Influence of the punched holes on thermohydraulic performance and flow pattern of rectangular channels with a pair of perforated vortex generators

The frictional pressure drops of gas-liquid two-phase flow in mini-pipes and mini-rectangular channels were investigated experimentally. The following test channels were used in the present experiments: commercial stainless-steel circular tubes with 0.6, 0.5 and 0.25 mm in inner diameter, FEP circular tube of 0.4 mm in inner diameter and rectangular channels, made of Acrylic resin, with 0.39 × 20.4 mm, 0.21 × 9.75 mm, 0.26 × 4.28 mm and 0.18 × 1.87 mm in height and width, respectively. The pressure drops of straight pipe, sudden enlargement and sudden contraction of gas-liquid two-phase flow in mini-pipes were measured for the test mini-channels. The pressure drops of rectangular minichannel were also measured. Experimental result showed that measured two-phase friction multipliers agreed well with a conventional Lockhart-Martinelli correlation for circular tubes and Mishima-Hibiki’s correlation for rectangular channels. Observed flow patterns by visualization were bubbly, slug, churn, ring and annular flow; the flow patterns in the present experiments were reproduced well by Baker’s flow pattern map.

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The Effects of Arrangement of Longitudinal Vortex Generators on the Flow and Heat Transfer in the Rectangular Channel

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.694.205 ◽

2014 ◽

Vol 694 ◽

pp. 205-210

Author(s):

Nan Cai ◽

Li Ting Tian ◽

Chun Hua Min ◽

Cheng Yin Qi

Keyword(s):

Heat Transfer ◽

Flow Resistance ◽

Heat Transfer Performance ◽

Rectangular Channel ◽

Vortex Generator ◽

Vortex Generators ◽

Longitudinal Vortex ◽

Flow And Heat Transfer ◽

Rectangular Channels ◽

Flow Drag

In this paper, the heat transfer performance and flow resistance characteristics of the asymmetric arrangement of the rectangular winglet longitudinal vortex generators in the rectangular channels are numerically studied. Results show that at Re=500~2000, comparing with the symmetric arrangement of the longitudinal vortex generator, the Nusselt number of the asymmetric arrangement of the longitudinal vortex generator only decreased by 4% ~ 6%,while,the friction factor f decreases by 11% ~ 22%,the effect of flow drag reduction is very obvious. The asymmetric arrangements of the longitudinal vortex generators show the better overall thermal performance with the increase of j/f by 5% ~ 20%.

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Flow Patterns Transition Criteria from Bubbly to Slug Flow during Flow Boiling in Confined Vertical Narrow Rectangular Channels

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.155-156.616 ◽

2012 ◽

Vol 155-156 ◽

pp. 616-620

Author(s):

Wei Chang ◽

Shu Sheng Zhang ◽

Can Zhao ◽

Yun Li Zhang

Keyword(s):

Flow Pattern ◽

Flow Boiling ◽

Bubbly Flow ◽

Relative Size ◽

Flow Patterns ◽

Channel Size ◽

Drift Flux Model ◽

Drift Flux ◽

Rectangular Channels ◽

Transition Criteria

To investigate new features of flow patterns transition during flow boiling in confined vertical narrow rectangular channels, both experiments and theoretical analysis were carried out in the present study. When the channel size was smaller than the bubble departure diameter, a new flow pattern was observed and defined as “confined bubbly flow”. According to the relative size between bubble departure diameter and channel size, two groups of flow pattern transition criteria were developed by using modified drift flux model, with taking features of flow boiling and narrow confinement into account. Satisfactory agreement was obtained by compare model prediction with experiment results. However, further verification and modification are still needed for wider applications.

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The Effects of Gap Size on Flooding in Vertical Narrow Rectangular Channels

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.616-618.959 ◽

2012 ◽

Vol 616-618 ◽

pp. 959-963

Author(s):

Xi Chuan Li ◽

Zhong Ning Sun

Keyword(s):

Pressure Drop ◽

Flow Pattern ◽

Current Flow ◽

Liquid Flow Rate ◽

Flow Characteristics ◽

Gap Size ◽

Gas Velocity ◽

Two Phase ◽

Rectangular Channels ◽

Counter Current

In this paper, counter-current gas--liquid two-phase flow and onset of flooding in vertical narrow rectangular channels were studied. In order to study the flow pattern, during counter-current flow and determine conditions associated with the onset of flooding, the flow pattern and pressure drop were investigated by visual experiments. The results show that the flow characteristics and the tendency of pressure drop in vertical narrow rectangular channels were similarly with the conventional channels. However, the maximum of pressure drop appeared at the completed carrying up of flooding in vertical narrow rectangular channels, and it appeared at the onset of flooding in conventional channels. Flooding gas velocities decrease as the gap size decreases; The gas velocity required for flooding increases as the gap size increases at the same liquid flow rate.

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Morphology and development of flow-pattern defect with extended nonagitated Secco etching

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100172073 ◽

1994 ◽

Vol 52 ◽

pp. 868-869

Author(s):

Y. Pan

Keyword(s):

Flow Pattern ◽

Silicon Crystal ◽

Gate Oxide ◽

Crystal Growth Rate ◽

Etch Depth ◽

Force Microscopy ◽

Etch Pit ◽

Float Zone ◽

Atomic Force ◽

Multiple Step

The D defect, which causes the degradation of gate oxide integrities (GOI), can be revealed by Secco etching as flow pattern defect (FPD) in both float zone (FZ) and Czochralski (Cz) silicon crystal or as crystal originated particles (COP) by a multiple-step SC-1 cleaning process. By decreasing the crystal growth rate or high temperature annealing, the FPD density can be reduced, while the D defectsize increased. During the etching, the FPD surface density and etch pit size (FPD #1) increased withthe etch depth, while the wedge shaped contours do not change their positions and curvatures (FIG.l).In this paper, with atomic force microscopy (AFM), a simple model for FPD morphology by non-crystallographic preferential etching, such as Secco etching, was established.One sample wafer (FPD #2) was Secco etched with surface removed by 4 μm (FIG.2). The cross section view shows the FPD has a circular saucer pit and the wedge contours are actually the side surfaces of a terrace structure with very small slopes. Note that the scale in z direction is purposely enhanced in the AFM images. The pit dimensions are listed in TABLE 1.

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