Residence time distribution studies in continuous thermal processing of liquid foods: a review

This paper presents a review on residence time distribution (RTD) studies in continuous thermal processing of liquid foods. The theoretical basis of the Danckwerts analysis is summarized, as well as the most important flow models, with special emphasis on tubular systems. Methods for experimental determination, modelling and estimation of RTD are critically described. While main design objectives in continuous thermal processes may be guaranteed by a proper minimum residence or holding time, process optimization requires the knowledge of the residence time distribution. Both concepts are reviewed and discussed. A significant scatter was noticed among published results and the need ,for a systematic work is clear It was concluded that future research should focus on studies at pasteurizationlsterilization temperatures, as well as on studies conducted with real food products or model food systems with FIO~INewtoniun flow bchaviour: Furthermore. information relating RTD to processing conditions would be a useful tool for process optimization

Penyisihan sosial terhadap orang kurang upaya

Orang Kurang Upaya (OKU) merupakan antara kumpulan marginal dan sering terpinggir dalam masyarakat khususnya di Malaysia. Walaupun pelbagai usaha dilakukan oleh kerajaan untuk merangkum OKU dalam masyarakat, sering kali kumpulan ini tercicir daripada arus pembangunan negara. Antara punca utama yang menyebabkan OKU kurang mendapat perhatian adalah kerana dua halangan utama iaitu faktor persekitaran yang tidak mesra OKU dan sikap masyarakat yang kurang cakna terhadap hak dan keperluan OKU. Bab ini mengupas senario OKU di Malaysia melalui aspek dasar dan perundangan, isu dan cabaran utama yang sering dihadapi OKU dan cara masyarakat dapat memperkasa OKU secara holistik dan berkesan melalui strategi yang sistematik dan berterusan

Thermal Extraction of Volatiles from Lunar and Asteroid Regolith in Axisymmetric Crank-Nicholson Modeling

A physics-based computer model has been developed to support the development of volatile extraction from regolith of the Moon and asteroids. The model is based upon empirical data sets for extraterrestrial soils and simulants, including thermal conductivity of regolith and mixed composition ice, heat capacity of soil and mixed composition ice, hydrated mineral volatile release patterns, and sublimation of ice. A new thermal conductivity relationship is derived that generalizes cases of regolith with varying temperature, soil porosity, and pore vapor pressure. Ice composition is based upon measurements of icy ejecta from the Lunar CRater Observation and Sensing Satellite (LCROSS) impact and it is shown that thermal conductivity and heat capacity equations for water ice provide adequate accuracy at the present level of development. The heat diffusion equations are integrated with gas diffusion equations using multiple adaptive timesteps. The entire model is placed into a Crank-Nicholson framework where the finite difference formalism was extended to two dimensions in axisymmetry. The one-dimensional version of the model successfully predicts heat transfer that matches lunar and asteroid data sets. The axisymmetric model has been used to study heat dissipation around lunar drills and water extraction in asteroid coring devices.Comment: 50 pages, 23 figure

Non-Newtonian fluid mixing in agitated vessels in the transitional flow regime

This thesis provides an original contribution to knowledge of fluid mixing in agitated vessels. This flow application has a critical importance in the manufacture of a wide range of intermediates and products in Johnson Matthey. The novelty of the research undertaken is twofold. Firstly, it presents quantitative investigations of the agitation of Newtonian and non-Newtonian fluids under transitional flow conditions. Despite the fact that transitional mixing is very common in industry, particularly for formulated products showing non-Newtonian rheology, most studies in the literature focus on fully laminar or fully turbulent mixing. Secondly, with the development of a methodology for 3D Particle Tracking Velocimetry measurements in laboratory scale vessels, this thesis has taken a step towards more accessible flow visualisation capabilities in industry. Numerical simulations have also been carried out to cross-validate the 3D-PTV data and provide additional information that could not be obtained experimentally. Experiments and simulations have been conducted for many combinations of fluid rheology and impeller speed and at two vessel sizes. The hydrodynamics of transitional flows have been shown to depend significantly on the Reynolds number and fluid rheological behaviour. Non-Newtonian fluids showed smaller values of shear rate, Lagrangian acceleration and flow numbers, compared to the Newtonian ones. For Newtonian fluids, the local energy dissipation rate scaled differently depending on the position relative to the impeller. Non-Newtonian fluids did not follow the same scaling. The information obtained in this thesis will help the design, optimisation and scale-up of mixing operations within Johnson Matthey

Upscaling reactive transport in porous media : laboratory visualization and stochastic models

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2007.Includes bibliographical references.Solute transport models are essential tools for understanding and forecasting chemical concentrations in groundwater. Advection-dispersion based models can adequately predict spatial averages of conservative solute concentrations without using explicit maps of pore structures or variations in hydraulic conductivity. However, coupling advection-dispersion based transport models to chemical reaction models is inaccurate because it implicitly assumes complete mixing. Mixing in natural porous media is a slow process that can control the overall rate of chemical reactions, and the lack of mixing causes concentrations to be spatially variable. This thesis develops and experimentally validates a new solute transport modeling framework that approximates the correct amount of chemical reaction and provides concentration probability density functions, which are needed to address laws and regulations based on maximum contaminant levels. To study solute mixing and reaction in porous media, we conducted highly detailed lab-scale experiments by digitally imaging the movement of colored dye tracers and colorimetric chemical reactions through illuminated clear homogeneous and heterogeneous porous media.(cont.) The resulting sequence of solute concentration maps demonstrates the problem of conventional solute transport models and shows that concentrations can be well approximated with Beta distributions. Conservative Beta distributions can be modeled with partial-differential equations for concentration mean and variance. These conservative distributions can then be transformed into joint reactant distributions, which produces product and remaining reactant distributions. This upscaling approach is verified by modeling the product and reactant means, variances, and distributions in heterogeneous media and product means in homogeneous media from our lab-scale experiments. We found that (co)variance production-destruction balances can approximate aqueous species covariance matrixes, which are necessary to form multivariate reactant distributions of complex reactive transport scenarios. Alternatively, these second moments can be used in upscaled reaction expressions derived from a second order Taylor series expansion. Incomplete mixing, parameterized by variance and covariance, causes an upscaled reaction rate to be almost an order of magnitude smaller compared to the conventional reaction rate that implicitly assumes complete mixing.(cont.) Finally, manipulating the flow field to be perpendicular to its original direction would increase the rate of reactive mixing by an order of magnitude. Thus generating a transient flow field would be a practical way to accelerate natural attenuation and bioremediation.by Peter M. Oates.Ph.D

Two Phase Flow, Phase Change and Numerical Modeling

The heat transfer and analysis on laser beam, evaporator coils, shell-and-tube condenser, two phase flow, nanofluids, complex fluids, and on phase change are significant issues in a design of wide range of industrial processes and devices. This book includes 25 advanced and revised contributions, and it covers mainly (1) numerical modeling of heat transfer, (2) two phase flow, (3) nanofluids, and (4) phase change. The first section introduces numerical modeling of heat transfer on particles in binary gas-solid fluidization bed, solidification phenomena, thermal approaches to laser damage, and temperature and velocity distribution. The second section covers density wave instability phenomena, gas and spray-water quenching, spray cooling, wettability effect, liquid film thickness, and thermosyphon loop. The third section includes nanofluids for heat transfer, nanofluids in minichannels, potential and engineering strategies on nanofluids, and heat transfer at nanoscale. The forth section presents time-dependent melting and deformation processes of phase change material (PCM), thermal energy storage tanks using PCM, phase change in deep CO2 injector, and thermal storage device of solar hot water system. The advanced idea and information described here will be fruitful for the readers to find a sustainable solution in an industrialized society

Macroscopic and microscopic characterization of non-reacting diesel sprays at low and very high injection pressures

En la exploración de nuevos métodos para el mejoramiento de la eficiencia y rendimiento del motor diésel, es claro que un gran esfuerzo debe estar enfocado en el proceso de inyección de combustible. La eficiencia de la combustión y las emisiones, se ven muy afectadas por el proceso de atomización, y se ha demostrado que incrementos en presiones de inyección conllevan un gran potencial para mejorar el ahorro de combustible, producir mejores mezclas de aire y combustible, y por tanto menor generación de emisiones contaminantes. Últimamente, las presiones de inyección han aumentado de alrededor de 50 MPa en los años 70 hasta 250 MPa en los días actuales. Presiones de inyección muy altas (250-300 MPa) o incluso ultra altas (> 300 MPa) vienen siendo materia de investigación con el fin de ser implementadas de manera comercial en un futuro próximo. La estructura y desarrollo del spray diésel pueden ser caracterizados desde un punto de vista microscópico por medio de la medición del tamaño de gotas del spray y sus velocidades. En condiciones no-evaporativas, técnicas como el PDPA (Phase Doppler Particle Analyzer) vienen siendo utilizadas para la obtención de perfiles de diámetros y velocidades de gota con una alta resolución temporal. Desde el punto de vista macroscópico, existen parámetros específicos que permiten caracterizar a un chorro diésel, estos son: la penetración de vapor y líquida junto con el ángulo de apertura del chorro. La penetración líquida es un indicador claro de la capacidad de evaporación del combustible utilizado, mientras que la penetración de vapor, por su parte, es indicativo del proceso de mezcla y la probabilidad de colisión con las paredes de la cámara de combustión; factores claves a la hora de la generación de emisiones contaminantes. En esta tesis se estudia la influencia de presiones bajas, medias y muy altas presiones inyección, sobre un amplio espectro de condiciones y diagnósticos experimentales, y desde el punto de vista macroscópico y microscópico. Se realizaron experimentos para tres diferentes inyectores, 2 solenoides y un piezo eléctrico, este último con la capacidad de alcanzar presiones de inyección cercanas a 270 MPa. Las medidas incluyen una caracterización hidráulica, compuesta por tasa de inyección; una visualización de alta velocidad del chorro líquido isotermo; una visualización de alta velocidad del chorro inerte evaporativo, con captura simultánea de las fases líquida y vapor; y finalmente, una caracterización microscópica por medio de la obtención de distribución de tamaño de gotas y sus velocidades. Con respecto a los ensayos microscópicos, se desarrolló una metodología para el aislamiento y alineación de sprays con un error de medición muy bajo de 0,22°. Se llevaron a cabo mediciones de velocidad de gotas, cuyos resultados mostraron buen ajuste con perfiles teóricos de velocidad. De igual manera, una correlación para el tamaño de gota SMD se obtuvo mostrando un alto nivel de ajuste y siendo representativa para todo el rango de presiones de inyección estudiados. En el caso de la caracterización macroscópica del chorro isotermo, se han detectado variaciones macroscópicas en el desarrollo del chorro con propiedades de gas, inclusive en condiciones de motor comunes. Para estimar estos efectos y otros que las presiones de inyección muy altas tendrían sobre la estructura del chorro, se incentivó la aparición de ondas de choque controlando la velocidad del sonido del ambiente. Se usaron tres gases ambientales (SF6 N2 y CO2) con diferentes velocidades de sonido, promoviendo de esta manera chorros supersónicos en determinados casos. Al comparar ensayos con mismas densidades y diferentes gases ambientales, se encontró que todas las tendencias cercanas al estado transónico (0.8 300 MPa) vénen sent matèria d'investigació a fi de ser implementades de manera comercial en un futur pròxim. L'estructura i desenrotllament de l'esprai dièsel poden ser caracteritzats des d'un punt de vista microscòpic per mitjà del mesurament de la grandària de gotes de l'esprai i les seues velocitats. En condicions no-evaporatives, tècniques com el PDPA (Phase doppler particle analyzer) vénen sent utilitzades per a l'obtenció de perfils de diàmetres i velocitats de gota amb una alta resolució temporal. Des del punt de vista macroscòpic, hi ha paràmetres específics que permeten caracteritzar a un doll dièsel, estos són: la penetració de vapor i la penetració líquida junt amb l'angle d'obertura del doll. La penetració líquida és un indicador clar de la capacitat d'evaporació del combustible utilitzat, mentres que la penetració de vapor, per la seua banda, és indicatiu del procés de mescla i la probabilitat de col·lisió amb les parets de la cambra de combustió; factors claus a l'hora de la generació d'emissions contaminants. En esta tesi s'estudia la influència de pressions d' injecció baixes, mitges i molt altes, sobre un ampli espectre de condicions i diagnòstics experimentals, i des del punt de vista macroscòpic i microscòpic. Es van realitzar experiments per a tres injectors diferents, 2 solenoides i un piezo elèctric, este últim amb la capacitat d'aconseguir pressions d'injecció pròximes a 270 MPa. Les medides inclouen una caracterització hidràulica, composta per taxa d'injecció; una visualització d'alta velocitat del doll líquid isoterm; una visualització d'alta velocitat del doll inert evaporativo, amb captura simultània de les fases líquida i vapor; i finalment, una caracterització microscòpica per mitjà de l'obtenció de distribució de grandària de gotes i les seues velocitats. Respecte als assajos microscòpics, es va desenrotllar una metodologia per a l'aïllament i alineació d'esprais amb un error de mesurament molt davall de 0,22°. Es van dur a terme mesuraments de velocitat de gotes, els resultats van mostrar bon ajust amb perfils teòrics de velocitat. De la mateixa manera, una correlació per a la grandària de gota SMD es va obtindre mostrant un alt nivell d'ajust i sent representativa per a tot el rang de pressions d'injecció estudiats. En el cas de la caracterització macroscòpica del doll isoterm, s'han detectat variacions macroscòpiques en el desenrotllament del doll amb propietats de gas, inclusivament en condicions de motor comú. Per a estimar estos efectes i altres que altes pressions d'injecció tindrien sobre l'estructura del doll, es va incentivar l'aparició d'ones de xoc controlant la velocitat del so de l'ambient. Es van usar tres gasos ambientals (SF6, N2 i CO2) amb diferents velocitats de so, promovent d'esta manera dolls supersònics en determinats casos. Al comparar assajos amb mateixes densitats i diferents gasos ambientals, es va trobar que totes les tendències pròximes a l'estat transónic (0.8 300 MPa) have been the subject of the scientific community in order to be implemented in future injection systems. The structure and development of the diesel spray can be characterized from a microscopic point of view by means of estimation of droplets size and velocities. At non-evaporative conditions, techniques such as PDPA (Phase Doppler Particle Analyzer) are being used to obtain diameters and velocity profiles a with high temporal resolution. From the macroscopic point of view, there are specific parameters that allow characterizing the diesel spray, these are: the liquid and vapor penetration along with the spray angle. The liquid penetration is a clear indicator of the evaporation capacity of the fuel used, whilst the vapor penetration, on the other hand, is an indicative of the mixing process and the probability of collision with the combustion chamber walls; key factors when generating polluting emissions. In this thesis the influence of low and very high injections pressures over the macro and micro characteristics of the diesel spray is studied, over a wide spectrum of conditions and experimental diagnoses. Experiments were carried out for three different injectors, two solenoids and one piezoelectric, the latter with the capacity to reach injection pressures close to 270MPa. The measurements include a hydraulic characterization; a high speed visualization of the liquid spray at isothermal conditions; a high-speed visualization of the evaporative spray, with simultaneous capture of the liquid and vapor phases; and finally, a microscopic characterization. Regarding the microscopic tests, a methodology was developed for the spray isolation and alignment with a very low measurement error of 0.22° Droplets velocity measurements were carried out, the results showed good adjustment with theoretical velocity profiles. Similarly, a correlation for SMD droplet size was obtained showing a high level of adjustment and being representative for the entire range of injection pressures studied. In the case of the macroscopic characterization of the isothermal spray, variations have been detected in the development of the jet with gas properties, even at common engine injection conditions. To estimate these effects and others that very high injection pressures would have on the spray structure, the apparition of shock waves was enhanced by controlling the speed of sound of the environment using three ambient gases with different speed of sound (SF6, N2 and CO2). When comparing tests with same densities and different ambient gases, it was found that all the tendencies near the transonic state (0.8 <M <1.2) had a higher penetration and lower spray angle. With respect to the evaporative jet, for very high injection pressures like 270MPa, the effects of the environmental and injection parameters remained the same with respect to all the macroscopic characteristics.Giraldo Valderrama, JS. (2018). Macroscopic and microscopic characterization of non-reacting diesel sprays at low and very high injection pressures [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/113643TESI

Multiscale mathematical models for simulation and scale-up of green processes in the perspective of industrial sustainability

The present work presents research studies aimed at developing tools useful to design engineering solutions moving in the direction of industrial sustainability. The investigations hereinafter discussed regard an extraction process of active compounds \u2013 polyphenols \u2013 from agro-food industry wastes (olive and grape pomaces) and a biorefinery exploiting waste frying oil, solid organic wastes and algal biomass to produce biofuels. In particular, for the former topic, a procedure aimed at the evaluation of the technological feasibility at pilot scale of said process is discussed. The proposed approach takes into consideration the extended kinetic route coupled with mathematical simulation. Detailed physically-based dynamic mathematical models, taking into account mass and energy balance equations, are adopted to describe both the lab-scale and the pilot-scale reactors. Chemical physical parameters appearing in the models are estimated from the experimental data at lab-scale or are partially taken from literature. Different heating systems are designed for the pilot scale reactor and their performance is tested by simulation. Characteristic times are evaluated also during start-ups and different control loops are analyzed in order to set-up the best process and operating variables. Average yields in polyphenols are finally evaluated for both the batch and the continuous operated pilot reactor, by considering feed variability and fluctuations of process parameters. For what concerns the biorefinery, special attention was devoted to the modeling of the airlift reactor, its most delicate and complex component. In fact, to optimize this interesting microalgae cultivation system, a precise description of the moving interfaces formed by the liquid and gas phase is critical. In this study, coupled front capturing methods (standard and conservative level set methods) and finite difference method are used to simulate gas bubbles dynamics in a pilot-scale external loop air-lift photobioreactor in which microalgae are used to capture CO2 from flue gas and to treat wastewater. Numerical simulations are carried out on rectangular domains representing different sections of the vertical axis of the riser. The data employed was either acquired from previous experimental campaigns carried out in the airlift reactor or found in the literature. The rise, shape dynamics and coalescence process of the bubbles of flue gas are studied. Moreover, for each analyzed applications, a procedure based on Buckingham \u3c0-theorem to perform a rigorous scale-up is proposed. In this way, scale-invariant dimensionless groups describing and summarizing the considered processes could be identified. For the research focused on the scale-up of photobioreactors used to cultivate Chlorella Vulgaris, an experimental campaign at three levels was designed and carried out to evaluate the characteristic dimensionless numbers individuated by the theoretical formulation. Since scale-up regards both geometrical dimensions and type of reactor, passing from lab-scale stirred tanks to pilot scale tubular and airlift, particular attention was devoted to define characteristic lengths inside the dimensionless numbers