• Journal of the Microelectronics and Packaging Society
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• v.29 no.4
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• pp.89-94
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• 2022

Thermoelectric materials can directly convert a temperature gradient to an electrical energy and vice-versa, and their performance is determined by the electrical conductivity, Seebeck coefficient, and thermal conductivity. However, it is difficult to establish an effective strategy for enhancing performance since electrical conductivity, Seebeck coefficient, and thermal conductivity are strongly dependent on the composition, crystal structure, and electronic structure of the material, and show a correlation with each other. Herein, based on the understanding of the formulas related to the performance of thermoelectric materials, we provide a methodology to establish feasible defect engineering strategies of thermal conductivity reduction for improving the performance of thermoelectric materials in connection with the experimental results.

• International Journal of Precision Engineering and Manufacturing
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• v.9 no.3
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• pp.72-74
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• 2008

We investigate the effect of mechanical damping and electrical conductivity on the dynamic performance of a new electromagnetic engine valve actuator that employs a permanent magnet. The key dynamic performance factors are the transition time and the landing velocity of the armature. Two-dimensional dynamic finite element analyses are performed to simulate a coupled system. The results show that mechanical damping and electrical conductivity have similar effects on the dynamic performance of the engine valve actuator. Subsequently, it is possible to replace the role of mechanical damping by controlling the electrical conductivity through the thickness and number of steel core laminations.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.03a
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• pp.625-630
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• 2010

Parametric study was performed using the SCW numerical model for evaluating the performance of the SCW. The five ground related parameters, which are porosity, hydraulic conductivity, thermal conductivity, specific heat, geothermal gradient, and five SCW design parameters, which are pumping rate, well depth well diameter, dip tube diameter, bleeding rate, were used in the study. Numerical simulations were performed for short-term (24-hour) simulation. The study results indicate that the parameters that have important influence on the performance of SCW were hydraulic conductivity, thermal conductivity, geothermal gradient, pumping rate, and bleeding rate. Overall, this study showed that various factors had a cumulative influence on the performance of the SCW, and a numerical simulation can be used to accurately predict the performance of the SCW.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.3142-3147
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• 2008

A simple transient simulation of ground source heat pump system was carried out to investigate the effects of ground thermal conductivity on its performance. The TRNSYS code with a simple water to water heat pump model was used to compare the COP variation of the system. A new ground heat exchanger called by semi-closed loop was proposed and constructed in the real site. The effective thermal conductivity was measured using the test equipment developed by according to the line source model. The simulation results showed that highly efficient thermal conductivity of the grout material could increase the performance of the heat pump system very well. And the new ground heat exchanger showed the increased effective thermal conductivity as the penetration water flow rate(PWFR) was increased. Therefore, the performance improvement of the heat pump system using the proposed ground heat exchanger can be expected.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2023.05a
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• pp.219-220
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• 2023

The thermal conductivity of the insulation material has a great influence on the heat transmission coefficient, which is currently used for energy evaluation of buildings. The thermal conductivity of insulation changes with changes in the environment, such as humidity and ultraviolet rays, and can be expected to with the passage of time. But there is a lack of data on this, so this study measured the thermal conductivity of organic insulation according to environmental conditions and time, As a result, in the case of XPS, the thermal conductivity value increased over time, which is estimated to be due to the decrease in insulation performance as the foaming gas escapes to the outside, and in the case of PIR class2 No.2 and PIR noncombustible, the increased thermal conductivity value is similar, but in the case of PIR class2 No.2, a relatively moderate increase can be seen, and in the case of PIR noncombustible, a large increase is seen at the beginning, which is judged to be due to the decrease in insulation performance as the internal foaming gas is substituted with air from the outside.

• Korean Journal of Materials Research
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• v.32 no.11
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• pp.474-480
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• 2022

Lithium-ion batteries (LIBs) are powerful energy storage devices with several advantages, including high energy density, large voltage window, high cycling stability, and eco-friendliness. However, demand for ultrafast charge/discharge performance is increasing, and many improvements are needed in the electrode which contains the carbon-based active material. Among LIB electrode components, the conductive additive plays an important role, connecting the active materials and enhancing charge transfer within the electrode. This impacts electrical and ionic conductivity, electrical resistance, and the density of the electrode. Therefore, to increase ultrafast cycling performance by enhancing the electrical conductivity and density of the electrode, we complexed Ketjen black and graphene and applied conductive agents. This electrode, with the composite conductive additives, exhibited high electrical conductivity (12.11 S/cm), excellent high-rate performance (28.6 mAh/g at current density of 3,000 mA/g), and great long-term cycling stability at high current density (88.7 % after 500 cycles at current density of 3,000 mA/g). This excellent high-rate performance with cycling stability is attributed to the increased electrical conductivity, due to the increased amount of graphene, which has high intrinsic electrical conductivity, and the high density of the electrode.

• Proceedings of the Korean Nuclear Society Conference
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• 1999.10a
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• pp.247-247
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• 1999

This paper describes a new mechanistic thermal conductivity model considering the heterogeneous microstructure of MOX fuel. Even though the thermal conductivities of MOX have been investigated numerously by experimental measurements and theoretical analyses, they show the large scattering making the performance analysis of MOX fuel difficult. Therefore, a thermal conductivity model that depends on the heterogeneous microstructure of MOX fuel has been developed by using a general two-phase thermal conductivity model. In order to apply this model for developing the thermal conductivity for heterogeneous MOX fuel, the fuel is assumed to consist of Purich particles and U02 matrix including Pu02 in solid solution. Since little relevant data on Purich particles is available, FIGARO and SiemensKWU results are only used to characterize the microstructure of unirradiated and irradiated fuel. Philliponneaus and HALDEN models are selected for the local thermal conductivities for Purich particles and matrix, respectively. Then by combining the two models, overall thermal conductivity of MOX fuel is obtained. The new proposed model estimates the MOX thermal conductivity about 10% less than the value of U02 fuel, which is in the range of MOX thermal conductivity from HALDEN. The developed thermal conductivity model has been incorporated into KAERIs fuel performance code, COSMOS, and then verified using the measured data in the FIGARO program. Comparison of predicted and measured temperatures shows the reasonable agreement within acceptable error bounds together with satisfactory results for the fission gas release and gap pressure.essure.

• Proceedings of the SAREK Conference
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• 2008.11a
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• pp.33-38
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• 2008

A ground-loop heat exchanger in a ground source heat pump system is an important unit that determines the thermal performance of a system and its initial cost. The Size and performance of this heat exchanger is highly dependent on ground thermal properties. A proper design requires certain site-specific parameters, most importantly the ground effective thermal conductivity, the borehole thermal resistance and the undisturbed ground temperature. This study was performed to investigate the effect of some parameters such as borehole lengths, various grouting materials and U-tube configurations on ground effective thermal conductivity. In this study, thermal response tests were conducted using a testing device with 9-different ground-loop heat exchangers. From the experimental results, the length of ground-loop heat exchanger affects to the effective thermal conductivity. Among the various grouting materials, the bentonite-based grout with silica sand shows the largest thermal conductivity value.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.28 no.4
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• pp.153-157
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• 2016

In case of metal insulation, which is produced by stacking stainless steel sheets and air layers in a multi-stack manner at a specific thickness, insulation performance will be evaluated based on thermal transmittance rather than the intrinsic physical properties of each material such as thermal conductivity. However, there is no standard for measuring thermal transmittance targeted for non-homogeneous insulation which is used in relatively high temperature conditions such as a power station. In this study, the thermal conductivity of homogeneous insulation acquired by the standardized guard hot plate method and the thermal conductivity of homogeneous insulation measured by the newly developed performance tester were compared to verify the confidence level of the tester. As a result, thermal conductivity acquired by the newly developed thermal transmittance tester was about 6% higher than the thermal conductivity measured by the existing guard hot plate method under the anticipated service temperature conditions.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.29 no.11
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• pp.716-719
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• 2016

In this paper, we fabricated flexible CNT/PVDF (carbon nanotube / polyvinylidene fluoride) piezoelectric composite device with flexible poly(3,4-ethylenedioxythiophene) : polystyrene sulfonate (PEDOT:PSS) conducting polymer electrode using spray coating method. We tried to improve the piezoelectric performance from the CNT/PVDF composite film by enhancing electrical conductivity of the PEDOT:PSS electrodes. Electrical conductivity of the PEDOT:PSS electrode was enhanced by dipping it into the EG (ethylene glycol) solvent. Changes of chemical composition of the PEDOT:PSS electrode were analyzed with the dipping time by XPS (x-ray photoelectron spectroscopy) in terms of oxygen (O1s). Finally, Piezoelectric performances such as output voltage and current were measured with the dipping time. We found that enhanced electrical conductivity of the PEDOT:PSS electrodes resulted in improvement of the piezoelectric performance of the CNT/PVDF films.