Дисертації з теми "Transient heat flux"
Оформте джерело за APA, MLA, Chicago, Harvard та іншими стилями
Ознайомтеся з топ-16 дисертацій для дослідження на тему "Transient heat flux".
Біля кожної праці в переліку літератури доступна кнопка «Додати до бібліографії». Скористайтеся нею – і ми автоматично оформимо бібліографічне посилання на обрану працю в потрібному вам стилі цитування: APA, MLA, «Гарвард», «Чикаго», «Ванкувер» тощо.
Також ви можете завантажити повний текст наукової публікації у форматі «.pdf» та прочитати онлайн анотацію до роботи, якщо відповідні параметри наявні в метаданих.
Переглядайте дисертації для різних дисциплін та оформлюйте правильно вашу бібліографію.
Calisto, Hugo Miguel Filipe. "Transient transpiration radiometer : development of a heat flux sensor for high aggressivity environments." Doctoral thesis, Universidade de Aveiro, 2013. http://hdl.handle.net/10773/12457.
Повний текст джерелаThe development of a new instrument for the measurement of convective and radiative is proposed, based on the transient operation of a transpiration radiometer. Current transpiration radiometers rely on steady state temperature measurements in a porous element crossed by a know gas mass flow. As a consequence of the porous sensing element’s intrinsically high thermal inertia, the instrument’s time constant is in the order of several seconds. The proposed instrument preserves established advantages of transpiration radiometers while incorporating additional features that broaden its applicability range. The most important developments are a significant reduction of the instrument’s response time and the possibility of separating and measuring the convective and radiative components of the heat flux. These objectives are achieved through the analysis of the instrument’s transient response, a pulsed gas flow being used to induce the transient behavior.
Propõe-se o desenvolvimento de um novo instrumento para medição de fluxos de calor convectivos e radiativos, baseado na operação de um radiómetro de transpiração em regime transitório. Os radiómetros de transpiração atuais baseiam-se em medições de temperatura em regime estacionário num elemento poroso atravessado por um caudal mássico gasoso conhecido. Como consequência da inércia térmica intrinsecamente elevada do elemento sensível poroso, a constante de tempo do instrumento é da ordem dos segundos. O instrumento proposto preservará as vantagens estabelecidas dos radiómetros de transpiração incorporando características adicionais que alargarão a gama de aplicabilidade. As novas características mais importantes serão uma redução significativa do tempo de resposta do instrumento e a possibilidade de medir separadamente as componentes radiativa e convectiva do fluxo de calor. Estes objetivos serão conseguidos através da análise da resposta transitória do instrumento, utilizando-se um caudal pulsado de gás para induzir o comportamento transitório.
Henderson, Alistair. "Predicting Ignition Time Under Transient Heat Flux Using Results from Constant Flux Experiments." University of Canterbury. Civil Engineering, 1998. http://hdl.handle.net/10092/8273.
Повний текст джерелаD'Elia, Christopher. "Development of Local Transient Heat Flux Measurements in an Axisymmetric Hybrid Rocket Nozzle." DigitalCommons@CalPoly, 2015. https://digitalcommons.calpoly.edu/theses/1349.
Повний текст джерелаPeabody, Hume L. "Evaluation of a Heat Flux Microsensor in a Transonic Turbine Cascade." Thesis, Virginia Tech, 1997. http://hdl.handle.net/10919/35495.
Повний текст джерелаMaster of Science
Veloo, Peter Surendran. "Scale modeling of the transient behavior of heat flux in enclosure fires." College Park, Md. : University of Maryland, 2006. http://hdl.handle.net/1903/3484.
Повний текст джерелаThesis research directed by: Dept. of Fire Protection Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
Kilic, Arif Nesimi 1963. "A multi-region transient erosion model for concrete with time-dependent surface heat flux." Diss., The University of Arizona, 1996. http://hdl.handle.net/10150/290695.
Повний текст джерелаBezuidenhout, Johannes Jurie. "Convective heat flux determination using surface temperature history measurements and an inverse calculation method." Thesis, Virginia Tech, 2000. http://hdl.handle.net/10919/35706.
Повний текст джерелаThe objective of this study is therefore to develop a cost-effective single gage that can be used to measure both skin friction and heat flux. The method proposed in this study is to install a coaxial thermocouple into an existing skin friction gage to measure the unsteady temperature on the surface of the gage. By using the temperature history and a computer program the heat flux through the surface can be obtained through an iterative guessing method. To ensure that the heat flux through the gage is similar to the heat flux through the rest of the surface, the gage is manufactured of a material very similar to the rest of the surface.
Walker developed a computer program capable of predicting the heat flux through a surface from the measured surface temperature history. The program is based on an inverse approach to calculate the heat flux through the surface. The biggest advantages of this method are its stability and the small amount of noise induced into the system. The drawback of the method is that it is limited to semi-infinite objects. For surfaces with a finite thickness, a second thermocouple was installed into the system some distance below the first thermocouple. By modifying the computer program these two unsteady temperatures can be used to predict the heat flux through a surface of finite thickness.
As part of this study, the effect of noise induced by the Cook-Felderman technique, found in the literature were investigated in detail and it was concluded that the method proposed in this study is superior to this Cook-Felderman method. Heat flux measurements compared well with measurements recorded with heat flux gages. In all cases evaluated the difference was less than 20%. It can therefore be concluded that heat flux gages on their own can measure surface heat flux very accurately. These gages are however too large to install in a skin-friction gage. The method introduced in this study is noisier than the heat flux gages on their own, but the size which is very important, is magnitudes smaller when using a coaxial thermocouple, to measure the surface temperature history.
Master of Science
Kang, Yong Tae. "Experimental investigation of critical heat flux in transient boiling systems with vertical thin rectangular parallel plate channels /." The Ohio State University, 1994. http://rave.ohiolink.edu/etdc/view?acc_num=osu1244826053.
Повний текст джерелаHernandez-Ontiveros, Cesar F. "Numerical analysis of heat transfer during jet impingement on curved surfaces." [Tampa, Fla.] : University of South Florida, 2007. http://purl.fcla.edu/usf/dc/et/SFE0002123.
Повний текст джерелаElsheikh, Mutasim Mohamed Sarour. "Numerical Simulations of Heat Transfer Processes in a Dehumidifying Wavy Fin and a Confined Liquid Jet Impingement on Various Surfaces." Scholar Commons, 2011. http://scholarcommons.usf.edu/etd/3090.
Повний текст джерелаNop, Raksmy. "Experimental investigation and modeling of the transient flow boiling crisis of water at moderate pressure and high subcooling." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPAST046.
Повний текст джерелаIn case of a reactivity insertion accident in an experimental nuclear reactor, heat generation in the core can grow exponentially in time, with a power escalation period ranging from a few to a few hundreds of milliseconds. Due to neutronic and thermohydraulic effects, boiling crisis may arise, possibly leading to an explosive reaction. If the boiling Crisis has been widely investigated in steady-state conditions, this has not been the case for transient heat inputs. The aim of the present work is to understand and to predict the transient flow boiling crisis in the conditions of moderate pressure and high subcooling. To this end, an experimental campaign has been realized making use of space and time highly resolved videos and IR thermography covering a wide range of experimental parameters. The analysis of the massive amount of data produced by these experiments gives a better insight on the dependency of the transient Critical Heat Flux to the different parameters of interest (power escalation period, flow velocity, subcooling, pressure, channel width, heating length). Moreover, their fine analysis enables to highlight the underlying mechanisms. For conditions of forced flow and high subcooling, the bubbles generated at the wall present a pulsating behavior. This specific process leads to an efficient heat transfer from the wall to the neighboring fluid. Boiling crisis is stated to occur when a thin layer of liquid contacting the wall reaches the saturation temperature. Starting from these observations, a model is developed which brings to light two non-dimensional parameters useful to describe the transient nature of the process and the dominant cooling processes. With the knowledge of the steady-state CHF, the model permits to conservatively estimate the value of the Critical Heat Flux for any power escalation period and subcooling. This model is now ready for implementation into simulation codes to investigate nuclear accidental transients
Omara, Abdeslam. "Étude de la convection mixte transitoire conjuguée dans une conduite verticale épaisse." Besançon, 2008. http://www.theses.fr/2008BESA2050.
Повний текст джерелаThe proposed survey in this thesis appears in the setting of the conjugated laminar and transient mixed convection in a thick vertical conduct submitted to a constant and uniform heat flux. The fluid penetrates to the top of the conduct to head downwards, therefore one is in presence of opposed mixed convection flow. The governing transport equations were solved using the finite volume formulation and the simple algorithm is adopted. We study the effect of physical and geometrical properties of the physical system on the transient evolution of the thermal magnitudes (interfacial heat flux and radial distribution of the temperature) and the hydrodynamic magnitudes (friction coefficient and vector velocities)
Наумова, Альона Миколаївна. "Теплопередаючі характеристики пульсаційних капілярних теплових труб, призначених для малогабаритних систем охолодження". Thesis, НТУУ "КПІ", 2016. https://ela.kpi.ua/handle/123456789/14940.
Повний текст джерелаThe dissertation is dedicated to the heat transfer characteristics of pulsating capillary heat pipes (PHP) depending on the regime and operational parameters. The experiments were conducted with glass and copper PHP with the internal diameter, respectively, 3,8mm and 1mm; number of turns 4 and 7. The water was used as a heat carrier; the filling ratio was approximately 50% of the internal volume. Cooling of the glass PHP was carried out by free air convection, and cooling of the copper one was carried out by forced convection of the liquid with different values of temperature and flow rate. The inclination angle of the copper PHP varied from -90° to + 90° in increments of 45 °. The PHP operation can be conditionally divided into two modes of heat transfer that are: convection-conductive mode that corresponds to small values of input heat power and pulsation mode that corresponds to middle and high of input heat power and to the heat carrier boiling. The heat flux called transient takes place at the transition from one mode of heat transfer to another. As a result of experimental studies the temperature of the PHP heating, transport, and condensation areas as well as thermal resistance and heat transfer coefficients are presented depending on the input heat flux and parameters of the cooling fluid. The dependence of the PHP heat transfer characteristics on external mechanical vibrations and PHP orientation in space was researched. The simplified semi-empirical formula for transient heat flux calculating is obtained. Given dissertation also presents a constructional calculation of the PHP number of loops when manufactured depending on the geometry of the capillary tube, and the lengths of the heater and the condenser. On the basis of the pulsation heat transfer mechanism some new heat transfer devices were designed, such as pulsating thermosyphon radiator with PHP. Comparing of the PHP with other cooling systems has shown that it is most effective for rejection of the heat fluxes over 6 W/cm2.
Диссертация посвящена исследованию теплопередающих характеристик пульсационных капиллярных тепловых труб (ПТТ) в зависимости от режимных и эксплуатационных параметров. Исследования проводились со стеклянной и медной ПТТ с внутренним диаметром, соответственно, 3,8мм и 1мм; количество петель 4 и 7. Теплоносителем служила вода с коэффициентом заполнения примерно 50% от внутреннего объема. Охлаждение стеклянной ПТТ осуществлялось за счет свободной конвекции воздуха, медной – за счет принудительной конвекции жидкости с разными значениями температуры и расхода. Угол наклона медной ПТТ к горизонту изменялся от -90° до +90° с шагом 45°. Работа ПТТ условно разделена на два режима передачи тепла: конвективно-кондуктивный, соответствующий малым значениям подведенной тепловой мощности, и пульсационный, соответствующий средним и высоким значениям подведенной тепловой мощности и началу кипения теплоносителя. Величина теплового по- тока, при котором происходит переход от одного режима передачи тепла к другому, называется переходным QПЕРЕХ. В результате экспериментальных исследований представлены зависимости температур в зонах нагрева (ЗН), транспорта (ЗТ) и конденсации (ЗК) ПТТ от времени и подведенного теплового потока. Показано влияние параметров охлаждающей жидкости – расхода и температуры – на величину QПЕРЕХ. Для медной ПТТ стабильный пульсационный режим теплопередачи устанавливается при 30-50 Вт в зависимости от параметров эксперимента. Величина термического сопротивления ПТТ различается только в области конвективно-кондуктивного режима теплопередачи и достигает значений 4-5 °С/Вт, после начала кипения эта цифра снижается на порядок и составляет примерно 0,3-0,6 °С/Вт. Влияние режима теплопередачи сказывается и на величину средних коэффициентов теплоотдачи в ЗН и ЗК ПТТ. Если для конвективно-кондуктивного режима теплопередачи средние коэффициенты теплоотдачи для ЗН составляют 400-450 Вт/(м2·К), а для ЗК – 200-250 Вт/(м2·К), то для пульсационного режима передачи тепла в ПТТ средние коэффициенты теплоотдачи в ЗН достигают 3,5-4 кВт/(м2·К), а в ЗК – 1,8 кВт/(м2·К), т.е. почти в 9 раз больше. Впервые исследована зависимость теплопередающих характеристик ПТТ от внешних механических колебаний. Эксперименты показали, что вибрации практически не оказывают влияния на величину термического сопротивления, однако способствуют тому, что QПЕРЕХ наступает при меньших значениях подведенной мощности. Например, если без вибраций QПЕРЕХ = 45-50 Вт, то для частоты 10 Гц это значение снижается до 40 Вт, а для частоты порядка 40 Гц – до 20-25 Вт. Приведена физическая модель процессов, возникающих в ЗН в момент начала кипения теплоносителя. На основе теплового баланса построена математическая модель, учитывающая зарождение, рост и дальнейший отрыв парового пузырька в ЗН. В результате решения математической модели получена упрощенная полуэмпирическая формула для расчета QПЕРЕХ. Расчетные значения величины QПЕРЕХ превышают экспериментальные данные в среднем на 21%, что не уменьшает работоспособности формулы. В работе представлен конструктивный расчет количества петель ПТТ при её изготовлении в зависимости от геометрии капиллярной трубки, а также длин ЗН и ЗК. Приведена методика инженерного расчета ПТТ. Зная максимальную температуру и геометрические параметры теплонагруженного элемента, а также отводимую мощность и условия охлаждения, можно рассчитать среднюю температуру и термическое сопротивление ПТТ. На основе пульсационного механизма передачи тепла разработаны новые конструкции теплопередающих устройств: пульсационный термосифон и радиатор с ПТТ.
Scheiff, Valentin. "Etude expérimentale et modélisation du transfert de chaleur de l'ébullition transitoire." Thesis, Toulouse, INPT, 2018. http://www.theses.fr/2018INPT0145/document.
Повний текст джерелаThe study of rapid transient boiling is an important issue in the nuclear safety. Such a phenomenon may occur in the case of a RIA (Reactivity Initiated Accident) in the core of a nuclear reactor powerplant, where a power excursion can trigger the formation of a vapour film around the fuel rod, leading to an important rise of the rod temperature and a risk of failure. Some studies in reactor conditions provided transient boiling curves but the modeling lacks of reliability. In collaboration with the IRSN (Institut de Radioprotection et de Sûreté Nucléaire), an experiment model was built at the Institute of Fluid Mechanics of Toulouse. It generates the flow of a refrigerant, HFE7000, in a semi-annular section channel, whose inner wall is made of a metal foil rapidly heated by Joule effect, simulating the heating of a fuel rod. Infrared thermography is used to measure the temperature of the metal foil, painted with a black paint to increase its emissivity, causing also an increase of the wall thermal resistance. The measurement accuracy of the interest temperature has been optimized according to the paint thickness and a correction on the energy balance takes account this parameter. These measurements are coupled with a high-speed camera that allows visualizing the boiling regimes and get bubble sizes using image processing algorithms. On a flux-temperature diagram, the heat transfers are represented both for steady and transient regimes. Each boiling regime is then reviewed : convection, onset of nucleate boiling, nucleate boiling, boiling crisis, film boiling and rewetting. Steady regimes are correctly modeled by usual correlations. Transient convection is characterized over the whole wall and its evolution is closed to the quasi-steady solution. It is shown that heat transfer during the transition to nucleate boiling are strongly related to the formation of a large vapor phase that spreads on the wall. A local study of this propagation is then necessary. In order to simulate and control transient temperature during nucleate boiling, a P.I.D. is implemented to impose a steady or ramps temperature (from 5 to 500 K.s 1 ). The results in nucleate boiling make it possible to recover the results of the literature in both steady and transient conditions. The experiment allows to study the heat transfer when a vapor film is formed and insulates the wall. The film boiling regime during heating or the cooling of the wall can thus be stabilized for several seconds with this system. The conditions for triggering of film boiling are thus characterized, as its spread dynamic and its transfers once established. Finally, the implementation of the physical characteristics of our experience in IRSN’s SCANAIR code allows us to begin to calculate and compare our experimental results with numerical simulations. Unsteady conduction calculations are applied to the measured temperature to analyze our results during the convection regime and after the onset of boiling
Miao, Lin Chun, and 林純妙. "Transient analysis of two-dimensional rectangular plate and cylinder fin with heat flux." Thesis, 2000. http://ndltd.ncl.edu.tw/handle/72762366778049522880.
Повний текст джерела逢甲大學
應用數學系
88
Discussing the heat flux of the transient state suddenly transfer to the root of two-dimensional rectangular plate fin and cylinder fin. The upside、underside and tip of the rectangular plate fin all have different heat convection effect. According to different Biot Number, there have different temperature distribution and heat transfer state. (1)The analysis of the heat transfer of the two dimensional rectangular via using eigenfunction expansion method to fit、top and bottom boundary condition and to compact variable. And to utilize coordinate transform making the homogeneous of right and left boundary condition of the two dimensional rectangular plate. Similarly, to utilize eigenfunction expansion method to satisfy the right and left boundary condition of two dimensional rectangular plate and to compact variable. The resolute answer of the two dimensional rectangular plate would be achieved via fundamental the differential equation method of the single variable. (2)When we research the analysis of the heat transfer of the two dimensional cylinder fin, as result of the symmetry of the cylinder fin, we only consider one chamfer. The research method primarily uses zero Bessel function to transfer the equation of the cylinder fin to dimensionless heat transfer equation. satisfy that the center temperature is finite , so we could resolve by using function to be eigenfunction expansion. It would be satisfied the right and left boundary condition of the two dimensional cylinder fin via the eigenfunction function expansion. The analytical answer of the two dimensional cylinder would be solved by using a general method of single variable differential equation. To solve the analysis and numerical solution using the method of numerical analysis and the program of Matlab. Compare the equivalent of analysis and numerical solution and non-dimensional heat transfer rate. The center temperature distributions of the rectangular plate have apparent differentia with different the Biot Number and thickness. The center temperature will gradually descend with raising the Biot Number. When the Biot Number of the end arise , then the temperature distribution of the end will show constringency status. When the Biot Number is very small , the slope of he center temperature distribution of the different thick fin is still identical. The diversity of temperature would be more with more small thickness. Heat quantity would be faster accumulated and lost. The temporal heat transfer rate will be difficult to reach steady state with arising thickness. The center temperature distributions of the cylinder fin have apparent differentia with different the Biot Number and thickness. The center temperature will gradually descend with raising the Biot Number. The heat quantity would be more accumulated with more large thickness. When the Biot Number of the end arise , then the temperature distribution of the end will show constringency status. When the Biot Number is very small , the slope of he center temperature distribution of the different thick fin is still identical. The temporal heat transfer rate will be difficult to reach steady state with arising thickness.
Lin, Yung-Lung, and 林永龍. "Transient oscillatory flow boiling heat transfer and associated bubble characteristics of FC-72 over a heated plate subject to an imposed heat flux oscillation." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/17138052576770149337.
Повний текст джерела國立交通大學
機械工程系所
96
An experiment is carried out in this study to investigate the transient flow boiling heat transfer performance and associated bubble characteristics of FC-72 flow over a small circular plate subject to a time varying heat flux with the plate flush mounted on the bottom of a horizontal rectangular channel. The imposed heat flux oscillates with time in the form of rectangular waves. The effects of the FC-72 inlet liquid subcooling, mass flux, and imposed heat flux oscillation on the FC-72 transient flow boiling characteristics are explored. In the experiment the inlet liquid subcooling △Tsub ranges from 0 to 10 ℃, the coolant mass flux G varies from 300 to 400 kg/m2s, mean imposed heat flux ranges from 0 to 10 W/cm2 and the amplitude of the heat flux oscillation is fixed at 10%, 30% and 50% of with the period of the heat flux oscillation varied from 10sec. to 30sec., covering the saturated and subcooled flow boiling. The transient flow boiling heat transfer characteristics are illustrated by the measured time variations of the heated plate temperature and boiling heat transfer coefficient. The experimental results show that the time-average FC-72 transient saturated and subcooled flow boiling heat transfer characteristics are not affected to a significant degree by the amplitude and period of the imposed heat oscillation. In fact, they resemble that for the stable flow boiling. However, the imposed heat flux oscillation causes significant temporal oscillations in the boiling heat transfer coefficient, bubble departure diameter and frequency, and active nucleation site density. These physical quantities oscillate at the same frequency as the heat flux oscillation and at a higher , a larger △q/ , and a longer tp they exhibit stronger oscillations except for tp=30 sec. Besides, a slight time lag in Tw oscillation is seen. Moreover, the size of departing bubbles, active nucleation size density and bubble departure frequency decrease as the heat flux is reduced to the low level of -△q. The opposite processes take place for the heat flux raised to the high level of +△q. Furthermore, at the mean imposed heat flux close to that for the ONB in the stable boiling we observe intermittent boiling in the transient saturated flow boiling and subcooled flow boiling. We also find that an increase in the inlet liquid subcooling results in stronger oscillations of these quantities.