Flows of fluids and solid particles through microchannels have a very wide range of applications in biological and medical science and engineering. Understanding the mechanism of microflows will help to improve the development of the devices and systems in those applications. The aim of this study is to develop a sophisticated simulation and analysis technique for the study of fluid-particle flow through microchannels. This work involves construction of mathematical models, development of analytical methods and numerical algorithms, and numerical investigation and analysis. / The study consists of three parts. The first part of the research focuses on the transient flow of an incompressible Newtonian fluid through a micro-annual with a slip boundary. The flow of the fluid is governed by the continuity equation and the Navier-Stokes equations, and is driven by the pressure field with a timevarying pressure gradient. By using the Fourier series expansion in time and Bessel functions in space, an exact solution is derived for the velocity field. The velocity solution is then used to obtain the exact solutions for the flow rate and the stress field. Based on the exact solutions, the influence of the slip parameter on the flow behaviour is then investigated. / The second part of the research focuses on the particle-fluid flow in microchannels. The transport of fluid in the vessel is governed by the continuity equation and the transient Navier-Stokes equations, while the motion of the particles is governed by Newton’s laws. The particle-wall and particle-particle interactions are modelled by the interacting forces, while the particle-fluid interaction is described by the fluid drag force. A numerical scheme based on the finite element method and the Arbitary Lagrangian-Eulerian method is developed to simulate the motion of the particles and the fluid flow in the vessels. The influence of boundary slip on the velocity field in the fluid is also investigated numerically. / Based on the work in the second part, the third part of the research focuses onthe control of the movement of particles in the fluid by applying an external magneticfield to the system. Maxwell’s equations are used to model the magnetic fieldgenerated by the external magnetic source, and a finite element based numericalscheme is developed to solve the underlying boundary value problem for the magneticflux density generated. From the computed flux density and magnetic vectorpotential, the magnetic forces acting on the particles are determined. These magneticforces together with the drag force and the particle-particle interacting forcesdominate the behaviour of the particle motion. A numerical scheme, similar to thatfor the second part of the research, is then developed to study the fluid-particle flowin microchannels under magnetic forces, followed by a numerical investigation onthe influence of the magnetic forces on the particle flow behaviour.

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Orientador: Elaine Maria Cardoso / Resumo: Dissipadores de calor compactos, baseados em microcanais, têm se mostrado um meio eficaz para o resfriamento de dispositivos de alta densidade de energia, tais como microprocessadores, além de proporcionarem redução de material utilizado para a fabri-cação e do inventário de fluido refrigerante necessário. Sistemas bifásicos que operam com fluidos refrigerantes proporcionam coeficientes de transferência de calor elevados para baixos valores de velocidade mássica e uma distribuição de temperatura mais uni-forme na superfície. O presente estudo teve por objetivo avaliar experimentalmente o desempenho de um dissipador de calor baseado em microcanais, em condições de ebuli-ção convectiva saturada do fluido HFE-7100. O dissipador, em cobre eletrolítico, possui 33 microcanais de seção retangular com dimensões de 10 mm de comprimento, 200 μm de largura, 500 μm de altura e espaçados 100 μm entre si. A eficiência térmica do dissi-pador foi avaliada utilizando como fluido de trabalho o HFE-7100 (fluido refrigerante com baixo ozone depleting potencial, ODP, e global warming potential, GWP). Dados experimentais para o coeficiente de transferência de calor (CTC) e perda de pressão fo-ram obtidos em condições de escoamento monofásico e bifásico saturados, para diferen-tes valores de velocidades mássicas. As condições testadas foram de fluxo de calor im-posto (footprint) variando de 50 a 700 kW/m², com velocidades mássicas do fluido entre 392 e 875 kg/m²s, obtendo coeficientes de transferên... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Microchannel-based heat sinks have been shown to be an effective way of cool-ing high-density energy devices such as microprocessors, as well as reducing the material used to manufacture the exchangers and the required refrigerant inventory. Two-phase flow systems that operate with refrigerant fluids provide high heat transfer coefficients with low mass flux values and more uniform temperature distribution on the surface. The present study aimed to evaluate experimentally the performance of a heat sink based on microchannels under saturated conditions of convective boiling of HFE-7100 fluid. The analyzed heat sink has 33 rectangular section microchannels measuring 10 mm length, 200 μm wide, 500 μm high and spaced 100 μm apart. The heat sink was evaluat-ed using HFE-7100 (low ozone-depleting potential, ODP, and global warming potential, GWP) as working fluid. Experimental data for the heat transfer coefficient and pressure drop were obtained under saturated single and two-phase flow conditions for different values of mass velocities. An experimental apparatus was assembled and validated for the accomplishment of testing. As experimental conditions, the heat flux was applied in a range from 50 to 700 kW/m², with mass flux from 392 and 875 kg/m²s, obtaining a heat transfer coefficient of 60 kW/m² and pressure drop up to 12 kPa. By decreasing the mass flux and the input of the subcooling the HTC increases; the pressure drop increases monotonically with the increase in the mass fl... (Complete abstract click electronic access below) / Mestre

This Ph.D. thesis is focused on theory and experimental investigations developing of new knowledge about polymeric hollow fiber heat exchanger (PHFHE). The state-of-the-art study of plastic heat exchangers shows that their usage is limited by several niches where their advantages significantly dominates, or where the use of non-plastic competitors is not impossible. On the other hand, plastic heat exchangers (and PHFHEs in particular) are devices of increasing interest. It is shown that use of small tubes (fibers) allows PHFHEs to be more competitive than conventional plastic heat exchangers. Small hydraulic diameter of a fiber causes high heat transfer coefficients, reduces thermal resistance of plastic wall and allows it to create light and compact design. Detailed study of fluid flow and heat transfer inside the hollow fiber showed that conventional approaches for single-phase laminar flow can be utilized. Poiseuille number equal to 64 and Nussel number about 4 are recommended to be used to predict pressure drops and heat transfer coefficient, respectively. Additional attention should be paid to careful determination of fiber diameter and liquid properties (viscosity). Scaling effects, such as axial heat conduction, thermal entrance region and viscous dissipation can be neglected. The study of outside heat transfer showed that heat transfer on fiber bunches are intense and are competitive to contemporary compact finned-tube heat exchangers. The Grimson approach showed clear correlation with experimental results and, thus is recommended to predict heat transfer coefficients on fiber bunches. Two types of fouling (particulate- and biofouling) of outer fiber surface were experimentally studied. It was found that particulate fouling by titanium oxide particles is not intense and deposits can be removed relatively easy. However, fouling is much more intense when it is associated with biofouling caused by wastewater. In this case, smooth and low-adhesive surface of plastic is not sufficient precaution to prevent deposit formation.

<p>Heat dissipation requirements of next-generation power electronics in electric vehicles, high-performance computing, and radar systems will far exceed the capabilities of conventional heat sink technologies such as single-phase liquid cold plates and air-cooled heat sinks. The leading candidate technology that promises to meet these needs is microchannel flow boiling. Compared to conventional heat sink technologies, flow boiling provides some of the highest heat transfer coefficients available and can dissipate heat at a lower pumping power and with more uniform surface temperatures. However, there are unique challenges associated with flow boiling that currently prevent practical implementation of the technology, including limited modeling capabilities, inherent critical heat flux (CHF) limitations, and the presence of two-phase flow instabilities. This thesis is targeted primarily at addressing the impact of dynamic two-phase flow instabilities on heat transfer and CHF in microchannel heat sinks, in contrast with earlier literature that has focused on prediction and characterization of the flow dynamics.</p> <p><br></p> <p>Two dynamic instabilities of importance in microchannel heat sinks are pressure drop oscillations (PDO) and parallel channel instabilities, both resulting from an interaction between the inertia of a two-phase mixture within a heated channel and a source of compressibility outside of the channel. However, the individual impact of these instabilities on heat transfer performance has not been quantified. In this thesis, an experimental facility is developed to isolate the individual and combined impact of PDOs and parallel channel instabilities on surface temperature and CHF in single- and parallel-microchannels. This is achieved by introducing a measurable compressible volume directly upstream of the test section and isolating the test section from any unwanted compressibility within components throughout the rest of the system. Experiments are first performed targeting the investigation of PDOs in single channels and then targeting PDOs and parallel channel instabilities in multi-channel heat sinks. In the case of parallel channels, inlet restrictors are introduced to suppress channel-to-channel interactions and provide a baseline case of stable boiling. Throughout these experiments, only moderate increases in time-average surface temperature are observed (6 °C) and reduction of CHF is negligible, despite drastically different flow pattern observations when instabilities are present. These observations are in stark contrast with other cases in the literature, for which significant deterioration of surface temperatures and CHF have been attributed to the presence of PDOs. For example, significant temperature oscillations have been observed in the literature studying silicon-etched microchannel heat sinks experiencing PDOs. A predictive model is clearly required to understand and detect the conditions when dynamic instabilities should be considered in heat sink design.</p> <p><br></p> <p>To better understand the conditions when PDOs might have significant impact on heat transfer performance, an investigation of thermal capacitance is performed using a dynamic two-phase model and a targeted experimental approach in heat sinks having different thermal masses. The model reveals that, if thermal capacitance is low, PDOs become more severe, and the amplitude of temperature oscillations increase. These predictions are confirmed by experimental observations, and, in addition, premature CHF is observed in the heat sink with lower thermal mass. With sufficient thermal capacitance, the system recovers before triggering CHF, preventing deterioration of performance due to PDOs. Among the wide range of flow conditions considered in this thesis, the reduction of thermal mass resulted in the greatest impact on transient response of a heat sink during flow boiling instabilities. This reveals thermal capacitance as a critical parameter when determining if dynamic instabilities will deteriorate performance in a microchannel heat sink application. This allows engineers to make an informed judgement on whether adding features to suppress instabilities, at the cost of increased pumping power, is warranted. In order for the practical implementation of two-phase heat sinks to be realized, further development of dynamic modeling capabilities is required, and these models should be backed by systematic experimental investigations into conditions where instabilities should be considered.</p>

<p>  </p> <p>As the power density of computing devices increases, advanced liquid cooling thermal solutions offer an attractive thermal management approach. In particular, the low thermal resistance offered by microchannel heat sinks used in liquid cooling systems may enable increased total heat dissipation within fixed component temperature limits. There has been extensive work on the design of microchannel heat sinks, with many recent efforts to explore novel geometries and emerging manufacturing techniques. Of particular interest is additive manufacturing to allow for designs having complex, non-traditional internal geometries and package structures that cannot be made through conventional means. Despite the potential benefits for design and construction, additive manufacturing introduces new geometric uncertainties that could affect device performance. Direct metal laser sintering methods suitable for printing metal heat sinks typically produce a high internal roughness and other shape deviations in the flow paths of the final part. This extreme relative roughness and potential tortuosity in fluid flow through additively manufactured microchannels could lead to significant deviations in pressure drop and heat transfer predicted with traditional correlations and models. This work seeks to characterize the effects of high relative roughness on the friction factor and Nusselt number in additively manufactured microchannels having a rectangular cross section. Straight microchannel samples of 500 µm, 750 µm, and 1000 µm channel heights, and aspect ratios from 1 to 10 were manufactured to identify the design dimensions that resulted in visibly open channels, albeit with deviations in cross-sectional shape for submillimeter channel sizes and high internal roughness. Heat sink test samples were then printed with an array of these microchannels connected in parallel by inlet and outlet headers. Using water as the working fluid, the pressure drop and heat transfer performance of these sample heat sinks were characterized to explore how their behavior deviated from conventional predictions assuming smooth-walled channels. Flow through these additively manufactured microchannels displayed higher pressure drops than predicted, as well as a flow rate dependence of the hydrodynamic and thermal performance. These observed deviations are explored as effects of the physical conditions inside the channel as a result of additive manufacturing. Severe constriction of the channel would account for the difference in magnitude between the experimental and predicted results, while the introduction of flow redevelopment could lead to a flow rate dependence.  By further understanding the impact of these artifacts and deviations, these factors can be accounted for in the design and modelling of more complex additively manufactured heat sinks. </p>

Cette thèse vise à caractériser la dynamique stochastique hors-équilibre de particules browniennes sous l’effet de confinement. Ce confinement est appliqué ici par des potentiels attractifs ou des frontières imperméables créant des barrières entropiques. Dans un premier temps, nous regardons la dispersion de particules sans interactions dans les milieux hétérogènes. Un nuage de particules browniennes s’étale au cours du temps sans atteindre la distribution d’équilibre de Boltzmann, et son étalement est alors caractérisé par une diffusivité effective inférieure à la diffusivité microscopique. Dans un premier chapitre, nous nous intéressons au lien entre la géométrie de confinement et la dispersion dans le cas particulier des microcanaux périodiques. Pour cela, nous calculons la diffusivité effective sans hypothèse de réduction de dimensionnalité, contrairement à l’approche standard dite de Fick-Jacobs. Une classification des différents régimes de dispersion est alors réalisée, pour toute géométrie autant pour les canaux continus que discontinus. Dans un second chapitre, nous étendons cette analyse à la dispersion dans les réseaux périodiques d’obstacles sphériques attractifs à courte portée. La présence d’un potentiel attractif peut, de manière surprenante, augmenter la dispersion. Nous quantifions cet effet dans le régime dilué, et montrons alors son optimisation pour plusieurs potentiels ainsi que pour une diffusion médiée par la surface des sphères. Ensuite, nous étudions la dynamique stochastique de particules browniennes dans un piège optique en présence d’une force non conservative créée par la pression de radiation du laser. L’expression perturbative des courants stationnaires, décrivant les vortex browniens, est dérivée pour les basses pressions en conservant le terme inertiel dans l’équation de Langevin sous-amortie. L’expression de la densité spectrale est également calculée permettant d’observer les anisotropies du piège et les effets de la force non conservative.La plupart des expressions analytiques obtenues durant cette thèse sont asymptotiquement exactes et vérifiées par des analyses numériques basées sur l’intégration de l’équation de Langevin ou la résolution d’équation aux dérivées partielles. / This thesis aims to characterize the out-of-equilibrium stochastic dynamics of Brownian particles under the effectof confinement. This confinement is applied here by attractive potentials or impermeable boundaries creatingentropic barriers. First, we look at the dispersion of particles without interaction in heterogeneous media. Acloud of Brownian particles spreads over time without reaching the Boltzmann equilibrium distribution, andits spreading is then characterized by an effective diffusivity lower than the microscopic diffusivity. In a firstchapter, we are interested in the link between the confinement geometry and the dispersion in the particularcase of periodic microchannels. For this, we calculate the effective diffusivity without dimensionality reductionassumption, instead of the standard Fick-Jacobs’ approach. A classification of the different dispersion regimesis then performed for any geometry for both continuous and discontinuous channels. In a second chapter, weextend this analysis to dispersion in periodic networks of short-range attractive spherical obstacles. The presenceof an attractive potential can surprisingly increase the dispersion. We quantify this effect in the dilute regimeand then show its optimization for several potentials as well as for diffusion mediated by the surface of thespheres. Later, we study the stochastic dynamics of Brownian particles in an optical trap in the presence ofa non-conservative force created by the radiation pressure of the laser. The perturbative expression of thestationary currents describing Brownian vortices is derived for the low pressures keeping the inertial term in theunderdamped Langevin equation. The expression of the power spectrum density is also calculated to observe thetrap anisotropies and the effects of the non-conservative force. Most of analytical expressions obtained duringthis thesis are asymptotically exact and verified by numerical analysis based on the integration of the Langevinequation or the resolution of partial differential equation.

A presente pesquisa envolve um estudo teórico-experimental da transferência de calor e da perda de carga na condensação e no escoamento monofásico de fluidos refrigerantes halogenados no interior de lâminas com micro canais. Os ensaios consideram o fluido refrigerante puro R-134-a e a mistura quase azeotrópica R-410A. As lâminas estudadas envolvem micro canais de seção quadrada de Dh = 1,214 mm e de seção circular de Dh = 1,494 mm. Os ensaios de líquido subresfriado compreendem velocidades mássicas de 390 a 1360 Kg/sm2 para um temperatura de saturação de 40ºC e subresfriamento de 10ºC. Por sua parte, os ensaios foram realizados considerando um fluxo de calor constante de 5 kW/m2, títulos de vapor de 0,1 a 0,9, velocidades mássicas de 410 a 1135 kg/sm2, temperaturas de saturação de 40 a 50ºC e misturas óleo-refrigerante com concentrações de óleo em massa de 0,25 e 0,45%. Para cada condição de ensaio foram avaliados o coeficiente de transferência de calor e a queda de pressão por atrito na lâmina ensaiada. Os resultados para escoamento monofásico apresentaram consistência com relação às correlações típicas aplicáveis a transferência de calor e perda de carga para regime turbulento em tubos convencionais, apresentando, em média, valores de 12% superiores. Na maioria das condições de ensaios de condensação, segundo mapas de escoamento disponíveis na literatura, foi identificado o domínio do padrão estreitamento anular. Este comportamento foi aferido pelos resultados experimentais de perda de carga mostrando dependência quase exclusiva do parâmetro de Martinelli, e o mecanismo conectivo como principal mecanismo de transferência de calor, característico no padrão anular. Os resultados de condensação foram correlacionados a partir de abordagens empíricas em função do parâmetro de Martinelli e o conceito de velocidade mássica equivalente. Assim como, a partir de uma abordagem semi-empírica considerando um modelo anular que permite avaliar os mecanismos principais de transferência de calor e quantidade de movimento, avaliando a espessura do filme de líquido na parede do canal. Finalmente, os resultados experimentais e os obtidos a partir das correlações desenvolvidas são comparados com estudos disponíveis na literatura relativos a lâminas com micro canais. / This project involves a theoretical-experimental study of heat transfer and pressure drop in condensation and single phase flow of halogen refrigerants in microchannel tubes. The tests include the pure refrigerant R-134a and quasi azeotropic mixture R-410A. The microchannel tubes tested include one with square ports of Dh = 1,214 mm and other with circular port of Dh = 1,494 mm. The subcooled liquid tests considered the mass velocities of 390 to 1360 kg/sm2, the saturation temperature of 40ºC and subcooled of 10ºC. The condensing tests considered a constant heat flux of 5 kW/m2, vapor quality of 0,15 to 0,9, mass velocities of 410 to 1135 kg/sm2, saturation temperature of 40 to 50ºC and oil-refrigerant mixtures with oil mass concentrations of 0,25 and 0,45%. For each test condition was evaluated the coefficient of heat transfer and frictional pressure drop in the microchannel tube. The single phase results agree with typical correlations used in conventional tubes to evaluate the heat transfer and pressure drop in turbulent flow, even though the most of experimental date are 12% higher. The most of flow patterns in condensation were identified as annular using the flow patterns maps available on literature. This behavior was verified through pressure drop results, which show exclusive dependence on Martinelli Parameter. The heat transfer results show that the main heat transfer mechanism was convective, typical in annular flow. The results of condensation were correlated from empirical approachs using the Martinelli parameter and the equivalent mass velocity concept. And, also a semi-empirical approach modeling the annular flow to evaluate the mechanism of heat transfer through the liquid film around the wall of the tube. Finally, the experimental results and the results obtained through the models were compared with correlations referred to microchannels available on the literature.

A micromanufatura via usinagem apresenta algumas dificuldades, principalmente aquelas relacionadas à formação do cavaco, pois a espessura de corte passa a ter a dimensão do tamanho de grão do material da peça e da microgeometria da aresta de corte. Em operações de microcorte, a microestrutura do material é um fator importante no controle da geração da superfície da peça, mecanismo de formação de cavaco, etc. Este trabalho de pesquisa avaliou o efeito do tamanho ultrafino dos grãos do material da peça sobre os fenômenos inerentes ao corte no microfresamento. As variáveis de usinagem investigadas foram avanço por dente (fz), velocidade de corte (vc), diâmetro da microfresa (d&#934) e raio de aresta de corte (re), visando avaliar o mecanismo de formação do cavaco, acabamento da peça e integridade superficial. Os materiais utilizados nos experimentos foram um aço bifásico (ferrita-perlita) com tamanho de grão ferrítico de 11 µm e outro de microestrutura homogênea de grãos ultrafinos com 0,7 µm, ambos com mesma composição química e baixo-carbono. Dois grupos de ensaios foram propostos: (1) macro e microfresamento e (2) microfresamento de canais. O tipo de usinagem foi o de fresamento de topo, sem emprego de fluido de corte. Os ensaios de usinagem foram executados em centros de usinagem CNC. As ferramentas de corte foram de metal duro com recobrimentos, diâmetro 16 mm na escala macro de usinagem, 200 e 800 µm na escala micro. A adequação da microestrutura do material da peça à redução da escala de usinagem, através do mecanismo de refino de grão, gerou alguns aspectos favoráveis à microusinagem, como melhor acabamento (Ssk&#8776;0 e Sku&#8776;3), formação de cavaco contínuo e menor formação de rebarbas com a redução da espessura de corte (fz&#8804re), possibilitando aplicações em microfabricação por corte com ferramenta de geometria definida utilizando aços baixo carbono, antes limitadas à estruturas na construção civil e peças obtidas por conformação mecânica. / Micro manufacturing by means of machining presents difficulties, mainly those related to chip formation, since chip thickness become as small as normal material grain size, as well as the cutting edge radius. At such micro cutting operations material microstructure ascends as a very important issue in terms of machining output, i.e. surface roughness, subsurface damages, cutting forces, etc. This research evaluated the effect of the intervention on the metallurgical microstructure of the material on the cutting phenomena inherent in micromachining. The variables investigated were the feed per tooth (ft), cutting speed (vc), micro end-mill diameter (d&#934) and cutting edge radius (re). The materials used in the experiments were a steel two-phase (ferrite-pearlite) with ferritic grain size of 11 µm and similar one with homogeneous microstructure and ultrafine grains (0.7 µm), both low carbon. The mechanism of chip formation, surface finish and surface integrity were investigated and correlated with the studied variables. Two groups of machining experiments were proposed: (1) macro and micro end-milling and (2) microchannels. Overall, the type of machining was the end milling, without using cutting fluid. The machining tests were carried on a CNC machining center. The cutting tools are coated, diameter 16 mm in macro scale of machining, 200 and 800 &#956m in micro scale. the adequacy of the microstructure of the workpiece material to the reduce the scale of machining generated some favorable aspects to micromachining, such as better finishing (Ssk&#8776;0 e Sku&#8776;3), continuous chip formation and lesser burr formation by reducing the cutting thickness (fz&#8804re), enabling micromanufacturing applications for low carbon steels, once limited to structures in the civil construction and pieces obtained by mechanical forming.

A presente dissertação trata de um estudo teórico-experimental sobre a perda de pressão em canais de diâmetro reduzido durante escoamento bifásico de refrigerantes halogenados. Trocadores de calor baseados na ebulição convectiva, em condições de micro-escala são amplamente estudados devido à intensificação da troca de calor proporcionada e a possibilidade de compactação de sistemas de resfriamento. Proporcionam também a redução do inventário de refrigerante e do material utilizado no processo de fabricação do trocador. Porém, o incremento da transferência de calor é acompanhada pelo aumento da perda de pressão, parâmetro também fundamental para o desempenho do sistema. Para o projeto satisfatório e otimizado destes dispositivos são necessários métodos de previsão de transferência de calor e perda de pressão. Entretanto, no caso de canais de diâmetro reduzido, tais ferramentas não encontram-se disponíveis e trocadores de calor baseados em escoamentos bifásicos no interior de canais de diâmetro reduzido vêm sendo desenvolvidos heuristicamente. Desta forma, inicialmente neste estudo, realizou-se uma revisão crítica da literatura envolvendo critérios de transição entre padrões de escoamento, fração de vazio superficial, perda de pressão no interior de canais com diâmetro reduzido durante escoamento bifásico e os principais métodos de estimativa da perda de pressão para macro e micro-escala. Resultados experimentais para perda de pressão levantados neste estudo em condições adiabáticas para os fluidos R245fa e R134a e tubo com 1,1 mm de diâmetro interno foram descritos e comparados aos métodos preditivos encontrados na literatura. Finalmente um novo método da previsão da perda de pressão foi proposto baseado na correlação de Müller-Steinhagen e Heck (1986), ajustando os valores do coeficiente e do expoente com base nos resultados experimentais levantados. / A theorical and experimental study on two-phase pressure drop inside micro-scale channels has been developed. Recently, the study of flow boiling in micro-scale channel have received special attention from academia and industry due to several advantages that they offer such as minimization of fluid inventory, high degree of compactness of the heat exchangers, better performance and the capacity of dissipate extremely high heat fluxes. The significant heat transfer coefficient enhancement provided by micro-scale channels comes together with a huge pressure drop penalty that impacts the efficiency of the overall cooling system. So, accurate predictive methods to evaluate the pressure drop are necessary for the appropriate design of the system and for its optimization. In the present study, firstly, a critical review on studies from literature was performed that covers criteria of transition between micro- and macro-scale flow boiling, void fraction, frictional pressure drop on micro-scale channels and the leading frictional pressure drop predictive methods. Experimental pressure drop results were acquired under adiabatic conditions for R245fa and R134a fluids and internal diameter tube of 1.1 mm. Then, the leading pressure drop predictive methods were compared against the present database. Also a new correlation based on Muller-Steinhagen e Heck (1986) method was proposed in this work by adjusting new empirical constants based on the present database together with previous results obtained by Tibiriçá et al. (2011) for a 2.3 mm ID tube.