Heat Transfer and Friction Characteristics in Rectangular Channels With Rib Turbulators

1988 ◽  
Vol 110 (2) ◽  
pp. 321-328 ◽  
Author(s):  
J. C. Han
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Aspect Ratio ◽  
Side Wall ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Published Data ◽  
Number Range ◽  
Rectangular Channels ◽  
Channel Aspect Ratio

The effect of the channel aspect ratio on the distribution of the local heat transfer coefficient in rectangular channels with two opposite ribbed walls (to simulate turbine airfoil cooling passages) was determined for a Reynolds number range of 10,000 to 60,000. The channel width-to-height ratios (W/H, ribs on side W) were 1/4, 1/2, 1, 2, and 4. The test channels were heated by passing current through thin, stainless steel foils instrumented with thermocouples. The local heat transfer coefficients on the ribbed side wall and on the smooth side wall of each test channel from the channel entrance to the fully developed regions were measured for two rib spacings (P/e = 10 and 20). The rib angle-of-attack was kept at 90 deg. The local data in the fully developed region were averaged and correlated, based on the heat transfer and friction similarity laws developed for ribbed channels, to cover the ranges of channel aspect ratio, rib spacing, rib height, and Reynolds number. The results compare well with the published data for flow in a square channel with two opposite ribbed walls. The correlations can be used in the design of turbine airfoil cooling passages.

A Comparative Study of Heat Transfer Characteristics and Pressure Drop in Matrix Structures

2019 ◽  
Author(s):  
Anjana N. Prajapati ◽  
Andallib Tariq
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Aspect Ratio ◽  
Friction Factor ◽  
Local Heat Transfer ◽  
Local Heat ◽  
The Matrix ◽  
Channel Aspect Ratio ◽  
Comparative Results

Abstract An experimental study on local heat transfer distributions and pressure loss in the closed matrix channels with an angle 45° has been conducted using liquid crystal thermography for a Reynolds number (Re) range 5800–14000. A total of five different configurations of matrixes have been considered for investigation. The thermo-hydraulic performance of the matrix structure with angle 45° is initially compared with that of the matrixes with angles 35° and 55° for a constant sub-channel aspect ratio (ARs) 0.8. Later, the sub-channel aspect ratio of matrix with angle 45° has been varied as 0.4 and 1.2 and the comparative results are presented. While comparing the performance parameters of different angles for the sub-channel aspect ratio 0.8, it is found that for lower Reynolds numbers (Re ≤ 8100), the angle 45° offers highest augmentation Nusselt number. However, for Re > 8100, the angle 55° showed the highest augmentation Nusselt number. It has been also observed that the sub-channel aspect ratio 0.8 presents the highest augmentation Nusselt numbers as compared to ARs = 1.2 and 0.4 for Re ≤ 12400. Whereas, the friction factor fairly decreases with the increase in the sub-aspect ratio. A significant effect of angle has been found for friction factor as compared to sub-channel aspect ratio. The highest thermal performance factor (1.13) is obtained for the matrix with angle 45° and sub-channel aspect ratio 0.8 at Reynolds number 8100.

Free-Stream Turbulence Effects on Local Heat Transfer from a Sphere

1972 ◽  
Vol 94 (1) ◽  
pp. 7-14 ◽  
Author(s):  
L. B. Newman ◽  
E. M. Sparrow ◽  
E. R. G. Eckert
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Reynolds Number ◽  
Free Stream ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Heat Flux Sensor ◽  
Forward Region ◽  
Number Range ◽  
Free Stream Turbulence

Experiments involving both heat-transfer and turbulence-field measurements were performed to determine the influence of free-stream turbulence on the local heat transfer from a sphere situated in a forced-convection airflow. The research was facilitated by a miniature heat-flux sensor which could be positioned at any circumferential location on the equator of the sphere. Turbulence grids were employed to generate free-stream turbulence with intensities of up to 9.4 percent. The Reynolds-number range of the experiments was from 20,000 to 62,000. The results indicate that the local heat flux in the forward region of the sphere is uninfluenced by free-stream turbulence levels of up to about 5 percent. For higher turbulence levels, the heat-flux increases with the turbulence intensity, the greatest heat-flux augmentation found here being about 15 percent. Furthermore, at the higher turbulence intensities, there appears to be a departure from the half-power Reynolds-number dependence of the stagnation-point Nusselt number. Turbulent separation occurred at Reynolds numbers of 42,000 and 62,000 for a turbulence level of 9.4 percent, these values being well below the transition Reynolds number of 2 × 105 for a sphere situated in a low-turbulence flow.

Heat Transfer and Friction Factor Measurements in Ducts With Staggered and In-Line Ribs

1993 ◽  
Vol 115 (1) ◽  
pp. 58-65 ◽  
Author(s):  
Ying-Jong Hong ◽  
Shou-Shing Hsieh
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Aspect Ratios ◽  
Friction Factors ◽  
Rectangular Channels ◽  
Channel Aspect Ratio ◽  
Semi Empirical ◽  
Rib Roughened

The combined effects of rib alignment and channel aspect ratio on the distributions of the local heat transfer coefficient and on the friction factors for developing and fully developed flow in short square and rectangular channels (L/DH = 13.5–18) with a pair of opposite rib-roughened walls were determined for Reynolds numbers ranging from 13,000 to 130,000. The channel aspect ratios are 1/2 and 1 and the rib alignment configurations are arranged as staggered and in-line types, respectively. The pitch to rib height ratio is 5.31 for all test channels. The local heat transfer distributions on the bottom rib-roughened wall from the channel entrance to the downstream region are presented and discussed. Semi-empirical heat transfer and friction correlations are developed, and the results are compared with those of previous investigations for similarly configured channels, which were roughened by regularly spaced transverse ribs.

Effect of Laminarization and Retransition on Heat Transfer for Low Reynolds Number Flow Through a Converging to Constant Area Duct

1982 ◽  
Vol 104 (2) ◽  
pp. 363-371 ◽  
Author(s):  
H. Tanaka ◽  
H. Kawamura ◽  
A. Tateno ◽  
S. Hatamiya
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Parallel Plate ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Parallel Plates ◽  
Number Range ◽  
Reynolds Number Flow ◽  
Turbulent Air Flow

A fully developed turbulent air flow between two parallel plates with the spacing of 15 mm was accelerated through a linearly converging passage of 200 mm in length, from which it flowed into a parallel-plate channel again. A foil heater was fastened on one wall surface over the entire channel, and local heat-transfer coefficient distribution was measured over the channel Reynolds number range of 5000 to 14,000 and also the slope of the accelerating section between 2/200 mm/mm and 10/200 mm/mm. (The acceleration parameter K ranged between 1.4 × 10−6 and 2 × 10−5.) The Nusselt number at the outlet of the accelerating section was considerably lower than in the initial fully turbulent state, suggesting laminarization of the flow. The measured Nusselt number continued to decrease in the first part of the downstream parallel-plate section to a minimum and then began to increase sharply, suggesting reversion to turbulent flow. Heat transfer along the parallel-converging-parallel plate system was reproduced fairly satisfactorily by applying a k-kL model of turbulence.

Pressure Loss Distribution in Three-Pass Rectangular Channels With Rib Turbulators

1989 ◽  
Vol 111 (4) ◽  
pp. 515-521 ◽  
Author(s):  
J. C. Han ◽  
P. Zhang
Keyword(s):  
Reynolds Number ◽  
Aspect Ratio ◽  
Channel Width ◽  
Local Pressure ◽  
Number Range ◽  
Pressure Drops ◽  
Rectangular Channels ◽  
First Pass ◽  
Rib Turbulators ◽  
Channel Aspect Ratio

The present study investigated the combined effects of the flow channel aspect ratio, the rib turbulator configuration, and the sharp 180-deg turn on the distributions of the local pressure drop in three-pass rectangular channels for a Reynolds number range of 15,000 to 60,000. The channel aspect ratios (the channel width-to-height ratios W/H; ribs on the channel width, W, side) were 1, 1/2, and 1/4. The rib height-to-hydraulic diameter ratios (E/D) were 0.063, 0.047, and 0.039; the rib pitch-to-height ratios (P/E) were 5, 7.5, 10, and 15; the rib angles of attack (α) were 90, 60, and 45 deg. The results showed that the rib turbulators dominated the pressure drops in the first pass of the three-pass channel. The pressure drops in the two-pass and the three-pass channels were caused by both the rib turbulators and the sharp 180-deg turns. The differences of the pressure drops caused by the different rib configurations (rib angle, spacing, and height) were significant in the first pass. The differences, however, were diluted by the sharp 180-deg turns in the two-pass and the three-pass channels, and by the smaller channel aspect ratio (W/H changed from 1 to 1/4). The friction factor correlations for the first pass, the first two-pass, and the three-pass were obtained to account for the rib configuration, the channel aspect ratio, and the Reynolds number. The correlations can be used in the design of the turbine airfoil cooling passages.

Heat Transfer for High Aspect Ratio Rectangular Channels in a Stationary Serpentine Passage With Turbulated and Smooth Surfaces

2013 ◽  
Author(s):  
Matthew A. Smith ◽  
Randall M. Mathison ◽  
Michael G. Dunn
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Aspect Ratio ◽  
Flow Behavior ◽  
Reynolds Numbers ◽  
Hydraulic Diameter ◽  
Internal Cooling ◽  
Number Range ◽  
Aspect Ratios ◽  
Parallel Configuration

Heat transfer distributions are presented for a stationary three passage serpentine internal cooling channel for a range of engine representative Reynolds numbers. The spacing between the sidewalls of the serpentine passage is fixed and the aspect ratio (AR) is adjusted to 1:1, 1:2, and 1:6 by changing the distance between the top and bottom walls. Data are presented for aspect ratios of 1:1 and 1:6 for smooth passage walls and for aspect ratios of 1:1, 1:2, and 1:6 for passages with two surfaces turbulated. For the turbulated cases, turbulators skewed 45° to the flow are installed on the top and bottom walls. The square turbulators are arranged in an offset parallel configuration with a fixed rib pitch-to-height ratio (P/e) of 10 and a rib height-to-hydraulic diameter ratio (e/Dh) range of 0.100 to 0.058 for AR 1:1 to 1:6, respectively. The experiments span a Reynolds number range of 4,000 to 130,000 based on the passage hydraulic diameter. While this experiment utilizes a basic layout similar to previous research, it is the first to run an aspect ratio as large as 1:6, and it also pushes the Reynolds number to higher values than were previously available for the 1:2 aspect ratio. The results demonstrate that while the normalized Nusselt number for the AR 1:2 configuration changes linearly with Reynolds number up to 130,000, there is a significant change in flow behavior between Re = 25,000 and Re = 50,000 for the aspect ratio 1:6 case. This suggests that while it may be possible to interpolate between points for different flow conditions, each geometric configuration must be investigated independently. The results show the highest heat transfer and the greatest heat transfer enhancement are obtained with the AR 1:6 configuration due to greater secondary flow development for both the smooth and turbulated cases. This enhancement was particularly notable for the AR 1:6 case for Reynolds numbers at or above 50,000.

Local Heat Transfer Distribution in a Rotating Serpentine Rib-Roughened Flow Passage

1993 ◽  
Vol 115 (3) ◽  
pp. 560-567 ◽  
Author(s):  
N. Zhang ◽  
J. Chiou ◽  
S. Fann ◽  
W.-J. Yang
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Performance ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Performance ◽  
Height Ratio ◽  
Nusselt Numbers ◽  
Rayleigh Numbers ◽  
Rib Roughened

Experiments are performed to determine the local heat transfer performance in a rotating serpentine passage with rib-roughened surfaces. The ribs are placed on the trailing and leading walls in a corresponding posited arrangement with an angle of attack of 90 deg. The rib height-to-hydraulic diameter ratio, e/Dh, is 0.0787 and the rib pitch-to-height ratio, s/e, is 11. The throughflow Reynolds number is varied, typically at 23,000, 47,000, and 70,000 in the passage both at rest and in rotation. In the rotation cases, the rotation number is varied from 0.023 to 0.0594. Results for the rib-roughened serpentine passages are compared with those of smooth ones in the literature. Comparison is also made on results for the rib-roughened passages between the stationary and rotating cases. It is disclosed that a significant enhancement is achieved in the heat transfer in both the stationary and rotating cases resulting from an installation of the ribs. Both the rotation and Rayleigh numbers play important roles in the heat transfer performance on both the trailing and leading walls. Although the Reynolds number strongly influences the Nusselt numbers in the rib-roughened passage of both the stationary and rotating cases, Nuo and Nu, respectively, it has little effect on their ratio Nu/Nuo.

scholarly journals Natural Convection From Isothermal Horizontal Cylinders

2009 ◽  
Author(s):  
Ian M. O. Gorman ◽  
Darina B. Murray ◽  
Gerard Byrne ◽  
Tim Persoons
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Separation Distance ◽  
Thermal Plume ◽  
Number Range ◽  
Vertically Aligned ◽  
Isothermal Cylinders ◽  
Horizontal Cylinders

The research described here is concerned with natural convection from isothermal cylinders, with a particular focus on the interaction between a pair of vertically aligned cylinders. Prime attention was focused on how the local heat transfer characteristics of the upper cylinder are affected due to buoyancy induced fluid flow from the lower cylinder. Tests were performed using internally heated copper cylinders with an outside diameter 30mm and a vertical separation distance between the cylinders ranging from two to three cylinder diameters. Plume interaction between the heated cylinders was investigated within a Rayleigh number range of 2×106 to 6×106. Spectral analysis of the associated heat transfer interaction is presented showing that interaction between the cylinders causes oscillation of the thermal plume. The effect of this oscillation is considered as a possible enhancement mechanism of the heat transfer performance of the upper cylinder.

Two Dimensional Simulations of Enhanced Heat Transfer in an Intermittently Grooved Channel

2000 ◽  
Author(s):  
M. Greiner ◽  
P. F. Fischer ◽  
H. M. Tufo
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Spectral Element ◽  
Local Heat ◽  
Navier Stokes ◽  
Computational Domain ◽  
Two Dimensional ◽  
Number Range ◽  
Element Technique ◽  
Outflow Boundary

Abstract Two-dimensional Navier-Stokes simulations of heat and momentum transport in an intermittently grooved passage are performed using the spectral element technique for the Reynolds number range 600 ≤ Re ≤ 1800. The computational domain has seven contiguous transverse grooves cut symmetrically into opposite walls, followed by a flat section with the same length. Periodic inflow/outflow boundary conditions are employed. The development and decay of unsteady flow is observed in the grooved and flat sections, respectively. The axial variation of the unsteady component of velocity is compared to the local heat transfer, shear stress and pressure gradient. The results suggest that intermittently grooved passages may offer even higher heat transfer for a given pumping power than the levels observed in fully grooved passages.

Experimental Investigation of Local Heat Transfer Distribution on Smooth and Roughened Surfaces Under an Array of Angled Impinging Jets

2001 ◽  
Author(s):  
Lamyaa A. El-Gabry ◽  
Deborah A. Kaminski
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Cross Flow ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Impinging Jets ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Roughened Surface

Abstract Measurements of the local heat transfer distribution on smooth and roughened surfaces under an array of angled impinging jets are presented. The test rig is designed to simulate impingement with cross-flow in one direction which is a common method for cooling gas turbine components such as the combustion liner. Jet angle is varied between 30, 60, and 90 degrees as measured from the impingement surface, which is either smooth or randomly roughened. Liquid crystal video thermography is used to capture surface temperature data at five different jet Reynolds numbers ranging between 15,000 and 35,000. The effect of jet angle, Reynolds number, gap, and surface roughness on heat transfer efficiency and pressure loss is determined along with the various interactions among these parameters. Peak heat transfer coefficients for the range of Reynolds number from 15,000 to 35,000 are highest for orthogonal jets impinging on roughened surface; peak Nu values for this configuration ranged from 88 to 165 depending on Reynolds number. The ratio of peak to average Nu is lowest for 30-degree jets impinging on roughened surfaces. It is often desirable to minimize this ratio in order to decrease thermal gradients, which could lead to thermal fatigue. High thermal stress can significantly reduce the useful life of engineering components and machinery. Peak heat transfer coefficients decay in the cross-flow direction by close to 24% over a dimensionless length of 20. The decrease of spanwise average Nu in the crossflow direction is lowest for the case of 30-degree jets impinging on a roughened surface where the decrease was less than 3%. The decrease is greatest for 30-degree jet impingement on a smooth surface where the stagnation point Nu decreased by more than 23% for some Reynolds numbers.

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