Influence of contact angle boundary condition on CFD simulation of T-Junction

“This is a post-peer-review, pre-copyedit version of an article published in Microgravity Science and Technology. The final authenticated version is available online at: https://doi.org/10.1007/s12217-018-9605-x ”.In this work, we study the influence of the contact angle boundary condition on 3D CFD simulations of the bubble generation process occurring in a capillary T-junction. Numerical simulations have been performed with the commercial Computational Fluid Dynamics solver ANSYS Fluent v15.0.7. Experimental results serve as a reference to validate numerical results for four independent parameters: the bubble generation frequency, volume, velocity and length. CFD simulations accurately reproduce experimental results both from qualitative and quantitative points of view. Numerical results are very sensitive to the gas-liquid-wall contact angle boundary conditions, confirming that this is a fundamental parameter to obtain accurate CFD results for simulations of this kind of problems.Peer ReviewedPostprint (published version

Generation of high-resolution surface temperature distributions

We have performed numerical calculations to study the generation of arbitrary temperature profiles with high spatial resolution on the surface of a solid. The characteristics of steady-state distributions and time-dependent heating and cooling cycles are examined, as well as their dependence on material properties and device geometry. Ideally, low-power consumption and fast response times are desirable. The simulations show that the achievable spatial resolution is on the order of the substrate thickness and that the response time t+ depends on the width of the individual heating elements. Moreover, the rise time t+ can be significantly shortened by deposition of a thermal insulation layer, which also reduces the power consumption and increases lateral resolution

ВЛИЯНИЕ ВЕНТИЛЯЦИОННОГО ОТВЕРСТИЯ В ОРОСИТЕЛЕ НА ТЕПЛОВУЮ РАБОТУ БАШЕННОЙ ИСПАРИТЕЛЬНОЙ ГРАДИРНИ В УСЛОВИЯХ ВЕТРА

Various aerodynamic design elements and technics (wind deflectors, wind walls, etc.) are utilized for improvement of the thermal efficiency of the natural draft cooling towers, particularly in conditions of cross wind. One of the technical methods, proposed by engineers of Belarus Academy of Sciences, is installation of the ventilation window in the center of the fill. This method is substantiated by the fact that the flow of cooling gas obtains maximum temperature and humidity near the center of the under-fill space of cooling tower and, as a consequence, performs minimal heat exchange. The influence of the fill ventilation window and wind deflectors in the inlet windows of the cooling tower on its thermal performance in condition of cross-wind is investigated in the paper numerically. The cooling tower of the “Woo-Jin” power plant (China) 150 m of the height and 114 m of the base diameter was taken as a prototype. The analogy (equivalence) between the heat and mass transfer was taken into consideration, which enabled us to consider single-phase flow and perform complicated 3D simulation by using modern personal computers. Heat transfer coefficient for the fill and its hydrodynamic resistance were defined by using actual data on total flow rate in the cooling tower. The numerical model and computational methods were tested and verified in numerous previous works. The non-linear dependence of the thermal performance of the cooling tower on wind velocity (with the minimum in vicinity of Ucr ~ 8 m/s for the simulated system) was demonstrated. Calculations show that in the condition of the average wind speed the fill ventilation window doesn’t improve, but slightly decrease (by 3–7 %) performance of the cooling tower. Situation changes in the condition of strong winds Ucw > 12 m/s, which are not typical for Belarus. Utilization of airflow deflectors at the inlet windows of cooling tower, conversely, increases thermal performance of the cooling tower on 10–12 % for the wide range of winds exceeding 2 m/s. Results of the investigation may be helpful for optimal design of natural draft and perspective “hybrid” cooling towers.Для улучшения тепловой работы башенных испарительных градирен, особенно в условиях ветровых нагрузок, могут использоваться разнообразные аэродинамические элементы и конструктивные решения (дефлекторы, ветроперегородки и т. п.). Одним из предложений, впервые сформулированных сотрудниками Национальной академии наук Беларуси, было сооружение центрального вентиляционного отверстия в оросителе градирни. Данное конструкционное решение обосновывалось тем, что паровоздушный поток вблизи центра подоросительного пространства градирни имеет максимум температуры и влагонасыщенности и вследствие этого слабо участвует в теплообмене. В статье численно исследуется влияние центрального вентиляционного отверстия в оросителе совместно с ветронаправляющими дефлекторами во входном окне градирни на ее тепловую работу в условиях ветра. В качестве прототипа взята градирня ТЭС «Ву-Джин», Китай, высотой 150 м и диаметром основания 114 м. При расчетах используется аналогия теплои массопереноса, что позволяет моделировать аэродинамику однофазного потока и выполнять детальные трехмерные расчеты на современных персональных вычислительных машинах. Коэффициент теплоотдачи оросителя и его гидродинамическое сопротивление устанавливаются в соответствии с экспериментальными данными по общему расходу воздуха в градирне. Численная модель протестирована и верифицирована в ряде предыдущих исследований. Продемонстрирована нелинейная зависимость тепловой производительности БИГ от скорости ветра с минимумом при Ucr ~ 8 м/с для моделируемой системы. Расчет показал, что при средних скоростях ветра устройство центрального отверстия не увеличивает, а наоборот, несколько уменьшает (на 3–7 %) эффективность работы градирни. Ситуация изменяется при очень сильных ветрах, превышающих 12 м/с, не характерных для условий Беларуси. Использование ветронаправляющих дефлекторов во входном окне градирни, напротив, увеличивает производительность градирни на 10–12 % в широком диапазоне скоростей ветра, превышающих 2 м/с. Результаты исследования могут быть полезны для оптимизации конструкции градирен, в том числе и перспективных градирен гибридного типа

Gas-liquid hydrodynamics in Taylor Flows with complex liquids

Universitá di Pisa Facoltá di Ingegneria Dipartimento di Ingegneria Chimica, Chimica Industriale e Scienza dei Materiali Relazione di tirocinio in Ingegneria Chimica Gas-liquid hydrodynamics in Taylor Flows with complex liquids Il candidato: Federico Alberini Il relatore: Prof. Elisabetta Brunazzi Controrelatore: Prof. Ing. Roberto Mauri Anno Accademico 2009-201

Comparació entre dades de simulacions numèriques 3D i experimentals en el procès de generació d’un tren gas-líquid en un capil·lar en forma de “T”

This document has been a study of the feasibility of a 3D numerical simulation on a two-phase flow in micro-gravity conditions. Specifically, the mixture of air and water in a T-shaped capillary in the absence of gravity. To accomplish our goals we have set all the parameters for numerical simulations (studio environment, fluids, simulation model...), we have performed tests of convergence for those who required it (temporary jump, mesh) and we have done studies to choose parameters such as the angle of contact between the tube and the interface. Once validated our simulations we performed the study. In this study we analysed the dependence of different parameters (velocity of the bubbles, characteristic lengths, average air volume fraction and frequency generation) with the velocity of the air. Once obtained these characteristic values, we have compared them with theoretical characterizations done by other studies and with results of actual experiments already published. From everything we have achieved in this procedure we have obtained conclusions in three different areas of work. First, we have managed to discover and delve into the world of numerical simulations and check the importance of the choice of parameters. From there we obtained results that have led us to conclude what were the values and trends of our study. And finally, we can also argue and discuss the comparison made with the theoretical characterizations and with the experiments already carried out

Two-Phase Pipe Flow in Microgravity with and without Phase Change: recent progress and future prospects

Gas-liquid and liquid-vapor pipe flows in microgravity have been studied for more than forty years because of theirpotential applications in space industries for thermal control of satellites, propellant supply for launchers, and wastewater treatment for space missions. Also, microgravity experiments provide unique conditions for highlighting and modeling capillary and inertia effects in the dynamics of two-phase flows. This paper discusses the results of flow pattern characterization, void fraction measurements, wall and interfacial shear stresses, and heat transfer coefficients. The main results are compared with ground experiments and classical correlations and models from the literature. Recent results from flow boiling in pipes are also discussed and perspectives on future studies are presented

Conflicts Related to Sexist US Advertisements and to Their Translation

This study discusses multiple conflicts within the context of advertising in relation to gender and translation, focusing on advertising in the US. To begin, it explores gender in advertising: First, it addresses the conflict between advertising (of the past and present)—a rather sexist industry—and subvertising, which includes the reconstruction of advertisements in order to criticize the original advertising messages. The next conflict arises between sexist representations of women in contemporary advertising and its audience’s increasing urge to break these rigid gender stereotypes, as critical comments on social media show. Furthermore, this paper focuses on the translation of advertising in relation to gender: More specifically, it analyzes the conflict between sexism in advertising language and the objectives of a translation process aimed at gender equality. Finally, it considers the feminist translator’s inner conflict, as they face the dilemma of creating either a profit-oriented translation or an equality-oriented translation, or even a possible combination of both

Adiabatic Gas-Liquid two-Phase Flow patterns

ABSTRACT Flow patterns of adiabatic gas-liquid two-phase flow in micro-channels were experimentally investigated. Using nitrogen and water, experiments were conducted in square micro-channels with hydraulic diameters of 0.209mm, 0.412mm and 0.622 mm, respectively. Gas and liquid superficial velocities were varied from 0.06-72.3 m/s and 0.02-7.13 m/s, respectively. Four defined flow patterns, bubbly-slug flow, slug-ring flow, dispersed-churn flow and annular flow, were observed in micro-channels of 0.412 mm and, 0.622 mm. In the micro-channel of 0.209 mm, the bubbly-slug flow became the slug-flow and the dispersed-churn flow disappeared due to the surface tension effect and the smooth gas-liquid interface. The flow regime maps for the current three microchannels were constructed and showed the transition lines shifted to higher gas superficial velocity due to the stronger surface tension effect with a smaller channel size in microchannels. They were also compared with some other microchannel flow regime maps and the mini-channel flow regime map based on the Weber number model, which showed the flow map for the micro-channel is significantly sensitive to the working fluid, channel geometry and channel size and the flow regime criteria developed for mini-channels should not be applied for micro-channels without further verification

Studies of Two-Phase Flow Dynamics and Heat Transfer at Reduced Gravity Conditions

The ability to predict gas-liquid flow patterns is crucial to the design and operation of two-phase flow systems in the microgravity environment. Flow pattern maps have been developed in this study which show the occurrence of flow patterns as a function of gas and liquid superficial velocities as well as tube diameter, liquid viscosity and surface tension. The results have demonstrated that the location of the bubble-slug transition is affected by the tube diameter for air-water systems and by surface tension, suggesting that turbulence-induced bubble fluctuations and coalescence mechanisms play a role in this transition. The location of the slug-annular transition on the flow pattern maps is largely unaffected by tube diameter, liquid viscosity or surface tension in the ranges tested. Void fraction-based transition criteria were developed which separate the flow patterns on the flow pattern maps with reasonable accuracy. Weber number transition criteria also show promise but further work is needed to improve these models. For annular gas-liquid flows of air-water and air- 50 percent glycerine under reduced gravity conditions, the pressure gradient agrees fairly well with a version of the Lockhart-Martinelli correlation but the measured film thickness deviates from published correlations at lower Reynolds numbers. Nusselt numbers, based on a film thickness obtained from standard normal-gravity correlations, follow the relation, Nu = A Re(sup n) Pr(exp l/3), but more experimental data in a reduced gravity environment are needed to increase the confidence in the estimated constants, A and n. In the slug flow regime, experimental pressure gradient does not correlate well with either the Lockhart-Martinelli or a homogeneous formulation, but does correlate nicely with a formulation based on a two-phase Reynolds number. Comparison with ground-based correlations implies that the heat transfer coefficients are lower at reduced gravity than at normal gravity under the same flow conditions. Nusselt numbers can be correlated in a fashion similar to Chu and Jones