2857

Table 5 shows that the discrete element predictions are much closer to the raw data for 5 out of the 8 surface conditions presented. The Erosion Cone surface and the Erosion 2 surface predictions are still considerably higher than the raw experimental measurements. One of the possible reasons the computer code is still predicting high is because of temperature change along the height of the roughness elements. This temperature change is analogous to the temperature change experienced along the length of an extended surface or fin. Temperature change along the blockage elements would decrease the average Stanton number predictions.

The Deposit surface and the Deposit Layered surface predictions are close to the raw experimental data, however, another aspect of ellipsoidal surfaces has not been considered. While the drag on the ellipsoidal blockages has been evaluated, the change in heat transfer coefficient and the increase in surface area caused by the change from circular to ellipsoidal blockages has not yet been considered.

The Erosion 2 Layered surface is also in agreement with the raw experimental data, and would not be changed much by considering temperature drop along the blockages. The Erosion 2 Layered surface is sparse and has very small diameter roughness elements that look like pin fins. While the blockage elements may have a moderately low "pin fin" efficiencies, the surface would have a high surface efficiency because it is sparse. Thus, considering temperature loss along the Erosion 2 Layered surface would not significantly change its average Stanton number prediction. Extended Surface Corrections

To further investigate whether temperature decrease along the height of the blockage elements could have caused the over prediction of the average Stanton number for the Erosion Cone surface and the Erosion 2 surface, the Erosion Cone surface blockage elements were modeled as extended surfaces to determine the temperature change along the cones and the fin efficiency of the cones. The fluid temperature profile and velocity profile generated by BLACOMP at the center of the Erosion Cone surface were used in the investigation. The current heat transfer model was used to calculate heat transfer coefficients along the cones. The general extended surface equation, equation (20), was numerically integrated to determine the temperature profile along the height of the cones.

dTb b

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