Thesis--University of Wisconsin--Madison. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 206-212).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1983. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 254-259).

Thesis (M.S.)--Rochester Institute of Technology, 1981. / Typescript. Includes bibliographical references (leaves 53-54).

The boiling of water droplets on hot metal surfaces is studied experimentally and mathematically in order to establish the conditions necessary for droplets to enter a film boiling mode. The subsurface temperature history within a plate undergoing droplet boiling on the surface is measured. A numerical model of the heat transfer in the plate is then used to deduce from these data the following characteristics of droplet boiling: (1) the effective heat transfer coefficient between water droplet and plate during the initial transient forming the spherical droplet, (2) the apparent time period needed to establish the droplet in the film boiling mode, and (3) the minimum plate surface temperature reached during the initial formation of the boiling droplet. The effective heat transfer coefficient, formation time, and minimum surface temperature are sufficient to develop a calculation method which predicts the minimum initial plate temperature necessary for a water droplet to enter film boiling. This numerical conduction model accounts for the influence of plate material, plate thickness, oxidation of the plate surface, the boundary condition on the plate lower surface, and the size of the droplet. The prediction method is successfully used to estimate the minimum film boiling temperature for brass, graphite, Pyrex, copper, aluminum, stainless steel, and Zircalloy II. The findings of the experiments and numerical studies are applied to the rewetting phase of a loss-of-coolant-accident in a light water reactor. This application, in turn, provides explanations for some of the phenomena observed in studies of the prequench heat transfer within rod bundles including the effect of multiple droplet impacts, and suggests possible reasons for some of the difficulties experienced in attempts to establish the effective rewetting temperature on reactor fuel rod surfaces.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / by Lawrence M. Hull. / Ph.D.

Thesis. 1977. M.S.--Massachusetts Institute of Technology. Dept. of Mechanical Engineering. / Includes bibliographical references. / Thesis. 1977. M.S.--Massachusetts Institute of Technology. Dept. of Mechanical Engineering.

Thesis (Ph. D.)--Ohio State University, 2005. / Title from first page of PDF file. Document formatted into pages; contains xxi, 225 p.; also includes graphics (some col.). Includes bibliographical references (p. 218-225). Available online via OhioLINK's ETD Center

AN ABSTRACT OF THE DISSERTATION OF PAYAM SHARIFI, for the Doctor of Philosophy degree in ENGINEERING SCIENCE, presented on April 2011, at Southern Illinois University Carbondale. TITLE: FUNDAMENTAL STUDIES ON THE EFFECT OF ELECTRIC FIELD ON INTERFACE INSTABILITY, FILM BOILING, AND FILM CONDENSATION MAJOR PROFESSOR: Dr. A. Esmaeeli This research focuses on investigation of uniform electric field on three inter-related interfacial phenomena including interface under electric field, film boiling under applied electric field, and film condensation under applied electric field. The idea of applying electric field to enhancement boiling and condensation heat transfer has been considered one of the active enhancement methods. However, understanding the details of interaction of electric field and phase change demands a strong tool to go beyond the limitations of experimental and theoretical approaches. We perform Direct Numerical Simulations (DNS) using front-tracking/finite-difference techniques to fully resolve the electric, flow, and heat transfer fields in continuum scales. In terms of electric field-induced interface instability problem, we studied the dynamics of interface under AC/DC uniform electric fields for a wide range of fluid physical properties and investigated the individual effect of their corresponding nondimensional numbers. We observed that application of DC electric field destabilizes the interface in such a way that it goes over several cycles of oscillations and then settles to its steady-state form and remains quiescent. However, for AC electric field, the interface oscillations follows the frequency of applied electric potential source. For the film boiling under applied electric field, we studied the effect of individual governing nondimensional numbers on the behavior of film boiling under DC/AC electric fields. Electric field makes the interface more unstable by elongating the bubbles, decreasing the most dangerous wavelength, and expediting the formation of bubbles. The impact of these effects on heat transfer can be observed from the evolution of Nu number in the course of film boiling. We realized that for the same conditions AC field alters the transient spatially averaged Nu number in a way that it follows the oscillations of applied electric potential source. However, the heat transfer enhancement does not get affected by applying either AC or DC electric fields. We extended our research to multimode film boiling to observe the interaction of bubbles growing next to each other. Also, we carried out a study on the effect of electric field on downward-facing film condensation over a horizontal flat plate. This problem is similar to film boiling over a horizontal flat plate which we already studied although the phase change occurs in opposite direction. Like the effect of electric field on film boiling, electric field made the interface of condensate more unstable by decreasing its most dangerous wave length. However, in this case, the enhancement becomes more effective due to cooperation of gravitational and electrical forces. Our studies show that phase change heat transfer coefficient can be enhanced in the presence of electric field by more that 70%. Condensation of vapors over the bank of horizontal tubes has always been the host of many engineering applications in power plants, chemical and petrochemical plants, etc. To take the first step toward the study of enhancement effect of electric field on complex geometries, we also carried out a study on the condensation over tube banks in the absence of electric field. This study mainly concentrates on the effect of tube distance on heat transfer coefficient in a vertically in-lined tube bank. Our study reveals that heat transfer coefficient can be highly dependent on tube diameter and spacing such that choosing an appropriate spacing can lead to a more than 50% enhancement.

Under normal operating conditions a CANDU reactor pressure tube (PT) is insulated from its outer calandria tube (CT) by a CO2 gas annulus. If the primary loop coolant flow is compromised the PT can overheat and, if still pressurized, balloon into contact with the CT. At this point the moderator acts as an emergency heat sink. If the heat transferred from the CT to the moderator exceeds the critical heat flux (CHF) the CT can overheat, begin to strain due to the contact pressure, and eventually fail. A mechanistic model is presented that describes ballooning contact of the PT and CT, the resulting thermal contact conductance, heat flux to the moderator, and, if CHF is exceeded, the development of film boiling and potential CT strain. The goal is to create a software package that predicts fuel channel failure during a pressure tube overheat event. / Thesis / Master of Applied Science (MASc) / Computer software was developed to predict CANDU fuel channel failure in the event of a total station blackout. The model created successfully predicted the available experimental data.

The critical heat flux (CHF) point for a reactor core system is one of the most important factors to discuss in regards to reactor safety. If this point is reached, standard coolant systems are not enough to handle the temperature increase in the cladding, and the likelihood of meltdown greatly increases. While the nucleate boiling and film boiling regimes have been well-investigated, the transition boiling regime between the point of departure from nucleate boiling (DNB) and the minimum film boiling temperature (T_min) remains difficult to study. This is due to both the complexity of the phenomena, as well as limitations in measurement, where experiments typically utilize thermocouples for temperature data acquisition. As a result of technological advancement in the field of fiber optics, it is possible to measure the quenching temperature to a much higher degree of precision. Optical fiber sensors are capable of taking many more measurements along a fuel simulator length than thermocouples, which are restricted to discrete points. In this way, optical fibers can act as an almost continuous sensor, calculating data at a resolution of less than one millimeter where a thermocouple would only be able to measure at one point. In this thesis, the results of a series of quenching experiments performed on stainless steel, Monel k500, and Inconel 600 rods at atmospheric pressure, with different subcooling levels and surface roughnesses, will be discussed. The rewetting temperature measurement is performed to compare results between thermocouples and optical fiber sensors in a 30 cm rod. These results are further discussed with regard to future application in two-phase flow experiments. / Master of Science / There are multiple types of boiling that can occur depending on the heat transfer capabilities of the system and the power applied to the coolant. The most common is nucleate boiling, where vapor produced at the surface forms bubbles and move away from the surface due to buoyancy. At a high enough power, the bubbles can coalesce into a film and lead to a point at which the liquid coolant can no longer contact the surface. Since vapor is not as effective at transferring heat from the surface, the temperature will increase drastically. In nuclear reactors, this situation (known as departure from nucleate boiling), can quickly lead to a meltdown of the fuel rods. Another important safety parameter in nuclear reactors is the minimum temperature at which this vapor film can be maintained, T_min. This parameter is a source of significant concern with regard to accident scenarios such as LOCA (loss of coolant accident), where reintroducing coolant to the rods efficiently is of top priority. While much research has been done on nucleate and film boiling, it has been difficult to study the transition period between the two regimes due to both its transient nature and the lack of continuous measurement capabilities. Typically, temperature is measured using thermocouples, which are point-source sensors that do not allow for high spatial resolution over a large area. This thesis deals with the utilization of optical fibers for temperature measurement, which are capable of calculating data at every millimeter, potentially a much more precise measurement system than with the thermocouples. The experiments performed in this paper are quenching experiments, where a rod embedded with thermocouples and an optical fiber is heated to well above T_min and quickly plunged into a volume of water, in order to view the transition from film to nucleate boiling.