• Korean Journal of Materials Research
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• v.10 no.10
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• pp.691-697
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• 2000

$Al_xGa_{1-x}N$ thin layers are promising materials for optical devices in the UV regions. $Al_xGa_{1-x}N$ thin layers w were grown on sapphire substrates by metalorgaruc chemical vapor deposition (MOCVD). The molar Al fraction and crystallinity of layers were deduced from synchrotron x-ray scattering experiment. Surface morphology were investigated using SEM and SPM. $Al_xGa_{1-x}N$ layers crystallinity were related with undoped GaN crystallinity. The Al mole fraction of $Al_xGa_{1-x}N$ layers affect the surface morphology of $Al_xGa_{1-x}N$ layers. The surface morphology was rough­e ened and the cracks were obse$\pi$ed by increasing the Al mole fractions.

• Korean Chemical Engineering Research
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• v.45 no.2
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• pp.117-123
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• 2007

The effect of aluminium addition to MCM-41 on product yield and carbon number distribution was investigated in the catalytic cracking of a polymer mixture, LDPE, LLDPE, and EVA copolymer, with a composition similar to that found in real agricultural film wastes. Al-MCM-41 catalyst synthesized by post-synthetic grafting method (Al-MCM-41-P) as well as Al-MCM-41 catalyst synthesized by direct sol-gel (Al-MCM-41-D). The catalytic cracking of polymer mixture was carried out in vapor phase contact as well as in liquid phase contact. The amount of acid sites increased with aluminium addition by post method as well as direct method, which was seemed to be due to Lewis acid sites. In liquid phase catalytic cracking, the yield of light hydrocarbon fraction increased with aluminium addition. The effect of aluminium addition on production of $C_5-C_{12}$ hydrocarbons over Al-MCM-41-P catalysts was greater than that over Al-MCM-41-D catalysts. In the case of vapor phase catalytic cracking, the effect of aluminium addition was smaller than that of liquid phase catalytic cracking. The selectivity to $C_{13}-C_{32}$ hydrocarbons was smaller in vapor phase catalytic cracking.

• Journal of the Korean Vacuum Society
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• v.7 no.3
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• pp.242-247
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• 1998

Hydrogenated amorphous carbon nitride[a-C:H(N)] films were deposited on p-type Si(100) at room temperature with bias voltage of 200 V by DC saddle-field plasma-enhanced chemical vapor deposition. Effects of the ratio of $N_2$ to $CH_4$($N_2/CH_4$), in the range of 0 and 4 on such properties as optical properties, microstucture, relative fraction of nitrogen and carbon, etc. of the films have been investigated. The thickness of the a-C:H(N) film was abruptly decreased with the addition of nitrogen, but at $N_2/CH_4$>0.5, the thickness of the film gradually decreased with the increase of the $N_2/CH_4$. The ratio of N to C(N/C) of the films was saturated at 0.25 with the increase of $N_2CH_4$. N-H, C≡N bonds of the films increased but C-H bond decreased with the increase of $N_2CH_4$.Optical band gap energy of the film decreased from 2.53 eV at the ratio of $N_2CH_4$=4.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.216-227
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• 2004

A new cavitating model by using bubble size distribution based on bubbles-mass has been proposed. Both liquid and vapor phases are treated with Eulerian framework as a mixture containing minute cavitating bubbles. In addition vapor phase consists of various sizes of vapor bubbles, which are distributed to classes based on their mass. The bubble number-density for each class was solved by considering the change of the bubble-mass due to phase change as well as generation of new bubbles due to heterogeneous nucleation. In this method, the bubble-mass is treated as an independent variable, and the other dependent variables are solved in spatial coordinates and bubble-mass coordinate. Firstly, we employed this method to calculate bubble nucleation and growth in stationary super-heated liquid nitrogen, and bubble collapse in stationary sub-cooled one. In the case of bubble growth in super-heated liquid, bubble number-density of the smallest class based on its mass is increased due to the nucleation. These new bubbles grow with time, and the bubbles shift to larger class. Therefore void fraction of each class is increased due to the growth in the whole class. On the other hand, in the case of bubble collapse in sub-cooled liquid, the existing bubbles are contracted, and then they shift to smaller class. It finally becomes extinct at the smallest one. Secondly, the present method is applied to a cavitating flow around NACA00l5 foil. Liquid nitrogen and liquid oxygen are employed as working fluids. Cavitation number, $\sigma$, is fixed at 0.15, inlet velocities are changed at 5, 10, 20 and 50m/s. Inlet temperatures are 90K in case of liquid nitrogen, and 90K and 1l0K in case of liquid oxygen. 110K of oxygen is corresponding to the 90K of nitrogen because of the same relative temperature to the critical one, $T_{r}$=$T/T_c^{+}$. Cavitating flow around the NACA0015 foils was properly analyzed by using bubble size distribution. Finally, the method is applied to a cavitating flow in an inducer of the LE-7A hydrogen turbo-pump. This inducer has 3 spiral foils. However, for simplicity, 2D calculation was carried out in an unrolled channel at 0.9R cross-section. The channel moves against the fluid at a peripheral velocity corresponding to the inducer revolutions. Total inlet pressure, $Pt_{in}$, is set at l00KPa, because cavitation is not generated at a design point, $Pt_{in}$=260KPa. The bubbles occur upstream of the foils and collapse between them. Cavitating flow in the inducer was successfully predicted by using the bubble size distribution.

• Proceedings of the KIEE Conference
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• 1999.07d
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• pp.1928-1930
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• 1999

This paper describes on the growth of a ${\mu}c$-Si:H film on low cost substrate like glass by Hot Wire CVD method. The ${\mu}c$-Si:H film, prepared in 50mTorr pressure, $1800^{\circ}C$ wire temperature, and $H_2/SiH_4$ 10 showed three clear peaks. (111), (220), and (311) in X-ray spectroscopy. The crystallite size and crystalline volume fraction, calculated from Raman spectroscopy, was about 6nm and 70%, respectively. The FTIR transmission spectra of the film showed a different absorption peak with a-Si:H film around $2000-2100cm^{-1}$.

• Journal of the Korean Vacuum Society
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• v.10 no.3
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• pp.341-349
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• 2001

Numerical calculation has been performed to investigate the fluid flow, heat transfer and local mass fraction of chemical species in the MOCVD(metalorganic chemical vapor deposition) manufacturing process. The mixing of reactants (trimethylgallium with hydrogen gas and ammonia) was presented by the concentration of each reactant to predict the uniformity of film growth. Effects of inlet size, location, mass flow rate and susceptor/cold wall tilt angle on the concentration were reported. From the numerical calculation, the concentration of reactants could be qualitatively predicted by the Nusselt number(heat transfer) and the optimum mass flow rate, wall tilt angle and inlet condition were considered.

• Journal of computational fluids engineering
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• v.17 no.4
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• pp.93-102
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• 2012

Once the condensation of water vapor in moist air around a thin airfoil occurs, liquid droplets nucleate. The condensation process releases heat to the surrounding gaseous components of moist air and significantly affects their thermodynamic and flow properties. As a results, variations in the aerodynamic performance of airfoils can be found. In the present work, the effects of upstream Mach number and thickness ratio of airfoil on the transonic flow of moist air around a thin airfoil are investigated by numerical analysis. The results shows that a significant condensation occurs as the upstream Mach number is increased at the fixed thickness ratio of airfoil($\epsilon$=0.12) and as the thickness ratio of airfoil is increased at the fixed upstream Mach number($M_{\infty}$=0.80). The condensate mass fraction is also increased and dispersed widely around an airfoil as the upstream Mach number and thickness ratio of airfoil are increased. The position of shock wave for moist air flow move toward the leading edge of airfoil when it is compared with the position of shock wave for dry air.

• Journal of the Korean Vacuum Society
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• v.4 no.S1
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• pp.168-173
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• 1995

$GaxIn{1_x}As$ epitaxial layers were grown by a simplified hydrode vapor phase epitaxy(VPE) method bsed on the utilization of Ga/In alloy as the source metal. The effects of a wide range of experimental variables(i.e.,inlet mole fraction of HCI, deposition temperature, Ga/In alloy composition) on the ternary composition and growth rate were investigated. Layers of $Ga_{0.47}In_{0.53}As$ lattice matched to InP were successfully grown from alloys containing 5 to 8 at.% Ga. These layers were used to produce state-of-the art p-i-n photodetectors having the following characteristics: dark current, $I_d$(-5V) = 10-20 nA: responsivity, R=0.84-0.86 A/W; dark current, Id(-5V)=10-20 nA; responsivity, R=0.84-0.86 A/W; capacitance, C=0.88-0.92 pF; breakdown voltage, $V_b$ >40V. This study demonstrated for the first time that a simplified hydride VPE process with a Ga/In alloy source is capable of producing device quality epitaxial layers.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.2
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• pp.144-151
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• 2003

An experimental study was carried out in a uniformly heated horizontal tube to examine heat transfer characteristics of pure refrigerants, R134a and R123, and their mixtures during flow boiling. The flow pattern was also observed through tubular sight glasses with an internal diameter of 10 mm located at the inlet and outlet of the test section. Tests were run at a pressure of 0.6 MPa and in the heat flux ranges of 5~100 kW/$m^2$, vapor Quality 0~100 percent and mass velocity of 150-600 kg/$m^2$s. The observed flow patterns were compared to the flow pattern map of Kattan et al., which predicted well the present data over the entire range of mass velocity employed in this study. Heat transfer coefficients of the mixture were less than the interpolated values between pure fluids both in the low quality region where the nucleate boiling is dominant and in the high quality region where the convective evaporation is dominant.

• Progress in Superconductivity and Cryogenics
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• v.3 no.2
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• pp.15-20
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• 2001

This paper describes a model flux pump experiment recently performed at the MIT Francis Bitter Magnet Laboratory. The results of the model flux pump will be used in the development of a prototype flux pump that will be couple to a high-temperature superconductor (HTS) insert coil of a high-field NMR (Nuclear Magnetic Resonance) magnet, Such an HTS insert is unlikely to operate in persistent model because of the conductors low index(n) The flux pump can compensate fro field decay in the HTS insert coil and make the insert operate effectively in persistent mode . The flux pump, comprised essentially of a transformer an two switches. all made of superconductor, transfers into the insert coil a fraction of a magnetic energy that is first introduced in the secondary circuit of the transformer by a current supplied to the primary circuit. A model flux pump has been designed. fabricated, and operated to demonstrate that a flux pump can indeed supply a small metered current into a load superconducting magnet. A current increment in the range of microamperes has been measured in the magnet after each pumping action. The superconducting model flux pump is made of Nb$_3$ Sn tape, The pump is placed in a gaseous environment above the liquid helium level to keep its heat dissipation from directly discharged in the liquid: the effluent helium vapor maintains the thermal stability of the flux pump.