• 대한기계학회논문집B
• /
• 제41권1호
• /
• pp.1-8
• /
• 2017

대기압 하에서 포화 상태를 유지하는 물의 내부에 잠긴 탠덤 튜브에 적용하기 위한 실험적 상관식을 새롭게 개발하였다. 상관식은 다발효과를 계산하기 위한 것으로 실험에서 측정한 값과 최소자승법을 사용하여 결정하였다. 상관식의 적절함을 평가하기 위해 통계분석을 수행하였다. 상관식은 실험값을 ${\pm}8%$ 범위 내에서 잘 예측함을 확인하였다. 상관식의 적용 범위는 피치=28.5~114mm, 방위각=$0^{\circ}{\sim}90^{\circ}$, 경사각=$0^{\circ}{\sim}90^{\circ}$, 상부 및 하부 튜브 열유속=$0{\sim}120kW/m^2$이다.

• 한국원자력학회:학술대회논문집
• /
• 한국원자력학회 1995년도 추계학술발표회논문집(1)
• /
• pp.358-363
• /
• 1995

A study on passive cooling systems for concrete containment of advanced pressurized water reactors has been performed. The proposed passive containment cooling system (PCCS) consist of (1) condenser units located inside containment, (2) a steam condensing pool outside containment at higher elevation, and (3) downcommer/riser piping systems which provide coolant flow paths. During an accident causing high containment pressure and temperature, the steam/air mixture in containment is condensed on the outer surface of condenser tubes transferring the heat to coolant flowing inside tubes. The coolant transfers the heat to the steam condensing pool via natural circulation due to density difference. This PCCS has the following characteristic: (1) applicable to concrete containment system, (2) no limitation in plant capacity expansion, (3) efficient steam condensing mechanism (dropwise or film condensation at the surface of condenser tube), and (4) utilization of a fully passive mechanism. A preliminary conceptual design work has been done based on steady-state assumptions to determine important design parameter including the elevation of components and required heat transfer area of the condenser tube. Assuming a decay power level of 2%, the required heat transfer area for 1,000MWe plant is assessed to be about 2,000 ㎡ (equivalent to 1,600 of 10 m-long, 4-cm-OD tubes) with the relative elevation difference of 38 m between the condenser and steam condensing pool and the riser diameter of 0.62 m.

• 중환자간호학회지
• /
• 제3권1호
• /
• pp.53-65
• /
• 2010

Purpose: The purpose of this study was to identify the intensity and types of discomfort caused by an endotracheal tube in patients during ventilator therapy after cardiac surgery, and to analyze the differences in the intensity and types of discomfort by sociodemographic and clinical characteristics and characteristics related to endotracheal tubes. Methods: The intensity of discomfort was measured using an 11-point numeric rating scale and the types of discomfort were measured using a 4-point numeric rating scale. Sociodemographic and clinical characteristics and characteristics related to endotracheal tube were collected by observation and the electronic medical chart using a structured questionnaire. Results: The mean intensity of discomfort in patients due to endotracheal tubes was 6,91 points, 84% of patients reported discomfort over 5 points, The most severe discomfort was pain during endotracheal suctioning, and dry mouth and breathing difficulties were also found to induce discomfort. Patients who had more severe surgical site pain, longer duration of intubation and higher cuff pressure demonstrated more severe discomfort due to the endotracheal tube. Conclusion: These results can be used as basic data for developing nursing intervention to relieve the discomfort caused by endotracheal tubes in patients during ventilator therapy.

• 한국신재생에너지학회:학술대회논문집
• /
• 한국신재생에너지학회 2009년도 추계학술대회 논문집
• /
• pp.549-552
• /
• 2009

Methane hydrate is crystalline ice-like compounds which formed methane gas enters within water molecules composed cavity at specially temperature and pressure condition, and water molecule and each other from physically-bond. $1m^3$ hydrate of pure methane can be decomposed to the maximum of $172m^3$ at standard condition. If these characteristics of hydrate are reversely utilized, natural gas is fixed into water in the form of hydrate solid. Therefore the hydrate is considered to be a great way to transport and store natural gas in large quantity. Especially the transportation cost is known to be 18~24% less than the liquefied transportation. However, when methane hydrate is formed artificially, the amount of consumed gas is relatively low due to a slow reaction rate between water and methane gas. In this study, for the better hydrate reaction rate, there is make nano fluid using ultrasonic dispersion of carbon nano tube. and then, Experiment with hydrate formation by nano fluid and methane gas reaction. The results show that when the carbon nano tubes of 0.004 wt% was added to pure water, the amount of consumed gas was about 300% higher than that in pure water and the hydrate formation time decreased.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2006년도 춘계학술대회논문집
• /
• pp.858-861
• /
• 2006

In this paper, a study on the noise reduction in a mobile fuel cell system is presented. Among various fuel cell systems around 20W capacities designed for mobile electronic devices, the active direct methanol fuel cell (DMFC) systems have been recently developed. In such systems, the primary noise source is the air pump which provides sufficient air flow ($5{\sim}6$ liter/min) for electrochemical reaction with methanol fuel while the noise contributions from other auxiliary parts are relatively small. Especially, the discrete noise tones generated by the air pump are dominant and those frequency peaks related to the rotor harmonics are needed to be suppressed by a silencer. Therefore. the Herschel/Quinke (HQ) tubes, which use the out-of-phase cancellation of acoustic waves propagating through direct and indirect pathways, are applied to the inlet of the air pump. Performance of noise reduction with HQ silencer is analytically estimated by calculating the transmission. The length and number of thin HQ tubes are optimized to decrease the radiated noise. As a result, the sound pressure level could be successfully reduced by about 10 dB after applying three serially connected HQ tubes.

• 한국정보디스플레이학회:학술대회논문집
• /
• 한국정보디스플레이학회 2005년도 International Meeting on Information Displayvol.I
• /
• pp.272-275
• /
• 2005

The high stability of a-Si:H TFTs device is studied with different deposited conditions of $SiN_x$ films by PECVD. The process parameters of $N_2$, $NH_3$ gas flow rate, RF power, and pressure s of hydrogenated amorphous silicon nitride are taken into account and analyzed by Taguchi experimental design method. The $NH_3$ gas flow rate and RF power are two major factors on the average threshold voltage and the a-SiNx:H film's structure. The hydrogen contents in $SiN_x$ films were measured by FTIR using the related Si-H/N-H bonds ratio in $a-SiN_x:H$ films. After the 330,000 sec gate bias stress is applied, the threshold voltages ($V_th$) shift less than 10%. This result indicates that the highly stable a-Si:H TFTs device can be fabricated with optimum gate $SiN_x$ insulator.

• Nuclear Engineering and Technology
• /
• 제37권2호
• /
• pp.201-206
• /
• 2005

Fretting, which is a special type of wear, is defined as small amplitude relative motion along the contacting interface between two materials. The structural integrity of steam generators in nuclear power plants is very much dependent upon the fretting wear characteristics of Inconel 690 U-tubes. In this study, a finite element model that can simulate fretting wear on the secondary side of the steam generator was developed and used for a quantitative investigation of the fretting wear phenomenon. Finite element modeling of elastic contact wear problems was performed to demonstrate the feasibility of applying the finite element method to fretting wear problems. The elastic beam problem, with existing solutions, is treated as a numerical example. By introducing a control parameter s, which scaled up the wear constant and scaled down the cycle numbers, the algorithm was shown to greatly reduce the time required for the analysis. The work rate model was adopted in the wear model. In the three-dimensional finite element analysis, a quarterly symmetric model was used to simulate cross tubes contacting at right angles. The wear constant of Inconel 690 in the work rate model was taken as $K=26.7{\times}10^{-15}\;Pa^{-1}$ from experimental data obtained using a fretting wear test rig with a piezoelectric actuator. The analyses revealed donut-shaped wear along the contacting boundary, which is a typical feature of fretting wear.

• 대한설비공학회:학술대회논문집
• /
• 대한설비공학회 2008년도 동계학술발표대회 논문집
• /
• pp.47-54
• /
• 2008

Capillary tubes are widely used as expansion device in small refrigeration systems. The refrigerant flowing in the capillary tube experiences frictional and accelerational head losses, and flashing, simultaneously. In this paper flow characteristics of adiabatic capillary tubes with various friction factor models, two-phase viscosity models, and two-phase frictional multiplier models were simulated. The predicted pressure distribution, mass flow rate are compared with experimental data reported in literature. It is confirmed that the predicting accuracy with homogeneous model can be improved by employing the suitable correlations of friction factor and two-phase viscosity model, and two-phase frictional multiplier.

• 열처리공학회지
• /
• 제31권2호
• /
• pp.49-55
• /
• 2018

A T-shape structure was manufactured by the superplastic forming and diffusion bonding process using two Ti-3Al-2.5V alloy tubes. A Ti-3Al-2.5V tube was prepared for the hydroforming in the superplastic condition until it reaches a surface area such as a roof welded in the hole of another Ti-3Al-2.5V tube. Afterward, the superplastic forming process and the diffusion bonding process were carried out simultaneously until the appropriate bonding along the interface area of two Ti-3Al-2.5V tubes was obtained. The bonding qualities were different at each location of the entire interface according to the applied process conditions such as strain, pressure, temperature, holding time, geometries, etc. The microstructures of bonding interface have been observed to understand the characteristics of the applied processes in this study.

• 대한설비공학회:학술대회논문집
• /
• 대한설비공학회 2006년도 하계학술발표대회 논문집
• /
• pp.1113-1118
• /
• 2006

A numerical investigation of single phase heat and flow characteristics in circular tubes with a single set of spiral micro fins was performed with varying geometrical parameters like fin height, spiral angle, and number of fins. The properties of $40^{\circ}C$ water was used as a working fluid to simulate a condenser and the RNG $k-{\epsilon}$ turbulence model was adopted. Calculation results were obtained in fully developed turbulent flow with constant surface heat flux boundary condition. Relative terms were introduced to investigate the substitution effect of conventional smooth tubes. The dimensionless terms were the heat transfer enhancement factor, the pressure drop penalty factor, and the efficiency index. Additionally, a numerical optimization was carried out to maximize thermal performance with the concept of the robust design. A statistical analysis showed that fin height interacts with number of fins and spiral angle.