Thesis (PhD (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 1992. / The effect of cross-winds on the performance of natural draft dry-cooling towers is studied by means of isothermal model tests, a numerical simulation and full scale measurements. The action of the wind on such towers is found to be complex and is influenced by a number of different parameters including the wind speed, the shape of the approaching wind profile, the inlet diameter to the inlet height ratio of the tower, the tower height, the shape of the tower shell, the pressure loss coefficient of the heat exchangers and the amount of heat rejected by the tower. For a horizontal arrangement of the heat exchangers the wind effect on the tower is shown to be strongly dependent on both the shape and pressure loss coefficient of the tower supports. In practical cooling towers the heat exchangers are either arranged horizontally in the inlet cross-section of the tower or vertically around the circumference of the tower and the wind effect is found to be dependent on the particular layout. The wind effect on a tower is furthermore found to increase if the heat exchangers are arranged in the form of A-frames. Additional reductions in the heat rejection rate of the tower are caused by a non-uniform air temperature distribution inside the tower and flow distortions through the heat exchanger. Significant reductions in the wind effect on a cooling tower can be achieved by installing windbreak walls below the heat exchangers if the latter are arranged horizontally in the tower inlet.

In this thesis I describe experimental work and present data on the guiding of Rubidium atoms along free-space propagating light beams as well as within hollow core glass fibres, namely photonic crystal fibres. I describe experiments, laser systems and vacuum trap assemblies designed to facilitate this guiding. These experiments are intended to aid progression within the field of cold atom guidance wherein narrow diameter, long distance hollow-fibre guides are a current goal. Realisation of these guides could lead to promising applications such as atom interferometers and spatially accurate, multi-source, atom depositors. Herein, guided fluxes are observed in free-space guiding experiments for distances up to 50mm and up to 10GHz red-detuning from resonance. Additionally hollow-core, Kagome structured, quasi- and true-photonic crystal fibres are characterised. Finally a number of detailed fibre-guiding magneto-optic traps are developed. Both cold atomic-beams and cold atomic clouds are reliably positioned above fibre entrance facets in conjunction with a guiding laser beam coupled into the fibre core. Issues regarding optical flux detection outwith fibre confinement appear to have hindered observation of guided atoms. A far more sensitive detection system has been developed for use in current, ongoing fibre-guide experiments.

published_or_final_version / Environmental Management / Master / Master of Science in Environmental Management

Climatic conditions inside the dairy barn do not concern dairy farmers until those conditions begin to affect productivity and, consequently, profits. As heat and humidity increase beyond the cow's comfort levels, milk production declines, as does fertility and the welfare of the cow in general. To reinforce the cooling mechanisms currently used, this work proposes an alternative system for reducing the risk of heat stress. This innovative conductive cooling system does not depend on current weather conditions, and it does not require significant modifications when it is installed or during its operation. Also, the system circulates water that can be reused. Given that a review of the literature found very few related studies, it is suggested that each freestall be equipped with a viable prototype in the form of a waterbed able to exchange heat. Such a prototype has been simulated using Computational Fluid Dynamics (CFD) and later verified by a set of experiments designed to confirm its cooling capacity. Furthermore, this investigation sets the foundation for modeling temperature in a water supply system linked to the waterbeds. EPANET, a software program developed by the Environmental Protection Agency, simulates the hydraulic model. Its Water Quality Solver has been modified according to an analogy in the governing equation that compares mass to heat transfer and serves to simulate water temperature as the water is transported from its source to the point of delivery and then as it returns to the same source.

Master of Science / Department of Architecture / Michael D. Gibson / The use of Natural Ventilation (NV) to cool buildings in mixed climates can conserve significant cooling energy. In mixed climates it is particularly important during the fall and the spring, where appropriately designed buildings should use very little energy for heating or cooling. Natural ventilation is also important in residential buildings, where internal heat gain can be managed, making cooling by natural ventilation easier. Earlier investigations have clearly shown the economic, social, and health benefits of the use of NV in built environment. Studies have shown that increased airflow or air-speed during ventilation can bring a significant rise in comfort range which further reduces the cooling energy required to maintain comfort. The climatic data of the central United States (U.S.) shows that the availability of frequent high speed wind and favorable seasonal humidity conditions make natural ventilation feasible in late spring and early fall, where NV can offset most of the cooling demand for a home or multifamily residential unit, though it is not possible to maintain thermal comfort during the entire summer with NV alone. In mixed climates, NV for multifamily residential units has not been investigated thoroughly. According to 2009 International Residential Code, multifamily residential buildings are typically designed to use a code minimum amount of operable or ventilating windows, 4% of the floor area being ventilated, while also using lightweight construction methods (such as wood framing) that is prone to fast thermal response during the overheated periods of the year. While climate may favor the use of NV in these building types, the sizing of windows and the building construction type limit the potential to save energy with NV. This study hypothesized that the maximum benefits from NV in the climate of the central U.S. requires further optimization of window openings beyond the energy code minimum, and a construction system incorporating mass that can slow thermal response during overheated periods. During the study, the climatic data of the central US was scrutinized to understand the most suitable time frames where NV could be applied in order to maintain indoor thermal comfort in various construction systems in residential buildings: mainly lightweight using wood framing, and heavier construction using concrete and masonry. The location of the housing unit, first level or second level, was also examined to account for the differences in thermal gains and losses as a result of ground coupling and additional heat gain from the roof. Further, computational fluid dynamics evaluated the comfort achieved with different ventilation areas. Change in comfort hours by using NV tested the practicability of the use of NV to maintain indoor thermal comfort for different scenarios. The study concluded with design recommendations for building orientation, operable window size, and construction type as these factors relate to thermal comfort and the optimization of multifamily residential buildings to utilize NV for energy savings in the U.S.

Regarding the great importance of fast cooling in steel industry for the production processes, a deep understanding of heat transfer and fluid dynamics must be held. A steel plate is heated up until a maximum temperature of 700 ⁰ C to be the n cooled down seconds later by a configuration of multi ple impinging water jets. Different flow rates are used simultaneously by different adjacent jets to perform quenching over the sample, so different hardness is obtained in the material over a small area . Temperature drop in time i s measured and monitored by embedded thermocouples and LabVIEW program. To achieve greater understanding of the quenching performance with different flow rates , several parameters are selected to be varied in order to achieve the best working conditions. Jet diameter takes values between 4 and 10 mm, initial temperature of quenching varies from 400 to 700 ⁰ C , subcooling temperature is tested for 65 and 75 K, and jet velocity varies between 1.9 and 3.9 m/s. The result of total number of 9 expe riments shown that v ariation of jet diam eter does not influence substantially on the cooling rate if flow rate is kept constant. High initial quenching temperature (600 - 700 ⁰ C ) led to slightly higher cooling rate in the stagnation region of water jets. The peak value of heat transfer rate in the upwash flow zone was more highlighted for initial quenching temperature 600 ⁰ C and below it. High er values of subcooling and jet velocity produce better cooling rates. The result shown higher jet velocity at one column of water jets changes position of upw ash flow slightly toward the adjacent column of jets with lower jet velocity. In general, the result shown that all the studied parameters did not have negative effect on obtaining various cooling rates over the steel plate.

Licopeno, um pigmento natural considerado o mais potente antioxidante dentre os carotenoides, é oque tem maior incidência no soro humano. Seu consumo regular está relacionado principalmente com a prevenção do câncer de próstata. Porém, estudos também demonstram sua relação com a prevenção de câncer de pâncreas e bexiga, doenças cardiovasculares como a aterosclerose e doenças neurodegenerativas. Todavia, por ser altamente insaturado o licopeno é susceptível à degradação, sendo degradado na presença de luz, oxigênio e se exposto a altas temperaturas. A microencapsulação entra como uma alternativa para tentar garantir maior estabilidade a este carotenoide. A técnica de spray-chilling, por dispensar o emprego de altas temperaturas e solventes durante o processo de atomização, representa uma alternativa promissora na encapsulação do licopeno. Os objetivos deste trabalho foram encapsular uma solução oleosa de licopeno (10%) através da técnica de spray-chilling,utilizando gordura vegetal low trans como carreador, caracterizar as micropartículas obtidas e avaliar a biodisponibilidade do licopeno livre e encapsulado em ratos wistars. Foram formulados seis tratamentos, que diferiam pela concentração de solução comercial de licopeno, sendo T1 com 20%, T2 com 23,1%, T3 com 28,6%, T4 com 33,3%, T5 com 17,9% mais 10% de goma arábica e T6 com 19,2% mais 5% de carboximetilcelulose (CMC). As micropartículas obtidas destes tratamentos foram avaliadas quanto a tamanho e distribuição, morfologia por microscopia eletrônica de varredura (MEV), espectroscopia de infravermelho com transformadas de Fourier (FT-IR), difração de raios-X (DRX). A estabilidade do licopeno encapsulado foi avaliada em diferentes condições de armazenamento (sob vácuo, umidade relativa de 33%, temperatura de refrigeração e ambiente) e também foi determinada por meio de quantificações periódicas de licopeno, bem como através da análise análise da cor instrumental. A biodisponibilidade foi avaliada utilizando-se 68 animais divididos em grupos, para os quais se administrou por gavagem o licopeno livre e o encapsulado. O tamanho das micropartículas obtidas ficou em torno de 60-110 µm e a distribuição foi polidispersa, independente da concentração de licopeno. A microscopia revelou micropartículas esféricas, com superfície rugosa, com alguns poros e tamanhos variados. No FT-IR verificou-se que não houve formação de ligações distintas na solução oleosa de licopeno e nas amostras atomizadas. Nos difratogramas observou-se a presença da forma polimórfica β para o agente carreador e para as micropartículas. Na estabilidade a adição da goma arábica e o armazenamento sob temperatura de refrigeração e vácuo, foram as melhores condições para retardar a degradação do licopeno. Os resultados dos ensaios de biodisponibilidade foram inconclusivos. Desta forma, conclui-se que é possível encapsular licopeno através da técnica de spray-chilling, porém, para trabalhos futuros, seriam necessários aprimoramentos na técnica de encapsulação e/ou na formulação para conferir maior proteção ao carotenoide, bem como adequações na metodologia para determinação de sua biodisponibilidade, para obtenção de resultados conclusivos. / Lycopene, a natural pigment considered the most potent antioxidant among the carotenoids, it has the higher incidence in the human serum. Its regular consumption is mainly related with the prevention of prostate cancer. However, studies also show its relation to the prevention of pancreatic cancer and bladder cancer, cardiovascular diseases such as atherosclerosis and neurodegenerative diseases. However, by being highly unsaturated the lycopene is susceptible to degradation, being degraded in the presence of light, oxygen and if exposed to high temperatures. The microencapsulation comes like an alternative to ensuring higher stability for this carotenoid. The technique of spray-chilling represents a promising alternative to encapsulation of lycopene. The aims of this study were to encapsulate an oily solution of lycopene (10%) through of the technique of spray-chilling, using a low-trans fat as carrier, to characterize the obtained microparticles and to evaluate the bioavailability of lycopene free and encapsulated in Wistar rats. Six treatments were formulated, that differed by the content of oily solution of lycopene:T1 with 20%, T2 with 23.1%, T3 with 28.6%, T3 with 28.6%, T4 with 33.3%, T5 with 17.9% plus 10% of Arabic gum and T6 with 19.2% plus 5% of carboxymethylcellulose (CMC). The microparticles obtained from these treatments were evaluated for size and distribution, morphology by scanning electron microscopy (SEM), infrared spectroscopy with Fourier transform (FT-IR) and X-ray difraction (XRD). The stability of the lycopene encapsulated was evaluated by its periodic quantification at different storage conditions (vacuum, relative humidity of 33%, refrigeration temperature and environment temperature). Instrumental color, \"L\" and \"a\" parameters, also was measured. The bioavailability was evaluated using 68 animals, for which the free and lycopene encapsulated were administered by gavage. The size of microparticles obtained was around 60-110 µm and the distribution was polydisperse, independent of the concentration of lycopene. The microscopy revealed spherical microparticles, with rough surface, with some pores and varying sizes. In the FT-IR it was found that there was no formation of distinct bonds in oily solution of lycopeno and the atomized samples. In the diffraction patterns observed the presence of polymorphic form \"β\" for the carrier agent and microparticles. On the stability the addition of Arabic gum and the storage at refrigerator temperature under vacuum, were the best conditions to delay the degradation of lycopene. The results of bioavailability assays were inconclusive. As conclusion, it is possible to encapsulate lycopene using the technique of spray-chilling but to future works, would be required improvements in the technique of encapsulation and/or formulations to give more protection to the carotenoid, as well as adjustments in the methodology for determination of their bioavailability, in order to obtaining conclusive results.

The continuing requirement for computational processing power, multi-functional devices and component miniaturization have emphasised the need for thermal management systems able to maintain the temperature at safe operating condition. The thermal management industry is constantly seeking for new cutting edge, efficient, cost effective heat transfer enhancement technologies. The aim of this study is to utilize the electron beam treatment for the improvement of the heat transfer area in liquid cooled plates and experimentally evaluate the performance. Considering the complexity of the technology, this thesis focuses on the design and production of electron beam enhanced test samples, construction of the test facility, testing procedure and evaluation of thermal and hydraulic characteristics. In particular, the current research presented in this thesis contains a number of challenging and cutting edge technological developments that include: (1) an overview of the semiconductor industry, cooling requirements, the market of thermal management systems, (2) an integral literature review of pin-fin enhancement technology, (3) design and fabrication of the electron beam enhanced test samples, (4) upgrade and construction of the experimental test rig and the development of the test procedure, (5) reduction of the experimental data and analysis to evaluate thermal and hydraulic performance. The experimental results show that the capability of the electron beam treatment to improve the thermal efficiency of current untreated liquid cooled plates is approximately three times. The highest heat transfer rate was observed for the sample S3; this is attributed to the irregularities of the enhanced structure, which improves the heat transfer area, mixing, and disturbs the thermal and velocity boundary layers. Enhancement of heat transfer for all three samples was characterised by an increase of pressure drop. The electron beam enhancement technique is a rapid process with zero material waste and cost effective. It allows thermal management systems to be produced smaller and faster, reduce material usage, without compromising safety, labour cost or the environment.

"Spray cooling has been important to control die temperature in forging processes for years. One area that has had little research is how thermal stresses in a metal are related to flow characteristics of the spray. Wyman-Gordon Corporation at its North Grafton MA facility uses spray cooling to cool their die after a forging process. The current system used is found to cause cracking along the surface of the impression in the die. The purpose of this project is to compare the nozzle system used by Wyman-Gordon to selected commercially available spray nozzles, and determine if there is a better spray cooling system than the one currently used. First the flow parameters, of Sauter mean diameter, particle velocity, and volumetric spray flux were experimentally found using a laser PDA system for four water driven nozzles, including the Wyman-Gordon nozzle, and one air-atomizing nozzle. The water atomizing nozzles were tested using pressures from 30 psi to 150 psi. For the air-atomizing nozzle, the water pressure was set at 60 psi and the air pressure was varied from 30 to 150 psi. Three nozzles were chosen, the Wyman-Gordon nozzle, the smaller orifice water atomizing nozzle, the air-atomizing nozzle, and an air stream, to conduct an inverse heat conduction experiment. Using the temperature gradients created by the cooling effects of each nozzle, the heat flux and induced thermal stresses were determined. The results showed the Wyman-Gordon nozzle was causing higher thermal stresses than the air/water and water nozzles. However, the air-atomizing nozzle and air stream, due to the high temperatures that the dies are subjected to, did not cool the die quick enough to be practical. The smaller orifice water atomizing nozzle proved to be the nozzle that would cool the surface of the dies within a practical time, and induce allowable thermal stresses, sufficiently enough below the yield strength of the die material. These results, although collected specifically to study the cooling of dies at Wyman-Gordon, could be generalized to include the cooling of any test piece with a high surface temperature. "

Low grade heat sources have a large amount of thermal energy content. Due to low temperature, the conventional power generation technologies result in lower efficiency and hence cannot be used. In order to efficiently generate power, alternate methods need to be used. In this study, a supercritical organic Rankine cycle was used for heat source temperatures varying from 125°C to 200°C. Organic refrigerants with zero ozone depletion potential and their mixtures were selected as working fluid for this study while the cooling water temperature was changed from 10-25°C. Operating pressure of the cycle has been optimized for each fluid at every heat source temperature to obtain the highest thermal efficiency. Energy and exergy efficiencies of the thermodynamic cycle have been obtained as a function of heat source temperature. Efficiency of a thermodynamic cycle depends significantly on the sink temperature. At areas where water cooling is not available and ambient air temperature is high, efficient power generation from low grade heat sources may be a challenge. Use of passive cooling systems coupled with the condenser was studied, so that lower sink temperatures could be obtained. Underground tunnels, buried at a depth of few meters, were used as earth-air-heat-exchanger (EAHE) through which hot ambient air was passed. It was observed that the air temperature could be lowered by 5-10°C in the EAHE. Vertical pipes were used to lower the temperature of water by 5°C by passing it underground. Nocturnal cooling of stored water has been studied that can be used to cool the working fluid in the thermodynamic cycle. It was observed that the water temperature can be lowered by 10-20°C during the night when it is allowed to cool. The amount of water lost was calculated and was found to be approximately 0.1% over 10 days. The different passive cooling systems were studied separately and their effects on the efficiency of the thermodynamic cycle were investigated. They were then combined into a novel condenser design that uses passive cooling technology to cool the working fluid that was selected in the first part of the study. It was observed that the efficiency of the cycle improved by 2-2.5% when passive cooling system was used.