• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.2
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• pp.176-184
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• 1999

Numerical and experimental studies were performed to examine the characteristics of heat and mass transfer processes for a Micro Heat Pipe(MHP) with a triangular cross-section. Solutions on mass flow rate, pressure variation, and radius of meniscus were obtained using the mathematical model developed by Faghri and Khrustalev. To obtain an increase in capillary limitation, a triangular tube with curved walls was designed and fabricated. The measurement by microscope showed that the radius at corners of the tube was ranging between 0.03-0.05mm. Performance test for MHPs using the triangular tube with curved walls proved a substantial increasement in heat transport limitation, with 4.5W and 2.0W in case of using water and ethanol as a working fluid, respectively. In the previous study by Faghri a limitation of 0.5W was reported for a water MHP with a regular triangular tube.

• Journal of the Korean Wood Science and Technology
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• v.40 no.5
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• pp.352-362
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• 2012

Mass transfer behavior in wood was estimated through its microscopic structure. The diffusion coefficients which were decided by theoretical equations are influenced by different anatomical properties of wood. From the experiment, the moisture flux was linear to the square root of time. The diffusion coefficients had a regular tendency during the time elapse. During the modeling, it is necessary to understand the limitation of parameters and consider the particular situation to be simulated. In hardwood, because the apertures were not considered, tangential mass transfer simulation was totally different from experiment. As a result, a hardwood model design should consider the apertures which are even on the fiber walls.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1546-1551
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• 2004

This paper presents a mathematical model to predict the frost properties and heal and mass transfer within the frost layer formed on a cold plate. The laminar flow equations for the air-side are analyzed. and the empirical correlations of local frost properties are employed in order to predict the frost layer growth. The correlations of local frost density and effective thermal conductivity of frost layer, obtained from various experimental conditions, are derived as functions of various frosting parameters (Reynolds number, frost surface temperature, absolute humidity and temperature of moist air, cooling plate temperature, and frost density). The numerical results are compared with experimental data and the results of various models to validate the present model, and agree well with experimental data within a maximum error of 10%. The heat and mass transfer coefficients obtained from the numerical analyses are presented, as the results, it is found that the model for frost growth using the correlation of heat transfer coefficient without solving air flow have a limitation in its application.

• Membrane and Water Treatment
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• v.3 no.3
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• pp.151-168
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• 2012

Gas sparging is one of the techniques used to control the concentration polarization during ultrafiltration. In this work, the effects of gas sparging in stratified flow regime were investigated during gel layer controlling cross flow ultrafiltration in a rectangular channel. Synthetic solution of pectin was used as the gel forming solute. The liquid and gas flow rates were selected such that a stratified flow regime was prevalent in the channel. A mass transfer model was developed for this system to quantify the effects of gas flow rates on mass transfer coefficient (Sherwood number). The results were compared with the case of no gas sparging. Gas sparging led to an increase of mass transfer coefficient by about 23% in this case. The limitation of the developed model was also evaluated and it was observed that beyond a gas flow rate of 20 l/h, the model was unable to explain the experimental observation, i.e., the decrease in permeate flux with flow rate.

• KSBB Journal
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• v.8 no.5
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• pp.417-423
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• 1993

The effect of moisture content of biocatalyst on the performance of a gas phase continuous bioreactor was investigated along with study on the mass transfer limitation. The biocatalysts whose moisture contents are 46.2% and 37.2%, respectively were prepared by immobilization of alcohol oxidase on Amberlite IRA-400, following by slow dehydration method, and packed into a column. Relative production rate (RPR), acetaldehyde composition ($X_p$) and conversion (X) of biocatalysts (37.2%) are better than those of biocatalysls (46.2%), and it was considered that these are attributed to the mass transfer enhancement in the gas phase compared with the aqueous phase.

• Journal of Hydrogen and New Energy
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• v.12 no.3
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• pp.231-238
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• 2001

Electrocatalytic activity of palladium for hydrogen oxidation and reduction was studied using AC impedance method. The system under study was arranged in electrolytic mode consisting of Pd electrode under study, Pt counter electrode and Nafion electrolyte between them. Two types of Pd electrodes were used - carbon-supported Pd (Pd/C) and Pd foil electrode. Pd/C anode contacting pure hydrogen showed a steady decrease of charge transfer resistance with the increase of anodic overpotential, which is an opposite trend to that found with Pd foil anode. But Pd foil cathode also exhibited a decrease of the resistance with the increase of cathodic overpotential. The relationship between imposition of overpotential and subsequent change of the charge transfer resistance is determined by the ratio of the rate of faradaic process to the rate of mass transportation; if mass transfer limitation holds, increase of overpotential accompanies the increase of charge transfer resistance. Regardless of the physical type of Pd electrode, the anode contacting hydrogen/oxygen gas mixture did not reveal any independent arc originated from local anodic oxygen reduction.

• 한국신재생에너지학회:학술대회논문집
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• 2010.11a
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• pp.133.2-133.2
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• 2010

Fischer-Tropsch synthesis (FTS) was carried out in heat-exchanger typed reactor with cobalt metallic foam catalyst. Considering the heat and mass transfer limitations in the cobalt catalyst, a Co-foam catalyst with an inner metallic foam frame and an outer cobalt catalyst was developed. The Co-foam catalyst was highly selective toward liquid hydrocarbon production and the liquid hydrocarbon productivity at $203^{\circ}C$ reached to $52.5ml/(kg_{cat}{\cdot}h)$, which was higher than that obtained by the Co-pellet. Furthermore, the heat-exchanger typed reactor was developed to efficiently control the highly exothermic reaction heat. The reaction heat generated in the FTS reaction on the cobalt active site was easily transferred to reactor wall by the metallic foam in the catalyst and the transferred reaction heat was directly removed by the hot oil which circulated the wall side of the heat-exchanger typed reactor.

• 한국생물공학회:학술대회논문집
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• 2002.04a
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• pp.269-270
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• 2002

Oxygen is a key substrate in animal cell metabolism and its consumption is thus a parameter of great interest for monitoring and control in animal cell culture bioreactor. The use of a gas-permeable membrane offered the possibility to provide the required quantity of oxygen into the culture. while avoiding problems of foaming or shear damage generally linked to sparging. For determining the optimum DO control strategy of this gas-permeable membrane aeration bioreactor, the oxygen transfer rate coefficient was measured with varying $N_2$ ratio in inlet air. The results showed that an increasing mass flow rate of nitrogen reduced the $K_La$ value. and 5% nitrogen in air did not result in any oxygen limitation.

• Coupled systems mechanics
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• v.3 no.1
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• pp.73-88
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• 2014

The paper deals with a model founded on the physical processes in concrete subject to high temperatures. The model is developed in the framework of continuum damage mechanics and the theory of porous media and is demonstrated on selected structures. The model comprises balance equations for heat transfer, mass transfer of water and vapour, for linear momentum and for reaction. The balance equations are completed by constitutive equations considering the special behaviour of concrete at high temperatures. Furthermore, the limitation and decline of admissible stresses is achieved by using a composed, temperature depending crack surface with a formulation for the damage evolution. Finally, the complete coupled model is applied to several structures and to different concrete in order to determine their influence on the high-temperature-behaviour.

• Journal of Korean Society of Environmental Engineers
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• v.27 no.12
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• pp.1292-1297
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• 2005

The use of ozone in water and wastewater treatment systems has been known to be a process that is limited by mass transfer. The most effective way to overcome this limitation is to increase the interfacial area available for mass transfer by decreasing the size of the ozone gas bubbles that are dispersed in solution. Electrostatic spraying(ES) of ozone into water was investigated in this work as a method of increasing the rate of mass transfer of ozone into a solution and thereby increasing the rate of phenol oxidation. Results were obtained for ES at input power levels ranging from 0 to 4 kV and compared with two different pore-size bubble diffusers($10{\sim}15{\mu}m$ and $40{\sim}60{\mu}m$). It was determined that the rate of mass transfer could be increased by as much as 40% when the applied voltage was increased from 0 to 4 kV as a result of the smaller bubbles generated by ES. In addition, ES was shown to be more effective than the medium-pore-size($10{\sim}15{\mu}m$) bubble diffuser and the best results were achieved at low gas flow rates.