570 research outputs found
A Local Condensation Analysis Representing Two-phase Annular Flow in Condenser/radiator Capillary Tubes
NASA's effort for the thermal environmental control of the Space Station Freedom is directed towards the design, analysis, and development of an Active Thermal Control System (ATCS). A two phase, flow through condenser/radiator concept was baselined, as a part of the ATCS, for the radiation of space station thermal load into space. The proposed condenser rejects heat through direct condensation of ATCS working fluid (ammonia) in the small diameter radiator tubes. Analysis of the condensation process and design of condenser tubes are based on the available two phase flow models for the prediction of flow regimes, heat transfer, and pressure drops. The prediction formulas use the existing empirical relationships of friction factor at gas-liquid interface. An attempt is made to study the stability of interfacial waves in two phase annular flow. The formulation is presented of a stability problem in cylindrical coordinates. The contribution of fluid viscosity, surface tension, and transverse radius of curvature to the interfacial surface is included. A solution is obtained for Kelvin-Helmholtz instability problem which can be used to determine the critical and most dangerous wavelengths for interfacial waves
Reexamination of METMAN, Recommendations on Enhancement of LCVG, and Development of New Concepts for EMU Heat Sink
METMAN is a 41-node transient metabolic computer code developed in 1970 and revised in 1989 by Lockheed Engineering and Sciences, Inc. This program relies on a mathematical model to predict the transient temperature distribution in a body influenced by metabolic heat generation and thermal interaction with the environment. A more complex 315-node model is also available that not only simulates the thermal response of a body exposed to a warm environment, but is also capable of describing the thermal response resulting from exposure to a cold environment. It is important to compare the two models for the prediction of the body's thermal response to metabolic heat generation and exposure to various environmental conditions. Discrepancies between the twi models may warrant an investigation of METMAN to ensure its validity for describing the body's thermal response in space environment. The Liquid Cooling and Ventilation Garment is a subsystem of the Extravehicular Mobility Unit (EMU). This garment, worn under the pressure suit, contains the liquid cooling tubing and gas ventilation manifolds; its purpose is to alleviate or reduce thermal stress resulting from metabolic heat generation. There is renewed interest in modifying this garment through identification of the locus of maximum heat transfer at body-liquid cooled tubing interface. The sublimator is a vital component of the Primary Life Support System (PLSS) in the EMU. It acts as a heat sink to remove heat and humidity from the gas ventilating circuit and the liquid cooling loop of the LCVG. The deficiency of the sublimator is that the ice, used as the heat sink, sublimates into space. There is an effort to minimize water losses in the feedwater circuit of the EMU. This requires developing new concepts to design an alternative heat sink system. Efforts are directed to review and verify the heat transfer formulation of the analytical model employed by METMAN. A conceptual investigation of regenerative non-venting heat-sink subsystem for the EMU is recommended
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An Experiment with Flipped Classroom Concept in a Thermodynamics Course
Flipped classroom is an instructional concept that reverses the traditional method of teaching by providing instructional content in advance outside of the classroom and bringing some of the outside activities such as solving problems into the classroom. Flipped classroom concepts was recently experimented in two sections of an introductory undergraduate course in thermodynamics. Students were assigned to read specific sections of the textbook and review previously prepared power point presentation of lectures before attending lecture periods. Electronic respond devices, such as I-Clickers, were used to gage students understanding of assigned reading material by starting class with a quiz. The concepts were explained in detail. When students had difficulties with the specific topics related to quiz questions, a second quiz was given later to see if the students’ understanding of the material were improved. A survey was conducted near the end of semester to seek student feedback on their experience with the flipped classroom concept. The paper includes the results of the student survey.Cockrell School of Engineerin
A Message-Passing Algorithm for Counting Short Cycles in a Graph
A message-passing algorithm for counting short cycles in a graph is
presented. For bipartite graphs, which are of particular interest in coding,
the algorithm is capable of counting cycles of length g, g +2,..., 2g - 2,
where g is the girth of the graph. For a general (non-bipartite) graph, cycles
of length g; g + 1, ..., 2g - 1 can be counted. The algorithm is based on
performing integer additions and subtractions in the nodes of the graph and
passing extrinsic messages to adjacent nodes. The complexity of the proposed
algorithm grows as , where is the number of edges in the
graph. For sparse graphs, the proposed algorithm significantly outperforms the
existing algorithms in terms of computational complexity and memory
requirements.Comment: Submitted to IEEE Trans. Inform. Theory, April 21, 2010
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Tracking Student Success in Order to Assess the Instructor Effectiveness to Improve Student Retention and Graduation Rates
This paper explores the metric of follow-on student success that can be considered when evaluating an instructor’s effectiveness. The metric is the follow-on course success rate which should be useful in engineering since many fundamental courses are prerequisites to follow-on courses. For example, students who pass thermodynamics 1 should be able to pass thermodynamics 2. The data shows that the follow-on success rate depends on the instructor who teaches the first course. As more universities focus on student retention and graduation rates, they should investigate metrics to gauge how well an instructor prepares students for subsequent academic success. This paper looks at course follow-on success rate in a two-semester sequence of thermodynamics courses.Cockrell School of Engineerin
An Efficient Algorithm for Finding Dominant Trapping Sets of LDPC Codes
This paper presents an efficient algorithm for finding the dominant trapping
sets of a low-density parity-check (LDPC) code. The algorithm can be used to
estimate the error floor of LDPC codes or to be part of the apparatus to design
LDPC codes with low error floors. For regular codes, the algorithm is initiated
with a set of short cycles as the input. For irregular codes, in addition to
short cycles, variable nodes with low degree and cycles with low approximate
cycle extrinsic message degree (ACE) are also used as the initial inputs. The
initial inputs are then expanded recursively to dominant trapping sets of
increasing size. At the core of the algorithm lies the analysis of the
graphical structure of dominant trapping sets and the relationship of such
structures to short cycles, low-degree variable nodes and cycles with low ACE.
The algorithm is universal in the sense that it can be used for an arbitrary
graph and that it can be tailored to find other graphical objects, such as
absorbing sets and Zyablov-Pinsker (ZP) trapping sets, known to dominate the
performance of LDPC codes in the error floor region over different channels and
for different iterative decoding algorithms. Simulation results on several LDPC
codes demonstrate the accuracy and efficiency of the proposed algorithm. In
particular, the algorithm is significantly faster than the existing search
algorithms for dominant trapping sets
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