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Flow Regime Transition Criteria for Vertical Downward Two-Phase Flow in Rectangular Channel
Vikrant Siddharudh Chalgeri,정지환 한국원자력학회 2022 Nuclear Engineering and Technology Vol.54 No.2
Narrow rectangular channels are employed in nuclear research reactors that use plate-type nuclear fuels,high heat-flux compact heat exchangers, and high-performance micro-electronics cooling systems. Twophase flow in narrow rectangular channels is important, and it needs to be better understood because itis considerably different than that in round tubes. In this study, mechanistic models were developed forthe flow regime transition criteria for various flow regimes in co-current air-water two-phase flow forvertical downward flow inside a narrow rectangular channel. The newly developed criteria werecompared to a flow regime map of downward air-water two-phase flow inside a narrow rectangularchannel with a 2.35-mm gap width under ambient temperature and pressure conditions. Overall, theproposed model showed good agreement with the experimental dat
Chalgeri, Vikrant Siddharudh,Jeong, Ji Hwan Elsevier 2019 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.132 No.-
<P><B>Abstract</B></P> <P>Better understanding of two-phase flow in narrow rectangular channels is important because it is considerably different from that in round tubes. Two-phase flow in narrow rectangular channels is invariably employed in most of the research reactors that use plate-type nuclear fuels around the world, high-heat-flux compact heat exchangers, and high-performance micro-electronics. In this study, an objective attempt was made to identify and classify various flow regimes in co-current air–water two-phase flow for vertical upward and downward direction flow inside a narrow rectangular channel. The void fraction and differential pressure data of the flow were measured. Flow regimes were identified based on visual observation, mean void fraction, and differential pressure data. A high-speed camera was used to capture images, and the void fraction was measured and analyzed by the electrical impedance method. In addition, digital image analysis was conducted, and differential pressures were measured using differential pressure transducers. Four flow patterns were identified for the vertical upward flow, and seven flow patterns were identified for the vertical downward flow in a narrow rectangular channel.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Flow regimes were identified for air–water flow in narrow rectangular channel. </LI> <LI> Experimental test section is 780 mm long, 66.6 mm wide and 2.35 mm in breadth. </LI> <LI> Flow patterns for vertical upward and downward flows were identified. </LI> <LI> Flow regime identification by visualization, void fraction, pressure difference. </LI> </UL> </P>
Kim, Tae Hyeon,Chalgeri, Vikrant Siddharudh,Yoon, Woosung,Yun, Byong Jo,Jeong, Ji Hwan Elsevier 2018 Annals of nuclear energy Vol.114 No.-
<P><B>Abstract</B></P> <P>Flow patterns in downward air–water two-phase flows in a narrow rectangular channel were visually observed. A test section was constructed using transparent acrylic plate with a test channel 2.35 mm thick, 66.6 mm wide, and 780 mm long. The experiments determined that at high liquid velocity the flow patterns for downward flow are similar to those observed in upward flow. However, at low liquid velocity some significant differences were observed between downward and upward flows. The new flow patterns, falling film flow, large-bubbly flow, and intermediate flow, were identified in the low liquid velocity region, where buoyancy force is influential. A flow regime map for downward flow in a narrow rectangular channel was constructed using the experimental data and analyses.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Plate type nuclear fuel has flow passage of narrow rectangular channel. </LI> <LI> The channel is 2.35 mm thick 66.6 mm wide and 780 mm long. </LI> <LI> Flow patterns of downward air-water two-phase flows are visually observed. </LI> <LI> The new flow patterns are identified and a flow regime map is constructed. </LI> </UL> </P>