Investigation of Endwall Heat Transfer in Staggered Pin Fin Arrays

The objective of this research has been to experimentally investigate the fluid dynamics of pin fin arrays in order to clarify the physics of heat transfer enhancement and uncover problems in conventional turbulence models. The fluid dynamics of a staggered pin fin array have been studied using hot wire anemometry with both single and x-wire probes at array Reynolds numbers of 3000; 10,000; and 30,000. Velocity distributions off the endwall and pin surface have been acquired and analyzed to investigate turbulent transport in pin fin arrays. Well resolved 3-D calculations have been performed using a commercial code with conventional two-equation turbulence models. Predictive comparisons have been made with fluid dynamic data. In early rows where turbulence is low, the strength of shedding increases dramatically with increasing in Reynolds numbers. The laminar velocity profiles off the surface of pins show evidence of unsteady separation in early rows. In row three and beyond laminar boundary layers off pins are quite similar. Velocity profiles off endwalls are strongly affected by the proximity of pins and turbulent transport. At the low Reynolds numbers, the turbulent transport and acceleration keep boundary layers thin. Endwall boundary layers at higher Reynolds numbers exhibit very high levels of skin friction enhancement. Well resolved 3-D steady calculations were made with several two-equation turbulence models and compared with experimental fluid mechanic and heat transfer data. The quality of the predictive comparison was substantially affected by the turbulence model and near wall methodology.

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Effect of tip clearance on the heat transfer and pressure drop performance in the micro-reactor with micro-pin–fin arrays at low Reynolds number

International Journal of Heat and Mass Transfer ◽

10.1016/j.ijheatmasstransfer.2013.11.060 ◽

2014 ◽

Vol 70 ◽

pp. 709-718 ◽

Cited By ~ 34

Author(s):

Deqing Mei ◽

Xinyang Lou ◽

Miao Qian ◽

Zhehe Yao ◽

Lingwei Liang ◽

...

Keyword(s):

Heat Transfer ◽

Reynolds Number ◽

Pressure Drop ◽

Low Reynolds Number ◽

Tip Clearance ◽

Pin Fin ◽

Low Reynolds ◽

Pin Fin Arrays ◽

Micro Reactor

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Row Removal Heat Transfer Study for Pin Fin Arrays

Volume 5A: Heat Transfer ◽

10.1115/gt2014-25348 ◽

2014 ◽

Cited By ~ 4

Author(s):

Kathryn L. Kirsch ◽

Jason K. Ostanek ◽

Karen A. Thole ◽

Eleanor Kaufman

Keyword(s):

Heat Transfer ◽

Reynolds Number ◽

High Reynolds Number ◽

Pin Fin ◽

Heat Transfer Augmentation ◽

Aspect Ratios ◽

Pin Fins ◽

High Reynolds ◽

Pin Fin Arrays ◽

Transfer Study

Arrays of variably-spaced pin fins are used as a conventional means to conduct and convect heat from internal turbine surfaces. The most common pin shape for this purpose is a circular cylinder. Literature has shown that beyond the first few rows of pin fins, the heat transfer augmentation in the array levels off and slightly decreases. This paper provides experimental results from two studies seeking to understand the effects of gaps in pin spacing (row removals) and alternative pin geometries placed in these gaps. The alternative pin geometries included large cylindrical pins and oblong pins with different aspect ratios. Results from the row removal study at high Reynolds number showed that when rows four through eight were removed, the flow returned to a fully-developed channel flow in the gap between pin rows. When larger alternative geometries replaced the fourth row, heat transfer increased further downstream into the array.

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Single-Phase and Boiling Cooling of Small Pin Fin Arrays by Multiple Nozzle Jet Impingement

Journal of Electronic Packaging ◽

10.1115/1.2792122 ◽

1996 ◽

Vol 118 (1) ◽

pp. 21-26 ◽

Cited By ~ 13

Author(s):

David Copeland

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Critical Heat Flux ◽

Single Phase ◽

Jet Impingement ◽

Transfer Coefficients ◽

Pin Fin ◽

Heat Transfer Coefficients ◽

Aspect Ratios ◽

Pin Fin Arrays

Experimental measurements of multiple nozzle submerged jet array impingement single-phase and boiling heat transfer were made using FC-72 and 1 cm square copper pin fin arrays, having equal width and spacing of 0.1 and 0.2 mm, with aspect ratios from 1 to 5. Arrays of 25 and 100 nozzles were used, with diameters of 0.25 to 1.0 mm providing nozzle area from 5 to 20 mm2 (5 to 20% of the heat source base area). Flow rates of 2.5 to 10 cm3/s (0.15 to 0.6 l/min) were studied, with nozzle velocities from 0.125 to 2 m/s. Single nozzles and smooth surfaces were also evaluated for comparison. Single-phase heat transfer coefficients (based on planform area) from 2.4 to 49.3 kW/m2 K were measured, while critical heat flux varied from 45 to 395 W/cm2. Correlations of the single-phase heat transfer coefficient and critical heat flux as functions of pin fin dimensions, number of nozzles, nozzle area and liquid flow rate are provided.

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Comparison of Pin Surface Heat Transfer in Arrays of Oblong and Cylindrical Pin Fins

Journal of Turbomachinery ◽

10.1115/1.4025213 ◽

2013 ◽

Vol 136 (4) ◽

Cited By ~ 7

Author(s):

Kathryn L. Kirsch ◽

Jason K. Ostanek ◽

Karen A. Thole

Keyword(s):

Heat Transfer ◽

Boundary Layer ◽

Boundary Layer Separation ◽

Diameter Ratio ◽

Pin Fin ◽

The Third ◽

Spacing Effects ◽

Pin Fins ◽

Turbine Airfoils ◽

Pin Fin Arrays

Pin fin arrays are most commonly used to promote convective cooling within the internal passages of gas turbine airfoils. Contributing to the heat transfer are the surfaces of the channel walls as well as the pin itself. Generally the pin fin cross section is circular; however, certain applications benefit from using other shapes such as oblong pin fins. The current study focuses on characterizing the heat transfer distribution on the surface of oblong pin fins with a particular focus on pin spacing effects. Comparisons were made with circular cylindrical pin fins, where both oblong and circular cylindrical pins had a height-to-diameter ratio of unity, with both streamwise and spanwise spacing varying between two and three diameters. To determine the effect of relative pin placement, measurements were taken in the first of a single row and in the third row of a multirow array. Results showed that area-averaged heat transfer on the pin surface was between 30 and 35% lower for oblong pins in comparison to cylindrical. While heat transfer on the circular cylindrical pin experienced one minimum prior to boundary layer separation, heat transfer on the oblong pin fins experienced two minimums, where one is located before the boundary layer transitions to a turbulent boundary layer and the other prior to separation at the trailing edge.

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Heat Transfer Measurements of Oblong Pins

Volume 5A: Heat Transfer ◽

10.1115/gt2014-25370 ◽

2014 ◽

Cited By ~ 1

Author(s):

Kathryn L. Kirsch ◽

Karen A. Thole

Keyword(s):

Heat Transfer ◽

Gas Turbine ◽

Flow Direction ◽

Effective Means ◽

Transfer Enhancement ◽

Pin Fin ◽

The Third ◽

Pin Fins ◽

Two Peaks ◽

Pin Fin Arrays

Pin fin arrays are employed as an effective means for heat transfer enhancement in the internal passages of a gas turbine blade, specifically in the blade’s trailing edge. Various shapes of the pin itself have been used in such arrays. In this study, oblong pin fins are investigated whereby their long axis is perpendicular to the flow direction. Heat transfer measurements were taken at the pin mid-span with unheated endwalls to isolate the pin heat transfer. Results show important differences in the heat transfer patterns between a pin in the first row and a pin in the third row. In the third row, wider spanwise spacing allows for two peaks in heat transfer over the pin surface. Additionally, closer streamwise spacing leads to consistently higher heat transfer for the same spanwise spacing. Due to the blunt orientation of the pins, the peak in heat transfer occurs off the stagnation point.

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