• Particle and aerosol research
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• v.9 no.3
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• pp.163-171
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• 2013

Soot particles emitted from combustion processes are often coated by non-absorbing organic materials, which enhance the global warming effect of soot particles. It is of importance to study the condensation characteristics of soot particles experimentally and theoretically to reduce the uncertainty of the climate impact of soot particles. In this study, the condensational growth of soot particles in a tubular coater was modeled by a one-dimensional (1D) plug flow model and a two-dimensional (2D) laminar flow model. The effects of 2D heat and mass transports on the predicted particle growth were investigated. The temperature and coating material vapor concentration distributions in radial direction, which the 1D model could not accounted for, affected substantially the particle growth in the coater. Under the simulated conditions, the differences between the temperatures and vapor concentrations near the wall and at the tube center were large. The neglect of these variations by the 1D model resulted in a large error in modeling the mass transfer and aerosol dynamics occurring in the coater. The 1D model predicted the average temperature and vapor concentration quite accurately but overestimated the average diameter of the growing particles considerably. At the outermost grid, at which condensation begins earliest due to the lowest temperature and saturation vapor concentration, condensing vapor was exhausted rapidly because of the competition between condensations on the wall and on the particle surface, decreasing the growth rate. At the center of the tube, on the other hand, the growth rate was low due to high temperature and saturation vapor concentration. The effects of Brownian diffusion and thermophoresis were not high enough to transport the coating material vapor quickly from the tube center to the wall. The 1D model based on perfect radial mixing could not take into account this phenomenon, resulting in a much higher growth rate than what the 2D model predicted. The result of this study indicates that contrary to a previous report for a thermodenuder, 2D heat and mass transports must be taken into account to model accurately the condensational particle growth in a coater.

• Proceedings of The Korean Society of Agricultural and Forest Meteorology Conference
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• 2003.09a
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• pp.115-128
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• 2003

o What is the flux \ulcorner Flux is the transfer of a quantity per unit area per unit time. The quantities are mass, heat, moisture, momentum and pollutant in micrometeorology. Kinematic flux (Fluid). The reduction in wind speed due to frictional drag transfers momentum from the atmosphere to the surface, creating turbulence that mixes the air and transports heat and water from the surface into the lower atmosphere. (omitted)

• Journal of the korean society of oceanography
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• v.38 no.1
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• pp.11-16
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• 2003

The three dimensional structure of thermohaline circulation in a D-plane is investigated using a conceptual two layer model and a scaling argument. In this simple model, the water mass formation region is excluded. The upper layer represents the oceans above the main thermocline. The lower layer represents the deep ocean below the thermocline and is much thicker than the upper layer. In each layer, geostrophy and the linear vorticity balance are assumed. The cross interfacial velocity that compensates for the deep water mass formation balances downward heat diffusion from the top. From the above relations, we can determine the thickness of the upper layer, which is the same as thermocline depth. The results we get is basically the same as that we get for an f-plane ocean or the classical thermocline theory. Mass budget using the velocity scales from the scaling argument shows that western boundary and interior transports are much larger than the net meridional transport. Therefore in the thermohaline circulation, horizontal circulation is much stronger than the vertical circulation occuring on a meridional plane.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.1912-1915
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• 2007

The disjoining pressure is critical in modeling the transport phenomena in small scales. They are very useful in characterizing the non-continuum effects that are not negligible in heat and mass transports in the film of less than submicro-scales. We present he disjoining pressure of thin film absorbed on solid substrate using Molecular Dynamics Simulation (MD). The disjoining pressure with respect to the film thickness is accurately calculated in the resolution of a molecular scale. The characteristics of the pressure are discussed regarding the molecular nature of the fluid system like molecular diameter and intermolecular interaction. Also, the MD results are compared with those based on the macroscopic approximation of the slab-like density profile. Significant discrepancy is observed when the effective film thickness is less than several molecular diameter

• Journal of the Korean Electrochemical Society
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• v.11 no.4
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• pp.273-283
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• 2008

GDL(Gas Diffusion Layer) is one of the main components of PEM fuel cell. It transports reactants from the channel to the catalyst and removes reaction products from the catalyst to the channels in the flow filed plate. It is known that higher permeability of GDL can make it possible to enhance the gas transport through GDL, leading to better performance. And MEA's temperature is determined by gas and heat transport. In this paper, three dimensional numerical simulation of PEM fuel cell of parallel channel and serpentine channel by the permeability of GDL is presented to analysis heat and mass transfer characteristics using a FLUENT modified to include the electrochemical behavior. Results show that in the case of parallel channel, performance variation with change of permeability of GDL was not so much. This is thought because mass transfer is carried out by diffusion mechanism in parallel channel. Also, in the case of serpentine channel, higher GDL permeability resulted in better performance of PEM fuel cell because of convection flow though GDL. And mass transfer process is changed from convection to diffusion when the permeability becomes low.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.679-682
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• 2002

Energy dissipations in a general PHE flow are the compounded effects of the piled corrugate geometries and its wall pressure and temperature distributions. In addition, although the exchangers are substantial pieces of engineering equipment, they are composed of a very large number of nominally identical and small geometrical elements. In the present numerical study, the three-dimensionally complicated energy dissipation fields and those wall-shape-induced flow destabilization are investigated in the cross-corrugated passages, which result in high energy transports with comparatively low pressure drop. We revealed the critical conditions as $Re=157.3 for the wall-shape-induced flow destabilization in a general PHE element by initial value method, or shooting method, and compare its value to that of analytical solution of plane Poiseille flow, two-dimensional grooved flow and so on. We also observed the detailed variation of flow field and energy transportation with changes in time and flow variables such as Reynolds number. Lastly, we considered the flow natural frequency, or Strouhal number, with variation of hydrodynamic conditions for the best use of active control, such as forced mass flow rate pulsative flow, to enhance energy transportation.