Browsing by Author "Hsu, Li-Chieh"

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An experimental study of inclination on the boiling heat transfer characteristics of a micro-channel heat sink using HFE-7100
(2015-03-01)
Hsu, Li-Chieh
;
Cion, Sian-Wun
;
Lin, Kuo-Wei
;
Wang, Chi-Chuan
;
機械工程學系
In this study, the effect of inclination on the two-phase convective boiling heat transfer characteristics of HFE-7100 is investigated experimentally in a multiport micro-channel having a hydraulic diameter of 440 mu m. The corresponding mass flux is 100 and 200 kg m(-2) S-1, respectively. The inclinations include -90, -45, 0, 45, and 90 degrees with respect to the horizon. Test results show that normally the heat transfer coefficient for upward arrangements is superior to those of downward arrangement at a supplied heat flux of 25 kW m(-2). Yet this is applicable for G = 100 or 200 kg m(-2) s(-1). The heat transfer coefficients increase with the vapor quality and peak again at a vapor quality of 0.6, suggesting a controlled mechanism of convective boiling. With the rise of heat flux to 40 kW m(-2), it appears that nucleate boiling may impose appreciable effect on the heat transfer mechanism. For G = 100 kg m(-2) s(-1), the heat transfer coefficients for all arrangements are insensitive to change of vapor quality (x < 0.6), implicating that nucleate boiling is in control. Analogous results prevail for G = 200 kg m(-2) s (-1). Six heat transfer correlations are used to predict experimental data in different orientation. It appears that the Kandlikar correlation shows the best-predictive ability against the present data with an overall mean deviation of 29.04% (C) 2015 Elsevier Ltd. All rights reserved.
Two-phase pressure drops and flow pattern observations in 90 degrees bends subject to upward, downward and horizontal arrangements
(2015-11-01)
Hsu, Li-Chieh
;
Chen, Ing Youn
;
Chyu, Chien-Min
;
Wang, Chi-Chuan
;
機械工程學系
In this study, single-phase/two-phase frictional characteristics and flow patterns of 900 bends are experimentally investigated. The two bends have inner diameters (D) of 5.5 and 9.5 mm with tube curvature ratio (2R/D) of 5.4 and 4.2, respectively. The bends are installed either an upward, horizontal or downward arrangement. For results concerned with single-phase flow, the bend friction factor (f(B)) is always greater than that of the straight tubes at the same liquid Reynolds number. On the other hand, the f(B) values for D = 9.5 mm with smaller curvature ratio are greater than those of D = 5.5 mm. The resultant two-phase frictional pressure drops of 90 bend are well predicted by the Sanchez Silva et al. [14]\'s correlation. For the two-phase frictional pressure gradient, the upward arrangement is greater than that of the horizontal arrangement due to swirled motion and liquid flow reversal. The flow reversals are observed for upward flow arrangement at specific flow pattern and pressure gradient. However, no swirled motion and liquid flow reversal is seen in the downward arrangement. As mass flux and quality increase, the differences of pressure drop among the three arrangements are getting smaller due to the appreciable offset by the rising flow inertia. Meanwhile, the liquid flow reversal is more evidently observed in the large diameter bend. Flow pattern map showing the region of liquid flow reversal is shown on the diagram of the superficial gas velocity (U-GS) versus superficial liquid velocity (U-LS). The region for liquid flow reversal for D = 9.5 mm is much greater than that of D = 5.5 mm. For D = 5 mm, there is no liquid flow reversal when U-GS is above 2 m/s. On the other hand, the threshold value is raised to 4 m/s for the 9.5 mm internal diameter tube. (C) 2015 Elsevier Inc. All rights reserved.