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Horizontal Buoyancy in Wind Tunnels

Description: Note presenting an examination of horizontal buoyancy in wind tunnels, including an examination of the relative flow, static pressure gradient, horizontal buoyancy computation, and methods of computation in practical use are provided.
Date: November 1920
Creator: Zahn, A. F.
Partner: UNT Libraries Government Documents Department

An Investigation of Preservice Teachers' Understanding of Buoyancy

Description: The purpose of this study was to examine the conceptual understandings of 55 elementary preservice teachers for the concept of buoyancy. This study used Ausubel’s Assimilation Theory (Ausubel, 1963) as a framework for a 15-week intervention that used pre/post concept maps (Cmaps), pre/post face-to-face semi-structured interviews, and drawings as evidences for change of formation of cognitive structures. Using a convergent parallel design and mixed methods approach, preservice teachers’ conceptions were analyzed using these evidences. Results of the study show that preservice teachers held both scientific conceptions and misconceptions about buoyancy as a force before and after an instructional intervention. Of importance were the existence of robust misconceptions about buoyancy that included inaccurate scientific knowledge about the foundational concepts of gravity, weight, mass, and density. The largest gains in scientific knowledge included the concepts of gravity, surface area, opposing forces, and the buoyant force. These concepts were consistently supported with evidence from post-concept maps, post, semi-structured interviews, and drawings. However, high frequencies of misconceptions were associated with these same aforementioned concepts as well as additional misconceptions about buoyancy-related concepts (i.e., weight, density, displacement, and sinking/floating). A paired t test showed a statistically significant difference (t = -3.504, p = .001) in the total number of scientifically correct concepts for the pre-concept maps (M = 0.51, SD = .879) and post-concept maps (M = 1.25, SD = 1.542). The Cohen’s d effect size was small, .47. Even through gains for the pre/post concept maps were noted, a qualitative analysis of the results indicated that not only were there serious gaps in the participant’s scientific understanding of buoyancy, after the instructional intervention an increased number of misconceptions were presented alongside the newly learned concepts. A paired t test examining misconceptions showed that there was a statistically significant difference (t = -3.160, p = ...
Date: May 2016
Creator: Kirby, Benjamin
Partner: UNT Libraries

Analysis of Buoyancy-Driven Ventilation of Hydrogen from Buildings: Preprint

Description: When hydrogen gas is used or stored within a building, as with a hydrogen-powered vehicle parked in a residential garage, any leakage of unignited H2 will mix with indoor air and may form a flammable mixture. One approach to safety engineering relies on buoyancy-driven, passive ventilation of H2 from the building through vents to the outside.
Date: August 1, 2007
Creator: Barley, C. D.; Gawlik, K.; Ohi, J. & Hewett, R.
Partner: UNT Libraries Government Documents Department

Mass and Mass Values

Description: Report discussing the different bases for determining mass values and instances where these differences may be crucial. The first part is a historical summary of weighing, standards, and the assignment of value; and the interfacing of mass measurements with civilization. The second part discusses in detail the methods of assigning mass values. Ways to convert from values on one basis to values on another basis are discussed.
Date: January 1974
Creator: Pontius, Paul E.
Partner: UNT Libraries Government Documents Department

Analysis of Buoyancy-Driven Ventilation of Hydrogen from Buildings

Description: The scope of work for this project includes safe building design, vehicle leak in residential garage, continual slow leak, passive, buoyancy-driven ventilation (versus mechanical), and steady-state concentration of hydrogen versus vent size.
Date: September 11, 2007
Creator: Barley, C. D.; Gawlik, K.; Ohi, J. & Hewett, R.
Partner: UNT Libraries Government Documents Department

On the fluid mechanics of fires

Description: Fluid mechanics research related to fire is reviewed with focus on canonical flows, multiphysics coupling aspects, experimental and numerical techniques. Fire is a low-speed, chemically-reacting, flow in which buoyancy plans an important role. Fire research has focused on two canonical flows, the reacting boundary-layer and the reacting free plume. There is rich, multi-lateral, bi-directional, coupling among fluid mechanics and scalar transport, combustion, and radiation. There is only a limited experimental fluid-mechanics database for fire due to measurement difficulties in the harsh environment, and the focus within the fire community on thermal/chemical consequences. Increasingly, computational fluid dynamics techniques are being used to provide engineering guidance on thermal/chemical consequences and to study fire phenomenology.
Date: February 29, 2000
Partner: UNT Libraries Government Documents Department

Influence of fluid-property variation on turbulent convective heat transfer in vertical annular channel flows.

Description: Influence of strongly-varying properties of supercritical-pressure fluids on turbulent convective heat transfer is investigated using direct numerical simulation. We consider thermally-developing upward flows in a vertical annular channel where the inner wall is heated with a constant heat flux and the outer wall is insulated. CO2 is chosen as the working fluid at a pressure to 8 Mpa, and the inlet Reynolds number based on the channel hydraulic diameter and the bulk velocity is Re0 = 8900. It is shown that turbulent convective heat transfer characteristics of supercritical flow are significantly different from those of constant-property flow mainly due to spatial and temporal variations of fluid density. Non-uniform density distribution causes fluid particles to be accelerated either by expansion or buoyancy force near the heated wall, while temporal density fluctuations change the transport characteristics of turbulent heat and momentum via the buoyancy production terms arising from the correlations such as p1u1x, p1u1r and p1h1. Among various turbulence statistics, the streamwise turbulent heat flux shows a very peculiar transitional behavior due to the buoyancy effect, changing both in sign and magnitude. Consequently, a non-monotonic temperature distribution is developed in the flow direction, causing severe impairment of heat transfer in supercritical flows.
Date: October 1, 2005
Creator: McEligot, D. M.; Bae, J. H.; Yoo, J. Y.; Choi, H. & Wolf, James R.
Partner: UNT Libraries Government Documents Department

Pilot Study of the Effects of Simulated Turbine Passage Pressure on Juvenile Chinook Salmon Acclimated with Access to Air at Absolute Pressures Greater than Atmospheric

Description: The impacts of pressure on juvenile salmon who pass through the turbines of hydroelectric dams while migrating downstream on the Columbia and Snake rivers has not been well understood, especially as these impacts relate to injury to the fish's swim bladder. The laboratory studies described here were conducted by Pacific Northwest National Laboratory for the US Army Corps of Engineers Portland District at PNNL's fisheries research laboratories in 2004 to investigate the impacts of simulated turbine passage pressure on fish permitted to achieve neutral buoyancy at pressures corresponding to depths at which they are typically observed during downstream migration. Two sizes of juvenile Chinook salmon were tested, 80-100mm and 125-145mm total length. Test fish were acclimated for 22 to 24 hours in hyperbaric chambers at pressures simulating depths of 15, 30, or 60 ft, with access to a large air bubble. High rates of deflated swim bladders and mortality were observed. Our results while in conclusive show that juvenile salmon are capable of drawing additional air into their swimbladder to compensate for the excess mass of implanted telemetry devices. However they may pay a price in terms of increased susceptibility to injury, predation, and death for this additional air.
Date: April 28, 2005
Creator: Carlson, Thomas J. & Abernethy, Cary S.
Partner: UNT Libraries Government Documents Department