• International Journal of Fluid Machinery and Systems
• /
• v.9 no.1
• /
• pp.66-74
• /
• 2016

Concerning the numerical simulation of high-speed water jet with intensive cavitation this paper presents a practical compressible mixture flow method by coupling a simplified estimation of bubble cavitation and a compressible mixture flow computation. The mean flow of two-phase mixture is calculated by URANS for compressible fluid. The intensity of cavitation in a local field is evaluated by the volume fraction of gas phase varying with the mean flow, and the effect of cavitation on the flow turbulence is considered by applying a density correction to the evaluation of eddy viscosity. High-speed submerged water jets issuing from a sheathed sharp-edge orifice nozzle are treated when the cavitation number, ${\sigma}=0.1$, and the computation result is compared with experimental data The result reveals that cavitation occurs initially at the entrance of orifice and bubble cloud develops gradually while flowing downstream along the shear layer. Developed bubble cloud breaks up and then sheds downstream periodically near the sheath exit. The pattern of cavitation cloud shedding evaluated by simulation agrees experimental one, and the possibility to capture the unsteadily shedding of cavitation clouds is demonstrated. The decay of core velocity in cavitating jet is delayed greatly compared to that in no-activation jet, and the effect of the nozzle sheath is demonstrated.

• Progress in Superconductivity
• /
• v.5 no.2
• /
• pp.132-135
• /
• 2004

We fabricated YBCO thick films by using a screen printing method with $Y_2$BaCuO$_{5}$(Y211) and BaCO$_3$ powders on Cu-substrate in $N_2$ atmosphere. Cu-sheathed YBCO thick film process is more simple and economic than YBCO coated conductor methods. The heat treatment is performed in the range of 860 - 875 $^{\circ}C$ for 5 min in the tube furnace of $N_2$ atmosphere. The flow rate of $N_2$ gas is fixed 60 $m\ell$/min. Microstructure and phases of thick films were investigated by optical microscope, X-ray diffraction(XRD) and SEM. At heat-treatment temperature, the thick films were partially melted by liquid reaction between CuO of oxidized copper substrate and the powders screen-printed on Cu-sheath. During the heat-treatment procedure, YBCO superconducting grains nucleate.e.

• Proceedings of the KAIS Fall Conference
• /
• 2008.05a
• /
• pp.163-166
• /
• 2008

This study developed matt used by thermoelectric device to use both cooling and heating. To develop this system, heating system used sheath heater and cooling system used thermoelectric device. A Flow of water controlled by a capillary tube system made by polymethyl. Results by this system very lowered spending of energy.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2014.02a
• /
• pp.218.1-218.1
• /
• 2014

In order to measure the absolute plasma density, various probes are proposed and investigated and microwave probes are widely used for its advantages (Insensitivity to thin non-conducting material deposited by processing plasmas, High reliability, Simple process for determination of plasma density, no complicate assumptions and so forth). There are representative microwave probes such as the cutoff probe, the hairpin probe, the impedance probe, the absorption probe and the plasma transmission probe. These probes utilize the microwave interactions with the plasma-sheath and inserted structure (probe), but frequency range used by each probe and specific mechanisms for determining the plasma density for each probe are different. In the recent studies, behaviors of each microwave probe with respect to the plasma parameters of the plasma density, the pressure (the collision frequency), and the sheath width is abundant and reasonably investigated, whereas relative diagnostic characteristics of the probes by a comparative study is insufficient in spite of importance for comprehensive applications of the probes. However, experimental comparative study suffers from spatially different plasma characteristics in the same discharge chamber, a low-reproducibility of ignited plasma for an uncertainty in external discharge parameters (the power, the pressure, the flow rate and so forth), impossibility of independently control of the density, the pressure, and the sheath width as well as expensive and complicate experimental setup. In this paper, various microwave probes are simulated by finite-different time-domain simulation and the error between the input plasma density in FDTD simulations and the measured that by the unique microwave spectrums of each probe is obtained under possible conditions of plasma density, pressure, and sheath width for general low-temperature plasmas. This result shows that the each probe has an optimum applicable plasma condition and reliability of plasma density measurement using the microwave probes can be improved by the complementary use of each probe.

• Proceedings of the KSME Conference
• /
• 2008.11b
• /
• pp.2059-2063
• /
• 2008

When a thermocouple is placed in a high temperature gas-flow stream, the measured temperature could be biased from the true gas temperature due to a large radiation heat loss from a thermocouple surface to its surroundings. In this study, two thermocouples of unequal diameters with 1/8 inch and 1/16 inch are used to correct the radiation effect. The method is called the reduced radiation error (RRE). The preliminary test results show that the radiation and the sheath conduction cannot be negligible for the gas temperature measurement. To minimize the sheath conduction effect, all the thermocouples will have a grounded junction and 1/8 inch thermocouple will be replaced with 1 mm thermocouples. In addition, the computational fluid dynamics code analysis shows that there is a negligible temperature difference between the positions where the thermocouples were installed.

• Bulletin of the Korean Chemical Society
• /
• v.23 no.2
• /
• pp.295-300
• /
• 2002

The construction of the T-shaped post-column flow cell has been changed to enhance the practicability as a UV-visible absorbance detector for capillary electrophoresis. In this new design, a rectangular cube-shaped inner structure is employed, which completely fits the outer rectangular tubing. This arrangement has greatly facilitated the fabrication of the T-cells. In addition, the volume for the auxiliary flow has been dramatically reduced down to 300 ${\mu}L$, and its volume flow rate is optimized at 4.2 ${\mu}L$/min. The short optical path length in the sheath flows (500 ${\mu}m$ on each side) minimizes background absorption, and thus enhances its performance in low-UV wavelengths. We have optimized the auxiliary flow rate at 50 ${\mu}m$/s, so that migration times are insensitive to the flow rate. This optimization has improved repeatabilities in migration times and peak heights. A double-beam detection scheme using a pair of photodiodes is employed to increase the signal-to-noise ratio.

• Proceedings of the KIEE Conference
• /
• 2003.07b
• /
• pp.976-978
• /
• 2003

Quench characteristics of HTS tapes, which are applied over-current were investigated. When the applied current exceeds the critical current of HTS tapes, the superconductor of HTS tape comes to be changed into normal conductor so that the current begins to flow through the metal sheath, which is made of good electrical conductor. In this study, the current, corresponds to 10 times $I_c$ was fed to HTS tapes. Using the V-I curves and resistance with temperature variation of HTS tapes, the distribution of the applied current between superconductor and metal sheath was analyzed. As the results, we could acquire the duration and magnitude of current to reach to thermal quench.

• Nuclear Engineering and Technology
• /
• v.35 no.5
• /
• pp.426-441
• /
• 2003

A reactor inlet header break experiment, B9401, performed in the RD-14M multi channel test facility was analyzed using RELAP5/MOD3.2 and RELAP5/CANDU[1]. The RELAP5 has been developed for the use in the analysis of the transient behavior of the pressurized water reactor. A recent study showed that the RELAP5 could be feasible even for the simulation of the thermal hydraulic behavior of CANDU reactors. However, some deficiencies in the prediction of fuel sheath temperature and transient behavior in athe headers were identified in the RELAP5 assessments. The RELAP5/CANDU has been developing to resolve the deficiencies in the RELAP5 and to improve the predictability of the thermal-hydraulic behaviors of the CANDU reactors. In the RELAP5/CANDU, critical heat flux model, horizontal flow regime map, heat transfer model in horizontal channel, etc. were modified or added to the RELAP5/MOD3.2. This study aims to identify the applicability of both codes, in particular, in the multi-channel simulation of the CANDU reactors. The RELAP5/MOD3.2 and the RELAP5/CANDU analyses demonstrate the code's capability to predict reasonably the major phenomena occurred during the transient. The thermal-hydraulic behaviors of both codes are almost identical, however, the RELAP5/CANDU predicts better the heater sheath temperature than the RELAP5/MOD3.2. Pressure differences between headers govern the flow characteristics through the heated sections, particularly after the ECI. In determining header pressure, there are many uncertainties arisen from the complicated effects including steady state pressure distribution. Therefore, it would be concluded that further works are required to reduce these uncertainties, and consequently predict appropriately thermal-hydraulic behaviors in the reactor coolant system during LOCA analyses.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.24 no.1
• /
• pp.1-7
• /
• 2014

Aluminum nitride, which has outstanding properties such as high thermal conductivity and electrical resistivity, has been received a great attention as a substrate and packaging material of semiconductor devices. Since aluminum nitride has a high sintering temperature of 2173 K and its properties depends on the impurity level, it is necessary to synthesize high-purity and nano-sized aluminum nitride powders for the applications. In this research, we synthesized high purity aluminum nitride nanopowders from aluminum using RF induction thermal plasma system. Sheath gas (NH3) flow was controlled to establish the synthesis condition of high purity aluminum nitride nanopowders. The obtained aluminum nitride nanopowders were evaluated by XRD, SEM, TEM, BET, FTIR and N-O analysis.

• KIEE International Transactions on Electrophysics and Applications
• /
• v.5C no.5
• /
• pp.196-203
• /
• 2005

A semi-empirical method to determine the electrostatic characteristics of a diode type corona aerosol charger based on ion current measurement and electrostatic charging theory was presented. Results from mathematical model were in agreement with those from experimental investigation of the charger. Current-voltage characteristics, $N_{i}t$ product and charge distribution against aerosol size were obtained. It was shown that the space charge was significant and must be taken into account at high ion number concentration and low flow rate. Additionally, significant particle loss was evident for particles smaller than 20 nm in diameter where their electrical mobility was high. Increase in charging efficiency may be achieved by introducing surrounding sheath flow and applying AC high voltage. Overall, the approach was found to be useful in characterizing the aerosol charger.