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Experimental investigation of free-convection heat transfer in vertical tube at large Grashof numbers

Description: Report presents the results of an investigation conducted to study free-convection heat transfer in a stationary vertical tube closed at the bottom. The walls of the tube were heated, and heated air in the tube was continuously replaced by fresh cool air at the top. The tube was designed to provide a gravitational field with Grashof numbers of a magnitude comparable with those generated by the centrifugal field in rotating-blade coolant passages (10(8) to 10(13)). Local heat-transfer coefficients in the turbulent-flow range and the temperature field within the fluid were obtained.
Date: June 30, 1952
Creator: Eckert, E. R. G. & Diaguila, A. J.
Partner: UNT Libraries Government Documents Department

NUFT USNT Thermal Input Parameters

Description: This document describes the thermal input parameters required to run the USNT module of the NUFT code. The USNT module handles multi-component transport of multiple fluid phases and heat through porous and fractured media. The thermal input parameters required to model the heat transport by conduction, convection, and radiation are summarized, and the relevant mixing rules outlined. This is followed by a table that describes the thermal input parameters in a typical NUFT input file used for YMP thermal-hydrological calculations. Most of the material presented here is summarized from the user's manual of the USNT module of NUFT (Nitao, 2000).
Date: September 1, 2000
Creator: Lee, K.H.
Partner: UNT Libraries Government Documents Department

Mixed Convection Heat Transfer Experiments in Smooth and Rough Verticla Tubes

Description: The mixed convection regime is a transitional heat transfer regime between forced convection and natural convection, where both the forced component of flow, and the buoyancy induced component are important. Aiding flow is when buoyancy forces act in the same direction as the forced flow (heated upflow or cooled downflow), while opposing flow is when the buoyancy force is in the opposite direction of the forced flow (cooled upflow or heated downflow). For opposing flow the buoyancy always increases the rate of heat transfer over the forced convection value. For aiding flow, as the heat flux increased, a reduction in heat transfer is encountered until a condition known as laminarization occurs, where the heat transfer is at a minimum value. Further increases in the wall heat flux causes re-transition to turbulence, and increased heat transfer. In this paper, for the first time, experiments were performed to characterize the effect of surface roughness on heat transfer in mixed convection, for the case of aiding flow. A correlation was developed to allow calculation of mixed convection heat transfer coefficients for rough or smooth tubes.
Date: December 22, 2004
Creator: Symolon, P; Neuhaus, W & Odell, R
Partner: UNT Libraries Government Documents Department

Final Technical Report for DOE Award DE-FG02-05ER63959

Description: The goals of this work were: (1) to improve the University of Washington shallow cumulus parameterization, first developed by the PI's group for better simulation of shallow oceanic cumulus convection in the MM5 mesoscale model (Bretherton et al., 2004, Mon. Wea. Rev.); (2) to explore its applicability to deep (precipitating) cumulus convection; and (3) to explore fundamental physical issues related to this cumulus parameterization.
Date: April 8, 2011
Creator: Bretherton, Christopher S.
Partner: UNT Libraries Government Documents Department

NATURAL CONVECTIONIN SHALLOW ENCLOSURES WITH DIFFERENTIALLY HEATED END WALLS AND NONADIABATIC HORIZONTAL WALLS

Description: Numerical studies of laminar natural convection at high Ra numbers in shallow enclosures are reported. In these studies the working fluid is allowed to interact with the horizontal walls. It is shown that even a small amount of heat loss from these walls can lead to a flow structure qualitatively different from the more commonly studied situation where the horizontal walls are adiabatic. This is particularly important in applications where the mass transfer and flow structure are of interest. The results highlight the difficulty in practice of both approximating the adiabatic horizontal wall condition, and interpreting experimental data.
Date: May 1, 1983
Creator: Gadgil, A. & Shiralkar, G.
Partner: UNT Libraries Government Documents Department

Role of eastward propagating convection systems in the diurnal cycle and seasonal mean summertime rainfall over the U. S. Great Plains

Description: By diagnosing the 3-hourly North American Regional Reanalysis rainfall dataset for the 1979-2003 period, it is illustrated that the eastward propagation of convection systems from the Rockies to the Great Plains plays an essential role for the warm season climate over the central U.S. This eastward propagating mode could be the deciding factor for the observed nocturnal rainfall peak over the Great Plains. The results also suggest that nearly half of the total summer mean rainfall over this region is associated with these propagating convection systems. For instance, the extreme wet condition of the 1993 summer may be attributed to the frequent occurrence of propagating convection events and enhanced diurnal rainfall amplitude over the Great Plains. Thus, proper representation of this important propagating component in GCMs is essential for simulating the diurnal and seasonal mean characteristics of summertime rainfall over the central US.
Date: June 7, 2006
Creator: Jiang, X; Lau, N C & Klein, S A
Partner: UNT Libraries Government Documents Department

Laminar Natural Convection From Isothermal Vertical Cylinders

Description: Laminar natural convection heat transfer from the vertical surface of a cylinder is a classical subject, which has been studied extensively. Furthermore, this subject has generated some recent interest in the literature. In the present investigation, numerical experiments were performed to determine average Nusselt numbers for isothermal vertical cylinders (103 < RaL < 109, 0.5 < L/D <10, and Pr = 0.7) with and without an adiabatic top in a quiescent ambient environment which will allow for plume growth. Results were compared with commonly used correlations and new average Nusselt number correlations are presented. Furthermore, the limit for which the heat transfer results for a vertical flat plate may be used as an approximation for the heat transfer from a vertical cylinder was investigated.
Date: August 2012
Creator: Day, Jerod
Partner: UNT Libraries

Measurements of average heat-transfer and friction coefficients for subsonic flow of air in smooth tubes at high surface and fluid temperatures

Description: An investigation of forced-convection heat transfer and associated pressure drops was conducted with air flowing through smooth tubes for an over-all range of surface temperature from 535 degrees to 3050 degrees r, inlet-air temperature from 535 degrees to 1500 degrees r, Reynolds number up to 500,000, exit Mach number up to 1, heat flux up to 150,000 btu per hour per square foot, length-diameter ratio from 30 to 120, and three entrance configurations. Most of the data are for heat addition to the air; a few results are included for cooling of the air. The over-all range of surface-to-air temperature ratio was from 0.46 to 3.5.
Date: December 31, 1950
Creator: Humble, Leroy V.; Lowdermilk, Warren H. & Desmon, Leland G.
Partner: UNT Libraries Government Documents Department

The Transient Behavior of Single-Phase Natural Circulation Water Loop Systems

Description: Report issued by the Argonne National Laboratory discussing single-phase water loop systems. As stated in the introduction, "the principal objective of this study was to determine the reliability of the calculations based upon numerical solutions of finite-difference energy and flow equations" (p. 9). This report includes tables, illustrations, and photographs.
Date: March 1956
Creator: Alstad, C. D.; Isbin, H. S.; Amundson, N. R. & Silvers, J. P.
Partner: UNT Libraries Government Documents Department

The Transmission of Heat into Steam Boilers

Description: Report discussing the results of investigations into the heat-absorbing abilities of the heating surfaces of boilers. Also discusses the laws that determine the rate of heat transfer from furnace gases through metal plates into boiler water and offers suggestions as to how these laws may be applied.
Date: 1912
Creator: Kreisinger, Hengry & Ray, Walter T.
Partner: UNT Libraries Government Documents Department

The Role of Gravity Waves in the Formation and Organization of Clouds during TWPICE

Description: All convective clouds emit gravity waves. While it is certain that convectively-generated waves play important parts in determining the climate, their precise roles remain uncertain and their effects are not (generally) represented in climate models. The work described here focuses mostly on observations and modeling of convectively-generated gravity waves, using the intensive observations from the DoE-sponsored Tropical Warm Pool International Cloud Experiment (TWP-ICE), which took place in Darwin, from 17 January to 13 February 2006. Among other things, the research has implications the part played by convectively-generated gravity waves in the formation of cirrus, in the initiation and organization of further convection, and in the subgrid-scale momentum transport and associated large-scale stresses imposed on the troposphere and stratosphere. The analysis shows two groups of inertia-gravity waves are detected: group L in the middle stratosphere during the suppressed monsoon period, and group S in the lower stratosphere during the monsoon break period. Waves belonging to group L propagate to the south-east with a mean intrinsic period of 35 h, and have vertical and horizontal wavelengths of about 5-6 km and 3000-6000 km, respectively. Ray tracing calculations indicate that these waves originate from a deep convective region near Indonesia. Waves belonging to group S propagate to the south-south-east with an intrinsic period, vertical wavelength and horizontal wavelength of about 45 h, 2 km and 2000-4000 km, respectively. These waves are shown to be associated with shallow convection in the oceanic area within about 1000 km of Darwin. The intrinsic periods of high-frequency waves are estimated to be between 20-40 minutes. The high-frequency wave activity in the stratosphere, defined by mass-weighted variance of the vertical motion of the sonde, has a maximum following the afternoon local convection indicating that these waves are generated by local convection. The wave activity is strongest in the ...
Date: September 27, 2013
Creator: Reeder, Michael J.; Lane, Todd P. & Hankinson, Mai Chi Nguyen
Partner: UNT Libraries Government Documents Department

SCALE ANALYSIS OF CONVECTIVE MELTING WITH INTERNAL HEAT GENERATION

Description: Using a scale analysis approach, we model phase change (melting) for pure materials which generate internal heat for small Stefan numbers (approximately one). The analysis considers conduction in the solid phase and natural convection, driven by internal heat generation, in the liquid regime. The model is applied for a constant surface temperature boundary condition where the melting temperature is greater than the surface temperature in a cylindrical geometry. We show the time scales in which conduction and convection heat transfer dominate.
Date: March 1, 2011
Creator: Crepeau, John
Partner: UNT Libraries Government Documents Department

NATURAL CONVECTION IN ROOM GEOMETRIES

Description: Computer programs have been developed to numerically simulate natural convection in room geometries in two and three dimensions. The programs have been validated using published data from the literature, results from a full-scale experiment performed at Massachusetts Institute of Technology, and results from a small-scale experiment reported here. One of the computer programs has been used to study the influence of natural convection on the thermal performance of a single thermal zone in a direct-gain passive solar building. The results indicate that the building heating loads calculated by standard building energy analysis methods may be in error by as much as 50% as a result of their use of common assumptions regarding the convection processes which occur in an enclosure. It is also found that the convective heat transfer coefficients between the air and the enclosure surfaces can be substantially different from the values assumed in the standard building energy analysis methods, and can exhibit significant variations across a given surface.
Date: June 1, 1980
Creator: Gadgil, A.; Bauman, Fred; Kammerud, R. & Ruberg, K.
Partner: UNT Libraries Government Documents Department

A Coupled Model for Natural Convection and Condensation in HeatedSubsurface Enclosures Embedded in Fractured Rock

Description: In heated tunnels such as those designated for emplacementof radioactive waste at Yucca Mountain, axial temperature gradients maycause natural convection processes that can significantly influence themoisture conditions in the tunnels and in the surrounding fractured rock.Large-scale convection cells would provide an effective mechanism foraxial vapor transport, driving moisture out of the formation away fromthe heated tunnel section into cool end sections (where no waste isemplaced). To study such processes, we have developed and applied anenhanced version of TOUGH2 (Pruess et al., 1999) adding a new module thatsolves for natural convection in open cavities. The new TOUGH2 simulatorsimultaneously handles (1) the flow and energy transport processes in thefractured rock; (2) the flow and energy transport processes in thecavity; and (3) the heat and mass exchange at the rock-cavity interface.The new module is applied to simulate the future thermal-hydrological(TH) conditions within and near a representative waste emplacement tunnelat Yucca Mountain. Particular focus is on the potential for condensationalong the emplacement section, a possible result of heat outputdifferences between individual waste packages.
Date: April 14, 2006
Creator: Halecky, N.; Birkholzer, J. T.; Webb, S. W.; Peterson, P. F. & Bodvarsson, G. S.
Partner: UNT Libraries Government Documents Department

Regular and chaotic flow patterns upon impulsive spin-up of a Rayleigh-Benard convection cell

Description: A cylindrical, completely enclosed Rayleigh-Benard convection cell with radius-to-height ratio {Gamma}={1/2} is subjected to impulsive spin-up about its vertical axis. The authors study produces TLC (thermochromic liquid crystal) temperature measurements and PIV (particle image velocimetry) velocity reconstruction of the transient state between the two regimes of turbulent convection corresponding to the cell at rest and in steady rotation. The most persistent transient feature emerging is a sharply defined ringlike pattern characterized by a decrease in temperature and high azimuthal shear. The latter leads to formation of Kelvin-Helmholz vortices. Initially azimuthally regular, the pattern of these vortices loses its regularity and thus completes the transition to rotating convection state.
Date: October 1, 1997
Creator: Vorobieff, P. & Ecke, R.E.
Partner: UNT Libraries Government Documents Department

Design predictions and diagnostic test methods for hydronic heating systems in ASHRAE standard 152P

Description: A new method of test for residential thermal distribution efficiency is currently being developed under the auspices of the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE). The initial version of this test method is expected to have two main approaches, or ``pathways,`` designated Design and Diagnostic. The Design Pathway will use builder`s information to predict thermal distribution efficiency in new construction. The Diagnostic Pathway will use simple tests to evaluate thermal distribution efficiency in a completed house. Both forced-air and hydronic systems are included in the test method. This report describes an approach to predicting and measuring thermal distribution efficiency for residential hydronic heating systems for use in the Design and Diagnostic Pathways of the test method. As written, it is designed for single-loop systems with any type of passive radiation/convection (baseboard or radiators). Multiloop capability may be added later.
Date: April 1, 1996
Creator: Andrews, J.W.
Partner: UNT Libraries Government Documents Department

Highly Unstable Double-Diffusive Finger Convection in a Hele-Shaw Cell: Baseline Experimental Data for Evaluation of Numerical Models

Description: An experimental investigation was conducted to study double-diffusive finger convection in a Hele-Shaw cell by layering a sucrose solution over a more-dense sodium chloride (NaCl) solution. The solutal Rayleigh numbers were on the order of 60,000, based upon the height of the cell (25 cm), and the buoyancy ratio was 1.2. A full-field light transmission technique was used to measure a dye tracer dissolved in the NaCl solution. They analyze the concentration fields to yield the temporal evolution of length scales associated with the vertical and horizontal finger structure as well as the mass flux. These measures show a rapid progression through two early stages to a mature stage and finally a rundown period where mass flux decays rapidly. The data are useful for the development and evaluation of numerical simulators designed to model diffusion and convection of multiple components in porous media. The results are useful for correct formulation at both the process scale (the scale of the experiment) and effective scale (where the lab-scale processes are averaged-up to produce averaged parameters). A fundamental understanding of the fine-scale dynamics of double-diffusive finger convection is necessary in order to successfully parameterize large-scale systems.
Date: December 21, 2000
Creator: PRINGLE,SCOTT E.; COOPER,CLAY A. & GLASS JR.,ROBERT J.
Partner: UNT Libraries Government Documents Department

DOE Final Technical Report for Grant Number DE-FG03-90ER14148

Description: OAK-B135 Thermal convection was studied in a horizontal layer of a binary fluid mixture of ethanol and water confined in a variety of cell geometries. In these mixtures, convection takes the form of traveling waves, thus providing a model for studying traveling-wave (TW) phenomena in non-equilibrium systems. A number of questions were addressed, including the evolution of initially chaotic states, the role of TW domains textures and convection-cell geometry in determining patterns, and the competition of TW and hexagonal patterns when non-Boussinesq effects are important.
Date: March 1, 2004
Creator: Surko, Clifford M.
Partner: UNT Libraries Government Documents Department

Stability and Dynamics of Spatio-Temporal Structures

Description: This document constitutes the final report for the grant. It provides a complete list of publications and presentations that arose from the project as well as a brief description of the highlights of the research results. The research funded by this grant has provided insights into the spontaneous formation of structures of increasing complexity in systems driven far from thermodynamic equilibrium. A classic example of such a system is thermally driven convection in a horizontal fluid layer. Highlights of the research are: (1) explanation of the localized traveling wave pulses observed in binary-mixture convection, (2) explanation of the localized waves in electroconvection, (3) introduction of a new diagnostics for spatially and temporally chaotic states, which is based on the statistics of defect trajectories, (4) prediction of complex states in thermally driven convection in rotating systems. Additional contributions provided insight into the localization mechanism for oscillons, the prediction of a new localization mechanism for traveling waves based on a resonant periodic forcing, and an analysis of the stability of quasi-periodic patterns.
Date: October 21, 2005
Creator: Riecke, Hermann
Partner: UNT Libraries Government Documents Department

Modeling Gas-Phase Transport in Polymer-Electrolyte FuelCells

Description: In this transaction, the equations and methodology for modeling convection and ordinary, Knudsen, and pressure diffusion of gases in a fuel-cell gas-diffusion layer are described. Some results examining the magnitudes of the various terms are also made. This derivation results in a self-consistent description of the various transport mechanisms and is robust for numerical solutions, especially for conditions involving different flow regimes or where the regime is not known a priori.
Date: August 17, 2006
Creator: Weber, A.Z. & Newman, J.
Partner: UNT Libraries Government Documents Department

Evolution of Intermediate and Low Mass Binary Systems

Description: There are a number of binaries, fairly wide and with one or even two evolved giant components, that do not agree very well with conventional stellar evolution: the secondaries are substantially larger (oversized) than they should be because their masses are quite low compared with the primaries. I discuss the possibility that these binaries are former triples, in which a merger has occurred fairly recently in a short-period binary sub-component. Some mergers are expected, and may follow a phase of contact evolution. I suggest that in contact there is substantial transfer of luminosity between the components due to differential rotation, of the character observed by helioseismology in the Sun's surface convection zone.
Date: October 25, 2005
Creator: Eggleton, P P
Partner: UNT Libraries Government Documents Department

Sea breeze Initiated Rainfall over the east Coast of India during the Indian Southwest Monsoon

Description: Sea breeze initiated convection and precipitation is investigated along the east coast of India during the Indian southwest monsoon season. The sea breeze circulations are observed approximately 70 to 80% of the days during the summer months (June to August) along the Chennai coast. Observations of average sea breeze wind speeds are stronger at a rural location as compared to the wind speeds observed inside the urban region of Chennai. The sea breeze circulation is shown to be the dominant mechanism for initiating rainfall during the Indian southwest monsoon season. Roughly 80% of the total rainfall observed during the southwest monsoon over Chennai is directly related to the convection initiated by sea breeze circulation.
Date: September 5, 2006
Creator: Simpson, M; Warrior, H; Raman, S; Aswathanarayana, P A; Mohanty, U C & Suresh, R
Partner: UNT Libraries Government Documents Department