• Journal of computational fluids engineering
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• v.14 no.4
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• pp.78-85
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• 2009

Cavitating flow simulation is of practical importance for many engineering systems, such as marine propellers, pump impellers, nozzles, injectors, torpedoes, etc. The present work has focused on the simulation of cavitating flow past cylinders with strong side flows. The governing equation is the Navier-Stokes equation based on the homogeneous mixture model. The momentum and energy equation is in the mixture phase while the continuity equation is solved liquid and vapor phase, separately. An implicit dual time and preconditioning method are employed for computational analysis. For the code validation, the results from the present solver have been compared with experiments and other numerical results. A fairly good agreement with the experimental data and other numerical results have been obtained. After the code validation, the strong side flow was applied to include the wake flow effects of the submarine or ocean tide.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.1
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• pp.61-69
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• 1998

Vapor Axial Deposition (VAD), one of optical fiber preform fabrication processes, is performed by deposition of submicron-size silica particles that are synthesized by combustion of raw chemical materials. In this study, flow field is assumed to be a forced uniform flow perpendicularly impinging on a rotating disk. Similarity solutions obtained in our previous study are utilized to solve the particle transport equation. The particles are approximated to be in a polydisperse state that satisfies a lognormal size distribution. A moment model is used in order to predict distributions of particle number density and size simultaneously. Deposition of the particles on the disk is examined considering convection, Brownian diffusion, thermophoresis, and coagulation with variations of the forced flow velocity and the disk rotating velocity. The deposition rate and the efficiency directly increase as the flow velocity increases, resulting from that the increase of the forced flow velocity causes thinner thermal and diffusion boundary layer thicknesses and thus causes the increase of thermophoretic drift and Brownian diffusion of the particles toward the disk. However, the increase of the disk rotating speed does not result in the direct increase of the deposition rate and the deposition efficiency. Slower flow velocity causes extension of the time scale for coagulation and thus yields larger mean particle size and its geometric standard deviation at the deposition surface. In the case of coagulation starting farther from the deposition surface, coagulation effects increases, resulting in the increase of the particle size and the decrease of the deposition rate at the surface.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.22 no.4
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• pp.342-349
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• 2009

This study investigated the growth characteristics of carbon nanotubes (CNTs) by changing a period of annealing time and a $C_{2}H_{2}/H_2$ flow ratio at temperature as low as $450^{\circ}C$ with inductively coupled plasma chemical vapor deposition. The 1-nm-thick Fe-Ni-Co alloy thin film served as a catalyst layer for the growth of CNTs, which was thermally evaporated on the 15-nm-thick Al underlayer deposited on the 50-nm-thick Ti diffusion barrier. The annealing at low temperature of $450^{\circ}C$ brought about almost no granulation of the catalyst layer, and the CNT growth was not affected by a period of annealing time. A study of changing the flow rate of $C_{2}H_{2}$ and $H_2$ showed that as the ratio of the $C_{2}H_{2}$ flow rate to the $H_2$ flow rate was lowered, the CNTs were grown to be longer With further decreasing the flow ratio, the length of CNTs reached the maximum and then became shorter. Under the optimized gas flow rates, we successfully synthesized CNTs with a uniform length over a 4-inch Si wafer at $450^{\circ}C$.

• Journal of the Korean Ceramic Society
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• v.38 no.11
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• pp.1037-1041
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• 2001

Silicon diosixde thick film using silica optical waveguide cladding was fabricated by Plasma Enhanced Chemical Vapor Deposition (PECVD) method, at a low temperature (32$0^{\circ}C$) and from (SiH$_4$+$N_2$O) gas mixtures. The effects of deposition parameters on properties of SiO$_2$thick films were investigated by variation of $N_2$O/SiH$_4$flow ratio and RF power. As the $N_2$O/SiH$_4$flow ratio decreased, deposition rate increased from 2.9${\mu}{\textrm}{m}$/h to maximum 10.1${\mu}{\textrm}{m}$/h. As the RF power increased from 60 W to 120 W, deposition rate increased (5.2~6.7 ${\mu}{\textrm}{m}$/h) and refractive index approached at thermally grown silicon dioxide (n=1.46).

• Journal of the Korean Society of Propulsion Engineers
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• v.6 no.4
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• pp.15-23
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• 2002

In most cryogenic liquid rocket engines, liquid oxygen manifold and injector are not thermally insulated from room temperature environment fur reducing system complexity and the weight. This feature of cryogenic liquid rocket engine results in the situation that cryogenic liquid oxygen flow is easy to be vaporized especially in the vicinity of the manifold and the injector wall. The research in this paper is focused on two-phase flow phenomena of liquid oxygen in rocket engine. Vapor fraction was estimated by comparing the measured two-phase flow pressure drop in engine manifold and the injector with ideal single phase pressure drop. Heat flux into cryogenic flow is estimated by measuring the wall temperature on the engine manifold to examine boiling characteristics. Suitable correlations for cryogenic two-phase flow were also reviewed to see their applicability. In addition, the effect of vapor generation in liquid rocket engine manifold and injector on engine performance and stability was considered.

• Composites Research
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• v.34 no.4
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• pp.249-256
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• 2021

In this paper, the densification of a carbon/carbon composite during a chemical vapor infiltration (CVI) process is studied using a chemo-mechanical model. The multi-physics numerical model, developed in the previous research, couples computational fluid dynamics and major chemical reactions in the reactor. The model is especially utilized to study the effect of flow behavior around the preform on the densification. Four different types of "flow-guide" structures are placed to alter the gas flow around the preform. It is shown that the flow pattern and speed around the preform can be controlled by the guide structures. The process simulations demonstrate that the average density and/or density distribution of the preform can be improved by controlling the gas flow around the perform. In this study, a full industrial-scale reactor and process parameter were used.

• 한국전산유체공학회:학술대회논문집
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• 2010.05a
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• pp.567-570
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• 2010

With continuously increasing flat panel display size, uniformity of thin film deposition has been drawing more attentions and associated fabrication methodologies are being actively investigated. Since the convective flow field of mixture gas plays a significant role for deposition characteristics of thin film in an APCVD system, it is greatly important to maintain uniform distribution and consistent concentration of mixture gas species. In this paper, computational study has been performed for the improvement of flow uniformity of mixture gas in an APCVD reactor during thin film deposition process. A diffuser slit has bee designed to spread the locally concentrated gas flow exiting from the flow distributor. A uniform flow distributor has been developed which has less dependency on operating conditions for global flow uniformity

• Journal of Mechanical Science and Technology
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• v.19 no.12
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• pp.2289-2295
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• 2005

Two-Phase flow pattern and pressure drop data were obtained for pure refrigerants R134a and R123 and their mixtures as test fluids in a horizontal tube. The flow pattern is observed through tubular sight glasses located at inlet and outlet of the test section. The flow map of Baker developed for air-water two-phase flow at atmospheric pressure failed to predict the observed flow patterns at the higher value of the mass velocity used in the present study. The map of Kattan et al. predicted the data well over the entire region of mass velocity selected in the present study. The measured pressure drop increased with an increase in vapor quality and mass velocity. A new two-phase multiplier was developed from a dimensional analysis of the frictional pressure drop data measured in the present experiment. This new multiplier was found successfully to correlate the frictional pressure drop.

• Journal of the Semiconductor & Display Technology
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• v.17 no.4
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• pp.91-96
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• 2018

In this study temperature distribution and gas flow inside a planetary type reactor in which a number of satellites on a spinning susceptor were rotating were analyzed using numerical simulation. Effects of flow rates on gas flow and temperature distribution were investigated in order to obtain design parameters. The commercial computational fluid dynamics software CFD-ACE+ was used in this study. The multiple-frame-of-reference was used to solve continuity, momentum and energy conservation equations which governed the transport phenomena inside the reactor. Kinetic theory was used to describe the physical properties of gas mixture. Effects of the rotation speed of the satellites was clearly seen when the inlet flow rate was small. Thickness of the boundary layer affected by the satellites rotation became very thin as the flow rate increased. The temperature field was little affected by the incoming flow rate of precursors.

• International Journal of Air-Conditioning and Refrigeration
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• v.10 no.3
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• pp.129-137
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• 2002

In this study, evaporation pressure drop experiments were conducted with two types of plate and shell heat exchangers (P&SHE) using R-22. An experimental refrigerant loop has been established to measure the evaporation pressure drop of R-22 in a vertical P&SHE. The flow channels were formed by stacking three plates having a corrugated channel of a chevron angle of 45 dog. The R-22 flows down in one channel exchanging heat with the hot water flowing up in the other channel. The effect of the refrigerant mass flux, average heat flux, system pressure and vapor quality were explored in detail. During the experiment, the quality change between the inlet and outlet of the refrigerant channel ranges from 0.03 to 0.15. The present data showed that two types of P&SHE have similar trends. The pressure drop in-creases with the vapor quality for both types of P&SHE. At a higher mass flux, the Pressure drop is higher for the entire range of the vapor quality. Also, the increase in the average heat flux increases the pressure drop. Finally, at a higher system pressure, the pressure drop is found to be slightly lower compared to the lower system pressure.