• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
• /
• v.16 no.5
• /
• pp.423-429
• /
• 1987

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.24 no.5
• /
• pp.611-618
• /
• 2018

In this study, numerical analysis of solid-liquid two-phase flow was conducted as a preliminary step to analyze the flow characteristics of drilling fluid using the commercial CFD code, ANSYS CFX 14.5. The homogeneous model and separated flow model were used to simulate solid-liquid two-phase flow phenomena. In the separated flow model, Gidaspow's drag force model was applied with the kinetic theory model was applied for solid particles. The validity of the numerical model used in this study was verified based on the published experimental results. Numerical analysis was carried out for volume fractions of 0.1 to 0.5 and velocities of 1 to 5 m/s in a horizontal tube with a diameter of 54.9 mm and a length of 3 m. The Pressure drop and volume fraction distribution of solid particles were confirmed. The pressure drop was predicted using the homogeneous model and separated flow model within the MAE of 17.04 % and 8.98 %, respectively. A high volume fraction was observed in the lower part of the tube, and the volume fraction decreased toward the upper part. As velocity increased, variations in volume fraction distribution at varying heights were decreased, and the numerical results predicted these flow characteristics well.

• Composites Research
• /
• v.34 no.4
• /
• pp.233-240
• /
• 2021

VaRI(Vacuum assisted Resin Infusion) process, which is cost effective and suitable for manufacturing large-sized composites, is an OoA(Out-of Autoclave) process. For rapid resin infusion in the VaRI process, a DM(distribution media) is placed on top of the fabric. The resin is rapidly supplied in plane direction of the fiber along the DM, and then the supplied resin is impregnated in the out-of-plane direction of fiber. It is difficult to predict the flow of resin because the flow of in-plane direction and the out-of-plane direction occur together, and a 3D numerical analysis program is used to simulate the resin infusion process. However, in order to analyze in 3D, many elements are required in the out-of-plane direction of fabric. And the product size is larger, the longer the analysis time needs. Therefore, in this study, a method was suggested to reduce the time required for flow analysis by simplifying the 3D flow analysis to 2D flow analysis. The usefulness was verified by comparing the 3D flow analysis with the simplified 2D flow analysis at the same conditions. The filling time error was about 7% and the reduction of flow analysis time was about 95%. In addition, by utilizing the constant difference in the flow front between the top, middle, and bottom of the fabric of the 3D analysis, the flow front of the top, middle, and bottom of the fabric can be also predicted in the 2D flow analysis.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.3 no.4
• /
• pp.83-92
• /
• 1999

A numerical analysis of two phase flow in the solid rocket nozzle was conducted. Stoke number was defined over the various aluminum oxide($AI_2$$O_3$) particle sizes and particle trajectories were treated by Lagrangian approach. Particle stability was considered by the definition of Weber number in a rocket nozzle. Large particles are divided after the nozzle throat as the flow accelerates rapidly. The division of particles changes the particle distribution at the nozzle exit. From the above results, it was found that the nozzle converge section surface might be affected by aluminum oxide particles. Also, Mechanical erosion rate of nozzle surface was predicted for different materials.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.14 no.5
• /
• pp.408-414
• /
• 2002

The instability of two-phase loop thermosyphons (TLTs) was investigated experimentally. Three orifice type inserts were used to study the effect of change in the pressure drop in the flow channel of the TLT on the flow instability and temperature fluctuation. It is observed that a decrease in the size of the orifice insert from 3.7mm (no insert) to 0.71mm drastically reduced the fluctuation of the temperature, especially at the evaporator section of the TLT With the orifice type insert of 0.71 mm for the TLT, the overall temperature fluctuation was almost completely eliminated, especially at higher power input to the TLT.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.23 no.1
• /
• pp.87-94
• /
• 2011

Characteristics of two-phase pressure drop in microchannels were investigated experimentally. The microchannels consisted of 9 parallel trapezoidal channels with each channel having $205\;{\mu}m$ of bottom width, $800\;{\mu}m$ of depth, $3.6^{\circ}$ of sidewall angle, and 7 cm of length. Pressure drops in convective boiling of Refrigerant 113 were measured in the range of inlet pressure 105~195 kPa, mass velocity $150{\sim}920\;kg/m^2s$, and heat flux $10{\sim}100\;kW/m^2$. The total pressure drop generally increased with increasing mass velocity and/or heat flux. Two-phase frictional pressure drop across the microchannels increased rapidly with exit quality and showed bigger gradient at higher mass velocity. A critical review of correlations in the literature suggested that existing correlations were not able to match the experimental results obtained for two-phase pressure drop associated with convective boiling in microchannels. A new correlation suitable for predicting two-phase friction multiplier was developed based on the separated flow model and showed good agreement with the experimental data.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.12 no.9
• /
• pp.870-878
• /
• 2000

An experimental study and a modeling are peformed to investigate the pressure drop of combining junctions in two-phase flows. Experiments on tripod geometry used in a condenser or an evaporator, are conducted with inlet mass fluxes from 200 to$ 400 kg/m^2$s, and pipe diameters of 7 m and 9.52 m. The working fluid is R22. The result shows that the pressure drop increases as the quality does, but the effect of the increase of the pressure decreases when the diameter of a pipe increases. When the mass flux increases, the pressure drop linearly does. Furthermore, when the pipe diameter decreases, the pressure drop has a quadratic increase.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.25 no.9
• /
• pp.1219-1226
• /
• 2001

Pressure drops were measured for the flow boiling process within horizontal rectangular channels. The gap between the upper and the lower plates of each channel ranges from 0.4 to 2mm while the channel width being fixed to 20mm. Refrigerant 113 was used as the test fluid. The mass flux ranges from 50 to 200kg/㎡s and the channel walls were uniformly heated up to 15kW/㎡. The quality range covers from 0.15 to 0.75. The present experimental conditions coincide with the operating conditions of compact heat exchangers in which the liquid and gas flows are laminar and turbulent. The measured results were well represented by the two-phase frictional multiplier of Lee (2001) which has been developed for air-water two-phase flows within the deviation of $\pm$20%.

• 한국신재생에너지학회:학술대회논문집
• /
• 2010.11a
• /
• pp.89.2-89.2
• /
• 2010

고체산화물 연료전지는 $800{\sim}1000^{\circ}C$인 고온에서 작동하므로 적용되는 밀봉재의 요구조건은 매우 중요하다. 본 연구에서는 SOFC 밀봉재로서 $SiO_2-B_2O_3-RO$계 결정화 유리를 선정하였으며 작동온도 부근에서 결정화를 유도하여 고온점성유동을 제어하고자 하였다. 따라서 $SiO_2-B_2O_3-RO$계에 RO인 CaO, SrO, BaO, MgO를 상호 치환하였을 때 결정상의 생성, 생성온도, 생성결정의 종류가 sealing 특성에 어떠한 영향을 주는가를 검토하였다. 결정화유리를 $800^{\circ}C$로 유지하였을 때 생성되는 주 결정상은 Calsium silicate, Strontium silicate, Barium silicate, Magnesium silicate이였으며 Strontium silicate 의 생성속도가 가장 빨랐으며 결정상은 불산으로 에칭하여 SEM으로 관찰하였다. Barium silicate를 유도한 결정화 유리가 $800^{\circ}C$에서 1000시간 유지하였을 경우 가장 내화학성이 우수하며 강도값도 154MPa로 가장 높았다. 또한 부분 결정화를 통해 $800^{\circ}C$ 점성유동이 제어됨을 고온현미경을 통해 관찰하였다.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.1 no.1
• /
• pp.15-22
• /
• 2000

There are lots of industrial machines of which functions are achieved by operation of multi-phase fluids. Some of them take advantage of the characteristics of counter-current two-phase flow The maximum flow rates of gas and liquid phases which flow in opposite-directions (counter-current flow) are limited by a phenomenon known as a Counter-Current Flow Limitation (CCFL or Flooding) The mass and momentum conservation equations for each Phase were established to build a first-order hyperbolic partial derivative equations system. A new CCFL model is developed based on the characteristic equation of the hyperbolic PDE system. The present model has its applicationto the case in which a non-uniform flow is developed around a square or sharp-edged entrance of liquid phase. The model is able to he used to Predict the operating-limit of components in which mass and heat transfer are taking place between liquid and gas phases.