Sample records for hot working
from WorldWideScience.org

Sample records 1 - 5 shown.



1

Propriedades termo-mecânicas de concretos refratários ligados por sílica coloidal/ Thermo-mechanical properties of colloidal silica-containing castable

Ismael, M. R.; Valenzuela, F. A. O.; Polito, L. A.; Pandolfelli, V. C.
2007-09-01

Resumo em português Os cimentos de aluminatos de cálcio (CAC) são os ligantes hidráulicos mais utilizados em concretos refratários. No entanto, a presença de CaO em sua composição pode limitar seu uso em elevadas temperaturas nos sistemas Al2O3-SiO2 e Al2O3-MgO. Como importante alternativa ao uso do CAC, destaca-se a sílica coloidal, que proporciona, dentre outras vantagens, maior velocidade de secagem e reatividade ao sistema. Estudos anteriores dos autores deste trabalho indicaram (mais) que a adição de microssílica e alumina hidratável podem otimizar o desempenho de concretos contendo sílica coloidal como agente ligante. No entanto, investigações sobre esses sistemas em elevadas temperaturas de trabalho são escassas na literatura. Neste trabalho, o comportamento em diferentes temperaturas de sistemas contendo sílica coloidal foi avaliado quanto à retração linear após queima, porosidade aparente, resistência mecânica a frio e a quente. Como referência, foi utilizada uma formulação de concreto contendo cimento de aluminato de cálcio como agente ligante. Resumo em inglês Calcium aluminate cements (CAC) are the most used hydraulic binders in refractory castables. However the presence of CaO in the castable composition reduces the refractoriness in the Al2O3-SiO2 and Al2O3-MgO systems. In this context, colloidal silica has been pointed out as an important alternative for the CAC use because promotes, among another advantages, easier drying behavior and higher reactivity to the system. Previous works of the authors have indicated that the mi (mais) crosilica and hydratable alumina addition to colloidal silica containing castables can optimize their performance. Nevertheless, researches in these systems at high working temperatures (above 350 ºC) are scarce in the literature. In this work, the colloidal silica bonded castables behaviors at different working temperature were analyzed through the fired linear shrinkage, apparent porosity, mechanical strength and hot modulus of rupture. The obtained results were compared to the CAC containing castable compositions.

Scientific Electronic Library Online (Portuguese)

2

Sistemas ligantes para concretos refratários mulitizáveis/ Binding systems for mulitized castables

Magliano, M. V. M; Pandolfelli, V. C
2010-06-01

Resumo em português Concretos mulitizados são comumente utilizados na indústria siderúrgica devido as suas excelentes propriedades. Entretanto, a presença de cimento de aluminato de cálcio, juntamente com SiO2, forma eutéticos e fases de baixo ponto de fusão, motivando assim a seleção de ligantes alternativos. Neste trabalho os três principais ligantes para refratários (cimento de aluminato de cálcio, alumina hidratável e sílica coloidal) foram incorporados em concretos com alt (mais) o potencial de mulitização e suas propriedades a verde e a quente foram comparadas, definindo quais ligantes apresentam melhor desempenho. Os resultados indicam que a sílica coloidal, além de facilitar a etapa de secagem, resulta em excelentes propriedades a quente e em menor teor de líquido residual após queima, quando comparados com uma composição referência de alta alumina. Resumo em inglês Mullite based castables are usually applied for lining steel industries processing ladles due to their superior working performance. However, the presence of aluminate cement and SiO2 can deteriorate their hot properties by the formation of eutectics and low melting point phases, which motivates the search for alternatives biding systems. In this paper, the three main binders for refractory castables (aluminate cement, hydratable alumina and colloidal silica) were added t (mais) o different compositions and their green and hot properties were compared, aiming to define which one presents better performance. The results indicated the colloidal silica as a promising substitute to the aluminate cement as it favors the drying process, provides excellent hot properties, higher refractoriness and generates low residual liquid phase after sintering, when compared to a high alumina composition.

Scientific Electronic Library Online (Portuguese)

3

Escoamento turbulento na saída de um duto curvo de seção retangular divergente: estudo experimental/ Turbulent flow at the outlet region of a curved rectangular divergent duct: experimental study

Indrusiak, Maria Luiza Sperb; Möller, Sergio Viçosa
1999-09-01

Resumo em português Neste trabalho é apresentado o estudo experimental do escoamento turbulento em um duto curvo simulando parte de uma caldeira de uma usina termoelétrica. As cinzas resultantes da queima de carvão mineral, transportadas pelos gases da combustão, incidem sobre o economizador, localizado após um duto curvo, e provocam erosão dos tubos, levando a falhas que provocam a parada da unidade. A distribuição do escoamento após a curva favorece a erosão na região próxima � (mais) � parede côncava do duto. A solução clássica para redistribuição do escoamento em curvas são as chapas direcionadoras. No caso presente elas não são aplicáveis, pois a erosão de seus componentes de sustentação iria aumentar os riscos operacionais. Este problema foi investigado em um modelo em escala do duto curvo, usando ar como fluido de trabalho. Foi feita visualização do escoamento com fios de lã na parede do duto. As medições foram realizadas com tubo de Pitot e anemômetro de fio quente. Foram feitas modificações na seção de testes usando técnicas de controle da camada limite. Os resultados mostram que a distribuição do escoamento após a curva foi melhorada e que as modificações, quando aplicadas à caldeira, propiciarão um funcionamento mais seguro e econômico. Resumo em inglês This paper presents an experimental study of the turbulent flow in a curved duct which simulates part of a thermal-electrical power plant. Ashes, carried in the power plant by the flow of gases from the furnace, impinge on the pipes of the economizer, after passing a curved duct, and produce erosion of the pipes, leading to failures which stop plant operation. Flow distribution after the curve increase the erosion near the concave wall of the duct. Classical solutions for (mais) flow redistribution in curves, like vanes, are not applicable since they could increase operational risks due to the erosion of the vanes. This problem was investigated in a scale model of the curved duct, in which, for simplicity, air was used as the working fluid. Flow visualizations with wall tuft method, Pitot tube and hot wire measurements were applied. Based on the results, modifications in the test section were made, using boundary-layer control techniques. The results show that the flow redistribution after the curve was improved, and the modifications, when implemented in the plant, may lead to safer and economical operational conditions.

Scientific Electronic Library Online (Portuguese)

4

Perfil farmacológico e fitoquímico de plantas indicadas pelos caboclos do Parque Nacional do Jaú (AM) como potenciais analgésicas: parte I/ Phytochemical and pharmacological profile of plants indicated by caboclos of Jaú National Park (AM) as potential analgesic: part I

Rodrigues, Eliana; Duarte-Almeida, Joaquim M.; Pires, Júlia Movilla
2010-12-01

Resumo em português Muitos estudos de plantas medicinais baseiam-se em informações etnofarmacológicas, na intenção de encurtar o tempo e diminuir os recursos financeiros no desenvolvimento de novas drogas. O presente trabalho teve como objetivo realizar estudos de farmacologia pré-clínica e fitoquímica com três extratos vegetais, obtidos de duas das 42 plantas com potenciais efeitos analgésico e/ou antiinflamatório, indicadas pelos moradores do Parque Nacional do Jaú, AM. Os extr (mais) atos hidroalcoólicos foram submetidos à caracterização fitoquímica por meio de cromatografia em camada delgada (CCD). Os testes de farmacologia pré-clínica empregados foram: screening inicial, rota rod, atividade motora, placa quente, tail flick e contorções abdominais, nas doses de 300 e 500 mg/kg. Os três extratos foram obtidos a partir das cascas da cumandá: Campsiandra comosa Benth., Fabaceae (EHCC) e das folhas (EHSF) e cascas (EHSC) da sucuuba: Himatanthus sucuuba (Spruce ex Müll. Arg.) Woodson, Apocynaceae. As análises fitoquímicas revelaram a presença de flavonóides, taninos, iridóides e triterpenos nos diferentes extratos; enquanto os alcalóides e cumarinas não foram detectados. A investigação farmacológica demonstrou atividade analgésica discreta apenas no teste de contorções abdominais para os extratos EHSF e EHCC; nenhuma alteração foi observada no aparelho de rota rod e de modo geral, observou-se diminuição da atividade motora em todos os extratos nas diferentes doses testadas. Diferentes extratos destas plantas estão sendo testados em outros modelos, pelo mesmo grupo de trabalho, a fim de aprofundar os conhecimentos acerca do perfil farmacológico destas espécies. Resumo em inglês This work aimed to study the pre-clinical pharmacology and phytochemistry of three plant extracts, obtained from two of the 42 plants with potential analgesic and / or anti-inflammatory, indicated by the residents of the National Park of Jaú, AM. The hydroalcoholic extracts were subjected to phytochemical characterization by thin-layer chromatography (TLC). Tests for pre-clinical pharmacology employed were: initial screening, rota rod, motor activity, hot plate, tail fli (mais) ck and abdominal contortions at doses of 300 and 500 mg / kg. The three extracts were obtained from the bark of cumandá: Campsiandra comosa Benth., Fabaceae (EHCC) and leaves (EHSF) and bark (EHSC) of sucuuba: Himatanthus sucuuba (Spruce ex Müll. Arg.) Woodson, Apocynaceae. The phytochemical analysis revealed the presence of flavonoids, tannins, triterpenes and iridoids in different extracts, while the alkaloids and coumarins were not detected. Research has shown pharmacological activity for EHSF and EHCC extracts, only in the mild analgesic test for abdominal contortions, while no change was observed in the rota rod; and in general, there was decrease in motor activity in all extracts at different doses tested. Different extracts of these plants are being tested in other models by the same working group, in order to deepen the knowledge about the pharmacological profile of these species.

Scientific Electronic Library Online (Portuguese)

5

Quantidade de água transpirada pelo cafeeiro cultivado ao sol

Franco, Coaraci M.; Inforzato, Romeu
1950-01-01

Resumo em inglês In determinations made with a porometer it was verified that the stomatal opening of coffee leaves increases in size immediately after the leaves are detached from the plant (fig. 1). This fact indicates that the method of rapid weighings of detached leaves is not suitable for studies on the transpiration of the coffee plant. The transpiration of coffee plants has been determined by the weighing potted plant method. Pots with a capacity for 51 liters were used. They were (mais) made of galvanized iron plate and had no drainage hole. When the moisture content of the soil approached the wilting point water was added to bring all the soil mass to fiel capacity. In order to avoid oxygen depletion the pots were not sealed. To decrease the direct evaporation at the soil surface a two-centimeter layer of rice hulls was used as mulch, and a celotex cover was placed on top of the pot. Three similar pots with the same type of protection, but without plants were used to measure the direct evaporation from the soil surface. The weight losses of these pots were subtracted from the weight losses of the pots with plants. Two to throe-year old plants of Coffea arabica var. bourbon were used. Three plants were employed each month and after this time their leaves were picked off, and the total leaf area was determined. The tests were carried out for a whole year. The transpiration rates were calculated in g/dm²/day. The total leaf area of an adult coffee plant was found to be 3,146 dm² (average of seven trees). Based on this average and on the transpiration rate of the experimental plants it was possible to calculate approximately the amount of water that an adult coffee plant would transpire under the same conditions. Since the plants submitted to the experiment did not suffer water shortage at any time, the present results show the approximate amount of water lost by the coffee plant under optimal soil-water conditions. The data are presented in table 1. The figure 1 shows the monthly amount of water lost by transpiration in a coffee* plantation compared with the monthly rainfall during a year. The environmental factors that influence plant transpiration vary much less between the same months of different years than between the different months of the same year. Hence the results obtained should not be far from the average; that would be obtained if the transpiration had been measured during a number of years. Comparing the water lost by transpiration of coffee trees with the average rainfall in'Campinas, State of São Paulo, Brazil, it is seen that from October to March rainfall exceeds water consumption. In April, June, and September the excess is small, and in May, July, and August the amount of water transpired exceeds the average rainfall (fig. 2). Since the rainfall distribution is variable, this figure may be different in a given year. The highest daily rate of transpiration encountered was 17.6 mg/dm²/m (over twelve; hours). Previous results obtained by the writers showed 18.2 mg/dm²/m to be the rate of transpiration in a very sunny and hot day. Nutman working in Africa (2) found a maximum daily rate of 20.67/dm²/m (over nine hours). These data are comparable and must represent approximately the maximum rate of transpiration of the coffee plant. The average daily transpiration encountered was 6.20 g/dm²/day and the total amount of water transpired by a coffee tree in one year was found to be 7,273 liters.

Scientific Electronic Library Online (Portuguese)