Theses and Dissertations from UMD
Permanent URI for this communityhttp://hdl.handle.net/1903/2
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
More information is available at Theses and Dissertations at University of Maryland Libraries.
Browse
3 results
Search Results
Item Forced Convective Boiling via Infrared Thermography(2012) Kommer, Eric; Kim, Jungho; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Multiphase heat transfer is an important mechanism across wide variety of engineering disciplines. The prediction of the heat transfer rate as a function of flow conditions and temperature has been based almost exclusively on experimentally derived correlations. The quality of these correlations depends on the accuracy and resolution of the measurement technique. In addition to the complexities of flow boiling phenomenon in earth gravity, engineering design of space systems requires knowledge of any gravity dependence for heat transfer characteristics. Current research has shown significant variation in the heat transfer characteristics during pool boiling as a function of gravity magnitude. Research into flow boiling in variable gravity environments is extremely limited at this time, but necessary before multiphase systems can be designed for space. The objective of this study is to develop, validate, and use a unique infrared thermometry method to quantify the heat transfer characteristics of flow boiling in earth gravity, prior to use of the apparatus in variable gravity environments. This new method allows high spatial and temporal resolution measurements, while simultaneously visualizing the flow phenomenon. Validation of this technique will be demonstrated by comparison to accepted correlations for single and multiphase heat transfer in earth gravity environments.Item Development and Testing of a Multiplexed Temperature Sensor(2008-08-08) Anderson, Greg; di Marzo, Marino; Kim, Jungho; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Researchers studying phenomena associated with steep surface temperature gradients, such as boiling, need to be able to obtain a detailed surface temperature distribution. Such a distribution can be obtained by taking measurements at a number of discrete locations on the surface using multiple individual temperature sensors. Because each sensor requires at least two electrical connections, this approach has historically been limited to relatively few temperature measurements; the most extensive measurements made this way are still limited to a 10 × 10 array. A new temperature sensor has been developed to address this measurement problem. The new sensor consists of a 32 × 32 array of diode temperature sensors in a 10.24 mm2 area, with each component diode measuring 100 × 100 micron^2. Unlike previous array-type sensors, the new sensor uses a multiplexing scheme to reduce the number of external leads required; only 64 leads are required to obtain measurements from over 1000 individual temperature sensors. The new sensor also incorporates eight resistive heater elements to provide the heat flux to initiate and sustain boiling. The heaters are capable of delivering up to 100 W/cm^2. This dissertation describes the design and testing of the new temperature sensor and the supporting hardware and software. The system is demonstrated by determining the local heat transfer coefficients for a jet of FC-72 from a 0.241 mm diameter nozzle. The surface temperature distribution is measured for various combinations of applied heat flux, jet velocity, and nozzle standoff distance; these measurements are then used to determine the local heat transfer coefficient distribution. These measured values compare favorably to those predicted using several correlations available in the literature.Item A Self-Contained Cold Plate Utilizing Force-Fed Evaporation for Cooling of High-Flux Electronics(2007-12-11) Baummer, Thomas Buchanan; Ohadi, Michael M; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In recent years, the rapid increase in the functionality, speed, and power density of electronics has introduced new challenges, which have led to demand for high heat flux electronics cooling at levels that cannot be met by conventional technologies. The next generation of high power electronics will require advanced cooling beyond the methodologies currently available. This thesis describes work done on a novel form of two-phase heat transfer, named "Force-Fed Evaporation," which addresses this need. This process utilizes evaporation of a liquid in a microchannel surface to produce high heat transfer coefficient cooling at very high heat flux while maintaining a low hydraulic pressure drop. Component level tests were conducted to demonstrate the capability of this process. This led to the development of a self-contained, two-phase cold plate suitable for cooling a high power circuit board. The results show that this technology bears promise for the future of electronics cooling.