An Experimental Investigation of the Effects of Subcooling and Velocity on Boiling of Freon-113

1996 ◽  
Vol 118 (2) ◽  
pp. 436-441 ◽  
Author(s):  
L. Huang ◽  
L. C. Witte
Keyword(s):  
Weber Number ◽  
Large Scale ◽  
Heat Fluxes ◽  
Film Boiling ◽  
Electric Resistance ◽  
Stagnation Line ◽  
Maximum Heat ◽  
Fluid Velocities ◽  
Wide Range ◽  
Minimum Heat

Boiling heat transfer correlations were obtained for the maximum and minimum heat fluxes. Relationships among qmin/qmax, Weber number, and liquid Jakob number were obtained. Compelling evidence was found to indicate that significant cooling of the wake and/or the forward stagnation line can be caused by large-scale liquid–solid contacts while other parts of the surface experienced film boiling with little or no contact in the transition-film boiling regime. A criterion for large-scale liquid-solid contacts was developed. Another purpose of this study was to investigate whether a stable transition of boiling exists, i.e., if the ratio of the minimum and maximum heat fluxes approaches unity as liquid subcooling and velocity are increased. Extensive data using Freon-113 were taken, covering a wide range of fluid velocities (1.5 to 6.9 m/s) and liquid subcooling (29 to 100°C) at pressures ranging from 122 to 509 kPa. Cylindrical electric resistance heaters of two diameters, 6.35 mm and 4.29 mm, and made of Hastelloy-C and titanium, respectively, were used. The maximum qmin/qmax achievable with the apparatus was 0.9.

Liquid-Solid Contact During Flow Film Boiling of Subcooled Freon-11

1990 ◽  
Vol 112 (2) ◽  
pp. 465-471 ◽  
Author(s):  
K. H. Chang ◽  
L. C. Witte
Keyword(s):  
Heat Transfer ◽  
Large Scale ◽  
Heat Fluxes ◽  
Film Boiling ◽  
Small Scale ◽  
Solid Contact ◽  
Heated Cylinder ◽  
Experimental Heat ◽  
Wall Superheat ◽  
Flow Film Boiling

Liquid-solid contacts were measured for flow film boiling of subcooled Freon-11 over an electrically heated cylinder equipped with a surface microthermocouple probe. No systematic variation of the extent of liquid-solid contact with wall superheat, liquid subcooling, or velocity was detected. Only random small-scale contacts that contribute negligibly to overall heat transfer were detected when the surface was above the homogeneous nucleation temperature of the Freon-11. When large-scale contacts were detected, they led to an unexpected intermediate transition from local film boiling to local transition boiling. An explanation is proposed for these unexpected transitions. A comparison of analytical results that used experimentally determined liquid-solid contact parameters to experimental heat fluxes did not show good agreement. It was concluded that the available model for heat transfer accounting for liquid-solid contact is not adequate for flow film boiling.

Transient Pool Boiling CHF in FC-72

2008 ◽  
Author(s):  
P. F. Sutopo ◽  
Katsuya Fukuda ◽  
Qiusheng Liu
Keyword(s):  
Pool Boiling ◽  
Heat Fluxes ◽  
Current Work ◽  
Film Boiling ◽  
Wide Range ◽  
Horizontal Cylinders

In the current work, critical heat fluxes (CHFs) and related boiling phenomena due to transient heat inputs, Q0exp(t/τ), to horizontal finite heaters were investigated in a pool of FC-72. Investigations were made on 1.0 mm diameter horizontal cylinders and a horizontal vertically oriented ribbon (4.0 mm × 0.1 mm × 31.5 mm) under a wide range of pressures ranged from 79.5 kPa up to 1278.1 kPa and liquid subcoolings ranged from saturated up to 140 K. The CHFs obtained from each heater with their dependency on pressure and liquid subcooling, and the typical ones against exponential period, τ, were observed and compared. The transition boiling processes to film boiling including mechanisms of incipient boiling and CHF, and vapor and bubble behaviors were also derived.

On the Minimum Film Boiling Conditions for Spherical Geometries

1980 ◽  
Vol 102 (2) ◽  
pp. 335-341 ◽  
Author(s):  
F. S. Gunnerson ◽  
A. W. Cronenberg
Keyword(s):  
Experimental Data ◽  
Heat Flux ◽  
Flat Plate ◽  
Analytical Method ◽  
Boiling Point ◽  
Film Boiling ◽  
Heater Surface ◽  
Wide Range ◽  
Minimum Heat ◽  
Good Agreement

An analytical method is presented for predicting the minimum heater temperature and the minimum heat flux at the onset of film boiling for spherical and flat plate heaters in saturated and subcooled liquids. Consideration is given to a variety of factors known to affect the minimum film boiling point, including transient liquid-heater contact, interfacial wettability, heater geometry, and liquid subcooling. The theoretical correlations developed are the first known predictions for spherical geometries. A comparison of theory with experimental data indicates good agreement for the minimum heat flux and the minimum film boiling temperature. Results indicate that the minimum conditions may span a wide range depending upon the thermophysical nature of the heater surface and the boiling liquid.

The Dominant Unstable Wavelength and Minimum Heat Flux During Film Boiling on a Horizontal Cylinder

1964 ◽  
Vol 86 (2) ◽  
pp. 220-225 ◽  
Author(s):  
J. H. Lienhard ◽  
P. T. Y. Wong
Keyword(s):  
Surface Tension ◽  
Heat Flux ◽  
Flat Plate ◽  
Transverse Direction ◽  
Horizontal Cylinder ◽  
Heat Fluxes ◽  
Taylor Instability ◽  
Film Boiling ◽  
Minimum Heat ◽  
Effect Of Surface

Predictions of the dominant unstable wavelength and the minimum heat flux during film boiling above a flat plate are found to be inapplicable in the case of boiling on small wires. New expressions are developed for the case of a horizontal cylinder, by accounting for the effect of surface tension in the transverse direction upon the Taylor instability of the interface. Original measurements of wavelengths and minimum heat fluxes on small wires are also provided. These data support the predictions.

On the scaling of air entrainment from a ventilated partial cavity

2013 ◽  
Vol 732 ◽  
pp. 47-76 ◽  
Author(s):  
Simo A. Mäkiharju ◽  
Brian R. Elbing ◽  
Andrew Wiggins ◽  
Sarah Schinasi ◽  
Jean-Marc Vanden-Broeck ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Weber Number ◽  
Large Scale ◽  
Air Entrainment ◽  
Small Scale ◽  
Length Scale ◽  
Entrainment Rate ◽  
Two Dimensional ◽  
Wide Range ◽  
Stable Cavity

AbstractThe behaviour of a nominally two-dimensional ventilated partial cavity was examined over a wide range of size scales and flow speeds to determine the influence of Froude, Reynolds, and Weber number on the cavity shape, dynamics, and gas entrainment rate. Two geometrically similar experiments were conducted with a 14:1 length scale ratio. The results were compared to a two-dimensional semi-analytical model of the cavity flow, and Froude scaling was found to be sufficient to match basic cavity shapes. However, the air flux required to maintain a stable cavity did not scale with Froude number alone, as the dynamics of the cavity closure changed with increasing Reynolds number. The required air flux differed over one order of magnitude between the lowest and highest Reynolds number flows. But, for sufficiently high Reynolds numbers, the rate of scaled entrainment appeared to approach Reynolds number independence. Modest changes in surface tension of the small-scale experiment suggested that the Weber number was important only at the lowest speeds and smaller length scale. Otherwise, the Weber numbers of the flows were sufficiently high to make the effects of interfacial tension negligible. We also observed that modest unsteadiness in the inflow to the large-scale cavity led to a significant increase in the required air flux needed to maintain a stable cavity, with the required excess gas flux nominally proportional to the flow’s perturbation amplitude. Finally, discussion is provided on how these results relate to model testing of partial cavity drag reduction (PCDR) systems for surface ships.

Framework for a Unified Model for Nucleate and Transition Pool Boiling

1989 ◽  
Vol 111 (3) ◽  
pp. 739-746 ◽  
Author(s):  
V. K. Dhir ◽  
S. P. Liaw
Keyword(s):  
Transfer Rate ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Heater Surface ◽  
Maximum Heat ◽  
Void Fractions ◽  
Thermal Layer ◽  
Averaged Model ◽  
Minimum Heat

An area and time-averaged model for saturated pool boiling heat fluxes has been developed. In the model, which is valid in the upper end of nucleate boiling and in transition boiling, the existence of stationary vapor stems at the wall is assumed. The energy from the wall is conducted into the liquid macro/micro thermal layer surrounding the stems and is utilized in evaporation at the stationary liquid–vapor interface. The heat transfer rate into the thermal layer and the temperature distribution in it are determined by solving a two-dimensional steady-state conduction equation. The evaporation rate is given by the kinetic theory. The heater surface area over which the vapor stems exist is taken to be dry. Employing experimentally observed void fractions, not only the nucleate and transition boiling heat fluxes but also the maximum and minimum heat fluxes are predicted from the model. The maximum heat fluxes obtained from the model are valid only for surfaces that are not well wetted and includes the contact angle as one of the parameters.

Local Heat Transfer in Internally Cooled Turbine Airfoil Leading Edge Regions: Part II—Impingement Cooling With Film Coolant Extraction

1990 ◽  
Vol 112 (3) ◽  
pp. 459-466 ◽  
Author(s):  
D. E. Metzger ◽  
R. S. Bunker
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Film Cooling ◽  
Large Scale ◽  
Internal Heat ◽  
Leading Edge ◽  
Stagnation Line ◽  
Nusselt Numbers ◽  
Wide Range

An experimental study has been designed and performed to measure very localized internal heat transfer characteristics in large-scale models of turbine blade impingement-cooled leading edge regions that allow extraction, or bleed-off, of a portion of the internal cooling flow to provide leading edge film cooling along the blade external surface. The internal impingement air is provided by a single line of equally spaced multiple jets, aimed at the leading edge apex and generally exiting, minus the bleed-off flow, in the opposite or chordwise direction. The film coolant flow extraction takes place through two lines of holes, one each on the blade suction side and the blade pressure side, both fairly close to the airfoil leading edge. Detailed two-dimensional local surface Nusselt number distributions have been obtained through the use of aerodynamically steady but thermally transient tests employing temperature-indicating coatings. The thin coatings are sprayed directly on the test surfaces, and are observed during a test transient with automated computer vision and data acquisition systems. A wide range of parameter combinations of interest in cooled airfoil practice is covered in the test matrix, including combinations of variations in jet Reynolds number, airfoil leading edge sharpness, jet pitch-to-diameter ratio, and jet nozzle-to-apex travel distance. Measured local Nusselt numbers at each chordwise location back from the stagnation line have been used to calculate both the spanwise-average Nusselt numbers and spanwise Nusselt number gradients as functions of chordwise position. The results without film coolant extraction, presented in the Part I companion paper, are used as a basis of comparison to determine the additional effects of the film cooling bleed. Results indicate that heat transfer is primarily dependent on jet Reynolds number with smaller influences from the flow extraction rate. The results also suggest that changes in the spanwise alignment of the impingement nozzles relative to the position of the film cooling holes can cause significant variations in leading edge metal temperatures.

Electron microscopy study of reactively sputter-deposited Ti/N films on silicon

1992 ◽  
Vol 50 (2) ◽  
pp. 1362-1363
Author(s):  
V. C. Kannan ◽  
A. K. Singh ◽  
R. B. Irwin ◽  
S. Chittipeddi ◽  
F. D. Nkansah ◽  
...  
Keyword(s):  
Integrated Circuits ◽  
Large Scale ◽  
Hexagonal Phase ◽  
Microscopy Study ◽  
Electron Microscopy Study ◽  
Process Conditions ◽  
Tin Films ◽  
Wide Range ◽  
Fcc Phase ◽  
Circuits Vlsi

Titanium nitride (TiN) films have historically been used as diffusion barrier between silicon and aluminum, as an adhesion layer for tungsten deposition and as an interconnect material etc. Recently, the role of TiN films as contact barriers in very large scale silicon integrated circuits (VLSI) has been extensively studied. TiN films have resistivities on the order of 20μ Ω-cm which is much lower than that of titanium (nearly 66μ Ω-cm). Deposited TiN films show resistivities which vary from 20 to 100μ Ω-cm depending upon the type of deposition and process conditions. TiNx is known to have a NaCl type crystal structure for a wide range of compositions. Change in color from metallic luster to gold reflects the stabilization of the TiNx (FCC) phase over the close packed Ti(N) hexagonal phase. It was found that TiN (1:1) ideal composition with the FCC (NaCl-type) structure gives the best electrical property.

THE SOME QUESTIONS OF AUTONOMOUS MOTION AND MANAGEMENT OF LAND-MOBILE ROBOTIC COMPLEXES FOR UKRAINIAN GROUND FORCESE

2019 ◽  
pp. 53-58
Author(s):  
О. Кravchuk ◽  
V. Symonenkov ◽  
I. Symonenkova ◽  
O. Hryhorev
Keyword(s):  
Large Scale ◽  
Armed Forces ◽  
Distributed Information ◽  
Wide Range ◽  
Highly Effective ◽  
Information Management Systems ◽  
Robotic Devices ◽  
Principles And Standards ◽  
And Control ◽  
The Eu

Today, more than forty countries of the world are engaged in the development of military-purpose robots. A number of unique mobile robots with a wide range of capabilities are already being used by combat and intelligence units of the Armed forces of the developed world countries to conduct battlefield intelligence and support tactical groups. At present, the issue of using the latest information technology in the field of military robotics is thoroughly investigated, and the creation of highly effective information management systems in the land-mobile robotic complexes has acquired a new phase associated with the use of distributed information and sensory systems and consists in the transition from application of separate sensors and devices to the construction of modular information subsystems, which provide the availability of various data sources and complex methods of information processing. The purpose of the article is to investigate the ways to increase the autonomy of the land-mobile robotic complexes using in a non-deterministic conditions of modern combat. Relevance of researches is connected with the necessity of creation of highly effective information and control systems in the perspective robotic means for the needs of Land Forces of Ukraine. The development of the Armed Forces of Ukraine management system based on the criteria adopted by the EU and NATO member states is one of the main directions of increasing the effectiveness of the use of forces (forces), which involves achieving the principles and standards necessary for Ukraine to become a member of the EU and NATO. The inherent features of achieving these criteria will be the transition to a reduction of tasks of the combined-arms units and the large-scale use of high-precision weapons and land remote-controlled robotic devices. According to the views of the leading specialists in the field of robotics, the automation of information subsystems and components of the land-mobile robotic complexes can increase safety, reliability, error-tolerance and the effectiveness of the use of robotic means by standardizing the necessary actions with minimal human intervention, that is, a significant increase in the autonomy of the land-mobile robotic complexes for the needs of Land Forces of Ukraine.

Stirring and aeration system for the upgrading of small waste water treatment plants

1994 ◽  
Vol 29 (12) ◽  
pp. 149-156 ◽  
Author(s):  
Marcus Höfken ◽  
Katharina Zähringer ◽  
Franz Bischof
Keyword(s):  
Waste Water ◽  
Water Treatment ◽  
Large Scale ◽  
Waste Water Treatment ◽  
Water Treatment Plants ◽  
Waste Water Treatment Plants ◽  
Basic Fluid ◽  
Aeration System ◽  
Technical Realization ◽  
Wide Range

A novel agitating system has been developed which allows for individual or combined operation of stirring and aeration processes. Basic fluid mechanical considerations led to the innovative hyperboloid design of the stirrer body, which ensures high efficiencies in the stirring and the aeration mode, gentle circulation with low shear forces, excellent controllability, and a wide range of applications. This paper presents the basic considerations which led to the operating principle, the technical realization of the system and experimental results in a large-scale plant. The characteristics of the system and the differences to other stirring and aeration systems are illustrated. Details of the technical realization are shown, which conform to the specific demands of applications in the biological treatment of waste water. Special regard is given to applications in the upgrading of small compact waste water treatment plants.

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