Conventional heat transfer enhancement methods have focused on the surface characteristics of the heat-exchanger. The enhancement of heat transfer through altering the characteristics of the working fluid has become a new subject of interest. Micro-encapsulated phase change material (MEPCM) slurries show improved heat transfer abilities compared to single phase heat transfer fluids such as water due to their higher specific heat values in their phase change temperature range. The present work is a numerical and experimental study towards fundamental understanding of the impact of using PCM on thermal and fluid flow characteristics of different single-phase and two-phase heat transfer applications. The mathematical formulation to represent the presence of single and multi-component MEPCM is developed and incorporated into the numerical model for single-phase and two-phase fluid flow systems. In particular, the use of PCM in its encapsulated form for heat transfer enhancement of liquid flow in the presence of evaporation is explored. In addition, an experimental study is conducted to validate the numerical model in a setting of natural convection flow. Finally, the application of PCM in its layered form on the effectiveness of drying of moist porous materials (e.g. paper) is investigated.

Evaporation, wetting and multiphase flows of drops and bubbles are everyday life phenomena with potential impact in many industrial, biological, medical or engineering applications. The understanding and controlling of the physical and chemical mechanisms governing these phenomena have become of paramount importance. This thesis encompasses three topics: evaporation of sessile droplets of polymer solutions, the role of thermocapillarity on self-rewetting fluid dynamics and migration of bubbles in liquid flows. Firstly, the evaporative behaviour of sessile droplets of aqueous polymer solutions and the effect of different molecular weights on the drying process has been studied. Drop shape analysis allowed monitoring the evolution of all stages during drying and indicating the transitions between stages. The mechanisms taking place during the crucial stages of pinning and depinning were illustrated, revealing the effects of adhesion and contact line friction forces on the final morphology of the dried polymeric deposits. Additionally, the effect of varying substrates from hydrophilic to hydrophobic was examined demonstrating the importance of interfacial interaction phenomena. The initial spreading dynamics of binary alcohol mixtures (and pure liquids) deposited on different substrates in partially wetting situations, under non-isothermal conditions was systematically investigated. Moreover, the temporal and spatial thermal dynamics within pure droplets and alcohol mixtures using IR thermography revealed the existence of characteristic thermal patterns due to thermal and/or solutal instabilities. The contribution of the Marangoni effect as an important heat transport mechanism within the evaporating droplets was investigated. The motion of buoyancy-driven bubbles in a vertical microchannel and the significant role of thermocapillarity was reported in this series of experiments. The behaviour of the bubbles in self-rewetting fluid flows departed considerably from that of pure liquids flows. Furthermore, heat transfer coefficient calculations in the single and two phase flows demonstrated that the presence of Marangoni (surface tension) stresses resulted in the enhancement of the heat transfer distribution in the self-rewetting fluid flows compared with the pure ones.

La cristallisation d'un sel initialement dissous dans l'eau contenue dans des matériaux poreux tels que les ciments, béton, mortiers, briques, ..., est une cause majeure de dégradations intervenant dans les constructions et dans certains éléments de notre patrimoine culturel (monuments, murs, sculptures, fresques, ...). Les sels cristallisés à la surface du milieu poreux (efflorescence) n'affectent pas généralement la durabilité de l'ouvrage mais pose un réel problème esthétique pour les façades des bâtiments. Dans le cas d'une cristallisation interne au milieu, les contraintes exercées sur la matrice solide peuvent endommager l'ouvrage allant jusqu'à l'apparition de fissures. Dans ce contexte, le présent travail porte sur l'évaporation avec cristallisation de sel en milieu granulaire et plus précisément sur l'étude de la localisation des cristaux et des déplacements mécaniques induits. La première partie de cette thèse porte sur l'étude des facteurs contrôlant la localisation des cristaux à la surface d'un milieu hétérogène et s'appuie sur l'identification de deux situations de base. Dans la première situation dite de mèche, le milieu poreux est en contact permanent avec une solution saline qui l'alimente à sa base. Cette situation peut correspondre à des parties basses de murs ou d'ouvrages, lorsque le matériau est proche de l'eau des sols. La deuxième situation dite de séchage peut correspondre à des matériaux situés suffisamment en hauteur dans un mur ou un ouvrage. Contrairement au cas de la situation de mèche, le milieu poreux n'est pas alimenté en solution quand l'évaporation se produit. Ces deux situations conduisent à des localisations exactement opposées: à la surface du milieu grossier en séchage, à la surface du milieu fin pour la situation de mèche. Dans le cas de la situation de mèche, la modélisation proposée montre que la structure de l'écoulement joue un rôle clé dans la localisation de la cristallisation alors que pour la situation de séchage, la désaturation préférentielle du milieu grossier est un effet dominant. Concernant la colonisation de la totalité de la surface du milieu poreux par l'efflorescence, l'étude suggère qu'il existe une vitesse d'évaporation critique au regard de laquelle ce phénomène apparait. La deuxième partie de la thèse est dédiée au phénomène de surrection de surface (" surface heave ") à l'aide d'expériences au sein de cellules quasi bidimensionnelles de type Hele Shaw complétés par des expériences en milieu granulaire confiné au sein de tubes cylindriques. Un modèle de croissance de la subflorescence est proposé dans lequel la loi de croissance de la subflorescence est contrôlée par l'évaporation. Ce modèle prédit une très légère sursaturation en haut de la subflorescence compatible avec l'existence d'une pression de cristallisation. Ce modèle permet d'identifier deux régimes principaux de déplacement: un régime dit de désaturation de la subflorescence et un régime de colmatage. Des expressions simples sont proposées pour estimer la croissance de la subflorescence et donc le déplacement induit. Ces relations permettent de déterminer la sursaturation au sommet de la subflorescence et donc la pression de cristallisation. / The crystallization of salt, initially dissolved in water, from porous materials (like cements, concrete, mortar, bricks) is a major cause of degradation occurring in buildings and in certain elements of our cultural landscape (monuments, walls, sculptures, frescoes,). Salt crystallization at the surface of a porous medium (efflorescence) don't affect structure durability but create an aesthetic problem for building construction. However, when salt crystallization occurs inside the porous media (subflorescence), pressure on the solid matrix can damage structures by cracking. In this context, the present work focuses on evaporation with salt crystallization in a granular medium and in particular on the locus of crystals and induced mechanical displacements. The first part of this thesis focuses on the study of the factors controlling the localization of crystals atthe surface of an heterogeneous medium. This study is based on the identification of two basic situations of evaporation. In the first so-called evaporation wicking situation, the porous medium is in contact at its bottom with an aqueous solution and the medium remains fully saturated by the solution during evaporation. This situation may correspond to lower parts of walls or structures, when the material is close to the ground water. The second so-called drying situation can correspond to materials located sufficiently high in a wall or a structure. Contrary to the case of wicking situation, the porous medium isn't supplied with a saline solution when evaporation occurs. These two situations lead to a markedly different locus of the efflorescence formation: on the surface of the coarse medium in drying situation and on the surface of the fine medium for the wicking situation. The study emphasizes the key-role of the velocity field induced in the porous domain in the case of the evaporation-wicking situation. In the case of the drying situation, a key aspect lies in the local increase in the ion mass fraction due to the local desaturation, i.e. the local shrinking of the liquid volume containing the ions. Regarding the colonization of the entire surface of the porous medium by efflorescence, the study suggests that there is a critical evaporation rate against which this phenomenon appears. The second part of the thesis deals with the study of surface heave phenomena using experiments in quasi-two-dimensional Hele-Shaw cell supplemented by experiments in a confined granular medium of cylindrical tubes. A growth model of subflorescence is proposed in which the growing subflorescence is controlled by evaporation and not by the precipitation of salt. This model predicts a very slight supersaturation on the top of the subflorescence compatible with the existence of a crystallization pressure. This model makes it possible to identify two main regimes of displacement: a regime known as desaturation of the subflorescence and a clogging regime. Simple expressions are proposed to estimate the growth of subflorescence and thus the induced displacement. These relationships make it possible to determine the supersaturation at the top of the subflorescence and therefore the crystallization pressure.

In order to obtain a sugar concentration of more than 100g.l-1of fermentable sugars, aspruce wood hydrolysate was subjected to high pressure and vacuum concentration andthe fermentability of each hydrolysate was assessed by fermentation experiments withflocculating S. cerevisiae. The hypothesis that high pressure evaporated hydrolysate(evaporation carried out at 108°C and 1.3 bar) would be more difficult to ferment thanvacuum evaporated hydrolysate (evaporation carried out at 80°C and 0.5 bar) was notconfirmed by the results. Minor amount of cells lost their flocculating ability afterfermentation which their ratio and their viability and vitality was assessed.By vacuum and high pressure concentration, the fermentable sugars (defined as theconcentration of glucose, mannose and galactose) in the hydrolysates reached to 120g.l-1and 129g.l-1 respectively. Compared to the initial hydrolysate the concentration factorrepresented a 3-fold increase of fermentable sugars. Furfural was evaporated in both trialsand its concentration reached to 0.03g.l-1 and 0.1g.l-1 after vacuum and high pressureevaporation respectively. Fermentation with both 0.14h-1and 0.22h-1 initial dilution rateswas possible, while more than 96% of furfural and to less extent formic and acetic acidsdisappeared from the hydrolyzates. However, HMF and levulinic acid remained in thehydrolyzates and concentrated proportionally. More than 84% of the fermentable sugarspresent in VEH were fermented by fed-batch cultivation using 12g.l-1 yeast and initialdilution rate (ID) of 0.22h-1, and resulted into 0.40±0.01g.g-1 ethanol in 21h.Fermentation of HPEH was as successful as VEH and resulted into more than 86% of thesugar consumption at the corresponding conditions. With an ID of 0.14h-1, more than97% of the total fermentable sugars were consumed, and ethanol yielded 0.44±0.01g.g-1.A viability and vitality determination from the supernatant of fermentation liquorrepresented that about 76% of the cells which lost their flocculating ability kept theirvitality. Cultivation of yeast with beet molasses was tricky in both batch and fed-batchcultivation as the concentration more than 50g.l-1 in batch cultivation prevent from yeastgrowing. / Uppsatsnivå: D

O solo fornece suporte e atua como reservatório de água para as plantas, promovendo condições fundamentais ao crescimento de raízes e à dinâmica da água e nutrientes. O conhecimento de suas propriedades hidráulicas, como a curva retenção da água, é de grande importância na descrição e predição dos processos de transporte da água e solutos. O objetivo deste trabalho foi determinar a curva de retenção pelo método tradicional dos funis e câmaras de pressão de ar com placa porosa, pelo método de campo utilizando tensiômetros e pelo método da evaporação da água em amostra de solo no laboratório munida de tensiômetro. O solo utilizado para estudo foi classificado como Nitossolo Vermelho eutrófico de textura argilosa, e estava sendo cultivado com café há mais de 10 anos. A comparação entre as curvas obtidas pelos três métodos indicou que o método da evaporação diferiu estatisticamente do método do funil e câmara e foi estatisticamente idêntico ao método do tensiômetro a campo. Por sua facilidade de execução, baixo custo e rapidez na determinação da curva de retenção até a tensão de aproximadamente 100 kPa, o método da evaporação aqui apresentado é uma boa opção de utilização. Com relação ao método do tensiômetro no campo, embora mais realístico, é muito trabalhoso. / Soil provides support and acts as a water reservoir to plants, promoting essential conditions to root growth and to water and nutrient dynamics. The understanding of its hydraulic properties, like the water retention curve, is of great importance for the description and prediction of the processes of water and solute transport. The objective of this study was to determine soil water retention curve through the traditional method using porous plate funnel and pressure chamber, through the field method using tensiometers and through the water evaporation in soil sample with tensiometer in the laboratory. The studied soil was classified as clayey Rhodic Hapludox, which had been cultivated with coffee for more than 10 years. The comparison of curves obtained through the three methods indicated that the evaporation method was statistically different from the method using funnel and chamber, and statistically equal to the method of tensiometers at field. For its easy execution, low cost and quickness to determine soil water retention curve until the tension of about 100 kPa, the evaportation method presented here is a feasible option. As for the method of tensiometers at field, although it is more realistic, it is very laborious.

Após setenta anos de sua descoberta, o vírus da zika surgiu no Brasil, espalhou-se rapidamente pelas Américas e trouxe complicações incomuns em doenças causadas por Flavivirus, como a microcefalia. A Organização Mundial da Saúde classifica a zika como a doença viral mais preocupante da atualidade e considera urgente desenvolver novos métodos de diagnóstico para ela e doenças correlatas como a dengue. Embora existam exames para identificar infecções pelos vírus dessas duas doenças, ainda não há um método rápido, específico e de baixo custo para o diagnóstico precoce. Visando preencher essa lacuna, este trabalho teve como objetivo construir dois tipos de biossensores eletroquímicos de DNA para detecção label-free desses dois vírus. Foram fabricados eletrodos descartáveis em substrato de politereftalato de etileno metalizado com filme fino de ouro nas configurações com um e três contatos. As sequências genéticas de iniciadores e sondas de captura foram desenhadas especialmente para este trabalho com base na análise dos genomas dos vírus. O primeiro biossensor utilizou o eletrodo em uma célula eletroquímica e foi capaz de identificar sequências de DNA da zika ou da dengue. As análises por espectroscopia de impedância eletroquímica mostraram que o biossensor é seletivo à sequência alvo com limite de detecção de (9,86 ± 0,89) nmol L-1. O segundo biossensor utilizou um eletrodo de três contatos para identificação de sequências de DNA em uma gota da amostra. No contato central, usado como eletrodo de trabalho, foi imobilizada a sequência de captura e os contatos laterais funcionaram como eletrodos de referência e auxiliar. Nesse sistema as medidas de impedância indicaram limite de detecção de (25,0 ± 1,7) nmol L-1. Os biossensores desenvolvidos mostraram seletividade para identificar o material genético dos vírus da zika e da dengue nos ensaios com DNA sintético e, portanto, são promissores para a análise de amostras reais, principalmente de produtos da polimerase da cadeia reversa. / After seventy years of its discovery, zika virus has emerged in Brazil, spread rapidly throughout the Americas, bringing unusual complications in diseases caused by flaviviruses, such as microcephaly. The World Health Organization classifies zika as the most harmful viral disease today and considers urgent the development of new diagnostic methods for zika and related diseases, such as dengue. Although there are tests to identify both infections, no current diagnostic method is rapid, specific and cost-efective. This thesis describes two types of electrochemical DNA biosensors for label-free detection of these zika and dengue. Disposable electrodes were fabricated on polyethylene terephthalate substrates covered with a nanometric gold layer by thermal evaporation, manufactured in one- and three-contact configurations. Genetic sequences of primers and complementary capture probes were designed based on the analysis of the virus genomes. The first biosensor we developed used the new electrode in an electrochemical cell and was able to identify zika or dengue DNA sequences. Analyses by electrochemical impedance spectroscopy showed that these biosensors are selective for zika or dengue with a detection limit of (9.86 ± 0.89) nmol L-1. A second type of biosensor used a three-contact electrode to identify DNA sequences in a drop of sample. In the central contact, used as a working electrode, the capture sequence was immobilized and the lateral contacts acted as reference and auxiliary electrodes. In this system the impedance measurements indicated a limit of detection of (25.0 ± 1.7) nmol L-1. The developed biosensors showed selectivity for zika and dengue in the synthetic DNA assays, and therefore are promising for the analysis of real samples, especially the polymerase chain reaction amplicon.

Este trabalho objetivou estabelecer relações entre evaporação de tanques Classe A e de 20 m2, em Piracicaba, SP e testar o desempenho de métodos meteorológicos de estimativa da evaporação de superfícies de água livre nessa localidade e em Jaboticabal, SP. Utilizou-se dados meteorológicos coletados em ambiente de um pequeno lago artificial em Piracicaba para cálculos dos métodos de balanço de energia-razão de Bowen, Penman, Priestley-Taylor e Penman simplificado. Dados meteorológicos observados sobre gramado foram usados para estimativa pelos métodos de Penman, Penman modificado, Dalton adaptado, Linacre e tanque Classe ASnyder. Os métodos foram avaliados utilizando índices de concordância e desempenho a partir de análise de regressão e de desvios por comparação com medidas do evaporímetro de 20 m2. Foram observadas relações lineares significativas entre os valores da evaporação dos tanques Classe A e de 20 m2 em todos os meses do ano em Piracicaba. A razão mensal entre as medidas dos evaporímetros apresentou variação ao longo do ano, com superestimativa pequena (até 3%) de fevereiro a junho e em novembro, e grande (10% a 15%) nos outros meses, em relação aos dados de Oliveira (1971) para a mesma localidade. A maior consistência estatística e representatividade da série de medidas, com 3 repetições de tanque Classe A, indicam que os fatores mensais de relações entre os dois evaporímetros podem substituir os obtidos por Oliveira (1971). Todos os métodos utilizados nos dois ambientes apresentaram boa concordância em termos médios com os observados no tanque de 20 m2, sempre com grande dispersão dos dados, diminuindo com o aumento do número de dias de contabilização da evaporação. O método de balanço de energia apresentou bom desempenho com cálculos realizados em períodos de 24 horas, mostrando desvios acentuados com contabilização no período diurno. O método de Penman mostrou bom desempenho quando utilizado para períodos de 24 horas, com subestimativas médias entre -6,0% e -10,5%, mas com superestimativas de +7,2 e +12,4% no período diurno. Os métodos de Priestley-Taylor (1972) e de Penman simplificado mostraram desvios médios pequenos (+2,7 e +5,7%), sendo considerados de bom desempenho. Para os métodos que usaram observações no posto meteorológico, o do tanque Classe ASnyder mostrou os menores desvios médios em Piracicaba (+3,9% a + 4,6%), mas apresentou maiores superestimativas (+14,0% a +14,4%) em Jaboticabal. Outra discrepância entre localidades foi observada para o método de Penmam modificado, com subestimativas entre 5,5 e 14,1% em Piracicaba, mas desvio de +1,0%, em Jaboticabal. O método original de Penman mostrou desvios similares em ambas localidades (-8,9% a 12,3%), enquanto o de Dalton adaptado apresentou desvios de +2,1% a 8,1%, mas com alta dispersão em todos dias de contabilização. Os métodos de Penman simplificado e o de Priestley-Taylor, no caso do lago, e o tanque Classe ASnyder, no caso do posto meteorológico, foram os que no geral apresentaram resultados mais comparáveis com os do tanque de 20 m2, sendo que par ao último deve-se atentar para o desvio sistemático em Jaboticabal. / This study aimed to establish relations between evaporation Class A pan and 20 m2 tank, in Piracicaba region, State of Sao Paulo, Brazil and to test the performance of meteorological methods to estimate open-water surfaces evaporation in this same region and also in Jaboticabal, SP. Computation of daily evaporation was performed by using weather data, collected in the environment of a small artificial lake in Piracicaba, and the following methods: energy balance-Bowen ratio, Penman, Priestley-Taylor and Penman simplified. The methods of Penman, Penman adapted, Dalton adapted, Linacre and of Class A pan-Snyder were evaluated by using weather station data in both regions. The results of the methods were compared with the measurements of the 20 m2 tank evaporation, in a daily basis, and also for two, three or for the mean values for all days of measurements in every month, using indexes of agreement and performance from the regression analysis and deviations from the estimated and measured values. The linear relations between evaporation measured by the two evaporimeters were significative for all months in Piracicaba. The ratio of the two measurements showed variation throughout the year, with a small overestimation (about 3%) from February to June and November, and greater (10% to 15%) in the other months, compared to results of Oliveira (1971) for the same region. Due to the statistical consistency and representativeness of the series of 9 years and 3 repetitions of Class A pan, it is indicated that the factors of monthly relations between the two evaporímeters observed in this study can advantageously replace those obtained by Oliveira (1971). All methods used in the two environments showed good agreement, in average basis, with measurements by 20 m2 tank, with large dispersion of data, which decreased with the increase of the time step. The energy balance method showed good performance when the calculations were performed in 24-h periods, but large deviations compared to the tank with data integrated over the daylight period. The Penman method showed good performance when used for periods of 24 h, with an average underestimation between - 6.0 and -10.5% when integrated over the 24-h period, but with overestimation of +7.2 and +12.4% for the daylight period. The methods of Priestley-Taylor (1972) and Penman simplified showed small deviations between +2.7 and + 5.7%, being considered as having good performance compared to the evaporimeter. Among the methods that used weather station data, the class A- Snyder was the one that showed the lowest average deviation in Piracicaba (+3.9 to + 4.6%), but the greatest overestimation (+14.0% to 14.4%) in Jaboticabal. Another discrepancy between locations was observed for the Penman method modified, with underestimation between 5.5% and 14.1% in Piracicaba, but deviation of +1.0% in Jaboticabal. The original Penman method showed similar deviations in the two regions (-8.9% to 12.3%), while Dalton adapted method showed deviations of +2.1% to 8.1%. The methods of Penman simplified and Priestley-Taylor, used in the lake environment, and the Class A pan-Snyder method, with the use of wheater station data, were those that showed most comparable results with the 20 m2 tank evaporation, but in Jaboticabal, it is necessary to take to account the observed systematic mean deviation.

Saline water evaporation from porous media with the associated salt precipitation patterns is frequently observed in a number of industrial and environmental applications and it is important in a variety of topics including, but not limited to, water balance and land-atmosphere interaction, terrestrial ecosystem functioning, geological carbon storage, and preservation of historical monuments. The excess accumulation of salt in soil is a global problem and is one of the most widespread soil degradation processes. Thus, it is important to understand the dominant mechanisms controlling saline water evaporation from porous media. This process is controlled by the transport properties of the porous medium, the external conditions, and the properties of the evaporating fluid. During saline water evaporation from porous media, the capillary induced liquid flow transports the solute towards the evaporation surface while diffusive transport tends to spread the salt homogeneously thorough the porous medium. Therefore, the solute distribution is influenced by the competition between the diffusive and convective transport. As water evaporates, salt concentration in the pore space increases continually until it precipitates. The formation of precipitated salt adds to the complexity of the description of saline water evaporation from porous media. In this dissertation, the effects of salt concentration, type of salt, and the presence of precipitated salt, on the evaporation dynamics have been investigated. The obtained results show that the precipitated salt has a porous structure and it evolves as the drying progresses. The presence of porous precipitated salt at the surface causes top-supplied creeping of the evaporating solution, feeding the growth of subsequent crystals. This could be visualized by thermal imaging in the form of appearance and disappearance of cold-spots on the surface of the porous medium, brought about by preferential water evaporation through the salt crust. My results show that such a phenomenon influences the dynamics of saline water evaporation from porous media. Moreover, a simple but effective tool was developed in this dissertation capable of describing the effects of ambient temperature, relative humidity, type of salt and its concentration, on the evaporative fluxes. Additionally, pore-scale data obtained by synchrotron x-ray tomography was used to study ion transport during saline water evaporation from porous media in 4D (3D space + time). Using iodine K-edge dual energy imaging, the ion concentration at pore scale with a high temporal and spatial resolution could be quantified. This enabled us to reveal the mechanisms controlling solute transport during saline water evaporation from porous media and extend the corresponding physical understanding of this process. Within this context, the effects of particle size distribution on the dispersion coefficient were investigated together with the evolution of the dispersion coefficient as the evaporation process progresses. The results reported in this dissertation shed new insight on the physics of saline water evaporation from porous media and its complex dynamics. The results of this dissertation have been published in 3 peer-reviewed journal papers together with one additional manuscript which is currently under review.

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Este trabalho experimental tem por objetivo apresentar os estudos experimentais realizados com jatos de líquidos evaporativos (\"flash boiling\") de iso-octano. Nos estudos, o jato emergia de um diminuto bocal que descarrega em uma grande câmara de baixa pressão. O líquido ao passar pelo bocal sofria uma expansão interna alcançando elevados graus de superaquecimento ou de metaestabilidade, já que se mantinha na fase líquida. Nos experimentos, eram controladas as condições de pressão e temperatura de injeção durante um período de alguns poucos segundos suficientes para que as condições de regime permanente fossem estabelecidas. Um dos métodos para a visualização do escoamento do jato evaporativo foi o \"Schlieren\", o qual permitia visualizar elevados gradientes de densidade como normalmente ocorrem com ondas de choque, presentes nesta investigação. Também foi empregada a técnica de visualização de \"iluminação por detrás\" para que fossem comparadas as imagens obtidas por este método com o do \"Schlieren\", bem como mostrar detalhes do fenômeno em estudo. Com isso, foi possível estudar a estrutura do processo evaporativo do jato e, com o auxílio de ferramentas de filtragem matemática e manipulação das imagens obtidas, os fenômenos compressíveis envolvidos. Os perfis dos jatos observados foram: (1) filete contínuo de líquido sem evaporação, (2) jato com fragmentações ou atomizado e (3) abrupta evaporação seguida por expansão com formação de ondas de choque. Neste último caso, a inspeção das fotografias indicou que a evaporação do líquido se dava externamente ao bocal, a partir de um núcleo metaestável de líquido, o qual apresentava o formato aproximado de um cone. Também foi aplicada a teoria de ondas oblíquas de evaporação para estudar o comportamento deste cone líquido. Os ensaios foram conduzidos com três bocais cônico-convergentes de dimensões e materiais diferentes, quais sejam: bocal de aço com diâmetro de saída de 0,3 mm, bocal de aço com 0,8 mm e bocal de vidro com 0,35 mm. / The main goal of this thesis is to present results of experiments with flashing liquid jets of iso-octane. The experiments were carried out with a liquid jet issuing from a small nozzle into a low-pressure chamber. High degrees of metastability were obtained as the liquid jet expanded within the nozzle. Injection pressure and temperature were controlled to the desired testing values for a few seconds, which were found long enough to reach and keep the steady state regime. The photographic documentation of the phenomenon was obtained from a \"Schlieren\" set up using CCD camera. The \"back-lightening\" visualization technique was also used in order to compare both image techniques and to unveil some flashing phenomenon details. Analyses of these images with the help of mathematical filters as well as other image manipulating techniques enabled a qualitative visualization of the flashing liquid jet structure and geometry leaving the nozzle. Three liquid jet regimes were observed: (1) continuous liquid jet (2) partially atomized, and (3) evaporation with the presence of shock waves. In this latter case, we speculate that the evaporation took part on the liquid jet surface, which had the approximate shape of a cone. Also it was employed the oblique evaporation wave theory to explain some of the behavior of the overall evaporation process. The tests were carried out using three conical-converging nozzles made of different materials: a 0.3 mm exit diameter steel nozzle, a 0.8 mm exit diameter steel nozzle, and a 0.35 mm exit diameter glass nozzle.