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This paper investigates the effects of hemispherical mounds on filmwise condensation heat transfer in micro-channels. Also investigated were the impacts that spatial orientation of the three-sided condensation surface (i.e., gravitational effects) on steam condensation, where the cooled surfaces were either the lower surface (i.e., gravity pulls liquid towards the condensing surfaces) or upper surface (i.e., gravity pulls liquid away from the condensing surfaces). Two test coupons were used with 1.9-mm hydraulic diameters and either a plain copper surface or a copper surface modified with 2-mm diameter hemispherical mounds. Heat transfer coefficients, film visualization, and pressure drop measurements were recorded for both coupons in both orientations at mass fluxes of 50 kg/m 2 s and 125 kg/m 2 s. For all test conditions, the mounds were found to increase condensation heat transfer coefficients by at minimum 13% and at maximum 79%. When the test section was inverted (i.e., condensing surface on the top of flowing steam), minimal differences were found in mound performance, while the plain coupon reduces heat transfer coefficients by as much as 14%. Flow visualization suggests that the mounds enhanced heat transfer due to the disruption of the film as well as by reducing the thermal resistance of the film. Pressure drops followed parabolic behavior with quality, being higher in the mound coupon than the plain coupon. No significant pressure drop differences in the inverted orientation were observed.
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Interrogation of Mid-build Internal Temperature Distributions within Parts Being Manufactured via the Powder Bed Fusion Process
This work reports on the measurement of the internal temperature distributions of parts being manufactured via the Powder Bed Fusion (PBF) process. Eight test coupons were machined from a piece of wrought 304 stainless steel (SS). Thermocouples were inserted into the test coupon interiors to sample internal thermal history. The coupons were then placed into the open architecture laser PBF machine housed at EWI and covered to their uppermost surfaces with 316 SS powder.Three tests were executed: First, the laser rastered over the coupons without inducing melting.Second, the laser rastered over the coupons while melting the exposed faces. Lastly, five layers of316 SS were built atop the coupons. The main result is a comprehensive data set of a multitude of measured physical inputs and outputs under typical build conditions: embedded thermocouple temperatures, laser centroid, laser power, and infrared imagery of the exposed coupon faces.
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- Award ID(s):
- 1738723
- PAR ID:
- 10162670
- Date Published:
- Journal Name:
- Proceedings of the 2019 Annual International Solid Freeform Fabrication Symposium
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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