Теплообмін при кипінні на гладких та пористих поверхнях в умовах обмеженого простору

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dc.contributor.authorАлексеїк, Ольга Сергіївна
dc.date.accessioned2021-04-26T10:02:47Z
dc.date.available2021-04-26T10:02:47Z
dc.date.issued2021
dc.description.abstractenThe dissertation is dedicated to studying of patterns and characteristics of heat transfer process at boiling on felt metal porous surfaces in conditions of limited space above the heat transfer surface. Complex experimental investigation of heat transfer intensity at boiling on porous structures was performed in this work, influence of felt sizes, porosity, structure thickness and height of free space above the heat transfer surface on heat transfer intensity was detected. The active development of the electronics, computer, energy and many other industries requires the development of new, more efficient methods of heat dissipation from heat loaded elements. The coating of the cooled surface with capillary structures is one of such methods. Applying a capillary-porous coating on the heat transfer surface can significantly increase the intensity of heat transfer during boiling and in most cases increase the maximum allowable heat flux density compared to smooth technical surfaces. Coating of porous structures is widely used in the elements of cooling systems of electronic, space equipment, power plants and other. In particular, they are used as wicks in various types of heat pipes, as well as in vapor chambers. However, the boiling of the heat carrier in such devices occurs in a limited space above the heat transfer surface, which has a significant impact on the processes of heat and mass transfer, and the intensity of heat transfer. Existing dependences for calculating the heat transfer coefficient at boiling on porous surfaces have been obtained for large volume conditions. Therefore, attempts to use them to calculate the intensity of heat transfer in the heating zone of two-phase heat transfer devices give a significant error, which complicates the design process of such devices. Hence the studying of the processes of boiling on porous structures in a limited volume is an actual task. Analysis of the literature has shown that there is no single theory for the case of boiling on the capillary structure, which would explain the full range of phenomena that occur. In addition, the results reported in the literature for some types of porous coatings are not enough to be able to unambiguously establish the nature of the influence of a factor on the intensity of the boiling process in a porous coating. There are almost no data on boiling in the capillary structure in conditions of the heat carrier capillary transport and at limited space. In dissertation thesis design of working chamber and main systems of experimental setup: system of creation and maintaining of constant conditions of experiments, system of supplying and measuring of heat load and system of data acquisition are described. Description of working elements of three types: for boiling investigation on small smooth surfaces (I type), on large smooth surfaces (II type), on large porous surfaces (III type) is presented. Characteristics of investigated porous structures are listed. Method of experimental data processing is described. Results of experimental investigation errors evaluation are presented. In order to check reliability of research methods comparison of obtained experimental data with literature data was performed. Results of experimental investigation of heat transfer intensity in dependence on the output heat flux, surface sizes and covering characteristics (such as fibrous sizes, porosity and thickness) and also height of free volume of liquid above the surface are presented. It was shown that influence of space limiting on heat transfer intensity at boiling on the smooth surface takes place at heights less than 4·lc (where lc – capillary constant). And character of this influence depends on density of output heat flux. At the same time, obtained experimental data have shown that for porous structures this value is equal to (7-9)·lc and depends on felt sizes and its porosity. It was found that decreasing of distance between porous and limiting surfaces can lead to decreasing of heat transfer intensity on 20-30% compared to boiling on porous surface in a large volume. Comparison of obtained data has shown that application of porous surface leads to 1,5-3 times increasing of heat transfer intensity compared to boiling on the smooth surface at the same conditions. Also, physical model of heat transfer at boiling on porous surface at conditions of limited space is presented. Four basic regimes of heat transfer were pointed out in dependence of intensity of heat input and distance between porous and limiting surfaces: free convective heat transfer; boiling on porous surface at conditions of its flooding with heat carrier and absence influence of vapor cloud at the top part of the working space and with presence of this influence; boiling on porous structure at conditions of heat carrier capillary transport. A physical description of heat and mass transfer processes is made for all regimes. The results of generalization of experimental data on heat transfer intensity at boiling on porous surface are also presented in this chapter. Obtained equations allow estimation of heat transfer coefficient in dependence of heat flux, height of volume under heat transfer surface and some characteristics of capillary structure. Mean deviation of estimated data from experimental ones is equal to 15%. Method of engineering calculation of a two-phase heat transfer devices was developed. Recommendations for choosing of calculation equations of such devices depending on features of their designs and mode parameters are given. Main criterion equations recommended for evaluation of separate components of overall thermal resistance are presented. Description of experimental setup for heat transfer characteristics of vapor chambers and experimental method is given. Comparison of the calculation results and experimental data for thermal resistance obtained for the actual designs of vapor chambers has shown that these values differ from each other not more than 12%.uk
dc.description.abstractukДисертаційна робота присвячена вивченню закономірностей та характеристик процесу теплообміну при кипінні на метало-волокнистих пористих поверхнях в умовах обмеження простору над поверхнею теплообміну. У роботі виконані комплексні експериментальні дослідження інтенсивності теплообміну при кипінні на пористих структурах, встановлено вплив на неї розмірів волокон, пористості та товщини пористого покриття, а також висоти вільного простору над поверхнею теплообміну. Розвинуто фізичну модель процесу тепломасопереносу при кипінні на пористих поверхнях в умовах обмеженого простору. Отримані емпіричні залежності для визначення інтенсивності теплообміну при кипінні на гладких та пористих поверхнях в умовах обмеженості простору із врахуванням характеристик пористої структури в широкому діапазоні підведених теплових потоків. Розроблена методика інженерного розрахунку двофазного теплопередавального пристрою на прикладі парової камери.uk
dc.format.page29 с.uk
dc.identifier.citationАлексеїк, О. С. Теплообмін при кипінні на гладких та пористих поверхнях в умовах обмеженого простору : автореф. дис. … канд. техн. наук. : 05.14.06 – технічна теплофізика та промислова теплоенергетика / Алексеїк Ольга Сергіївна. – Київ, 2021. – 29 с.uk
dc.identifier.urihttps://ela.kpi.ua/handle/123456789/40778
dc.language.isoukuk
dc.publisherКПІ ім. Ігоря Сікорськогоuk
dc.publisher.placeКиївuk
dc.subjectдвофазна системаuk
dc.subjectкипінняuk
dc.subjectінтенсивність теплообмінуuk
dc.subjectметало-волокнисті структуриuk
dc.subjectобмежений простірuk
dc.subjectпарова камераuk
dc.subjectпориста структураuk
dc.subjectфазове перетворенняuk
dc.subjectфізична модельuk
dc.subjecttwo-phase systemuk
dc.subjectboilinguk
dc.subjectheat transfer coefficientuk
dc.subjectfelt metal structuresuk
dc.subjectlimited spaceuk
dc.subjectvapor chamberuk
dc.subjectporous structureuk
dc.subjectphase changeuk
dc.subjectphysical modeluk
dc.subject.udc536.24uk
dc.titleТеплообмін при кипінні на гладких та пористих поверхнях в умовах обмеженого просторуuk
dc.typeThesisuk

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