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收集所有交通大學研究人員與學生個人或團體所發表之各項學術著作，涵蓋期刊論文、教師專書、學位論文等項。;;Collections of Publications of NCTU Researchers and Students Like Journal Papers and Thesis.

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🏛️國立陽明交通大學機構典藏

Author: search.filters.author.Lu, Ming-ChangSubject: search.filters.subject.Heat transfer coefficient

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    The suppression effect of easy-to-activate nucleation sites on the critical heat flux in pool boiling
    (2018-07-01)
    Liu, Yi
    ;
    Lu, Ming-Chang
    ;
    Xu, Dongyan
    ;
    機械工程學系
    ;
    Department of Mechanical Engineering
    We report experimental studies of the role of easy-to-activate nucleation sites in pool boiling on hybrid hydrophobic-hydrophilic surfaces. Microstructured surfaces with controlled wettability and nucleation sites are designed and fabricated to investigate their individual and collective effects on the boiling heat transfer performance. Our results reveal that excellent critical heat flux (CHF) up to 231.5 W/cm(2) is attainable only when the surface has good wettability but is free of easy-to-activate nucleation sites. However, with the presence of easy-to-activate nucleation sites on the boiling surface, only limited CHFs can be achieved irrespective of the surface wettability, suggesting a suppression effect of nucleation sites on the CHF. Based on the previous experimental observation of the dynamic network-like wetting pattern at high heat fluxes, a wetting-deterioration mechanism is proposed to explain the suppression effect of easy-to-activate nucleation sites on the CHF. Easy-to activate nucleation sites continuously generate bubbles that pose a large flow resistance for the liquid to wet the hot surface and thus lead to early dry-out.
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    Enhanced immersion cooling using two-tier micro- and nano-structures
    (2018-02-25)
    Hsu, Ya-Tzu
    ;
    Li, Jia-Xiong
    ;
    Lu, Ming-Chang
    ;
    機械工程學系
    ;
    Department of Mechanical Engineering
    Continual increases in the functionality and miniaturization of electronic devices have resulted in a rapid increase in the power density of such devices. Thus, an efficient cooling technology is required to maximize heat dissipation and prevent electronic failure. Immersion cooling is a promising technique for the thermal management of high-power-density electronics. However, common working fluids in immersion cooling have high global warming potential, and the heat transfer performance of immersion cooling requires improvement to achieve efficient cooling of state-of-the-art high-power-density electronics. In this study, Novec 649, which has low global warming potential and a low boiling point, was applied as a working fluid for immersion cooling. A Si nanowire (SiNW) array, Si micropillar (SiMP) array, and Si nanowires on a Si micropillar (SiNW/MP) two-tier structure were employed to enhance boiling performance. The SiMP surface exhibited the highest critical heat flux (CHF) of 23.5 +/- 1.3 W/cm(2), whereas the SiNW surface exhibited the lowest CHF but a relatively high heat transfer coefficient (HTC). The SiNW/MP surface exhibited the highest HTC of 23611.7 +/- 1586.2 W/m(2) K and a relatively large CHF of 17.4 +/- 1.2 W/cm(2). Compared with a plain SiO2 surface, the CHF and HTC of the SiNW/MP two-tier structure could be enhanced by 30% and 455%, respectively. These results suggest that the SiNW/MP surface is effective for enhancing immersion cooling. (C) 2017 Elsevier Ltd. All rights reserved.
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    Investigation of the two-phase convective boiling of HFO-1234yf in a 3.9 mm diameter tube
    (2013-10-01)
    Lu, Ming-Chang
    ;
    Tong, Jing-Rei
    ;
    Wang, Chi-Chuan
    ;
    機械工程學系
    ;
    Department of Mechanical Engineering
    In this study, the influences of heat flux and mass flux on the two-phase convective boiling heat transfer performance are reported for refrigerants HFO-1234yf and HFC-134a in a 3.9 mm smooth diameter tube. Tests are performed with a saturation temperature of 10 degrees C. It is found that at lower vapor quality region the nucleate boiling is the dominant heat transfer mechanism while the convective evaporation mechanism takes control at the higher vapor quality region. Both HFC-134a and HFO-1234yfshows similar trend and the difference in heat transfer coefficient between HFO-1234 and HFC-134a is quite small. The comparable heat transfer performance between HFC-134a and HFO-1234yf is attributed to similar physical properties and nucleate boiling contribution. The present test results are in line with some existing reports but are inconsistent with one other study having a tube diameter of 1.1 mm. It is found that the departure of heat transfer coefficients between the available publications is mainly attributed to the different flow phenomena caused by the difference of the channel size and channel geometry. A noticeable deterioration of the heat transfer coefficient for HFO-1234yf is encountered in the microchannel. The pressure drops for HFC-134a is about 5-15% higher than that of HFO-1234yf. (C) 2013 Elsevier Ltd. All rights reserved.