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 Cryogenic Design and Thermal Analysis of the CURIE CryoTrap(2022) Osborn, Rebecca Caroline; Koeth, Timothy W; Chemical Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The decay rates of electron capture (EC) radioisotopes, such as 7Be, are demonstrativelysusceptible to alteration with change to the electron orbital structure [1] [2] [3] [4]. The Cryogenic Ultra-high vacuum Radioactive Isotope Experiment (CURIE) Project aims to isolate the various charge states of the low-Z radioisotope 7Be stably to perform novel half-life measurements. To achieve this, the system must be cooled to 4K to reach extreme high vacuum (XHV) conditions in excess of 10E−15 mbar and to ensure single ion resolution detection. The cryogenic design which achieves this is presented here. The design consists of the actively cooled 45K radiation shield, and the 4K stage which houses the Penning trap. The 4K stage is brought to XHV and maintained at these pressures through the design of a rotary “cryovalve”. This thesis details the entire apparatus, the heat loads incident on both stages through simulation, and outlines an experimental method for testing the “cryovalve”.Item High Reynolds Number Vertical Up-Flow Parameters For Cryogenic Two-Phase Helium I(2014) Mustafi, Shuvo; Kim, Jungho; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The two phase flow characteristics of helium I are of interest since under most operational scenarios this cryogenic fluid exists in both liquid and vapor form because of its extremely low boiling point and latent heat of vaporization. There is a significant knowledge gap in the flow boiling parameters of helium (heat transfer coefficient, pressure drop and dryout heat flux) for high Reynolds number vertical up-flows (Re =10^5-10^6). This dissertation fills this gap and helps to expand the use of helium as an inert simulant for hydrogen. Since no prior correlations for the flow boiling parameters existed for vertical up-flows of helium at these Reynolds numbers, any predictions of these parameters were dependent on correlations that were tested at lower Reynolds numbers, or correlations based on other fluids. The thermophysical properties of helium I are significantly different from most other fluids; therefore the capability of prior correlations in predicting experimental observations was limited. As part of this research new correlations are proposed for the flow boiling parameters. This research begins the investigation of a new regime for two-phase helium I flows at Reynolds numbers above 3e5. The techniques described will enable future work to address other gaps in knowledge for helium I flows that still remain. The prior heat transfer coefficient correlation over-predicted the data that was collected for this research. The new correlation improves the agreement with data by a factor of 98. Two prior models for pressure drop, the separated flow model and the homogeneous flow model, under-predict the observed pressure drop. The newer versions of the separated flow and the homogeneous flow correlations improve agreement with the data by about a factor of 3 and by more than a factor of 2 respectively. The previous dryout heat flux correlation considerably over predicts the observed dryout heat flux. The new correlation improves agreement with the data by a factor of 21. Significant cryogenic challenges were overcome to collect the research data. The strategies described for surmounting the diverse challenges such as thermal acoustic oscillations and low dryout heat flux could be used by future two-phase cryogenic flow researchers.Item FLOW AND ATOMIZATION CHARACTERISTICS OF CRYOGENIC FLUID FROM A COAXIAL ROCKET INJECTOR(2007-11-28) Gautam, Vivek; Gupta, Ashwani K; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)High thrust-to-weight ratio and consistent performance over a range of operating conditions make cryogenic rocket engines one of the best options for space propulsion. However, future space explorations and missions to moon, mars and beyond require improvements in our present knowledge of the rocket engine combustion technology. In order to help improve the performance and reliability of current rocket engine combustors, several key issues need to be considered. Injector performance is one such issue related to the development of a new generation of rocket engine combustors. Previous research has suggested that coaxial injectors are most preferable for injection of cryogenic propellants inside the combustion chamber because of their simple design, low losses and high combustion stability. An experimental facility was designed and fabricated to simulate a single element shear coaxial injector. Gases of different densities were injected through the annulus between the two injector tubes over a large range of velocities, while liquid nitrogen flows through the inner tube. In this research, liquid nitrogen was used to simulate liquid oxygen because it is very similar to liquid oxygen, chemically inert, easy and safe to install in laboratory testing. High speed cinematography and Schlieren imaging have been used to examine the evolutionary flow behavior and global features of the liquid nitrogen jet, while PIV imaging was used to characterize the gaseous flow. This research has analyzed the transient behavior and unfolds the detailed evolutionary characteristics of both the cryogenic liquid and gaseous phase evolving from the shear coaxial injector for the first time. The effect of density ratio, velocity ratio and momentum ratio on the behavior of steady-state liquid nitrogen jet from a coaxial injector at atmospheric pressure has also been examined in detail. The impact of these parameters on primary instability of liquid core, the shear/spreading angle and its potential core length have been examined. Furthermore, the impact of some of the important non-dimensional numbers such as, Reynolds number, Weber number and Prandtl number, have been examined to develop scaling laws for the prediction of cryogenic potential core lengths. New correlations have been provided that describes the cryogenic jet behavior under simulated rocket injector operating conditions.