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.

Uneven Wall Temperature Effect on Local Heat Transfer in a Rotating Two-Pass Square Channel With Smooth Walls

1993 ◽  
Vol 115 (4) ◽  
pp. 912-920 ◽  
Author(s):  
J.-C. Han ◽  
Y.-M. Zhang ◽  
Kathrin Kalkuehler
Keyword(s):  
Heat Transfer ◽  
Wall Temperature ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Diameter Ratio ◽  
Transfer Coefficients ◽  
Square Channel ◽  
Heat Transfer Coefficients ◽  
Buoyancy Forces ◽  
Flow Heat

The influence of uneven wall temperature on the local heat transfer coefficient in a rotating, two-pass, square channel with smooth walls is investigated for rotation numbers from 0.0352 to 0.352 by varying Reynolds numbers from 25,000 to 2500. The two-pass square channel, composed of 12 isolated copper sections, has a length-to-hydraulic diameter ratio of 12. The mean rotating radius to the channel hydraulic diameter ratio is kept at a constant value of 30. Three cases of thermal boundary conditions are studied: (A) four walls at the same temperature, (B) four walls at the same heat flux, and (C) trailing wall hotter than leading with side walls unheated and insulated. The results for case A of four walls at the same temperature show that the first channel (radial outward flow) heat transfer coefficients on the leading surface are much lower than that of the trailing surface due to the combined effect of Coriolis and buoyancy forces. The second channel (radial inward flow) heat transfer coefficients on the leading surface are higher than that of the trailing surface. The difference between the heat transfer coefficients for the leading and trailing surface in the second channel is smaller than that in the first channel due to the opposite effect of Coriolis and buoyancy forces in the second channel. However, the heat transfer coefficients on each wall in each channel for cases B and C are higher than case A because of interactions between rotation-induced secondary flows and uneven wall temperatures in cases B and C. The results suggest that the effect of uneven wall temperatures on local heat transfer coefficients in the second channel is greater than that in the first channel.

Effect of Blockage-Ratio on Developing Heat Transfer for a Rectangular Duct With Transverse Ribs

2013 ◽  
Author(s):  
Zahra Ghorbani-Tari ◽  
Lei Wang ◽  
Bengt Sunden
Keyword(s):  
Heat Transfer ◽  
Rectangular Channel ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Uniform Heat Flux ◽  
Blockage Ratio ◽  
Heat Transfer Characteristics ◽  
Liquid Crystal Thermography ◽  
Transfer Characteristics ◽  
Transfer Behavior

The developing heat transfer characteristics in a rectangular channel (AR = 4) equipped with continuous transverse ribs are experimentally investigated. The ribs were regularly spaced over a section of the channel which was heated by a uniform heat flux. The blockage ratio e/Dh varied from 0.039 to 0.078. Two values of the rib pitch to rib height ratio (10 and 20) were considered, with the Reynolds number from 57,000 to 127, 000. The studied geometry is relevant to turbine structures between high pressure and low pressure turbines in aircraft engines. The maps of local heat transfer coefficient in the inter-rib regions were obtained by using the steady state liquid crystal thermography. The main purpose is to investigate the effect of blockage ratio (e/Dh) on the developing heat transfer behavior. In particular, the heat transfer characteristics between the first repeated ribs, i.e., in the inter-rib regions were studied, where the flow field is fully developed while the thermal field is not yet periodically fully developed.

Surface Heating Effect on Local Heat Transfer in a Rotating Two-Pass Square Channel With 60° Angled Rib Turbulators

1993 ◽  
Author(s):  
Y. M. Zhang ◽  
J. C. Han ◽  
J. A. Parsons ◽  
C. P. Lee
Keyword(s):  
Heat Transfer ◽  
Rotation Number ◽  
Wall Temperature ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Diameter Ratio ◽  
Transfer Coefficients ◽  
Square Channel ◽  
Heat Transfer Coefficients ◽  
First Pass

The influence of uneven wall temperature on the local heat transfer coefficient in a rotating, two-pass, square channel with 60° ribs on the leading and trailing walls was investigated for Reynolds numbers from 2,500 to 25,000 and rotation numbers from 0 to 0.352. Each pass, composed of six isolated copper sections, had a length-to-hydraulic diameter ratio of 12. The mean rotating radius-to-hydraulic diameter ratio was 30. Three thermal boundary condition cases were studied: (A) all four walls at the same temperature, (B) all four walls at the same heat flux, and (C) trailing wall hotter than leading with side walls unheated and insulated. Results indicate that rotating ribbed wall heat transfer coefficients increase by a factor of 2 to 3 over the rotating smooth wall data and at reduced coefficient variation from inlet to exit. As rotation number (or buoyancy parameter) increases, the first pass (outflow) trailing heat transfer coefficients increase and the first pass leading heat transfer coefficients decrease, whereas, the reverse is true for the second pass (inflow). The direction of the Coriolis force reverses from the outflow trailing wall to the inflow leading wall. Differences between the first pass leading and trailing heat transfer coefficients increase with rotation number. A similar behavior is seen for the second pass leading and trailing heat transfer coefficients, but the differences are reduced due to buoyancy changing from aiding to opposing the inertia force. The results suggest that uneven wall temperature has a significant impact on the local heat transfer coefficients. The heat transfer coefficients on the first pass leading wall for cases B and C are up to 70–100% higher than that for case A, while the heat transfer coefficients on the second pass trailing wall for cases B and C are up to 20–50% higher.

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.

Experimental and Numerical Study of Turbulent Heat Transfer in Twisted Square Ducts

2001 ◽  
Vol 123 (5) ◽  
pp. 868-877 ◽  
Author(s):  
Liang-Bi Wang ◽  
Wen-Quan Tao ◽  
Qiu-Wang Wang ◽  
Ya-Ling He
Keyword(s):  
Heat Transfer ◽  
Cross Section ◽  
Numerical Study ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Turbulent Heat Transfer ◽  
Uniform Heat Flux ◽  
Turbulent Heat ◽  
Square Duct ◽  
Square Ducts

This paper describes the experimental and numerical study of three mildly twisted square ducts (twisted uniform cross section square duct, twisted divergent square duct and twisted convergent square duct). Experiments are conducted for air with uniform heat flux condition. Measurements are also conducted for a straight untwisted square duct for comparison purpose. Numerical simulations are performed for three-dimensional and fully elliptic flow and heat transfer by using a body-fitted finite volume method and standard k−ε turbulence model. Both experimental and numerical results show that the twisting brings about a special variation pattern of the spanwise distribution of the local heat transfer coefficient, while the divergent and convergent shapes lead to different axial local heat transfer distributions. Based on the test data, the thermal performance comparisons are made under three constraints (identical mass flow rate, identical pumping power and identical pressure drop) with straight untwisted square duct as a reference. Comparisons show that the twisted divergent duct can always enhance heat transfer, the twisted convergent duct always deteriorates heat transfer, and the twisted constant cross section duct is somewhat in between.

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.

Surface Heating Effect on Local Heat Transfer in a Rotating Two-Pass Square Channel With 60 deg Angled Rib Turbulators

1995 ◽  
Vol 117 (2) ◽  
pp. 272-280 ◽  
Author(s):  
Y. M. Zhang ◽  
J. C. Han ◽  
J. A. Parsons ◽  
C. P. Lee
Keyword(s):  
Heat Transfer ◽  
Rotation Number ◽  
Wall Temperature ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Diameter Ratio ◽  
Transfer Coefficients ◽  
Square Channel ◽  
Heat Transfer Coefficients ◽  
First Pass

The influence of uneven wall temperature on the local heat transfer coefficient in a rotating, two-pass, square channel with 60 deg ribs on the leading and trailing walls was investigated for Reynolds numbers from 2500 to 25,000 and rotation numbers from 0 to 0.352. Each pass, composed of six isolated copper sections, had a length-to-hydraulic diameter ratio of 12. The mean rotating radius-to-hydraulic diameter ratio was 30. Three thermal boundary condition cases were studied: (A) all four walls at the same temperature, (B) all four walls at the same heat flux, and (C) trailing wall hotter than leading with side walls unheated and insulated. Results indicate that rotating ribbed wall heat transfer coefficients increase by a factor of 2 to 3 over the rotating smooth wall data and at reduced coefficient variation from inlet to exit. As rotation number (or buoyancy parameter) increases, the first pass (outflow) trailing heat transfer coefficients increase and the first pass leading heat transfer coefficients decrease, whereas the reverse is true for the second pass (inflow). The direction of the Coriolis force reverses from the outflow trailing wall to the inflow leading wall. Differences between the first pass leading and trailing heat transfer coefficients increase with rotation number. A similar behavior is seen for the second pass leading and trailing heat transfer coefficients, but the differences are reduced due to buoyancy changing from aiding to opposing the inertia force. The results suggest that uneven wall temperature has a significant impact on the local heat transfer coefficients. The heat transfer coefficients on the first pass leading wall for cases B and C are up to 70–100 percent higher than that for case A, while the heat transfer coefficients on the second pass trailing wall for cases B and C are up to 20–50 percent higher.

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.

Effects of Rib Arrangements on Pressure Drop and Heat Transfer in a Rib-Roughened Channel With a Sharp 180 deg Turn

1997 ◽  
Vol 119 (3) ◽  
pp. 610-616 ◽  
Author(s):  
S. Mochizuki ◽  
A. Murata ◽  
M. Fukunaga
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Secondary Flow ◽  
Flow Direction ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Diameter Ratio ◽  
Equivalent Diameter ◽  
Before And After ◽  
Rib Roughened

The objective of this study was to investigate, through experiments, the combined effects of a sharp 180 deg turn and rib patterns on the pressure drop performance and distributions of the local heat transfer coefficient in an entire two-pass rib-roughened channel with a 180 deg turn. The rib pitch-to-equivalent diameter ratio P/de was 1.0, the rib-height-to-equivalent diameter ratio e/de was 0.09, and the rib angle relative to the main flow direction was varied from 30 ∼ 90 deg with an interval of 15 deg. Experiments were conducted for Reynolds numbers in the range 4000 ∼ 30,000. It was disclosed that, due to the interactions between the bend-induced secondary flow and the rib-induced secondary flow, the combination of rib patterns in the channel before and after the turn causes considerable differences in the pressure drop and heat transfer performance of the entire channel.

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.

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