A study of the condensation of hydrocarbons and zeotropic hydrocarbon mixtures in smooth horizontal tubes was conducted. Measurements of condensation heat transfer coefficients and frictional pressure drop were taken over a range of mass fluxes (G = 150 – 450 kg m-2 s-1), a range of reduced pressures (Pr = 0.25 - 0.95), for two tube diameters (D = 7.75 and 14.45 mm), several working fluid-to-coolant temperature differences (ΔTLM = 3 – 14°C) and temperature glides (ΔTGlide) between 7 - 14°C. The wide range of conditions investigated in this study provides considerable insight on the transport phenomena influencing condensation in pure fluids and their mixtures. The trends in heat transfer coefficient and frictional pressure gradient are discussed and compared with the predictions of correlations from the literature. The results of the experiments, combined with previous flow visualization studies on hydrocarbons, were used to develop physically consistent heat transfer and frictional pressure gradient models that are applicable to pure fluids and zeotropic mixtures. A framework was developed for zeotropic mixture condensation that recommends a specific modeling approach based on the observed trends in the heat transfer coefficient and the points of deviations from pure fluid trends. The documentation of the condensation heat transfer and pressure drop behavior of environmentally friendly refrigerants, and the development of accurate correlations, will facilitate their widespread introduction as a working fluid for refrigeration cycles. Furthermore, the accurate pure fluid models, which serve as a baseline case for zeotropic mixture modeling, yield more effective predictions of zeotropic mixture condensation, which will lead to increased efficiencies of chemical processing plants.

Heat transfer and pressure drop during condensation of propane flowing through minichannels is investigated in this study. Studies of condensation of hydrocarbons are important for applications in the petrochemical industry. Insights into the mechanisms of propane condensation are required for accurate design of heat transfer equipment for use in hydrocarbon processing. At present, there is very little research on vertical condensation, especially of hydrocarbons, for the tube sizes and flow conditions of interest to the present study. An experimental facility was designed and fabricated to measure the frictional pressure drop and heat transfer coefficients during condensation of propane in plain tubes with an inner diameter of 1.93 mm. Measurements were taken across the vapor-liquid dome in nominal quality increments of 0.25 for two saturation temperatures (47°C and 74°C) and four mass flux conditions (75 – 150 kg m‾² s‾¹). The data were compared to the predictions of relevant correlations in the literature. The data from this study were also used to develop models for the frictional pressure drop and heat transfer coefficient based on the measurements and the underlying condensation mechanisms. These results and the corresponding correlations contribute to the understanding of condensation of hydrocarbons in vertical minichannels.

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.

In this study, radial solid density distributions in upward flowing water-feldspar mixtures through a concentric annulus were investigated. Local solid density measurements were performed at a test cross-section in the fully developed flow region of a concentric annulus, which is a part of a closed-loop system consisting of a head tank, a variable speed slurry pump, an orificemeter, a heat exchanger, an annulus, a temperature probe, and a drain line. The solid particles with mean diameters of 72 and 138 &amp / #61549 / m at two different feed solid concentrations of 1 and 2 % v/v were used in the prepared slurries. The dependent variables being local solid density, local mixture velocity, and axial frictional pressure drop along the test-section, an experimental work was performed to obtain the radial solid density profiles and axial pressure gradients at different operating conditions. To determine the local solid densities, a sampling probe was used. At the beginning, this probe was used as a pitot tube to measure the local velocities in the test cross-section. Making use of these data, local solid densities were measured with the same probe under isokinetic and nonisokinetic conditions to compare both. For this purpose, an isokinetic sampling unit was designed and constructed to withdraw the samples under isokinetic flow conditions, at which the sampling velocity in the probe equated to the true flow velocity in the annulus very closely. The required constant back-pressure was supplied by pressurized N2 gas to equate these velocities to each other. The amounts of solids in the slurry samples collected at seven different radial locations in the test area under isokinetic and non-isokinetic conditions were determined by the gravimetric method. Local solid densities showed more uniform trends at the feed solid concentration of 1% v/v than those at 2% v/v. Increasing the feed solid concentration and particle size changed the shape of these profiles. The obtained local solid densities were generally higher near the outer wall than those near the inner wall / this result was consistent with the literature. As a general trend, local solid densities showed a decreasing trend at around a dimensionless radial distance of &amp / #61548 / =0.4, where the slurry velocity profile had its maximum value. It was observed that the two-phase axial frictional pressure gradients along the test section in the fully developed flow region increased with increasing feed solid concentration and the particle size at a constant slurry flow rate. Isokinetic sampling results showed that the local solid densities increased consistently with the increasing slurry velocity at all radial distances in the annular gap, while this trend was not observed clearly in the non-isokinetic measurements. Also the variations of the local solid densities along the radial distance were more obvious in the isokinetic results while these variations were obscured under nonisokinetic conditions by the experimental error at a higher level.

An experimental investigation of condensation of hydrocarbons and hydrocarbon/refrigerant mixtures in horizontal tubes was conducted. Heat transfer coefficients and frictional pressure drops during condensation of a zeotropic binary mixture of R245fa and n-pentane in a 7.75 mm internal diameter round tube were measured across the entire vapor-liquid dome, for mass fluxes ranging from 150 to 600 kg m-2 s-1, and reduced pressures ranging from 0.06 to 0.23. Condensation experiments were conducted for the mixture, as well as its pure constituents over a similar range of conditions. In addition, condensing flow of the hydrocarbon propane was documented visually using high-speed video recordings. Results from these experiments were used to establish the two-phase flow regimes, void fractions, and liquid film thicknesses during condensation of propane flowing through horizontal tubes with internal diameters of 7 and 15 mm. These measurements were made over mass fluxes ranging from 75 to 450 kg m-2 s-1, operating pressures ranging from 952 to 1218 kPa, and vapor qualities ranging from 0.05 to 0.95. Liquid film thickness and void fraction data were subsequently be used to assist the development of heat transfer and pressure drop models. In particular, the heat transfer coefficients and pressure drops observed in the mixture were compared with the corresponding values for the pure constituents. Models for heat transfer and pressure drop in the pure components as well as the mixtures were developed based on the data from the present study. This work extends the available literature on two-phase flow regimes for air-water mixtures, steam, and refrigerants to include hydrocarbons. Additionally, the limited information on condensation in multi-constituent hydrocarbon-hydrocarbon and refrigerant-refrigerant mixtures was extended to include hydrocarbon-refrigerant mixtures. The findings of this study are expected to benefit applications such as refrigeration, low-grade heat-driven power generation, and the development of heat exchangers for the chemical and process industries.

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.