임재환 교수

Abstract In this study, the two-phase pressure drop of a one-side heated swirl tube (twist ratio = 3, 5) was experimentally studied. If the a heat flux is gradually increased, the vapor blocks the flow path, thus leading to an increase in the differential pressure. As the inset sub-cooling and mass flow rate increase, the vapor is removed by condensation more rapidly, and thus, the rate of increase of differential pressure is reduced. From the evaluation of the prediction performance of the exis

Herein, the heat-transfer characteristics of the subcooled flow boiling of swirl tubes are evaluated experimentally under one-side high heat load conditions. As the twist ratio of the tape decreased and the flow rate increased, the forced convective heat transfer was enhanced; thus, the single-phase heat transfer was enhanced, and the onset of nucleate boiling (ONB) heat flux increased. As the degree of subcooling increased, the ONB heat flux increased because of the faster condensation rate. As

Abstract In this study, the onset of flow instability (OFI) of the hypervapotron channel was experimentally explored under one-side high heat load conditions. The OFI was detected based on the heat flux ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msup> <mml:mrow> <mml:mi>q</mml:mi> </mml:mrow> <mml:mrow> <mml:mo accent="true">″</mml:mo> </mml:mrow> </mml:msup> </mml:math> ) where the standard deviation of the inlet pressure rapidly increased. Moreover, the

In this study, the heat transfer characteristics of one-side heated screw tubes were analyzed using subcooled flow boiling experiments. The experiments were performed until the critical heat flux was reached, while the applied heat flux was gradually increased. Subsequently, the boiling curves derived from the experimental results were divided into partial nucleate boiling (PDB) and fully developed nucleate boiling (FDB) regimes. As the flow rate increases, the forced convective heat transfer is

In this study, the two-phase pressure drop in a one-sided high-heat-loaded screw tube was analyzed under subcooled flow boiling conditions. When the loaded heat flux is gradually increased under one-sided heating conditions, although the pressure drop changes slightly in the single phase, it starts to increase when loading above the onset of significant void (OSV) heat flux. The effect of system parameters on the two-phase pressure drop in relation to the change of heat transfer mechanism or flu

Abstract As the hypervapotron (HV) heat sink is used to cool many areas inside the fusion tokamak, it is essential to understand its heat transfer performance to calculate the thermal efficiency of the power generation system. Therefore, in this study, the single-phase (SP) heat transfer performance of HV heat sink was evaluated through sub-cooled flow boiling experiments under one-side high-heat load conditions. When vapor is generated inside the heat sink, flow instability and a potential risk

Abstract For the cooling system of the future, nuclear fusion tokamak, to operate stably and continuously, it is important to identify potential hazards that may occur in the system in advance. Among the various hazards associated with the nuclear fusion tokamak, the onset of nucleate boiling (ONB) is a point at which the heat-transfer mechanism changes dramatically and is a crucial factor that must be addressed. In particular, the equipment inside the tokamak is loaded with a heat flux of sever

Abstract The heat removal capacity of a flat heat sink was studied using subcooled flow boiling experiments, to address the thermal peaking problem. Based on the Bowring criteria, the boiling curve is divided into a partially developed nucleate boiling regime (PDB) and fully developed nucleate boiling regime (FDB), and the existing heat transfer correlations for each flow regime are evaluated. In the PDB regime, the Baburajan correlation exhibited the highest prediction rate with an average erro

Abstract In order to stably operate the equipment inside the tokamak, which is loaded with a heat flux of several MW m −2 under the one-side heating condition, it is necessary to thoroughly prepare for various thermal engineering limits that may occur under the high heat flux load condition. In this study, we have experimentally explored critical heat flux (CHF) and onset of flow instability (OFI), which are considered potential threats in a DEMO fusion power plant. Specifically, the effect of s

Abstract The onset of nucleate boiling (ONB) is the point at which the heat transfer mechanism in fluids changes and is one of the thermo-hydraulic factors that must be considered when establishing a cooling system operation strategy. Because the high heat flux of several MW m −2 , which is loaded within a tokamak, is applied under a one-side heating condition, it is necessary to determine a correlative relation that can predict ONB under special heating conditions. In this study, the ONB of a o

Abstract In this study, the onset of flow instability (OFI) heat flux of a one-side heated swirl tube is experimentally investigated. The OFI heat flux means the minimum heat flux that can cause flow instability by the vapor generated in the flow path. An analysis of the effect of system parameters on the OFI heat flux indicates that as the pressure increases, the bubble size decreases. Therefore, the void fraction decreases and, consequently, the OFI heat flux tends to increase. Similarly, the

The effect of the hypervapotron (HV) fin angle on heat transfer was analyzed through visualization experiments and subcooled flow boiling experiments. An HV channel with a fin angle of 45 deg had a higher onset-of-nucleate-boiling heat flux than the typical HV channel. Additionally, as the heat flux increased, the bubble-sliding effect caused by the tilted fin was visualized, and it was observed that the vapor inside the fin was agglomerated by the sliding flow and driven into the side slot. Whe