Sergio Leal Braga

Obstruction of pipelines due to paraffin deposition during the flow of crude oils

Heavy hydrocarbons tend to precipitate off waxy crude oils as they flow through tubes. The precipitated paraffin deposits on the tube inner wall, narrowing the flow passage and eventually reducing drastically the rate of flow. A simple theory that gives the thickness of deposited layer as a function of axial position and time is presented. Experiments were carried out in order to validate the theoretical model. Results are presented in the form of time evolution of axial distributions of pressure, temperature and layer thickness. It is shown that the simple model is capable of predicting the correct order of magnitude of important engineering quantities such as pressure and flow rates as functions of time.

Performance and Gaseous Emissions Characteristics of a Natural Gas/Diesel Dual Fuel Turbocharged and Aftercooled Engine

The aim of this paper is to investigate the performance and emissions characteristics of a turbocharged and aftercooled diesel engine operated with natural gas as primary fuel, and diesel fuel as ignition source. In such dual fuel operation, much of the energy released comes from the combustion of the gaseous fuel, while only a small amount of diesel fuel provides ignition through timed cylinder injection. The effects of diesel-natural gas substitution ratios, engine speed, and load on the equivalent brake specific fuel consumption and gaseous emissions of hydrocarbons, carbon monoxide and nitrogen oxides are examined for natural gas-diesel fuel operation and, afterward, compared with the original diesel operation. The results show that, over a wide range of operating conditions (engine speed, load), the dual fuel engine clearly shows the benefits of reduced NOX emissions. However, under low loads, the results indicate high CO and HC emissions and a higher BSFC when compared to those of the corresponding diesel engine. Keywords : diesel, dual fuel engine, emissions, natural gas

A visual study of R-404A/oil flow through adiabatic capillary tubes

The present study explores the potential of using visualization techniques to investigate refrigerant/oil flow through adiabatic capillary tubes. A literature review shows that these techniques have been used before for capillary tube investigations, but none of these studies focused on the refrigerant/oil phenomena. Therefore, the main objective is to investigate the flow of a refrigerant/oil mixture through a glass capillary tube, with special emphasis on the behavior of the vaporization point. The test fluids are R-404A (a near azeotropic blend) and a polyolester-type oil. Experimental data cover oil concentrations ranging from 5.6 to 6.9% (by mass), degrees of subcooling ranging from 6.2 to 21.5 °C (11.2 F to 38.7 F), and a condensing pressure of 1825 kPa (250 psig). The results show trends of mass flow rate, and give some useful insights about the location of the vaporization point for various oil concentrations and operating conditions.

Nucleate Boiling in Large Arrays of Impinging Water Sprays

The nucleate boiling of subcooled water, under 100 cm2 square arrays of impinging sprays, was experimentally investigated. Three types of commercially available full cone pressure nozzles, of distinct flow capacities, allowed for runs where the average impinging coolant mass flux spanned the 0.3–7.2 kg/m2-s range. Array geometry was varied adjusting nozzle-to-nozzle and nozzle-to-impingement surface distances. Experimental construction allowed for good drainage of spent coolant and unrestricted air entrainment to spray cones. The average heat flux through the heated, upward-facing, copper impingement surface was found to be equal to the sum of single-phase and nucleate boiling heat flux components. The phase-change component was experimentally observed to depend upon wall excess temperature only. The proposed heat transfer correlation reproduces original experimental data with a mean absolute error of 10.6%. Non-critical-heat-flux (non-CHF) cooling capacity and efficiencies of up to, respectively, 2000 kJ/kg and 83% were observed.

Comparing Single Phase Heat Transfer to Arrays of Impinging Jets and Sprays

The single phase heat transfer characteristics of square arrays of impinging water sprays were investigated experimentally. A total of 230 experimental points, covering a wide range of flow rates and different spray array geometries were obtained with three different models of commercially available full cone spray nozzles. Results were compared to an available correlation for the area average heat transfer coefficient of impinging arrays of submerged jets. It is shown that spray impingement techniques may provide the same heat transfer coefficient obtained with impinging jets under much smaller coolant flow rates per unit heated area. Coolant pumping power required by both techniques was also compared. It is shown that spray arrays require, for the establishment of a given area average heat transfer coefficient, more pumping power than submerged jet arrays.Copyright

Qualification of a 3D structured light sensor for a reverse engineering application

This paper deals with the qualification of a 3D structured light scanning system for an application of reverse engineering of a mechanical part. As this white light scanner is an electro-optical device and based on the principle of optical triangulation, the measurement accuracy is affected by the measured part geometry and its position within the scanning window. The effects of the scan depth and the projected angle, characterizing the surface normal of the measured surface to the scanning point of view, on the measurement of accuracy are not considered in the standard calibration process of manufacturers and have been identified by experiments in the present work. The digitization errors are analyzed and characterized thanks to a measurement protocol based on quality indicators. Theses quality indicators are evaluated thanks to simple calibrated artifacts. The aim of this work is to redefine the ideal relative distance and relative angle for minimizing the digitizing errors in relation to those stated by the manufacturer for a reverse engineering application.

Evaluation of Different Alternatives of Power Augmentation for an Existing Combined Cycle Power Plant in Brazil

Not only in simple cycle power plants, but also in combined cycle power plants based on gas turbines, the power output is considerably reduced with the increase of the ambient temperature. Many technologies for power augmentation of gas turbines have been proposed along the last decades, and several systems have already been applied in real plants. Power augmentation techniques are concentrated on the philosophy of increasing the mass flow rate going through the gas turbine. The goal of this paper is to review the state-of-the-art of the different technologies of power augmentation available today for gas turbines, as well as to evaluate and to select the best alternative of power augmentation for an existing combined cycle power plant in Brazil. The calculations are carried out using an in-house computer program, called the Power Augmentation Technologies (PAT) model, developed for thermal performance modeling and financial analysis. In order to validate the computational model developed, the authors carried out comparisons between the results obtained with this model and data obtained from literature. For the specific combined cycle power plant analyzed in this work, and considering the internal rate of return and the pay-back period as the main investment economic indicators determining the implementation of a project developed for increasing the plant power output, the results show that the power augmentation systems based on evaporative coolers are the most suitable for this plant.Copyright

Energy Efficiency of Series Hybrid Electric Vehicles

[pt] Nesta dissertacao apresenta-se a avaliacao da eficiencia energetica do Veiculo Eletrico Hibrido em Serie mediante o desenvolvimento teorico de dois prototipos de sistemas de propulsao eletrica e o estudo experimental do consumo de combustivel do veiculo original. A analise experimental foi feita mediante o desenvolvimento de uma bancada de teste, composta principalmente por um dinamometro de chassis, um piloto automatico e um medidor de vazao de combustivel, acompanhado de toda a eletronica que fez possivel a aquisicao de dados em cada teste. Neste estudo desenvolvem- se dois modelos teoricos de arquitetura para o sistema de propulsao do VEH, o primeiro composto de quatro motores, cada um embutido nas rodas do veiculo, e o segundo composto por dois motores, cada um embutido nas rodas do eixo traseiro do veiculo. Existem diversos procedimentos para poder embutir um motor na roda do veiculo, o que se deve ter em conta e o peso, a potencia e a eficiencia na transmissao de potencia. No desenvolvimento teorico do sistema de propulsao em cada roda, faz-se necessario o uso do redutor cicloidal, o qual permite uma reducao de 3:1 ate 119:1 em um so estagio com uma eficiencia de transmissao de 93 por cento, conjuntamente com um motor de corrente continua sem escovas, o qual tem uma alta densidade de potencia. Os resultados da avaliacao do sistema de propulsao eletrica dos prototipos mostram que o modelo de quatro motores nas rodas e mais eficiente em comparacao com o modelo de dois motores embutidos nas rodas. Isto se deve ao fato do segundo modelo ser mais pesado, ja que precisa uma maior quantidade de baterias e alem disso de motores mais robustos. Na avaliacao do consumo energetico do VEH em comparacao com o modelo original a gasolina, obtiveram-se resultados interessantes referentes a economia na utilizacao do recurso energetico. O VEH teve um comportamento melhor em ciclos urbanos que em ciclos de estrada e a economia do recurso energetico alcanca 57,6 por cento quando se testa com ciclos urbanos e 11,4 por cento em ciclos de estrada.%%%%[en] This dissertation presents the evaluation of the energy efficiency of a series hybrid electric vehicle through the theoretical development of two electric propulsion systems and an experimental study of fuel consumption of the original vehicle. The experimental analysis was done by a test setting, consisting mainly by a chassis dynamometer, an autopilot system and a fuel flowmeter, all connected to the data acquisition system. In this study it was developed two theoretical models of propulsion systems for HEV. The first one consists of four in-wheel motors and the second one consists of two in-wheel motors on the rear axle. There are various methods for embedding a motor in the wheel. It is necessary to consider the weight, power and transmission efficiency. In the theoretical model it was considered a cycloidal reducer, which allows a reduction of 3:1 to 119:1 in one stage with an efficiency of 93 percent, together with a brushless DC motor, which has a high power density. The…

A Numerical Parametric Study of the Growth of Ice Formation Around a Vertical Tube, During the Full Charging Process of an Indirect, Area-Constrained, Ice-on-Pipe Storage Tank

A parametric numerical investigation regarding the ice layer growth outside a vertical tube is investigated. It encompasses heat transfer and removal of energy, applicable to indirect, area-constrained, ice-on-pipe storage tanks. The study is carried out in a vertical annulus, with the inner vertical wall representing one of the tubes packed into a typical storage tank. Further, the outer vertical wall determines the maximum border for the ice layer growth under the conditions established in the present study, corresponding to a full charging process in such devices. Our task is to provide helpful qualitative results for the investigation of ice storage tank heat transfer performance, considering changes in the following parameters: aspect ratio, radius ratio, Grashof and Stefan numbers. For the mathematical model adopted to simulate transient natural convection of water with phase-change (solidification), it was utilized a model based on the finite volume method to solve the set of coupled conservation equations of mass, momentum and energy.Copyright