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Experimental investigation of homogeneous nucleation of water in various gases using an expansion chamber
Lukianova, Tetiana ; Lukianov, Mykola ; Hrubý, Jan
Nucleation is an integral part of phase transitions and plays an important role in technology. The control of nucleation in devices such as turbines, rocket and jet engines, wind tunnels, and combustion processes is key to achieving efficient, ecologically sound operation. Our paper presents information about a modernized experimental setup used for homogeneous water nucleation research.\nThe main goal of the study is an analysis of the influence of carrier gas on homogeneous nucleation.The experimental setup based on an expansion chamber has been used for research of homogeneous nucleation over several decades and has undergone various technical improvements. In the Institute of Thermomechanics, the setup was been completely disassembled and cleaned. Pressure transducers, laser, and the data acquisition system have been replaced with modern parts. After that, the chamber was assembled, and thoroughly tested and calibrated.Our investigations were carried with argon and nitrogen as carrier gases in a range of nucleation temperatures 220 – 260 K, pressure range 80-150 kPa, at several concentrations of water vapour. The results thus obtained are consistent with literature data.The findings suggest that this experimental approach is useful for homogeneous water nucleation research.
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Nucleation rate in binary cavitating systems - A comparison of experimental data and classical nucleation theory predictions
Němec, Tomáš
A brief review of recent literature on proton exchange membrane fuel cell (PEMFC) modelling is presented and the governing equations of the transport processes in the proton exchange membrane are presented. Consequently, the model of water transport in the membrane electrode assembly of a fuel cell in commercial software FLUENT is investigated. The aim of this work is to test the possibilities of the PEMFC modelling using FLUENT. Special attention is given to the water management and the properties of the fuel cell membrane.of four binary mixtures, i.e. diethylether - nitrogen, propane - carbon dioxide, isobutane - carbon dioxide, and chlorodifluoromethane - carbon dioxide. The predictions of the classical nucleation theory show very good agreement with the measured nucleation rates.
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Klasická nukleační teorie a modelování kavitačních jevů
Němec, Tomáš
Práce podává teoretický popis nukleace bublin a jejich růstu při kavitaci ve vodě vhodný pro použití ve výpočtech mechaniky tekutin. Klasická teorie nukleace je použita k odhadu nukleačních rychlostí při kavitaci ve vodě, a dále je uveden jednoduchý model růstu bublin díky difúzi. Výsledky lze použít pro zpřesnění numerických řešičů proudění s kavitačními jevy, které doposud používaly empirické odhady pro rozložení velikostí bublin v proudu tekutiny.
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