Analysis of the heat transfer and friction in a ribbed square channel using numerical and experimental methods

2007 ◽  
Vol 221 (3) ◽  
pp. 151-159 ◽  
Author(s):  
H. K. Kang ◽  
S. W. Ahn ◽  
S. T. Bae ◽  
D. H. Lee
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Uniform Heat Flux ◽  
Square Channel ◽  
Numerical Predictions ◽  
Transfer Channel ◽  
Flow Through

Numerical predictions and experiment of a hydrodynamic and thermally developed turbulent flow through square channels with one or two ribbed walls were performed to determine the pressure drop and heat transfer. The CFX (version 5.7) software package was used for the computations. The rough wall had 45°-inclined square ribs. All four walls in the channel were heated, and a uniform heat flux was maintained on the entire inner heat transfer channel area. Experimental data were also obtained for four Reynolds numbers ranging from 7600 to 24 900, a pitch-to-rib-height ratio of 8.0, and a rib-height-to-channel hydraulic diameter ratio of 0.0667. The numerical results were in agreement with the experimental data and showed that the values of the local heat transfer coefficient and friction factor in a square channel with two ribbed walls were greater than those with one ribbed wall.

Heat Transfer and Pressure Drop Correlations for Square Channels With 45 Deg Ribs at High Reynolds Numbers

2009 ◽  
Vol 131 (7) ◽  
Author(s):  
Akhilesh P. Rallabandi ◽  
Huitao Yang ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Turbine Blade Cooling ◽  
Square Channel ◽  
Heat Transfer Coefficients ◽  
High Reynolds ◽  
Cooling Passage

Systematic experiments are conducted to measure heat transfer enhancement and pressure loss characteristics on a square channel (simulating a gas turbine blade cooling passage) with two opposite surfaces roughened by 45 deg parallel ribs. Copper plates fitted with a silicone heater and instrumented with thermocouples are used to measure regionally averaged local heat transfer coefficients. Reynolds numbers studied in the channel range from 30,000 to 400,000. The rib height (e) to hydraulic diameter (D) ratio ranges from 0.1 to 0.18. The rib spacing (p) to height ratio (p/e) ranges from 5 to 10. Results show higher heat transfer coefficients at smaller values of p/e and larger values of e/D, though at the cost of higher friction losses. Results also indicate that the thermal performance of the ribbed channel falls with increasing Reynolds numbers. Correlations predicting Nusselt number (Nu) and friction factor (f¯) as a function of p/e, e/D, and Re are developed. Also developed are correlations for R and G (friction and heat transfer roughness functions, respectively) as a function of the roughness Reynolds number (e+), p/e, and e/D.

Experimental Investigation of Local Heat Transfer in a Square Duct With Continuous and Truncated Large Ribs

2004 ◽  
Author(s):  
Lei Wang ◽  
Bengt Sunde´n
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Diameter Ratio ◽  
Uniform Heat Flux ◽  
Enhance Heat Transfer ◽  
Square Duct ◽  
Square Channel ◽  
Liquid Crystal Thermography ◽  
Turbulent Flow Regime

Repeated ribs are frequently employed to promote turbulence and to enhance heat transfer in various ducts. In the present study, liquid crystal thermography has applied to the study of heat transfer from a square channel having one surface heated at uniform heat flux and roughened by repeated ribs. The continuous and truncated ribs, having square sections, with height-to-hydraulic diameter ratio of 0.15, were deployed normal to the mainstream direction of flow. Detailed distributions of the local heat transfer coefficient were obtained at various Reynolds number within the turbulent flow regime. Averaged data were calculated in order to evaluate the augmentation of heat transfer by the presence of different ribs.

Augmented Heat Transfer in Square Channels With Parallel, Crossed, and V-Shaped Angled Ribs

1991 ◽  
Vol 113 (3) ◽  
pp. 590-596 ◽  
Author(s):  
J. C. Han ◽  
Y. M. Zhang ◽  
C. P. Lee
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Diameter Ratio ◽  
Hydraulic Diameter ◽  
Square Channel ◽  
Heat Transfer Augmentation ◽  
Better Than

The effect of the rib angle orientation on the local heat transfer distributions and pressure drop in a square channel with two opposite in-line ribbed walls was investigated for Reynolds numbers from 15,000 to 90,000. The square channel composed of ten isolated copper sections has a length-to-hydraulic diameter ratio of 20; the rib height-to-hydraulic diameter ratio is 0.0625; the rib pitch-to-height ratio equals 10. Nine rib configurations were studied: 90 deg rib, 60 and 45 deg parallel ribs, 60 and 45 deg crossed ribs, 60 and 45 deg ∨-shaped ribs, and 60 and 45 deg ∧-shaped ribs. The results show that the 60 deg (or 45 deg) ∨-shaped rib performs better than the 60 deg (or 45 deg) parallel rib and, subsequently, better than the 60 deg (or 45 deg) crossed rib and the 90 deg rib. The ∨-shaped rib produces the highest heat transfer augmentation, while the ∧-shaped rib generates the greatest pressure drop. The crossed rib has the lowest heat transfer enhancement and the smallest pressure drop penalty.

scholarly journals Velocity Measurements and Local Heat Transfer in a Rotating Ribbed Two-Pass Square Channel With Uneven Wall Heat Flux

1997 ◽  
Author(s):  
Shou-Shing Hsieh ◽  
Ming-Hung Chiang ◽  
Ping-Ju Chen
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Wall Heat Flux ◽  
Velocity Measurements ◽  
Mean Velocity ◽  
Square Channel ◽  
Rotation Numbers

The influence of rotation and uneven wall heat flux effect on the local velocity distribution as well as local heat transfer coefficient in a rotating, two pass rib roughened (rib height e/DH = 0.20; rib pitch p/e = 5) square channel were studied for Reynolds numbers from 5000 to 10000 and rotation numbers from 0 to 0.1602 (≤ 300 rpm). The measured mean velocity under different wall heat flux condition for the specified rib configuration at ReH = 5000 and 10000, ReH = 0, 267, 534 and 801 are presented. Regionally averaged Nusselt number variations with rotation (≤ 800 rpm)along the duct have been determined over the trailing and leading surfaces for a two pass channel. Moreover, LDV measurements with heating were examined. It was found that the Coriolis force as well as centrifugal buoyancy is significant as the rotational speed increases.

Heat Transfer in Separated, Reattached, and Redevelopment Regions Behind a Double Step at Entrance to a Flat Duct

1967 ◽  
Vol 89 (2) ◽  
pp. 163-167 ◽  
Author(s):  
E. G. Filetti ◽  
W. M. Kays
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Duct Flow ◽  
Double Step ◽  
Maximum Heat ◽  
Transfer Rates ◽  
Maximum Heat Transfer ◽  
Flow Cross

Experimental data are presented for local heat transfer rates near the entrance to a flat duct in which there is an abrupt symmetrical enlargement in flow cross section. Two enlargement area ratios are considered, and Reynolds numbers, based on duct hydraulic diameter, varied from 70,000 to 205,000. It is found that such a flow is characterized by a long stall on one side and a short stall on the other. Maximum heat transfer occurs in both cases at the point of reattachment, followed by a decay toward the values for fully developed duct flow. Empirical equations are given for the Nusselt number at the reattachment point, correlated as functions of duct Reynolds number and enlargement ratio.

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.

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.

Three-Dimensional Natural Convection From Vertical Heated Plates With Adjoining Cool Surfaces

1992 ◽  
Vol 114 (1) ◽  
pp. 115-120 ◽  
Author(s):  
B. W. Webb ◽  
T. L. Bergman
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Control Volume ◽  
Three Dimensional ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Uniform Heat Flux ◽  
Infrared Thermal Imaging ◽  
Transfer Rates ◽  
Thermal Boundary Conditions

Natural convection in an enclosure with a uniform heat flux on two vertical surfaces and constant temperature at the adjoining walls has been investigated both experimentally and theoretically. The thermal boundary conditions and enclosure geometry render the buoyancy-induced flow and heat transfer inherently three dimensional. The experimental measurements include temperature distributions of the isoflux walls obtained using an infrared thermal imaging technique, while the three-dimensional equations governing conservation of mass, momentum, and energy were solved using a control volume-based finite difference scheme. Measurements and predictions are in good agreement and the model predictions reveal strongly three-dimensional flow in the enclosure, as well as high local heat transfer rates at the edges of the isoflux wall. Predicted average heat transfer rates were correlated over a range of the relevant dimensionless parameters.

Local Heat Transfer in Rotating Smooth and Ribbed Two-Pass Square Channels With Three Channel Orientations

1996 ◽  
Vol 118 (3) ◽  
pp. 578-584 ◽  
Author(s):  
S. Dutta ◽  
J.-C. Han
Keyword(s):  
Heat Transfer ◽  
Rotation Number ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Channel Changes ◽  
Square Channel ◽  
Heat Transfer Coefficients ◽  
Experimental Heat ◽  
Channel Orientation

This paper presents experimental heat transfer results in a two-pass square channel with smooth and ribbed surfaces. The ribs are placed in a staggered half-V fashion with the rotation orthogonal to the channel axis. The channel orientation varies with respect to the rotation plane. A change in the channel orientation about the rotating frame causes a change in the secondary flow structure and associated flow and turbulence distribution. Consequently, the heat transfer coefficient from the individual surfaces of the two-pass square channel changes. The effects of rotation number on local Nusselt number ratio distributions are presented. Heat transfer coefficients with ribbed surfaces show different characteristics in rotation number dependency from those with smooth surfaces. Results show that staggered half-V ribs mostly have higher heat transfer coefficients than those with 90 and 60 deg continuous ribs.

Jet-to-Plate Distance Effect on Heat Transfer From a Flat Plate to an Impinging Jet at Various Reynolds Numbers

2012 ◽  
Author(s):  
Patricia Streufert ◽  
Terry X. Yan ◽  
Mahdi G. Baygloo
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Reynolds Number ◽  
Flat Plate ◽  
Numerical Solutions ◽  
Stokes Equations ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Air Jet ◽  
Plate Distance

Local turbulent convective heat transfer from a flat plate to a circular impinging air jet is numerically investigated. The jet-to-plate distance (L/D) effect on local heat transfer is the main focus of this study. The eddy viscosity V2F turbulence model is used with a nonuniform structured mesh. Reynolds-Averaged Navier-Stokes equations (RANS) and the energy equation are solved for axisymmetric, three-dimensional flow. The numerical solutions obtained are compared with published experimental data. Four jet-to-plate distances, (L/D = 2, 4, 6 and 10) and seven Reynolds numbers (Re = 7,000, 15,000, 23,000, 50,000, 70,000, 100,000 and 120,000) were parametrically studied. Local and average heat transfer results are analyzed and correlated with Reynolds number and the jet-to-plate distance. Results show that the numerical solutions matched experimental data best at low jet-to-plate distances and lower Reynolds numbers, decreasing in ability to accurately predict the heat transfer as jet-to-plate distance and Reynolds number was increased.

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