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.

Heat Transfer and Bubble Movement of Double- and Single-Side Heating Subcooled Flow Boiling in Narrow Channels

2005 ◽  
Author(s):  
Liang-Ming Pan ◽  
Chuan He ◽  
Ming-Dao Xin ◽  
Tien-Chien Jen ◽  
Qinghua Chen
Keyword(s):  
Heat Transfer ◽  
Flow Boiling ◽  
Narrow Channel ◽  
Nucleate Boiling ◽  
Bubble Behavior ◽  
Subcooled Flow Boiling ◽  
Narrow Channels ◽  
Subcooled Flow ◽  
Single Side ◽  
Micro Channels

Compared with conventional channels, narrow and micro channels have significant heat transfer enhancement characteristic. With smooth internal surface, such channels can efficiently avoid encrustation at the washing of the high-speed liquid. Moreover, heat transfer elements can be easily assembled. These types of channels have been adopted extensively in many engineering applications, e.g. microelectronic cooling, advanced nuclear reactor, cryogenic, aviation and space technology and thermal engineering. Geometrical size of flow passage-away affects heat exchange of flow boiling, with the result that the bubble in narrow channel acts very different from those in non-narrow channel. This paper experimentally compared the bubble behavior with different heating methods of narrow rectangular channels, and the bubble behavior of subcooled flow boiling of R-12 in the narrow channels both with double side and single heating. Experimental settings are: the heating length of test-section is 400 mm, the cross-section is 35 mm in width and 2mm in gap size, mass flux is 700∼1500 kg.m−2.s−1, the heat flux is 25∼70kW.m−2 and the pressure is 1.3∼2.0 MPa. Comparisons were made on Onset of Nucleate Boiling (ONB) point and bubble characters with various flow patterns. Results revealed that the characteristics of double and single side heating shown good agreement with proper modifications.

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.

Study of Flow-Induced Vibrations of a Plate in Narrow Channels

1967 ◽  
Vol 89 (4) ◽  
pp. 824-830 ◽  
Author(s):  
S. R. Bland ◽  
R. H. Rhyne ◽  
H. B. Pierce
Keyword(s):  
Rocket Engine ◽  
Strong Dependence ◽  
Narrow Channel ◽  
Two Dimensional ◽  
Rigid Plate ◽  
Narrow Channels ◽  
The Core ◽  
Flow Induced Vibrations ◽  
Nuclear Rocket ◽  
Time Of Failure

Vibration phenomena associated with narrow channel flow have come under study as a result of the core failure of an early nuclear rocket engine. Since the mechanism of this vibration instability was not well understood at the time of failure, an investigation of a simple system consisting of a rigid plate with two degrees of spring-restrained freedom in a two-dimensional channel has been made both experimentally and analytically. The results show a strong dependence of the flow rate required for plate oscillation on the channel width (normal to plate).

Note on a Micoquian Tool from a Raised Beach in Morbihan

1956 ◽  
Vol 21 ◽  
pp. 1-2
Author(s):  
Henri Breuil
Keyword(s):  
Sea Level ◽  
Late Stage ◽  
Narrow Channel ◽  
Stone Tools ◽  
Vertical Position ◽  
Glacial Period ◽  
English Channel ◽  
Chipped Stone ◽  
Raised Beaches ◽  
Geological Position

During the years between 1932–40 I went many times to Carnac (Morbihan) to visit megaliths in that neighbourhood and copy the decorations on them. I was astonished to note, amongst the chipped stone tools in the museum there, a very small yellowish flint bifaced implement picked up by Zachary Le Rouzic on the island of Téviec, noted for the excavations and magnificent Mesolithic discoveries of M. and Mme. St.-Just Péquart. This, of course, was not a tool from their Mesolithic site, but was a stray find from the island, where it was found by Le Rouzic in the gravelly section near the neck of land joining the Quiberon peninsula. Téviec consists of two islands divided by a narrow channel of sea. The section is opposite to the mainland, on the bigger island forming the edge of this channel. It shows threé beds of sea-worn pebbles of medium and small size; the upper two beds are separated by red sand. In the uppermost bed, the pebbles have taken a vertical position, similar to those in the upper part (the so-called head) of the lower raised beaches of the English Channel. This phenomenon is due to the cryoturbation during a glacial period. The upper bed is pre-Würmian, though not necessarily very much so, for it suffered through cryoturbation during the Würmian stage. The angles of the stone implement are sharp, i.e. it had not been rolled—and it came therefore from the red sandy bed, that is from a late stage in the Riss-Würm, when the sea slightly retreated between two periods of slight rises in sea-level. This implement thus has some importance owing to its geological position. I visited the site with Zachary Le Rouzic on the ioth October, 1936, but I found no sign of worked stone tools in any of these levels, which are very slightly above the modern sea-level.

Interaction of Asymmetric Films Around Boiling Cylinder Array: Homogeneous Interface to Chaotic Phenomenon

2017 ◽  
Vol 139 (4) ◽  
Author(s):  
Akash Deep ◽  
Chandan Swaroop Meena ◽  
Arup Kumar Das
Keyword(s):  
Source Term ◽  
Film Growth ◽  
Numerical Study ◽  
Film Boiling ◽  
Water Pool ◽  
Time Interaction ◽  
Saturated Water ◽  
Finite Volume Discretization ◽  
Horizontal Cylinders ◽  
Four Cylinders

We report numerical study of film boiling around hot and horizontal cylinders in a saturated water pool to establish interfacial interactions leading toward dryout. Volume of fluid-based finite-volume discretization is performed in the domain for incorporation of source term in mass momentum and energy conservation equations due to phase change. At first, film boiling around single cylinder is simulated at different surface temperatures to understand unconstrained film growth and subsequent film bubble release due to buoyancy. Using velocity vectors and temperature contours, effect of film flow dynamics on bubble departure is depicted. This study has been extended further with multiple cylinders in three different stacking arrangements in order to understand the interaction of films in vicinity. Vertical interaction between cylinders leads to suppression of bubble release at the lower cylinder in comparison to the upper one. In the case of horizontal interactions, bubbles attract each other and merge, provided favorable pitch between cylinders and temperatures of the surfaces is maintained. Offset four cylinders stack maintaining vertical and horizontal pitch allows both lateral vapor affinity and bubble suppression in the lower most cylinder simultaneously. With time interaction of accumulated vapor films around cylinders hinders replenishment of fresh liquid to the hot surfaces leading toward chaotic phenomena or dryout in boiling heat transfer.

Bubble behavior of high subcooling flow boiling at different system pressure in vertical narrow channel

2011 ◽  
Vol 31 (16) ◽  
pp. 3512-3520 ◽  
Author(s):  
De-wen Yuan ◽  
Liang-ming Pan ◽  
Deqi Chen ◽  
Hui Zhang ◽  
Jing-hua Wei ◽  
...  
Keyword(s):  
Flow Boiling ◽  
Narrow Channel ◽  
Bubble Behavior ◽  
System Pressure

scholarly journals Bubble departure diameter determination for pool boiling on surface with microchannels

2018 ◽  
Vol 70 ◽  
pp. 02008
Author(s):  
Robert Kaniowski ◽  
Robert Pastuszko ◽  
Joanna Kowalczyk ◽  
Łukasz Nowakowski
Keyword(s):  
Atmospheric Pressure ◽  
Buoyancy Force ◽  
Pool Boiling ◽  
Surface Tension Force ◽  
Copper Sample ◽  
Heat Fluxes ◽  
Force Balance ◽  
Saturated Water ◽  
Open Microchannel ◽  
Parallel Microchannels

The paper presents visualization investigations into pool boiling heat transfer for open microchannel surfaces. The experiments were carried out with saturated water, ethanol, FC-72 and Novec-649 at atmospheric pressure. Parallel microchannels fabricated by machining copper sample were about 0.2 to 0.5 mm wide and 0.2 to 0.5 mm deep. The diameter of departing bubble was calculated for the microchannel surface on the basis of buoyancy force and surface tension force balance. The visualization carried out was aimed at determining the diameters of the departing bubbles at various heat fluxes for four working fluids.

Critical Heat Flux for Subcooled Water Flowing Normal to a Cylinder

1964 ◽  
Vol 86 (1) ◽  
pp. 68-74 ◽  
Author(s):  
G. C. Vliet ◽  
G. Leppert
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Atmospheric Pressure ◽  
Marked Effect ◽  
Fractional Power ◽  
Nucleate Boiling ◽  
Water Velocity ◽  
Critical Flux ◽  
Vapor Cavity ◽  
Saturated Water

Empirical data are presented which show the effects of diameter, water velocity, and subcooling on the critical heat flux from an electrically heated, cylindrical lube or wire. The maximum flux which can be accommodated in subcooled nucleate boiling is found to vary directly with the water velocity and subcooling and inversely with a fractional power of the heater diameter. The exponent which describes the diameter dependence is itself a function of both velocity and subcooling. Measurements of the critical flux are reported for water at atmospheric pressure over a range of subcooling from 3 to 100 deg F, velocity from 0.5 to 11 ft/sec, and heater diameter from 0.010 to 0.189 in. Visual and photographic observations indicate a marked effect of subcooling on the flow mechanism near the critical heat flux. High subcooling prevents the formation of the vapor cavity which was described in the previous paper [1] for nearly saturated water, although the failure of nucleate boiling still occurs at the rear of the cylinder and is accompanied by a concentration of vapor in that region.

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