Effect of Channel Orientation on the Heat Transfer Coefficient in the Smooth and Dimpled Rotating Rectangular Channels

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
Seokbeom Kim ◽  
Eun Yeong Choi ◽  
Jae Su Kwak
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Orientation Angle ◽  
Rotating Speed ◽  
Rectangular Channels ◽  
Smooth Channel ◽  
Channel Orientation ◽  
Transient Liquid Crystal Technique ◽  
The Heat Transfer Coefficient

The detailed distribution of the heat transfer coefficient on rotating smooth and dimpled rectangular channels were measured using the transient liquid crystal technique. The rotating speed of the channel was fixed at 500 rpm and the tested Reynolds number based on the channel hydraulic diameter was 10,000. A stationary surface and two different channel rotating orientations of 90 deg and 120 deg were tested in order to investigate the effects of channel orientation on the distribution of the heat transfer coefficient in smooth and dimpled rotating surfaces. Results show that the heat transfer coefficient on the trailing surface is higher than that on the leading surface. For the 120 deg channel orientation angle cases, a higher heat transfer coefficient was observed near the outer surface. In the dimpled channel, the effect of the Coriolis force induced secondary flow on the heat transfer coefficient was not as significant as that for the smooth channel case.

Effect of Channel Orientation on the Distribution of the Heat Transfer Coefficient in Smooth and Dimpled Rotating Rectangular Channels

2010 ◽  
Author(s):  
Seokbeom Kim ◽  
Eun Yeong Choi ◽  
Jae Su Kwak
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Transfer Coefficients ◽  
Rotating Speed ◽  
Heat Transfer Coefficients ◽  
Rectangular Channels ◽  
Channel Orientation ◽  
Transient Liquid Crystal Technique ◽  
The Heat Transfer Coefficient

The detailed heat transfer coefficients on rotating smooth and dimpled rectangular channels were measured by the transient liquid crystal technique. The rotating speed of the channel was fixed at 500rpm and the tested Reynolds number based on the channel hydraulic diameter was varied from 10,000 to 30,000. A stationary case and two different channel rotating orientations of 90° and 120° were tested in order to investigate the effects of channel orientation on the distribution of the heat transfer coefficient in smooth and dimpled rotating surfaces. Results showed high and low heat transfer coefficient regions caused by flow separation and reattachment by dimple and Coriolis force induced flows. Also, measured data indicated that the heat transfer coefficients on the dimpled surface were strongly affected by the rotation and channel rotating orientation. In the dimpled cases, the higher heat transfer coefficient is showed in the 120° orientated channel rather than the 90° orientated channel.

Heat Transfer Measurements in an Annular Cascade of Transonic Gas Turbine Blades Using the Transient Liquid Crystal Technique

1995 ◽  
Vol 117 (3) ◽  
pp. 425-431 ◽  
Author(s):  
R. F. Martinez-Botas ◽  
G. D. Lock ◽  
T. V. Jones
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Liquid Crystal ◽  
Transfer Coefficient ◽  
Turbine Blades ◽  
Video Camera ◽  
Exit Mach Number ◽  
Annular Cascade ◽  
Transient Liquid Crystal Technique ◽  
The Heat Transfer Coefficient

Heat transfer measurements have been made in the Oxford University Cold Heat Transfer Tunnel employing the transient liquid crystal technique. Complete contours of the heat transfer coefficient have been obtained on the aerofoil surfaces of a large annular cascade of high-pressure nozzle guide vanes (mean blade diameter of 1.11 m and axial chord of 0.0664 m). The measurements are made at engine representative Mach and Reynolds numbers (exit Mach number 0.96 and Reynolds number 2.0 × 106). A novel mechanism is used to isolate five preheated blades in the annulus before an unheated flow of air passes over the vanes, creating a step change in heat transfer. The surfaces of interest are coated with narrow-band thermochromic liquid crystals and the color crystal change is recorded during the run with a miniature CCD video camera. The heat transfer coefficient is obtained by solving the one-dimensional heat transfer equation for all the points of interest. This paper will describe the experimental technique and present results of heat transfer and flow visualization.

Heat Transfer in Trailing Edge Wedge-Shaped Pin-Fin Channels With Slot Ejection Under High Rotation Numbers

2010 ◽  
Author(s):  
Akhilesh P. Rallabandi ◽  
Yao-Hsien Liu ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Significant Enhancement ◽  
Trailing Edge ◽  
Pin Fin ◽  
High Heat Transfer ◽  
Smooth Channel ◽  
Pin Fins ◽  
The Heat Transfer Coefficient

The heat transfer characteristics of a rotating pin-fin roughened wedge shaped channel have been studied. The model incorporates ejection through slots machined on the narrower end of the wedge, simulating a rotor blade trailing edge. The copperplate regional average method is used to determine the heat transfer coefficient; pressure taps have been used to estimate the flow discharged through each slot. Tests have been conducted at high rotation (≈ 1 ) and buoyancy (≈ 2) numbers, in a pressurized rotating rig. Reynolds Numbers investigated range from 10,000 to 40,000 and rotational speeds range from 0–400rpm. Pin-fins studied are made of copper as well as non-conducting garolite. Results show high heat transfer coefficients in the proximity of the slot. A significant enhancement in heat transfer due to the pin-fins, compared with a smooth channel is observed. Even the non-conducting pin-fins, indicative of heat transfer on the end-wall show a significant enhancement in the heat transfer coefficient. Results also show a strong rotation effect, increasing significantly the heat transfer coefficient on the trailing surface — and reducing the heat transfer on the leading surface.

scholarly journals Heat Transfer Measurements in an Annular Cascade of Transonic Gas Turbine Blades Using the Transient Liquid Crystal Technique

1994 ◽  
Author(s):  
R. F. Martinez-Botas ◽  
G. D. Lock ◽  
T. V. Jones
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Liquid Crystal ◽  
Transfer Coefficient ◽  
Turbine Blades ◽  
Video Camera ◽  
Flow Visualisation ◽  
Annular Cascade ◽  
Transient Liquid Crystal Technique ◽  
The Heat Transfer Coefficient

Heat transfer measurements have been made in the Oxford University Cold Heat Transfer Tunnel employing the transient liquid crystal technique. Complete contours of the heat transfer coefficient have been obtained on the aerofoil surfaces of a large annular cascade of high pressure nozzle guide vanes (mean blade diameter of 1.11 m and axial chord of 0.0664 m). The measurements are made at engine representative Mach and Reynolds numbers (exit Mach number 0.96 and Reynolds number 2.0 × 106). A novel mechanism is used to isolate five preheated blades in the annulus before an unheated flow of air passes over the vanes, creating a step change in heat transfer. The surfaces of interest are coated with narrow-band thermochromic liquid crystals and the colour crystal change is recorded during the run with a miniature CCD video camera. The heat transfer coefficient is obtained by solving the one dimensional heat transfer equation for all the points of interest. This paper will describe the experimental technique and present results of heat transfer and flow visualisation.

scholarly journals Pressure Loss and Heat Transfer in Channels Roughened on Two Opposed Walls

1989 ◽  
Author(s):  
R. E. Mayle
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Pressure Loss ◽  
Flow Direction ◽  
Height Ratio ◽  
Cooling Effectiveness ◽  
Rectangular Channels ◽  
Logarithmic Law ◽  
The Heat Transfer Coefficient

In order to selectively increase cooling effectiveness, coolant channels in gas turbine components are often only roughened on one or two walls of the channel. A model is presented for flow in rectangular channels having two opposed roughened walls and a theory is developed for both the pressure loss and heat transfer. The theory allows one to calculate the heat transfer coefficient on each wall separately in addition to the overall friction factor and heat transfer coefficient. Comparisons are made to data for similarly configured channels, tubes and surfaces roughened by regularly spaced transverse ribs placed normal to the flow direction. Correlations for the displacement velocity in the logarithmic law and the roughness Stanton number in terms of the rib pitch-to-height ratio and roughness Reynolds number are also presented.

Pressure Loss and Heat Transfer in Channels Roughened on Two Opposed Walls

1991 ◽  
Vol 113 (1) ◽  
pp. 60-66 ◽  
Author(s):  
R. E. Mayle
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Pressure Loss ◽  
Flow Direction ◽  
Height Ratio ◽  
Cooling Effectiveness ◽  
Rectangular Channels ◽  
Logarithmic Law ◽  
The Heat Transfer Coefficient

In order to increase cooling effectiveness selectively, coolant channels in gas turbine components are often only roughened on one or two walls of the channel. A model is presented for flow in rectangular channels having two opposed roughened walls and a theory is developed for both the pressure loss and heat transfer. The theory allows one to calculate the heat transfer coefficient on each wall separately in addition to the overall friction factor and heat transfer coefficient. Comparisons are made to data for similarly configured channels, tubes, and surfaces roughened by regularly spaced transverse ribs placed normal to the flow direction. Correlations for the displacement velocity in the logarithmic law and the roughness Stanton number in terms of the rib pitch-to-height ratio and roughness Reynolds number are also presented.

scholarly journals Determination of heat transfer criterial equation when cooling aluminum ingots

2021 ◽  
Vol 2088 (1) ◽  
pp. 012017
Author(s):  
A S Gorshenin ◽  
N P Krasnova ◽  
J I Rakhimova
Keyword(s):  
Heat Transfer ◽  
Heat Treatment ◽  
Mathematical Model ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Criterial Equation ◽  
Rectangular Channels ◽  
Casting Aluminum ◽  
Cooling Air ◽  
The Heat Transfer Coefficient

Abstract A big problem when casting aluminum ingots is the uneven structure formation, which leads to an increased rejection of products. Nonequilibrium structure elimination is carried out by heat treatment. To obtain the required aluminum ingots’ physicochemical properties, it is necessary to know the conditions of heat transfer between the ingots and the cooling air, i.e. a mathematical model of conjugate heat transfer is needed. The mathematical model obtained by the authors makes it possible to analytically investigate the ingots temperature and cooling air during heat treatment. This mathematical model assumes the heat transfer coefficient calculation. The existing criterion equations for determining the heat transfer coefficient have a drawback - the heat transfer coefficient according to these equations is calculated in circular channels, while heat transfer between aluminum ingots and air occurs in rectangular channels. The article describes the criterion equation identification for heat transfer, used in the analytical study, by the data of the experimental study.

Evaporation of lignin-lean black liquor

TAPPI Journal ◽  
2015 ◽  
Vol 14 (7) ◽  
pp. 441-450
Author(s):  
HENRIK WALLMO, ◽  
ULF ANDERSSON ◽  
MATHIAS GOURDON ◽  
MARTIN WIMBY
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Black Liquor ◽  
Salt Content ◽  
Solubility Limit ◽  
Lignin Removal ◽  
Kraft Black Liquor ◽  
Black Liquors ◽  
The Heat Transfer Coefficient

Many of the pulp mill biorefinery concepts recently presented include removal of lignin from black liquor. In this work, the aim was to study how the change in liquor chemistry affected the evaporation of kraft black liquor when lignin was removed using the LignoBoost process. Lignin was removed from a softwood kraft black liquor and four different black liquors were studied: one reference black liquor (with no lignin extracted); two ligninlean black liquors with a lignin removal rate of 5.5% and 21%, respectively; and one liquor with maximum lignin removal of 60%. Evaporation tests were carried out at the research evaporator in Chalmers University of Technology. Studied parameters were liquor viscosity, boiling point rise, heat transfer coefficient, scaling propensity, changes in liquor chemical composition, and tube incrustation. It was found that the solubility limit for incrustation changed towards lower dry solids for the lignin-lean black liquors due to an increased salt content. The scaling obtained on the tubes was easily cleaned with thin liquor at 105°C. It was also shown that the liquor viscosity decreased exponentially with increased lignin outtake and hence, the heat transfer coefficient increased with increased lignin outtake. Long term tests, operated about 6 percentage dry solids units above the solubility limit for incrustation for all liquors, showed that the heat transfer coefficient increased from 650 W/m2K for the reference liquor to 1500 W/m2K for the liquor with highest lignin separation degree, 60%.

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