Investigations of Heat-Transfer Coefficients for Air Flow Through Round Jets Impinging Normal to a Heat-Transfer Surface

1963 ◽  
Vol 85 (3) ◽  
pp. 237-243 ◽  
Author(s):  
G. C. Huang
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Surface ◽  
Practical Application ◽  
Transfer Coefficients ◽  
Average Heat ◽  
Round Jets ◽  
Heat Transfer Coefficients ◽  
High Magnitude ◽  
Single Jet ◽  
Flow Through

In this paper, empirical equations of local as well as average heat-transfer coefficients of single jet system were derived. Two aspects of multiple jet systems have been studied. One concerns mainly the uniform distribution of heat-transfer coefficients and economy of power consumption. The other concerns the high magnitude of heat-transfer coefficients and the interference among jets. The experiments were conducted at Reynolds number from 103 to 104 and hole size from 1/8 to 1/4 in. diameter. An attempt was made to correlate empirical data to render practical application possible.

Heat Transfer Enhancement for Turbulent Flow Through Blockages With Round and Elongated Holes in a Rectangular Channel

2007 ◽  
Vol 129 (11) ◽  
pp. 1611-1615 ◽  
Author(s):  
H. S. Ahn ◽  
S. W. Lee ◽  
S. C. Lau
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Rectangular Channel ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Pressure Drops ◽  
Average Heat ◽  
Heat Transfer Coefficients ◽  
Aspect Ratios ◽  
Flow Through

Experiments were conducted to determine the average heat transfer coefficients on three wall segments between blockages with holes in a wide rectangular channel. Eight different configurations of the holes in the blockages—two diameters and four aspect ratios of the holes—were examined. The pressure drops across the blockages were also measured. The results showed that the elongated holes in the blockages in this study enhanced more heat transfer than the round holes, but they also caused larger pressure drops across the blockages.

An Analytical Study of the Optimized Performance of an Impingement Heat Sink

2004 ◽  
Vol 126 (4) ◽  
pp. 528-534 ◽  
Author(s):  
S. B. Sathe ◽  
B. G. Sammakia
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Heat Sink ◽  
High Performance ◽  
Cross Flow ◽  
High Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
High Heat Transfer ◽  
Flow Through

The results of a study of a new and unique high-performance air-cooled impingement heat sink are presented. An extensive numerical investigation of the heat sink performance is conducted and is verified by experimental data. The study is relevant to cooling of high-power chips and modules in air-cooled environments and applies to workstations or mainframes. In the study, a rectangular jet impinges on a set of parallel fins and then turns into cross flow. The effects of the fin thickness, gap nozzle width and fin shape on the heat transfer and pressure drop are investigated. It is found that pressure drop is reduced by cutting the fins in the central impingement zone without sacrificing the heat transfer due to a reduction in the extent of the stagnant zone. A combination of fin thicknesses of the order of 0.5 mm and channel gaps of 0.8 mm with appropriate central cutout yielded heat transfer coefficients over 1500 W/m2 K at a pressure drop of less than 100 N/m2, as is typically available in high-end workstations. A detailed study of flow-through heat sinks subject to the same constraints as the impingement heat sink showed that the flow-through heat sink could not achieve the high heat transfer coefficients at a low pressure drop.

An Experimental Investigation of the Rib Surface-Averaged Heat Transfer Coefficient in a Rib-Roughened Square Passage

1997 ◽  
Vol 119 (2) ◽  
pp. 381-389 ◽  
Author(s):  
M. E. Taslim ◽  
C. M. Wadsworth
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Thermal Performance ◽  
Blockage Ratio ◽  
Transfer Coefficients ◽  
Height Ratio ◽  
Average Heat ◽  
Heat Transfer Coefficients ◽  
The Heat Transfer Coefficient

Turbine blade cooling, a common practice in modern aircraft engines, is accomplished, among other methods, by passing the cooling air through an often serpentine passage in the core of the blade. Furthermore, to enhance the heat transfer coefficient, these passages are roughened with rib-shaped turbulence promoters (turbulators). Considerable data are available on the heat transfer coefficient on the passage surface between the ribs. However, the heat transfer coefficients on the surface of the ribs themselves have not been investigated to the same extent. In small aircraft engines with small cooling passages and relatively large ribs, the rib surfaces comprise a large portion of the passage heat transfer area. Therefore, an accurate account of the heat transfer coefficient on the rib surfaces is critical in the overall design of the blade cooling system. The objective of this experimental investigation was to conduct a series of 13 tests to measure the rib surface-averaged heat transfer coefficient, hrib, in a square duct roughened with staggered 90 deg ribs. To investigate the effects that blockage ratio, e/Dh and pitch-to-height ratio, S/e, have on hrib and passage friction factor, three rib geometries corresponding to blockage ratios of 0.133, 0.167, and 0.25 were tested for pitch-to-height ratios of 5, 7, 8.5, and 10. Comparisons were made between the rib average heat transfer coefficient and that on the wall surface between two ribs, hfloor, reported previously. Heat transfer coefficients of the upstream-most rib and that of a typical rib located in the middle of the rib-roughened region of the passage wall were also compared. It is concluded that: 1 The rib average heat transfer coefficient is much higher than that for the area between the ribs; 2 similar to the heat transfer coefficient on the surface between the ribs, the average rib heat transfer coefficient increases with the blockage ratio; 3 a pitch-to-height ratios of 8.5 consistently produced the highest rib average heat transfer coefficients amongst all tested; 4 under otherwise identical conditions, ribs in upstream-most position produced lower heat transfer coefficients than the midchannel positions, 5 the upstream-most rib average heat transfer coefficients decreased with the blockage ratio; and 6 thermal performance decreased with increased blockage ratio. While a pitch-to-height ratio of 8.5 and 10 had the highest thermal performance for the smallest rib geometry, thermal performance of high blockage ribs did not change significantly with the pitch-to-height ratio.

Periodic Streamwise Variations of Heat Transfer Coefficients for Inline and Staggered Arrays of Circular Jets with Crossflow of Spent Air

1980 ◽  
Vol 102 (1) ◽  
pp. 132-137 ◽  
Author(s):  
L. W. Florschuetz ◽  
R. A. Berry ◽  
D. E. Metzger
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Transfer Surface ◽  
Test Surface ◽  
Heat Transfer Characteristics ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Circular Jets ◽  
Impinging Flow

Heat transfer characteristics were measured for inline and staggered arrays of circular jets impinging on a surface parallel to the jet orifice plate. The impinging flow was constrained to exit in a single direction along the channel formed by the jet plate and the heat transfer surface. In this configuration the air discharged from upstream transverse rows of jet holes imposes a crossflow of increasing magnitude on the succeeding downstream jet rows. Streamwise heat transfer coefficient profiles were determined for a streamwise resolution of one-third the streamwise hole spacing, utilizing a specially constructed test surface. These profiles are characterized by significant periodic variations. The downstream amplitudes are diminished by the increasing crossflow magnitude, but can persist for at least ten rows of holes. Results were obtained for streamwise hole spacings of 5, 10, and 15 hole diameters; transverse hole spacings of 4, 6, and 8 diameters; and channel heights of 1, 2, and 3 diameters. The number of transverse hole rows was fixed at ten for all configurations. The characteristics of the periodic variations are presented and discussed as a function of the geometric parameters, including the effect of hole pattern.

Effect of Rib Configuration and Lateral Ejection on a High Aspect Ratio Trailing Edge Channel

2013 ◽  
Author(s):  
Rui Kan ◽  
Li Yang ◽  
Jing Ren ◽  
Hongde Jiang
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Local Heat Transfer ◽  
Large Aspect Ratio ◽  
Thermochromic Liquid Crystal ◽  
Transfer Coefficients ◽  
Trailing Edge ◽  
Average Heat ◽  
Edge Channel ◽  
Heat Transfer Coefficients

Thermal issues of gas turbine blade trailing edge are complex and challenging, due to limited space for effective cooling. The trailing edge cavities are usually large aspect ratio ducts with lateral ejection. The objective of this study is to investigate the effects of different rib configurations and lateral ejection on heat transfer characteristics inside a trailing edge channel. The investigations were conducted on a large aspect ratio wedge-shaped channel with square ribs of e/Dh = 0.05, under Reynolds number 15,000. Twelve different configurations were tested: 1)three rib types, including a symmetry V-shaped rib configuration and two non-symmetry V-shaped rib configurations, of which the rib angles are 60 degrees, 2) two rib pitches, P/e = 10 and P/e = 5, 3) two flow directions, with an open tip outlet or with lateral ejection. Spatially resolved heat transfer distributions were obtained using the transient thermochromic liquid crystal experimental method. The configurations were also investigated numerically for the detailed flow field and for the validation of CFD codes. Results show that with lateral ejection, the heat transfer coefficients decrease from inlet to outlet. The heat transfer near the ejection holes is enhanced while heat transfer coefficients near the wall opposite to the exit holes decrease. The curvature of the streamlines creates a large separation area near the end of the channel and thus results in low local heat transfer coefficients. The P/e = 10 configurations have higher average heat transfer compared with P/e = 5 configurations. Average heat transfer coefficient is the highest with the center of the V-shaped rib placed at the middle of the channel, and is the lowest when the V-shaped rib center is located near the narrow part of the channel.

Heat Transfer From Rectangular Plates Inclined at Different Angles of Attack and Yaw to an Air Stream

1985 ◽  
Vol 107 (2) ◽  
pp. 307-312 ◽  
Author(s):  
D. G. Motwani ◽  
U. N. Gaitonde ◽  
S. P. Sukhatme
Keyword(s):  
Heat Transfer ◽  
Reynolds Numbers ◽  
Rectangular Plates ◽  
Average Heat Transfer Coefficient ◽  
Transfer Coefficients ◽  
Average Heat ◽  
Heat Transfer Coefficients ◽  
Aspect Ratios ◽  
Air Stream ◽  
Angle Of Yaw

Average heat transfer coefficients during forced convection air flow over inclined and yawed rectangular plates have been experimentally determined. Tripping wires at the edges ensured that a turbulent boundary layer prevailed over the plates. The experiments were carried out for a constant surface temperature and covered two plates of different aspect ratios, angles of attack from 0 to 45 deg, angles of yaw from 0 to 30 deg, and Reynolds numbers from 2 times; 104 to 3.5 times; 105. The results show that the average heat transfer coefficient is essentially insensitive to the aspect ratio and angle of yaw. However, it is a function of Reynolds number and the angle of attack. Correlation equations for various angles of attack are suggested.

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