Velocity of a Large Bubble Rising in an Inclined Rectangular Channel

2003 ◽  
Author(s):  
Hachiro Hamaguchi
Keyword(s):  
Aspect Ratio ◽  
Cross Section ◽  
Inclination Angle ◽  
Circular Tube ◽  
Silicone Oil ◽  
Rectangular Channel ◽  
Large Bubble ◽  
Channel Axis ◽  
Test Channel ◽  
Bubble Rising

Velocity of a large single bubble rising in a stationary liquid in an inclined rectangular channel was measured using silicone oil having a kinematic viscosity of 1000mm2/s. The size of cross section of the test channel was 5mm × (5–40)mm, i.e., the aspect ratio was from 1 to 8. Experiments were carried out changing the aspect ratio of cross section of the channel, the inclination angle and “posture angle”, where the “posture angle” is an angel by which the channel is rotated around the channel axis. Movement of a large bubble in an inclined circular tube is determined by the inclination angle. On the other hand, it is shown that movement of a large bubble in an inclined channel is influenced also by the posture angle beside the inclination angel, i.e., the posture angle is an important parameter in an inclined rectangular channel. Relations among the rising velocity, the inclination angle, the posture angle and the aspect ratio were obtained by the experiments.

Axially Tapered Microchannels of High Aspect Ratio for Evaporative Cooling Devices

2004 ◽  
Vol 126 (3) ◽  
pp. 453-462 ◽  
Author(s):  
R. H. Nilson ◽  
S. K. Griffiths ◽  
S. W. Tchikanda ◽  
M. J. Martinez
Keyword(s):  
Aspect Ratio ◽  
Cross Section ◽  
Analytical Solutions ◽  
High Aspect Ratio ◽  
Cooling Capacity ◽  
Channel Axis ◽  
Gravitational Forces ◽  
Triangular Cross Section ◽  
Cooling Devices ◽  
Channel Bottom

Analytical solutions are derived for evaporating flow in open rectangular microchannels having a uniform depth and a width that decreases along the channel axis. The flow generally consists of two sequential domains, an entry domain where the meniscus is attached to the top corners of the channel followed by a recession domain where the meniscus retreats along the sidewalls toward the channel bottom. Analytical solutions applicable within each domain are matched at their interface. Results demonstrate that tapered channels provide substantially better cooling capacity than straight channels of rectangular or triangular cross section, particularly under opposing gravitational forces. A multiplicity of arbitrarily tapered channels can be microfabricated in metals using LIGA, a process involving electrodeposition into a lithographically patterned mold.

High Rotation Number Effects on Heat Transfer in a Rectangular (AR=2:1) Two Pass Channel

2009 ◽  
Author(s):  
Michael Huh ◽  
Jiang Lei ◽  
Yao-Hsien Liu ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Rotation Number ◽  
Rectangular Channel ◽  
Transfer Enhancement ◽  
First Passage ◽  
Test Channel ◽  
Buoyancy Parameter ◽  
Sharp Turn ◽  
First Pass

This paper experimentally investigated the rotational effects on heat transfer in a smooth two-pass rectangular channel (AR=2:1), which is applicable to the cooling passages in the mid portion of the gas turbine blade. The test channel has radially outward flow in the first passage and radially inward flow in the second passage after a 180° sharp turn. In the first passage, the flow is developing and heat transfer is increased compared to the fully developed case. Rotation slightly reduces the heat transfer on the leading surface and increases heat transfer on the trailing surface in the first pass. Heat transfer is highly increased by rotation in the turn portion of the first pass on both leading and trailing surfaces. Rotation increased heat transfer enhancement in the tip region up to a maximum Nu ratio (Nu/Nus) of 1.83. In the second passage, under rotating conditions, the leading surface experienced heat transfer enhancements above the stationary case while the trailing surface decreased. The current study has more than 4 times the range of the rotation number previously achieved for the 2:1 aspect ratio channel. The increased range of the rotation number and buoyancy parameter reached in this study are 0–0.45 and 0–0.8, respectively. The higher rotation number and buoyancy parameter have been correlated very well to predict the rotational heat transfer in the two-pass, 2:1 aspect ratio flow channel.

scholarly journals Stability of convection in a horizontal channel subjected to a longitudinal temperature gradient. Part 1. Effect of aspect ratio and Prandtl number

2009 ◽  
Vol 635 ◽  
pp. 275-295 ◽  
Author(s):  
T. P. LYUBIMOVA ◽  
D. V. LYUBIMOV ◽  
V. A. MOROZOV ◽  
R. V. SCURIDIN ◽  
H. BEN HADID ◽  
...  
Keyword(s):  
Temperature Gradient ◽  
Aspect Ratio ◽  
Prandtl Number ◽  
Cross Section ◽  
Horizontal Channel ◽  
Channel Cross Section ◽  
Instability Mode ◽  
Channel Axis ◽  
Longitudinal Temperature Gradient ◽  
Longitudinal Temperature

The paper deals with the numerical investigation of the steady convective flow in a horizontal channel of rectangular cross-section subjected to a uniform longitudinal temperature gradient imposed at the walls. It is shown that at zero Prandtl number the solution of the problem corresponds to a plane-parallel flow along the channel axis. In this case, the fluid moves in the direction of the imposed temperature gradient in the upper part of the channel and in the opposite direction in the lower part. At non-zero values of the Prandtl number, such solution does not exist. At any small values of Pr all three components of the flow velocity differ from zero and in the channel cross-section four vortices develop. The direction of these vortices is such that the fluid moves from the centre to the periphery in the vertical direction and returns to the centre in the horizontal direction. The stability of these convective flows (uniform along the channel axis) with regard to small three-dimensional perturbations periodical in the direction of the channel axis is studied. It is shown that at low values of the Prandtl number the basic state loses its stability due to the steady hydrodynamic mode related to the development of vortices at the boundary of the counter flows. The growth of the Prandtl number results in the strong stabilization of this instability mode and, beyond a certain value of the Prandtl number depending on the cross-section aspect ratio, a new steady hydrodynamic instability mode becomes the most dangerous. This mode is characterized by the localization of the perturbations near the sidewalls of the channel. At still higher values of the Prandtl number, the spiral perturbations (rolls with axis parallel to the temperature gradient) become the most dangerous modes, at first the oscillatory spiral perturbations and then the Rayleigh-type steady spiral perturbations. The influence of the channel width on these different instabilities is also emphasized.

Isoparametric Timoshenko Elements for Dynamic Analysis of Structures and Mechanical Systems

1995 ◽  
Author(s):  
Ahmad Smaili ◽  
Ismail Bagci ◽  
Muhammad Sannah
Keyword(s):  
Exact Solution ◽  
Aspect Ratio ◽  
Cross Section ◽  
Natural Frequencies ◽  
Circular Tube ◽  
Shear Locking ◽  
Various Boundary Conditions ◽  
Beam Elements ◽  
Stiffness Matrices ◽  
Thin Beams

Abstract This paper presents 4-, 5-, 6- and 7-node isoparametric Timoshenko beam elements for modeling constant and varying cross-section thick and thin beams with various boundary conditions. Numerical integration is employed to determine the mass and stiffness matrices to facilitate modeling of varying cross-section beams. The accuracy of each proposed element is illustrated by determining the natural frequencies of: Thick and thin beams with constant and varying cross-section; linearly tapered cantilever circular tube with small wall thickness; chimney structure; and of a four-bar mechanism. In all examples, the results obtained using the proposed elements are compared, whenever available, with exact solution and with solutions determined when other elements available in the literature are used. The proposed elements did not cause shear locking when tested on thin beams of aspect ratio 500.

Heat Transfer in a Rotating Two-Pass Rectangular Channel Featuring Reduced Cross-Sectional Area After Tip Turn (AR=4:1 to 2:1) With Profiled 60 Deg Angled Ribs

2018 ◽  
Author(s):  
Andrew F. Chen ◽  
Chao-Cheng Shiau ◽  
Je-Chin Han ◽  
Robert Krewinkel
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Aspect Ratio ◽  
Cross Section ◽  
Flow Direction ◽  
Rectangular Channel ◽  
Secondary Flows ◽  
Internal Cooling ◽  
First Passage ◽  
Aspect Ratios

The internal cooling channels of an advanced gas turbine blade typically have varying aspect ratios from one pass to another due to the varying thickness of the blade profile. Most of the fundamental internal cooling studies found in the open literature used a fixed aspect ratio for multi-pass channels. Studies on a reduced cross-section and aspect ratio channel are scarce. The current study features a two-pass rectangular channel with an aspect ratio AR = 4:1 in the first pass and an AR = 2:1 in the second pass after a 180 deg tip turn. In addition to the smooth-wall case, ribs with a profiled cross-section are placed at 60 deg to the flow direction on both the leading and trailing surfaces in both passages (P/e = 10, e/Dh ≈ 0.11, parallel and inline). Regionally averaged heat transfer measurement method was used to obtain the heat transfer coefficients on all surfaces within the flow passages. The Reynolds number (Re) ranges from 10,000 to 70,000 in the first passage, and the rotational speed ranges from 0 to 400 rpm. Under pressurized condition (570 kPa), the highest rotation number achieved was Ro = 0.39 in the first passage and 0.16 in the second passage. Rotation effects on both heat transfer and pressure loss coefficient for the smooth and rib-roughened cases are presented. The results showed that the turn induced secondary flows are reduced in an accelerating flow. The effects of rotation on heat transfer are generally weakened in the ribbed case than the smooth case. Significant heat transfer reduction on the tip wall was seen in both the smooth and ribbed cases under rotating condition. A reduced overall pressure penalty was seen for the ribbed case under rotation. Reynolds number effect was found noticeable in the current study. The heat transfer and pressure drop characteristics are sensitive to the geometrical design of the channel and should be taken into account in the design process.

The Vaporization of Superheated Sodium in a Vertical Channel

1972 ◽  
Vol 94 (3) ◽  
pp. 300-304 ◽  
Author(s):  
Ralph M. Singer ◽  
Robert E. Holtz
Keyword(s):  
Cross Section ◽  
Thin Liquid Film ◽  
Rectangular Channel ◽  
Vertical Channel ◽  
Growth Patterns ◽  
Single Bubble ◽  
Bulk Liquid ◽  
Channel Cross Section ◽  
Channel Axis ◽  
Vapor Growth

Measurements of the vapor growth patterns and rates following the nucleation of superheated sodium in a vertical rectangular channel are presented and discussed. The vapor was found to grow as a single bubble for incipient bulk-liquid superheats greater than about 10 deg C, and this single bubble tended to completely fill the channel cross section (except for a thin liquid film on the walls) and to grow as a vapor slug for incipient bulk-liquid superheats greater than about 50 deg C. The temperature gradients in the liquid both normal and parallel to the channel axis prior to nucleation were found to have an important effect upon the dynamics of the vapor slug. Experimental data on the vapor growth and collapse rates and the associated pressure transients are presented for boiling pressures up to 1 atm and incipient superheats up to about 180 deg C.

High Rotation Number Effects on Heat Transfer in a Rectangular (AR=2:1) Two-Pass Channel

2010 ◽  
Vol 133 (2) ◽  
Author(s):  
Michael Huh ◽  
Jiang Lei ◽  
Yao-Hsien Liu ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Rotation Number ◽  
Rectangular Channel ◽  
Transfer Enhancement ◽  
First Passage ◽  
Test Channel ◽  
Buoyancy Parameter ◽  
Sharp Turn ◽  
First Pass

This paper experimentally investigated the rotational effects on heat transfer in a smooth two-pass rectangular channel (AR=2:1), which is applicable to the cooling passages in the midportion of the gas turbine blade. The test channel has radially outward flow in the first passage and radially inward flow in the second passage after a 180 deg sharp turn. In the first passage, the flow is developing and heat transfer is increased compared with the fully developed case. Rotation slightly reduces the heat transfer on the leading surface and increases heat transfer on the trailing surface in the first pass. Heat transfer is highly increased by rotation in the turn portion of the first pass on both leading and trailing surfaces. Rotation increased heat transfer enhancement in the tip region up to a maximum Nu ratio (Nu/Nus) of 1.83. In the second passage, under rotating conditions, the leading surface experienced heat transfer enhancements above the stationary case while the trailing surface decreased. The current study has more than four times the range of the rotation number previously achieved for the 2:1 aspect ratio channel. The increased range of the rotation number and buoyancy parameter reached in this study are 0–0.45 and 0–0.8, respectively. The higher rotation number and buoyancy parameter have been correlated very well to predict the rotational heat transfer in the two-pass, 2:1 aspect ratio flow channel.

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