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Thermosyphon transient operation was numerically modeled. The numerical model presented in this work overcame the limitations of previous studies by including transient conduction in the vessel wall, shear stress between the rising vapor and the falling film in the thermosyphon, the influence of the mass in the liquid pool in the evaporator, and by using a more refined and accurate numerical grid. Unique to this model was the accounting for temporal changes in the effective length of the vapor space due to the expanding and contracting of non-condensable gases in the vapor space. The model assumed quasi-steady one-dimensional vapor flow, transient one-dimensional flow in the falling liquid film, and transient behavior in the liquid pool in the evaporator. The model also assumed transient two-dimensional conduction in the thermosyphon wall. Using fundamental principles, the governing equations used in the numerical model were developed and then written in finite difference form. The finite difference forms of the governing equations were integrated using an explicit scheme. A sensitivity study was performed and found that the numerical model was accurate to 4%. An experiment was also conducted to validate the numerical model. The experiment used three distinct transient heat loads to simulate gradual, moderate and sharp increases in temperature. The uncertainty of the experiment was shown to be 2.3%. The temperatures from the numerical model were then compared to those measured during the physical experiment to determine the validity of the numerical model. The model was further exercised to develop a useful engineering relationship that can be used to predict the transient performance of a thermosyphon.

Turbulent flow induced pipe vibration is a phenomenon that has been observed but not fully characterized. This thesis presents research involving numerical simulations that have been used to characterize pipe vibration resulting from fully developed turbulent flow. The vibration levels as indicated by: pipe surface displacement, velocity, and acceleration are characterized in terms of the parameters that exert influence. The influences of geometric and material properties of the pipe are investigated for pipe thickness in the range 1 to 8 mm at a diameter of 0.1015 m. The effects of pipe elastic modulus are explored from 3 to 200 GPa. The range of pipe densities investigated is 3,000 to 12,000 kg/m3. All pipe parameters are varied for both a short pipe (length to diameter ratio = 3) and a long pipe (length to diameter ratio = 24). Further, the effects of varying flow velocity, fluid density and fluid viscosity are also explored for Reynolds numbers ranging from 9.1x104 to 1.14x106. A large eddy simulation fluid model has been coupled with a finite element structural model to simulate the fluid structure interaction using both one-way and two-way coupled techniques. The results indicate a strong, nearly quadratic dependence of pipe wall acceleration on average fluid velocity. This relationship has also been verified in experimental investigations of pipe vibration. The results also indicate the pipe wall acceleration is inversely dependant on wall thickness and has a power-law type dependence on several other variables. The short pipe and long pipe models exhibit fundamentally different behavior. The short pipe is not sensitive to dynamic effects and responds primarily through shell modes of vibration. The long pipe is influenced by dynamic effects and responds through bending modes. Dependencies on the investigated variables have been non-dimensionalized and assembled to develop a functional relationship that characterizes turbulence induced pipe vibration in terms of the relevant parameters. The functional relationships are presented for both the long and short pipe models. The functional relationships can be used in applications including non-intrusive flow measurement techniques. These findings also have applications in developing design tools in pipe systems where vibration is a problem.

This work determines a suitable value for a dispersion coefficient to be used in the One-Dimensional Advection-Dispersion equation to model dispersion within sewer collection systems. Dispersion coefficients for sewer systems have only recently begun to be studied, and there is not yet an established value that is commonly accepted. The work described in this paper aimed, through observational study, to find a suitable value to be used. Salt tracers were placed in two separate reaches of sewer line. The first line studied was a straight, linear reach of sewer that included three manholes. The tracer was placed in the first manhole and the conductivity was measured at the two consecutive manholes downstream. These measurements were compared to a model developed using the 1D Advection-Dispersion Equation. The flow information and sewer network geometry was used in the model and the dispersion coefficient was adjusted to find a best fit. It was found that a value of 0.18 m2/s for the dispersion coefficient provided the best statistical match. The next reach of sewer that was studied was a reach with a 90 degree angle. This section was chosen to observe the effect that mixing has on dispersion, because of the change in direction of flow. The same procedure was applied, and an optimal dispersion coefficient of 0.22 m2/s was found. These values represent optimal dispersion coefficients under a specific set of conditions. It should not be assumed that they will provide accurate results in all circumstances, but are rather a base point for average flows under dry, stable conditions. Using these values inferences can begin to be made about dispersion characteristics throughout the entire sewer network. This can lead to specific engineering applications, and well as applications in other fields of study.

The efficient delivery of potable water for a community through its distribution system has historically been the backbone of nearly all metropolitan developments. Much of these systems are comprised of pipe networks made of various materials including concrete, iron, PVC, and even steel. As these communities expand and urbanize, water demand and population density simultaneously increase. This develops higher strains and stresses in the community‟s water distribution network causing pipes to corrode, crack, or rupture prematurely while in service. As a result, the deterioration of water distribution systems in growing cities is increasingly becoming a major concern for our nation. There have been several publications on the subject of evaluating pipe conditions within a water distribution network that use statistical models, estimation, and other mathematical analyses. However, many of these publications are cumbersome and are difficult to understand from a non-engineering perspective. In order to simplify the evaluation process for all varying professions in a city‟s public works division, the primary objective of this study was to develop a user-friendly risk assessment model that was practical, cost effective, and easy to follow. This risk assessment model focuses primarily on the physical condition of pipes in a water distribution system. It assesses the installation year, age, material, and break history of these water mains. It does not consider pipe fittings, pumps, or other network components. A pipe‟s probability of failure is determined from its physical condition. Page v The model then considers various economic degrees of impact that may affect the rehabilitation or replacement of these water mains. These degrees of impact include raw material costs, customer criticality, land use, demand, pipe material, and traffic impact. By focusing on pipes having the highest probability of failure and considering their economic impacts, this model identifies and prioritizes the most vulnerable water mains that require immediate attention. In order to validate this developed risk assessment model, the method was applied to a real water distribution system. Data from the City of Arroyo Grande, California was used in conjunction with WaterCAD and geographic information systems (ArcGIS) software during analysis. Application of the risk assessment model identified six cast iron pipes in Arroyo Grande‟s water distribution system as having a high risk of failure. Of the city‟s 3,057 individual pipe segments, recognizing only five of these pipes as high risk indicated that the assessment model was functional. Developing and testing this risk assessment model with real city data effectively demonstrated its practicality and easy application to a real water distribution system. If utilized, city officials can quickly identify and prioritize pipes needing rehabilitation or replacement by using reliable, up-to-date water distribution data from their city with this risk assessment model. Furthermore, use of this model may also simplify allocation of capital funds for future pipe improvement projects as the city continues its urbanization.

No / This paper considers both the linear elastic and creep buckling of polymeric pipe linings used for the rehabilitation of gravity pipes, for which external groundwater pressure has been identified as the prime source of loading. Theoretically perfect and imperfect conditions are considered, with the imperfections taken to be in the form of a concentric or eccentric annulus between the rigid host pipe (cylindrical constraint) and polymeric lining. Under these conditions two recently obtained mathematical procedures for the prediction of linearly and non-linearly elastic buckling are compared with the results of complementary laboratory testing. Linear elastic conditions are shown to be well approximated by undertaking short-term (¿30 min) testing under increasing pressure to failure. Controlled imperfections are introduced into the laboratory tests and excellent correlation with the theoretical predictions is obtained. In particular, the dominant geometrical imperfections are shown to be major influences on the obtained buckling pressure. The mathematical models are then adapted to simulate the creep buckling process under long-term constant pressure. The results obtained are again compared with those provided by complementary physical testing, and appropriate conclusions are made.

Heat pipe is a passive heat transport device, engineered to harness latent heat of vaporization of contained working fluid to efficiently transfer sensible energy of one fluid stream to another. Heat pipes have observed applications in HVAC, electronics cooling, space equipment cooling, etc. due to their high effective thermal conductivity. Heat pipe heat exchanger (HPHE) employs finned heat pipes for performance enhancement. A mathematical model was developed into a Mathcad based tool for properly sizing and optimizing gravity-assisted HPHE designs. A charging station was setup to fabricate heat pipes under deep vacuum using a liquid nitrogen cold trap. A wind test tunnel was constructed to conduct experiments on a HPHE prototype. The thermal performance testing resulted in 11.4 kW of heat duty with 54% effectiveness of the HPHE. Parametric studies were also conducted for varying input heat and air flow rates, followed by the result comparison with program predictions.

Multiple oscillating heat spreaders (OHS) were fabricated for the purpose of effectively transporting heat fluxes from vehicular electronics. The OHSs possessed modified evaporators for enhanced thermal spreading capabilities; one OHS was designed for pressure shorting, i.e. the ‘Slots OHS’, and the other for thermal shorting, i.e. the ‘Perforated Evaporator OHS’. These OHSs were tested in the axial heating configuration with the evaporator length-wise opposite the condenser, as well as in a centralized heating configuration implemented with the condenser thick-wise opposite the heat source to characterize thermal spreading effectiveness. The condensing location and heat input were varied in the central heating and axial configuration to determine thermal spreading effectiveness dependency to condenser location, heat removal, and heat input. Both OHSs were experimentally compared to an OHS of similar dimensions with no modified evaporator, and the results indicate the modified evaporators improve OHS thermal spreading ability for high heat flux thermal management.