Development of a pattern recognition methodology with thermography and implementation in an experimental study of a boiler for a WHRS-ORC

Waste heat dissipated in the exhaust system in a combustion engine represents a major source of energy to be recovered and converted into useful work. A waste heat recovery system (WHRS) based on an Organic Rankine Cycle (ORC) is a promising approach, and it gained interest in the last few years in an automotive industry interested in reducing fuel consumption and exhaust emissions. Understanding the thermodynamic response of the boiler employed in an ORC plays an important role in steam cycle performance prediction and control system design. The aim of this study is, therefore, to present a methodology to study these devices by means of pattern recognition with infrared thermography. In addition, the experimental test bench and its operating conditions are described. The methodology proposed identifies the wall coordinates, traces the paths, and tracks the wall temperature along them in a way that can be exported for subsequent post-processing and analysis. As for the results, through the wall temperature paths on both sides (exhaust gas and working fluid), it was possible to quantitatively estimate the temperature evolution along the boiler and, in particular, the beginning and end of evaporation

Analysis of the local growth and density evolution of soot deposits generated under hydrocarbon condensation: 3D simulation and detailed experimental validation

The utilization of the Exhaust Gas Recirculation (EGR) system during atypical engine operating conditions in order to meet future type-approval criteria exposes the internal surfaces of the devices to exhaust gas with elevated concentrations of particulate matter and greater amounts of hydrocarbon species, leading to the formation of dense and wet sludge deposits. To broaden the understanding of this phenomenon and contribute to the development of advanced EGR devices, this study presents an extended Computational Fluid Dynamics (CFD) model that, in addition to simulating the growth of fouling deposits caused by the accumulation of soot particles, also takes into account the condensation of hydrocarbons. Two scenarios with varying hydrocarbon concentrations in the exhaust flow are analysed, and the evolution of the deposit's thickness and density is determined. A sequential validation process is carried out by comparing the numerical results to actual deposit profiles at different stages of the fouling process. Additionally, hyperspectral images of the fouling layer have been acquired and analysed to validate the regions where hydrocarbon condensation is predicted to play a crucial role, enabling the verification of the hydrocarbon condensation phenomenon predicted by the numerical model. The results obtained under the studied conditions indicate that, on average, 77.4% of the analysed area exhibits a low level of relative error, demonstrating that the proposed model and the methodology used serve as a valuable tool for examining the propensity for deposit formation in devices subjected to fouling exacerbated by hydrocarbon condensation.Agencia Estatal de Investigación | Ref. PDC2021-121778-10

Estudio experimental de la influencia de la rugosidad superficial en la ebullición nucleada en flujo de agua subenfriada a baja presión

El estudio del proceso de ebullición en flujo subenfriado de refrigerante es básico para la mejora de los procesos de transferencia de calor. Elemento fundamental de este proceso es la superficie en la cual se produce el intercambio térmico y sobre la cual se genera la ebullición. En este trabajo se estudia la influencia de la rugosidad de la superficie en un intercambio térmico entre un flujo de agua desionizada subenfriado y una pequeña superficie plana de cobre. Para el estudio se han utilizado tres superficies con diferentes acabado superficial obtenidos con diferentes procesos de mecanizado. La revisión bibliográfica representa una primera parte esencial en la investigación, ésta ha seguido dos caminos paralelos. Uno ligado a la adquisición de conocimientos relacionados con el proceso de ebullición y los parámetros de influencia y el otro encaminado a desarrollar un equipo experimental que permita el estudio de las variables del proceso que se plantean como objetivo. Para poder llevar a cabo el estudio del proceso de ebullición fue necesario diseñar, construir e instrumentar una instalación experimental que permita la recirculación de refrigerante subenfriado y la formación de flujo bifásico líquido-vapor. Con la instalación creada se pueden modificar las condiciones de flujo refrigerante así como la superficie calentadora. En base a los objetivos planteados se han diseñado experimentos que permiten la evaluación de la rugosidad de la superficie, el envejecimiento de la misma y las condiciones del flujo, velocidad, presión y temperatura. Como herramienta de adquisición se emplea un sistema de grabación de alta velocidad de imagen, con equipo de iluminación propio. Ha sido necesario implementar una herramienta de procesado de imagen con el apoyo de un software de reconocimiento óptico. Este equipo permite el análisis y medición de los parámetros básicos asociados a la dinámica de burbujas, principalmente se ha utilizado para medir los diámetros de burbuja, la frecuencia de nucleación y para la identificación de los sitios de nucleación. Con un equipo de interferometría óptico se han caracterizado las superficies de ebullición, realizando el análisis de las muestras antes y después de realizar los experimentos, evaluando las alteraciones producidas. Los experimentos diseñados se han aplicado a tres superficies de distintas rugosidades con la finalidad de analizar y estudiar los efectos que produce sobre la trasmisión de calor en una superficie el acabado superficial de la misma. Para el estudio se han combinado los resultados procedentes de la instrumentación asociada a la instalación experimental con los datos obtenidos del análisis de imagen. Obteniendo resultados que permiten evaluar las alteraciones producidas en los parámetros asociados a la dinámica de burbujas ya comentados. Para finalizar, han sido declarados factores de ajuste el función de la rugosidad, para el diámetro de burbuja y los sitios de nucleación según correlaciones de la bibliografía

On the width and mean value of bubble size distributions under subcooled flow boiling

In this work, a new comprehensive dataset about bubble sizes in flow boiling of water is presented. The experimental setup basically consists of a lower copper heated plate embedded in a horizontal rectangular channel flow. Several experimental conditions, ranging bulk velocities: 0.1–0.9 [m·s−1]; mass fluxes: 96.9–871.8 [kg·m−2·s−1]; subcooling degrees: 16–36 [°C]; heat fluxes: 200–650 [kW·m−2] and pressures: 110–190 [kPa] were set for three cooper plates of different roughness, with Sa: 0.45, 1.23 and 7.43 [µm], respectively. Based on the current samples, the probability function for the normalized bubble diameter has been described by a lognormal pdf for any plate and experimental condition and a dimensionless correlation for the standard deviation of the bubble size distribution is presented. In order to completely describe the diameter distribution for bubbles in subcooled boiling systems, an improved correlation for the mean bubble diameter value is also presented here, after a deep review of previously published datasets. Further work is required to accommodate different channel configurations and surface morphologies.Agencia Estatal de Investigación | Ref. RTC2019-006955-

Experimental study of soot particle fouling on ribbed plates : applicability of the critical local wall shear stress criterion

This article examines the notion of critical wall shear stress as the key control parameter of the local fouling removal process. In this study, an experimental setup was developed for measuring fouling on enhanced surfaces. Specifically, the experimental configuration consists of a forced convection plate heat exchanger containing a one-pass rectangular channel with two ribbed plates arranged in a symmetrically staggered manner. The exhaust gases flow by the rib-roughened sides of the plates, and the flat sides can be cooled with water from the independent external coolant circuit. As a result of soot particle deposition from exhaust gases, a layer of fouling is deposited over the ribs. After asymptotic conditions were reached during the tests, detailed fouling thickness measurements were conducted. The dimensionless particle relaxation time during these tests was determined to be in the range of 0.3–10. The measurements were then complemented with a numerical analysis. In particular, the local wall shear stress was calculated using a commercial computational fluid dynamics (CFDs) software package. The fouling thickness profiles deposited over the ribs and the local critical shear stress values were compared and discussed for two different geometries. The results obtained clearly support the idea that critical wall shear stress is an appropriate criterion for facilitating the understanding of the local behaviour of fouling deposits

On the effect of surface roughness and material on the subcooled flow boiling of water : experimental study and global correlation

In this paper, a new correlation based on experimental results for subcooled flow boiling of water at low pressure is proposed, preceded by a brief review on how the solid–fluid interaction has been dealt with in past correlations. The experimental sample comprises seven heating surfaces of different material (copper, aluminium and stainless steel) and roughness. The experimental facility is presented in detail and the surface morphology of each test specimen is analysed by means of an optical interferometer. The correlation is based on the assumption that the effect of material and roughness can be captured by means of modifiers of a general expression. The surfaces chosen in this work were selected to capture a broad range of industrial applications, and, though the correlation found fits well in the range of commercial and relatively high values of Ra (up to 7 μm in the case of copper), further study is needed for larger values, as a discontinuity in the effect was observed, which has been previously determined by some authors. Thus, the proposed global correlation permits the calculation of the boiling heat flux taking into account, in addition to the more classical parameters such as pressure and bulk temperature, the effect of both the roughness and material of the wall heater, allowing its general use in low pressure applications such as those commonly found in the automotive industry.BorgWarner Emissions System

Turbomáquinas hidraúlicas

Este libro explica los fundamentos de las Turbomáquinas Hidráulicas empleando imágenes, esquemas y fotografías de elementos y dispositivos reales, alejándose de las simplificaciones excesivas e idealizaciones, por lo que la obra es de interés para cualquier profesional que quiera analizar con rigor el comportamiento de estos dispositivos, y con extensión suficiente como para poder profundizar en el conocimiento de componentes singulares. Por otra parte, se pretende que este libro sirva como referencia a las materias relacionadas con las Turbomáquinas Hidráulicas, que se imparten en titulaciones técnicas como Ingeniería de Minas y Energía, Ingeniería Industrial o Aeroespacial, si bien, los contenidos que en el se recogen son impartidos en todas las titulaciones de carácter tecnológico-industrial. Es necesario tener en cuenta que la literatura previa existente en este campo es escasa, para temas concretos incluso es necesario acudir a información técnica de fabricantes, no es reciente, y además se encuentra muy diseminada. Los autores, profesores desde hace varios años en esta disciplina, consideran importante la recopilación y actualización de estos contenidos en una monografía de referencia unificada