Please read the abstract in the dissertation. Copyright / Dissertation (MEng)--University of Pretoria, 2010. / Chemical Engineering / unrestricted

South Africa is located in the sub tropics with an elevated plateau which is located approximately 1500 m above mean sea level (a.m.s.l). Every year, snow occurs on the mountains of Lesotho, but on occasions this snow descends to lower elevations which impacts on the livelihood of people. Severe weather originating from extra-tropical weather systems has been well documented in South Africa and yet very little research has been done to predict significant snowfall from these weather systems. The main aim of this research is to identify those weather systems responsible for snow and to understand the processes causing snow to form when these systems occur. A comprehensive database of significant snowfall events is supplied from 1981 to 2011. The database is subjectively classified into characteristic synoptic patterns. The snow cases are then objectively classified using self-organising maps (SOMs) to obtain synoptic configurations most typically associated with significant snowfall over South Africa. Case studies which aim to explain the synoptic conditions, formation mechanisms as well as critical surface temperature and relative humidity during snowfall events are described. This is done by analysing each case study with respect to synoptic circulations, surface observations, atmospheric soundings, satellite imagery as well as atmospheric thickness. Conclusions are drawn and critical threshold values of atmospheric thickness, surface temperature and humidity are identified when snowfall occurs. A methodical snow forecasting decision tree is devised. It takes the synoptic classification of circulation patterns during significant snowfall, atmospheric thickness, height of the freezing level, surface temperature, and relative humidity into account. This process is explained by case studies. It is recommended that results from this dissertation are made available to weather forecasters in South Africa and that the results are implemented in the operational forecasting environment. Further case study investigations are suggested, taking the mesoscale processes effects into account. / Dissertation (MSc)--University of Pretoria, 2013. / am2013 / Geography, Geoinformatics and Meteorology / MSc / Unrestricted

The objective of this work was to evaluate the fundamentals of the currently available CO2 separation technologies and provide a solution for the efficient capture of carbon dioxide from various point source emitting industries. In order to realize a robust approach to advancing the solution to this global issue, the versatility of the process to the range of compounds contained within the stream(s) to be processed must be maintained. It is clear that adsorption, membrane, and aqueous amine based processes are all capable. However, only aqueous amine scrubbing appears economically viable at the current stage of development. In order to challenge this, and potentially drive the separation costs lower, this work centered on hybridizing aqueous amine chemistry and dry adsorption based separations to produce a novel nano-porous material capable of efficient removal of CO2 from flue gas (5% CO2 balance N2 with moisture). In order to combine aqueous amine scrubbing with dry adsorption, a few approaches were considered and evaluated. These included, amine impregnation within the vast pore volume of PE-MCM-41, surface grafting of various amino silane compounds, and finally, a novel approach of volume based amine functionalization (3D grafting). Application of pore-expanded MCM-41 (PE-MCM-41) mesoporous silica coated with 3-[2-(2-aminoethyl-amino)ethylamino]propyltrimethoxysilane (TRI) has been extensively examined for the adsorption of CO2 from N2. A systematic study of the amine loading as a function of the relative amounts of TRI and water used during the grafting procedure, and the temperature of the grafting reaction was carried out. Extremely high levels of active amine content were achieved using prehydrated silica surfaces at grafting temperatures below reflux in order to facilitate thermally controlled water-aided surface polymerization of the aminosilanes. Abstract iii The CO2 adsorption capacities and rates were determined for all materials as a function of the amount of TRI and water per gram of support added to the grafting mixture. The optimal TRI grafted PE-MCM-41 adsorbent exhibited a 2.65 mmol/g adsorption capacity at 25 °C and 1.0 atm for a dry 5% CO2 in N2 feed mixture, which exceeded all literature reported values, for both meso- and microporous materials under the conditions used in this study. Further, the apparent adsorption and desorption rates with the amine functionalized materials were exceedingly high. When considering the grafted amine quantity, the adsorption capacity and rate were found to be mutually dependent on each other, exhibiting an apparent optimal combination. In comparison to zeolite 13X, the optimally loaded TRI-PE-MCM-41 was far superior in terms of dynamic adsorption and desorption performance. These results were further enhanced when the adsorbents were challenged with a humid stream of 5% CO2/N2. The TRIPE-MCM-41 exhibited a 10% increase in CO2 adsorption capacity, whereas the 13X zeolite did not retain any significant CO2 adsorption capacity. The novel concept of an internally variably staged permeator was introduced. A theoretical model was developed and used as the basis for simulation studies. The advantage of the internal variably staged design was shown to permit a very high extent of separation similar to a two stage permeator for purity, while maintaining similar flux rates as per a single stage permeator. This IVSP concept has also taken existing membrane materials and mechanically translated their process performance to a higher level. As such, the unit should prove effective for front end process stream cleanup requirements prior to an adsorption process with the novel TRI-PE-MCM-41 nano-porous adsorbent.

Orientadores: Daniella Jorge de Moura, Irenilza de Alencar Naas / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Agricola / Made available in DSpace on 2018-08-08T00:23:24Z (GMT). No. of bitstreams: 1 Lima_KarlaAndreaOliveirade_M.pdf: 1645623 bytes, checksum: afa43b69c047d8214563bc3a0f3a1a1d (MD5) Previous issue date: 2006 / Resumo: Fenômenos climáticos de dimensões sem precedentes registrados nos últimos anos fizeram aumentar as preocupações na sociedade, pois estão de acordo com as projeções dos cientistas, segundo os quais qualquer mudança quanto ao clima médio afetará inevitavelmente a freqüência de acontecimentos climáticos extremos tais como ondas de calor e chuvas intensas. Onda de calor é um período de calor desconfortável anormal, geralmente acompanhado de alta umidade relativa com duração de pelo menos um dia, mas se estendendo por alguns dias ou mesmo semanas (AMS, 1989). A ocorrência destes eventos pode ocasionar o estresse térmico influenciando negativamente a produção animal, causando grandes perdas nos processos produtivos e reprodutivos. O presente trabalho teve como objetivo geral estimar as perdas da produção leiteira, em função da ocorrência de ondas de calor, nas bacias leiteiras do Estado de São Paulo, baseado no Índice de Temperatura e Umidade (ITU) médio. Para tanto foi determinada a freqüência de ocorrências de ITU acima do nível crítico. Foi elaborado um histórico de ocorrência de onda de calor no Estado de São Paulo baseado em dados climatológicos num intervalo de anos variando de três a dez anos. Também se quantificou as perdas médias estimadas de produção de leite nas principais regiões leiteiras durante os períodos identificados de onda de calor e por fim validaram-se os índices médios estimados de perdas na produção de leite com dados do controle leiteiro de uma fazenda comercial. Os resultados mostraram que os municípios da bacia leiteira do Vale do Paraíba e a cidade de Presidente Prudente foram os que apresentaram o maior número de ondas de calor por ano e que nem sempre as ondas de calor de maior duração apresentaram maior intensidade de ocorrência. Ao simular o Declínio na Produção Leiteira (DPL) das Bacias do Vale do Paraíba, São José do Rio Preto e Ribeirão Preto não foram encontradas diferenças bioclimáticas entre as mesmas. Observou-se que o DPL estimado superestimou as perdas produtivas efetivamente ocorridas, pois não considerou o efeito da adaptação dos animais ao calor nem a presença de equipamentos de climatização. Concluiu-se que o estudo da ocorrência de ondas de calor mostra de forma mais efetiva o efeito nocivo do ambiente térmico / Abstract: Climate phenomena recorded in the last years with dimensions without precedent raised the worry of society, as they are in accordance with the projections made by scientists who predicted that any change regarding the average weather may affect the frequency of occurrence of weather extremes such as heat waves and thunderstorms. Heat wave is a period of abnormal intense heat generally followed by high relative humidity with the duration of at least one day; however conventionally being extended by some days or even some weeks (AMS, 1989). The occurrence of heat waves can cause heat stress that input a negative influence in animal production causing high losses in production and reproduction processes. High environmental temperatures associated to high relative humidity almost lead to thermal discomfort which induces negatively metabolic and physiological responses. Thus this research has as general objective to estimate milk production losses as function of heat wave incidence in the dairy regions of São Paulo state based on the average temperature and humidity index (THI). Therefore it was determined the THI frequency of occurrence above the critical level. A historical of heat wave occurrence was developed based on climatic data in an interval of three to ten years. It was also quantified the estimated average milk production loss in the major dairy regions during the identified heat wave periods, finally the estimating production index was validated with milk production data from a commercial dairy farm. The results showed that the counties within the Paraiba Valley dairy region as well as Presidente Prudente County presented the highest number of heat wave occurrence per year, and that not always the heat wave with longest period presented higher intensity of occurrence. It was not found statistical difference in the bio climate when simulating the milk decline index (MDEC) for the regions of Paraiba valley, São José do Rio Preto, and Ribeirão Preto. It was observed that the simulated MDEC index present overestimated values for the milk production losses when compared to the real ones as it did not considered the effect of the animal adaptation to the heat neither the presence of acclimation equipments. The conclusion is that the study of heat wave occurrence shows in a more effective way the heat stress effect on dairy production which is not practically identified when studying just the average THI occurrence / Mestrado / Construções Rurais e Ambiencia / Mestre em Engenharia Agrícola

[pt] Recentemente, a umidade vem sendo um dos parâmetros cujas necessidades de medição e controle mais se desenvolvem especialmente em processos os farmacêuticos, de biotecnologia, automobilísticos, além de instalações de ar condicionado. A necessidade de expansão da rede de laboratórios de calibração de umidade, rastreados à Rede Brasileira de Calibração, torna-se cada vez maior para atender a demanda da indústria, além de contribuir para a melhoria dos níveis de incerteza de medição. Este trabalho tem como objetivo uma análise crítica das diferentes metodologias de medição de umidade para uso em laboratórios de calibração. Foram avaliadas as mais utilizadas expressões para a pressão parcial de vapor, visando o cálculo de umidade, e foi realizada uma comparação com a formulação de Sonntag, a mais aceita na comunidade metrológica internacional. Foi também analisada uma comparação entre alguns dos softwares disponíveis na internet para o cálculo dos principais parâmetros de umidade, tomando como referência a mesma formulação. Dentre os fatores de possível influência nas medições de umidade, foi avaliado o comportamento da mistura ar seco-vapor d´água como gás ideal e real, bem com as alterações na composição do ar. Foi feita uma análise das principais fontes de incerteza de medição seguindo a metodologia de medição de umidade a partir da temperatura de ponto de orvalho. Finalmente, o objetivo deste trabalho é apresentar aos laboratórios de calibração de umidade uma análise crítica das metodologias disponíveis para medição de umidade, juntamente com as incertezas alcançadas. / [en] Recently, the need of humidity measurement and control has been shown to be of growing interest, especially in processes like pharmaceuticals, biotechnology, automotives, as well as in air conditioning installations. Increasing the number of laboratories, which are traceable to the Brazilian Calibration Network, is a requirement for attending the industry demands, besides contributing towards improving the measurement uncertainty level. This work has as an objective to critically analyze different methods for humidity measurement, to be used by calibration laboratories. The mostly used expressions for calculating vapor partial pressure were evaluated, aiming humidity determination in comparison with Sonntag´s one, the most accepted formulation by the international metrological community. Also, a comparison was made between different softwares, which were available through internet, for calculating the most important humidity parameters, in comparison with results obtained by the same formulation. Among several factors, the dry air and water vapor mixture properties were calculated, considering it as an ideal or a real one, as well as the effect air composition changes on humidity measurement. The contribution of several sources of errors on the combined uncertainty of humidity measurement was examined, following the methodology that uses the dew point as a starting measurement parameter. Finally, the objective of this work is to present the humidity calibration laboratories a critical analysis of the available methodologies for measuring humidity, together with the achieved uncertainties.

Temperature and relative humidity of produce throughout the cold chain can greatly affect the quality and safety of the food product. Different packaging systems or containers can provide better cooling environments for food products that could decrease temperature abuse and ultimately safety risks. In this study we compiled temperature and relative humidity profiles of broccoli packed in different shipping containers throughout the produce supply chain. The shipping containers looked at were the wax corrugated box, reusable plastic containers (RPC), and Eco Pack Green Box with and without a lid. Large differences were seen in the temperature profiles of each package during the first 15 hours of the cold chain with the wax-corrugated boxes showing the slowest rate of cooling. Growth rates of Salmonella sp. and Listeria monocytogeneson broccoli at different temperatures were also determined. Salmonella sp.showed a greater ability to grow on inoculated broccoli than Listeria monocytogenesduring higher temperatures such as 20° C and 37° C. Temperature profiles along with microbial counts from produce lots have been previously recorded; this is the first study to record temperature and relative humidity profiles in conjunction with bacterial growth data of lab inoculated produce.

This study investigates the possibilities of applying water generated from the atmosphere for agricultural processes, particularly hydroponic systems. A solar powered, off-grid greenhouse system is proposed as a theoretical solution to food production, in areas affected by water scarcity. Two experiments are conducted with the purpose of testing atmospheric water quality and how it performs in a hydroponic setting. The plausibility of powering said greenhouse system using solar energy is investigated, considering several available solar technologies. Ultimately, the footprint area required to install enough capacity to power the system is discussed, and the potential site of such a system is modelled and visualized. The experiments concluded that atmospheric water is likely suitable for hydroponic use. The study also found that the footprint area required for the greenhouse system probably can be considered reasonable for certain applications, but more research and advances within solar power technology would be beneficial / <p>2021-06-08</p>

Presented master’s thesis is focused on the experimental research of influence of climate conditions on wheel-rail adhesion, where climate conditions are meant two parameters: ambient air temperature and air humidity. These parameters always affect wheel-raid contact and their values change significantly during the year. For presented experimental research was used tribometer Mini Traction Machine (MTM) in configuration „ball on disc“. For determination of influence climate conditions was first found out the influence of air humidity on adhesion at certain temperatures, which varied between (1 to 50) °C. These experiments were performed for two types of discs, where one disc was exposed to leaf extract contamination. After that was assembled influence of both parameters (air humidity and ambient air temperature) on adhesion in the form of a 3D map, where were distinctioned states, when condensation has occured and when didn‘t. Obtained results in this thesis will be used for optimalization of rail vehicle control systems.

The diploma thesis is about designing device which monitors temperature and humidity. In the first part of thesis are explained basic terms, importance of key variables and on market offered products are described. After that the thesis describes device concept design with schematic designs. From designed schematics are described printed circuit board designs. Next part is about device commissioning and correction of errors caused by incorrect design. Last part is about program designing and device testing.

Graphene is a semimetal with zero band gap. Position of Fermi level can be changed by applied gate voltage, which results in a change of free carier concentration. This work focuses on a simultaneous measurement of surface potential by Kelvin probe force microscopy (KPFM) and transport response of graphene Hall bars in different relative humidities and with applying gate voltage. The transport response was also observed in case of graphene Hall bar structure modified by local anodic oxidation (LAO).