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Research Papers

Scaling Roughness Effects on Pressure Loss and Heat Transfer of Additively Manufactured Channels

[+] Author and Article Information
Curtis K. Stimpson

Mem. ASME
Department of Mechanical
and Nuclear Engineering,
The Pennsylvania State University,
3127 Research Drive,
State College, PA 16801
e-mail: curtis.stimpson@psu.edu

Jacob C. Snyder

Mem. ASME
Department of Mechanical
and Nuclear Engineering,
The Pennsylvania State University,
3127 Research Drive,
State College, PA 16801
e-mail: jacob.snyder@psu.edu

Karen A. Thole

Mem. ASME
Department of Mechanical
and Nuclear Engineering,
The Pennsylvania State University,
136 Reber Building,
University Park, PA 16802
e-mail: kthole@psu.edu

Dominic Mongillo

Pratt & Whitney,
400 Main Street,
East Hartford, CT 06118
e-mail: dominic.mongillo@pw.utc.com

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received July 21, 2016; final manuscript received August 8, 2016; published online September 27, 2016. Editor: Kenneth Hall.

J. Turbomach 139(2), 021003 (Sep 27, 2016) (10 pages) Paper No: TURBO-16-1166; doi: 10.1115/1.4034555 History: Received July 21, 2016; Revised August 08, 2016

Additive manufacturing (AM) with metal powder has made possible the fabrication of gas turbine components with small and complex flow paths that cannot be achieved with any other manufacturing technology presently available. The increased design space of AM allows turbine designers to develop advanced cooling schemes in high-temperature components to increase cooling efficiency. Inherent in AM with metals is the large surface roughness that cannot be removed from small internal geometries. Such roughness has been shown in previous studies to significantly augment pressure loss and heat transfer of small channels. However, the roughness on these channels or other surfaces made from AM with metal powder has not been thoroughly characterized for scaling pressure loss and heat transfer data. This study examines the roughness of the surfaces of channels of various hydraulic length scales made with direct metal laser sintering (DMLS). Statistical roughness parameters are presented along with other parameters that others have found to correlate with flow and heat transfer. The pressure loss and heat transfer previously reported for the DMLS channels studied in this work are compared to the physical roughness measurements. Results show that the relative arithmetic mean roughness correlates well with the relative equivalent sand grain roughness. A correlation is presented to predict the Nusselt number of flow through AM channels, which gives better predictions of heat transfer than correlations currently available.

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References

Figures

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Fig. 1

Build orientation and support structures of the DMLS coupons

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Fig. 2

Comparison of (a) CT scan reconstruction and (b) surface rendering from optical profilometer data of the same location on a downward-facing surface of a CoCr coupon

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Fig. 3

Comparison of (a) SEM micrographs and (b) surface rendering from optical profilometer data of the same location on a vertical surface of a CoCr coupon

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Fig. 4

Sample of roughness slice from optical profilometer data (axis scales are equal)

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Fig. 5

Autocorrelation plotted versus offset length for several slices along a simple surface; λ indicates the correlation length

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Fig. 6

SEM micrographs of each surface type for both Inco and CoCr coupons: (a) Inco upward-facing, (b) Inco downward-facing, (c) Inco vertical, (d) CoCr upward-facing, (e) CoCr downward-facing, and (f) CoCr vertical

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Fig. 7

Angled SEM micrographs of Inco coupon detailing roughness features on vertical and upward-facing surfaces at (a) low magnification and (b) high magnification, and (c) cavities formed on downward-facing surfaces

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Fig. 8

Averaged roughness parameters with statistical uncertainty of each surface orientation from OP measurements

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Fig. 9

Relative arithmetic mean roughness, Ra/Dh, plotted versus relative equivalent sand grain roughness, ks/Dh, for DMLS channels and rough channel data from the literature

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Fig. 10

Friction factor data [2] of DMLS coupons compared to predictions from Eqs. (9) and (10)

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Fig. 11

Nusselt number data [2] of Inco coupons compared to predictions from Eq. (12) where f is calculated using Eqs. (9) and (10)

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Fig. 12

Nusselt number data [2] of CoCr coupons compared to predictions from Eq. (12) where f is calculated using Eqs. (9) and (10)

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Fig. 13

Nusselt number data [2] of Inco coupons compared to predictions from Eq. (12) where f is from Ref. [2]

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Fig. 14

Nusselt number data [2] of CoCr coupons compared to predictions from Eq. (12) where f is from Ref. [2]

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