• Membrane Journal
• /
• v.32 no.2
• /
• pp.150-162
• /
• 2022

In the field of water treatment and pharmaceutical bio an alumina hollow fiber membrane used for mixture separation. However, due to the lack of strengths it is very brittle to handle and apply. Therefore, it is necessary to study and improve the bending strength of the membrane to 100 MPa or more. In this study, as the mixing ratio of the nano-particles increased to 0, 1, 3, and 5 wt%, the viscosity of the fluid mixture increased. The pore structure of the hollow membrane produced by interrupting the diffusion exchange rate of the solvent and non-solvent during the spinning process suppresses the formation of the finger-like structure and gradually increases the ratio of the sponge-like structure to improve the membrane mechanical strength to more than 100 MPa. As a result, an interparticle space was ensured to improve the porosity of the sponge-like structure with high permeability, and it showed excellent N2 permeability of about 100000 GPU and high water permeability of 3000 L/m² h. Therefore, it can be concluded, that the addition of γ-Al₂O₃ nanoparticles as sintering aid is an important method to enhance the mechanical strength of the α-alumina hollow fiber membrane to maintain high permeability.

• Advances in aircraft and spacecraft science
• /
• v.9 no.5
• /
• pp.415-431
• /
• 2022

Secondary flows have a huge impact on losses generation in modern low pressure gas turbines (LPTs). At design point, the interaction of the blade profile with the end-wall boundary layer is responsible for up to 40% of total losses. Therefore, predicting accurately the end-wall flow field in a LPT is extremely important in the industrial design phase. Since the inlet boundary layer profile is one of the factors which most affects the evolution of secondary flows, the first main objective of the present work is to investigate the impact of two different inlet conditions on the end-wall flow field of the T106A, a well known LPT cascade. The first condition, labeled in the paper as C1, is represented by uniform conditions at the inlet plane and the second, C2, by a flow characterized by a defined inlet boundary layer profile. The code used for the simulations is based on the Discontinuous Galerkin (DG) formulation and solves the Reynolds-averaged Navier-Stokes (RANS) equations coupled with the Spalart Allmaras turbulence model. Secondly, this work aims at estimating the influence of viscosity and turbulence on the T106A end-wall flow field. In order to do so, RANS results are compared with those obtained from an inviscid simulation with a prescribed inlet total pressure profile, which mimics a boundary layer. A comparison between C1 and C2 results highlights an influence of secondary flows on the flow field up to a significant distance from the end-wall. In particular, the C2 end-wall flow field appears to be characterized by greater over turning and under turning angles and higher total pressure losses. Furthermore, the C2 simulated flow field shows good agreement with experimental and numerical data available in literature. The C2 and inviscid Euler computed flow fields, although globally comparable, present evident differences. The cascade passage simulated with inviscid flow is mainly dominated by a single large and homogeneous vortex structure, less stretched in the spanwise direction and closer to the end-wall than vortical structures computed by compressible flow simulation. It is reasonable, then, asserting that for the chosen test case a great part of the secondary flows details is strongly dependent on viscous phenomena and turbulence.

• Resources Recycling
• /
• v.31 no.6
• /
• pp.60-65
• /
• 2022

This study presents the carburization process for recycling sludge, which was formed during silicon wafer machining. The sludge used in the carburization process is a mixture of silicon and silicon carbide (SiC) with iron as an impurity, which originates from the machine. Additionally, the sludge contains cutting oil, a fluid with high viscosity. Therefore, the sludge was dried before carburization to remove organic matter. The dried sludge was washed by acid cleaning to remove the iron impurity and subsequently carburized by heat treatment under vacuum to form the SiC powder. The ratio of silicon to SiC in the sludge was varied depending on the sources and thus carbon content was adjusted by the ratio. With increasing SiC content, the carbon content required for SiC formation increased. It was demonstrated that substoichiometric SiC_x (x<1) was easily formed when the carbon content was insufficient. Therefore, excess carbon is required to obtain a pure SiC phase. Moreover, size reduction by high-energy milling had a beneficial effect on the suppression of SiC_x, forming the pure SiC phase.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.28 no.5B
• /
• pp.575-589
• /
• 2008

In the present work, we investigate the hydrodynamic behavior of a turbulent bore, such as tsunami bore and tidal bore, generated by the removal of a gate with water impounded on one side. The bore generation system is similar to that used in a general dam-break problem. In order to the numerical simulation of the formation and propagation of a bore, we consider the incompressible flows of two immiscible fluids, liquid and gas, governed by the Navier-Stokes equations. The interface tracking between two fluids is achieved by the volume-of-fluid (VOF) technique and the M-type cubic interpolated propagation (MCIP) scheme is used to solve the Navier-Stokes equations. The MCIP method is a low diffusive and stable scheme and is generally extended the original one-dimensional CIP to higher dimensions, using a fractional step technique. Further, large eddy simulation (LES) closure scheme, a cost-effective approach to turbulence simulation, is used to predict the evolution of quantities associated with turbulence. In order to verify the applicability of the developed numerical model to the bore simulation, laboratory experiments are performed in a wave tank. Comparisons are made between the numerical results by the present model and the experimental data and good agreement is achieved.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.26 no.4
• /
• pp.345-363
• /
• 2024

Steel pipe reinforced grouting method has been widely used to strengthen the crown of tunnel face and prevent groundwater leakage during tunnel excavation. Various injection procedures without sealing have recently been suggested to enhance efficiency. There are two representative injection methods. One is simultaneous injection in segmented batches, and the other is multiple injection using the external packer. The pros and cons of each method were discussed in terms of construction duration and equipment. However, it has yet to be discussed how the injection procedure affects the grout diffusion range in the ground. This study aims to evaluate the grout diffusion range quantitatively by considering the practical grouting sequences. The grout viscosity was measured by laboratory testing. Then, the numerical modeling was structured using the commercial computational fluid dynamics software. Finally, the grout diffusion range affected by the injection procedure and ground conditions was evaluated by performing the numerical parametric study. The results showed that the injection method highly affected the grout diffusion range, especially for inhomogeneous soil. Consequently, it is anticipated that the proper method of steel pipe reinforced grouting will be suggested.

• Food Science and Preservation
• /
• v.20 no.6
• /
• pp.827-833
• /
• 2013

In this study we investigated physicochemical properties of Zanthoxylum schinifolium seeds oil base extracts. Supercritical fluid extraction (SFE), roast pressure (RPM) and steam pressure (SPM) method were used for oil base extracts. The pressure and temperature conditions of SFE method were $70{\sim}80kgf/cm^2$ and below $30^{\circ}C$, respectively, by newly designed SFE-$CO_2$ system. The yield of extraction was 38.5% at the SFE method and others were 30% in each. Refractive index of oil base extracts, there was also no difference between them as 1.470~1.473. At the SFE method, viscosity observed higher value better than two method that showed as 181.88~209.93 according to the extraction time. Three oil base extracts showed difference in color which was low in b value at SFE, especially. The result of acid value at RPM that was lower as 0.93 mg/g than 2.36~2.64 mg/g of SFE method. Saponification value ranged $182.96{\sim}196.57mg{\cdot}KOH/g$ in three extraction method. At SPM, TBA value showed as 158.96 mg/kg, but in the SFE method ranged higher value as 201.30~347.14 mg/kg. Fatty acids analysed with 18 varieties in all oil base extracts and the composition of saturated/unsaturated fatty acids was 17:83(v/v) at SEF. Especially, ${\omega}$-3,6,9 fatty acids observed at SFE and SPM, but did not appeared at RPM. Fatty acid of ${\omega}$-6,9 detected in all cases.

• Journal of Korean Society of Environmental Engineers
• /
• v.34 no.4
• /
• pp.223-231
• /
• 2012

The purpose of this study is to investigate basically the mechanism of heat transfer by the resolution of complex fluid flow inside a sophisticated designed screw dryer for the treatment of sewage sludge by using numerical analysis and experimental study. By doing this, the result was quite helpful to obtain the design criteria for enhancing drying efficiency, thereby achieving the optimal design of a multiple screw type dryer for treating inorganic and organic sludge wastes. One notable design feature of the dryer was to bypass a certain of fraction of the hot combustion gases into the bottom of the screw cylinder, by the fluid flow induction, across the delicately designed holes on the screw surface to agitate internally the sticky sludges. This offers many benefits not only in the enhancement of thermal efficiency even for the high viscosity material but also greater flexibility in the application of system design and operation. However, one careful precaution was made in operation in that when distributing the hot flue gas over the lump of sludge for internal agitation not to make any pore blocking and to avoid too much pressure drop caused by inertial resistance across the lump of sludge. The optimal retention time for rotating the screw at 1 rpm in order to treat 200 kg/hr of sewage sludge was determined empirically about 100 minutes. The corresponding optimal heat source was found to be 150,000 kcal/hr. A series of numerical calculation is performed to resolve flow characteristics in order to assist in the system design as function of important system and operational variables. The numerical calculation is successfully evaluated against experimental temperature profile and flow field characteristics. In general, the calculation results are physically reasonable and consistent in parametric study. In further studies, more quantitative data analyses such as pressure drop across the type and loading of drying sludge will be made for the system evaluation in experiment and calculation.

• Journal of the Korean Vacuum Society
• /
• v.18 no.1
• /
• pp.66-72
• /
• 2009

The detection methods are required to monitor and diagnose the abnormality on the insulation condition inside a gas-insulated switchgear (GIS). Due to a good sensitivity to the products decomposed by partial discharges (PDs) in $SF_6$ gas, the development of a SWNT gas sensor is actively in progress. However, a few numerical studies on the diffusion mechanism of the $SF_6$ decomposition products by PD have been reported. In this study, we modeled $SF_6$ decomposition process in a chamber by calculating temperature, pressure and concentration of the decomposition products by using a commercial CFD program in conjunction with experimental data. It was assumed that the mass production rate and the generation temperature of the decomposition products were $5.04{\times}10^{-10}$ [g/s] and over 773 K respectively. To calculate the concentration equation, the Schmidt number was specified to get the diffusion coefficient functioned by viscosity and density of $SF_6$ gas instead rather than setting it directly. The results showed that the drive potential is governed mainly by the gradient of the decomposition concentration. A lower concentration of the decomposition products was observed as the sensors were placed more away from the discharge region. Also, the concentration increased by increasing the discharge time. By installing multiple sensors the location of PD is expected to be identified by monitoring the response time of the sensors, and the information should be very useful for the diagnosis and maintenance of GIS.