The equation for the conservation of momentum in the mushy zone during solidification is derived using the volume averaging technique. The conditions under which the momentum equation reduces to Darcy's law are elucidated. Permeabilities for flow of interdendritic liquid in Al-Cu alloys with equiaxial structures are measured using a simple, cost-effective permeameter. Center-to-center distance between grains (180 μm to 450 μm), specific surface (3.21 x 10⁻² μm⁻¹ to 3.095 x 10⁻¹ μm⁻¹), and volume fraction liquid (0.166 to 0.434) are the structural parameters studied in this investigation. Permeability in Al-Cu alloys with equiaxial grains is structure sensitive. For example, permeabilities for globular structures (nondendritic) are approximately one order of magnitude greater than permeabilities for the dendritic-globular structures, when the volume fraction liquid is approximately 0.3. To better understand the dependence of permeability on structure morphology, structure evolution during the permeability testing was studied in isothermal coarsening experiments. Dimensionless permeabilities based on specific surface, and center-to-center distance between grains are presented along with the theoretical results for flow through different arrays (simple cubic, body-centered cubic and face-centered cubic) of uniform spheres. With dimensionless permeability defined as KSᵥ², where Sᵥ is the specific surface of the solid, the empirical data compare reasonably well with theoretical curves for flow through arrays of uniform spheres. Numerical experiments are performed to obtain permeabilities for flow parallel to primary dendrites in columnar structures with high volume-fraction liquid where physical experiments may fail. The results of numerical experiments are presented along with the analytical results for flow parallel to cylinders arranged in square and triangular packing, analytical results for flow through periodically constricted tubes and the available empirical data. The results indicate that there is a transition in the behavior of permeability in the neighborhood of volume fraction liquid equal to 0.65.

Master of Science / Department of Architectural Engineering and Construction Science / Fred L. Hasler / This paper discusses the advantages of applying a utility centralized chilled water system as the district cooling choice for facilities in the high-density urban areas of China and how it will influence China’s development in the next decades. Presently, the Chinese government is trying to contribute to the world’s energy-saving goals as well as determine its sustainable development framework. As air pollution has become one of the main problems in China, indoor air quality (IAQ) is likely to gain priority as a building design consideration in the future. Consistent with this fact, this paper proposes an optimum HVAC system for cooling purposes to the Chinese government. Compared to unitary HVAC systems, the centralized HVAC system has significant advantages in system efficiency, energy reduction and cost savings and can, therefore, be a better choice. Furthermore, the paper will focus on the centralized chilled water system and demonstrate why they better match the development model in China. The application of the system in high-density urban areas will also be discussed. Due to a lack of understanding that the energy consumption of unitary systems, the first comparison presented is between unitary HVAC systems and centralized HVAC systems in individual buildings. The comparison presented will focus on the energy-saving benefits of the centralized HVAC system in individual buildings and its contribution to sustainable development. Consequently, prescribing a centralized chilled water system as a utility district cooling system and applying a centralized chilled water system to each individual building in the highdensity urban areas will be compared. Cost savings, including initial cost and life cycle cost, are the metrics used in this comparison. Additionally, energy consumption and system reliability will be explored in determining which model will be more appropriate for China's development. The paper concludes that the centralized chilled water system should become the mainstream in the high-density urban area in China. Several recommendations are also made to the Chinese government on setting up utility centralized chilled water systems.

Lactobacillus acidophilus e Bifidobacterium lactis são microrganismos probióticos frequentemente utilizados em alimentos funcionais. No entanto, estes microrganismos devem resistir ao processamento, à estocagem do alimento, e sobreviver à passagem pelo trato-gastrointestinal, para chegarem ativos ao intestino e exercerem seus efeitos benéficos. Uma vez que os probióticos são sensíveis a uma série de fatores, tais como meio ácido, sais biliares e presença de oxigênio, a microencapsulação tem sido estudada com objetivo de protegê-los aos efeitos adversos do ambiente, além de promover a liberação controlada no local de ação do microrganismo, melhorando sua eficiência. Este trabalho teve como objetivo a produção e avaliação de micropartículas lipídicas contendo B. lactis ou L. acidophilus, produzidas por spray chilling, utilizando gorduras de baixo ponto de fusão, tais como gordura de palma e manteiga de cacau, como agente encapsulante. O diâmetro médio e a morfologia das partículas foram avaliados. Ensaios de sobrevivência foram conduzidos com objetivo de avaliar a resistência dos microrganismos ao processo encapsulação, resistência in vitro aos fluidos gástrico e intestinal simulados e estabilidade das células durante 90 dias de armazenamento a -18, 7 e 20 ou 37°C, dependendo da gordura utilizada. As micropartículasapresentaram-se em formato esféricoe com diâmetro médio que pode permitir o fácil escoamento no alimento, sem proporcionar impacto tecnológico negativo.A tecnologia de encapsulação por spray chilling, utilizando gordura de palma e manteiga de cacau, como agentes encapsulantes, proporcionou a obtenção de micropartículas eficientes na proteção dos probióticos frente ao processo de encapsulação e na manutenção da estabilidade das células quando estocados sob congelamento. Entretanto, aeficiência das micropartículas frente aos fluidos gastrointestinais e a estabilidade das células quando estocadas a 7 e 20 ou 37°C variaram de acordo com a gordura utilizada e com o microrganismo encapsulado. As micropartículas lipídicas obtidas são, portanto, uma matriz inovadora para a aplicação de probióticos, de baixo custo e com grande possibilidade de obtenção em escala industrial. O desafio futuro para o presente estudo é a seleção de um agente encapsulante que aumente a estabilidade das células, nas temperaturas ambiente e de refrigeração, a fim de aumentar as possibilidades de aplicação destas microcápsulas em produtos alimentícios. / L. acidophilus and Bifidobacterium lactis are probiotic microorganisms frequently used in food product. However they must remain viable during processing, entire shelf life of product and passing-through the gastrointestinal tract to provide beneficial effects on human health. Since theses microorganisms are sensitive to a series of factors, especially presence of oxygen and acid medium, microencapsulation has been studied as an alternative to increase probiotic cells viability and to provide the controlled release in the site of action, improving their efficiency. The aim of this study was to produce and evaluate lipid microparticles of L. acidophilus or B. lactis produced by spray chilling technology using low melting point fats, such as palm fat and cocoa butter, as the encapsulant agent. The mean diameter and morphology of the microparticles were evaluated. Survival assays were conducted to evaluate the resistance of the microorganisms to the spray chilling process, viability to the in vitro simulated gastric and intestinal fluids and viability during 90 days of storage at -18, 7 and 20/37°C, depending on the fat used. Microparticles presented a spherical shape and mean diameter that allows the flow of material in the food product without conferring technology influence. Spray chilling technology using fat palm or cocoa butter as the encapsulant agent was efficient in protecting the microorganism to the encapsulation process and 90 days of storage at -18°C. However the efficiency of the microparticles on the gastric and intestinal fluids and the cells stability during storage at 7 e 20 or 37°C varied according to the fat and microorganism used. The lipid microparticles seem to be a relatively innovative matrix for the application of probiotics with low costs and possibility of scale up. The future challenge in this study is to choose an encapsulant agent that improves cells resistance and viability at refrigerator and room temperatures to increase the possibility of application of these microcapsules in food products.

No description available.

The backbone of the expanding Information and Communication Technology (ICT)-sector are data centers. In these, Information Technology (IT) equipment is housed which provides computational power for e.g. cloud computing and internet services. Data centers consume massive amount of electricity, estimated to 1% of the global demand. All this power is however not used directly by the IT equipment, to keep the operating conditions in the desired range 21-61% of the electricity is used by the cooling solution. This is mainly due to the extensive use of vapor-compression refrigeration systems (VCRS) which provide a dependable cooling solution that works independent of climate conditions. To get around VCRS the concept of free cooling has been utilized in data centers, this can be done in many ways but the main idea is to introduce a natural cooling source without compromising the operating environment. Previous studies have showed that direct airside economization, i.e. using outdoor air directly in the data center have potential to reduce the energy demand of the cooling solution. This is however directly dependent on the outdoor conditions, by combining direct airside economization with direct evaporative cooling and recirculation of hot air from the IT equipment the cooling solution can handle a wider range of weather conditions and still keep the operating environment in desired conditions. Simulations of similar cooling solutions have been been done by Endo et al. and Ham et al. and showed promising results, but no study of an experimental setup have been published. To test how direct airside economization with direct evaporative cooling technology performs and find its characteristics an experimental setup was constructed, coolers with direct airside economziation and direct evaporative cooling was installed in a data center module at RISE SICS North data center ICE. The setup consisted of 12 racks of OCP Winterfell servers in a hot and cold aisle setup with containment, ducts on the ceiling connected the hot aisle to the coolers and made recirculation of hot air possible. A test schedule was developed to test the cooling solution in two of its four operating modes where the IT-load and setpoint temperatures where adjusted in predefined steps. The IT equipment consumed between 60 - 100kW and the facility power varied between 1.5 - 7kW, which results in a power usage effectiveness (PUE) value between 1.02 and 1.08. Compared to traditional VCRS systems these are very low values. By running the coolers in evaporative cooling mode the PUE was consistently lower compared to ventilation mode, the supply air temperature drop was up to 10°C while in cooling mode. The water consumption, and the corresponding water usage effectiveness (WUE) value was not measured or calculated due to limitations of the test rig that made long tests unstable. Direct airside economization with direct evaporative cooling is not the cooling solution for all data centers in all climates. But if the right conditions are present it is a simple cooling solution that without VCRS or heat exchangers (HEX) shows impressive PUE capabilities. Due to the psychical limitations of the system it can not handle high temperature and/or humidity levels, the data center either needs to be shut down, operated in undesirable conditions or complemented with a separate cooling system to operate in these conditions. To find the limits for this system supply air alteration and removal of exhaust air needs to be implemented. Due to the natural limitations of evaporative cooling combined with the ASHRAE guidelines the technology needs to be further researched to find what climate conditions it can handle. The water consumption which according to previous studies can be substantial also needs to be further studied.

No description available.

Thesis (Master of Engineering in Electrical Engineering)--Cape Peninsula University of Technology, 2018. / Gas turbines have achieved widespread popularity in industrial fields. This is due to the high power, reliability, high efficiency, and its use of cheap gas as fuel. However, a major draw-back of gas turbines is due to the strong function of ambient air temperature with its output power. With every degree rise in temperature, the power output drops between 0.54 and 0.9 percent. This loss in power poses a significant problem for utilities, power suppliers, and co-generations, especially during the hot seasons when electric power demand and ambient temperatures are high. One way to overcome this drop in output power is to cool the inlet air temperature. There are many different commercially available means to provide turbine inlet cooling. This disserta-tion reviews the various technologies of inlet air cooling with a comprehensive overview of the state-of-the-art of inlet fogging systems. In this technique, water vapour is being used for the cooling purposes. Therefore, the water quality requirements have been considered in this thesis. The fog water is generally demin-eralized through a process of Reverse Osmosis (RO). The drawback of fogging is that it re-quires large amounts of demineralized water. The challenge confronting operators using the fogging system in remote locations is the water scarcity or poor water quality availability. However, in isolated hot areas with high levels of radiation making use of solar PV energy to supply inlet cooling system power requirements is a sustainable approach. The proposed work herein is on the development of a photovoltaic (PV) application for driv-ing the fogging system. The design considered for improved generation of Acaica power plant in Cape Town, South Africa. In addition, this work intends to provide technical infor-mation and requirements of the fogging system design to achieve additional power output gains for the selected power plant.

High turbine inlet temperature becomes necessary for increasing thermal efficiency of modern gas turbines. To prevent failure of turbine components, advance cooling technologies have been applied to different portions of turbine blades. The detailed film cooling effectiveness distributions along a rotor blade has been studied under combined effects of upstream trailing edge unsteady wake with coolant ejection by the pressure sensitive paint (PSP). The experiment is conducted in a low speed wind tunnel with a five blade linear cascade and exit Reynolds number is 370,000. The density ratios for both blade and trailing edge coolant ejection range from 1.5 to 2.0. Blade blowing ratios are 0.5 and 1.0 on suction surface and 1.0 and 2.0 on pressure surface. Trailing edge jet blowing ratio and Strouhal number are 1.0 and 0.12, respectively. Results show the unsteady wake reduces overall effectiveness. However, the unsteady wake with trailing edge coolant ejection enhances overall effectiveness. Results also show that the overall effectiveness increases by using heavier coolant for ejection and blade film cooling. Leading edge film cooling has been investigated using PSP. There are two test models: seven and three-row of film holes for simulating vane and blade, respectively. Four film holes’ configurations are used for both models: radial angle cylindrical holes, compound angle cylindrical holes, radial angle shaped holes, and compound angle shaped holes. Density ratios are 1.0 to 2.0 while blowing ratios are 0.5 to 1.5. Experiments were conducted in a low speed wind tunnel with Reynolds number 100,900. The turbulence intensity near test model is about 7%. The results show the shaped holes have overall higher effectiveness than cylindrical holes for both designs. As increasing density ratio, density effect on shaped holes becomes evident. Radial angle holes perform better than compound angle holes as increasing blowing and density ratios. Increasing density ratio generally increases overall effectiveness for all configurations and blowing ratios. One exception occurs for compound angle and radial angle shaped hole of three-row design at lower blowing ratio. Effectiveness along stagnation row reduces as increasing density ratio due to coolant jet with insufficient momentum caused by heavier density coolant, shaped hole, and stagnation row.

A detailed investigation of ion crystals produced by laser and sympathetic cooling in a linear RF trap has been conducted. The laser cooling methods were examined and applied to the trapped ^24Mg^(positive) ions. The crystals produced by the laser cooling were studied, including the dependence on RF voltage, end cap DC voltage, laser power and laser frequency. By manipulating the different RF voltages and endcap DC voltages, the structure phase transition of the ion crystals was observed. In addition, the sympathetic cooling of different ion species with the laser cooled 24Mg^(positive) was carried out. In this process, the mixed Mg^(positive) and He^(positive) crystals were created andidentified, and mixed Mg^(positive) and H2^(positive) crystals were produced. The effect of an unwanted chemical reaction of Mg^(positive) and H2 was observed and minimized. After sympathetic cooling of light ion species, the sympathetic cooling of heavy molecular ions such as fullerene ions was also carried out. The efficiencies and final temperature in both cases are very different. Theoretically to interpret the results, molecular dynamics simulations of the laser cooling and sympathetic cooling were implemented. And the simulations were compared with the experimental results. In the process of carrying out this research, the optics were rebuilt to provide reliable UV sources for the photoionization and laser cooling of Mg ions. The imaging system was reconfigured to take the images of ion crystals. New elements were added tin the ion trap to improve the ability to manipulate ions.

South Africa contributes approximately 0.5 percent to the total world milk demand and is the third largest producer of fresh cow milk in Africa after Sudan and Kenya. In comparison to any other enterprise, the cost of milk production is influenced by numerous factors, that in turn affect the profitability of the farm enterprise; however one of such factors is high electricity cost. In this regard, there is need for efficient operation of the milk processing plant at all stages and at the same time maximising on product quality and minimising on the cost of production including energy. At the dairy farm, milk handling mainly commences as the milk leaves the cow udder at 35°C–37°C and must be cooled rapidly to a storage temperature of 4°C in a bid to stop microbial activity. The cooling of the milk can be done directly by the bulk milk cooler (BMC) from 37°C to the required storage temperature of 4°C or it can be done successively through pre-cooling. The process of pre-cooling involves the use of a heat exchanger where in most instances the plate heat exchanger (PHE) is used as the pre-cooler (PC) thereby leading to energy savings in a dairy facility. Cooling of milk involves significant amount of energy and it could account for about 20 percent of the total energy consumed on a farm. The aim of the research was to develop mathematical models that could be used to predict the electrical energy performance and capture the cooling saving of an on-farm direct expansion bulk milk cooler (DXBMC) during the milk cooling process. Accordingly, data acquisition system (DAS) was designed and built to accurately measure the power consumption of the BMC, temperature of raw milk, room temperature, temperature of cold water, relative humidity and ambient temperature. The volume of milk produced per day was extracted from the daily records on the farm. In addition, the temperature sensors were connected to a four channel HOBO data loggers which were configured to log at every five-minutes interval. The results were analysed and the mathematical models were developed using MATLAB. The statistical Toolbox in MATLAB was used to rank the predictors according to their weight of importance using the ReliefF Algorithm test. The results showed that on average, the daily electrical energy consumed by the BMC at the two milking times was higher during the peak period (127.82 kWh and 93.86 kWh) than the off-peak period (48.31 kWh and 43.23 kWh). On average, the electricity used for cooling of milk on the dairy farm was 17.06 kWh/m3 of milk. The average monthly electricity used per cow on the farm was 8.03 kWh/cow which translated to an average of 0.26 kWh/cow/day The average specific energy consumption of the cooling system per litre of milk cooled was 0.02 kWh/L and was almost constant throughout the whole period of monitoring. Furthermore, the BMC was able to cool 57.33 L/kWh during the off-peak period which increased by 7.7 percent to 62.13 L/kWh during the peak period. Furthermore, mathematical models represented as multiple linear regression (MLR) models were built and developed using the experimental data. The developed mathematical models had good agreement with the experimental data as evidenced by the correlation coefficients of 0.922 and 0.8995 along with 0.935 and 0.930. The ReliefF Algorithm test revealed that the volume of milk was the principal contributor to the energy consumption of the BMC for both the morning (AM) and afternoon (PM) milking period. The Relative Prediction Error (RPE) was used to evaluate the suitability of the developed models. In this light, the AM off-peak model had RPE of 18.54 percent while the PM off-peak model had 14.42 percent. In addition, the AM peak and PM peak models had RPE of 19.23 percent and 18.95 percent respectively. This suggested that the MLR models for the off-peak and peak milking periods (both AM and PM) had acceptable prediction accuracy since the RPE values were between 10 percent and 20 percent. The findings from the experimental study showed that the coefficient of performance (COP) of the AM milking period was higher (2.20) than that of the PM milking period of the BMC (1.93). Increase in the milk volume led to an increase in the COP such that the peak period with higher milk volumes recorded a high COP increase of 12.61 percent and 19.81 percent for the AM and PM milking periods respectively.