In this work, two different manufacturing approaches are presented that create waterrepellency (hydrophobicity and super-hydrophobicity) for acrylonitrile butadiene styrene (ABS) structures. In particular, this is the first study to render .three-dimensional (3D) printed ABS surfaces with internal flow paths to be superhydrophobic. The first approach uses standard wet-based chemical processing for surface preparation after which a fluorocarbon layer is deposited by dip coating or with vapor deposition. This first approach creates hydrophobic surfaces with roll-off angles of less than 30 o . In the second approach, the ABS structures are dip-coated with a commercial rubber coating solution and subsequently surface-modified by Reactive Ion Etching (RIE) with fluorinated gases to render the samples superhydrophobic, with roll-off angles as low as 6 o . In order to further enhance their water-repellency, the dip-coating rubber solution is mixed with polytetrafluoroethylene (PTFE) colloidal dispersions to form a nanocomposite layer prior to the RIE process. The PTFE particles induce surface roughness as well as hydrophobicity. The modified surfaces created by the two approaches are further characterized by scanning electron microscopy and water drainage performance. Water Downloaded by [New York University] at 05:46 22 July 2015 2drainage (prevention of water retention) is especially important for high thermal efficiency of 3D printed heat exchangers. However, water-repellency for ABS is also interesting for a broader range of applications that use this material.
A 105‐m, 13‐MW two‐bladed downwind Segmented Ultralight Morphing Rotor (SUMR‐13) blade was gravo‐aeroelastically scaled by 20% to a 20.87‐m‐long demonstrator blade and confirmed through structural ground testing. The subscale model was achieved through geometric scaling and by aeroelastic scaling principles based on operational flapwise deflections combined with rotational and structural frequencies while retaining the turbine tip‐speed ratio. In particular, the subscale demonstrator was designed to replicate, as closely as possible, the nondimensional geometry, the ratio of centrifugal to gravitational moments, the tip‐speed ratio, and the nondimensional rotation rate. The intent for this demonstrator was to achieve the same nondimensional flapwise blade deflections and dynamics of the full‐scale 13‐MW rotor. The manufactured SUMR‐D blade resulted in less than half of the mass of the conventional two‐bladed Controls Advanced Research Turbine (CART2) rotor blade based on scaling and a lower power rating, though with some differences in mass and stiffness from the ideal scaled‐down design to meet safety requirements at the test site. To achieve proper scaling, operational pitch control set points were altered to account for the differences by evaluating simulated operation of both the SUMR‐13 and SUMR‐D rotors. Structural testing of the SUMR‐D blade investigated the response to well‐defined flapwise loads and indicated that the subscale blade had the appropriate elastic properties needed for both scaling and for safe operational field testing.
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