• Journal of Mechanical Science and Technology
• /
• v.17 no.9
• /
• pp.1371-1379
• /
• 2003

The effects of change in injection pressure on spray structure in high temperature and pressure field have been investigated. The analysis of liquid and vapor phases of injected fuel is important for emissions control of diesel engines. Therefore, this work examines the evaporating spray structure using a constant volume vessel. The injection pressure is selected as the experimental parameter, is changed from 22 MPa to 112 MPa using a high pressure injection system (ECD-U2). Also, we conducted simulation study by modified KIVA-II code. The results of simulation study are compared with experimental results. The images of liquid and vapor phase for free spray were simultaneously taken by exciplex fluorescence method. As experimental results, the vapor concentration of injected fuel is leaner due to the increase of atomization in the case of the high injection pressure than in that of the low injection pressure. The calculated results obtained by modified KIVA-II code show good agreements with experimental results.

• Journal of Advanced Marine Engineering and Technology
• /
• v.23 no.1
• /
• pp.47-53
• /
• 1999

Small compression-ignition direct injection engines have been developed as a measure to improve a fuel efficiency and reduce harmful exhaust gases. Those small engines generally employ high injection pressure increase on the spray impacting on a wall is discussed in this paper. The gas phase is modelled by the Eulerian continuum conservation equations of mass momentum energy and fuel vapour fraction. The liquid phases is modelled following the discrete droplet model approach in Lagrangian form and the droplet wall interaction is modelled as a func-tion of the velocity normal to impaction lands. The droplet distributions vapor fractions and gas flows are analyzed in various injection pres-sure cases. The penetrations of wall spray and vapor increase and the Sauter mean diameter decreases with increasing injection pressure.

• Journal of Power System Engineering
• /
• v.9 no.4
• /
• pp.214-219
• /
• 2005

The effects of change in injection pressure on spray structure in high temperature and pressure field have been investigated. The analysis of liquid and vapor phases of injected fuel is important for emissions control of diesel engines. Therefore, this work examines the evaporating spray structure using a constant volume vessel. The injection pressure is selected as the experimental parameter, is changed from 72MPa to 112MPa by using a common rail injection system(ECD-U2). The images of liquid and vapor phase in the evaporating free diesel spray are simultaneously taken by exciplex fluorescence method. As a result, it can be confirmed that the distribution of vapor concentration is more uniform in the case of the high injection than in that of the low injection pressure.

• Journal of Power System Engineering
• /
• v.16 no.4
• /
• pp.37-43
• /
• 2012

This paper performed experimental research in order to measure boiling heat transfer coefficient of water in microchannel with hydraulic diameter of $500{\mu}m$. Tests were conducted within the ranges of heat fluxes from 100 to 400 kW/$m^2$, vapor qualities from 0 to 0.2, and mass fluxes of 200, 400, and 600 kg/$m^2s$. From the experimental results, it was found that flow boiling heat transfer coefficient is not dependent on mass flux or vapor quality, but instead on heat flux to a certain degree. The measured data of heat transfer are compared to a few available correlations proposed for mini-channels. Among them, Sun and Mishima's correlation is found to predict the present data well, within the mean absolute error of 17.84%.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.14 no.10
• /
• pp.844-853
• /
• 2002

A dynamic model which simulates the coupled heat and mass transfer within a vertical tube absorber was developed. The liquid film is a binary mixture of two components, and both of these components are present in the vapor phase. The pressure, concentration, temperature and mass flow rate of the vapor are obtained by assuming that the pressure is uniform within an absorber. The model was applied to an absorber for an ammonia/water absorption refrigerator. The transient behaviors of the pressure, the outlet temperature and the concentration of the solution and the cooling water outlet temperature on a step change at the absorber inlet of the cooling water temperature, the vapor mass flow rate and the concentration of the solution were shown.

• Journal of Powder Materials
• /
• v.10 no.3
• /
• pp.186-189
• /
• 2003

A chemical vapor condensation (CVC) process using the pyrolysis of metal-organic precursors was applied to produce the nanosized $WO_3$ powders. Morphology and phase changes of the synthesized $WO_3$ powder as a function of CVC parameters were investigated by XRD, BET and TEM. The agglomerated nanosized monoclinic $WO_3$ powders with nearly spherical shape and 10-38 nm in mean diameter could be obtained. Conditions to produce the $WO_3$ nanopowders are presented in this paper.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.24 no.2
• /
• pp.54-58
• /
• 2014

AlN (Aluminum Nitride) crystals were grown by a PVT (Physical Vapor Transport) method and were characterized to phases on the growth temperature. The crystals phase and morphology were analyzed using an optical stereo-microscope and the optimum temperature for the growing was determined. In this report, the characteristics of the AlN crystals grown at various temperatures were reported.

• Bulletin of the Korean Chemical Society
• /
• v.32 no.10
• /
• pp.3571-3574
• /
• 2011

Nano-scaled metal oxides have been attractive materials for sensors, photocatalysis, and dye-sensitization for solar cells. We report the controlled synthesis and characterization of single crystalline $TiO_2$ nanowires via a catalyst-assisted vapor-liquid-solid (VLS) and vapor-solid (VS) growth mechanism during TiO powder evaporation. Scanning electron microscope (SEM) and transmission electron microscope (TEM) studies show that as grown $TiO_2$ materials are one-dimensional (1D) nano-structures with a single crystalline rutile phase. Also, energy-dispersive X-ray (EDX) spectroscopy indicates the presence of both Ti and O with a Ti/O atomic ratio of 1 to 2. Various morphologies of single crystalline $TiO_2$ nano-structures are realized by controlling the growth temperature and flow rate of carrier gas. Large amount of reactant evaporated at high temperature and high flow rate is crucial to the morphology change of $TiO_2$ nanowire.

• ETRI Journal
• /
• v.33 no.4
• /
• pp.645-647
• /
• 2011

In this study, a microcapillary pumped loop (MCPL) that can be used as a cooling device for small electronic and telecommunications equipment has been developed. For thin devices such as an MCPL, securing a vapor flow space is a critical issue for enhancing the thermal performance. In this letter, such enhancement in thermal performance was accomplished by eliminating condensed droplets from the vapor line. By fabricating the grooves in the vapor line to eliminate droplets, a decrease in thermal resistance of about 63.7% was achieved.

• Journal of Advanced Marine Engineering and Technology
• /
• v.20 no.3
• /
• pp.11-18
• /
• 1996

Liquid droplets of water and argon surrounded by their vapor have been simulated by the milecular dynamics method. To explore the surface phenomena of clusters, each molecule is classified into 'liquid', 'surface', or 'vapor' with respect to the number of neighbor molecules. The contribution of a 'surface' molecule of the water cluster to the far infrared spectrum is almist the same as that of the 'liquid' molecule. Hence, the liquid-vapor interface is viewed as geometrically and temporally varying boundary of 'liquid' molecules with only a single layer of 'surface' molecules that might have different characteristics from the 'liquid' molecules. The time scale of the 'phase change' of each molecule is estimated for the argon cluster by observing the instantancous kinetic and potential energies of each molecule. To compare the feature of clusters with macroscopic droplets, the temperature dependence of the surface tension of the argon cluster is estimated.