• Korean Chemical Engineering Research
• /
• v.60 no.2
• /
• pp.217-222
• /
• 2022

It is very important to analyze the OCV change behavior during the open circuit potential holding (OCV holding) process, which accelerates the evaluation of the electrochemical durability of the PEMFC membrane. In this study, an empirical formula using the experimental data of three MEAs with different durability was created and compared. The durability evaluation time of the reinforced membrane MEA without radical scavenger inside the membrane was 383 h, and the durability evaluation time of the reinforced membrane MEA with radical scavenger inside the membrane was 1,000 and 1,650 h, respectively. The degradation of the membrane was divided into the reversible degradation that can be recovered by activation and the irreversible degradation that is not recovered. The irreversible degradation of the membrane was indicated by an increase in hydrogen permeability, and the change in hydrogen permeability was similar to the irreversible degradation constant c of all three MEAs. The initiation of irreversible deterioration without recovery is indicated by an increase in hydrogen permeability, and the OCV is not recovered due to an increase in hydrogen permeability, so the slope of the OCV recovery line (ORL) decreases, which can be confirmed by an increase in the constant c value of the empirical formula.

• Journal of the Microelectronics and Packaging Society
• /
• v.30 no.3
• /
• pp.64-72
• /
• 2023

In this study, after transferring graphene on a Cu substrate and printing a Sn-3.0Ag-0.5Cu Pb-free solder paste on the Cu substrate, effects of the transferred graphene on formations and growths of intermetallic compound (IMC) at the interface between the Cu substrate and the solder were reported during processes of reflow soldering and isothermal aging for 1000 h with various temperatures (125, 150, and 175 ℃). Thicknesses of Cu₆Sn₅ and Cu₃Sn IMCs at the interfaces with graphene were decreased during the reflow soldering and isothermal aging processes compared to those without graphene. The transferred graphene layers also showed that the growth rate constant and square of growth rate constant which related to the growth mechanisms of Cu₆Sn₅ and Cu₃Sn IMCs with t he t emperature a nd t ime of t he i sothermal aging c ould dramatically decreased.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.19 no.2
• /
• pp.90-96
• /
• 2018

Tracer experiments were carried out on two laboratory modes, "without media mode" and "with media mode", to examine the hydraulic characteristics of the anaerobic fluidized bed bioreactor (AFBR). For both configurations, a formula was derived for the hydraulics and data interpretation to obtain the actual characteristics of the reactor. The dispersion model is based on the assumption that carriers are non-reacting and the dispersion coefficient is constant. The model represents the one-dimensional unsteady-state concentration distribution of the non-reacting tracer in the reactors. The experimental results showed that the media increased the mixing conditions in the reactor considerably. For the reactor without media, in the range tested, the dispersion coefficient was at least an order of magnitude smaller than that of the reactor with media. Advective transport dominates and the flow pattern approaches the plug flow reactor (PFR) regime. The dispersion coefficient increased significantly as us, the superficial liquid velocity, was increased proportionally to 0.82cm/s. On the other hand, for the reactor with media, the flow pattern was in between a PFR and a completely mixed flow reactor (CMFR) regime, and the dispersion coefficient was saturated at us=0.41cm/s, remaining relatively constant, even at us=0.82cm/s. The dispersion coefficient depends strongly on the liquid Reynolds number (Re) or the particle Reynolds number (Rep) over the range tested.

• Korean Journal of Food Science and Technology
• /
• v.27 no.6
• /
• pp.845-851
• /
• 1995

To improve the utilization of pear in its processing, the cloudy and clear juice concentrates were prepared and their rheological properties were investigated in the range of temperatures($5{\sim}60^{\circ}C$) and concentrations($15{\sim}60^{\circ}Brix$). Pear juice concentrates showed flow behavior close to Newtonian fluids. Their flow behavior was also explained by applying Power law model and Herschel-Bulkley model. Flow behavior index did not have good correlation with concentration, but decreased with the increase of temperature, showing pseudoplastic properties. Consistency index increased with the increase of concentration and with the decrease of temperature. The effect of temperature and concentration on the apparent viscosity at 1500 1/s shear rate was examined by applying Arrhenius equation. The activation energy for flow of the cloudy and clear pear juice concentrates increased from $1.5140{\times}10^4\;to\;3.4141{\times}10^4\;J/kg{\cdot}mol$, and from $1.4762{\times}10^4\;to\;3.4963{\times}10^4\;J/kg{\cdot}mol$ with the increase of concentration, respectively. The influence of temperature on the apparent viscosity was more pronounced at higher concentration. And the concentration-dependent constant A decreased from $0.0789\;to\;0.0484^{\circ}Brix^{-1}$, and from $0.0786\;to\;0.0476^{\circ}Brix^1$ with the increase of temperature, respectively.

• Journal of the Korean Society for Marine Environment & Energy
• /
• v.11 no.3
• /
• pp.164-174
• /
• 2008

In this study we try to identify the three-dimensional mixing characteristics of Seomjin River discharges in Seomjin River Estuary and Gwangyang Bay using a seasonal field observation (CTD) during spring tide and a three-dimensional numerical model with EFDC (Environmental Fluid Dynamics Code). The tidal elevation conditions of the four main tidal harmonic constituents on the open boundary and river discharges and thermal effluents at the specific boundary are considered. The calculated harmonic constants of tide and tidal current agreed well with those of observations at two stations for tide and two stations for tidal current. The model successfully reproduced well known the estuarine circulation in Seomjin River Estuary where tide and river discharges are dominant forcings. In the winter mean discharges case, tidal currents move Seomjin River discharges in Seomjin River mouth and in the summer mean discharges case, river flows move Seomjin River discharges near ae Seomjin River Estuary. A three-dimensional mixing characteristics of Seomjin River Estuary show well a three-dimensional estuarine circulation and thermal effluents effect to the seasonal variation of river discharges.

• The Proceedings of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.9 no.1
• /
• pp.47-53
• /
• 1995

In this paper, the characteristics of breakdown voltage($\textrm{V}_{Brms}$) -temperature(T) for air insulated power installation in flowing air with variation of T(30[$^{\circ}C$] -180[$^{\circ}C$]) are presented. To study these subjects, needle-to-needle gap in the circular pipe(inner diameter 5[cm]) are used. Also, theories of gas discharge and hydrodynamics in pipe were used to analysis for the characteristics. The $\textrm{V}_{Brms}$ is proportional to flow velocity. At high velocity, $\textrm{V}_{Brms}$ is described the saturation. At high T(180[$^{\circ}C$]), $\textrm{V}_{Brms}$ is about 4.7(kV] lower than low T(30[$^{\circ}C$]). The empirical equation obtained from this study is $\textrm{V}_{Brms}=A\times{Log[Re}+B$. Where A, B : Constant.

• Fire Science and Engineering
• /
• v.22 no.3
• /
• pp.181-187
• /
• 2008

Numerical simulation of natural convection along a vertical wall was carried out to evaluate the computational fluid dynamics simulator, which is to be utilized for study of vertical wall fires. The computed velocity and temperature profiles were compared with measurements over the turbulent boundary layer formed along the wall of 4m high and constant temperature. It fumed out that the simulator with default parameters failed to predict the turbulent natural convection showing the boundary layer flow laminar. The grid size $\Delta$x=5mm, ${\Delta}y={\Delta}z=10mm$ and Smagorinsky constant of the large eddy simulation $C_s$=0.1 were chosen through parametric investigations. Though turbulent mixing was not enough, the velocity distribution near wall, peak velocity, and temperature profile in the turbulent boundary layer agreed well with the measurements.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.10 no.3
• /
• pp.343-348
• /
• 1986

An optical interference method was developed for measuring rapidly growing and evaporating liquid condensate films (e.g., Na$_{2}$SO$_{4}$, $K_{2}$SO$_{4}$) on solid surface exposed to flowing combustion product gases at film thicknesses well below the onset of complications due to run-off. To develop this optical system, this study investigated the optical parameters (e.g., polarization state, incident angle, target roughness, etc.) Trends for the Na$_{2}$SO$_{4}$(l) and $K_{2}$SO$_{4}$(l) deposition rates as a function of target temperature using this optical measuring system agree with the theoretical prediction of the vapor deposition. This study was able to extend the experimental range for vapor plus condensed phase transport and deposition. While previously unable to measure the evaporation rates interferometrically, these rates are estimated from the results of the investigation of polarization states.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.7 no.4
• /
• pp.305-312
• /
• 1995

In general, the radiation stresses based on the linear wave theory are overestimated which result in the discrepancy between the computed results and laboratory data of mean water level in the surf zone. Oh (1995) estimated the mean water level by using Svendsen's radiation stress model (1984) and compared with the experimental data. In this study. the computed results showed good agreements with the experimental data in the case of small wave steepness. while the results were overestimated in the case of large wave steepness. In this paper. the dimensionless radiation stress proposed by Svendsen (1984) is expressed in terms of relative water depth at breaking point and deep water wave steepness. The computed results are compared with the results calculated by d linear wave theory, Stive's model (1984). Sawaragi et al's model (1984) based on the spectrum of breaking wave components. and published laboratory data. The computed results of the modified Svendsen's model arc favourably compared with the laboratory data.

• The Journal of Engineering Geology
• /
• v.14 no.3 s.40
• /
• pp.287-300
• /
• 2004

By using a simple conceptual model, a sensitivity analysis is performed to examine the effects of changing model parameters on the model outputs, the groundwater discharge and the radius of influence, induced by tunnel construction. The results indicate that the model outputs are most sensitive to the tunnel depth and the hydraulic conductivity, and their sensitivities vary with time. It is also revealed that the sensitivity of the specific yield in- creases constantly with time, and therefore it is as important as the hydraulic conductivity for constructing a wet-system tunnel. A transient model is suggested to simulate the stepwise tunnel excavation and the watertight lining. The model is used for a tunnel construction site to predict groundwater mow into the tunnel and the transient response of the surrounding aquifer system. The predicted results are highly sensitive to the hydraulic conductivites assigned by model calibration. Thus, a postaudit should be made to reduce the uncertainty of the predictive model.