Browsing by Author "Lie, Y. M."

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Experimental study of evaporation pressure drop characteristics of refrigerants R-134a and R-407C in horizontal small tubes
(2008-01-01)
Lie, Y. M.
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Su, F. Q.
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Lai, R. L.
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Lin, T. F.
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機械工程學系
An experiment is carried out in the present study to investigate the characteristics of the frictional pressure drops for the evaporation of refrigerants R-134a and R-407C in horizontal small tubes having the same inside diameter of 0.83 mm or 2.0 mm. In the experiment for the 2.0-mm tubes, the refrigerant mass flux G is varied from 200 to 400 kg/m(2) s, imposed heat flux q from 5 to 15 kW/m(2), inlet vapor quality x(in) from 0.2 to 0.8, and refrigerant saturation temperature T-sat from 5 to 15 degrees C. While for the 0.83-mm tubes, G is varied from 800 to 1500 kg/m(2) s with the other parameters varied in the same ranges as those for D-i = 2.0 mm. In this study, the effects of the inlet refrigerant vapor quality, mass flux, saturation temperature and imposed heat flux on the measured frictional pressure drops are examined in detail. Our experimental data clearly show that both the R-134a and R-407C frictional pressure drops increase significantly with the inlet vapor quality of the refrigerant, except at low mass flux and high heat flux. Besides, the effect of the imposed heat flux on the frictional pressure drop is rather weak. Moreover, a significant decrease in the frictional pressure drop results for a rise in T-sat. Furthermore, both the R-134a and R-407C frictional pressure drops increase substantially with the refrigerant mass flux. We also note that under the same x(in), T-sat, q and D-i, refrigerant R-407C has a lower frictional pressure drop when compared with that for R-134a. For the same refrigerant, a reduction in the duct size from 2.0-mm to 0.83-mm causes a significant increase in Delta P-f. Finally, an empirical correlation for the friction factor for the R-134a and R-407C evaporation in the 0.83-mm and 2.0-mm small tubes is proposed. (C) 2007 Elsevier Ltd. All rights reserved.
Saturated flow boiling heat transfer and associated bubble characteristics of FC-72 on a heated micro-pin-finned silicon chip
(2007-09-01)
Lie, Y. M.
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Ke, J. H.
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Chang, W. R.
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Cheng, T. C.
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Lin, T. F.
An experiment is carried out here to investigate flow boiling heat transfer and associated bubble characteristics of FC-72 on a heated micro-pin-finned silicon chip flush-mounted in the bottom of a horizontal rectangular channel. Besides, three different micro-structures of the chip surface are examined, namely, the smooth, pin-finned 200 and pin-finned 100 surfaces. The pin-finned 200 and 100 surfaces, respectively, contain micro-pin-fins of size 200 mu m x 200 mu m x 70 mu m (width x length x height) and 100 mu m x 100 mu m x 70 mu m. The pitch of the fins is equal to the fin width for both surfaces. The effects of the FC-72 mass flux, imposed heat flux, and surface microstructures of the silicon chip on the FC-72 saturated flow boiling characteristics are examined in detail. The experimental data show that an increase in the FC-72 mass flux causes a delay in the boiling incipience. However, the flow boiling heat transfer coefficient is not affected by the coolant mass flux. But adding the micro-pin-fin structures to the chip surfaces can effectively enhance the single-phase convection and flow boiling heat transfer. Moreover, the mean bubble departure diameter and active nucleation site density are reduced for a rise in the FC-72 mass flux. A higher coolant mass flux results in a higher mean bubble departure frequency. Furthermore, larger bubble departure diameter, higher bubble departure frequency, and higher active nucleation site density are observed at a higher imposed heat flux. We also note that adding the micro-pin-fins to the chips decrease the bubble departure diameter and increase the bubble departure frequency. However, the departing bubbles are larger for the pin-finned 100 surface than the pin-finned 200 surface but the bubble departure frequency exhibits an opposite trend. Finally, empirical equations to correlate the present data for the FC-72 single-phase liquid convection and saturated flow boiling heat transfer coefficients and for the bubble characteristics are provided. (c) 2007 Elsevier Ltd. All rights reserved.
Saturated flow boiling heat transfer of R-407C and associated bubble characteristics in a narrow annular duct
(2008-07-15)
Hsieh, F. C.
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Li, K. W.
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Lie, Y. M.
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Chen, C. A.
;
Lin, T. F.
Experiments are conducted here to investigate how the channel size affects the R-407C saturated flow boiling heat transfer and associated bubble characteristics in a horizontal narrow annular duct. The gap of the duct is fixed at 1.0 and 2.0 mm in this study. The measured data indicate that the saturated flow boiling heat transfer coefficient increases with a decrease in the duct gap. Besides, raising the imposed heat flux can cause a significant increase in the boiling heat transfer coefficients. However, the effects of the refrigerant mass flux and saturated temperature on the boiling heat transfer coefficient are milder. The results from the flow visualization show that the mean diameter of the bubbles departing from the heating surface decreases noticeably at increasing R-407C mass flux. Moreover, the bubble departure frequency increases at reducing duct size and at a high imposed heat flux many bubbles generated from the cavities in the heating surface tend to merge together to form big bubbles. Meanwhile comparison of the present heat transfer data for R-407C with R-134a in the same duct and with some existing correlations is conducted. Furthermore, correlation for the present R-407C saturated flow boiling heat transfer data is proposed. Additionally, the present data for some quantitative bubble characteristics such as the mean bubble departure diameter and frequency and the active nucleation site density are also correlated. (C) 2008 Elsevier Ltd. All rights reserved.
Saturated flow boiling heat transfer of R-410A and associated bubble characteristics in a narrow annular duct
(2011-11-01)
Chen, C. A.
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Li, K. W.
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Lie, Y. M.
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Lin, T. F.
;
機械工程學系
Experiments are conducted here to investigate how the channel size affects the R-410A saturated flow boiling heat transfer and associated bubble characteristics in a horizontal narrow annular duct. The gap of the duct is fixed at 1.0 and 2.0 mm in this study. The measured data indicate that the saturated flow boiling heat transfer coefficient increases with increasing refrigerant mass flux and saturated temperature and with a decrease in the gap size. Besides, raising the imposed heat flux can cause a significant increase in the boiling heat transfer coefficient. The results from the flow visualization show that the mean diameter of the bubbles departing from the heating surface decreases slightly with increasing refrigerant mass flux and saturated temperature. Moreover, the bubble departure frequency increases at reducing duct size and increasing mass flux. And at a high imposed heat flux many bubbles generated from the cavities in the heating surface tend to merge together to form big bubbles. Meanwhile, comparisons of the present heat transfer data for R-410A with R-407C and R-134a in the same duct and with some existing correlations are conducted. Furthermore, an empirical correlation for the present R-410A saturated flow boiling heat transfer data is proposed. (C) 2011 Elsevier Ltd. All rights reserved.
Saturated flow boiling heat transfer of refrigerant R-410A in a horizontal annular finned duct
(2007-04-01)
Hsieh, Y. Y.
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Lie, Y. M.
;
Lin, T. F.
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機械工程學系
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Department of Mechanical Engineering
An experiment is conducted here to investigate the saturated flow boiling heat transfer characteristics of ozone friendly refrigerant R-410A in a horizontal annular finned duct. Meanwhile the associated bubble characteristics in the duct are also inspected from the flow visualization. The experimental data are presented in terms of saturated flow boiling curves, boiling heat transfer coefficients and flow photos. In addition, empirical correlation equations for the saturated flow boiling heat transfer coefficient and mean bubble departure diameter are proposed. The saturated flow boiling curves show that boiling hysteresis is insignificant in the flow and the wall superheat needed for the onset of nucleate boiling is slightly affected by the refrigerant mass flux. Besides, the boiling curves are mainly affected by the imposed heat flux and refrigerant mass flux. Moreover, the measured saturated flow boiling heat transfer coefficient increases with the imposed heat flux and refrigerant mass flux. Furthermore, at a higher refrigerant mass flux the departing bubbles are smaller. (c) 2006 Elsevier Ltd. All rights reserved.
Subcooled flow boiling heat transfer of R-407C and associated bubble characteristics in a narrow annular duct
(2009-06-01)
Chen, C. A.
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Chang, W. R.
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Li, K. W.
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Lie, Y. M.
;
Lin, T. F.
An experiment is conducted here to investigate how the channel size affects the subcooled flow boiling heat transfer and the associated bubble characteristics of refrigerant R-407C in a horizontal narrow annular duct with the gap of the duct fixed at 1.0 and 2.0 mm. The measured boiling curves indicate that the temperature overshoot at ONB is relatively significant for the subcooled flow boiling of R-407C in the duct. Besides, the subcooled flow boiling heat transfer coefficient increases with a reduction in the duct gap, but decreases with an increase in the inlet liquid subcooling. Moreover, raising the heat flux imposed on the duct can cause a significant increase in the boiling heat transfer coefficients. However, the effects of the refrigerant mass flux and saturated temperature on the boiling heat transfer coefficient are slighter. Visualization of the subcooled flow boiling processes in the duct reveals that the bubbles are suppressed to become smaller and less dense by raising the refrigerant mass flux and inlet subcooling. Raising the imposed heat flux, however, produces positive effects on the bubble population, coalescence and departure frequency. Meanwhile, the present heat transfer data for R-407C are compared with the R-134a data measured in the same duct and with some existing correlations. We also propose empirical correlations for the present data for the R-407C subcooled flow boiling heat transfer and some quantitative bubble characteristics such as the mean bubble departure diameter and frequency and the active nucleation site density. (C) 2009 Elsevier Ltd. All rights reserved.