FLOW VISUALIZATION OF SUBMERGED JETS IN NARROW CHANNELS

2009 ◽  
Vol 23 (03) ◽  
pp. 377-380
Author(s):  
JIAN-HONG SUN ◽  
CHIN-TSAU HSU
Keyword(s):  
Reynolds Numbers ◽  
Narrow Channel ◽  
Laser Induced Fluorescence ◽  
Turbulent Jet ◽  
Narrow Channels ◽  
Submerged Jets ◽  
Flow Motion ◽  
Turbulent Plane ◽  
Plane Jet ◽  
Turbulent Water

In order to study the effect of wall on the flow pattern of a submerged turbulent water jet in narrow channels, the flow field was visualized by a laser-induced fluorescence (LIF) system at different Reynolds numbers. Those images showed that flow motion in a narrow channel is different from that of a turbulent plane jet without narrow channels. There are three flow patterns in narrow channels: stable impinging, stable jet with recirculation vortices and flapping turbulent jet.

Acoustically Induced Enhancement of Widening and Fluctuation Intensity in a Two-Dimensional Turbulent Jet

1986 ◽  
Vol 108 (3) ◽  
pp. 331-337 ◽  
Author(s):  
F. O. Thomas ◽  
V. W. Goldschmidt
Keyword(s):  
Turbulent Jet ◽  
Flow Structures ◽  
Jet Flows ◽  
Underlying Structure ◽  
Detailed Data ◽  
Initial Region ◽  
Acoustic Disturbance ◽  
Fine Grained ◽  
Turbulent Plane ◽  
Plane Jet

The enhancement of widening rate and turbulence intensity in a turbulent plane jet, due to an acoustic disturbance are considered. Detailed data at a representative Strouhal number suggest a well organized symmetric structural array in the initial region of the flow. These highly organized flow structures act as efficient agents in the transport of energy to the fine-grained turbulence, leading to greater diffusivity, enhanced turbulence and an increase in widening. The data also suggest significant differences in the underlying structure of the natural and excited jet flows, hence putting in jeopardy any generalization of coherent motions especially excited to facilitate their study.

Signal Transit Velocities in a Turbulent Plane Jet

1976 ◽  
Vol 98 (3) ◽  
pp. 443-446
Author(s):  
A. K. Stiffler
Keyword(s):  
Nozzle Exit ◽  
Flow Direction ◽  
Turbulent Jet ◽  
Measured Signal ◽  
Centerline Velocity ◽  
Pressure Gradients ◽  
Periodic Pressure ◽  
Turbulent Plane ◽  
Plane Jet ◽  
Signal Time

A turbulent jet is perturbed transverse to the flow direction by periodic pressure gradients near the nozzle exit. Transit velocities are defined in terms of the measured signal time delay for stations 8, 12, 16 nozzle widths downstream of the nozzle exit. Excitation frequencies to 800 cps are considered. Transit velocities are found to be much less than the jet centerline velocity. The results are related to the convection velocity of turbulence.

Decay of momentum flux in submerged jets

1985 ◽  
Vol 154 ◽  
pp. 91-110 ◽  
Author(s):  
Wilhelm Schneider
Keyword(s):  
Flow Field ◽  
Momentum Flux ◽  
Turbulent Jets ◽  
Critical Distance ◽  
Axisymmetric Jet ◽  
Axisymmetric Jets ◽  
Submerged Jets ◽  
Classical Boundary ◽  
Turbulent Plane ◽  
Plane Jet

Slender laminar and turbulent, plane and axisymmetric jets emerging from orifices in plane or conical walls are studied at large distances from the orifices. The entrainment of momentum coupled with the entrainment of volume into a jet is determined, and its effect on the flow field is analysed by combining inner and outer expansions with a multiple scaling approach.In turbulent (plane or axisymmetric) jets, the axial velocity decreases more rapidly than predicted by classical boundary-layer solutions, and the momentum flux vanishes as the distance from the orifice tends to infinity. The analysis unveils a source of discrepancies in previous experimental data on turbulent jets.In a laminar plane jet, the momentum flux changes but little. In a laminar axisymmetric jet, the momentum flux changes slowly, yet considerably. When a critical distance from the orifice is approached, the momentum flux in the jet becomes very small, the jet diameter very large, and a toroidal viscous eddy is predicted. The structure of the flow field is briefly discussed.

Friction-Factor Characteristics for Narrow Channels With Honeycomb Surfaces

1992 ◽  
Vol 114 (4) ◽  
pp. 714-721 ◽  
Author(s):  
T. W. Ha ◽  
G. L. Morrison ◽  
D. W. Childs
Keyword(s):  
Reynolds Number ◽  
Friction Factor ◽  
Reynolds Numbers ◽  
Narrow Channel ◽  
Test Results ◽  
Jump Phenomenon ◽  
Narrow Channels ◽  
Friction Factors ◽  
Factor Data

The experimental determination of friction-factors for the flow of air in a narrow channel lined with various honeycomb geometries has been carried out. Test results show that, generally, the friction-factor is nearly constant or slightly decreases as the Reynolds number increases, a characteristic common to turbulent flow in pipes. However, in some test geometries this trend is remarkably different. The friction factor dramatically drops and then rises as the Reynolds number increases. This phenomenon can be characterized as a “friction-factor jump.” Further investigations of the acoustic spectrum and friction-factor measurements for a broad range of Reynolds numbers indicate that the “friction-factor jump” phenomenon is accompanied by an onset of a normal mode resonance excited coherent flow fluctuation structure, which occurs at Reynolds number of the order of 104. The purpose of this paper is not to present the friction-factor data but to explain the friction-factor-jump phenomenon and friction-factor characteristics.

An experimental study of submerged jets at low reynolds numbers

2013 ◽  
Vol 39 (5) ◽  
pp. 421-423 ◽  
Author(s):  
V. V. Lemanov ◽  
V. I. Terekhov ◽  
K. A. Sharov ◽  
A. A. Shumeiko
Keyword(s):  
Experimental Study ◽  
Reynolds Numbers ◽  
Low Reynolds Numbers ◽  
Submerged Jets ◽  
Low Reynolds

Development of Advanced High Heat Flux Cooling System for Power Electronics

2009 ◽  
Author(s):  
Yasuhisa Shinmoto ◽  
Shinichi Miura ◽  
Koichi Suzuki ◽  
Yoshiyuki Abe ◽  
Haruhiko Ohta
Keyword(s):  
Heat Flux ◽  
Power Electronics ◽  
Critical Heat Flux ◽  
Heating Surface ◽  
Narrow Channel ◽  
High Heat ◽  
High Heat Flux ◽  
Gap Size ◽  
Narrow Channels ◽  
Very High

Recent development in electronic devices with increased heat dissipation requires severe cooling conditions and an efficient method for heat removal is needed for the cooling under high heat flux conditions. Most researches are concentrated on small semiconductors with high heat flux density, while almost no existing researches concerning the cooling of a large semiconductor, i.e. power electronics, with high heat generation density from a large cooling area. A narrow channel between parallel plates is one of ideal structures for the application of boiling phenomena which uses the cooling for such large semiconductors. To develop high-performance cooling systems for power electronics, experiments on increase in critical heat flux (CHF) for flow boiling in narrow channels by improved liquid supply was conducted. To realize the cooling of large areas at extremely high heat flux under the conditions for a minimum gap size and a minimum flow rate of liquid supplied, the structure with auxiliary liquid supply was devised to prevent the extension of dry-patches underneath flattened bubbles generated in a narrow channel. The heating surface was experimented in two channels with different dimensions. The heating surfaces have the width of 30mm and the lengths of 50mm and 150mm in the flow direction. A large width of actual power electronics is realizable by the parallel installation of the same channel structure in the transverse direction. The cooling liquid is additionally supplied via sintered metal plates from the auxiliary unheated channels located at sides or behind the main heated channel. To supply the liquid to the entire heating surface, fine grooves are machined on the heating surface for enhance the spontaneous liquid supply by the aid of capillary force. The gap size of narrow channels are varied as 0.7mm, 2mm and 5mm. Distribution of liquid flow rate to the main heated channel and the auxiliary unheated channels were varied to investigate its effect on the critical heat flux. Test liquids employed are R113, FC72 and water. The systematic experiments by using water as a test liquid were conducted. Critical heat flux values larger than 2×106W/m2 were obtained at both gap sizes of 2mm and 5mm for a heated length of 150mm. A very high heat transfer coefficient as much as 1×105W/m2K was obtained at very high heat flux near CHF for the gap size of 2mm. This paper is a summary of experimental results obtained in the past by the present authors.

Visualization of Boiling in Inclined Rectangular Narrow Long Channels

2006 ◽  
Author(s):  
Sang W. Noh ◽  
Jae S. Yoo ◽  
Kune Y. Suh
Keyword(s):  
Inclination Angle ◽  
Atmospheric Pressure ◽  
Narrow Channel ◽  
Vertical Position ◽  
Bubble Behavior ◽  
Water Pool ◽  
Narrow Channels ◽  
Saturated Water ◽  
Test Parameters ◽  
Reactor Pressure

During the Three-Mile Island Unit 2 (TMI-2) accident, the lower part of the reactor pressure vessel had been overheated and then rather rapidly cooled down, as it was later found out in a vessel investigation project. These findings triggered a great deal of investigations to determine the critical heat flux (CHF) in narrow channels. Experiments were conducted to determine the CHF on a long downward heated rectangular narrow channel by changing the orientation of a copper crevice (5×105 mm2) type heater assembly. The test heater was placed in a demineralized, saturated water pool at atmospheric pressure. This work aims also to investigate the general boiling phenomena and the triggering mechanism for the CHF in the narrow channel through visualization of the bubble behavior in the vicinity of CHF. The test parameters include the channel size of 5 mm and the surface orientation angles from the downward facing position (180°) to the vertical position (90°). It was found that the CHF decreases as the surface inclination angle increases and as the gap size decreases. It was also shown that there exists a transition angle at which the CHF changes with a rapid slope, and that the inclination angle affects the bubble layer and the bubble discharge from the narrow gap.

scholarly journals Self-oscillating modes of penetration of free or submerged jets through the surface of a liquid

2019 ◽  
Vol 46 (2) ◽  
pp. 142-148
Author(s):  
V. P. Karlikov ◽  
A. T. Nechaev ◽  
S. L. Tolokonnikov
Keyword(s):  
Vertical Axis ◽  
Oscillation Period ◽  
State University ◽  
Axially Symmetric ◽  
Narrow Channels ◽  
New Class ◽  
Water Jets ◽  
Submerged Jets ◽  
Empirical Experiment ◽  
Moscow State University

A brief review was conducted of the most significant results of studies performed at the Institute of Mechanics of Moscow State University regarding a new class of unsteady flow of incompressible fluid. Examples include such fluids arising upon the penetration of vertical submerged or free flat and axially symmetric water jets through the surface of water in relatively narrow channels, such as when free thin-walled water jets flowing from a conical slit nozzle with a vertical axis form in a rectangular vessel. A broad range of values of characteristic parameters was found to be generated by the previously unknown self-oscillating flow modes formed in the liquid. Different mechanisms for the occurrence of such modes and characteristics of the dependencies of the self-oscillation period on the main determining parameters were uncovered through empirical experiment and numerical modeling. These mechanisms and characteristics as well as possible applications of the obtained results are presented.

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