goal of storing the available energy more efficiently. A model was also developed to gain a better understanding of the adsorption system to improve this developing technology.

No description available.

Effective application of thermal interface materials (TIM) sandwiched between silicon and a heat spreader in a microelectronic package for improved heat dissipation is studied through thermal and mechanical characterization of high thermally conductive carbon nanotubes (CNTs) integrated into eutectic gallium indium liquid metal (LM) wetting matrix. Thermal conductivity data from Infrared microscopy tool reveals the dependence of experimental factors such as matrix types, TIM contacting interfaces, orientation of CNTs and wetting of CNTs in the matrix on the thermal behavior of TIM composite. Observed generalized trend on LM-CNT TIM shows progressive decrease in effective thermal conductivity with increasing CNT volume fractions. Further thermal characterizations LM-CNT TIM however show over 2x increase in effective thermal conductivity over conventional polymer TIMs (i.e. TIM from silicone oil matrix) but fails to meet 10x improvement expected. Poor wetting of CNT with LM matrix is hypothesized to hinder thermal improvement of LM-CNT TIM composite. Thus, wetting enhancement technique through electro-wetting and liquid crystal (LC) based matrix proposed to enhance CNT-CNT contact in LM-CNT TIM results in thermal conductivity improvement of 40 to 50% with introduction of voltage gradient of 2 to 24 volts on LM-CNT TIM sample with 0.1 to 1 percent CNT volume fractions over non voltage LM-CNT TIM test samples. Key findings through this study show that voltage tests on LC- CNT TIM can cause increased CNT-CNT networks resulting in 5x increase in thermal conductivity over non voltage LC-CNT TIM and over 2x improvement over silicone-CNT TIMs. Validation of LM wetting of CNT hypothesis further shows that wetting and interface adhesion mechanisms are not the only factors required to improve thermal performance of LM-CNT TIM. Anisotropic characteristic of thermal conductivity of randomly dispersed CNTs is a major factor causing lower thermal performance of LM-CNTs TIM composite. Other factors resulting in LM-CNT TIM decreasing thermal conductivity with increasing CNT loading are (i) Lack of CNT-CNT network due to large difference in surface tension and mass density between CNTs and LM in TIM composite (ii) Structural stability of MWCNT and small MFP of phonons in ~5um MWCNTs compared to the system resulted in phonon scattering with reduced heat flow (iii) CNT percolation threshold limit not reached owing to thermal shielding due to CNT tube interfacial thermal resistance. While mixture analytical models employed are able to predict thermal behaviors consistent with CNT-CNT network and CNT- polymer matrix contact phenomenon, these models are not equipped to predict thermo-chemical attributes of CNTs in LM-CNT TIM. Extent of LM-CNT wetting and LM-solid surface interfacial contact impacts on interfacial thermal resistance are investigated through LM contact angle, XPS/AES and SEM-EDX analyses on Au/Ni and Ni coated copper surfaces. Contact angle measurements in the range of 120o at both 55oC and 125oC show non wetting of LM on CNT, Au and Ni surfaces. Interface reactive wetting elemental composition of 21 days aged LM on Au/Ni and Ni surfaces reveals Ga dissolution in Au and Ni diffusion of ~0.32um in Au which are not present for similar analysis of 1 day LM on Au/Ni surface. Formation of Au-Ni-Ga IMC and IMC-oxide iono-covalency occurrence at the interface causes reduction in surface tension and reduction in interfacial contact resistance.

No description available.