• Proceedings of the SAREK Conference
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• 2005.11a
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• pp.335-340
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• 2005

Nonlinear and forced oscillations of supported viscous droplet were focused in the present study. The droplet has a free contact line with solid plate and inviscid fluid. Natural frequencies of a pendant droplet have been investigated experimentally by imposing the acoustic wave while the frequency is being increased at a fixed amplitude. The evaporation was observed at atmosphere pressure. The droplet was recorded throughout the entire evaporation process and transient variations of the volume was measured. The evaporation process of oscillating droplet with thermofoil has been also observed to investigate analyzing the resonance effect on the thermal characteristics of droplet. It is found that a pendant droplet shows the resonant behaviors at each mode similar to the theoretical analysis. During imposing the acoustic wave, the pendant droplet makes a rotating motion in its longitudinal axis which is a new shape oscillation mode. The evaporation rate of a pendant droplet at resonant frequency is significantly enhanced.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.5
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• pp.1338-1346
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• 1994

The objective of this study is to investigate the effect of various parameters, such as temperature, mean current density and voltage on the performance of phosphoric acid fuel cell (PAFC) by numerical analysis. Two types of flow passages, which are Z-parallel type and Z-counter type, are evaluated to obtain the best current density and temperature distribution. Parametric studies and sensitivity analysis of the PAFC system's operation in single cell are accomplished. A steady state simulation of the entire system is developed using nonlinear ordinary differential equations. The finite difference method and trial and error procedures are used to obtain a solution.

• Proceedings of the Membrane Society of Korea Conference
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• 1998.04a
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• pp.105-109
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• 1998

1. Introduction : In microfiltration the transport, deposition and removal of particles control cake formation on a filter. In this connection a new model on cake formation, based on the wall shear stress, was tested here in comparison with experiments of fine particle slurry under Taylor-vortex flow. The model expresses the deposition process for particles as two first-order steps in series of mass transfer and adhesion, and their removal process as a linear relation to the wall shear stress. This embraces characteristics of both dead-end and crossflow filtration. The correlation resulting from fitting to experimental data represented the experimental data reasonably well. This study will be helpful in analyzing fouling in heat exchangers.

• 한국연소학회:학술대회논문집
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• 1998.10a
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• pp.1-8
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• 1998

Waste combustion above a grate is the core process of incineration systems, stability of which should be guaranteed for emission minimization. However, complicated reactions and heat and mass transfer phenomena make understanding the process difficult. One dimensional bed combustor with a numerical combustion model is utilized to investigate the combustion process of the bed, using cubic wood particles as a simulated fuel. Bed combustion behavior is characterized with apparent flame propagation speed, which has close relationship with air supply rate and chemical and physical characteristics of the fuel. Base on the availability of oxygen, two distinct reaction zone is identified; the oxygen-limited and the reaction-limited zone leading to the extinction by excessive convection cooling. The numerical modeling shows good agreement with the experimental results. The transient bed combustion behavior of local temperature and oxygen consumption rate is adequately reproduced. The numerical model is extended to model the waste bed combustion of a commercial incineration plant, which shows meaningful results as well.

• Transactions of the Korean hydrogen and new energy society
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• v.14 no.3
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• pp.195-206
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• 2003

Polymer electrolyte membrane fuel cells(PEMFC) are very interesting power source due to high power density, simple construction and operation at low temperature. But they have problems such as high cost, improvement of performance and effect of temperature. This problems can be approached using mathematical models which are useful tools for analysis and optimization of fuel cell performance and for heat and water management, in this paper, transient model consists of various energy terms associated with fuel cell operation using the mass and energy balance equation. And water transfer in the membrane is composed of back diffusion and electro-osmotic drag. The temperature calculated by transient model approximately agreed with the temperature measured by experiment in constant current condition.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.17 no.5
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• pp.583-589
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• 1988

Condensation of water vapor into an absorbent liquid of LiBr-water solution falling over a bank of water cooled horizontal tubes was investigated theoretically. The governing conservation equation for a re-defined physical transport phenomena were solved numerically using a finite difference method. Raw parameters were used in this study, since reliable experimental data is required prior to a dimensionless parametric study. The average values of wall heat transfer coefficient and interfacial absorption rate were defined to see the system performance. Other parameters include tube diameter, streamwise coordinate (and number of tubes in row), mass flow rate, and the wall temperature. The effects of these quantities on the absorption processes and suggestions for a rational system design have been presented.

• Proceedings of the SAREK Conference
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• 2008.11a
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• pp.3-8
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• 2008

Effect of external heating rate on the conversion efficiency for the steam reforming of methanol is investigated numerically considering both heat and mass transfer of the species in a packed bed microreactor. In a results from the numerical simulation, the conversion efficiency of methanol has been obtained for the external heating rate. The axial variation of mole fraction of methanol has been additionally presented for several cases of external heating rates. The results show that for the constant inlet temperature condition the conversion efficiency of methanol increases with external heating rate over the range of operating conditions.

• Proceedings of the SAREK Conference
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• 2008.11a
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• pp.624-629
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• 2008

The problem was derived from a simple process in solar water heating system. In a new designed electro less separated system we involved a kind of bubble pump. Beside experiment analysis, numerical simulation of the core of bubble pump is also very important. In this paper we investigated the motion of bubbles in vertical tube in two dimensions. The heat and mass transfer was simulated. The result of numerical simulation give a significant help of optimize design of bubble pump.

• International Journal of Air-Conditioning and Refrigeration
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• v.13 no.3
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• pp.158-166
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• 2005

The present study investigated experimentally and numerically the enhancement of absorption performance due to the waviness of falling film in the vertical absorber tube. The momentum, energy and mass diffusion equations were utilized to find out temperature and concentration profiles at both the interfaces of liquid solution and refrigerant vapor and the wall. Flow visualization was performed to find out the wetting characteristics of the falling film. The maximum heat transfer coefficient was obtained for the wavy flow using spring as an insert device through both numerical and experimental studies. Based on the numerical and experimental results, the maximum absorption rate was found for the wavy-flow using spring as the insert device. The differences between experimental and analytical results ranged from $5.0\;to\;25\%\;when\;Re_j>100$.

• Journal of ILASS-Korea
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• v.19 no.2
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• pp.82-87
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• 2014

Nanofluids are that metallic or nonmetallic nanometer-sized particles are dispersed in liquid. They can be used in various fields to increase the heat transfer rate because the thermal conductivity of nanofluids can be increased significantly. Nanofluids may be used as a good alternative of coolants in spray cooling. This study conducted experiments to compare the characteristics of sprays between water and nanofluid sprays. The radial distributions of droplet velocities and diameters of water, 0.2% wt.(weight), and 0.5% wt. $Al_2O_3$ nanofluids at the pressure of 0.2 and 0.3 MPa were measured by laser doppler instruments. The radial distributions of droplet diameters and velocities at two axial positions with water and 0.2% wt. nanofluid sprays didn't show much difference. A big difference, however, was observed between 0.5% wt. nanofluid and water sprays. With the increase of the mass of nano-particles, the average droplet diameters were increased and the average droplet velocities were decreased.