Browsing by Author "Tu, Cheng-Wei"

Now showing 1 - 6 of 6

A novel oxidized composite braided wires wick structure applicable for ultra-thin flattened heat pipes
(2017-11-01)
Yang, Kai-Shing
;
Tu, Cheng-Wei
;
Zhang, Wen-Hua
;
Yeh, Chih-Ting
;
Wang, Chi-Chuan
This present study proposed a novel low-cost and high performance braided wire wick structure having superhydrophilic treatment applicable for ultra-thin heat pipe. The test wick structures include mono and composite wick structure. The composite braided wire adopts two different diameter wire design, using a large diameter (0.1 mm) in the core while the exterior of the core is covered by smaller diameter copper wire (0.05 mm). The mono design contains only one uniform wire diameter (0.1 mm) in core region. Test results indicate that via oxidizing the surface of the braided wires can largely enhance the surface roughness and result in a much higher capillary force as comparing to the un-oxidized one. In addition, both mono (m-FHP) and composite braided wire (c-FHP) with oxidization could possess a maximum heat transfer capability over 15 W under horizontal operation, and test results showed that the heat transfer capability of composite design outperforms mono one by more than 32.5% in all orientations. It is also found that the filling loading ratio plays essential role on the overall performance of FHP. Either a low filling loading ratio or a high filling loading ratio may yield a lower maximum heat transfer capability and a higher thermal resistance. An optimum filling loading ratio of 125% yields the lowest thermal resistance around 0.12 K/W with the best heat transfer capability of 20W.
Experimental investigation of moist air condensation on hydrophilic, hydrophobic, superhydrophilic, and hybrid hydrophobic-hydrophilic surfaces
(2017-12-01)
Yang, Kai-Shing
;
Lin, Kai-Hsiang
;
Tu, Cheng-Wei
;
He, Yu-Zhen
;
Wang, Chi-Chuan
This study experimentally investigates the condensation performance amid hydrophobic, hydrophilic, superhydrophilic and hydrophobic-hydrophilic hybrid patterned surfaces with air velocity ranging from 0.5 m/s to 4.0 m/s and relative humidity of 85%, 60% and 40%. The hybrid novel surface employs inverted V shape channels design with alternate hydrophilic and hydrophobic channel to direct condensate, and the accumulated condensate is gathered at vertical hydrophilic channel for further effective condensate removal. It is found that the heat transfer coefficient for hydrophobic surface is higher than that of hydrophilic surface irrespective of the operational velocity and relative humidity. Dropwise condensation prevails for the hydrophobic surface and a twig-like structure of condensate is seen for the hydrophilic surface, and this phenomenon becomes more pronounced when the relative humidity is increased. The superhydrophilic surface shows the worst heat transfer performance due to filmwise condensation. The hybrid surface shows superior heat transfer performance over other surfaces. The heat transfer coefficient obtained is around 3-9% higher than that of hydrophobic surface and is about 6-16% higher than hydrophilic one. The proposed novel design offers a shorter cyclic condensate removal time and better condensate drainage. It is found that the maximum diameter.for the hybrid surface is about 80-90% smaller than the hydrophobic surface and the droplet size before falling off is relatively independent of operational velocity. (C) 2017 Elsevier Ltd. All rights reserved.
Fabrication of superhydrophobic and superoleophilic polystyrene surfaces by a facile one-step method
(2007-12-03)
Tu, Cheng-Wei
;
Tsai, Chia-Hua
;
Wang, Chih-Feng
;
Kuo, Shiao-Wei
;
Chang, Feng-Chih
A facile one-step method has been developed to prepare both superhydrophobic and superoleophilic surfaces of polystyrene (PS) without any chemical modification. A rough film consisting of micro-bead and nano-fiber mixed structures is formed by spraying a PS solution onto a large area and any type of substrate. The mixed structures with such unique wettability properties can be used in oil/water separation and as oil sorbents.
Heat Transfer of Semicrystalline Nylon Nanofibers
(2020-03-24)
Chien, Hsin-Che
;
Peng, Wei-Tsu
;
Chiu, Te-Hsuan
;
Wu, Pei-Hsiu
;
Liu, Yueh-Ju
Polymers are generally regarded as thermal insulators. The efficient heat transfer observed in the low-dimensional polymers in the literature mainly result from the larger crystallinity or improved polymer chain orientation in the low-dimensional polymers. However, the role of the amorphous domain on heat transfer in polymers remains unexplored. In this work, we report that the semicrystalline nylon polymer nanofibers can exhibit a very large thermal conductivity of 59.1 +/- 3.1 W m(-1) K-1 and the heat transfer in the semicrystalline polymer nanofibers was time-dependent. The thermal conductivity of the nanofibers could be modulated to span 3 orders of magnitude from being nearly insulated (similar to 0.27 +/- 0.02 W m(-1) K-1) to being highly thermal conductive after annealing (similar to 59.1 +/- 3.1 W m(-1) K-1). The time-dependent thermal conductivity was observed at a temperature lower than the gamma transition temperature of the polymer and was a result of the physical aging of the semicrystalline polymer. A phenomenological model was adopted to explain the time-dependent heat transfer of the semicrystalline nanofibers. The physical aging reduced the configuration disorder in the polymer and caused the heat transfer of the semicrystalline polymer to increase during the annealing process.
Investigation of the drawing mechanism of UHMWPE fibers
(2008-07-01)
Yeh, Jen-Taut
;
Lin, Shui-Chuan
;
Tu, Cheng-Wei
;
Hsie, Kuo-Huang
;
Chang, Feng-Chih
The influence of draw ratios (DR) of gel-spun ultrahigh molecular weight polyethylene (UHMWPE) fibers on resultant morphologies, tensile, degrees of orientation, and crystal phase transition properties were investigated using wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). The anisotropic crystalline structure with full concentric circular rings originally shown on the WAXD patterns of the as-prepared and drawn UHMWPE fibers gradually transform into oriented fibers with azimuthal spots on the equator as their DR values increase from 1 to 20, in which their orthorhombic crystals, percentage crystallinity, crystalline orientation, and the birefringence values increase significantly. As evidenced by SEM and WAXD analysis, the chain-folded molecules originally present in kebab crystals of the as-prepared UHMWPE fiber specimens gradually transformed into shish-like crystals with relatively high orientation as their DR values increase from 1 to 20. In contrast, the crystallinity and crystal orientation values of the drawn UHMWPE specimens increase only slightly, as their DR values increase from 20 to 40, wherein both crystallinity values of orthorhombic and monoclinic crystals increase slightly. In fact, barely any oriented kebab but only shish crystals were observed on the surfaces of drawn UHMWPE fiber specimens with DR values higher than 20. The birefringence values increase only slightly with further increasing DR values, while crystallinity and crystal orientation values of the drawn UHMWPE fiber specimens remained relatively unchanged as their DR values increase from 40 to 150. In the meantime, the monoclinic crystals gradually grow at the expense of the orthorhombic form crystals as the DR values of drawn UHMWPE fiber specimens increase from 40 to 150. Possible reasons accounting for these interesting properties found for the drawn UHMWPE fibers with varying draw ratios are proposed in this study.
Supramolecular self-assembly through inclusion complex formation between poly(ethylene oxide-b-N-isopropylacrylamide) block copolymer and alpha-cyclodextrin
(2009-06-19)
Tu, Cheng-Wei
;
Kuo, Shiao-Wei
;
Chang, Feng-Chih
;
應用化學系
;
Department of Applied Chemistry
A well-defined poly(ethylene oxide-block-N-isopropylacrylamide) (PEO-b-PNIPAM) diblock copolymer was synthesized by atom transfer radical polymerization and formed the inclusion complexes (ICs) after selective threading of the PEO segment of the block copolymer through the cavities of alpha-cyclodextrin (alpha-CD) units. The formation of the alpha-CD/PEO ICs between alpha-CD and PEO segment of the PEO-b-PNIPAM transformed the system from its original random coil conformation into a rod/coil-like structure. The stacking of the alpha-CD/PEO ICs and phase separation within the alpha-CD/PEO-b-PNIPAM IC resulted in the self-assembly of long-range-ordered lamellar structure exhibiting alternating layers of (i) alpha-CD/PEO ICs with hexagonally packed plates and (ii) amorphous phase of unincluded PEO/PNIPAM with brush conformation. (C) 2009 Elsevier Ltd. All rights reserved.