Uneven Wall Heat Flux Effect on Local Heat Transfer in Rotating Two-Pass Channels With Two Opposite Ribbed Walls

1996 ◽  
Vol 118 (4) ◽  
pp. 864-876 ◽  
Author(s):  
Shou-Shing Hsieh ◽  
Wei-Jen Liu
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Secondary Flows ◽  
Fluid Temperature ◽  
Bulk Fluid ◽  
Aspect Ratios ◽  
Uneven Heating

The influence of rotation and uneven heating condition on the local heat transfer coefficient in rotating, two-pass rib-roughened (rib height e/DH ≈ 0.17 − 0.20; rib pitch p/e = 5) rectangular channels with cross-sectional aspect ratios of 1 and 1.5 were studied for Reynolds numbers from 5000 to 25,000 and rotation numbers from 0 to 0.6152. Regionally averaged Nusselt number variations along the duct have been determined over the trailing and leading surfaces for two pass channels. In general, Coriolis-induced secondary flows are shown to enhance local heat transfer over the trailing (leading) surface in the first (second) pass compared to a duct without rotation. Centrifugal buoyancy is shown to influence the heat transfer response with heat transfer being imposed on both leading and trailing surfaces as the wall-to-bulk fluid temperature difference is increased with other controlling parameters fixed. Results also indicate a slight decrease in heat transfer coefficient for an increase in passage aspect ratio. Results are compared with previous studies. It is found that the results agree quite well with those reported by other works for two-pass flow channels.

Numerical Prediction of 45° Angled Ribs Effects on U-shaped Channels Heat Transfer and Flow under Multi Conditions

2020 ◽  
Vol 37 (1) ◽  
pp. 41-59 ◽  
Author(s):  
Longfei Wang ◽  
Songtao Wang ◽  
Xun Zhou ◽  
Fengbo Wen ◽  
Zhongqi Wang
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Characteristics ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Narrow Channel ◽  
Aspect Ratios ◽  
Cooling Air Flow

AbstractRibs effects on the heat transfer performance and cooling air flow characteristics in various aspect ratios (AR) U-shaped channels under different working conditions are numerically investigated. The ribs angle and channel orientation are 45° and 90°, respectively, and the aspect ratios are 1:2, 1:1, 2:1. The inlet Reynolds number changes from 1e4 to 4e4 and rotational speeds include 0, 550 rpm, 1,100 rpm. Local heat transfer coefficient, endwall surface heat transfer coefficient ratio and augmentation factor are the three primary criteria to measure channel heat transfer. Ribs increase the heat transfer area and improve heat transfer coefficient of ribbed surfaces significantly, especially in the 1st pass, while the endwall surface contributes more to channel heat transfer because of the larger area and relatively smaller heat transfer coefficient. The wide channel (AR =2:1) owns the better augmentation factor than the narrow channel (AR =1:2) and ribs heat transfer weight increases with an increase of the inlet Reynolds number. Rotating slightly reduces the ribs heat transfer weight in channel and the trailing surface in 1st pass is the main influence object of rotating.

Improvement of Heat Transfer Performance of Turbulence Promoter Ribs

2006 ◽  
Author(s):  
Yasuhiro Horiuchi ◽  
Nobuaki Kizuka ◽  
Shinya Marushima
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Transfer Performance ◽  
Comparative Method ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Secondary Flows ◽  
Transfer Performance ◽  
Pressure Loss Coefficient

Numerical and experimental approaches were taken to improve the heat transfer performance of V-shaped staggered (VSG) ribs. At first, a numerical method using Large Eddy Simulations (LES) was employed to determine the effect of VSG rib-induced flow on the local heat transfer coefficient distributions. The results revealed that the secondary flows generated by the rib configuration carry cold coolant air from the passage core region to the rib-roughened wall, thus enhancing heat transfer. Conversely, behind each rib there is a recirculation zone that does not contribute to enhanced heat transfer. Based on said results, six types of the advanced V-shaped staggered (AVSG) rib configurations were proposed. The test apparatus employing a comparative method was used to measure the total heat transfer coefficient and pressure loss coefficient of the VSG and AVSG ribs. It was concluded that thermal performance of the most effective type was 25% higher than that of VSG.

A Data Reduction Procedure for Transient Heat Transfer Measurements in Long Internal Cooling Channels

1998 ◽  
Vol 120 (2) ◽  
pp. 314-321 ◽  
Author(s):  
J. von Wolfersdorf ◽  
R. Hoecker ◽  
C. Hirsch
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Data Reduction ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Local Heat Transfer Coefficient ◽  
Transient Heat Transfer ◽  
Temperature History ◽  
Fluid Temperature

The effect of streamwise fluid temperature variation on the local heat transfer coefficient measurements in transient heat transfer tests in long channels is addressed. Previous methods are shown to result in considerable errors. A simplified model is proposed to characterize the local fluid temperature, which drives the heat transfer. With it, analytical solutions for the local wall temperature history are derived, which involve two unknowns, the local heat transfer coefficient and a lumped upstream heat transfer parameter. Using these solutions in the data reduction, these two parameters are determined from surface temperature measurements. Numerical experiments that simulate the physical experiment show the applicability and robustness of the proposed method. The method is finally demonstrated experimentally by investigating heat transfer in a smooth, square duct.

Latticework (Vortex) Cooling Effectiveness: Part 1 — Stationary Channel Experiments

2004 ◽  
Author(s):  
Ronald S. Bunker
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Local Heat Transfer ◽  
Suction Side ◽  
Local Heat ◽  
Test Methods ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Aspect Ratios

The present investigation provides detailed information concerning the heat transfer coefficients and pressures in latticework (vortex) cooling channels. Two test methods are used to determine the local and overall heat transfer coefficients for a vortex channel with crossing angle of 45-degrees. Both liquid crystal and infrared thermography methods are used on acrylic and metallic models to discern the heat transfer coefficients without and with the effects of internal rib fin effectiveness. Tests with insulating ribs determine the heat transfer on the primary surfaces representing the pressure and suction side walls of an airfoil. Tests with integral metal ribs determine the additional impact of the fin effectiveness provided by the ribs. A simple radial vortex channel design is employed throughout with subchannel aspect ratios near unity, and Reynolds numbers from 20,000 to 100,000. Pressure loss variations through typical vortex channels are also measured. The objectives of this research are to show the detailed development of heat transfer in vortex channels leading to an understanding of the two main effects of turning and fin enhancements. Detailed primary surface heat transfer coefficients average about 1.5 over smooth duct behavior, but reach local values of about 3 immediately after each turn. Pressure distributions show high turning losses on the order of those associated with serpentine 180-degree turn circuits. Local heat transfer coefficient distributions are remarkably uniform throughout the channels excepting the turns themselves. Turn enhancements are retained for relatively long distances. Overall vortex channel heat transfer coefficient enhancement levels are shown to be 2.5 to 3. The effects of subchannel internal ribs, which act as fins, are shown to be very important in the overall thermal picture. Test results show that treatment of the ribs as simple fins is appropriate and that each rib surface has about the same heat transfer coefficient on average as that of the primary surface. This first detailed study shows that latticework channels have significant potential and should be further investigated.

scholarly journals Local Heat Transfer and Pressure Drop in a Rotating Two-Pass Ribbed Rectangular Channel

2001 ◽  
Vol 7 (3) ◽  
pp. 183-194 ◽  
Author(s):  
Shou-Shing Hsieh ◽  
Hsiu-Cheng Liao
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Aspect Ratio ◽  
Transfer Coefficient ◽  
Rectangular Channel ◽  
Three Dimensional ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Uneven Heating

The influences of rotation and uneven heating condition as well as passage aspect ratio on the local heat transfer coefficient and pressure drop in a rotating, two pass ribroughened (rib heighte/DH≈0.27; rib pitchp/e=8) rectangular channel with a crosssection aspect ratio of 3 was studied for Reynolds numbers from 5000 to 25,000 and rotation numbers from 0 to 0.24. Regionally averaged Nusselt number variations along the duct have been determined over the trailing and leading surfaces for two pass straight channels and U-bend region. Implementing with the data from Hsieh and Liu (1996) forAR=1and 1.5 withp/e=5ande/DH=0.17and 0.20, passage aspect ratio effect was further examined. Furthermore, data for180∘U-bend region with ribroughened turbulator on heat transfer were also measured. It was found that a complicated three-dimensional accelerated flow and secondary flow in this U-bend region caused higher heat transfer on both leading/trailing walls. Enhancement performance ratios are also presented and discussed. Results again indicate a slight decrease in heat transfer coefficient for an increase in passage aspect ratio as compared to those of previous studies.

Identification of Dominant Heat Transfer Modes Associated With the Impingement of an Elliptical Jet Array

1999 ◽  
Vol 122 (2) ◽  
pp. 240-247 ◽  
Author(s):  
S. C. Arjocu ◽  
J. A. Liburdy
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Impinging Jets ◽  
Thermochromic Liquid Crystal ◽  
Aspect Ratios ◽  
Low Reynolds ◽  
The Heat Transfer Coefficient

The characteristics of the impinging heat transfer of a three-by-three square array of submerged, elliptic impinging jets was studied. Low Reynolds number conditions, 300 to 1500, are considered for two different elliptic jet aspect ratios, with the impingement distance ranging from 1 to 6 jet hydraulic diameters. A transient thermochromic liquid crystal method was used to map the local heat transfer coefficient distribution. The results are reported for the unit cell under the center jet and detail the mean heat transfer as well as the characteristics of the spatial variation of the heat transfer coefficient. The average heat transfer is found to depend inversely on the elliptic jet aspect ratio at these low Reynolds numbers. Distributions of the heat transfer coefficient, h, are also used to obtain proper orthogonal decompositions of h which are used to identify major spatially distributed features. [S0022-1481(00)02102-2]

Local Heat Transfer Measurements in Turbulent Flow Around a 180-deg Pipe Bend

1987 ◽  
Vol 109 (1) ◽  
pp. 43-48 ◽  
Author(s):  
J. W. Baughn ◽  
H. Iacovides ◽  
D. C. Jackson ◽  
B. E. Launder
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Turbulent Flow ◽  
Transfer Coefficient ◽  
Secondary Flow ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Pipe Bend ◽  
Streamline Curvature

The paper reports extensive connective heat transfer data for turbulent flow of air around a U-bend with a ratio of bend radius:pipe diameter of 3.375:1. Experiments cover Reynolds numbers from 2 × 104 to 1.1 × 105. Measurements of local heat transfer coefficient are made at six stations and at five circumferential positions at each station. At Re = 6 × 104 a detailed mapping of the temperature field within the air is made at the same stations. The experiment duplicates the flow configuration for which Azzola and Humphrey [3] have recently reported laser-Doppler measurements of the mean and turbulent velocity field. The measurements show a strong augmentation of heat transfer coefficient on the outside of the bend and relatively low levels on the inside associated with the combined effects of secondary flow and the amplification/suppression of turbulent mixing by streamline curvature. The peak level of Nu occurs halfway around the bend at which position the heat transfer coefficient on the outside is about three times that on the inside. Another feature of interest is that a strongly nonuniform Nu persists six diameters downstream of the bend even though secondary flow and streamline curvature are negligible there. At the entry to the bend there are signs of partial laminarization on the inside of the bend, an effect that is more pronounced at lower Reynolds numbers.

An Experimental Study of High Rayleigh Number Mixed Convection in a Rectangular Enclosure With Restricted Inlet and Outlet Openings

1987 ◽  
Vol 109 (2) ◽  
pp. 446-453 ◽  
Author(s):  
L. Neiswanger ◽  
G. A. Johnson ◽  
V. P. Carey
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Rayleigh Number ◽  
Mixed Convection ◽  
Transfer Coefficient ◽  
Heated Surface ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Test Fluid ◽  
Rectangular Enclosure

Measured local heat transfer data and the results of flow visualization studies are reported for cross-flow mixed convection in a rectangular enclosure with restricted inlet and outlet openings at high Rayleigh number. In this study, experiments using water as the test fluid were conducted in a small-scale test section with uniformly heated vertical side walls and an adiabatic top and bottom. As the flow rate through the enclosure increased, the enhancement of heat transfer, above that for natural convection alone, also increased. The variation of the local heat transfer coefficient over the heated surface was found to be strongly affected by the recirculation of portions of the forced flow within the enclosure. Mean heat transfer coefficients are also presented which were calculated by averaging the measured local values over the heated surface. A correlation for the mean heat transfer coefficient is also proposed which agrees very well with the experimentally determined values. A method of predicting the flow regime in this geometry for specified heating and flow conditions is also discussed.

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