Geraldo Lombardi

Experiments on the local heat transfer characteristics of a circulating fluidized bed

Abstract The role of particle diameter in the heat transfer of a gas–solid suspension to the walls of a circulating fluidized bed was studied for particles of uniform size. This work reports and analyzes new experimental results for the local bed to wall heat transfer coefficient, not including the radiation component, in a long active heat transfer surface length laboratory bed, which extend previous findings and clear up some divergences. The research included determining the effects of extension and location of the heat transfer surface, circulating solids mass flux and average suspension density. An experimental set-up was built, with a 72.5 mm internal diameter riser, 6.0 m high, composed of six double pipe heat exchangers, 0.93 m high, located one above the other. Five narrow sized diameter quartz sand particles − 179, 230, 385, 460 and 545 μm − were tested. Temperature was kept approximately constant at 423 K and the superficial gas velocity at 10.5 m/s. The major influence of suspension density on the wall heat transfer was confirmed, and contrary to other authors, a significant effect of particle size was found, which becomes more relevant for smaller particles and increasing suspension density. It was observed that the extension of the heat transfer surface area did not influence the heat transfer coefficient for lengths greater than 0.93 m.The heat transfer surface location did not show any effect, except for the exchanger at the botton of the riser. A simple correlation was proposed to calculate the heat transfer coefficient as a function of particle diameter and suspension density.

Performance of a tuyère gas distributor

The flow discharge coefficient of tuyere gas distributors with six radial holes was obtained as a function of the tuyere head holes diameter Reynolds number, with the holes to riser flow cross-sectional area ratio as parameter. The fraction of the pressure drop which occurred in the tuyere head holes, a significant parameter for satisfactory operation of a fluidized bed, was also determined. The flow phenomena in the thin-plate standard square-edged orifice meter and in the tuyere discharge holes were studied; the differences in the corresponding discharge coefficient values are discussed in the light of the flow pattern dissimilarities. The possibility of adopting the standard thin-plate square-edged orifice meter or perforated-plate discharge coefficients to calculate the tuyere coefficient was analyzed, as well as the influence of the presence or absence of a solids fluidized bed over the distributor plate.

POTENCIALIDADES DE GENERACIÓN DE ELETRICIDAD A PARTIR DE BIOMASA

An ethanol distillery, included in the project for the Generation of Renewable Energy Integrated to Production of Foods (GERIPA), shows outstanding advantages in comparison with the traditional disti lleries. The biomass constitutes one of the main sources for generation of clean and cheap energy, leaving the category of sub-product, and being a fu ndamental material for the productive process. In this paper the available energy from sugar cane and sorghum, bagasse and straw, as well as biogas, is u sed to produce vapor for the process and electricity, using a traditional boiler (efficiency 88%) and a condensation and extraction turbine (efficiency 70% ). For a production plant of Renewable Energy Integrated to the Production of Fo ods of 125 000 L ethanol/day, the generation of electricity using th e biomass produced by this industry, reaches 6.0 MW of power surplus to the National Electro-energet ic System. It constitutes a pole for economic, social and strategic development,

New particulate solids pneumatic feeding device with mass flowrate control

Abstract A new solids feed valve design was developed, based on the destruction of the repose cone resulting from the deposition of solid particles over a horizontal surface by fluidization of its base, followed by pneumatic transport of the fallen particles. Tests were carried out to determine the mass flowrate of solids of types A, B, C and D, according to Geldarts classification, as a function of the air flowrate.

Ensinar Sigma=p ou Sigma =-p? – Eis a questão!

A experiencia mostra que, na mecânica dos fluidos, a totalidade dos autores consultados, quando apresentam, nas equacoes de forca e quantidade de movimento para fluidos, a tensao s “dita normal”, eles a igualam a -p , ou seja, a pressao do fluido com sinal negativo. A Mecânica dos Fluidos usa definicoes basicas ja consagradas na literatura, que estabelecem as propriedades s e p como grandezas escalares ao se analisar seu efeito sobre uma superficie. Assumir os sinais na igualdade s = -p equivale a atribuir a p uma propriedade vetorial de oposicao a s , fato que, de forma desnecessaria, contradiz a identidade de escalar do modulo de uma forca, a Segunda e Terceira Leis de Newton e outras equacoes delas decorrentes. Neste trabalho demonstra-se que s = p (isto e, com sinal positivo) atraves de definicoes univocas da mecânica dos fluidos. Este e um aspecto importante para os formadores de profissionais.

The performance of a fluidized particulate feeding system with multiple discharge sections

A particulate feeding system based on air flluidization principles was developed at the Thermal and Fluids Engineering Group at EESC-USP. The system is basically formed of a cylindrical chamber comprising two levels of fluid bed distributor plates. The performance of the system was addressed. Repeatability experiments were performed in order to check out for the possibility of solids feeding control through a sphere valve which controls the air feed rate. Silica sand particles of three different size were used, with mean diameters of 152, 287 and 484 µm. Experiments showed that the total particulate discharge depends on the primary air feeding rate, the distance between the exit of the feeding hopper and the primary air distributor plate, and the particulate diameter, but independs on the secondary air feeding rate. The system was observed to be of difficult control and showed poor repeatability. However, the system was found to be an excellent device for distributing the flow of solids throughout several discharge sections. For the operational conditions considered and air volumetric flowrates above 3×10-3 m3/s the deviation on the particulate mass flowrate through a given discharge section related to the average value through the four sections of the injector was always below 5 %.