• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.19 no.5
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• pp.403-410
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• 2007

In this study, natural refrigerants and their mixtures that can supplement and replace R12 and R134a in automobile air-conditioners are studied. R134a is currently used as the refrigerant in new motor vehicle air conditioners, replacing the ozone depleting refrigerant R12. Although R134a has no ozone depletion potential, it has a relatively large global warming potential, approximately 1300 times that of $CO_2$ over a 100 year time horizon. For this reason, performance of natural refrigerants and their mixtures containing R152a, RE170 (Dimethylether, DME) and R600a (Isobutane) are measured under 2 different temperature conditions. They were tested in a refrigerating bench tester with an open type compressor. The test bench provided about 4 kW capacity and water and water/glycol mixture were employed as the secondary heat transfer fluids. Test results show that the coefficient of performance (COP) of these refrigerants is up to 21.55% higher than that of R12 in all temperature conditions. Overall, these fluids provide good performance with reasonable energy savings without any environmental problem and thus can be used as long term alternatives for automobile air-conditioners.

• Journal of the Korean Society for Railway
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• v.20 no.3
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• pp.356-364
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• 2017

The process of inspecting electric railway vehicles is complicated and these vehicles accompany a risk of safety accidents. This developed system will be a great help in simplifying the shunting process and be very useful in terms of ensuring safety and providing user convenience. In this paper, the results of performance evaluation tests are studied on a movable catenary system for railway vehicles that secured mechanical durability, convenience, and operator safety by applying a specific rigid bar catenary of an existing mobile train line. We presented an analysis of the basic characteristics for site installation including sorting. In conclusion, this developed system was obtained in good results through durability test, durable mechanical load test and safety test in require specifications.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.10
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• pp.761-767
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• 2006

In this study, performance of 2 pure hydrocarbons R290 and R1270 was measured in an attempt to substitute R22 under 3 different temperature conditions. They were tested in a refrigerating bench tester with a hermetic rotary compressor. The test bench provided about 3.5 kW capacity and water and water/glycol mixture were employed as the secondary heat transfer fluids. All tests were conducted under the same external conditions resulting in the average saturation temperatures of $7/45^{\circ}C$ and $-7/41^{\circ}C$ and $-21/28^{\circ}C$ in the evaporator and condenser, respectively. Test results show that the coefficient of performance (COP) of these refrigerants is up to 11.54% higher than that of R22 in all temperature conditions. Compressor discharge temperatures were reduced by $14{\sim}31^{\circ}C$ with these fluids. There was no problem with mineral oil since the mixtures were mainly composed of hydrocarbons. The amount of charge was reduced up to 58% as compared to R22. Overall, these fluids provide good performance with reasonable energy savings without any environmental problem and thus can be used as long term alternatives for residential air-conditioning and heat pumping application.

• Proceedings of the SAREK Conference
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• 2006.06a
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• pp.58-63
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• 2006

In this study, performance of 2 pure hydrocarbons and 3 mixtures was measured in an attempt to substitute R22 under 3 different temperature conditions. The mixtures were composed of R1270(propylene), R290(propane) and R152a. They were tested in a refrigerating bench tester with a hermetic rotary compressor The test bench provided about 3.5 kW capacity and water and water/glycol mixture were employed as the secondary heat transfer fluids. All tests were conducted under the same external conditions resulting in the average saturation temperatures of $7^{\circ}C/45^{\circ}C$ and $-7^{\circ}C/41^{\circ}C$ and $-21^{\circ}C/28^{\circ}C$ in the evaporator and condenser, respectively. Test results show that the coefficient of performance (COP) of these refrigerants is up to 11.54% higher than that of R22 in all temperature conditions. Compressor discharge temperatures were reduced by $14{\sim}31^{\circ}C$ with these fluids. There was no problem with mineral oil since the mixtures were mainly composed of hydrocarbons. The amount of charge was reduced up to 58% as compared to R22. Overall, these fluids provide good performance with reasonable energy savings without any environmental problem and thus can be used as long term alternatives for residential air-conditioning and heat pumping application.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.31 no.5
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• pp.228-232
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• 2021

Ca_1-xZrO₃:xPr phosphor with perovskite structure was successfully synthesized by using skull melting method. The crystal structure, morphology and optical properties of synthesized phosphor were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet fluorescence reaction and photoluminescence. The XRD results indicated that single crystals of CaZrO₃:Pr³⁺ belongs to orthorhombic perovskite system. The synthesized phosphor could be excited by UV light (254 nm) and the emission spectra results indicated that green luminescence of CaZrO₃:Pr³⁺ due to charge transfer transition ³P₀ → ³H₄, ³P₁ → ³H₅ and ³P₀ → ³H₅ at 506, 536 and 548 nm was dominant.

• Journal of IKEEE
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• v.25 no.3
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• pp.534-539
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• 2021

Induction heating method that allows the maximum heating power to be delivered by varying switching frequency in the inductance change of the work coil of induction heater was proposed in this paper. Depending on the type of work piece in the work coil and proximity to the work coil, the resonance frequency of the resonant circuit will be changed. It may be difficult to deliver the maximum power due to the damage of the induced heater element or switching loss depending on the resonance frequency and switching frequency operating relationship. The switching frequency was variable to maintain the maximum power transmission by sensing the heating power due to the change of the resonance frequency. Through the result of the proposed method that can be controlled within the required output change range according to the change of the switching frequency corresponding to the change of the resonance frequency, the induction heater having a variable switching frequency characteristic that can transmit almost constant output power (within 0.43 dB) power efficiency was achieved.

• The Transactions of the Korean Institute of Power Electronics
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• v.26 no.2
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• pp.82-89
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• 2021

This study proposes a DAB two-stage series structure with insulated bidirectional DC-DC converter for two-way power transfer between the renewable energy of high voltages (1 kV and above). The proposed circuit transforms the existing DAB converter into a two-stage series structure to reduce the pressure in the switch. The problem of power imbalance occurring in the design of the DAB converter second-stage series is improved by applying the cell balancing method circuit and the common mode coupled inductor using an external flying capacitor instead of reflecting the existing improvement measures, voltage balance control, and inductor current control. In addition, a no-load supercharging sequence is proposed in high voltages and high-speed switching by using the fixed duty output method. This study presents the analysis results through the structure of the proposed circuit, the principle of improving the power imbalance problem, and simulations. Prototypes were manufactured to meet the specifications of input/output voltage of 1700 V, maximum load of 65 kW, and switching frequency of 51kHz, and the validity of the topology was verified using the experimental results and efficiency data.

• Journal of Microbiology and Biotechnology
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• v.31 no.4
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• pp.570-583
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• 2021

Pyrococcus furiosus α-amylase can hydrolyze α-1,4 linkages in starch and related carbohydrates under hyperthermophilic condition (~ 100℃), showing great potential in a wide range of industrial applications, while its relatively low productivity from heterologous hosts has limited the industrial applications. Bacillus subtilis, a gram-positive bacterium, has been widely used in industrial production for its non-pathogenic and powerful secretory characteristics. This study was conducted to increase production of P. furiosus α-amylase in B. subtilis through three strategies. Initial experiments showed that co-expression of P. furiosus molecular chaperone peptidyl-prolyl cis-trans isomerase through genomic integration mode, using a CRISPR/Cas9 system, increased soluble amylase production. Therefore, considering that native P. furiosus α-amylase is produced within a hyperthermophilic environment and is highly thermostable, heat treatment of intact culture at 90℃ for 15 min was performed, thereby greatly increasing soluble amylase production. After optimization of the culture conditions (nitrogen source, carbon source, metal ion, temperature and pH), experiments in a 3-L fermenter yielded a soluble activity of 3,806.7 U/ml, which was 3.3- and 28.2-fold those of a control without heat treatment (1,155.1 U/ml) and an empty expression vector control (135.1 U/ml), respectively. This represents the highest P. furiosus α-amylase production reported to date and should promote innovation in the starch liquefaction process and related industrial productions. Meanwhile, heat treatment, which may promote folding of aggregated P. furiosus α-amylase into a soluble, active form through the transfer of kinetic energy, may be of general benefit when producing proteins from thermophilic archaea.

• Design & Manufacturing
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• v.13 no.2
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• pp.37-43
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• 2019

This study conducted a research as to condensation heat transfer friction loss headby using three types of flat micro multi-channel tubes with different processing of micro-fin and number of channels inside the pipes and different sizes of appearances. In addition, identical studies were conducted by using smoothing circular tubes with 5mm external diameter to study heat enhancement factor and pressure drop penalty factor. 1) The friction head loss showed an increase as the vapor quality and mass flux increased. In case of saturation temperature, it shows an increase as it gets lower. These factors are the reason occurring as the lower the saturation temperature is, the higher the density of refrigerant vapor gets. The influence of heat flux is similar as the dryness is low, but as it gets higher, it lowers in heat flux, and as the high temperature of high heat flux, it is a factor that occurs as the density gets lower. 2) RMS error of the in case of friction head loss, it showed to be predicted as 0.45~0.67 by Chisholm, Friedel, Lockhart and Martinelli. 3) As forfriction head loss penalty factor, the smaller the aspect ratio is, the larger the penalty factor gets, and as for the effect of micro-fin, the penalty factor increased because it decreases to the gas fluid the way groove for the refrigerant's flow.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.12 no.3
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• pp.218-223
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• 2019

To prevent the low heating effect of heating system caused by the high sheet resistance of CVD graphene, multi-layered graphene was laminated to implement a Transparent plane heating system with good optical properties of low-resistance. Low-resistance plane heating system implemented by $300{\times}400{\times}5mm$ heating plane laminated multi-layered CVD graphene film and PWM control system to drive efficient power. A plane resistance value of $85.5{\Omega}/sq$ was measured on average for 4-layer CVD graphene film used as a heating plane. Thus, the transfer by thermal film as the method of implementing low-resistance CVD graphene is reasonable. The experimental results of heat test show that an average heat-rise rate in low-resistance, transperent plane heating system using CVD graphene is $10^{\circ}C/min$ and has an optical transmittance rate of 86.44%. Therefore, the proposed heating system is applicable to large window glass and vehicle heating window-shild-glass.