Thermoeconomic analysis: A criterion for the selection of cogeneration systems

The economical viability of three cogeneration schemes as supplying alternatives for a hypothetical industrial process has been studied. A cost appropriation method based on Valero's studies (1986) has been used. This method enables the determination of exergetic flows, the Second Law efficiency of equipment and the monetary costs of the products acquired by the industrial process (steam and electrical energy). The criterion adopted for the selection is the global cost of the supplied products to the industrial process as regarding in Brazilian conditions.

Reduction of dissolved oxygen in water: Hydrazine and its organic substitutes

In industrial processes using aqueous solutions, corrosion of metal surfaces may occur at various locations. Much of the damage to steam generators and boilers is caused by corrosion. Dissolved oxygen in water is one of the most potent corrosion-causing factors, and therefore oxygen should be eliminated from steam-generating systems' feedwater. Chemical reduction, by reagents such as hydrazine or organic compounds, generally is used for the deoxygenation of water. This article reviews the major oxygen scavengers currently available.

Study of a fuel cell cogeneration system applied to a Brazilian tertiary sector

In this paper, a methodology for the study of a molten carbonate fuel cell cogeneration system and applied to a computer center building is developed. This system permits the recovery of waste heat, available between 600°C and 700°C, which can be used to the production of steam, hot and cold water, hot and cold air, depending on the recuperation equipment associated. Initially, some technical information about the most diffusing types of the fuel cell demonstration in the world are presented. In conclusion, the fuel cell cogeneration system may have an excellent opportunity to strengthen the decentralized energy production in the Brazilian tertiary sector.

Mean-field description of collapsing and exploding Bose-Einstein condensates

Numerical simulations based on the time-dependent mean-field Gross-Pitaevskii equation was performed to explain the dynamics of collapsing and exploding Bose-Einstein condensates (BEC) of 85Rb atoms. The atomic interaction was manipulated by an external magnetic field via a Feshbach resonance. On changing the scattering length of atomic interaction from a positive to a large negative value, the condensate collapsed and ejected atoms via explosion.

Thermoeconomic analysis of a cogeneration system of a university campus

In this paper, a thermoeconomic analysis method based on the First and the Second Law of Thermodynamics and applied to analyse the replacement of an equipment of a cogeneration system is presented. The cogeneration system consists of a gas turbine linked to a waste boiler. The electrical demand of the campus is approximately 9 MW but the cogen system generates approximately one third of the university requirement as well as 1.764 kg/s of saturated steam (at 0.861 MPa), approximately, from a single fuel source. The energy-economic study showed that the best system, based on pay-back period and based on the maximum savings (in 10 years), was the system that used the gas turbine M1T-06 of Kawasaki Heavy Industries and the system that used the gas turbine CCS7 of Hitachi Zosen, respectively. The exergy-economic study showed that the best system, which has the lowest EMC, was the system that used the gas turbine ASE50 of Allied Signal. © 2002 Elsevier Science Ltd. All rights reserved.

Dynamics of a collapsing and exploding Bose-Einstein condensed vortex state

The dynamics of small repulsive Bose-Einstein condensed vortex states of 85Rb atoms in a cylindrical traps with low angular momentum was studied. The time-dependent mean-field Gross-Pitaevskii equation was used for the study. The condensates collapsed and atoms ejected via explosion and a remnant condensate with a smaller number of atoms emerges that survived for a long time.

Fatores que afetam a oviposição de Bemisia tabaci (Genn.) biótipo B (Hemiptera: Aleyrodidae) em tomateiro

The aim of the present work was to determine the oviposition preference of the silverleaf whitefly on tomato (Lycopersicon esculentum). Preferred plant age and leaflet position on the plant were studied and the number of adults per plant necessary for selecting hosts was determined. Bruna VFN hybrid plants at different ages (30-, 45- and 60-days old) were offered to adult whiteflies in free choice test and 30-day old plants in no-choice test. Leaves were collected from upper and lower part of the plant; the leaflets were divided into three categories: basis (those near the steam of plant), middle and apex (terminal leaflet). The 30-day old plants were more preferred for oviposition in free choice test. In the upper part of the plant, whitefly adults preferred to oviposit on the leaflets at the apex and the middle of the leaves. However, in the lower part of the plant, the basal leaflets were preferred in relation to middle and apex. The densities of 100 or 150 adults per tomato plant were considered adequate for genotypes screening, using no-choice test.

Efeitos do fósforo do solo no desenvolvimento inicial de Genipa americana L.

A greenhouse experiment was carried out to evaluate the effects of soil phosphorus in the development of plants of Genipa americana L. Five doses of P (0, 50, 100, 200, and 400 mg dm -3) were applied in pots with 10 dm 3 of three Neossolos Quartzarênicos (NQ 1, NQ 2 and NQ 3) and one Latossolo Vermelho (LV), that were used in an experiment with Eucalyptus plants during three months. After this period, the soils were analyzed and a 30 cm height seedling of G. americana was planted in each pot. The experiment design was completely randomized, in 5 × 4 factorial scheme, with five replications. The largest biomass of the stem was obtained with 45 mg dm -3 of P in the soil NQ 1 (9% of clay) and 59 mg dm -3 in the soil NQ 3 (14% of clay). In the LV (40% of clay), the biomass of the stem increased linearly in the band of 3 to 148 mg dm -3 of P. The phosphorus critical level in the soil for 80% of the steam and leaves dry matter production of G. americana at planting phase is 15 mg dm -3, using an anion-exchange resin as extractor.

Faixas de controle de plantas daninhas e seus reflexos no crescimento de plantas de eucalipto

Two field trial were conducted in Eucalyptus grandis W. Hill ex Maiden x Eucalyptus urophylla S.T. Blake crops at Três Lagoas, Mato Grosso do Sul State and Brotas, São Paulo State, Brazil, to evaluate the effects of weed control in strip of different width on the Eucalyptus plant growth. The experiments consisted of two groups treatments: group 1 - with constant width control strips being kept during the first 12 months, i.e., at 0, 25, 50, 100, 125 and 150cm on each side of the Eucalyptus row and, group 2: with increasing width control strips being adopted along the experimental period, i.e., at 25 to 150, 25-50-150, 50 to 150, 50-125-150, 100-125-150, 100 tot 150 and 125 to 150 cm on each side of the Eucalyptus row during the first 12 months. At 49 moths after planting it was verified that the Eucalyptus plants that had grown both in the constant and increasing width control strips, equal to or higher than 100 and 50 cm, respectively, showed higher steam diameter, plant height, volume and annual increment average of wood. These results led to the conclusion that the minimum control strip width should be 100 cm on each side of the Eucalyptus row in order to keep the crop free of weed interference.

Mean-field model of jet formation in a collapsing Bose-Einstein condensate

We perform a systematic numerical study, based on the time-dependent Gross-Pitaevskii equation, of jet formation in collapsing and exploding Bose-Einstein condensates as in the experiment by Donley et al (2001 Nature 412 295). In the actual experiment, via a Feshbach resonance, the scattering length of atomic interaction was suddenly changed from positive to negative on a pre-formed condensate. Consequently, the condensate collapsed and ejected atoms via explosion. On disruption of the collapse by suddenly changing the scattering length to zero, a radial jet of atoms was formed in the experiment. We present a satisfactory account of jet formation under the experimental conditions and also make predictions beyond experimental conditions which can be verified in future experiments.

Caracterização anatômica da folha de Cymbopogon citratus (DC.) Stapf (Poaceae) e perfil químico do óleo essencial

The objective of the work was to accomplish an anatomical and ultrastructural study of mature leaf of Cymbopogon citratus (Poaceae) and analyze the essential oil through Gas Chromatography (GC). For the anatomical study, the material was fixed in FAA, followed bytheethyl dehydration and infiltration of the material in synthetic resin. For the ultrastructural study, the material was fixed and Kamovsky, dehydrated in acetone, dried to the critical point and metallized. For the analysis in GC, the essential oil it was obtained by steam distillation of leaves and analyzed by Gas Chromatography. Through the anatomical study it was observed that the faces of mesophyll are distinctly, the bulliform cells occupy the adaxial surface of the leaf and in the medium region are situated the biggest vascular bundles involved by sclerenchymatous hem with extensions reaching both epidermis. Between the biggest vascular bundles are observed three to five small vascular bundles, linkage only in the abaxial epidermis. Shortly, pointed and unicellular structures, called prickle-hair, had been observed inserted above the veins and micro-hair, that they consist of a long basal cell and an oval distal cell, that are located between the regions of vascular bundles. The chromatogram sample shows that the analyzed essential oil presented three majority components, responsible for 87% of the relative composition of the oil. These components are monoterpenos, justifying the strong smell of the essential oil.

Study of a hybrid solid oxide fuel cell: Energetic analysis and sankey diagram

In this paper a hybrid solid oxide fuel cell (SOFC) system is analyzed. This system applies a combined cycle utilizing gas turbine associated to a SOFC for rational decentralized energy production. Initially the relative concepts about the fuel cell are presented, followed by some chemical and technical informations such as the change of Gibbs free energy in isothermal fuel oxidation (or combustion) directly into electricity. This represents a very high fraction of the lower heating value (LHV) of a hydrocarbon fuel. In the next step a methodology for the study of SOFC associated with a gas turbine system is developed, considering the electricity and steam production for a hospital, as regard to the Brazilian conditions. This methodology is applied to energetic analysis. Natural gas is considered as a fuel. In conclusion, it is shown by a Sankey Diagram that the hybrid SOFC system may be an excellent opportunity to strengthen the decentralized energy production in Brazil. It is necessary to consider that the cogeneration in this version also is a sensible alternative from the technical point of view, demanding special methods of design, equipment selection and mainly of the contractual deals associated to electricity and fuel supply.

A constructive heuristic algorithm to Short Term Transmission Network Expansion Planning

In this paper a method for solving the Short Term Transmission Network Expansion Planning (STTNEP) problem is presented. The STTNEP is a very complex mixed integer nonlinear programming problem that presents a combinatorial explosion in the search space. In this work we present a constructive heuristic algorithm to find a solution of the STTNEP of excellent quality. In each step of the algorithm a sensitivity index is used to add a circuit (transmission line or transformer) to the system. This sensitivity index is obtained solving the STTNEP problem considering as a continuous variable the number of circuits to be added (relaxed problem). The relaxed problem is a large and complex nonlinear programming and was solved through an interior points method that uses a combination of the multiple predictor corrector and multiple centrality corrections methods, both belonging to the family of higher order interior points method (HOIPM). Tests were carried out using a modified Carver system and the results presented show the good performance of both the constructive heuristic algorithm to solve the STTNEP problem and the HOIPM used in each step.

Production of Ti-35Nb alloy by powder metallurgy for aerospace application

Titanium and its alloys provide high strength-to-weight ratios, good fatigue strength and increased corrosion resistance compared with others materials. Its acceptance in aerospace has been limited by costs considerations such as high cost of raw material, high buy-to-fly ratios and expensive machining operations. Significant cost reductions can be obtained by vacuum sintering and powder metallurgy (P/M) techniques by producing near net shapes and consequently minimizing material waste and machining time. The Ti 35Nb alloy exhibit a low modulus of elasticity. Stemming from the unique combination of high strength, low modulus of elasticity and low density, this alloy is intrinsically more resistant to shock and explosion damages than most other engineering materials. Samples were produced by mixing of initial metallic powders followed by uniaxial and cold isostatic pressing with subsequent densification by sintering between 900 and 1600 °C, in vacuum. Sintering behavior was studied by means of dilatometry. Sintered samples were characterized for phase composition, microstructure and microhardness by X-ray diffraction, scanning electron microscopy and Vickers indentation, respectively. Density was measured by Archimedes method. Copyright © 2004 Society of Automotive Engineers, Inc.

Bioatividade de plantas medicinais no controle de Sclerotinia isolado de Stevia rebaudiana (Bert.) Bertoni

The microorganism Sclerotinia was isolated from roots of Stevia rebaudiana (Bert.) Bertoni in plantations in the northwest of Parana and submitted to the cultivation in the presence of extracts and vegetable balsams of Tarragon (Artemisia draconculus), Thyme (Thymus vulgaris), Manjerona (Origanum majorona), Mint citrata (Mintpiperita var. citrata), Purple Basil (Ocimum basilicum L.), Andiroba (Carapa guanensis) and Copaíba (Copaifera reticulata Ducke). The first five oils were extracted by steam drags, after the drying of the vegetable in greenhouse with circulation of air at 45°C. The last two were used in natura. A suspension (100ìl) of fungus previously cultivated, was added to each plate. The results show that after 7 days of incubation the thyme oils 10ìl, purple basil 25ìl, manjerona 25ìl, mint citrata 50ìl, tarragon 50ìl were capable to inhibit the growth of Sclerotinia, while the andiroba oil only reached this result with 200ìl. The copaiba balsam, even in the concentration of 500ìl, was unable to inhibit the growth of the microorganism.