Ash Particle Erosion on Steam Boiler Convective Section

In this study, equations for the calculation of erosion wear caused by ash particles on convective heat exchanger tubes of steam boilers are presented. Anew, three-dimensional test arrangement was used in the testing of the erosion wear of convective heat exchanger tubes of steam boilers. When using the sleeve-method, three different tube materials and three tube constructions could be tested. New results were obtained from the analyses. The main mechanisms of erosionwear phenomena and erosion wear as a function of collision conditions and material properties have been studied. Properties of fossil fuels have also been presented. When burning solid fuels, such as pulverized coal and peat in steam boilers, most of the ash is entrained by the flue gas in the furnace. In bubbling andcirculating fluidized bed boilers, particle concentration in the flue gas is high because of bed material entrained in the flue gas. Hard particles, such as sharp edged quartz crystals, cause erosion wear when colliding on convective heat exchanger tubes and on the rear wall of the steam boiler. The most important ways to reduce erosion wear in steam boilers is to keep the velocity of the flue gas moderate and prevent channelling of the ash flow in a certain part of the cross section of the flue gas channel, especially near the back wall. One can do this by constructing the boiler with the following components. Screen plates can beused to make the velocity and ash flow distributions more even at the cross-section of the channel. Shield plates and plate type constructions in superheaters can also be used. Erosion testing was conducted with three types of tube constructions: a one tube row, an inline tube bank with six tube rows, and a staggered tube bank with six tube rows. Three flow velocities and two particle concentrations were used in the tests, which were carried out at room temperature. Three particle materials were used: quartz, coal ash and peat ash particles. Mass loss, diameter loss and wall thickness loss measurements of the test sleeves were taken. Erosion wear as a function of flow conditions, tube material and tube construction was analyzed by single-variable linear regression analysis. In developing the erosion wear calculation equations, multi-variable linear regression analysis was used. In the staggered tube bank, erosion wear had a maximum value in a tube row 2 and a local maximum in row 5. In rows 3, 4 and 6, the erosion rate was low. On the other hand, in the in-line tube bank the minimum erosion rate occurred in tube row 2 and in further rows the erosion had an increasing value, so that in a six row tube bank, the maximum value occurred in row 6.

Collaborative explicit plasticity framework: a conceptual scheme for the generation of plastic and group-aware user interfaces

The advent of new advances in mobile computing has changed the manner we do our daily work, even enabling us to perform collaborative activities. However, current groupware approaches do not offer an integrating and efficient solution that jointly tackles the flexibility and heterogeneity inherent to mobility as well as the awareness aspects intrinsic to collaborative environments. Issues related to the diversity of contexts of use are collected under the term plasticity. A great amount of tools have emerged offering a solution to some of these issues, although always focused on individual scenarios. We are working on reusing and specializing some already existing plasticity tools to the groupware design. The aim is to offer the benefits from plasticity and awareness jointly, trying to reach a real collaboration and a deeper understanding of multi-environment groupware scenarios. In particular, this paper presents a conceptual framework aimed at being a reference for the generation of plastic User Interfaces for collaborative environments in a systematic and comprehensive way. Starting from a previous conceptual framework for individual environments, inspired on the model-based approach, we introduce specific components and considerations related to groupware.

Characteristics of 2D convective structures in Catalonia (NE Spain): an analysis using radar data and GIS

Flood simulation studies use spatial-temporal rainfall data input into distributed hydrological models. A correct description of rainfall in space and in time contributes to improvements on hydrological modelling and design. This work is focused on the analysis of 2-D convective structures (rain cells), whose contribution is especially significant in most flood events. The objective of this paper is to provide statistical descriptors and distribution functions for convective structure characteristics of precipitation systems producing floods in Catalonia (NE Spain). To achieve this purpose heavy rainfall events recorded between 1996 and 2000 have been analysed. By means of weather radar, and applying 2-D radar algorithms a distinction between convective and stratiform precipitation is made. These data are introduced and analyzed with a GIS. In a first step different groups of connected pixels with convective precipitation are identified. Only convective structures with an area greater than 32 km2 are selected. Then, geometric characteristics (area, perimeter, orientation and dimensions of the ellipse), and rainfall statistics (maximum, mean, minimum, range, standard deviation, and sum) of these structures are obtained and stored in a database. Finally, descriptive statistics for selected characteristics are calculated and statistical distributions are fitted to the observed frequency distributions. Statistical analyses reveal that the Generalized Pareto distribution for the area and the Generalized Extreme Value distribution for the perimeter, dimensions, orientation and mean areal precipitation are the statistical distributions that best fit the observed ones of these parameters. The statistical descriptors and the probability distribution functions obtained are of direct use as an input in spatial rainfall generators.

Robust watermarking scheme based on the JPEG2000 standard

Peer reviewed

Secure logarithmic audio watermarking scheme based on the human auditory system

Peer-reviewed

Test automation scheme for LTE core network element

Modern sophisticated telecommunication devices require even more and more comprehensive testing to ensure quality. The test case amount to ensure well enough coverage of testing has increased rapidly and this increased demand cannot be fulfilled anymore only by using manual testing. Also new agile development models require execution of all test cases with every iteration. This has lead manufactures to use test automation more than ever to achieve adequate testing coverage and quality. This thesis is separated into three parts. Evolution of cellular networks is presented at the beginning of the first part. Also software testing, test automation and the influence of development model for testing are examined in the first part. The second part describes a process which was used to implement test automation scheme for functional testing of LTE core network MME element. In implementation of the test automation scheme agile development models and Robot Framework test automation tool were used. In the third part two alternative models are presented for integrating this test automation scheme as part of a continuous integration process. As a result, the test automation scheme for functional testing was implemented. Almost all new functional level testing test cases can now be automated with this scheme. In addition, two models for integrating this scheme to be part of a wider continuous integration pipe were introduced. Also shift from usage of a traditional waterfall model to a new agile development based model in testing stated to be successful.

Modeling and simulation of forced-air cooling of strawberries using variable convective coefficient

In the forced-air cooling process of fruits occurs, besides the convective heat transfer, the mass transfer by evaporation. The energy need in the evaporation is taken from fruit that has its temperature lowered. In this study it has been proposed the use of empirical correlations for calculating the convective heat transfer coefficient as a function of surface temperature of the strawberry during the cooling process. The aim of this variation of the convective coefficient is to compensate the effect of evaporation in the heat transfer process. Linear and exponential correlations are tested, both with two adjustable parameters. The simulations are performed using experimental conditions reported in the literature for the cooling of strawberries. The results confirm the suitability of the proposed methodology.

Effective diffusivity and convective mass transfer coefficient during the drying of bananas

In this article, a methodology is used for the simultaneous determination of the effective diffusivity and the convective mass transfer coefficient in porous solids, which can be considered as an infinite cylinder during drying. Two models are used for optimization and drying simulation: model 1 (constant volume and diffusivity, with equilibrium boundary condition), and model 2 (constant volume and diffusivity with convective boundary condition). Optimization algorithms based on the inverse method were coupled to the analytical solutions, and these solutions can be adjusted to experimental data of the drying kinetics. An application of optimization methodology was made to describe the drying kinetics of whole bananas, using experimental data available in the literature. The statistical indicators enable to affirm that the solution of diffusion equation with convective boundary condition generates results superior than those with the equilibrium boundary condition.

Meal-feeding scheme: twenty years of research in Brazil

Naomi Shinomiya Hell was the first researcher to investigate the physiological adaptations to a meal-feeding scheme (MFS) in Brazil. Over a period of 20 years, from 1979 to 1999, Naomi's group determined the physiological and metabolic adaptations induced by this feeding scheme in rats. The group showed the persistence of such adaptations even when MFS is associated with moderate exercise training and the performance to a session of intense physical effort. The metabolic changes induced by the feeding training were discriminated from those caused by the effective fasting period. Naomi made an important contribution to the understanding of the MFS but a lot still has to be done. One crucial question still remains to be satisfactorily answered: what is the ideal control for the MFS?

Marolo (Annona crassiflora Mart.): a study of value chain and processing

This article aims to discuss the needs and problems of marolo value chain, as well as to evaluate the rehydration process of this fruit as a possibility of using it as a by-product during the interharvest growth periods. The study of the value chain included interviews with producers, handlers, and fruit and by-product sellers. In order to evaluate the rehydration process of this fruit, marolo was dehydrated using a conventional procedure and freeze-drying. The experiments were conducted in a completely randomized design and a triple factorial scheme (2 × 2 × 6). ANOVA was performed, followed by the Tukey's test (p < 0.05). Regression models were generated and adjusted for the time factor. The precariousness of the value chain of marolo was observed. The best procedure for marolo dehydration should be determined according to the intended use of the dehydrated product since the water-absorption capacity of the flour is higher and convective hot-air-drying is more effective in retaining soluble solids and reducing damage to the fruit. These results aim at contributing to the marolo value chain and to the preservation of native trees in the Brazilian savanna biome and can be used to analyze other underutilized crops.

An artificial neural network model for prediction of quality characteristics of apples during convective dehydration

In this study, the effects of hot-air drying conditions on color, water holding capacity, and total phenolic content of dried apple were investigated using artificial neural network as an intelligent modeling system. After that, a genetic algorithm was used to optimize the drying conditions. Apples were dried at different temperatures (40, 60, and 80 °C) and at three air flow-rates (0.5, 1, and 1.5 m/s). Applying the leave-one-out cross validation methodology, simulated and experimental data were in good agreement presenting an error < 2.4 %. Quality index optimal values were found at 62.9 °C and 1.0 m/s using genetic algorithm.