• Transactions of the Korean hydrogen and new energy society
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• v.22 no.2
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• pp.129-138
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• 2011

Performance changes of an anode-supported tubular SOFC including current collectors are analyzed at different current collecting methods using numerical simulation. From the two dimensional numerical model of the solid oxide fuel cell with nickel felts as anodic current collectors and silver wires as cathodic ones, the performance curves and the distributions of temperature, concentration, current density are obtained. Also, the voltage loss of the cell is divided into three parts: activation loss, concentration loss and ohmic loss. The results show that the performance change of the cell is dominantly influenced by the ohmic loss. Although the temperature and concentration distributions are different, the total activation loss and concentration loss are nearly same. And the ohmic loss is divided into each parts of the cell components. The ohmic loss of the anodic current collectorreaches about 60~80% of the cell's total ohmic loss. Therefore, the reduction of the ohmic loss of the anodic current collector is very important for stack power enhancement. It is also recommended that the load should be connected to the both ends of the anodic current collector.

• Journal of Korean Society of Environmental Engineers
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• v.32 no.4
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• pp.357-362
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• 2010

Electricity can be directly generated from organic matter even wastewaters using a microbial fuel cell. To achieve high power in MFCs, finding factors decreasing activation and Ohmic losses is very important. In this study we determined activation loss at the anode and cathode and Ohmic loss using the current interruption technique in a H-type MFC. Activation loss at the cathode was four times higher that that of anode activation loss even if pt-coated carbon (0.5 $mg/cm^2$;10%Pt) was used as the cathode. Ohmic loss determined using current interruption technique (1146 ${\Omega}$) was almost same as the internal resistance (1167 ${\Omega}$) measured using AC impedance. The sum of activation losses at the anode and cathode was the same as the value of activation loss of the cell.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.32A no.7
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• pp.16-22
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• 1995

Electrically-short wire antennas, widely used for mobile communications and EMI measurements, have low rediation efficiency and gain due to the ohmic loss predominant over the radiation power. A very short dipole antenna for wideband EMI measurements has been analyzed using the Method of Moments with the incorporatio of the ohmic loss calculated by the Phenomenological Loss Equivalennce Method(PEM). The calculated results show the rediation gain and efficiency very with the ohmic loss in a wide range of frequencies. Thses results can be effectively used for optimum design of very small antennas and probes for mobile communications and non-disturbing EMI measurements.

• 한국신재생에너지학회:학술대회논문집
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• 2009.11a
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• pp.139-142
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• 2009

In this study, the performance degradation of SOFC single cell caused by the delamination between a cathode and an electrolyte is investigated. As the delamination rate increases, the voltage sharply decreases due to the decrease of reaction sites and losses increase. The current is concentrated to the intact area so that the current density is increased and the ohmic loss and the activation loss become higher. Most part of loss is due to the ohmc loss of electrolyte.

• Transactions of the Korean hydrogen and new energy society
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• v.20 no.4
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• pp.283-290
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• 2009

This study focuses on the performance characteristics of polymer electrolyte membrane fuel cell (PEMFC) using the AC impedance technique. The experiment was carried out to investigate the optimal operating conditions of PEMFC such as cell temperature, flow rate, humidified temperature and back-pressure. The fuel cell performance was analyzed by DC electronic-loader with constant voltage mode and expressed by voltage-current density. Additionally, AC impedance was measured to analysis of ohmic and activation loss and expressed by Nyquist plot. The results showed that the cell performance increased with increase of cell temperature, air flow rate, humidified temperature and backpressure. Also, the activation loss decreased as the increase of cell temperature, air flow rate, humidified temperature and backpressure.

• Applied Chemistry for Engineering
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• v.29 no.6
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• pp.789-798
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• 2018

The role of empirical equation to predict the performance of polymer electrolyte membrane fuel cell is important. The activation, ohmic and mass transfer losses were separated in a polarization curve, and the curve fitting according to each region was performed using Kim's model and Hao's model. Changes of each loss were compared according to operation variables of the temperature, pressure, oxygen concentration and membrane thickness. The existing model showed a good fitting convergence, but less fitting accuracy in the separated loss region. A new model using the convergence coefficient was suggested to improve the accuracy of performance prediction of fuel cells of which results were demonstrated.

• Korean Journal of Metals and Materials
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• v.49 no.4
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• pp.329-333
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• 2011

To develop wide-band noise absorbers with a special design for low-frequency performance, this study proposes a tin oxide (Sn-O) thin films as the noise absorbing materials in a microstrip line. Sn-O thin films were deposited on polyimide film substrates by reactive sputtering of the Sn target under flowing $O_{2}$ gas, exhibiting a wide variation of surface resistance (in the range of $10^{0}-10^{5}{\Omega}$) depending on the oxygen partial pressure during deposition. The microstrip line with characteristic impedance of $50\Omega$ was used for the measurement of noise absorption by the Sn-O films. The reflection parameter $(S_{11})$ increased with a decrease of surface resistance due to an impedance mismatch at the boundary between the film and the microstrip line. Meanwhile, the transmission parameter $(S_{21})$ diminished with a decrease of surface resistance resulting from an Ohmic loss of the Sn-O films. The maximum noise absorption predicted at an optimum surface resistance of the Sn-O films was about $150{\Omega}$. For this film, greater power absorption is predicted in the lower frequency region (about 70% at 1 GHz) than in conventional magnetic sheets of high magnetic loss, indicating that Ohmic loss is the predominant loss parameter for the conduction noise absorption in the low frequency band.

• Korean Journal of Food Science and Technology
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• v.30 no.4
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• pp.842-847
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• 1998

Ohmic thawing in combination with conventional water immersion thawing was investigated. Frozen meat chunks $(10{\times}10{\times}10{\;}cm)$ were immersed in a water reservoir $(12{\times}12{\times}12{\;}cm)$ which temperature was maintained at $10^{\circ}C{\;}or{\;}20^{\circ}C$, and were positioned between two stainless-steel electrodes $(10{\times}10{\;}cm)$ having no direct contact with the samples. Alternating current $(60{\;}V{\sim}210{\;}V)$ at various frequency $(60{\;}Hz{\sim}60{\;}kHz)$ was used to generate internal heat by the electrical resistance. When the frequency was fixed to 60Hz, thawing time was reduced as the voltage increased. Frequency changes gave no significant effect on thawing time. Ohmically-thawed samples treated with lower voltage showed lower drip loss and higher water holding capacity.

• Food Science of Animal Resources
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• v.27 no.4
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• pp.416-423
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• 2007

This study investigated the effect of ohmic thawing on the physicochemical properties of pork meat. The physicochemical properties of pork meat thawed by brine immersion and electrode contact ohmic systems were compared. A more rapid thawing rate was seen with the electrode contact thawing system than with brine immersion. No significant differences in pH were found with increasing voltage for both thawing methods (p>0.05). Increasing the voltage level tended to decrease drip loss, resulting in increased water holding capacity. The shear forces of pork thawed at 50 V did not differ from the control (p>0.05) for both thawing methods. Although significantly high TBARS (p<0.05) values were found at 20 and 40 V for immersion, and 0 V for contact thawing, increasing the voltage level tended to decrease the TBARS values. Regarding TVBN, no significant effect was observed with increasing voltage levels (p>0.05). The total color difference of pork was significantly higher (p<0.05) with immersion thawing than with electrode contact thawing. These results indicate that brine immersion thawing is favorable at high voltage levels, while lower voltage levels are applicable for electrode contact thawing.

• Journal of Biosystems Engineering
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• v.40 no.3
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• pp.250-260
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• 2015

Purpose: Dual cylindrical microwave chambers equipped with an ohmic heating tube were designed and fabricated to maximize the electric field strength for expeditious heat treatment of particulate foods. Methods: The efficacy of the combination heater was investigated by simulating the electric field distribution by using COMSOL Multiphysics software. Results: All components of the designed microwave heating unit were suitable for transmitting maximal microwave power to the load. The simulated electric field distribution implied that single-mode microwave heating would be sufficient for the steady generation of a highly localized heating zone in the cavity. During impedance matching, the calculated reflection coefficient ($S_{11}$) was small, possibly implying minimal power loss and wave reflection in the designed microwave heating chamber. Conclusions: This study demonstrates the possibility of concentrating the microwave power at the centerline for a single-frequency microwave, for thermal treatment of multiphase foods without attenuating the microwave power.