Effects of Varying Streamwise and Spanwise Spacing in Pin-Fin Arrays

Pin-fin channels are commonly used for cooling the trailing edges in turbine blades and vanes. While many studies have investigated heat transfer performance of pin-fin channels, few studies have investigated pin-fin flowfields. The present study compares the time-dependent near wake flow and the time-mean surface heat transfer for varying pin-fin configurations at a Reynolds number of 2.0e4. Pin-fin aspect ratio showed little influence on pin-surface heat transfer coefficients when increasing H/D from 1.0 to 2.0. Changes in streamwise and spanwise spacing, however, were found to significantly impact the behavior of the near wake flow and local heat transfer coefficients. Decreasing spanwise spacing from S/D = 3.0 to 1.5 in a single pin-fin row was found to suppress downstream vortex shedding and create biased, asymmetric wakes. Local heat transfer coefficients on the trailing side of the pin-fin reflected that vortex shedding, observed for spanwise spacings S/D ≥ 2.0, was beneficial for heat transfer on the pin-surface. Similarly, decreasing streamwise spacing from X/D = 3.03 to 2.16 was found to suppress vortex shedding in the first row of a seven row array. For those cases that support vortex shedding, X/D ≥ 2.60, pin-fin heat transfer increased on the trailing side but array heat transfer in downstream rows decreased.

Effect of Uneven Wall Temperature on Local Heat Transfer in a Rotating Square Channel With Smooth Walls and Radial Outward Flow

Journal of Heat Transfer ◽

10.1115/1.2911892 ◽

1992 ◽

Vol 114 (4) ◽

pp. 850-858 ◽

Cited By ~ 50

Author(s):

J.-C. Han ◽

Y. M. Zhang

Keyword(s):

Heat Transfer ◽

Wall Temperature ◽

Local Heat Transfer ◽

Local Heat ◽

Surface Heat ◽

Transfer Coefficients ◽

Surface Heat Transfer ◽

Square Channel ◽

Rotation Numbers

The influence of uneven wall temperature on the local heat transfer coefficient in a rotating square channel with smooth walls and radial outward flow was investigated for Reynolds numbers from 2500 to 25,000 and rotation numbers from 0 to 0.352. The square channel, composed of six 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 were studied: (A) four walls uniform temperature, (B) four walls uniform heat flux, and (C) leading and trailing walls hot and two side walls cold. The results show that the heat transfer coefficients on the leading surface are much lower than that of the trailing surface due to rotation. For case A of four walls uniform temperature, the leading surface heat transfer coefficient decreases and then increases with increasing rotation numbers, and the trailing surface heat transfer coefficient increases monotonically with rotation numbers. The decreased (or increased) heat transfer coefficients on the leading (or trailing) surface are due to the cross-stream and centrifugal buoyancy-induced flows from rotations. However, the trailing surface heat transfer coefficients, as well as those for the side walls, for case B are higher than for case A and the leading surface heat transfer coefficients for cases B and C are significantly higher than for case A. The results suggest that the local uneven wall temperature creates the local buoyancy forces, which change the effect of the rotation. Therefore, the local heat transfer coefficients on the leading, trailing, and side surfaces are altered by the uneven wall temperature.

Pin-Fin Heat Transfer: Contribution of the Wall and the Pin to the Overall Heat Transfer

Volume 4: Heat Transfer; Electric Power; Industrial and Cogeneration ◽

10.1115/92-gt-242 ◽

1992 ◽

Cited By ~ 6

Author(s):

A. M. Ai Dabagh ◽

G. E. Andrews

Keyword(s):

Heat Transfer ◽

Heat Transfer Coefficient ◽

Transfer Coefficient ◽

Local Heat Transfer ◽

Local Heat ◽

Diameter Ratio ◽

Duct Flow ◽

Transfer Coefficients ◽

Pin Fin ◽

The differences in the heat transfer coefficient between the pin and the wall in pin-fin heat transfer was determined for three pin length to diameter ratios. A staggered pin-fin array was used with a 50% duct flow blockage by the pins. The axial pitch-to-pin diameter ratio, X/D, was 1.5 and the transverse pitch-to-diameter ratio, S/D, was 2.0. Three pin length-to-diameter ratios, T/D, of 0.7. 1.0 and 2.2 were investigated. The mean heat transfer coefficient results were very similar to previous work for similar geometries. The axial variation of heat transfer coefficient showed this to be fairly uniform with a small peak at the fourth row. Around each pin four measurements of the heat transfer coefficients were made with four on the fin surface at each end. Thus 12 local heat transfer coefficients were made per pin-fin. These showed that for all three geometries the wall or fin heat transfer was always greater by 15–35% than the pin for the same velocity and Re.

A Comparison of the Transient and Heated-Coating Methods for the Measurement of Local Heat Transfer Coefficients on a Pin Fin

Journal of Heat Transfer ◽

10.1115/1.3250800 ◽

1989 ◽

Vol 111 (4) ◽

pp. 877-881 ◽

Cited By ~ 40

Author(s):

J. W. Baughn ◽

P. T. Ireland ◽

T. V. Jones ◽

N. Saniei

Keyword(s):

Heat Transfer ◽

Liquid Crystal ◽

Local Heat Transfer ◽

Local Heat ◽

Uniform Heat Flux ◽

Fluid Temperature ◽

Transfer Coefficients ◽

Pin Fin ◽

The Difference

Measurements of the local heat transfer coefficients on a pin fin (i.e., a short cylinder in crossflow) in a duct have been made using two methods, both of which employ liquid crystals to map an isotherm on the surface. The transient method uses the liquid crystal to determine the transient response of the surface temperature to a change in the fluid temperature. The local heat transfer coefficient is determined from the surface response time and the thermal properties of the substrate. The heated-coating method uses an electrically heated coating (vacuum-deposited gold in this case) to provide a uniform heat flux, while the liquid crystal is used to locate an isotherm on the surface. The two methods compare well, especially the value obtained near the center stagnation point of the pin fin where the difference in the thermal boundary condition of the two methods has little effect. They are close but differ somewhat in other regions.

THE USE OF SQUARE WAVE SURFACE HEAT FLUXES AND PHASE DELAY INFORMATION TO MEASURE LOCAL HEAT TRANSFER COEFFICIENTS

Proceeding of International Heat Transfer Conference 11 ◽

10.1615/ihtc11.3100 ◽

1998 ◽

Author(s):

Wayne O. Turnbull ◽

Patrick H. Oosthuizen

Keyword(s):

Heat Transfer ◽

Local Heat Transfer ◽

Local Heat ◽

Surface Heat ◽

Heat Fluxes ◽

Phase Delay ◽

Wave Surface ◽

Transfer Coefficients ◽

Surface Heat Fluxes ◽

Influence of Surface Heating Condition on Local Heat Transfer in a Rotating Square Channel With Smooth Walls and Radial Outward Flow

Journal of Turbomachinery ◽

10.1115/1.2928269 ◽

1994 ◽

Vol 116 (1) ◽

pp. 149-158 ◽

Cited By ~ 34

Author(s):

J. C. Han ◽

Y. M. Zhang ◽

C. P. Lee

Keyword(s):

Heat Transfer ◽

Local Heat Transfer ◽

Local Heat ◽

Surface Heat ◽

Heating Condition ◽

Transfer Coefficients ◽

Surface Heat Transfer ◽

Square Channel ◽

Rotation Numbers

The effect of a surface heating condition on the local heat transfer coefficient in a rotating square channel with smooth walls and radial outward flow was investigated for Reynolds numbers from 2500 to 25,000 and rotation numbers from 0 to 0.352. The square channel, composed of six 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. Four surface heating conditions were tested: (1) four walls at uniform temperature, (2) temperature ratio of leading surface to side wall and trailing surface to side wall is 1.05 and 1.10, respectively, (3) trailing surface hot and remaining three walls cold, and (4) leading surface hot and remaining three walls cold. The results show that the heat transfer coefficients on the leading surface are much lower than that of the trailing surface due to rotation. For case (1) of four walls at uniform temperature, the leading surface heat transfer coefficient decreases and then increases with increasing rotation numbers, and the trailing surface heat transfer coefficient increases monotonically with rotation numbers. However, the trailing surface heat transfer coefficients for cases (2) and (3) are slightly lower than case (1), and the leading surface heat transfer coefficients for cases (2) and (4) are significantly higher than for case (1). The results suggest that the local wall heating condition creates the local buoyancy forces, which reduce the effects of the bulk buoyancy and Coriolis forces. Therefore, the local heat transfer coefficients on the leading and trailing surfaces are altered by the surface local heating condition.

A Comparison of the Transient and Heated-Coating Methods for the Measurement of Local Heat Transfer Coefficients on a Pin Fin

Volume 4: Heat Transfer; Electric Power; Industrial and Cogeneration ◽

10.1115/88-gt-180 ◽

1988 ◽

Cited By ~ 5

Author(s):

J. W. Baughn ◽

P. T. Ireland ◽

T. V. Jones ◽

N. Saniei

Keyword(s):

Heat Transfer ◽

Liquid Crystal ◽

Local Heat Transfer ◽

Local Heat ◽

Uniform Heat Flux ◽

Fluid Temperature ◽

Transfer Coefficients ◽

Pin Fin ◽

The Difference

Measurements of the local heat transfer coefficients on a pin fin (i.e., a short cylinder in crossflow) in a duct have been made using two methods, both of which employ liquid crystals to map an isotherm on the surface. The transient method uses the liquid crystal to determine the transient response of the surface temperature to a change in the fluid temperature. The local heat transfer coefficient is determined from the surface response time and the thermal properties of the substrate. The heated-coating method uses an electrically heated coating (vacuum-deposited gold in this case) to provide a uniform heat flux while the liquid crystal is used to locate an isotherm on the surface. The two methods compare well, especially the value obtained near the center stagnation point of the pin fin where the difference in the thermal boundary condition of the two methods has little effect. They are close but differ somewhat in other regions.

Influence of Surface Heating Condition on Local Heat Transfer in a Rotating Square Channel With Smooth Walls and Radial Outward Flow

Volume 4: Heat Transfer; Electric Power; Industrial and Cogeneration ◽

10.1115/92-gt-188 ◽

1992 ◽

Cited By ~ 1

Author(s):

J. C. Han ◽

Y. M. Zhang ◽

C. P. Lee

Keyword(s):

Heat Transfer ◽

Local Heat Transfer ◽

Local Heat ◽

Surface Heat ◽

Heating Condition ◽

Transfer Coefficients ◽

Surface Heat Transfer ◽

Square Channel ◽

Rotation Numbers

The effect of surface heating condition on the local heat transfer coefficient in a rotating square channel with smooth walls and radial outward flow was investigated for Reynolds numbers from 2,500 to 25,000 and rotation numbers from 0 to 0.352. The square channel, composed of six 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. Four surface heating conditions were tested: (1) four walls uniform temperature, (2) temperature ratio of leading surface to side wall and trailing surface to side wall is 1.05 and 1.10, respectively, (3) trailing surface hot and remaining three walls cold, and (4) leading surface hot and remaining three walls cold. The results show that the heat transfer coefficients on the leading surface are much lower than that of the trailing surface due to rotation. For case (1) of four walls uniform temperature, the leading surface heat transfer coefficient decreases and then increases with increasing rotation numbers, and the trailing surface heat transfer coefficient increases monotonically with rotation numbers. However, the trailing surface heat transfer coefficients for cases (2) and (3) are slightly lower than case (1), and the leading surface heat transfer coefficients for cases (2) and (4) are significantly higher than for case (1). The results suggest that the local wall heating condition creates the local buoyancy forces which reduce the effects of the bulk buoyancy and Coriolis forces. Therefore, the local heat transfer coefficients on the leading and trailing surfaces are altered by the surface local heating condition.

LOCAL HEAT TRANSFER COEFFICIENTS IN FILM BOILING OF LIQUID NITROGEN ON A VERTICAL SURFACE

10.1615/ihtc5.290 ◽

1974 ◽

Author(s):

K. N. Seetharamu ◽

Muralidhar V. Krishnamurthy ◽

A. Ramachandran

Keyword(s):

Heat Transfer ◽

Liquid Nitrogen ◽

Local Heat Transfer ◽

Local Heat ◽

Vertical Surface ◽

Film Boiling ◽

Transfer Coefficients ◽

The Effect of Regulating Elements on Convective Heat Transfer along Shaped Heat Exchange Surfaces

Chemical and Process Engineering ◽

10.2478/cpe-2013-0002 ◽

2013 ◽

Vol 34 (1) ◽

pp. 5-16 ◽

Cited By ~ 3

Author(s):

Jozef Cernecky ◽

Jan Koniar ◽

Zuzana Brodnianska

Keyword(s):

Heat Transfer ◽

Heat Exchange ◽

Cfd Simulation ◽

Local Heat Transfer ◽

Local Heat ◽

Temperature Fields ◽

Transfer Coefficients ◽

Heat Transfer Intensification ◽

Forced Air

Abstract The paper deals with a study of the effect of regulating elements on local values of heat transfer coefficients along shaped heat exchange surfaces with forced air convection. The use of combined methods of heat transfer intensification, i.e. a combination of regulating elements with appropriately shaped heat exchange areas seems to be highly effective. The study focused on the analysis of local values of heat transfer coefficients in indicated cuts, in distances expressed as a ratio x/s for 0; 0.33; 0.66 and 1. As can be seen from our findings, in given conditions the regulating elements can increase the values of local heat transfer coefficients along shaped heat exchange surfaces. An optical method of holographic interferometry was used for the experimental research into temperature fields in the vicinity of heat exchange surfaces. The obtained values correspond very well with those of local heat transfer coefficients αx, recorded in a CFD simulation.

Heat Transfer Coefficient Determination in a Gravity Die Casting Process with Local Air Gap Formation and Contact Pressure Using Experimental Evaluation and Numerical Simulation

International Journal of Metalcasting ◽

10.1007/s40962-021-00663-y ◽

2021 ◽

Author(s):

T. Vossel ◽

N. Wolff ◽

B. Pustal ◽

A. Bührig-Polaczek ◽

M. Ahmadein

Keyword(s):

Heat Transfer ◽

Contact Pressure ◽

Local Heat Transfer ◽

Casting Process ◽

Local Heat ◽

Air Gap ◽

Gap Formation ◽

Transfer Coefficients ◽

Die Casting Process

AbstractAnticipating the processes and parameters involved for accomplishing a sound metal casting requires an in-depth understanding of the underlying behaviors characterizing a liquid melt solidifying inside its mold. Heat balance represents a major factor in describing the thermal conditions in a casting process and one of its main influences is the heat transfer between the casting and its surroundings. Local heat transfer coefficients describe how well heat can be transferred from one body or material to another. This paper will discuss the estimation of these coefficients in a gravity die casting process with local air gap formation and heat shrinkage induced contact pressure. Both an experimental evaluation and a numerical modeling for a solidification simulation will be performed as two means of investigating the local heat transfer coefficients and their local differences for regions with air gap formation or contact pressure when casting A356 (AlSi7Mg0.3).