• Journal of Mechanical Science and Technology
• /
• v.14 no.2
• /
• pp.236-250
• /
• 2000

Compression ignition direct injection diesel engines employed a high pressure injection system have been developed as a measure to improve a fuel efficiency and reduce harmful emissions. In order to understand the effects of the pressure variation, many experimental works have been done, however there are many difficulties to get data in engine condition. This work gives numerical results for the high pressure effects on spray characteristics in wide or limited space with near walls. The gas phase is modelled by Eulerian continuum conservation equations of mass, momentum, energy and fuel vapour fraction. The liquid phase is modelled using the discrete droplet model approach in Lagrangian form and the drop behavior on a wall is calculated with a new droplet-wall interaction model based on the experiments observing individual drops. The droplet distributions, vapour fractions and gas flows are shown in various injection pressure cases. In free spray case which the injection spray has no wall impaction, the spray dispersion and vapour fraction increase and drop sizes decrease with increasing injection pressure. The same phenomena appears more clearly in wall impaction cases.

• 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%.

• Journal of Power System Engineering
• /
• v.9 no.4
• /
• pp.65-70
• /
• 2005

A liquid storage rectangular tank structures are used in many fields of civil, mechanical and marine engineering. Especially, Ship structures have many tanks in contact with inner or outer fluid, like ballast, fuel and cargo tanks. Fatigue damages are sometimes observed in these tanks which seem to be caused by resonance with exciting force of engine and propeller. Vibration characteristics of these thin walled tanks in contact with fluid near engine propeller are strongly affected by added mass of containing fluid. Therefore it is essentially important to estimate the added mass effect to predict vibration of the tank structures. Many authors have studied vibration of cylindrical and rectangular tanks structures containing fluid. Few research on dynamic interaction among tank walls through fluid are reported in the vibration of rectangular tanks recently. In case of rectangular tanks, structural coupling between adjacent panels and effect of vibration modes of multiple panels on added mass have to be considered. In the present paper, coupling effect between panels of tank structure on added mass of containing fluid, the effect of structural constraint between panels on each vibration mode for fluid region have investigated numerically and experimentally.

• Journal of ILASS-Korea
• /
• v.2 no.2
• /
• pp.8-15
• /
• 1997

Combustion chamber systems using spray impinged on walls have been studied for improving combustion characteristics in high speed direct injection diesel engines. The fuel spray injected in a small combustion chamber may be easily impinged and deposited on the wall. The fuel deposit has been considered as the cause for unburned emission due to difficulty of fuel-air mixing. In this paper w-shaped combustion chamber which has four raised pips on the side wall is introduced and discussed by comparing with conventional chamber with no pips. The computer code employing new spray-wall interaction model in general non-orthogonal grids is used in here. The model is applied into the new chamber shape with raised pips. In this chamber system four-hole nozzle is used, and the sprays injected from the each hole impact on lands raised from the chamber wall surface. After impacting, the sprays break up into much smaller drops and distribute over all the chamber space, instead of distributing just near the wall surface in conventional omega-shape. The results showed the potential of the w-shaped chamber employing pips for dispersing droplets so as tn avoid the fuel deposit regions.

• Journal of the Korean Ceramic Society
• /
• v.50 no.6
• /
• pp.416-422
• /
• 2013

Cullet-loess tile bodies are successfully fabricated using cullet, loess, hollow microspheres, and sintering additives (borosilicate glass frit, boric acid, or fumed silica) as starting materials. The effects of the additive composition and sintering temperature on the sintered density and flexural strength of the cullet-loess tile bodies are investigated. The sintered density of the cullet-loess tile bodies increases with an increase in the sintering temperature as a result of the enhanced densification of pore walls through the viscous flow of a liquid phase formed from the glass frit and sintering additives. The flexural strength of the cullet-loess tile bodies increases with increases in the sintering temperature and the cullet content in the starting composition. A maximal flexural strength of 40 MPa is obtained in cullet-loess tile bodies sintered with glass frit at $800^{\circ}C$ in air.

• Nuclear Engineering and Technology
• /
• v.49 no.4
• /
• pp.781-786
• /
• 2017

The presence of crust on the inner walls of metallic ducts impairs transportation because crust completely or partially hinders the passage of fluid to the processing unit and causes damage to equipment connected to the production line. Its localization is crucial. With the development of the electronic imaging system installed at the Argonauta/Nuclear Engineering Institute (IEN)/National Nuclear Energy Commission (CNEN) reactor, it became possible to visualize crust in the interior of metallic piping of small diameter using real-time neutron radiography images obtained with a low neutron flux. The obtained images showed the resistance offered by crust on the passage of water inside the pipe. No discrepancy of the flow profile at the bottom of the pipe, before the crust region, was registered. However, after the passage of liquid through the pipe, images of the disturbances of the flow were clear and discrepancies in the flow profile were steep. This shows that this technique added the assembled apparatus was efficient for the visualization of the crust and of the two-phase flows.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.24 no.11
• /
• pp.1497-1505
• /
• 2000

A numerical study is made on the ice-formation for a laminar flow in a curved channel. When the water flows through the curved channel with the walls specified below the freezing temperature, the ice layer has been formed on the curved surface, different from that of a straight channel. The fluctuation of ice layer has been predicted, considering the variation of velocity and temperature near the curved portion of channel. The study also takes into account the interaction existing between the laminar flow and the curved channel. In the solution strategy, the present study is substantially different from the existing works in that the complete set of governing equations in both the solid and liquid regions are resolved. The results from this study have been mainly presented, focusing on the variation of ice layer close to the curved portion. Numerical results have been obtained parametrically by varying the curved angle and the radius of curvature of channel, in addition to the variation of Reynolds numbers and wall temperatures of channel. The results show that the curved shape of channel has the great effect on the thickness of the solidification layer. The wave of ice layer thickness appears in the vicinity of curved portion. This behavior of ice layer has been amplified as is the increasing of curved angle and the radius of curvature of channel. In addition, the ice layer becomes thin as Reynolds numbers in increasing. And also, as the wall temperature of channel increases, the width of channel becomes to be shrunk due to the growth of ice layers in the upper and lower wall of channel.

• Korean Journal of Microbiology
• /
• v.40 no.2
• /
• pp.115-120
• /
• 2004

A Gram (-), rod-shaped bacterium in size of 1.3∼$1.8{\times}0.35{\mu}m$ inhibiting the growth of cyanobacterium (Ana-baena cylindrica) was isolated and designated NG-2 in this manuscript. This isolate showed positive reactions for catalase and oxidase, and optimal growth conditions of 35∼TEX>$40<^{\circ}C$ and pH 9.0. In a mixed-culture of A. cylindrica and the isolate, each microorganism grew inverse-proportionally, and the cyanobacterial vegetative cells almost completely disappeared within 24 hours. NG-2 lysed A. cylindrica only under light, which means that lytic activity of NG-2 was dependent on the photosynthetic activity of host. When observed under phase contrast microscope, the isolate lysed vegetative cells of A. cylindrica in scattered state in a liquid medium, whereas het-erocysts have not been lysed. When cyanobacterial cell walls have been lysed partly, NG-2 attatched around A. cylindrica filament and formed colony, then encouraged complete lysis of cyanobacterial cells. The isolate showed similar lytic activity in natural water as in an artificial medium. And lytic activity of NG-2 was enhanced when attached on expandable polystyrene bead.

• Journal of Microbiology and Biotechnology
• /
• v.14 no.6
• /
• pp.1114-1119
• /
• 2004

The biofilms on pipe walls in water distribution systems are of interest since they can lead to chlorine demand, coliform growth, pipe corrosion, and water taste and odor problems. As such, the study described in this paper is part of an AWWARF and Tampa Bay Water tailored collaboration project to determine the effect of blending different source waters on the water quality in various distribution systems. The project was based on 18 independent pilot distribution systems (PDS), each being fed by a different water blend (7 finished waters blended in different proportions). The source waters compared were groundwater, surface water, and brackish water, which were treated in a variety of pilot distribution systems, including reverse osmosis (RO) (desalination), both membrane and chemical softening, and ozonation-biological activated carbon (BAC), resulting in a total of 7 different finished waters. The observations from this study consistently demonstrated that unlined ductile iron was more heavily colonized by a biomass than galvanized steel, lined ductile iron, and PVC (in that order) and that the fixed biomass accumulation was more influenced by the nature of the supporting material than by the water quality (including the secondary residual levels). However, although the bulk liquid water cultivable bacterial counts (i.e. heterotrophic plate counts or HPCs) did not increase with a greater biofilm accumulation, the results also suggested that high HPCs corresponded to a low disinfectant residual more than a high biofilm inventory. Furthermore, temperature was found to affect the biofilms, plus the AOC was important when the residual was between 0.6 and 2.0 mg $Cl_2/l$. An additional aspect of the current study was that the potential of the exoproteolytic activity (PEPA) technique was used along with a traditional so-called destructive technique in which the biofilm was scrapped off the coupon surface, resuspended, and cultivated on an R2A agar. Both techniques indicated similar trends and relative comparisons among the PDSs, yet the culturable biofilm values for the traditional method were several orders of magnitude lower than the PEPA values.

• Journal of Korean Society of Water and Wastewater
• /
• v.26 no.5
• /
• pp.609-617
• /
• 2012

A dynamic water quality model is presented in order to simulate water quality under slowly varying flow conditions over time. To improve numerical accuracy, the proposed model uses a lumped system approach instead of extended period simulation, unlike the other available models. This approach can achieve computational efficiency by assuming liquid and pipe walls to be rigid, unlike the method of characteristics, which has been successfully implemented in rapidly varying flows. The discrete volume method is applied to resolve the advection and reaction terms of the transport equation for water quality constituents in pipes. Numerical applications are implemented to the pipe network examples under steady and unsteady conditions as well as hydraulic and water quality simulations. The numerical results are compared with EPANET2, which is a widely used simulation model for a water distribution system. The model results are in good agreement with EPANET2 for steady-state simulation. However, the hydraulic simulation results under unsteady flows differ from those of EPANET2, which causes a deviation in water quality prediction. The proposed model is expected to be a component of an integrated operation model for a water distribution system if it is combined with a computational model for rapidly varying flows to estimate leakage, pipe roughness, and intensive water quality.