Heat Transfer from a Plate Elevated above a Host Surface and Washed by a Separated Flow Induced by the Elevation Step

1981 ◽  
Vol 103 (3) ◽  
pp. 441-447 ◽  
Author(s):  
E. M. Sparrow ◽  
F. Samie ◽  
S. C. Lau
Keyword(s):  
Heat Transfer ◽  
Flow Separation ◽  
Angle Of Attack ◽  
Separated Flow ◽  
Active Surface ◽  
Reynolds Numbers ◽  
Transfer Coefficients ◽  
Reynolds Number Flow ◽  
Heat Transfer Coefficients ◽  
High Reynolds

Wind tunnel experiments were performed to determine heat transfer coefficients and fluid flow patterns for a thermally active surface elevated above a parallel host surface. The step-like blockage associated with the elevation causes flow separation and recirculation on the forward portion of the thermally active surface. Four parameters were varied during the course of the experiments, including the angle of attack of the oncoming airflow relative to the surface, the step height, the extent of the host surface which frames the active surface (i.e., the skirt width), and the Reynolds number. Flow visualization studies, performed with the oil-lampblack technique, showed that the streamwise extent of the separation zone increases with decreasing angle of attack, with larger step heights and skirt widths, and at higher Reynolds numbers. At larger angles of attack, separation does not occur. The experimentally determined heat transfer coefficients were found to increase markedly due to the flow separation, and separation-related enhancements as large as a factor of two were encountered. The enhancement was accentuated at small angles of attack, at large step heights and skirt widths, and at high Reynolds numbers. A main finding of the study is that the separation-affected heat transfer coefficients are generally greater than those for no separation, so that the use of the latter may underestimate the heat transfer rates. For an application such as a retrofit solar collector, such an underestimation of the wind-related heat loss would yield an optimistic prediction of the collector efficiency.

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.

A Numerical and Experimental Investigation of Turbulent Heat Transport Downstream From an Abrupt Pipe Expansion

1983 ◽  
Vol 105 (4) ◽  
pp. 862-869 ◽  
Author(s):  
R. S. Amano ◽  
M. K. Jensen ◽  
P. Goel
Keyword(s):  
Heat Transfer ◽  
Numerical Solutions ◽  
Numerical Study ◽  
Separated Flow ◽  
Flow Region ◽  
Reynolds Numbers ◽  
Turbulent Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Pipe Expansion

An experimental and numerical study is reported on heat transfer in the separated flow region created by an abrupt circular pipe expansion. Heat transfer coefficients were measured along the pipe wall downstream from an expansion for three different expansion ratios of d/D = 0.195, 0.391, and 0.586 for Reynolds numbers ranging from 104 to 1.5 × 105. The results are compared with the numerical solutions obtained with the k ∼ ε turbulence model. In this computation a new finite difference scheme is developed which shows several advantages over the ordinary hybrid scheme. The study also covers the derivation of a new wall function model. Generally good agreement between the measured and the computed results is shown.

Turbulent Convective Heat Transfer in Forced Cooled Underground Electric Transmission Systems

1985 ◽  
Vol 107 (2) ◽  
pp. 327-333 ◽  
Author(s):  
R. Ghetzler ◽  
J. C. Chato ◽  
J. M. Crowley
Keyword(s):  
Heat Transfer ◽  
Reynolds Numbers ◽  
Scale Model ◽  
Transfer Coefficients ◽  
Transmission Systems ◽  
Number Range ◽  
Heat Transfer Coefficients ◽  
Electric Transmission ◽  
Friction Factors ◽  
High Reynolds

Heat transfer and friction factors were experimentally determined in a scale model of high-voltage, pipe-type underground transmission systems for Reynolds numbers to 8000. Dielectric insulating oil (Sun No. 4) with a Prandtl number of 120 was utilized for the coolant. Two ratios of cable to enclosure pipe diameters, corresponding to standard and oversize enclosure pipes, were examined for the three-cable system. Helical wire wrap was included to simulate protective skid wires around the cables. Three configurations of cable positioning were considered—open triangular, close triangular, and cradled. A method of generalizing the heat transfer coefficients was developed and tested for rough pipe cables based on extensions of previous work in the literature. The generalized correlation, without correction factors, was found to be applicable only in two cases with appropriate flow pattens and geometries. Heat transfer to the pipe wall could be correlated by standard methods in the high Reynolds number range.

An Experimental Investigation of Boundary Layer and Heat Transfer in the Region of Separated Flow Downstream of Normal Injection Slots

1975 ◽  
Vol 97 (2) ◽  
pp. 260-266 ◽  
Author(s):  
R. C. Foster ◽  
A. Haji-Sheikh
Keyword(s):  
Heat Transfer ◽  
Experimental Investigation ◽  
Flow Separation ◽  
Film Cooling ◽  
Flow Characteristics ◽  
Separated Flow ◽  
Transfer Coefficients ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Heat Transfer Coefficients

An experimental investigation was conducted to determine the flow characteristics, heat transfer coefficients, and film cooling effectiveness in the region immediately downstream of flush, normal injection slots. Air was injected through these slots into a turbulent primary flow produced by a small wind tunnel. Velocity measurements and tuft studies indicated that there was a significant region of separated flow immediately downstream of the slot. The heat transfer coefficients were appreciably increased as a result of this flow separation, and the film cooling effectiveness was decreased in comparison to previous studies involving no flow separation.

Heat Transfer Coefficients and Patterns of Fluid Flow for Contacting Spheres at Various Angles of Attack

1983 ◽  
Vol 105 (1) ◽  
pp. 48-55 ◽  
Author(s):  
E. M. Sparrow ◽  
R. F. Prieto
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Separated Flow ◽  
Reynolds Numbers ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Flow Features ◽  
Baseline Information ◽  
Single Sphere ◽  
Parameter Ranges

Wind tunnel experiments were performed to determine heat transfer coefficients and fluid flow patterns for two contacting spheres. The experiments were carried out at three different angles of attack and for Reynolds numbers in the range from 4000 to 26,000. Three heat transfer conditions were considered: (a) both spheres thermally active, (b) forwardmost sphere thermally active and rearmost sphere adiabatic, and (c) forwardmost sphere adiabatic and rearmost sphere thermally active. Complementary experiments for a single sphere, encompassing the same parameter ranges, yielded baseline information for comparison with the two-sphere results. It was found that the largest effects of the sphere-to-sphere interaction on the heat transfer occurred when the two spheres were in line. At this orientation and for higher Reynolds numbers in the investigated range, there was substantial enhancement of the heat transfer with respect to that for the single sphere. At the other angles of attack, there was lesser enhancement. The visualization studies revealed such key fluid flow features as the reattachment of the separated flow from the first sphere on the second, the presence of strong recirculations, and the delay of separation due to pressure-driven transverse flows.

Heat Transfer and Pressure Drop Measurements for a Square Channel With 45 deg Round-Edged Ribs at High Reynolds Numbers

2010 ◽  
Vol 133 (3) ◽  
Author(s):  
Akhilesh P. Rallabandi ◽  
Nawaf Alkhamis ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Friction Factor ◽  
Reynolds Numbers ◽  
Transfer Coefficients ◽  
Height Ratio ◽  
Square Channel ◽  
Heat Transfer Coefficients ◽  
Friction Factors ◽  
High Reynolds ◽  
The Cost

Experiments to determine heat transfer coefficients and friction factors are conducted on a stationary 45 deg parallel rib-roughened square channel, which simulates a turbine blade internal coolant passage. Copper plates fitted with silicone heaters and thermocouples are used to measure regionally averaged heat transfer coefficients. Reynolds numbers studied range from 30,000 to 400,000. The ribs studied have rounded (filleted) edges to account for manufacturing limitations of actual engine blades. The rib height (e) to hydraulic diameter (D) ratio (e/D) ranges from 0.1 to 0.2, while spacing (p) to height ratio (p/e) ranges from 5 to 10. Results indicate an increase in the heat transfer due to the ribs at the cost of a higher friction factor, especially at higher Reynolds numbers. Round-edged ribs experience a similar heat transfer coefficient and a lower friction factor compared with sharp-edged ribs, especially at higher values of the rib height. Correlations predicting Nu and f as a function of e/D, p/e, and Re are presented. Also presented are correlations for the heat transfer and friction roughness parameters (G and R, respectively).

Heat Transfer and Pressure Drop Correlations for Square Channels With V-Shaped Ribs at High Reynolds Numbers

2011 ◽  
Vol 133 (11) ◽  
Author(s):  
Nawaf Y. Alkhamis ◽  
Akhilesh P. Rallabandi ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Friction Factor ◽  
Thermal Performance ◽  
Reynolds Numbers ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
High Reynolds Numbers ◽  
High Reynolds ◽  
Rib Roughened

Heat transfer coefficients and friction factors are measured in a 45 deg V-shaped rib roughened square duct at high Reynolds numbers, pertaining to internal passages of land-based gas turbine engines. Reynolds numbers in this study range from 30,000 to 400,000, which is much higher than prior studies of V-shaped rib roughened channels. The dimensions of the channel are selected to ensure that the flow is in the incompressible regime. Blockage ratio e/D ranges from 0.1 to 0.18 and the spacing ratio P/e ranges from 5 to 10. Reported heat transfer coefficients are regionally averaged, measured by isothermal copper plates. Results show that the heat transfer enhancement decreases with increasing Reynolds number. The friction factor is found to be independent of the Reynolds number. The thermal performance decreases when the Reynolds number increases. 45 deg V-shaped ribs show a higher thermal performance than corresponding 45 deg angled ribs, consistent with the trend established in literature. Correlations for the Nusselt number and the friction factor as function of Re, e/D, and P/e 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+).

Heat Transfer in a Rotating, Blade-Shaped Serpentine Cooling Passage With Discrete Ribbed Walls at High Reynolds Numbers

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
Lesley M. Wright ◽  
Shang-Feng Yang ◽  
Hao-Wei Wu ◽  
Je-Chin Han ◽  
Ching-Pang Lee ◽  
...  
Keyword(s):  
Heat Transfer ◽  
High Reynolds Number ◽  
Reynolds Numbers ◽  
Pressure Side ◽  
Transfer Coefficients ◽  
First Passage ◽  
Heat Transfer Coefficients ◽  
The Third ◽  
High Reynolds Numbers ◽  
High Reynolds

Abstract This paper experimentally investigates the effect of rotation on heat transfer in a typical turbine blade, three-pass, serpentine coolant channel with discrete ribbed walls at high Reynolds numbers. To achieve the high Reynolds number (Re → 190,000) and low rotation number conditions, pressurized Freon R-134a vapor is utilized as the working fluid. Cooling flow in the first passage is radial outward; after the 180 deg tip turn, the flow is radial inward through the second passage; and after the 180 deg hub turn, the flow is radial outward in the third passage. The effects of rotation on the heat transfer coefficients were investigated at rotation numbers as low as 0.07 and Reynolds numbers from 85,000 to 187,000 (based on the first passage geometry and flow conditions). Heat transfer coefficients were measured using thermocouples embedded in copper plates to provide regionally averaged heat transfer coefficients. Heat transfer enhancement due to rotation is observed on the first passage, pressure-side with radially outward flow and the second passage, suction-side with radially inward flow, but a reduction in heat transfer is observed on the third passage pressure-side with radially outward flow. In addition, results from the discrete, broken ribs are compared with those from the same serpentine coolant passage with conventional, angled ribbed walls. A significant increase in the heat transfer due to the discrete ribs is observed in the first passage. These results can be useful for understanding real rotor blade coolant passage heat transfer under high Reynolds number and low rotation number conditions.

Augmentation of Laminar Flow Heat Transfer in Tubes by Means of Twisted-Tape Inserts

1976 ◽  
Vol 98 (2) ◽  
pp. 251-256 ◽  
Author(s):  
S. W. Hong ◽  
A. E. Bergles
Keyword(s):  
Heat Transfer ◽  
Laminar Flow ◽  
Reynolds Numbers ◽  
Twisted Tape ◽  
Transfer Coefficients ◽  
Constant Property ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
Flow Heat ◽  
High Reynolds

Heat transfer coefficients for laminar flow of water and ethylene glycol in an electrically heated metal tube with two twisted-tape inserts were determined experimentally. The Nusselt number for fully developed flow was found to be a function of tape twist ratio, Reynolds number, and Prandtl number. These Nusselt numbers were as much as nine times the empty tube constant property values. The correlation of these data is in fair agreement with the only available analytical predictions. The friction factor is affected by tape twist only at high Reynolds numbers, in accordance with analytical predictions. The performance of these augmented tubes is compared with that of empty tubes under similar heating conditions.

Heat Transfer and Pressure Drop Measurements for a Square Channel With 45Deg Round Edged Ribs at High Reynolds Numbers

2009 ◽  
Author(s):  
Akhilesh P. Rallabandi ◽  
Nawaf Alkhamis ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Friction Factor ◽  
Reynolds Numbers ◽  
Transfer Coefficients ◽  
Height Ratio ◽  
Square Channel ◽  
Heat Transfer Coefficients ◽  
Friction Factors ◽  
High Reynolds ◽  
The Cost

Experiments to determine heat transfer coefficients and friction factors are conducted on a stationary 45 deg parallel rib roughened square channel which simulates a turbine blade internal coolant passage. Copper plates fitted with silicone heaters and thermocouples are used to measure regionally averaged heat transfer coefficients. Reynolds numbers studied range from 30,000 to 400,000. The ribs studied have rounded (filleted) edges to account for manufacturing limitations of actual engine blades. The rib height (e) to hydraulic diameter (D) ratio (e/D) ranges from 0.1 to 0.2; spacing (p) to height ratio (p/e) ranges from 5 to 10. Results indicate an increase in heat transfer due to ribs at the cost of a higher friction factor, especially at higher Reynolds Numbers. Round edged ribs experience a similar heat transfer coefficient and a lower friction factor compared to sharp edged ribs, especially at higher values of rib height. Correlations predicting Nu and f as a function of e/D, p/e and Re are presented. Also presented are correlations for heat transfer and friction roughness parameters (G and R).

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