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Статті в журналах з теми "Volume fraction of water vapor"
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Grabarczyk, Marcin, Mateusz Żbikowski, Łukasz Mężyk, and Andrzej Teodorczyk. "Temperature effect on explosion parameters of hydrogen-air deflagrations in presence of water vapor." Challenges of Modern Technology 7, no. 3 (September 29, 2016): 39–44. http://dx.doi.org/10.5604/01.3001.0009.5449.
Повний текст джерелаАнотація:
Results of investigation of hydrogen-air deflagrations phenomenon in closed vessel in various initial temperatures and volume fraction of water vapor are presented in following paper. Tests were performed in apparatus which construction complies with EN 15967 recommendations—20-litre sphere. Studied parameters were explosion pressure (Pex) and maximum explosion pressure (Pmax). Defining the influence of the initial conditions (temperature and amount of water vapor) on the maximum pressure of the hydrogen-air deflagration in a constant volume was the main aim. Initial temperatures were equal to 373K, 398K and 413K. Initial pressure was ambient (0.1 MPa). Hydrogen volume fraction differed from 15% to 80%, while humidity volume fraction from 0% to 20%. Ignition source was placed in geometrical center of testing chamber and provided energy between 10-20J from burnout of fuse wire with accordance to abovementioned standard. Common features of all experimentally obtained results were discussed. Maximum explosion pressure (Pmax) decreases with increasing the initial temperature. Furthermore, addition of the water vapor for constant initial temperature decreases value of Pmax and shifts the maximum peak to the direction of lean mixtures. Data provided in paper can be useful in assessment of explosion risk of industry installations working with hydrogen-air atmospheres with high water vapor addition.
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SU, Yongqiang, Jinfa SHI та Yahui WANG. "Numerical Simulation of Cavitation of Water Jet Nozzle Based on Realizable k-ε Model". Mechanics 28, № 1 (17 лютого 2022): 12–18. http://dx.doi.org/10.5755/j02.mech.28583.
Повний текст джерелаАнотація:
In order to study the cavitation characteristics of water jet nozzles, a realizable model was selected to simulate the flow field inside the nozzle at the inlet pressure of 15 MPa. The pressure at the starting point of the nozzle throat section dropped to the minimum, and the liquid velocity reached the maximum. From the vapor volume distribution map of the nozzle, it can be seen that the vapor fraction is the largest on the wall of the expansion section, and a local reflux is formed in the expansion section, which results in the gradual diffusion of the vapor fraction distribution along the wall of the expansion section. In addition, the influence of nozzle inlet pressure on the vapor fraction and vapor fraction distribution region in the expansion section is analyzed. The results show that the larger vapor fraction and vapor fraction distribution region can be produced under the 25 MPa inlet pressure. At the pressure inlet of 25 MPa, six groups of numerical simulations were carried out with different the length to diameter ratio of the nozzle throat section (L4/d0). The results show that when L4/d0 is 2, it is more conducive to the formation of cavitation and the quality of cavitation is better.
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Hu, Xiao, and Ye Gao. "Investigation of the Disk Cavitator Cavitating Flow Characteristics under Relatively High Cavitation Number." Applied Mechanics and Materials 29-32 (August 2010): 2555–62. http://dx.doi.org/10.4028/www.scientific.net/amm.29-32.2555.
Повний текст джерелаАнотація:
Simulations on two-phase cavitating flows containing water and vapor, on axisymmetric body with disk cavitator have been implemented through the cavitation model in Fluent 6.2, the flow field around cavitator under different incoming conditions is studied respectively, and analyses to parameters pertinent to cavity including dimension, streamlines, vapor volume fractions and pressure distributions along the body surface are given when the incoming cavitation number ranges from 0.3 to 0.8, the results show that the vapor volume fraction and threshold phase-change pressure within the cavity under the same cavitation number gradually ascends as the Reynolds number increases ; the effects of incoming pressure on threshold phase-change pressure inside the cavity is insignificant.
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Greco, Antonio, C. Esposito Corcione, and Alfonso Maffezzoli. "Water Vapor Permeability of Clay Nanocomposites Based on Amorphous PET." Defect and Diffusion Forum 297-301 (April 2010): 422–26. http://dx.doi.org/10.4028/www.scientific.net/ddf.297-301.422.
Повний текст джерелаАнотація:
In this work nanocomposites based on amorphous poly(ethylene terephthalate) (PETg) were developed using melt intercalation. X-ray analysis performed on the PETg nanocomposites showed that intercalation and exfoliation took place during static mixing. The water vapor permeability of PETg nanocomposites was correlated to the volume fraction of the impermeable inorganic part of the omMMT.
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Nielsen, O. F., M. Bilde, and M. Frosch. "Water Activity." Spectroscopy: An International Journal 27 (2012): 565–69. http://dx.doi.org/10.1155/2012/414635.
Повний текст джерелаАнотація:
Microorganisms require water for their metabolic activities. Only a fraction of water in foodstuffs, the so-called free water, is available for this purpose. The amounts of free water previously estimated by two different methods (Frosch et al. (2010), Frosch et al. (2011), and Low (1969)) are compared for aqueous solutions of four electrolytes, NaCl, NH4Cl, Na2SO4, (NH4)2SO4: (i) vapour pressure measurements of the solutions relative to that of pure water (water activities) and (ii) low-wavenumber Raman spectra in the R(ν)-representation. For each electrolyte deviations were found between results from the two methods. All water molecules in the illuminated volume contribute to the Raman data. The vapor pressure measurements refer to water molecules at the water/atmosphere interface where surface tension is important. Differences in surface tension for the four electrolytes qualitatively explain deviations between the amounts of “free water” observed by the two methods.
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Han, Xiangdong, Yong Kang, Deng Li, and Weiguo Zhao. "Effects of surface roughness on self-excited cavitating water jet intensity in the organ-pipe nozzle: Numerical simulations and experimental results." Modern Physics Letters B 33, no. 27 (September 30, 2019): 1950324. http://dx.doi.org/10.1142/s021798491950324x.
Повний текст джерелаАнотація:
This study was conducted to investigate effects of surface roughness on self-excited cavitating water jet intensity in an organ-pipe nozzle. Roughness average (Ra) values are 0.8, 1.6, 3.2, 6.3, 12.5, and 25 [Formula: see text]m, respectively. Numerical simulation results indicate that at inlet pressure of 10 MPa, the maximum, minimum, and real-time pressures in the self-excited oscillation chamber reach their respective peak values. The turbulent kinetic energy intensity in the external flow region is also most intense at this point, the vapor volume fraction in orifice is the highest, the vortex distribution scope in the orifice is the largest under [Formula: see text], and the self-excited cavitating water jet intensity is the strongest. The opposite variations emerge at [Formula: see text] compared to those of [Formula: see text], where the intensity is weakest. Pressure varies only slightly as Ra varies from 0.8 [Formula: see text]m to 6.3 [Formula: see text]m. Turbulent kinetic energy intensity behaves similarly as Ra increases from 0.8 [Formula: see text]m to 3.2 [Formula: see text]m. At [Formula: see text], it was weaker than at Ra = 0.8–3.2 [Formula: see text]m. Similarly, there are only slight differences in vapor volume fraction and vortex distribution scope with Ra from 0.8 [Formula: see text]m to 6.3 [Formula: see text]m. The intensities at Ra = 0.8–3.2 [Formula: see text]m are similar, and weaker at Ra = 6.3 [Formula: see text]m. Pressure values are maximal at inlet pressure of 20 MPa, turbulent kinetic energy intensity is most intense, vapor volume fraction is highest, vortex distribution scope is largest under [Formula: see text] [Formula: see text]m, and intensity is strongest. Distinctions among pressure, turbulent kinetic energy intensity, vapor volume fraction, and vortex distribution scope values with Ra from 0.8 [Formula: see text]m to 3.2 [Formula: see text]m are slight. Differences in the corresponding intensities are also slight; all decrease with Ra from 12.5 [Formula: see text]m to 25 [Formula: see text]m as the intensity gradually weakens. Numerical simulation results were validated by comparison against corresponding experimental phenomena.
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Tang, Pan, Juan Manzano Juárez, and Hong Li. "Investigation on the Effect of Structural Parameters on Cavitation Characteristics for the Venturi Tube Using the CFD Method." Water 11, no. 10 (October 22, 2019): 2194. http://dx.doi.org/10.3390/w11102194.
Повний текст джерелаАнотація:
The venturi tube is a special kind of pipe which has been widely applied in many fields. Cavitation is one of the most important research issues for the Venturi tube. Hence, three key structural parameters (contraction angle, diffusion angle and contraction ratio) were selected to investigate the influence of different factors on cavitation characteristics, using the computational fluid dynamics (CFD) method. A series of experiments for measuring the relationship between differential pressure and flow rate were carried out to verify the accuracy of the simulation method. Results showed that the simulation results had a high accuracy and the numerical method was feasible. The average vapor volume fraction of cross-section from the throat in the axial direction increased with increasing contraction angle. The cavity length increased with increasing contraction angle. The average volume fraction in the diffusion section rapidly decreased with increasing diffusion angle. The diffusion angle had no significant effect on the cavitation characteristics in the throat section and had a significant influence in the diffusion section. The average vapor volume fraction increased with decreasing contraction ratio. The contraction ratio had no significant effect on the cavity length under the same differential pressure. The average vapor volume fraction increased with decreasing contraction ratio. However, the variation in the throat section was less than the diffusion section. Under the same inlet and outlet pressure, the cavity lengths for different contraction ratios were basically the same, which indicated that the contraction ratio had no significant effect on the cavity length.
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Warren, B. A., and J. F. Klausner. "Developing Lengths in Horizontal Two-Phase Bubbly Flow." Journal of Fluids Engineering 117, no. 3 (September 1, 1995): 512–18. http://dx.doi.org/10.1115/1.2817292.
Повний текст джерелаАнотація:
An air-water two-phase flow facility with a 19.1 mm i.d. test section has been fabricated. Local measurements of pressure drop for two-phase horizontal bubbly flow and single-phase flow downstream of various orifices have been obtained over a range of flow conditions. The wall shear stress developing length is obtained from the pressure drop profile. A developing length correlation is presented in which the relative deviation is 6 percent. The fully developed vapor volume fraction has also been measured up- and downstream of the orifice. A simple correlation for vapor volume fraction is presented in which the relative deviation is 7 percent. Photographs of the two-phase flow pattern in the developing region reveal that the flow structure is extremely complex and continuously evolves until approximately fully developed flow conditions are achieved.
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Dhar, BK, SK Mahapatra, SK Maharana, A. Sarkar, and SS Sahoo. "Numerical study on phase change of water flowing across two heated rotating circular cylinders in tandem arrangement." Journal of Computational Multiphase Flows 8, no. 4 (October 24, 2016): 201–12. http://dx.doi.org/10.1177/1757482x16674218.
Повний текст джерелаАнотація:
The problems of fluid flow and heat transfer phenomena over an array of cylinders are quite prominent in fluid dynamics and industry applications. The current work focuses on fluid flow and heat transfer analysis over two heated rotating cylinders arranged in tandem. The flow of water over heated cylinders faces a phenomenon of phase change from liquid (water) to vapor phase (steam). The mechanism of this phase change is studied through a numerical simulation supplemented with verification of the code and validation. The problem is simulated when flows from two cylinders in a tandem arrangement become interacting and non-interacting. The Eulerian model is used during simulation to comprehend the multiphase phenomena. The volume fractions of both the phases such as water and vapor and heat transfer coefficients of both the cylinders have been computed and presented as findings of the problem. The mass and heat transfer mechanism is unidirectional from one phase to the other phase. The vapor fraction of each phase is to be observed and compared when three different rotations are given to the two cylinders immersed in a turbulent flow of water.
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Yousef, Khaled, Ahmed Hegazy, and Abraham Engeda. "Experimental and CFD Investigation into Using Inverted U-Tube for Gas Entrainment." Applied Sciences 10, no. 24 (December 18, 2020): 9056. http://dx.doi.org/10.3390/app10249056.
Повний текст джерелаАнотація:
An experimental and numerical study is presented in the current work for gas entrainment using an inverted vertical U-tube. Water flows vertically up in an inverted U-tube which creates a low-pressure region in the tube upper portion. This low-pressure region can be used to extract gases by connecting it to a branch pipe. The extracted gases considered in this work are a mixture of air and water vapor. The water vapor from the side branch pipe is mixed with the flowing water under the siphon effect. This results in a progressive water vapor condensation as the mixture proceeds towards the exit due to an increase in vapor partial pressure. The air is drawn by inertia to be released out at the tube lower exit of the inverted U-pipe. The current study deals with these complicated flow behaviors due to the mixing undergoing condensation. A test rig is designed for experimentally studying the behavior of water flow in an inverted U-tube where the air is mixed with the flowing water at the top region of this tube. The CFD computations are accomplished for a side gas mixture with volume fractions up to 0.7 with water vapor mass fractions in this mixture to be 0.1–0.5. The tested water mass flow rates in the main tube are 2, 4, 6, 8 kg/s to account for all possible flow mass ratios. The CFD computations are validated with water and air two phase flow with the measurements of both the experiments of the current research and the literature. The present results reveal that slightly raising the water mass flow rate at a constant side mixture mass ratio produces a reduced generated pressure in the upper tube part. This is attributed to extra water vapor condensation taking place rapidly by increasing the water flow rate in the tube upper part. Furthermore, the turbulence quantities begin to break down at a side mixture volume fraction of 0.55 with water and air mass flow rates of 2 kg/s and 0.002 kg/s, respectively. On the other side, raising the air mass flow rate at the higher values of water vapor and water mass flow rates breaks the generated vacuum pressure and turbulence due to entrainment. Moreover, this proposed framework can produce a lower static pressure, reaching 55.1 kPa, which makes it attractive for gas extraction. This new technique presents innovative usage with less consumable energy for extracting gases in engineering equipment.
Дисертації з теми "Volume fraction of water vapor"
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Рачинський, Артур Юрійович. "Гідродинаміка і тепломасообмін в контактному утилізаторі теплоти газокрапельного типу". Thesis, КПІ ім. Ігоря Сікорського, 2017. https://ela.kpi.ua/handle/123456789/19313.
Повний текст джерелаАнотація:
Роботу присвячено експериментальним дослідженням, що направлені на підвищення ефективності роботи контактних тепломасообмінних апаратів шляхом збільшення міжфазної поверхні тепломасообміну при розпилені рідини відцентровими форсунками, впровадження яких приводить до суттєвої економії матеріальних та енергетичних ресурсів. Виконано комплексні експериментальні дослідження характеристик факелу розпилу рідини (густини зрошення, кута розкриття факела форсунки, середнього об’ємно-поверхневого діаметра крапель рідини). Встановлено вплив вхідних параметрів на відповідні характеристики та визначено площу поверхні крапель розпиленої рідини. Експериментально встановлено значення граничної температури нагріву води та її залежність від початкового паровмісту, при якій вода нагрівається до граничної температури в залежності від початкового паровмісту й витрати сухого повітря. Визначено параметричні границі ефективного використання відцентрової механічної форсунки без випаровування крапель нагрітої рідини. Експериментально досліджено інтенсивність тепло- і масоовіддачі в контактному апараті газокрапельного типу з відцентровою форсункою в умовах утилізації теплоти відхідних газів енергетичних агрегатів. Вперше отримано емпіричні залежності для розрахунку середніх коефіцієнтів тепловіддачі та масовіддачі, які відносяться до дійсної поверхні крапель розпиленої води. Встановлено особливості процесів переносу в газокрапельній системі та отримано узагальнювальні залежності для процесів тепло- і масовіддачі. На основі експериментальних досліджень характеристик розпилу та процесів тепломасообміну при конденсації пари з парогазової суміші на краплях розпиленої рідини розроблено методику розрахунку крапельного контактного утилізаційного апарату.Dissertation is devoted to experimental research, aimed at improving the efficiency of contact heat and mass transfer units by increasing the interfacial surface of heat and mass transfer during the liquid spraying by centrifugal nozzles, implementation of which results in significant savings of material and energy resources. Comprehensive experimental study of the characteristics of the liquid spraying torch (irrigation density, expansion angle of nozzle torch, the average volume-surface diameter of liquid droplets) was done. The influence of input parameters to the relevant properties was shown and surface area of the sprayed liquid droplets was defined. The limit temperature of water heating and its dependence on initial vapor content in which water is heated to the limit temperature depending on the initial vapor content and dry air output were experimentally set. The parametric borders of effective use of centrifugal mechanical nozzle without evaporation of heated liquid drops were defined. Intensity of heat and mass transfer in the contact gas-droplet unit with centrifugal nozzle in terms of heat utilization of energy units’ exhaust gases was experimentally researched. The empirical dependences for calculating the average heat transfer and mass transfer coefficients relating to the actual surface of the sprayed liquid droplets are obtained for the first time. The peculiarities of transfer processes in the gas-droplet system were determined and generalized dependence for heat and mass transfer were received. Based on experimental studies of spraying characteristics and heat and mass transfer processes at vapor condensation from vapor-gas mixture on the sprayed liquid droplets, the method of calculating the droplet contact utilization unit was developed.
Диссертация посвящена исследованиям, направленным на повышение эффективности работы контактных аппаратов путем увеличения межфазной поверхности теплообмена путем распыления жидкости, внедрение которых приводит к существенной экономии материальных и энергетических ресурсов. Работа содержит результаты экспериментальных исследований характеристик распыла и процессов тепломассоотдачи при конденсации пара из парогазовой смеси на каплях распыленной жидкости. Исследовано влияние температуры и давления воды на тонкость распыла (величину среднего объемно-поверхностного диаметра капель) для центробежной форсунки в параметрических условиях ее работы и применительно к условиям работы контактного утилизатора теплоты отходящих газов. На основании проведенных опытов получены новые зависимости величины среднего объемно-поверхностного диаметра капель для параметров распыливания жидкости с помощью центробежной форсунки в новом диапазоне изменения избыточного давления и температуры воды перед форсункой. В результате теоретического анализа движения капель жидкости в факеле распыления центробежной форсунки и использования экспериментальных данных по средним объемно-поверхностным диаметрам капель предложена методика определения действительной межфазной поверхности процессов тепломассообмена в контактных газожидкостных аппаратах капельного типа. Экспериментально определена зависимость граничной температуры нагрева воды в контактном аппарате газокапельного типа с центробежной форсункой применительно к условиям утилизации теплоты отходящих газов энергетических агрегатов. Исследования проведены в диапазоне избыточных давлений воды перед форсункой (0,2–0,6) МПа и объемной доли водяных паров парогазовой смеси на входе в аппарат от 0,02 до 0,45. Показано использование полученной зависимости для рас чета предельных значений параметров парогазового потока, ограничивающих область эффективной работы контактного аппарата с конденсацией пара и отсутствием режима испарения капель нагретой жидкости. Экспериментально определена интенсивность тепло- и массоотдачи в контактном аппарате газокапельного типа с центробежной форсункой в условиях утилизации теплоты отходящих газов энергетических агрегатов. Исследование проведены в диапазоне избыточного давления воды перед форсункой (0,2 - 0,6) МПа и объемной долей водяного пара парогазовой смеси на входе в аппарат от 0,08 до 0,35. По результатам экспериментальных исследований определены коэффициенты тепло- и массоотдачи, которые были отнесены к реальной поверхности капель. Полученные в работе результаты экспериментальных исследований коэффициентов тепло- и массоотдачи сравнивались с известными литературными данными для одиночной капли. Установлено, что интенсивность теплоотдачи для капель жидкости с парогазовым потоком выше, чем для одиночной капли, а для массоотдачи, ниже. Установлены особенности процессов переноса в газокапельной системе и получены обобщающие зависимости для процессов тепло- и массообмена для факела капель конуса распыла. В результате указанного комплекса работ предложена методика теплового расчета контактного газокапельного утилизатора теплоты низкотемпературных отходящих газов при распылении жидкости механической центробежной форсункой, которая учитывает реальные условия протекания процессов переноса в рассматриваемой двухфазной системе. Приведенная процедура теплового расчета утилизационной установки позволяет при заданных параметрах отходящих газов и воды на входе получить тип и количество распылителей для генерирования капель воды, выполнить компоновку в штатном коробе для отвода газов, рассчитать параметры теплоносителей на выходе с установки и определить ее теплопроизводительность.
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Рачинський, Артур Юрійович. "Гідродинаміка і тепломасообмін в контактному утилізаторі теплоти газокрапельного типу". Doctoral thesis, Київ, 2017. https://ela.kpi.ua/handle/123456789/19312.
Повний текст джерелаАнотація:
Роботу присвячено експериментальним дослідженням, що направлені на підвищення ефективності роботи контактних тепломасообмінних апаратів шляхом збільшення міжфазної поверхні тепломасообміну при розпилені рідини відцентровими форсунками, впровадження яких приводить до суттєвої економії матеріальних та енергетичних ресурсів. Виконано комплексні експериментальні дослідження характеристик факелу розпилу рідини (густини зрошення, кута розкриття факела форсунки, середнього об’ємно-поверхневого діаметра крапель рідини). Встановлено вплив вхідних параметрів на відповідні характеристики та визначено площу поверхні крапель розпиленої рідини. Експериментально встановлено значення граничної температури нагріву води та її залежність від початкового паровмісту, при якій вода нагрівається до граничної температури в залежності від початкового паровмісту й витрати сухого повітря. Визначено параметричні границі ефективного використання відцентрової механічної форсунки без випаровування крапель нагрітої рідини. Експериментально досліджено інтенсивність тепло- і масоовіддачі в контактному апараті газокрапельного типу з відцентровою форсункою в умовах утилізації теплоти відхідних газів енергетичних агрегатів. Вперше отримано емпіричні залежності для розрахунку середніх коефіцієнтів тепловіддачі та масовіддачі, які відносяться до дійсної поверхні крапель розпиленої води. Встановлено особливості процесів переносу в газокрапельній системі та отримано узагальнювальні залежності для процесів тепло- і масовіддачі. На основі експериментальних досліджень характеристик розпилу та процесів тепломасообміну при конденсації пари з парогазової суміші на краплях розпиленої рідини розроблено методику розрахунку крапельного контактного утилізаційного апарату.
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Ghodsinezhad, Hadi. "Experimental investigation on natural convection of AI2O3-water nanofluids in cavity flow." Diss., University of Pretoria, 2016. http://hdl.handle.net/2263/61292.
Повний текст джерелаАнотація:
The thermophysical properties of nanofluids have attracted the attention of researchers to a far greater extent than the heat transfer characteristics of nanofluids have. Contradictory results on the thermal-fluid behaviour of nanofluids have been numerically and experimentally reported on in the open literature. Natural convection has not been investigated experimentally as much as the other properties of nanofluids. In this study, the characteristics and stability of Al2O3-water nanofluids (d = 20 30 nm) were analysed using a Malvern zetasizer, zeta potential and UV-visible spectroscopy. The natural convection of Al2O3- water nanofluids (formulated with a single-step method) was experimentally studied in detail for the volume fractions 0, 0.05, 0.1, 0.2, 0.4 and 0.6% in a rectangular cavity with an aspect ratio of 1, heated differentially on two opposite vertical walls for the Rayleigh number (Ra) range 3.49 x 10⁸ to 1.05 x 10⁹. The viscosity of Al2O3-water nanofluids measured between 15 and 50 °C. The effect of temperature and volume fraction on viscosity was also investigated. A detailed study of the nanoparticle concentration effect on the natural convection heat transfer coefficient was performed. It was found that increasing the concentration of nanoparticles improves the heat transfer coefficient by up to 15% at a 0.1% volume fraction. Further increasing the concentration of nanoparticles causes the natural convection heat transfer coefficient to deteriorate. This research also supports the idea that "for nanofluids with thermal conductivity more than the base fluids an optimum concentration may exist that maximises heat transfer in an exact condition as natural convection, laminar force convection or turbulence force convection".Dissertation (MEng)--University of Pretoria, 2016.
Mechanical and Aeronautical Engineering
MEng
Unrestricted
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Ottermann, Tanja Linda. "Experimental and numerical investigation into the natural convection of TiO2-water nanofluid." Diss., University of Pretoria, 2016. http://hdl.handle.net/2263/61323.
Повний текст джерелаАнотація:
This Master of Engineering investigation focuses on the natural convection of nanofluids in rectangular cavities. The governing equations applied to analyse the heat transfer and fluid flow occurring within the cavity are given and discussed. Special attention is given to the models that were developed to predict the thermal conductivity and dynamic viscosity of such nanofluids.
A review concerning past investigations into the field of natural convection of nanofluids in cavities is made. The investigation is divided into experimental works and computational fluid dynamics (CFD) numerical investigations.
Through the literature review, it was discovered that many numerical models exist for the prediction of the thermophysical properties of nanofluids, specifically thermal conductivity and viscosity. Depending on the nanofluid and the application, different models can be used.
The literature study also revealed that most previous works were done in the CFD field. Very few experimental studies have been performed. Numerical CFD investigations, however, need experimental results for validation purposes, leading to the conclusion that more experimental work is needed.
The heat transfer capability and thermophysical properties of the nanofluid are investigated based on models found in literature. The investigation incudes measuring the heat transfer inside a cavity filled with a nanofluid and subjected to a temperature gradient. The experiment is performed for several volume fractions of particles. An optimum volume fraction of 0.005 is obtained. At this volume fraction the heat transfer enhancement reaches a maximum for the present investigation.
The investigation is repeated as a numerical investigation using the commercially available CFD software ANSYS-FLUENT. The same case as used in the experimental investigation is modelled as a two-dimensional case and the results are compared. The same optimum volume fraction and maximum heat transfer is obtained with an insignificantly small difference between the two methods of investigation. This error can be attributed to the minor heat losses experienced from the experimental setup as in the CFD adiabatic walls considered. It is concluded that, through the inclusion of TiO2 particles in the base fluid (deionised water), the thermophysical properties and the heat transfer capability of the fluid are altered. For a volume fraction of 0.005 and heat transfer at a temperature difference of 50 °C, the heat transferred through the fluid in the cavity is increased by more than 8%.
From the results, it is recommended that the investigation is repeated with TiO2 particles of a different size to determine the dependency of the heat transfer increase on the particle size. Various materials should also be tested to determine the effect that material type has on the heat transfer increase.Dissertation (MEng)--University of Pretoria, 2016.
Mechanical and Aeronautical Engineering
MEng
Unrestricted
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Dahlbäck, Per. "Modeling a novel sorption dehumidication method : super saturation of water vapour in a closed volume using the finite volume method." Thesis, Uppsala universitet, Avdelningen för beräkningsvetenskap, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-208511.
Повний текст джерелаАнотація:
This thesis develops and evaluates a method to simulate energy consumption and water production for a novel sorption dehumidication pro-cess. The system consists of a chamber comprising a hygroscopic materialand a heating device. The process consists of an adsorption phase anda regeneration phase. For both the regeneration phase and the adsorp-tion phase the model considers the heat distribution by thermal diusionand convection and the water transport by diusion and convection. Forthe regeneration phase the radiation is also considered since the radia-tive power increases with temperature to the power of four. Further, amodel for the condensation process is implemented and a model for thecondensation is suggested. To model the properties of the hygroscopicmaterials, the adsorption curves for SiO2 and AlO2 are investigated. Themodel were evaluated by comparing the simulated values with experimen-tal measurements.The results from the the simulation of the regeneration phase showsa good agreement with experimental data for the power and the energyconsumption even though the simulated values are a bit underestimated,about 10%. The water production is simulated to be about 25% higherthan the measured values. This discrepancy could be explained by aleakage of water vapour that was found in the experimental set up, whichis not considered in the model. This could also explain the underestimatedenergy consumption since the condensation energy in the system is toogreat. To improve the accuracy for the model the water leakage wouldneed to be implemented. The overestimation of water seemed to be thesame for the measurements from the same apparatus.For the adsorption phase a developed model, from an article for ad-sorption in silica, was implemented and tuned for the specic system. Thesimulations are in good agreement with the measurements but could betested further for more certainty.
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Beyer, M., D. Lucas, J. Kussin, and P. Schütz. "Air-water experiments in a vertical DN200-pipe." Forschungszentrum Dresden, 2011. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-74486.
Повний текст джерелаАнотація:
The extensive experimental results presented in this report provide a high-quality database for air-/water flows in a vertical pipe with a nominal diameter of 200 mm. This database can be used for the development and validation of CFD-like models for two-phase flows, e.g. for bubble coalescence and fragmentation. In particular, the investigations aim on the evolution of the two-phase flow along the pipe height. Therefore, up to 18 single measurements with varying distances between the gas injection and measurement plane were realised for each of the 92 combinations of gas and water flow rates. The pressure at the position of the activated gas injection was kept constant at 0.25 MPa(a). This boundary condition has the advantage that the measured data represent exactly the evolution of the flow along the pipe, i.e. they reflect a configuration at which the gas injection is at a fixed height position, while the measurement plane varies. Important results of this test series are time averaged radial profiles of the gas fraction, and the gas velocity, as well as the time and cross-section averaged bubble size distributions. Furthermore, gas fraction data resolved regarding the bubble size and spatial distribution are presented. As in previous test series, flow patterns were analysed, whereby the classification results from the bubble size. A substantial part of these new air/water experiments were quality and plausibility checks of the measured data. In the result, a clear and consistent trend regarding their evolution with increasing distance from the position of the gas injection was found. Comparisons of the trend of time and cross section averaged gas volume fraction along the pipe height with the theoretically expected values were carried out. The influence of the orifice diameter of the gas injection on flow patterns is also discussed in the report.
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Beyer, M., D. Lucas, J. Kussin, and P. Schütz. "Air-water experiments in a vertical DN200-pipe." Forschungszentrum Dresden-Rossendorf, 2008. https://hzdr.qucosa.de/id/qucosa%3A22143.
Повний текст джерелаАнотація:
The extensive experimental results presented in this report provide a high-quality database for air-/water flows in a vertical pipe with a nominal diameter of 200 mm. This database can be used for the development and validation of CFD-like models for two-phase flows, e.g. for bubble coalescence and fragmentation. In particular, the investigations aim on the evolution of the two-phase flow along the pipe height. Therefore, up to 18 single measurements with varying distances between the gas injection and measurement plane were realised for each of the 92 combinations of gas and water flow rates. The pressure at the position of the activated gas injection was kept constant at 0.25 MPa(a). This boundary condition has the advantage that the measured data represent exactly the evolution of the flow along the pipe, i.e. they reflect a configuration at which the gas injection is at a fixed height position, while the measurement plane varies. Important results of this test series are time averaged radial profiles of the gas fraction, and the gas velocity, as well as the time and cross-section averaged bubble size distributions. Furthermore, gas fraction data resolved regarding the bubble size and spatial distribution are presented. As in previous test series, flow patterns were analysed, whereby the classification results from the bubble size. A substantial part of these new air/water experiments were quality and plausibility checks of the measured data. In the result, a clear and consistent trend regarding their evolution with increasing distance from the position of the gas injection was found. Comparisons of the trend of time and cross section averaged gas volume fraction along the pipe height with the theoretically expected values were carried out. The influence of the orifice diameter of the gas injection on flow patterns is also discussed in the report.
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Pereira, Cléber Carvalho. "Estudo experimental e modelagem do escoamento estratificado ondulado óleo-água." Universidade de São Paulo, 2011. http://www.teses.usp.br/teses/disponiveis/18/18147/tde-15052011-101158/.
Повний текст джерелаАнотація:
O escoamento estratificado óleo-água é bastante comum na indústria do petróleo, especialmente em poços direcionas offshore, oleodutos e gasodutos. Entretanto, existem poucos trabalhos na literatura sobre a natureza da estrutura ondulatória observada no escoamento em dutos ascendentes ou descendentes a partir da horizontal. O objetivo deste trabalho foi estudar as propriedades geométricas e cinemáticas da onda interfacial, i.e, forma média, comprimento, amplitude e celeridade, e assim contribuir para a compreensão do papel da onda interfacial na dinâmica do escoamento estratificado. Um software baseado em plataforma Labview® possibilitou a automação para obtenção dos dados das ondas interfaciais extraídas de imagens de vídeos de alta resolução. Além das propriedades das ondas, também se coletaram valores de fração volumétrica in situ e de gradiente de pressão bifásico para cinco ângulos de inclinação (-20°, -10°, 0°, 10° e 20°) em diferentes pares de vazões de óleo e água. Desenvolveu-se um modelo fenomenológico considerando os termos ondulatórios do escoamento para o cálculo da fração volumétrica in situ e do gradiente de pressão bifásico, sendo comparado com modelos disponíveis na literatura e dados experimentais. A concordância do modelo proposto com os dados coletados neste trabalho se mostrou muito boa, o que sugere um avanço em comparação ao existente na literatura. O estudo da equação da onda de perturbação interfacial para o escoamento estratificado óleo-água indicou que a natureza da onda observada é cinemática e não dinâmica; e baseado na equação da celeridade da onda cinemática pode-se confrontar a celeridade experimental com a teórica, revelando boa concordância.The oil-water stratified flow is quite common in the oil industry, especially in offshore directional wells and pipelines. However, there are few studies on the physics of the wavy structure observed in upward and downward stratified flow. The goal of this work was to study the geometric and kinematic properties of interfacial waves, i.e., the average shape, wavelength, amplitude and celerity. A homemade Labview®-based software enabled the automatic acquisition of data extracted from frames obtained via high resolution video recording. In situ volume fraction and two-phase pressure gradient data for five inclination angles (-20°, -10°, 0°, 10° and 20°) at several pairs of oil and water flow rates were also collected. A phenomenological model that takes into account the wavy structure is proposed to calculate volume fractions and two-phase pressure gradient and it was compared with available models from the literature and experimental data. The good agreement of the proposed model with the data collected in this study is promising and suggests that it may provide better predictions in comparison with models from the literature. The study of the interfacial perturbation wave equation for stratified flow indicates that the observed waves nature is kinematic and not dynamic; and based on the kinematic wave velocity equation we could compare the experimental celerity with the theoretical one, with good agreement.
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Boháček, Jan. "EFFECT OF FLOW PARAMETERS OF WATER AND AIR ATOMIZED SPRAYS ON COOLING INTENSITY OF HOT SURFACES." Doctoral thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2011. http://www.nusl.cz/ntk/nusl-233959.
Повний текст джерелаАнотація:
Práce komplexně popisuje vodní a vodovzdušné chlazení pomocí metod CFD (Computational Fluid Dynamics) konkrétně s využitím software ANSYS FLUENT. Skládá se ze dvou hlavních částí, z nichž první se zabývá numerickým popisem jediné vodní kapky a druhá popisem směsí kapek představující paprsek válcové a ploché trysky. Je založena převážně na vícefázových modelech proudění a vlastních uživatelsky definovaných funkcí (User Defined Functions, UDF) představujících stěžejní část práce. Uvedené výpočtové modely jsou ve většině případů verifikovány pomocí experimentálních dat nebo jiných numerických modelů. V první části práce jsou teoreticky postupně rozebrány všechny tři použité vícefázové modely proudění. První z nich, Volume Of Fluid model (VOF), byl použit pro modelování jediné kapky (mikromodel). Zatímco zbývající dva, Euler-Euler model a Euler-Lagrange model, byly aplikovány v modelu celého paprsku trysky (makromodel). Mikromodel popisuje dynamiku volného pádu vodní kapky. Pro malé průměry kapek (~100µm) standardní model povrchového napětí (Continuum Surface Force, CSF) způsoboval tzv. parazitní proudy. Z toho důvodu je v práci rozebrána problematika výpočtu normál, křivostí volných povrchů a povrchového napětí jako zdroje objemových sil v pohybových rovnicích. Makromodel se zabývá studiem dynamiky celého paprsku tj. oblastí od ústí trysky po dopad na horký povrch, bere v úvahu kompletní geometrii, tzn. např. podpůrné válečky, bramu, spodní část krystalizátoru apod. V práci je rozebrána 2D simulace dopadu paprsku válcové trysky pomocí VOF modelu Euler-Lagrange modelu na horký povrch. Pro případ s VOF modelem byl navržen model blánového varu. Euler-Euler model a Euler-Lagrange model byly využity pro simulaci paprsku ploché trysky horizontálně ostřikující horkou bramu přímo pod krystalizátorem nad první řadou válečků. Pro Euler-Euler model byl navržen model sekundárního rozpadu paprsku založený na teorii nejstabilnější vlnové délky (Blob jet model). Jelikož diskrétní Lagrangeovy částice tvořily v určitých místech spíše kontinuální fázi, byl navržen a otestován model pro konverzi těchto částic do VOF.
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Hamad, Faik A., S. He, M. Khurshid Khan, and Hans H. Bruun. "Development of kerosene–water two-phase up-flow in a vertical pipe downstream of A 90° bend." 2011. http://hdl.handle.net/10454/9515.
Повний текст джерелаАнотація:
NoThe development of kerosene–water up-flow in a vertical pipe of 77.8 mm inner diameter and 4500 mm, length downstream of a 90◦bend, hasbeen investigated using a Pitot tube and dual optical probe. The CFD ANSYS Fluent 12.0 is used to model the flow and the results are comparedwith experimental data. The CFD provides detailed information on flow structure which is difficult to obtain in experiments. The experimentalmeasurements of the local parameters demonstrate that the single phase and two-phase flows reached the fully developed axisymmetricalconditions at L/D = 54. These results also show the severe asymmetry distributions of the two-phase flow parameters at the entrance region(L/D = 1). The predictions from Fluent are found to be in close agreement with experimental data for L/D ≥ 16 but there is a significant discrepancyat L/D = 1.
Книги з теми "Volume fraction of water vapor"
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Bansal, Narottam P. CVD silicon carbide monofilament reinforced SrO-Al₂O₃-2SiO₂ (SAS) glass-ceramic composites. [Washington, D.C.]: National Aeronautics and Space Administration, 1995.
Знайти повний текст джерела
2
Mihaylov, Vyacheslav, Elena Sotnikova, and Nina Kalpina. Eco-friendly air protection systems for motor transport facilities. ru: INFRA-M Academic Publishing LLC., 2022. http://dx.doi.org/10.12737/1093106.
Повний текст джерелаАнотація:
The textbook considers the issue of assessing the heat and humidity state of air in the processes of its processing in various systems, provides requirements for air protection means, taking into account their environmental friendliness, shows ways of energy saving in cooling, heating and year-round air conditioning systems, as well as when protecting the atmosphere from harmful emissions. The way of energy saving with individual thermal protection of the operator by means of local cooling during air treatment in an irrigated intensified nozzle is shown and recommendations for reducing its material consumption are developed. The method and means of reducing the toxicity of emissions of tractor internal combustion engines during its operation in rooms of limited volume by water vapor humidification of the fuel-air mixture are demonstrated. The ways of noise reduction of air protection systems are shown.
Meets the requirements of the federal state educational standards of higher education of the latest generation.
It is intended for students studying in the specialties "Ground transport and technical means", "Operation of transport and technological machines and complexes", "Power engineering", "Ground transport and technological complexes", "Refrigeration, cryogenic equipment and life support systems", "Technosphere safety", "Ecology and nature management".
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Geodetic Mobile Solar Spectrometer. (Geodatisch-geophysikalische Arbeiten in der Schweiz, Achtundsechzigster Band, Volume 68). Institut fur Geodasie & Photogrammetrie, 2005.
Знайти повний текст джерелаЧастини книг з теми "Volume fraction of water vapor"
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Ding, Nan, Shubi Zhang, Xin Liu, and Yili Xia. "Voxel Nodes Model Parameterization for GPS Water Vapor Tomography." In China Satellite Navigation Conference (CSNC) 2017 Proceedings: Volume I, 233–42. Singapore: Springer Singapore, 2017. http://dx.doi.org/10.1007/978-981-10-4588-2_20.
Повний текст джерела
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Liu, Zhimin, Yangyang Li, Fei Li, and Jinyun Guo. "Estimation and Evaluation of the Precipitable Water Vapor from GNSS PPP in Asia Region." In China Satellite Navigation Conference (CSNC) 2017 Proceedings: Volume I, 85–95. Singapore: Springer Singapore, 2017. http://dx.doi.org/10.1007/978-981-10-4588-2_8.
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Valdés, Julio J., Antonio Pou, and Yaimara Céspedes-González. "Process Mining Capabilities Extended to Time Series Analysis as Applied to Meteosat Water Vapor Images." In Proceedings of the Future Technologies Conference (FTC) 2021, Volume 1, 650–67. Cham: Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-89906-6_43.
Повний текст джерела
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Jing, Chunguo, Guangzhong Xing, Bin Liu, and Qiuguo Bai. "Determination of Gas and Water Volume Fraction in Oil Water Gas Pipe Flow Using Neural Networks Based on Dual Modality Densitometry." In Advances in Neural Networks - ISNN 2006, 1248–53. Berlin, Heidelberg: Springer Berlin Heidelberg, 2006. http://dx.doi.org/10.1007/11760191_182.
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Li, Li, Zhimin Yuan, Ping Luo, Jun Shen, Sichun Long, Liya Zhang, and Zongli Jiang. "A System Developed for Monitoring and Analyzing Dynamic Changes of GNSS Precipitable Water Vapor and Its Application." In China Satellite Navigation Conference (CSNC) 2015 Proceedings: Volume I, 95–105. Berlin, Heidelberg: Springer Berlin Heidelberg, 2015. http://dx.doi.org/10.1007/978-3-662-46638-4_10.
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Brock, Fred V., and Scott J. Richardson. "Hygrometry." In Meteorological Measurement Systems. Oxford University Press, 2001. http://dx.doi.org/10.1093/oso/9780195134513.003.0007.
Повний текст джерелаАнотація:
The objective of atmospheric humidity measurements is to determine the amount of water vapor present in the atmosphere by weight, by volume, by partial pressure, or by a fraction (percentage) of the saturation (equilibrium) vapor pressure with respect to a plane surface of pure water. The measurement of atmospheric humidity in the field has been and continues to be troublesome. It is especially difficult for automatic weather stations where low cost, low power consumption, and reliability are common constraints. Pure water vapor in equilibrium with a plane surface of pure water exerts a pressure designated e's. This pressure is a function of the temperature of the vapor and liquid phases and can be obtained by integration of the Clausius-Clapeyron equation, assuming linear dependence of the latent heat of vaporization on temperature, L = L0(1+∝ (T-T0)], where T0 = 273.15K, L0 = 2.5008 x 106Jkg-1, the latent heat of water vapor at T0, Rv = 461.51Jkg-1K-1, the gas constant for water vapor, e's0 = 611.21 Pa, the equilibrium water vapor pressure at T = T0, and ∝ = - 9.477 x 10-4 K-1 = average rate of change coefficient for the latent heat of water vapor with respect to temperature. Since water vapor is not a perfect gas, the above equation is not an exact fit. The vapor pressure as a function of temperature has been determined by numerous experiments.
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"3. Classical mass-fraction Henry’s constants of water vapor in molten polymers." In CRC Handbook of Thermodynamic Data of Aqueous Polymer Solutions, 83. CRC Press, 2004. http://dx.doi.org/10.1201/9780203998205-39.
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"Independent Component Analysis for Separating Water Vapor Spectrum from Terahertz Spectra." In Intelligent Engineering Systems Through Artificial Neural Networks, Volume 17, 585–91. ASME Press, 2007. http://dx.doi.org/10.1115/1.802655.paper92.
Повний текст джерела
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Yoon, Hongkyu, A. J. Valocchi, and C. J. Werth. "Impact of spatially distributed nonaqueous phase liquid saturation and water content on soil vapor extraction in heterogeneous porous media." In Computational Methods in Water Resources: Volume 1, 757–66. Elsevier, 2004. http://dx.doi.org/10.1016/s0167-5648(04)80097-2.
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Parlance, Marc B., and John D. Albertson. "Evaporation : Use of Fast-Response Turbulence Sensors, Raman Lidar, and Passive Microwave Remote Sensing." In Vadose Zone Hydrology. Oxford University Press, 1999. http://dx.doi.org/10.1093/oso/9780195109900.003.0014.
Повний текст джерелаАнотація:
Since evaporation represents some 60% of precipitation over land surfaces, it is crucial for hydrologic purposes to know with some degree of certainty the magnitude of the water vapor flux into the atmosphere. Actual evaporation (E) from drying land surfaces is often formulated, in hydrology, as a fraction of some measure of potential evaporation (Ep), which can be written as a bulk transfer relationship: . . . Ep =CE up(qs* -q) (10.1) . . . where CE is the bulk mass transfer coefficient for water vapor, u is the mean wind speed at reference height z above the surface, r is the density of the air, q is the mean specific humidity at z, and q*s is the saturation specific humidity at the temperature of the surface (Ts) (Brutsaert, 1982, 1986).
Тези доповідей конференцій з теми "Volume fraction of water vapor"
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Hong, S. W., J. H. Kim, B. T. Min, I. K. Park, and H. D. Kim. "Suppression Features of a Vapor Explosion With Prototypic Reactor Materials." In 16th International Conference on Nuclear Engineering. ASMEDC, 2008. http://dx.doi.org/10.1115/icone16-48770.
Повний текст джерелаАнотація:
The suppression of a vapor explosion is reviewed from a void fraction point of view from previous research results and the results of an experiment and analysis for TROI using a prototypic reactor material. In a tin-water system, a high fraction of air which played the role of a steam reduced the peak pressure of a steam explosion. According to the sensitivity analysis that was carried out with an increase in the vapor volume fraction, an energetic vapor explosion hardly took place in the mixture with a high void fraction. In higher vapor fraction conditions (αv> 0.3), the vapor explosion was very weak. A prototypic corium shows a relatively high void fraction compared to the ZrO2 which is known as an explosive material because the corium system generated many smaller particles compared to the ZrO2 system. The corium system shows a relatively low explosivity compared to the ZrO2 system because the high void fraction of the corium system plays the role of preventing a contact between the water and the hot melt drops in the triggering stage. When considering the experimental results for the role of air instead of steam, an air supply system to provide a high volume fraction during a premixing process can radically prevent and/or mitigate a steam explosion.
2
Jiang, Kecheng, Xuebin Ma, and Songlin Liu. "CFD Application to Subcooled Boiling Analyses on the First Wall of WCCB Blanket for CFETR." In 2017 25th International Conference on Nuclear Engineering. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/icone25-66216.
Повний текст джерелаАнотація:
In this paper, by using the CFD method, the efforts have been tried to conduct the investigation on the subcooled flow boiling in the first wall channel of Water cooled ceramic breeder (WCCB) blanket for CFETR. The detailed 3D distribution of temperature and vapor in the flowing passage have been presented under the heat flux of 0.5MW/m2 and 1MW/m2, respectively. Due to the high heat flux from plasma, the vapor distribution in the channel decreases from the plasma side to the breeder side along the radial direction. Undoubtedly, the volume fraction of vapor increases along the flowing direction because of the heating. Besides, the distribution of the channel wall along the toroidal direction presents the U-shaped tendency. As demonstrated by the results, the vapor is more likely to be generated at the corner of the square channel, and this can easily cause the Critical Heat Flux (CHF), which will destroy the structural integrity and materials melting. To avoid the enrichment of vapor in the corner, the optimization on the flowing channel has been performed by smoothing the corner. The results show that the volume fraction of vapor can be effectively decreased compared with the original square channel. Moreover, from the perspective of thermal hydraulics, the circular tube is the optimized channel which can not only avoid the concentration of vapor, but also can decrease the peak volume fraction.
3
Gokaltun, S., P. V. Skudarnov, and C. X. Lin. "Verification and Validation Studies for a Laminar Non-Premixed Methane/Air Flame." In ASME 2006 International Mechanical Engineering Congress and Exposition. ASMEDC, 2006. http://dx.doi.org/10.1115/imece2006-15086.
Повний текст джерелаАнотація:
In this paper, verification and validation analysis for a nonpremixed methane/air laminar flame is presented. Numerical results were obtained using the finite volume method on structured grids. The verification of the numerical solutions was performed by using the Grid Convergence Index (GCI) and Richardson extrapolation techniques. A set of three different grids is used to calculate the error due to discretization where each grid was generated by doubling the number of cells in each direction of the coarser grid. The local value of GCI was used to calculate the observed order of convergence of the numerical method for local values of temperature and mass fractions of reaction products at various points along the flow domain. The largest error band at the finest grid solution was observed to be 4.6% for the static temperature, 0.5% for the mass fraction of methane and 2.9% for the mass fraction of water vapor. Finally the numerical results were validated with experimental data using the local measurements of temperature and species mass fractions. The results indicate that there is relatively good agreement between the present results and experimental data although a simple one-step reaction model was used for the methane/air combustion. The average deviation was found to be around 25%, 21% and 10% for temperature, methane mass fraction and water vapor mass fraction respectively.
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Wang, DeMing, and Chao Zhang. "Numerical Modeling of Heat Transfer and Water Shedding in Automotive Evaporator Louvered Fins." In ASME 2000 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2000. http://dx.doi.org/10.1115/imece2000-1530.
Повний текст джерелаАнотація:
Abstract A mathematical model has been developed to simulate mass and heat transfer of humid air flows at the airside of automobile air conditioning evaporators. The phenomenon of water condensation and water shedding in louvered fins are modeled based on extension of the existing Eulerian two-fluid method which treats water and air as two continuous media. A species transport equation for the mass fraction of water vapor in humid air is solved. The condensation of water from the air mixture translates into a sink term for the vapor transport equation and an equal source in the continuity equation for the volume fraction of liquid water in the two-fluid system of equations. A critical element in modeling the condensate transport in louvered fins calls for a surface tension force sub-model, since the surface tension force is the primary resistance against water shedding and draining. A formulation is proposed to evaluate the surface tension force based on searching for the most probable liquid-air interface where sharp gradient of water volume fraction exists. Numerical aspect of the implementation is discussed. In order to validate the model and demonstrate the applicability of the present methodology, a six-louver two-dimensional test case is established. The relative influence of the stopping force on liquid distribution pattern and flow was illustrated. The simulation is then carried out on a full-scale 2-D louvered fin design for different operating conditions. This study has demonstrated the feasibility of modeling “wet” heat transfer and water shedding in evaporator fins with an Eulerian two-fluid based method.
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Yin, Zhan, Jianjun Wen, Min Zeng, and Qiuwang Wang. "Numerical Investigation of Laminar Filmwise Condensation of Water Vapor in Horizontal Tube With VOF Method in the Presence of Air." In ASME 2014 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/imece2014-37331.
Повний текст джерелаАнотація:
A steady three-dimensional numerical simulation of laminar film condensation of vapor in the presence of air inside a 1 mm horizontal tube is presented. The volume of fluid (VOF) method is used to capture the liquid-vapor interface with a phase change model. According to a generally accepted flow regime map, annular flow pattern is to be expected. Uniform wall temperature and interface temperature are assumed to be boundary condition. The influence of gravity is obvious while the effect of surface tension is neglected. At inlet, the liquid film is thin and evenly distributed around tube wall. Moving downstream the tube, film at the bottom half becomes thicker under the influence of gravity, while film on upper half remains almost constant. Correspondingly, local heat transfer coefficient on bottom half declines gradually and global average heat transfer coefficient shows little difference along axial direction. Existence of air makes heat transfer coefficient decrease sharply compared with that of pure vapor condensation, caused by an existed air layer which increases the thermal resistance during condensation process. As inlet volume fraction of air increases from 0.5% to 3%, the decline trend of heat transfer coefficient slows down.
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Zhao, Z., D. Poulikakos, and S. Glod. "Pressure and Power Generation During Explosive Vaporization on a Thin-Film Microheater." In ASME 1998 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 1998. http://dx.doi.org/10.1115/imece1998-1222.
Повний текст джерелаАнотація:
Abstract When a liquid is superheated above its boiling point to temperatures near or at the homogeneous nucleation limit, the energy released could create a so-called explosive vaporization, if a significant fraction of this energy is manifested in the form of vapor expansion. In this study, a thin-film microheater (100μm × 110μm) was placed on the underside of a water layer. The surface temperature of the heater was rapidly (6μs) raised electrically, well above the boiling point of water. As a result, rapid vaporization took place. Due to its rapid growth, the vapor volume performs mechanical work on its surrounding and emits acoustic pressure waves. By measuring the acoustic emission from an expanding volume, the dynamic growth of the vapor microlayer is reconstructed where a linear expansion velocity of 17 m/s was reached. Using the Rayleigh-Plesset equation, an absolute vapor pressure of 7 bar was calculated from the data of the acoustic pressure measurement. The amount of extractable mechanical energy produced from the explosive expansion of a vapor microlayer on a thin-film microheater surface, its rate of production, and the energy conversion efficiency was also quantified in this work.
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Yousef, Khaled, Ahmed Hegazy, and Abraham Engeda. "Effect of Moisture Content on Mixing Air With Water-Liquid Flowing Through Inverted U-Tube for Power Plant Condenser Applications." In ASME-JSME-KSME 2019 8th Joint Fluids Engineering Conference. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/ajkfluids2019-4902.
Повний текст джерелаАнотація:
Abstract Computational Fluid Dynamics (CFD) for air/water-vapor and water-liquid two-phase flow mixing with condensation in a vertical inverted U-tube is presented in this paper. This study is to investigate the flow behaviors and underlying some physical mechanisms encountered in air/water-vapor and water-liquid mixing flow when condensation is considered. Water-liquid flows upward-downward through the inverted U-tube while the air/water-vapor mixture is extracted from a side-tube just after the flow oriented downward. The CFD simulation is carried out for a side air/water-vapor mixture volume fraction (αm) of 0.2–0.7, water-vapor mass fraction (Xv) of 0.1–0.5 in the side air/water-vapor mixture and water-liquid mass flowrate (mw) of 2,4,6, and 8 kg/s. The present results reveal that, at lower air mass flow rate, no significant effect of Xv on the generated static pressure at the inverted U-tube higher part. However, by increasing the air mass flow rates, ma ≥ 0.001 at mw = 2 kg/s, and ma ≥ 0.00125 at mw = 4 kg/s, we can infer that the lowest static pressure can be attained at Xv = 0.1. This may be attributed to the increased vapor and air mass flow rates from the side tube which results in shifting the condensation from the tube highest part due to air accumulation. This leads to increasing the flow pressure and decelerating the water-liquid flow. Raising mw from 2 to 4 kg/s at the same vapor mass ratio results in a lower static pressure due to more condensation of water vapor. The turbulent intensity and kinetic energy starts to drop approximately at ma = 0.002 kg/s, and αm = 0.55–0.76 at mw = 2 kg/s for all Xv values but no noticeable change at mw = 4 kg/s occurs. These findings estimate the operational values of air and water mass flow rates for stable air entrainment from the side-tube. Increasing the air and vapor mass ratio over these values may block the evacuation process and fails the system continuance. Likewise more air entrainment from the side-tube will decelerate the water flow through the inverted U-tube and hence the flow velocity will decrease thereafter. Moreover, this study reveals that the inverted U-tube is able to generate a vacuum pressure down to 55.104 kPa for the present model when vapor condensation is considered. This generated low-pressure helps to vent an engineering system from the non-condensable gases and water vapor that fail its function if these are accumulated with time. Moreover, the water-liquid mass flow rate in the inverted U-tube can be used to sustain the required operating pressure for this system and extract the non-condensable gases with a less energy consuming system. The present CFD model provides a good physical understanding of the flow behavior for air/water-vapor and water-liquid flow for possible future application in the steam power plant.
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Li, Wei, Weiqiang Li, Weidong Shi, Ling Zhou, and Bing Pei. "Influence of Different Impeller Diameter on Cavitation Performance in an Engine Cooling Water Pump." In ASME/JSME/KSME 2015 Joint Fluids Engineering Conference. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/ajkfluids2015-09754.
Повний текст джерелаАнотація:
The engine cooling water pump (ECWP) is an important part in the motor and engine. Using the advanced numerical methods and tools to enhance the ECWP performance, not only could reduce the power consumption and weight, but also can promote the safety and reliability of the vehicle system. The cavitation damage in the ECWP shortens the reliability and life of the motor cooling system, as well as produces vibration and noise. Cavitation in the ECWP has been become an important research topic. To investigate the cavitation performance of ECWP with different impeller diameter, the three dimensional turbulent flow in the ECWP with different impeller diameter was numerically simulated employing the time averaged N-S equation, the standard k-ε turbulent model and multiphase flow model by ANSYS-CFX software. The structured hexahedral mesh has been generated for improving the accuracy of numerical simulation. Comparing with the experimental pump performance results, the cavitation performance is accurately predicted based on structured mesh and cavitation model. The comparison of fluid static pressure and vapor volume fraction contours, hydraulic and cavitation performance was made among different impeller diameter. The cavitation performance curve and bubble distributions under different impeller diameter were compared and analyzed, we find that absolute pressure at the critical cavitation point becomes higher with the decreasing of the impeller diameter, and the anti-cavitation performance becomes worse caused by the increasing of the volume fraction in the impeller. Therefore, there is an optimum impeller diameter value to guarantee the anti-cavitation performance and hydraulic performance of the investigated pump.
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Li, Huiying, Sergio A. Vasquez, Hemant Punekar, and R. Muralikrishnan. "Prediction of Boiling and Critical Heat Flux Using an Eulerian Multiphase Boiling Model." In ASME 2011 International Mechanical Engineering Congress and Exposition. ASMEDC, 2011. http://dx.doi.org/10.1115/imece2011-65539.
Повний текст джерелаАнотація:
The present paper concerns the development and validation of an Eulerian multiphase boiling model to predict boiling and critical heat flux within the general-purpose computational fluid dynamics (CFD) solver FLUENT. The governing equations solved are generalized phase continuity, momentum and energy equations. Turbulence effects are accounted for using mixture, dispersed or per-phase multiphase turbulence models. Wall boiling phenomena are modeled using the baseline mechanistic nucleate boiling model, developed in Rensselaer Polytechnic Institute (RPI). Modifications have been introduced to the quenching heat flux model to achieve mesh-independent solutions. The influences of boiling model parameters have also been systematically investigated. To model non-equilibrium boiling and critical heat flux, the PRI model is extended to the departure from nucleate boiling (DNB) by partitioning wall heat flux to both liquid and vapor phases and considering the existence of thin liquid wall film. Topological functions are introduced to consider the wall boiling regime transition from the nucleate boiling to critical heat flux (CHF), and the corresponding flow regime change from bubbly flows to mist flows. A range of sub-models are implemented to model the interfacial momentum, mass and heat transfer and turbulence-bubble interactions. To validate the Eulerian multiphase boiling model, it has been used to predict nucleating boiling and critical heat flux in a range of 2D and 3D boiling flows. The examples presented in the paper include: (1). Nucleate boiling of sub-cooled water in an upward heated pipe; (2) R113 liquid flows through a vertical annulus with internal heated walls; (3). 3D boiling flows in a rectangular-sectioned duct; and (4). Critical heat flux and post dryout in vertical pipes. The results demonstrate that the model is able to predict reasonably well the distributions of wall temperature, the bulk fluid sub-cooling temperature and cross-sectional averaged vapor volume fraction in the vertical pipe. The computed profiles of the vapor volume fraction, liquid temperature, and the liquid and vapor velocity profiles are generally in good agreement with available experiments in the 2D annular case. In the 3D rectangular duct, the cross-sectional averaged vapor volume fractions are well captured in all the ten cases under investigation. In the case of critical heat flux and post dryout, the model is also able to predict reasonably well the location and the temperature rise under critical heat flux conditions. The computed wall temperature distributions along the pipes are in overall good agreement with available experiments.
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Shao, Huaishuang, Yungang Wang, Haidong Ma, and Qinxin Zhao. "Numerical Investigation on Two-Phase Flow Characteristic in the Separated Structure Shell-and-Tube Waste Heat Boiler." In ASME 2017 Power Conference Joint With ICOPE-17 collocated with the ASME 2017 11th International Conference on Energy Sustainability, the ASME 2017 15th International Conference on Fuel Cell Science, Engineering and Technology, and the ASME 2017 Nuclear Forum. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/power-icope2017-3283.
Повний текст джерелаАнотація:
The shell-and-tube waste heat boiler is a common facility to recover and utilize the energy of flue gas in industries. To improve the ability and efficiency of the boiler, a steam dome is configured above the drum so as to arrange more heat exchange tubes. Simulation and analysis of vapor-liquid two-phase flow across tube bundles arranged in the drum are of vital importance to design and safety operation. Numerical simulation of boiling two-phase flow across tube bundles in the drum was carried out to analyze the shell side thermal-hydraulics. Commercial software ANSYS FLUENT 14.5 was adopted for modeling and computational calculations. The applied modeling approach was validated against experimental results with a good agreement. In order to analyze the vapor-liquid two-phase flow performance under various working conditions, the inlet velocity of downcomer tubes of 3m·s−1, 4m·s−1 as well 5m·s−1 for saturated water were simulated, respectively. The pressure field, flow characteristic, void fraction distribution and heat transfer characteristic were analyzed to have a good knowledge of the boiler operation. The following conclusions have been drawn through analyzing simulation results. (1)The total pressure drop on shell side increased with increasing the inlet velocity of downcomer tubes of saturated water. (2)The velocity of saturated water decreased after flowing into the drum less than z = 0.1m as the flow area increasing, and then increased rapidly as the volume of the mixture two-phase flow increasing. (3)The integral average void fraction of the drum decreased as the mass flow rate of inlet saturated water increasing. (4)The HTC (heat transfer coefficient) of the heat exchange tubes varied with the flow direction, which is related to the vapor-water void fraction. The conclusions obtained above can be used as a reference for the design of the separated structure shell-and-tube waste heat recovery boiler.
Звіти організацій з теми "Volume fraction of water vapor"
1
Cohen, Shabtai, Melvin Tyree, Amos Naor, Alan N. Lakso, Terence L. Robinson, and Yehezkiel Cohen. Influence of hydraulic properties of rootstocks and the rootstock-scion graft on water use and productivity of apple trees. United States Department of Agriculture, 2001. http://dx.doi.org/10.32747/2001.7587219.bard.
Повний текст джерелаАнотація:
This one year exploratory project investigated hydraulic architecture of apple dwarfing rootstocks. The hypothesis was that hydraulic conductance is correlated with rootstock vigor. A previous study of trees on three rootstocks in Israel showed that dwarfed trees used less water than un-dwarfed trees. Analysis showed that if the tree maintains leaf water potentials above minimum values, then this implies that the dwarfed trees have lower leaf conductance, which may also be the cause of dwarfing. The current project studied small 2-year old unworked rootstock trees, and full sized trees bearing commercial yields. In both cases hydraulic conductance was determined with two methods - the non-destructive evaporative flux (EF)-leaf water potential (L WP) method, and a destructive method in which water was forced through the plant at known pressure using the "high pressure flow meter" (HPFM). Detailed work allowed measurement of conductance of the rootstock-scion union. This was achieved both with the HPFM and with the EF-LWP methods, the former in the US and the latter in Israel. Direct measurements of leaf conductance were made, and carbon isotope ratios ( d ¹³ C) were determined for leaves sampled at the end of the season. The latter can indicate sustained differences in leaf conductance behavior. HPFM and EF-LWP methods did not give the same results. In the small plants results were similar in magnitude, but not significantly correlated. In large trees, EF- L WP measurements were a fraction of those obtained with the HPFM. The latter indicates that some of the xylem is not normally functional but transports water when pressurized. Additional experimental work targeted this result. Xylem was stained before and after perfusion with water at high pressure. This showed that at least for one rootstock a significant amount of xylem was blocked before perfusion. The "air method" for determining xylem vessel properties was improved and employed. Length, radius and density of xylem vessels of different rootstocks were found to be similar, and significant differences found were not clearly related to rootstock vigor. Measurements in the commercial orchard in Israel showed that the graft union in a dwarfing rootstock was a large obstacle for water transport (i.e. had a high resistance). This apparently led to low leaf conductance to water vapor, as indicated by lower d ¹³ C, which implies low internal CO ₂ concentrations. In the US orchard, d ¹³ C in 2001 was correlated with rootstock vigor, and significant differences were found in leaf conductance. However, the d ¹³ C differences were not observed in 2002, were opposite to those found in the Israeli orchard, and measurements of the graft union with the HPFM did not find large resistances. We speculate that the graft union is not necessarily a large impediment to water transport unless the scion starts to separate from the rootstock. It was concluded that significant differences in hydraulic conductance exist between different dwarfing rootstocks. These differences may be caused by differences in xylem properties and in the degree of cavitation, as well as resistance in the graft union. However, no general relationship to rootstock vigor was found. Therefore, hydraulic conductance alone cannot explain dwarfing, but may be one of two or more factors that lead to dwarfing. Future work should integrate more factors with hydraulic relations, e.g. nutrient and solute transport and production of hormones.
2
MacDonald, James D., Aharon Abeliovich, Manuel C. Lagunas-Solar, David Faiman, and John Kabshima. Treatment of Irrigation Effluent Water to Reduce Nitrogenous Contaminants and Plant Pathogens. United States Department of Agriculture, July 1993. http://dx.doi.org/10.32747/1993.7568092.bard.
Повний текст джерелаАнотація:
The contamination of surface and subterranean drinking water supplies with nitrogen-laden agricultural wastewater is a problem of increasing concern in the U.S. and Israel. Through this research, we found that bacteria could utilize common organic wastes (e.g. paper, straw, cotton) as carbon sources under anaerobic conditions, and reduce nitrate concentrations in wastewater to safe levels. Two species of bacteria, Cellulomonas uda and a Comamonas sp., were required for dentitrification. Celulomonas uda degraded cellulose and reduced nitrate to nitrite. In addition, it excreted soluble organic carbon needed as a food source by the Comamonas sp. for completion of denitrification. We also found that recirculated irrigation water contains substantial amounts of fungal inoculum, and that irrigating healthy plants with such water leads to significant levels of root infection. Water can be disinfected with UV, but our experiments showed that Hg-vapor lamps do not possess sufficient energy to kill spores in wastewater containing dissolved organics. Excimer lasers and Xenon flashlamps do possess the needed power levels, but only the laser had a high enough repetition rate to reliably treat large volumes of water. Ozone was highly efficacious, but it's use as a water treatment is probably best suited to moderate or low volume irrigation systems. This research provides critical data needed for the design of effective water denitrification and/or pathogen disinfection systems for different growing operations.
3
Russo, David, and William A. Jury. Characterization of Preferential Flow in Spatially Variable Unsaturated Field Soils. United States Department of Agriculture, October 2001. http://dx.doi.org/10.32747/2001.7580681.bard.
Повний текст джерелаАнотація:
Preferential flow appears to be the rule rather than the exception in field soils and should be considered in the quantitative description of solute transport in the unsaturated zone of heterogeneous formations on the field scale. This study focused on both experimental monitoring and computer simulations to identify important features of preferential flow in the natural environment. The specific objectives of this research were: (1) To conduct dye tracing and multiple tracer experiments on undisturbed field plots to reveal information about the flow velocity, spatial prevalence, and time evolution of a preferential flow event; (2) To conduct numerical experiments to determine (i) whether preferential flow observations are consistent with the Richards flow equation; and (ii) whether volume averaging over a domain experiencing preferential flow is possible; (3) To develop a stochastic or a transfer function model that incorporates preferential flow. Regarding our field work, we succeeded to develop a new method for detecting flow patterns faithfully representing the movement of water flow paths in structured and non-structured soils. The method which is based on application of ammonium carbonate was tested in a laboratory study. Its use to detect preferential flow was also illustrated in a field experiment. It was shown that ammonium carbonate is a more conservative tracer of the water front than the popular Brilliant Blue. In our detailed field experiments we also succeeded to document the occurrence of preferential flow during soil water redistribution following the cessation of precipitation in several structureless field soils. Symptoms of the unstable flow observed included vertical fingers 20 - 60 cm wide, isolated patches, and highly concentrated areas of the tracers in the transmission zone. Soil moisture and tracer measurements revealed that the redistribution flow became fingered following a reversal of matric potential gradient within the wetted area. Regarding our simulation work, we succeeded to develop, implement and test a finite- difference, numerical scheme for solving the equations governing flow and transport in three-dimensional, heterogeneous, bimodal, flow domains with highly contrasting soil materials. Results of our simulations demonstrated that under steady-state flow conditions, the embedded clay lenses (with very low conductivity) in bimodal formations may induce preferential flow, and, consequently, may enhance considerably both the solute spreading and the skewing of the solute breakthrough curves. On the other hand, under transient flow conditions associated with substantial redistribution periods with diminishing water saturation, the effect of the embedded clay lenses on the flow and the transport might diminish substantially. Regarding our stochastic modeling effort, we succeeded to develop a theoretical framework for flow and transport in bimodal, heterogeneous, unsaturated formations, based on a stochastic continuum presentation of the flow and a general Lagrangian description of the transport. Results of our analysis show that, generally, a bimodal distribution of the formation properties, characterized by a relatively complex spatial correlation structure, contributes to the variability in water velocity and, consequently, may considerably enhance solute spreading. This applies especially in formations in which: (i) the correlation length scales and the variances of the soil properties associated with the embedded soil are much larger than those of the background soil; (ii) the contrast between mean properties of the two subdomains is large; (iii) mean water saturation is relatively small; and (iv) the volume fraction of the flow domain occupied by the embedded soil is relatively large.