Browsing by Author "Chen, Chiao-Hsin"

Now showing 1 - 4 of 4

DROPLET SIZE CHARACTERIZATION FOR MIST FLOW IN A SINGLE-SIDE HEATED VERTICAL SQUARE DUCT
(2014)
Liu, Yao-Hsien
;
Lin, Chia-Cheng
;
Chen, Chiao-Hsin
;
機械工程學系
;
Department of Mechanical Engineering
Cooling with mist flow can achieve higher heat transfer rates to meet the cooling requirements in recent industry applications. The mist flow was produced by introducing the dispersed water droplets in the air stream, and was used for cooling a heated surface in a vertical square duct with the hydraulic diameter of 4 cm. Digital image analysis method was developed to obtain the size of the droplets ranging from 20 to 110 mu m. The digital images were segmented using the optimal threshold gray level for droplets sizing. Droplet size variation subjected to a single-side heated wall with constant heat flux was investigated. Infrared thermography was applied to obtain the surface temperature distribution during the cooling test. The air-water mist flow gave much lower surface temperature compared to the air cooling, and the mean droplet diameter decreased as it flowed over the heated surface.
NON-BOILING HEAT TRANSFER OF AIR/WATER MIST FLOW IN A SQUARE DUCT WITH ORTHOGONAL RIBS
(2016)
Huang, Yi-Hsuan
;
Chen, Chiao-Hsin
;
Liu, Yao-Hsien
;
機械工程學系
;
Department of Mechanical Engineering
Heat transfer of mist flow in a rib-roughened square duct was experimentally determined using infrared thermography. The mist flow was generated by introducing fine dispersed water droplets into the air stream. A constant heat flux was applied to the surface during the test and the surface temperature was kept below the boiling point. The heat transfer measurement was performed on a heated surface located inside a vertical square duct with a hydraulic diameter of 4cm. The air/water mist flow was carried upward by air flow from a blower placed at the bottom of the duct. The flow passed through a flow straightener and entered the heated region of the square duct. The Reynolds numbers of the carrier fluid were 7900, 16000 and 24000. The results showed that mist flow cooling achieved higher heat transfer rates compared to the air cooling. Thin liquid films formed on the heated surface by the mist flow and the evaporation from the droplets and liquid film contributed to a higher heat removal rate. The heat transfer enhancement on the smooth surface by the mist flow was 4 to 6 times higher compared to the air flow. Rib turbulators were typically applied in channel walls for heat transfer enhancement in gas turbine blades or heat exchangers. Ribs caused flow reattachment and promoted flow mixing. The higher Nusselt number induced by flow reattachment can be visualized using infrared thermography. For the ribbed case, the heat transfer contours were reported based the regions between ribs. Square brass ribs were used and the rib height-to-hydraulic diameter ratio was 0.05. The rib pitch-to-height ratios were 10 and 20 in the current study. For the mist flow in the ribbed duct, the intense flow mixing and secondary flow caused by the ribs blew away liquid films on the surface. The heat transfer enhancement near the reattachment region was mainly influenced by the droplet impingement on the surface. In the ribbed duct, the heat transfer enhancement from using the mist flow was 2.5 to 3.5 times higher compared to the air flow.
Nonboiling Heat Transfer and Friction of Air/Water Mist Flow in a Square Duct With Orthogonal Ribs
(2017-12-01)
Huang, Yi-Hsuan
;
Chen, Chiao-Hsin
;
Liu, Yao-Hsien
;
機械工程學系
;
Department of Mechanical Engineering
Heat transfer of air/water mist flow in a single-side heated vertical duct was experimentally investigated. The mist flow was produced by introducing fine dispersed water droplets into the air stream, and the water-air mass flow ratios were up to 15%. The Reynolds numbers of the air flow were 7900, 16,000, and 24,000. The rib spacing-to-height ratios were 10 and 20 in the current study. Mist flow cooling achieved higher heat transfer rates mainly because of the droplet deposition and liquid film formation on the heated surface. The heat transfer enhancement on the smooth surface by the mist flow was 4-6 times as high as the air flow. On the ribbed surface, a smaller rib spacing of 10 was preferred for air cooling, since the heat transfer enhancement by the flow reattachment was better utilized. However, the rib-induced secondary flow blew away the liquid films on the surface, and the heat transfer enhancement was degraded near the reattachment region for the mist cooling. A larger rib spacing-to-height ratio of 20 thus achieved higher heat transfer because of the liquid film formation beyond the reattachment region. The heat transfer enhancement on the ribbed surface using mist flow was 2.5-3.5 times as high as the air flow. The friction factor of the mist flow was two times as high as the air flow in the ribbed duct.
The growth of heteroepitaxial CuInSe2 on free-standing N-polar GaN
(2014-12-01)
Shih, Cheng-Hung
;
Lo, Ikai
;
You, Shuo-Ting
;
Tsai, Cheng-Da
;
Tseng, Bae-Heng
We report that chalcopyrite CuInSe2 thin films were grown on free-standing N-polar GaN (000 (1) over bar) by molecular beam epitaxy. X-ray diffraction showed that the CuInSe2 thin film was grown in (112) orientation, and its peak of rocking curve with full width at half maximum of about 897.8 arc-sec indicated the epitaxial growth of CuInSe2 (112) film on N-polar GaN. Microstructure analysis of the CuInSe2 showed that the large lattice mismatch (28.5%) between CuInSe2 and GaN is accommodated by domain matching, and no interface reaction occurs between CuInSe2 and GaN. Our experimental results show that GaN is stable for the epitaxial growth of CuInSe2 thin film, which exhibits a promising potential for optoelectronic applications. (C) 2014 Author(s).