• Nuclear Engineering and Technology
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• v.54 no.3
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• pp.860-866
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• 2022

An accurate prediction of the pressure drop along the flow paths is crucial in the design of advanced passive systems cooled by heavy liquid metal coolants. To date, a generic pressure drop correlation over spacer grids by Rehme has been applied extensively, which was obtained from substantial experimental data with multiple types of components. However, a few experimental studies have reported that the correlation may give large discrepancies. To provide a more reliable correlation for ring-type spacer grids, the current numerical study aims at figuring out the most critical factor among four hypothetical parameters, namely the flow area blockage ratio, number of fuel rods, type of fluid, and thickness of the spacer grid in the flow direction. Through a set of computational fluid dynamics simulations, we observed that the flow area blockage ratio dominantly influences the pressure loss characteristics, and thus its dependence should be more emphasized, whereas the other parameters have little impact. Hence, we suggest a new correlation for the drag coefficient as C_B = C_ν,m/ε^2.7, where C_ν,m is formulated by a nonlinear fit of simulation data such that C_ν,m = -11.33 ln(0.02 ln(Re_b)).

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.12
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• pp.1681-1691
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• 2002

The heat transfer and pressure drop characteristics of heat exchangers with louver fins were experimentally investigated. The samples had small fin pitches (1.0 mm to 1.4 mm), and experiments were conducted up to a very low frontal air velocity (as low as 0.3 m/s). At a certain Reynolds number (critical Reynolds number), the flattening of the heat transfer coefficient curve was observed. The critical Reynolds number was insensitive to the louver angle, and decreased as the louver pitch to fin pitch ratio (L$_{p}$F$_{p}$) decreased. Existing correlations on the critical Reynolds number did not adequately predict the data. It is suggested that, for proper assessment of the heat transfer behavior, the louver pattern in addition to the flow characterization need to be considered. The heat transfer coefficient increased as the fin pitch decreased. At low Reynolds numbers, however, the trend was reversed. Possible explanation is provided considering the louver pattern between neighboring fins. Different from the heat transfer coefficient, the friction factor did not show the flattening characteristic. The reason may be attributed to the form drag by louvers, which offsets the decreased skin friction at a low Reynolds number. The friction factor increased as the fin pitch decreased and the louver angle increased. A new correlation predicted 92% of the heat transfer coefficient and 90% of the friction factor within $\pm$10%.10%.

• Geomechanics and Engineering
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• v.25 no.4
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• pp.283-294
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• 2021

This paper presents a rigorous solution for spherical cavity expansion in unsaturated soils under constant suction condition. The hydraulic behavior that describes the saturation-suction relationship is modeled by a void ratio-dependent soil-water characteristic curve, which allows the hydraulic behavior to fully couple with the mechanical behavior that is described by an extended critical state soil model for unsaturated soil through the specific volume. Considering the boundary condition and introducing an auxiliary coordinate, the problem is formulated to a system of first-order differential equations with three principal stress components and suction as basic unknowns, which is solved as an initial value problem. Parameter analyses are conducted to investigate the effects of suction and the overconsolidation ratio on the overall expansion responses, including the pressure-expansion response, the distribution of the stress components around the cavity, and the stress path of the soil during cavity expansion. The results reveal that the expansion pressures and the distribution of the stress components in unsaturated soils are generally higher than those in saturated soils due to the existence of suction.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.1
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• pp.88-94
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• 2002

For the pressurized propellant supply system of liquid rocket, feed pressure is determined with respect to the chamber pressure of normal combustion state. However, during ignition period the initial chamber pressure is atmosopheric. This may cause overflow, hard-start and even critical damage for the engine. This paper proposes an improved propellant feed system for the stable combustion of liquid rocket. The proposed system utilizes the cavitating venturi to provide stable mass flow rate. Cavitating venturi offers unique flow control capabilities at normal and abnormal combustion state, because flow rate is soley dependent on the upstream absolute pressure and fluid properties, but independent on th downstream condition. Experimental variables are propellant feed pressure and chamber pressure. The effectiveness of cavitating venturi increased when the ratio of actual feed pressure to the cavitating venturi design pressure is increased. It is also found that Kerosene if more effective to supply stable mass flow rate than LOx.

• Tuberculosis and Respiratory Diseases
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• v.82 no.4
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• pp.335-340
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• 2019

Background: Snoring is the cardinal symptom of obstructive sleep apnea (OSA). Snoring and upper airway obstruction associated with major oxygen desaturation may occur in populations undergoing flexible bronchoscopy. Methods: To evaluate the prevalence of patients at a high risk of having OSA among patients undergoing bronchoscopy with sedation and to investigate whether snoring during the procedure predicts patients who are at risk of OSA, we prospectively enrolled 517 consecutive patients who underwent the procedure with moderate sedation. Patients exhibiting audible snoring for any duration during the procedure were considered snorers. The STOP-Bang (Snoring, Tiredness, Observed apnea, high blood Pressure-Body mass index, Age, Neck circumference and Gender) questionnaire was used to identify patients at high (score ${\geq}3$ out of 8) or low risk (score <3) of OSA. Results: Of the 517 patients, 165 (31.9%) snored during bronchoscopy under sedation. The prevalence of a STOP-Bang score ${\geq}3$ was 61.9% (320/517), whereas 200 of the 352 nonsnorers (56.8%) and 120 of the 165 snorers (72.7%) had a STOP-Bang score ${\geq}3$ (p=0.001). In multivariable analysis, snoring during bronchoscopy was significantly associated with a STOP-Bang score ${\geq}3$ after adjustment for the presence of diabetes mellitus, chronic obstructive pulmonary disease, chronic kidney disease, and stroke (adjusted odds ratio, 1.91; 95% confidence interval, 1.26-2.89; p=0.002). Conclusion: Two-thirds of patients undergoing bronchoscopy with moderate sedation were at risk of OSA based on the screening questionnaire. Snoring during bronchoscopy was highly predictive of patients at high risk of OSA.

• Korean Journal of Rural Living Science
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• v.7 no.1
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• pp.23-29
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• 1996

The purpose of this study is to observe the relationship between smoking and control factors to blood pressure, such as sodium and potassium levels of dietary intake and serum in 67 rural university male students(smoker: 35 persons, non smoker: 32 persons). 3-day dietary record and blood sampling were conducted for measurements of the levels of dietary intake and serum. The results were as follows: 1) There are no significance between smokers and non-smokers in height, weight, and BMI. 2) Mean systolic and diastolic blood pressure of smokers and non-smokers were $131.33\pm93.75mmHg, \;119.37\pm80.62mmHg, $ respectively. Blood pressure of smoker was higher than that of non-smokers(p＜0.05). 3) There was no significant difference between smoker and non smoker in dietary potassium intake but dietary sodium intake and Na/K ratio of smoker were higher than those of non-smokers(p＜0.05, p＜0.05). And significant correlation was found between dietary sodium intake and blood pressure of smokers(p＜0.05). 4) Smokers of optimum gustation of salt(0.52%) was higher than that of non-smokers(0.49%). Even though blood pressure of smokers was not critical level, if they smoke continuosely until middle age, their blood pressure will be increased by smoking. The results of this study suggest that no smoking education program for smokers including the information about desirable food habits for prevention of hypertension should be developed.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.35 no.6
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• pp.563-567
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• 2002

Developing base data on luring fish schools into netting position by the use of underwater audible sound on japanese parrot fish Oplegnathus fasciatus found in the coastal waters of Jeju Island, S. Korea. Auditory threshold was determined by the heartbeat condition technique using pure tones coupled with a delayed electric shock. The audible range of japanese parrot fish extended from 80 Hz to 500 Hz with a peak sensitivity at 200 Hz. The mean auditory thresholds at the frequencies of 80 Hz, 100 Hz, 200 Hz,300 Hz and 500 Hz were 104 dB, 95 dB, 91 dB, 99 dB and 113 dB, respectively. As the frequency became higher than 200 Hz, the auditory threshold increased almost linearly with increasing frequency. Critical ratios of fishes measured in the presence of masking noise in the spectrum level range of 69$\~$78 dB (0 dB re 1$\mu$Pa/$\sqrt{Hz}$) ranged from 21 dB to 40 dB at test frequencies. The noise spectrum level at the start of masking was about 70 dB within the test frequency range. The sound pressure level of 100$\~$200 Hz recognized by japanese parrot fish under the ambient noise is above 91 dB and the critical ratio for them is above 21 dB.

• Geotechnical Engineering
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• v.9 no.4
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• pp.37-44
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• 1993

Model pile tests in calibration chamber are performed in order to study the two factors that the pile bearing capacity is significantly influenced by. Those factors are the critical depth concept and the scale effect caused by pile diameters. Firstly, the predicted values of end bearing capacity from the various static formulae were compared with the measured ones from model pile tests. Secondly, the critical depth concept and the scale effect were investigated by using two different soil conditions in a series of calibration chamber tests : the one is uniform sand : and the other is weathered granites overlayered by sand. Main results obtained from the model tests can be summarized as follows : (1) The end bearing capacity was increased with pile penetration depth up to penetration ratio of 7 to 8 when the cell pressure is high, and the critical depth was observed in the current chamber tests with uniform sand layer , (2) The predicted end bearing capacities were mostly lager than the measured, and it was found that the differences between the predicted and the measured values became smaller as the pile penetration ratio was increased : (3) The end bearing capacity of the small diameter pile in weathered granites layer was mostly less than that of the larger pile, while in uniform sand layer it was vice.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.45-50
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• 2001

This experimental study concerns the characteristics of a transitional flow in a concentric annulus with a diameter ratio of 0.52, whose outer cylinder is stationary and inner one rotating. The pressure losses and skin-friction coefficients have been measured for the fully developed flow of a 0.2 % aqueous solution of sodium carbomethyl cellulose (CMC) at a inner cylinder rotational speed of $0{\sim}600$ rpm. The transitional flow has been examined by the measurement of pressure losses, to reveal the relation of the Reynolds numbers with the skin-friction coefficients, in the laminar and transitional flow regimes. The occurrence of transition has been checked by the gradient change of pressure losses and skin-friction coefficient with respect to the Reynolds numbers. The increasing rate of skin-friction coefficient due to the rotation is uniform for laminar flow regime, whereas it is suddenly reduced for transitional flow regime and, then, it is gradually declined for turbulent flow regime. Consequently, the critical(axial-flow) Reynolds number decrease as the rotational speed increases. Thus, the rotation of inner cylinder promotes the early occurrence of transition due to the onset of taylor vortices.

• Journal of Sensor Science and Technology
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• v.27 no.6
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• pp.397-402
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• 2018

Proper seat design is critical to the safety, comfort, and ergonomics of automotive driver's seats. To ensure effective seat design, quantitative methods should be used to evaluate the characteristics of automotive seats. This paper presents a system that is capable of simultaneously monitoring body pressure distribution and surface deformation in a textile material. In this study, a textile-based capacitive sensor was used to detect the body pressure distribution in an automotive seat. In addition, a strain gauge sensor was used to detect the degree of curvature deformation due to high-pressure points. The textile-based capacitive sensor was fabricated from the conductive fabric and a polyurethane insulator with a high signal-to-noise ratio. The strain gauge sensor was attached on the guiding film to maximize the effect of its deformation due to bending. Ten pressure sensors were placed symmetrically in the hip area and six strain gauge sensors were distributed on both sides of the seat cushion. A readout circuit monitored the absolute and relative values from the sensors in realtime, and the results were displayed as a color map. Moreover, we verified the proposed system for quantifying the body pressure and fabric deformation by studying 18 participants who performed three predefined postures. The proposed system showed desirable results and is expected to improve seat safety and comfort when applied to the design of various seat types. Moreover, the proposed system will provide analytical criteria in the design and durability testing of automotive seats.