# 燃氣輪機期末報告 -- Roughness Effects and Build Direction Effects on Heat Transfer for Additively Manufactured Channels

# 草稿整理
## [Build Direction Effects on Additively Manufactured Channels](https://pennstate.pure.elsevier.com/en/publications/build-direction-effects-on-additively-manufactured-channels)
> Snyder, J. C., Stimpson, C. K., Thole, K. A., and Mongillo, D. (January 20, 2016). "Build Direction Effects on Additively Manufactured Channels." ASME. J. Turbomach. May 2016; 138(5): 051006. https://doi.org/10.1115/1.4032168
### Abstract
隨著直接金屬激光燒結 (DMLS)（通常也稱為增材製造 (AM)）的進步，用於燃氣輪機冷卻的內部通道的新穎幾何特徵可以超越使用傳統製造技術的這些特徵。 然而，在 DMLS 過程中有許多變量會影響零件的最終質量。 燃氣輪機傳熱設計人員最感興趣的是內部通道可以保持的==粗糙度水平(roughness level)== 和 ==公差水平(tolerance levels)==。本研究調查了 DMLS 構建方向和通道形狀對小型通道的壓力損失和傳熱測量的影響。 結果表明，具有不同通道形狀和構建方向的測試案例之間會出現壓力損失差異，而==傳熱性能幾乎沒有變化==。
- the goal of this study is to evaluate the effect of DMLS build direction on the pressure loss and heat transfer performance of small (mini) channels.
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- figure 2 : 3d printing in three different build directions
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- figure 3 : all of the designed channel shapes

- the horizontal build: need support in the channel of the upper surface, but it is hard to remove support in the channel
- upper surface collapse: This collapsed upper surface was mitigated(減輕) with the teardrop- and diamond-shaped channels.
- cross section area: teardrop-shaped channel $\approx$ circular-shaped channel
- the vertical build direction shows the least degradation in the channel shape, which was expected since all channel surfaces were supported.
- Surface Roughness: 
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- vertical-build: most smooth, because there is no downward surface
- all coupons exhibited an internal surface roughness much greater than traditional manufacturing techniques.
- friction factor
- vertically built coupons had the lowest friction factor, while the diagonally built coupons had the highest friction factor
- the teardrop had the lowest friction factor while allowing the channel to retain a cylindrical form in the horizontal build direction.
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- horizontal build
- The smoothest coupon, which was the teardrop shape, has the lowest heat transfer.
- The cylindricalshaped channel was the roughest and had the highest heat transfer
- Comparing these surfaces, the upper sides of the teardrop shape have fused together to form a smoother surface. Without the large roughness peaks, there are less features to promote turbulence and increase heat transfer.
- vertically built
- vertically built channels lie separate from the trend of the other coupons
- These roughness features are more effective at augmenting heat transfer without penalizing friction factor
- 45 deg build direction results in higher friction drag than a vertical build direction for round channels.
- cylindrical diagonal dataset
- The fixed pressure ratio for the analysis at Re 10,000
- it had the highest friction factor, and therefore, the largest mass flow reduction
- heat transfer lost
- at a fixed pressure ratio the rough DMLS surface helps to recover heat transfer lost due to the drop in mass flow from a theoretically smooth channel.
- Therefore, the augmentation of the heat transfer due to the roughness partially compensates for the decrease in the heat transfer from the reduced mass flow.

## [Roughness Effects on Flow and Heat Transfer for Additively Manufactured Channels ](https://asmedigitalcollection.asme.org/turbomachinery/article-abstract/138/5/051006/378615/Build-Direction-Effects-on-Additively-Manufactured)
> Stimpson, C. K., Snyder, J. C., Thole, K. A., and Mongillo, D. (January 27, 2016). "Roughness Effects on Flow and Heat Transfer for Additively Manufactured Channels." ASME. J. Turbomach. May 2016; 138(5): 051008.https://doi.org/10.1115/1.4032167
### Abstract
增材製造 (AM) 領域的最新技術進步，特別是直接金屬激光燒結 (DMLS)，增加了使用 AM 製造燃氣輪機部件的潛力。將 DMLS 用於渦輪機部件拓寬了設計空間，並允許在幾乎不增加時間或成本的情況下製造越來越小和復雜的幾何形狀。在嘗試評估 DMLS 在特定應用中的優勢時會出現挑戰，特別是因為對錶面粗糙度的影響知之甚少。本文介紹了通過使用 DMLS 製造的小通道的壓降和傳熱結果，以便更好地了解粗糙度。在這項研究中評估了 DMLS 製成的十種不同的試樣，它們都具有多個矩形通道。在各種流動條件下收集測量值並簡化為==摩擦因數==和==努塞爾數==。結果表明，與光滑通道相比，這些參數顯著增加，尤其是==小水力直徑的微型通道的摩擦係數==。然而，努塞爾數的增加並沒有隨著摩擦係數的增加而成比例地增加。
- the goal of this study was to evaluate the surface roughness prodcued by DMLS process and measure its influence on flow losses and convective heat transfer through rectagular minichannels.
- 11 coupons were fabricated for this study.
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- The friction factors were significantly increased relative to smooth channels due to the roughness levels
- Decreasing hydraulic diameters, the friction factors increased as a consequence of higher roughness-to-hydraulic diameter ratios.
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- High augmentations resulted in increased pressure losses, the Nusselt number augmentations did not linearly scale with the friction factors
- Analysis showed, however, that for a given pressure ratio across the coupons, the higher pressure losses resulted in much lower mass flow and heat transfer rates.
- That for a given pressure ratio across the coupons, the higher pressure losses resulted in much lower mass flow and heat transfer rates.
- The reduction in heat transfer was not as large as the reduction in mass flow rate because of the augmentations that occur for the rough DMLS coupons.
- Comparisons of friction and heat transfer augmentation between AM channels and channels with grooves show that channels made with DMLS have relatively comparable thermal performance.

## [Scaling Roughness Effects on Pressure Loss and Heat Transfer of Additively Manufactured Channels](https://asmedigitalcollection.asme.org/turbomachinery/article/139/2/021003/378795/Scaling-Roughness-Effects-on-Pressure-Loss-and)
> Stimpson, C. K., Snyder, J. C., Thole, K. A., and Mongillo, D. (September 27, 2016). "Scaling Roughness Effects on Pressure Loss and Heat Transfer of Additively Manufactured Channels." ASME. J. Turbomach. February 2017; 139(2): 021003. https://doi.org/10.1115/1.4034555
### Abstract
使用金屬粉末的增材製造 (AM) 使製造具有小而復雜的流動路徑的燃氣輪機部件成為可能，這是目前可用的任何其他製造技術無法實現的。 AM 增加的設計空間使渦輪機設計人員能夠在高溫部件中開發先進的冷卻方案，以提高冷卻效率。金屬增材製造中固有的大表面粗糙度無法從小的內部幾何形狀中去除。先前的研究表明，這種粗糙度會顯著增加小通道的壓力損失和熱傳遞。然而，這些通道或由 AM 和金屬粉末製成的其他表面的粗糙度尚未完全表徵為縮放壓力損失和傳熱數據。本研究檢查了使用直接金屬激光燒結 (DMLS) 製成的各種水力長度尺度的通道表面的粗糙度。統計粗糙度參數與其他人發現的與流動和傳熱相關的其他參數一起顯示。先前報告的 DMLS 通道的壓力損失和熱傳遞與物理粗糙度測量值進行了比較。結果表明，相對算術平均粗糙度與相對等效砂粒粗糙度有很好的相關性。提出了一種相關性來預測通過 AM 通道的流量的 Nusselt 數，與目前可用的相關性相比，它可以更好地預測傳熱。

The coupons used in this study are the same as those used in the authors’ previous study. Ten coupons were investigated.

- Roughness Quantification: 3種method
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- Ra: arithmetic mean roughness,
- Rq: root-mean-square (RMS) roughness,
- Rz: mean roughness depth,
- Rsk: skewness
- Rku: kurtosis
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> autocorrelation function
- calculating the correlation length for the surfaces(was done by first taking several slices of each surface in the direction of flow)
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- combined roughness density and shape factor
- A is the flat reference area (i.e., area of a flat surface without roughness)
- Af is the total frontal area relative to the flow direction
- Aw is the total windward wetted area.
### Surface Roughness
- individual roughness features on all surfaces look very much like the spherical-shaped powder used to fabricate the coupons.
- The diameter of these features is around 30 lm suggesting that much of the roughness comes from powder particles being sintered or partially melted to the surface.
- spherical features num: CoCr > Inco
- CoCr powder had a greater propensity to sinter to the surfaces than the Inco powder
- the downward-facing surface appears much different than the other faces


- `8(a)` shows that Ra of the CoCr coupons is higher for both the upward-facing and vertical surfaces
- The downward-facing surfaces have a much greater Ra than the upward-facing and vertical surfaces, and it is nearly identical for both materials even though the morphology observed in Figs
- `8(b)` shows similar trends to those of Ra.
- `8(c)` the downward-facing surface of the Inco coupons has a larger Rz than the others.
- `8(d)` is similar for all surfaces except the Inco downward-facing surface.
- positive Rsk values denote that these surfaces are strongly dominated by positive features
- low Rsk: it has fewer peaks than the other surfaces
- `8(f)` $\lambda$ identifies dominant length scales and periodic patterns

- $\Lambda$: the resulting difference between the two materials is even more dramatic. However, within each set of coupons of the same material, there is little variation in this parameter.
### Heat transfer
- the same geometry were not very different between the two materials, $\Lambda$ was not an effective parameter to correlate with.
- friction factor approach:
- predict: 
- Although some data are underpredicted and others are overpredicted, there is good agreement for the most part

### Conclusion
- the relative arithmetic mean roughness, Ra/Dh, relates best with the relative equivalent sand grain roughness, ks/Dh
- A heat transfer correlation is also presented which predicts the Nusselt number of flow through DMLS microchannels using predictions or measurements of friction factor.
- This new correlation agrees well with the experimental data and significantly improves upon correlations widely used for flow through channels.
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