• Horticultural Science & Technology
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• v.19 no.4
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• pp.488-494
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• 2001

Seedlings of strawberry, 'Reiko' were planted in plastic pots of 24 cm in diameter in the middle of September in 1995, 1996, and 1997. Ten plants were transferred to greenhouse with artificial illumination at 5-day interval from late September to late January. The deepest dormancy of 'Reiko' in Daegu area was found to be on November 5, October 25, and October 31 in 1995, 1996, and 1997, respectively. The time for moving plants to make the plants grow in semi-dormant state in the greenhouse occurred between Nov. 10 and Nov. 20 in both 1995 and 1996, and between Nov. 10 and Nov. 30 in 1997. The time passing approximately 100-200 cumulative hours of exposure to below $5^{\circ}C$ canopy temperature from the peak dormancy, which is required for breaking dormancy of 'Reiko', was between November 16 and 25 in 1996, and November 24 and December 5 in 1997. 'Reiko' yielded high every year when seedlings were moved into greenhouse during the period of October to November. The plants gave good response to forcing culture under lighting. The right time for moving plants into greenhouse in semi-forcing culture appeared to be the time passing 50-150 cumulative hours of exposure to below $5^{\circ}C$ canopy temperature from the peak dormancy.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.3
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• pp.223-229
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• 2015

Surface modification is a technology to form a new surface layer and overcome the intrinsic properties of the base material by applying thermal energy or stress onto the surface of the material. The purpose of this technique is to achieve anti-corrosion, beautiful appearance, wear resistance, insulation and conductance for base materials. Surface modification techniques may include plating, chemical conversion treatment, painting, lining and surface hardening. Among which, a surface modification process using electrolytes has been investigated for a long time in connection with research on its industrial application. The technology is highly favoured by various fields because it provides not only high productivity and cost reduction opportunities, but also application availability for components with complex geometry. In this study, an electrochemical experiment was performed on the surface of 5083-O Al alloy to determine an optimal electrolyte temperature, which produces surface with excellent corrosion resistance under marine environment than the initial surface. The experiment result, the modified surface presented a significantly lower corrosion current density with increasing electrolyte temperature, except for $5^{\circ}C$ of electrolyte temperature at which premature pores was created.

• International Journal of Safety
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• v.1 no.1
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• pp.36-42
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• 2002

This paper is aimed at predicting the life of rubber insulating gloves under normal operating stresses from relatively rapid test performed at higher stresses. Specimens of rubber insulating gloves are subject to multiple stress conditions, i.e. combined electrical and thermal stresses. Two modes of electrical stress, step voltage stress and constant voltage stress are used in specimen aging. There are two types of test for electrical stress in this experiment: the one is Breakdown Voltage (BDV) test under step voltage stress and thermal stress and the other is lifetime test under constant voltage stress and temperature stress. The ac breakdown voltage defined as the break-down point of insulation that leakage current excesses a limit value, l0mA in this experiment, is determined. Because the very high variability of aging data requires the application of statistical model, Weibull distribution is used to represent the failure times as the straight line on Weibull probability paper. Weibull parameters are deter-mined by three statistical methods i.e. maximum likelihood method, graphical method and least squares method, which employ SAS package, Weibull probability paper and FORTRAN, respectively. Two chosen models for predicting the life under simultaneous electrical and thermal stresses are inverse power model and exponential model. And the constants of life equation for multistress aging are calculated using numerical method, such as Gauss Jordan method etc.. The completion of life equation enables to estimate the life at normal stress based on the data collected from accelerated aging test. Also the comparison of the calculated lifetimes between the inverse power model and the exponential model is carried out. And the lifetimes calculated by three statistical methods with lower voltage than test voltage are compared. The results obtained from the suggested experimental method are presented and discussed.

• The Journal of the Acoustical Society of Korea
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• v.22 no.7
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• pp.545-553
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• 2003

This paper is concerned with protecting piezoelectric transducers used in an ultrasonic flowmeter from the high temperature of hot fluid in a pipe by using a waveguide and with improving the propagation of ultrasonic longitudinal vibration in the waveguide. Waveguide material has been chosen for efficient insulation of heat transferred in the waveguide, and the minimum length of the waveguide for protecting piezoelectric transducer has been estimated. Forced response of the longitudinal vibration in a uniform circular rod has been obtained and the length of the waveguide has been selected for maximum amplitude. Longitudinal vibration response of a conically-tapered rod excited at a natural frequency has been obtained to confirm that wave motion is amplified as the cross-sectional size of the waveguide decreases along the axial direction. The fact that dispersion of a pulse wave in a waveguide is reduced as the cross-sectional radius is decreased has been examined theoretically and confirmed experimentally by using a single-rod waveguide. A bundle-type waveguide has proven to be a practical one through the evaluation of the wave propagation performance.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2006.05a
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• pp.35-38
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• 2006

This study investigated fundamental properties of lightweight foamed concrete using cement kiln dust (CKD) and both fly ash(FA) and stability agent. Test results showed that concrete incorporating more amounts of admixture decreased slump flow and it caused increase of superplasiticizer in order to secure the fluidity performance. In addition concrete adding stability agent showed stable flow state, resisting segregation of materials and decreasing bleeding capacity. Sinking depth of concrete incorporating 20% of CKD and adding 0.002% of stability agent was indicated at 0mm. For the properties of hardened concrete. compressive strength of concrete incorporating CKD declined due to a lower appearance density, compared with other specimens. The difference of that was not very significant and the value of ail specimen was higher than KS range. Moreover strength of concrete incorporating CKD was even higher at curing temperature $5^{\circ}C$. Tensile strength ratio of concrete incorporating CKD was indicated between 0.50 to 0.59, which is higher value than control concrete. Heat conductivity of concrete incorporating FA was under the KS range while concrete incorporating 20% of CKD was satisfied in KS. Concrete adding stability agent improved insulation performance due to the lower heat conductivity. In conclusion, it is possible that concrete incorporating 20% of CKD and adding 0.002% of stability agent can secure high quality of lightweight foamed concrete.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.28 no.1
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• pp.28-33
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• 2015

The needle electrode is inserted into the cross-linked polyethylene(XLPE) which is the ultra high voltage cable for electric power. By changing the tilt of the needle electrode, we investigated how the void and the thickness of the insulating layer influence the partial discharge(PD) characteristics and the insulating breakdown. In order to investigate the PD characteristics, The XLPE cable was used to the specimens and the tungsten electrode was used with the needle electrode. And the inner semi-conductive layer material of XLPE cable was used with the negative electrode by bonding with the use of conduction tape. The size of the specimens was manufactured to be $16{\times}40{\times}30[mm^3]$. We confirmed the effect on changing the PD characteristics according to the changing voltage and the tilt of the electrode after applying the voltage on the electrode from 1[kV] to 40[kV] at room temperature. In the PD characteristics, it was confirmed that the PD current of air void specimens with tilt was unstable more than that of no void specimens with tilt. It was also confirmed that the breakdown voltage was decreased because the effect of air void is more active than the change of the needle electrode tilt in the specimen with air void inside the insulation.

• Proceedings of the SAREK Conference
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• 2008.06a
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• pp.288-293
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• 2008

The cooling load in winter is significant in many commercial buildings and hotels because of the usage of office equipments and the high efficiency of wall insulation. The development of a multi-heat pump that can cover heating and cooling simultaneously for each indoor unit is required. In this study, the performance of a multi-heat pump with 3-piping system was investigated as a function of refrigerant charge and its performance was analyzed in cooling mode, heating mode, and heat recovery mode. COP in the heating or cooling mode showed little dependence on refrigerant charge at overcharge conditions, while those were strongly dependent on refrigerant charge at undercharge conditions and outdoor inlet temperature. In the heat recovery mode, the performance of the system was very sensitive to charge amount at all conditions. Optimum charge amount in the heat recovery mode was 14% lower than that in the cooling mode at the standard condition because the refrigerant only passed the indoor units. It is required to store the excessive refrigerant charge in a storage tank to optimize the system performance at operating modes.

• Journal of Hydrogen and New Energy
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• v.22 no.5
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• pp.609-615
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• 2011

A 5 kW class SOFC system for cogeneration power units was consisted of a hot box part and cold BOPs. High temperature components such as a stack, a fuel reformer, a catalytic combustor, and heat exchanges are arranged in the bot box considering their operating temperatures for the system efficiency. The hot box was made of ceramic boards for the thermal insulation. A 5 kW class SOFC stack was composed of 2 sub-modules and each module had 64 cells with $15{\times}15cm^2$ area and stainless steel interconnects. The 5 kW class SOFC system was operated with a hydrogen and a city gas. With a hydrogen, the total power of the stacks was about 7.1 kWDC and electrical efficiency was about 49.3% at 80 A. With a city gas, the total power of the stacks was about 5.7 $kW_{DC}$ and electrical efficiency was about 38.8% at 60 A. Under self-sustained operating condition, the system efficiency including a power conditioning loss and a consumed power by BOPs was about 30.2%.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.4
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• pp.449-455
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• 2015

Owing to the trend of an increase in capacity and high-efficiency requirement, the life and reliability of power transformer depend significantly on the amount of heat generation per unit volume and the degradation of insulation oil. These problems can be solved by enhancing the cooling performance of the radiator. The purpose of this study was to find a suitable position of fans for a better cooling effect given by the forced-convection of air in an ONAF (Oil Natural Air Forced) type transformer. In the simulation, commercial software was used for flow analysis, and the cooling passage of the oil was simplified to shorten the time taken for computation. With the diameter of the fan fixed at a constant value, the analysis was performed only by changing the position of the fans. As a result, a vertical position change of the fans does not affect the cooling performance significantly. However, the temperature drop given by the fans positioned on the front region of the transformer is larger than that on the rear region.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.20 no.7
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• pp.492-499
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• 2008

The cooling load in winter is significant in many commercial buildings and hotels because of the usage of office equipments and the high efficiency of wall insulation. The development of a multi-heat pump that can cover heating and cooling simultaneously for each indoor unit is required. In this study, the performance of a multi-heat pump with 3-piping system was investigated as a function of refrigerant charge and its performance was analyzed in cooling mode, heating mode, and heat recovery mode. COP in the heating or cooling mode showed little dependence on refrigerant charge at overcharge conditions, while those were strongly dependent on refrigerant charge at undercharge conditions and outdoor inlet temperature. In the heat recovery mode, the performance of the system was very sensitive to charge amount at all conditions. Optimum charge amount in the heat recovery mode was 14% lower than that in the cooling mode at the standard condition because the refrigerant only passed the indoor units. It is required to store the excessive refrigerant charge in a storage tank to optimize the system performance at operating modes.