1,187 Matching Results

Search Results

Advanced search parameters have been applied.

Gliding in Convection Currents

Description: "A survey of the possibilities of gliding in convection currents reveals that heretofore only the most simple kind of ascending convection currents, that is, the "thermic" of insolation, has been utilized to any extent. With the increasing experience in gliding, the utilization of the peculiar nature of the "wind thermic" and increased glider speed promises further advances. Evening, ocean, and height "thermic" are still in the exploration stage, and therefore not amenable to survey in their effects" (p. 1).
Date: January 1935
Creator: Georgii, W.
Partner: UNT Libraries Government Documents Department

Natural convection inside a flat rotating container

Description: Report presenting an exploration of Froude number, which is found to be the parameter that determines the effect of body rotations on internal natural convection flows. Explicit forms of Froude number are determined for the cases of predominant rotation and predominant axial force. Results indicated that in a heated cylindrical container no significant convective effects are generated by rotations alone.
Date: September 1958
Creator: Ostrach, Simon & Braun, Willis H.
Partner: UNT Libraries Government Documents Department

Theoretical and experimental investigation of heat transfer by laminar natural convection between parallel plates

Description: Report presenting a theoretical and experimental investigation of heat transfer involving laminar natural convection of fluids enclosed between parallel walls oriented in the direction of body force. The results are presented in the form of equations for the velocity and temperature profiles and ratio of actual temperature drop across the fluid to the temperature drop for pure conduction.
Date: December 1954
Creator: Lietzke, A. F.
Partner: UNT Libraries Government Documents Department

Free Convection Under the Conditions of the Internal Problem

Description: Convection is called free is the stresses (including the normal pressure) to which the fluid is subjected at its boundaries do not perform mechanical work, that is, if all the boundaries of the fluid are stationary. The case where this is not true is termed forced convection. It corresponds to the action on the fluid of some mechanical suction pumping the fluid.
Date: April 1958
Creator: Ostroumov, G. A.
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

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

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

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

Laminar Natural-Convection Flow and Heat Transfer of Fluids With and Without Heat Sources in Channels With Constant Wall Temperatures

Description: Note presenting an analysis of the natural-convection phenomenon, which shows that the flow and heat transfer, in general, are not only functions of the Prandtl and Grashof numbers but also depend on a new dimensionless parameter. If the parameter is not negligibly small, the compression work and frictional heating may appreciably affect this mode of heat transfer. Results regarding the velocity and temperature distributions and heat transfer are provided.
Date: December 1952
Creator: Ostrach, Simon
Partner: UNT Libraries Government Documents Department

Forced-Convection Heat Transfer to Water at High Pressures and Temperatures in the Nonboiling Region

Description: "Forced-convection heat-transfer data have been obtained for water flowing in an electrically heated tube of circular cross section at water pressures of 200 and 2000 pounds per square inch, and temperatures in the nonboiling region, for water velocities ranging between 5 and 25 feet per second. The results indicate that conventional correlations can be used to predict heat-transfer coefficients for water at pressures up to 2000 pounds per square inch and temperatures in the nonboiling region" (p. 1).
Date: November 29, 1951
Creator: Kaufman, S. J. & Henderson, R. W.
Partner: UNT Libraries Government Documents Department

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

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

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


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

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

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

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


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


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