Caracterização quantitativa do volume de cavidades em um dispositivo de cavitação hidrodinâmica usando dinâmica de fluidos computacional

Hydrodynamic cavitation has been extensively studied for its potential to remove emerging pollutants. Despite the advance of the experimental studies involving this phenomenon, computational studies that evaluate the influence of the geometry of the cavitation devices on the flow parameters are still necessary. The purpose of this article was to evaluate the influence of the change in the geometry of a Venturi device on the volume of cavities formed in its divergent section using Computational Fluid Dynamics (CFD). The geometric parameters modified in the Venturi were: the diffuser angle and the relation between the height and the width of the throat (h/w). The volume of cavities is an important parameter because it influences the cavitation intensity. A cavitational bench system was constructed in order to obtain input data for simulation. The results showed that the increase in the diffuser angle from 6.5° to 18.5° gradually reduced the volume of cavities from 93 mm3to 10 mm3. Between the relations h/w = 0.05 and h/w = 0.45 was observed the formation of cavities between 106 mm3 and 77 mm3, however between h/w = 0.45 and h/w = 1.0 there was the formation of 213 mm3. Therefore, Venturi’s with diffuser angle less than 6.5º and relation h/w greater than 0.45 produce greater volume of cavities. The greater volume of cavities will not necessarily produce greater cavitational intensity, since cavitation clouds can be formed and reduce the implosion intensity of the cavitation bubbles

Caracterização quantitativa do volume de cavidades em um dispositivo de cavitação hidrodinâmica usando dinâmica de fluidos computacional

Hydrodynamic cavitation has been extensively studied for its potential to remove emerging pollutants. Despite the advance of the experimental studies involving this phenomenon, computational studies that evaluate the influence of the geometry of the cavitation devices on the flow parameters are still necessary. The purpose of this article was to evaluate the influence of the change in the geometry of a Venturi device on the volume of cavities formed in its divergent section using Computational Fluid Dynamics (CFD). The geometric parameters modified in the Venturi were: the diffuser angle and the relation between the height and the width of the throat (h/w). The volume of cavities is an important parameter because it influences the cavitation intensity. A cavitational bench system was constructed in order to obtain input data for simulation. The results showed that the increase in the diffuser angle from 6.5° to 18.5° gradually reduced the volume of cavities from 93 mm3 to 10 mm3. Between the relations h/w = 0.05 and h/w = 0.45 was observed the formation of cavities between 106 mm3 and 77 mm3, however between h/w = 0.45 and h/w = 1.0 there was the formation of 213 mm3. Therefore, Venturi’s with diffuser angle less than 6.5º and relation h/w greater than 0.45 produce greater volume of cavities. The greater volume of cavities will not necessarily produce greater cavitational intensity, since cavitation clouds can be formed and reduce the implosion intensity of the cavitation bubbles.A cavitação hidrodinâmica tem sido amplamente estudada por seu potencial em remover poluentes emergentes. Apesar do avanço dos estudos experimentais envolvendo este fenômeno, ainda são necessários estudos computacionais que avaliem a influência da geometria dos dispositivos de cavitação nos parâmetros de escoamento. O objetivo deste artigo foi avaliar, por meio da Dinâmica de Fluidos Computacional (CFD), a influência da mudança da geometria de um dispositivo de Venturi sobre o volume de cavidades formadas em sua seção divergente. Os parâmetros geométricos modificados no Venturi foram: o ângulo divergente e a relação entre a altura e a largura da garganta (h/w). O volume das cavidades é um parâmetro importante porque influencia a intensidade da cavitação. Um sistema de bancada cavitacional foi construído a fim de obter dados de entrada para simulação. Os resultados mostraram que o aumento do ângulo divergente de 6,5° para 18,5° reduziu gradativamente o volume das cavidades de 93 mm3 para 10 mm3. Entre as relações h/w = 0,05 e h/w = 0,45 observou-se a formação de cavidades entre 106 mm3 e 77 mm3, porém entre h/w = 0,45 e h/w = 1,0 ocorreu a formação de 213 mm3. Portanto, Venturi's com ângulo divergente menor que 6,5º e relação h/w maior que 0,45 produzem maior volume de cavidades. O maior volume de cavidades não necessariamente produzirá maior intensidade cavitacional, uma vez que nuvens de cavitação podem se formar e reduzir a intensidade de implosão das bolhas de cavitação

Remoção de matéria orgânica natural em águas usando cavitação hidrodinâmica e peróxido de hidrogênio (CH-H2O2)

The presence of natural organic matter (NOM) in water does not present direct risk to the human body or to the environment. However, its presence along with other pollutants can lead to countless issues and damage human health and the environment. The hydrodynamic cavitation (HC) phenomenon started being used in the early 21st century as a process capable of treating supply-water and wastewater based on pollutant and pathogen degradation. Process effectiveness increases when it is combined to chemical agents, creating an advanced oxidation process (AOP). Although several studies have presented broaden applications for the HC process, its use for NOM removal from supply-water was not yet assessed; therefore, it remains a gap in scientific knowledge. The aim of the current study is to assess HC potential in NOM removal. In order to do so, the experiments were carried out in bench scale hydrodynamic cavitation system operated at batch model within 15-min duration period-of-time. In addition, decantation experiments (24-h period-of-time) were performed in order to check HC influence on molecules found in reaction medium after the exposure of NOM to the phenomenon. NOM was produced by a synthetic humic acid (HA) matrix at fixed concentration of 100 ppm. In total, 16 experiments were carried out; each experiment was featured by the following pair: pH (2.6, 3.0, 3.5 and 5.5) and hydrogen peroxide (0, 1, 5 and 30 mL). The best removal efficiencies (34%-36%) were observed in the most acidic pH ranges (2.6-3.0) at H2O2 concentration of 15mL. Results have presented high NOM removal efficiency (approximately 90%) after decantation at the most acidic pH ranges, as well. It can be explained by the fact that hydrodynamic cavitation in acid solution can break molecular structures suspended in the liquid medium, which favors decantation. Based on the present study, hydrodynamic cavitation with hydrogen peroxide addition can remove NOM from water; moreover, pH control is an essential factor for process development

Remoção de matéria orgânica natural em águas usando cavitação hidrodinâmica e peróxido de hidrogênio (CH-H2O2)

The presence of natural organic matter (NOM) in water does not present direct risk to the human body or to the environment. However, its presence along with other pollutants can lead to countless issues and damage human health and the environment. The hydrodynamic cavitation (HC) phenomenon started being used in the early 21st century as a process capable of treating supply-water and wastewater based on pollutant and pathogen degradation. Process effectiveness increases when it is combined to chemical agents, creating an advanced oxidation process (AOP). Although several studies have presented broaden applications for the HC process, its use for NOM removal from supply-water was not yet assessed; therefore, it remains a gap in scientific knowledge. The aim of the current study is to assess HC potential in NOM removal. In order to do so, the experiments were carried out in bench scale hydrodynamic cavitation system operated at batch model within 15-min duration period-of-time. In addition, decantation experiments (24-h period-of-time) were performed in order to check HC influence on molecules found in reaction medium after the exposure of NOM to the phenomenon. NOM was produced by a synthetic humic acid (HA) matrix at fixed concentration of 100 ppm. In total, 16 experiments were carried out; each experiment was featured by the following pair: pH (2.6, 3.0, 3.5 and 5.5) and hydrogen peroxide (0, 1, 5 and 30 mL). The best removal efficiencies (34%-36%) were observed in the most acidic pH ranges (2.6-3.0) at H2O2 concentration of 15mL. Results have presented high NOM removal efficiency (approximately 90%) after decantation at the most acidic pH ranges, as well. It can be explained by the fact that hydrodynamic cavitation in acid solution can break molecular structures suspended in the liquid medium, which favors decantation. Based on the present study, hydrodynamic cavitation with hydrogen peroxide addition can remove NOM from water; moreover, pH control is an essential factor for process development.A presença de matéria orgânica natural (MON) em águas não apresenta riscos diretos relacionados ao seu contato com o organismo humano e nem mesmo ao meio ambiente. Entretanto, sua presença, em conjunto a outros poluentes, pode acarretar inúmeros problemas e danos à saúde humana e ao meio ambiente. O fenômeno de cavitação hidrodinâmica (CH) passou a ser utilizado no início do século XXI como um processo capaz de realizar o tratamento de águas de abastecimento ou residuárias a partir da degradação de poluentes e patógenos. A efetividade do processo aumenta quando aliado à adição de agentes químicos no meio reacional, configurando um processo oxidativo avançado (POA). Por mais que diversos trabalhos apresentem amplas aplicações para o processo de CH, sua utilização para remoção de MON de águas de abastecimento ainda não foi avaliada e, portanto, apresenta-se como uma lacuna no conhecimento científico. O objetivo deste trabalho é avaliar o potencial da CH em remover MON. Para tanto, os experimentos foram realizados em um sistema de cavitação hidrodinâmica, em escala de bancada, operado em modo batelada com duração de 15 minutos. Adicionalmente, experimentos de decantação (período de 24 horas) foram conduzidos com intuito de verificar a influência da CH sobre as moléculas presentes no meio reacional após exposição ao fenômeno. A MON foi constituída por uma matriz de ácido húmico (AH) sintética à uma concentração fixa de 100 ppm. No total foram realizados 16 experimentos, no qual cada experimento foi caracterizado pelo par: pH (2,6; 3,0; 3,5; e 5,5) e peróxido de hidrogênio (0; 1; 15 e 30 mL). As melhores eficiências de remoção (34-36%) foram encontradas para faixas de pH mais ácidas (2,6-3,0), para uma concentração de 15 mL de H2O2. Após decantação, os resultados apresentaram uma elevada eficiência de remoção de MON (aproximadamente 90%), também para faixas de pH mais ácidas. Isso pode ser explicado pelo fato de que, em soluções ácidas, a cavitação hidrodinâmica consegue romper estruturas moleculares suspensas no meio líquido, favorecendo a decantação. Este estudo mostrou que a cavitação hidrodinâmica aliada a peróxido de hidrogênio é capaz de remover MON presentes em águas e que o controle do pH é fator crucial para o desempenho do processo

西漢與匈奴在西域爭戰之研究

本論文總共約捌萬位千字。共分五章：一、西漢與匈奴在西域爭戰之前奏；二、西漢與匈奴在西域爭戰之因素；三、漢匈勢力在西域之消長；四、西漢在西域之軍政措施：五、結論。第一章分三節：一、漢初西北之國際形勢與漢國力之運作；二、大戰略；三、漢匈對抗之政略與戰略的運用。第二章亦分三節：一、西域之政治經濟特質；匈奴與西城之關係；三、漢通西域之目的。第三章分四節：一、漢在河西之經營方略；二、漢匈與西域之地理交通；三、大宛之役；四、匈奴勢力在西域之衰微。第四章分三節：一、漢在西域之戰略佈署；二、都護制度；三、陳湯滅郅支之戰。第五章為結論。匈奴是一個機動而活躍的民族，其活躍表現在軍事方面時，便顯示了戰士的勇武和戰馬的慓悍；當表現於經濟方面時，則顯示了商業性格的強烈。漢朝為了對付匈奴這一強敵，乃實施一連串的富強安內政策，並有「斷匈奴右臂」的政略指導，蓋西域乃漢政治生存空間之前線地帶，漢通西域一方面是基於國防安全的考慮，另一方面方可因此而威脅匈奴之右翼，斷其府藏，絕其西方之援國。匈奴卒因漢朝的撻伐而窮蹙、而衰微，終於分裂為二部，最後則呼韓邪單于南降漢，郅支單于被滅於康居