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In this study, we measured void fractions in vertical air–water bubbly flow using echo intensity and visualization techniques. To check the reliability of the echo intensity technique, void fractions obtained from the visualization technique was used. For echo intensity technique, ultrasonic wave amplitudes were acquired at different gas flow rates, and the amplitudes varied with gas flow rates. The averaged value of the amplitude kept decreasing with increasing gas flow rates. Images of bubbly flow were captured by a high-speed camera to evaluate void fractions. The images were processing to obtain area-averaged void fractions, then averaged over time to obtain time-averaged void fractions. The amplitudes obtained from the echo intensity and void fraction obtained from visualization can be correlated in the form of an exponential function: as the amplitude increases, the void fraction exponentially decreases.
Geoseong Na; Ji-Hwan Park; Hongrae Jo; DaeSeong Jo. Measuring void fraction in vertical air–water bubbly flow using echo intensity and visualization techniques. Progress in Nuclear Energy 2021, 136, 103731 .
AMA StyleGeoseong Na, Ji-Hwan Park, Hongrae Jo, DaeSeong Jo. Measuring void fraction in vertical air–water bubbly flow using echo intensity and visualization techniques. Progress in Nuclear Energy. 2021; 136 ():103731.
Chicago/Turabian StyleGeoseong Na; Ji-Hwan Park; Hongrae Jo; DaeSeong Jo. 2021. "Measuring void fraction in vertical air–water bubbly flow using echo intensity and visualization techniques." Progress in Nuclear Energy 136, no. : 103731.
This study aims to investigate the pressure changes, bubble dynamics, and flow physics inside the U- and C-shaped pipes with four different gravitational directions. The simulation is performed using a 1D centerline-based mesh generation technique along with a two-fluid model in the open-source software, OpenFOAM v.6. The continuity and momentum equations of the two-fluid model are discretized using the pressure-implicit method for the pressure-linked equation algorithm. The static and hydrostatic pressures in the two-phase flow were consistent with those of single-phase flow. The dynamic pressure in the two-phase flow was strongly influenced by the effect of the buoyancy force. In particular, if the direction of buoyancy force is the same as the flow direction, the dynamic pressure of the air phase increases, and that of the water phase decreases to satisfy the law of conservation of mass. Dean flows are observed on the transverse plane of the curve regions in both C-shaped and U-shaped pipes. The turbulent kinetic energy is stronger in a two-phase flow than in a single-phase flow. Using the 1D centerline-based mesh generation technique, we demonstrate the changes in pressure and the turbulent kinetic energy of the single- and two-phase flows, which could be observed in curve pipes.
Thinh Pham; Jichan Jeon; DaeSeong Jo; Sanghun Choi. Two-Phase Flow Simulations Using 1D Centerline-Based C- and U-Shaped Pipe Meshes. Applied Sciences 2021, 11, 2020 .
AMA StyleThinh Pham, Jichan Jeon, DaeSeong Jo, Sanghun Choi. Two-Phase Flow Simulations Using 1D Centerline-Based C- and U-Shaped Pipe Meshes. Applied Sciences. 2021; 11 (5):2020.
Chicago/Turabian StyleThinh Pham; Jichan Jeon; DaeSeong Jo; Sanghun Choi. 2021. "Two-Phase Flow Simulations Using 1D Centerline-Based C- and U-Shaped Pipe Meshes." Applied Sciences 11, no. 5: 2020.
The effects of boiling behaviors and critical heat flux (CHF) under rolling motion were investigated using different directions and magnitude of additional accelerations. The rolling conditions are amplitudes of 10° and 30° and periods of 10 s and 20 s. Vapor behaviors and CHF were opposite between the heated surface placed above and below the rolling axis. When the heated surface was placed above the rolling axis, the centrifugal acceleration acts away from the heated surface, pulling the vapor to detach. However, the centrifugal acceleration acts toward the heated surface when the heated surface was placed below the rolling axis, increasing vapor attachment to the heated surface. By placing the heated surface above the rolling axis, CHF enhanced approximately by 31% and were reduced to approximately 23% compared to when the heated surface was placed below the rolling axis as the platform rolls faster and slower, respectively.
Elvira F. Tanjung; Byoung Jae Kim; DaeSeong Jo. Effects on pool boiling critical heat flux (CHF) with different direction and magnitude of additional accelerations due to rolling. Annals of Nuclear Energy 2021, 154, 108095 .
AMA StyleElvira F. Tanjung, Byoung Jae Kim, DaeSeong Jo. Effects on pool boiling critical heat flux (CHF) with different direction and magnitude of additional accelerations due to rolling. Annals of Nuclear Energy. 2021; 154 ():108095.
Chicago/Turabian StyleElvira F. Tanjung; Byoung Jae Kim; DaeSeong Jo. 2021. "Effects on pool boiling critical heat flux (CHF) with different direction and magnitude of additional accelerations due to rolling." Annals of Nuclear Energy 154, no. : 108095.
Experiments were performed to understand the critical heat flux (CHF) mechanism on a vertical heated surface under rolling motion. The maximum rolling amplitude and periods were set to 30° and 10 and 30 s, respectively. Because of the rolling motion, there are two additional accelerations on the working fluid: centrifugal and tangential. When the platform rolled clockwise or counter-clockwise, combination of tangential acceleration and inclined surface has significant effects on boiling. When the platform rolled faster, early CHF occurred at a higher tangential acceleration. Boiling behaviors on the heated surface under the rolling conditions were compared with those under static conditions. Under static conditions, early CHF occurred at -30° inclination angle as the heated surface faced downward. Boiling behavior at -30° inclination angle under static condition was similar to that under rolling motion when the rolling platform rolled counter-clockwise at the angle between -23° and -27°, where CHF occurs.
Samah A. Albdour; Elvira F. Tanjung; DaeSeong Jo. Experimental study of critical heat flux mechanism on a vertical heated surface under rolling motion. Annals of Nuclear Energy 2020, 151, 107967 .
AMA StyleSamah A. Albdour, Elvira F. Tanjung, DaeSeong Jo. Experimental study of critical heat flux mechanism on a vertical heated surface under rolling motion. Annals of Nuclear Energy. 2020; 151 ():107967.
Chicago/Turabian StyleSamah A. Albdour; Elvira F. Tanjung; DaeSeong Jo. 2020. "Experimental study of critical heat flux mechanism on a vertical heated surface under rolling motion." Annals of Nuclear Energy 151, no. : 107967.
A statistical method based on temperature change with heat flux in a single-phase flow is proposed to determine the onset of nucleate boiling (ONB) incipience. Experiments under forced and natural convections were performed with different inlet temperatures. ONB wall temperatures determined by the proposed method were compared with that determined by the intersection method. The difference between ONB wall temperatures obtained by the proposed and intersection methods under forced convection was insignificant; however, the difference was significant under natural convection. In addition, ONB wall temperatures for forced and natural convections were compared for predictions by existing ONB correlations, namely, Bergles and Rohsenow (1964), Jens and Lottes (1951), and Thom et al. (1965). The results showed that the Jens-Lottes correlation overestimated the ONB incipience, whereas the Bergles-Rohsenow correlation underestimated the ONB incipience. However, the existing correlations are still applicable for predicting ONB wall temperatures at extremely low flow rates.
Ji-Hwan Park; Ilchung Park; DaeSeong Jo. Statistical method for determining the onset of nucleate boiling under forced and natural convections in a rectangular channel. Annals of Nuclear Energy 2020, 150, 107863 .
AMA StyleJi-Hwan Park, Ilchung Park, DaeSeong Jo. Statistical method for determining the onset of nucleate boiling under forced and natural convections in a rectangular channel. Annals of Nuclear Energy. 2020; 150 ():107863.
Chicago/Turabian StyleJi-Hwan Park; Ilchung Park; DaeSeong Jo. 2020. "Statistical method for determining the onset of nucleate boiling under forced and natural convections in a rectangular channel." Annals of Nuclear Energy 150, no. : 107863.
Experiments are conducted to study bubble flow behavior during the instability of subcooled boiling under uniform and non-uniform transverse heating. The non-uniform heat distribution introduces non-uniform bubble generation and condensation rates on the heated surface, which is different from the uniform heating. These bubble generation and condensation characteristics introduce a non-uniform local pressure distribution in the transverse direction, which creates an extra non-uniform pressure on the flowing bubbles. Therefore, different bubble flow behavior can be observed between uniform and non-uniform heating conditions. In the uniform heating, bubble velocity fluctuations are low, and the bubbles travel straight along the axial direction. In the non-uniform heating, more fluctuation in the bubble velocity occurs at low mass flow rate and high subcooled inlet temperatures, and reverse flow is observed. Additionally, the bubbles show a zigzag trajectory when they pass through the channel, which indicates the existence of cross flow in the transverse direction.
Omar S. Al-Yahia; Ho Joon Yoon; DaeSeong Jo. Experimental study of bubble flow behavior during flow instability under uniform and non-uniform transverse heat distribution. Nuclear Engineering and Technology 2020, 52, 2771 -2788.
AMA StyleOmar S. Al-Yahia, Ho Joon Yoon, DaeSeong Jo. Experimental study of bubble flow behavior during flow instability under uniform and non-uniform transverse heat distribution. Nuclear Engineering and Technology. 2020; 52 (12):2771-2788.
Chicago/Turabian StyleOmar S. Al-Yahia; Ho Joon Yoon; DaeSeong Jo. 2020. "Experimental study of bubble flow behavior during flow instability under uniform and non-uniform transverse heat distribution." Nuclear Engineering and Technology 52, no. 12: 2771-2788.
In the present study, the partial loss and distortion of turbine blades were acoustically detected while the turbine was rotating. An ultrasonic signal of a specific frequency (300 kHz) was transmitted in the form of continuous sine waves to the rotating turbine model. The signal was reflected on the turbine blade and received by a receiver. The amplitude of the given frequency component in the received signal was analyzed by signal processing. Because ultrasounds are attenuated easily when propagated into air and have a straight characteristic like light, the characteristics of the signals were examined by a quantitative test. The signal attenuation with respect to distance and the signal reduction by eccentricity were observed and compared with the experimental results. Partial loss decreased the sound reflection area; thus, the signal amplitude was reduced. The signal amplitude was inversely proportional to the size of the defect. Distortion caused larger eccentricity between the transmitter and the receiver. Weaker signals were detected with the more distorted blade. When the blade was distorted by more than 20dg, the amplitude of the signal decreased significantly. In short, defects of turbine blades cause a reduction in the acoustic signal. It was verified that acoustic diagnosis can be applied to detect the partial loss and distortion of turbine blades.
Hongrae Jo; Yeongmin Kim; DaeSeong Jo. Acoustically monitoring defects on rotating turbine blades. Journal of Mechanical Science and Technology 2020, 34, 1913 -1923.
AMA StyleHongrae Jo, Yeongmin Kim, DaeSeong Jo. Acoustically monitoring defects on rotating turbine blades. Journal of Mechanical Science and Technology. 2020; 34 (5):1913-1923.
Chicago/Turabian StyleHongrae Jo; Yeongmin Kim; DaeSeong Jo. 2020. "Acoustically monitoring defects on rotating turbine blades." Journal of Mechanical Science and Technology 34, no. 5: 1913-1923.
Vapor behavior and critical heat flux (CHF) mechanism under rolling motion were experimentally analyzed in the present study using a rolling platform system. It was observed that the combination of centrifugal and tangential acceleration affected the vapor behavior and occurrence of CHF. When the platform rolled more quickly, CHF occurred earlier, while CHF occurred every time the platform rolled back after reaching its maximum rolling amplitude. Therefore, the observations of vapor behavior focused on the period during which the platform rolled to its maximum rolling amplitude and then rolled back down. When the platform rolled up to its maximum amplitude, the vapor drifted slowly due to the effect of tangential acceleration, which acted in the opposite direction to the platform. On the other hand, as the amount of vapor grew, it readily detached from the heated surface due to the lower centrifugal acceleration, significantly reducing the size and duration of dry patches on the heated surface. When the platform rolled back down, the tangential acceleration pulled the vapor bubbles down because it acted in the same direction as the platform. Consequently, the vapor bubbles pushed against the bubbles, causing them to coalesce and produce larger dry patches on the heated surface. At the same time, the effect of centrifugal acceleration became stronger, which pushed the vapor towards the heated surface, resulting in vapor could not detach easily from the heated surface. This process led to a further increase in the size and duration of dry patches on the surface. When the platform rolled down, more of the heated surface was covered with a vapor layer for a longer time, hindering the fluid from replenishing the surface and triggering CHF.
Elvira F. Tanjung; DaeSeong Jo. Visualization study on pool boiling critical heat flux under rolling motion. International Journal of Heat and Mass Transfer 2020, 153, 119620 .
AMA StyleElvira F. Tanjung, DaeSeong Jo. Visualization study on pool boiling critical heat flux under rolling motion. International Journal of Heat and Mass Transfer. 2020; 153 ():119620.
Chicago/Turabian StyleElvira F. Tanjung; DaeSeong Jo. 2020. "Visualization study on pool boiling critical heat flux under rolling motion." International Journal of Heat and Mass Transfer 153, no. : 119620.
A new method for detecting a gas–water interface in a circular pipe is proposed. In the method, ultrasonic signals are used for non-intrusive measurement and three types of signal analyses are conducted: time-of-flight (TOF), local amplitude, and global amplitude analyses. Horizontal, 45° inclined, and vertical pipe configurations were used to verify the applicability of the proposed detection method. In the case of a horizontal pipe with an acoustic beam directed perpendicular to the water surface, TOF and amplitude analyses detect the water level. In the cases of a horizontal pipe with an acoustic beam directed parallel to the water surface, a 45° inclined pipe, and a vertical pipe, when the pipes were filled with water, TOF analysis was not applicable and amplitude analysis detects the water level. In conclusion, the gas–liquid interface in circular pipes could be analyzed qualitatively and quantitatively through the proposed non-intrusive acoustic method.
Hongrae Jo; Yong Jae Song; DaeSeong Jo. Non-intrusive detection of gas–water interface in circular pipes inclined at various angles. Annals of Nuclear Energy 2020, 139, 107267 .
AMA StyleHongrae Jo, Yong Jae Song, DaeSeong Jo. Non-intrusive detection of gas–water interface in circular pipes inclined at various angles. Annals of Nuclear Energy. 2020; 139 ():107267.
Chicago/Turabian StyleHongrae Jo; Yong Jae Song; DaeSeong Jo. 2020. "Non-intrusive detection of gas–water interface in circular pipes inclined at various angles." Annals of Nuclear Energy 139, no. : 107267.
Experimental investigations were attempted to simultaneously observe the vapor behaviors and critical heat flux under static and rolling conditions. From visualization results, vapor initiated, grew, and detached individually in a vertical direction from the static heated surfaces (at 10, 20, and 30°). While under rolling motion, initiated vapor grew, and interacted with each other, resulting in forming a wider dry spot on the heated surface. Also, it was observed that the vapor drifted upward and stayed on the heated surface longer compared to under static condition. The faster the platform rolls, the longer the vapor stay on the heated surface, significantly decreasing the CHF. On the other hand, as the platform rolls slower (at high rolling period), CHF increases. CHF was decreased with increasing maximum rolling amplitude and inclination angle under both conditions (static and rolling). CHF under rolling conditions was noticed to be lower than under static condition except at maximum rolling amplitude of 10°. The bubble departure frequency at a maximum rolling amplitude of 10° was the highest among all of rolling amplitudes, thereby enhancing the CHF. These results indicate that rolling motion significantly affects vapor behaviors and CHF.
Elvira F. Tanjung; Samah A. Albdour; Yeon Uk Jeong; DaeSeong Jo. Critical heat flux (CHF) in pool boiling under static and rolling conditions. Nuclear Engineering and Technology 2019, 52, 520 -529.
AMA StyleElvira F. Tanjung, Samah A. Albdour, Yeon Uk Jeong, DaeSeong Jo. Critical heat flux (CHF) in pool boiling under static and rolling conditions. Nuclear Engineering and Technology. 2019; 52 (3):520-529.
Chicago/Turabian StyleElvira F. Tanjung; Samah A. Albdour; Yeon Uk Jeong; DaeSeong Jo. 2019. "Critical heat flux (CHF) in pool boiling under static and rolling conditions." Nuclear Engineering and Technology 52, no. 3: 520-529.
Unexpected gas accumulation in a safety system of nuclear power plants can damage system elements and degrade cooling performance. To prevent the gas accumulation, it is important to define the mechanism of gas accumulation occurred by separation of dissolved gas. In the current research, it is investigated how the variations of temperature and pressure affect separation of dissolved gases and accumulation of non-condensable gases. The experimental study is conducted on three subjects; gas accumulations by variations of (1) pressure, (2) temperature and (3) order of temperature and pressure changes. Before performing each experiment, demineralized water is stabilized under the initial condition (20 °C and atmospheric pressure) for more than 24 h. In a closed system, the gas accumulation cannot be occurred by pressure change. By heating water, the gas accumulation is generated. When the water is kept in higher temperature, the more gases are accumulated. Even if the water is cooled back to the initial condition, the accumulated gas is remained more than 50%. By changing the order of temperature and pressure variations, the gas is accumulated. In results, it is found that the gas accumulation can be generated if the solubility of dissolved gas becomes lower than initial condition. Additionally, it is found that the gas already accumulated in the system is difficult to remove without additional venting process.
Hongrae Jo; Yong Jae Song; DaeSeong Jo. Observation of dissolved gas separation and accumulation in stationary water. Annals of Nuclear Energy 2019, 131, 305 -316.
AMA StyleHongrae Jo, Yong Jae Song, DaeSeong Jo. Observation of dissolved gas separation and accumulation in stationary water. Annals of Nuclear Energy. 2019; 131 ():305-316.
Chicago/Turabian StyleHongrae Jo; Yong Jae Song; DaeSeong Jo. 2019. "Observation of dissolved gas separation and accumulation in stationary water." Annals of Nuclear Energy 131, no. : 305-316.
A visualization study on boiling phenomena at various surface orientations was conducted to investigate the bubble behaviors and the critical heat flux (CHF) mechanism. The vapor behavior observed in this study indicates that the pool boiling can be categorized into three regions: upward facing (0° ≤ θ < 90°), vertical and near-downward facing (90° ≤ θ ≤ 165°), and downward facing (165° < θ ≤ 180°). In the upward-facing region, the vapor was generated and detached easily in the vertical direction of the heated surface. In the vertical and near-downward facing region, the vapor grew and drifted upward the surface in a wavy shape owing to the vapor flow. When the heater faced downward (165° < θ ≤ 180°), the vapor was trapped and blanketed the entire heated surface. According to the vapor behaviors at various inclination angles, the CHF decreased with the increase of the surface orientation from horizontal facing upward to downward. The vapor film thickness decreased as the surface orientation increased from 0° to 180°. The vapor velocity affected the distance between the two wavelength peaks of the vapor. Faster vapor flow yielded a shorter wavelength. Additionally, the CHF location was affected by the surface orientation owing to the vapor behavior. These results indicate that the surface orientation significantly affects the vapor behavior, CHF, CHF location, vapor velocity, wavelength, and maximum and minimum vapor thicknesses on a printed circuit board in a saturated water pool.
Elvira F. Tanjung; DaeSeong Jo. Surface orientation effects on bubble behaviors and critical heat flux mechanism in saturated water pool. International Journal of Heat and Mass Transfer 2018, 133, 179 -191.
AMA StyleElvira F. Tanjung, DaeSeong Jo. Surface orientation effects on bubble behaviors and critical heat flux mechanism in saturated water pool. International Journal of Heat and Mass Transfer. 2018; 133 ():179-191.
Chicago/Turabian StyleElvira F. Tanjung; DaeSeong Jo. 2018. "Surface orientation effects on bubble behaviors and critical heat flux mechanism in saturated water pool." International Journal of Heat and Mass Transfer 133, no. : 179-191.
This paper proposes a system for estimating the level of danger when a driver accesses the center console of a vehicle while driving. The proposed system uses a driver monitoring platform to measure the distance between the driver’s hand and the center console during driving, as well as the time taken for the driver to access the center console. Three infrared sensors on the center console are used to detect the movement of the driver’s hand. These sensors are installed in three locations: the air conditioner or heater (temperature control) button, wind direction control button, and wind intensity control button. A driver’s danger level is estimated to be based on a linear regression analysis of the distance and time of movement between the driver’s hand and the center console, as measured in the proposed scenarios. In the experimental results of the proposed scenarios, the root mean square error of driver H using distance and time of movement between the driver’s hand and the center console is 0.0043, which indicates the best estimation of a driver’s danger level.
Hyun-Soon Lee; Sunyoung Oh; DaeSeong Jo; Bo-Yeong Kang. Estimation of Driver’s Danger Level when Accessing the Center Console for Safe Driving. Sensors 2018, 18, 3392 .
AMA StyleHyun-Soon Lee, Sunyoung Oh, DaeSeong Jo, Bo-Yeong Kang. Estimation of Driver’s Danger Level when Accessing the Center Console for Safe Driving. Sensors. 2018; 18 (10):3392.
Chicago/Turabian StyleHyun-Soon Lee; Sunyoung Oh; DaeSeong Jo; Bo-Yeong Kang. 2018. "Estimation of Driver’s Danger Level when Accessing the Center Console for Safe Driving." Sensors 18, no. 10: 3392.
Experiments were performed to investigate bubble behaviors and pool boiling Critical Heat Flux (CHF) on a thin flat rectangular copper heater fabricated on Printed Circuit Board (PCB), at various inclination angles. The surface inclination angles were 0°, 45°, 90°, 135°, and 180°. Results showed the Onset of Nucleate Boiling (ONB) heat flux increased with increasing heater orientation from 0° to 90°, while early ONB occurred when the heater faced downwards (135° and 180°). The nucleate boiling was observed to be unstable at low heat flux (1–21% of CHF) and changed into typical boiling when the heat flux was above 21% of CHF. The result shows the CHF decreased with increasing heater orientation from 0° to 180°. In addition, the bubble departure diameter at the heater facing upwards (0°, 45°, and 90°) was more prominent compared to that of the heater facing downward (135°). The nucleation site density also observed increased with increasing heat flux. Moreover, the departed bubbles with larger size were observed to require a longer time to re-heat and activate new nucleation sites. These results proved that the ONB, CHF, and bubble dynamics were strongly dependent on the heater surface orientation.
Elvira F. Tanjung; Bernard O. Alunda; Yong Joong Lee; DaeSeong Jo. Experimental study of bubble behaviors and CHF on printed circuit board (PCB) in saturated pool water at various inclination angles. Nuclear Engineering and Technology 2018, 50, 1068 -1078.
AMA StyleElvira F. Tanjung, Bernard O. Alunda, Yong Joong Lee, DaeSeong Jo. Experimental study of bubble behaviors and CHF on printed circuit board (PCB) in saturated pool water at various inclination angles. Nuclear Engineering and Technology. 2018; 50 (7):1068-1078.
Chicago/Turabian StyleElvira F. Tanjung; Bernard O. Alunda; Yong Joong Lee; DaeSeong Jo. 2018. "Experimental study of bubble behaviors and CHF on printed circuit board (PCB) in saturated pool water at various inclination angles." Nuclear Engineering and Technology 50, no. 7: 1068-1078.
It is necessary to accurately predict the minimum point of pressure drop to ensure the safety of nuclear reactors. However, the non-uniform heat flux distribution along the transverse direction is encountered when the plate-type nuclear fuels are used. This study shows the effect of a transversely non-uniform heat flux on the minimum point of the pressure drop. The pressure drop-flow rate curve under the non-uniform heat flux was obtained by the experiment, and the trend of curve was different with the one of uniform heat flux case. Under the non-uniform heat flux, even when the inlet mass flow rate decreased, the value of the pressure drop was constant for a while with the development of a two-phase flow. With further reduction of inlet mass flow rate, the pressure drop started to decrease until the minimum point of the pressure drop was reached. Moreover, the inlet mass flow rate at the minimum point of pressure drop is much lower than that in the uniform heat flux case. For a detail analysis, the numerical approach is proposed along with the application of multi-channel concept. A single narrow rectangular channel is divided along the transverse direction, and the heat flux is given non-uniformly to the divided channels. Although the pressure drop is separately calculated for each divided channel, the mass is transferred between the channels. In the calculation, the mass flow rate is non-uniformly distributed in the transverse direction. If the mass flow rate is uniformly distributed, the non-uniform heat flux causes an unbalanced pressure drop because of the non-uniform distribution of void fraction. As a result, at the edges where the void fraction is high, the mass flow rate is transferred to the middle of channel to balance the pressure drop in transverse direction. When the void fraction in the middle becomes significantly large, the minimum point of the pressure drop can be obtained.
Taewoo Kim; Yong Jae Song; Omar S. Al-Yahia; DaeSeong Jo. Prediction of the minimum point of the pressure drop in a narrow rectangular channel under a transversely non-uniform heat flux. Annals of Nuclear Energy 2018, 122, 163 -174.
AMA StyleTaewoo Kim, Yong Jae Song, Omar S. Al-Yahia, DaeSeong Jo. Prediction of the minimum point of the pressure drop in a narrow rectangular channel under a transversely non-uniform heat flux. Annals of Nuclear Energy. 2018; 122 ():163-174.
Chicago/Turabian StyleTaewoo Kim; Yong Jae Song; Omar S. Al-Yahia; DaeSeong Jo. 2018. "Prediction of the minimum point of the pressure drop in a narrow rectangular channel under a transversely non-uniform heat flux." Annals of Nuclear Energy 122, no. : 163-174.
Onset of Nucleate Boiling (ONB) in a narrow rectangular channel was experimentally studied under transversely non-uniform and uniform heating conditions. The experiment was performed under various mass fluxes and inlet subcooling conditions. The behavior of the bubbles was recorded using a high-speed camera, and was analyzed using an image processing technique. In the case of uniform heat flux, the wall temperature was uniformly distributed in the transverse direction. In the case of non-uniform heat flux, the wall temperature had the lowest value in the middle of the heated surface, and increased along the transverse direction toward the edges. At the same mass flux and inlet subcooling temperature, the thermal power at the ONB under non-uniform heat flux was lower than that under uniform heat flux. However, the local heat flux and wall temperature at the ONB were similar at both heating conditions. In the subcooled boiling region, it was found that the boiling heat transfer under non-uniform heat flux was lower than that under uniform heat flux. Additionally, the slope of the wall temperature-thermal power curve after the ONB was higher in the non-uniform heat flux case. Using the results elicited from image processing, the evaporation and quenching heat transfers were evaluated to analyze the differences in boiling heat transfers. The boiling heat transfer was less affected by evaporation and quenching in the case of non-uniform heat flux.
Taewoo Kim; Omar S. Al-Yahia; DaeSeong Jo. Experimental study on the Onset of Nucleate Boiling in a narrow rectangular channel under transversely non-uniform and uniform heating. Experimental Thermal and Fluid Science 2018, 99, 158 -168.
AMA StyleTaewoo Kim, Omar S. Al-Yahia, DaeSeong Jo. Experimental study on the Onset of Nucleate Boiling in a narrow rectangular channel under transversely non-uniform and uniform heating. Experimental Thermal and Fluid Science. 2018; 99 ():158-168.
Chicago/Turabian StyleTaewoo Kim; Omar S. Al-Yahia; DaeSeong Jo. 2018. "Experimental study on the Onset of Nucleate Boiling in a narrow rectangular channel under transversely non-uniform and uniform heating." Experimental Thermal and Fluid Science 99, no. : 158-168.
Kyung-O Kim; Hae Sun Jeong; DaeSeong Jo. Numerical analysis for multi-group neutron-diffusion equation using Radial Point Interpolation Method (RPIM). Annals of Nuclear Energy 2017, 99, 193 -198.
AMA StyleKyung-O Kim, Hae Sun Jeong, DaeSeong Jo. Numerical analysis for multi-group neutron-diffusion equation using Radial Point Interpolation Method (RPIM). Annals of Nuclear Energy. 2017; 99 ():193-198.
Chicago/Turabian StyleKyung-O Kim; Hae Sun Jeong; DaeSeong Jo. 2017. "Numerical analysis for multi-group neutron-diffusion equation using Radial Point Interpolation Method (RPIM)." Annals of Nuclear Energy 99, no. : 193-198.
Highlights•Effect of oxide layer on fuel temperature is investigated for mini fuel plates.•The highest power is released from the BOC during the first cycle.•The growth of the oxide layer is predicted with pH ranging from 5 to 7.•The maximum fuel temperature is not observed when the power is the highest. AbstractThe effect of the oxide layer formed on the mini fuel plates is studied to evaluate fuel centerline temperature. For a part of U-Mo fuel qualification program, mini fuel plates, double-stacked as upper and lower plates, will be irradiated in the HANARO reactor for four cycles. In the present study, fuel performance and thermal hydraulic behavior during irradiation are numerically investigated using the MCNP and TMAP codes. The power released from the mini fuel plates is estimated using the MCNP code. From the neutronic analysis results, it is observed that the lower plate at the BOC during the 1st cycle releases the highest power, and the power gradually decreases during the irradiation test. The growth of the oxide layer thickness during the irradiation test is predicted using many correlations with various pH values ranging from 5.0 to 7.0. The pH value in the HANARO reactor is controlled between 5.7 and 6.2, and the oxide layer thickness is predicted by the Boehmite model for these two pH values. The oxide layer thickness predicted using the other correlations are bounded by these two predicted values. The maximum oxide layer thickness at the end of irradiation is approx. 9 and 68 μm with pH of 5.7 and 6.2, respectively. The Pawel model with a rate factor of 16 predicts the maximum oxide layer as 25 μm. Using the predictions of the oxide layer thickness, the centerline fuel temperatures are evaluated using the TMAP code. The maximum fuel temperature is not observed when the power released from the fuel is the highest. Because the temperature rise through the oxide layer is significant, the oxide layer thickness must be considered in the fuel temperature evaluation. The oxide formation saturates with time, and the fuel reaches the maximum temperature at the end of the saturation. After the maximum fuel temperature is reached, it starts decreasing, because the power decreases.
Kwon-Yeong Lee; Young-Wook Tahk; DaeSeong Jo. Effect of oxide layer growth on fuel temperature of mini fuel plates. Progress in Nuclear Energy 2016, 91, 153 -158.
AMA StyleKwon-Yeong Lee, Young-Wook Tahk, DaeSeong Jo. Effect of oxide layer growth on fuel temperature of mini fuel plates. Progress in Nuclear Energy. 2016; 91 ():153-158.
Chicago/Turabian StyleKwon-Yeong Lee; Young-Wook Tahk; DaeSeong Jo. 2016. "Effect of oxide layer growth on fuel temperature of mini fuel plates." Progress in Nuclear Energy 91, no. : 153-158.
An appropriate method for selecting the axial power distribution that results in the most conservative thermal margins was developed in this study. Nuclear physics calculations provided axial power distributions with various shapes based on the core states and cycles. A total of 17 cycles were required to reach the equilibrium core from the initial core. The axial power distributions were sorted based on the power peaking and sum-to-peak (STP) values. In the present study, three different power peaking criteria were used to sort the axial power distributions: the upper 50%, upper 25%, and upper 10%. After the first sorting based on the power peaking, the axial power distributions were grouped based on the power peak location in the axial direction. In each group, the axial power distribution with the highest STP was chosen for thermal margin analyses. In addition, the axial power distributions in the hottest channel and fuel assembly from the initial to the equilibrium core were obtained. Since the axial power distributions in the hottest channel and fuel assembly were bounded by the axial power distribution with the upper 10% FQ, the thermal hydraulic analysis results gave the more conservative thermal margins using the selection method presented in this study. The Onset of Nucleate Boiling (ONB) temperature margin with the upper 10% FQ was 22.5 °C, but it was 25.0 °C for the hottest channel. Therefore, the axial power distribution used for thermal hydraulic and safety analyses should be selected using the appropriate method presented in this study.
Kyung-O Kim; Chang Je Park; DaeSeong Jo. RETRACTED: A new strategy to select axial power distribution for thermal hydraulic analysis. Annals of Nuclear Energy 2016, 88, 265 -271.
AMA StyleKyung-O Kim, Chang Je Park, DaeSeong Jo. RETRACTED: A new strategy to select axial power distribution for thermal hydraulic analysis. Annals of Nuclear Energy. 2016; 88 ():265-271.
Chicago/Turabian StyleKyung-O Kim; Chang Je Park; DaeSeong Jo. 2016. "RETRACTED: A new strategy to select axial power distribution for thermal hydraulic analysis." Annals of Nuclear Energy 88, no. : 265-271.
To predict local interfacial area in a packed bed under the trickling flow, a wavy annular flow model was developed by introducing the shape of waves in a thin liquid film. The trickling flowin a packed bed was approximated by an annular flow through a number of equivalent channels in which the continuous gas and liquid were completely separated by a wavy interface. Film thicknesses were measured by parallel wire probes to estimate the wave structure on the interface. By integrating the interfacial areas over a certain time period, the time-averaged local interfacial area was evaluated from a low to high interaction flow regime: 1) from trickling to bubbly flow and 2) from trickling to pulsing flow. The interfacial area predicted by the wavy annular flow model in the trickling flow was moderately higher than those predicted with the empirical correlations developed by others. The results show that the interfacial area increases more significantly as the flow regime changes from trickling to pulsing flow than that increases as the flow regime changes from trickling to bubbly flow. As a result, the wave structure on the interface should be considered to predict more accurate interfacial area in a packed bed.
DaeSeong Jo. Hydrodynamic model of interfacial area for trickling flow in a packed bed. Journal of Mechanical Science and Technology 2016, 30, 171 -178.
AMA StyleDaeSeong Jo. Hydrodynamic model of interfacial area for trickling flow in a packed bed. Journal of Mechanical Science and Technology. 2016; 30 (1):171-178.
Chicago/Turabian StyleDaeSeong Jo. 2016. "Hydrodynamic model of interfacial area for trickling flow in a packed bed." Journal of Mechanical Science and Technology 30, no. 1: 171-178.