• Journal of the Korean Society of Propulsion Engineers
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• v.15 no.1
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• pp.55-62
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• 2011

In this study, we tried to improve the thrust control performance through the thrust control combustion experiment of the hybrid rocket. We constructed the system which controls the oxidizer flow by combining a needle valve with a stepping motor and controlling the stepping motor drive according to the thrust control command order. Gas oxygen was used as the oxidizer for two different propellants, PE(Polyethylene), PC(Polycarbonate), respectively. To improve the slow response time and the oscillation phenomenon in the beginning stage of the thrust control combustion experiment, we measured and analyzed the change of the flow speed of the propellant pipe. The revised thrust control combustion experiment showed that the thrust was stably controlled with the margin or error from the thrust command within ${\pm}1$ N.

• Tribology and Lubricants
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• v.28 no.6
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• pp.278-282
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• 2012

Various bearings such as deep-groove ball bearings, angular-contact ball bearings, and roller bearings are used to support the load and to lubricate between the shaft and the housing. The bearings of potential rolling systems in a turbo pump are the deep-groove ball bearings as comparing with the bearings with rolling elements such as cylindrical rollers, tapered cylindrical rollers, and needle rollers. The deep-groove ball bearings consist of rolling elements, an inner raceway, an outer raceway and a retainer that maintain separation and help to lubricate the rolling element that is rotating in the raceways. In the case of water-lubricated ball bearings, however, fluid friction between the ball and raceways is affected by the entry direction of flow, rotation speed, and flow rate. In addition, this friction is the key factor affecting the bearing life cycles and reliability. In this paper, the characteristics of flow conditions corresponding to a deep-groove ball bearing are investigated numerically, with particular focus on the friction distribution on the rolling element, in order to extend the analysis to the area that experiences solid friction. A simple analysis model of fluid flow inside the water-lubricated ball bearing is analyzed with CFD, and the flow characteristics at high rotation speeds are presented.

• Transactions of the Korean Society of Automotive Engineers
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• v.9 no.2
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• pp.59-66
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• 2001

This experimental study is to investigate the flow characteristics of the multi-hole nozzle used in the fuel injection system of a heavy-duty diesel engine. A multi-hole diesel nozzle with a 2-spring nozzle holder was used in this study and without changing the total orifice exit area, its hole number varied from 3($d_n$=0.42mm) to 8($d_n$=0.25mm). The injection pressure and needle lift were measured and Bosch type injection rates measurement system was used. The discharge flowrates of each orifice in the multi-hole nozzle changed by the flow conditions inside the nozzle sac hole. In case that pump speed and injection quantity were low, the orifice located in the vertex of nozzle tip had a great deal of injection quantity compared with that of others. As the increment of multi-hole number, the injection duration and the mean injection pressure decrease. The mean and peak injection rates, however, increase. Actually, the mean flow coefficient(${C_d}_{(mean)}$) increases, too. The flow coefficient of the multi 8 hole was evaluated as Cd(mean)=0.74 and that is the maximum value among the examined conditions.

• Transactions of the Korean Society of Automotive Engineers
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• v.8 no.1
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• pp.48-53
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• 2000

The effects of the internal flow in a diesel injection nozzle on the atomization of the spray has been investigated experimentally. Flow visualization was made using a transparent acrylic model nozzle. And also, measurement of the sac chamber pressure was made for clartfying the effect of pressure fluctuation in the sac chamber on the wpray behaviors. The geometry of the model nozzle was scaled up 10 times of the actual nozzle and the injection pressure for the model nozzle was adjusted so as to achieve a Reynolds number at the discharge hole which was the same as the actual nozzle. Polystyrene tracers, a laser sheet light and a still/high speed video camera were used to visualize the flow pattern in the sac chamber. When the needle lift was small, the high turbulence in the sac chamber generated by the high velocity seat flow made the spread angle of the spray large. Cavitation which arose in the sky chamber induced the pressure fluctuation and then affects the spread angle of the spray.

• Macromolecular Research
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• v.13 no.1
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• pp.62-67
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• 2005

This paper investigated the effect of biodegradation behavior on the oxidation of cellulose nanofiber mats. The cellulose mats were produced through electro spinning. The diameter of an electrospun fiber varied from 90 to 240 nm depending on the electrospinning parameters, such as the solution concentration, needle diameter, and rotation speed of a grounded collector. Oxidized cellulose (OC).mats containing different carboxyl contents were prepared using $NO_2$ as an oxidant. The total carboxyl content of the cellulose nanofiber mats obtained after oxidation for 20 h was $20.6\%$. The corresponding carboxyl content was important from a commercial point of view because OC containing $16-24\%$ carboxyl content are used widely in the medical field as a form of powder or knitted fabric. Degradation tests of the OC mats were performed at $37^{\circ}C$ in phosphate-buffered saline (pH 7.4). Microscopy techniques were introduced to study the morphological properties and the degradation behavior of the OC mats. Morphological changes of the mats were visualized using optical microscopy. Within 4 days of exposure to PBS, the weight loss of the OC mats was $>90\%$.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.05a
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• pp.326-330
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• 2010

A laser based needle-free liquid drug injection device has been developed. A laser beam is focused inside the liquid contained in the rubber chamber of micro scale. The focused laser beam causes explosive bubble growth, and the sudden volume increase in a sealed chamber drives a microjet of liquid drug through the micronozzle. The exit diameter of a nozzle is 125 ${\mu}m$ and the injected microjet reaches an average velocity of 264 m/s. This device adds the time-varying feature of microjet to the current state of liquid injection for drug delivery.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.467-467
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• 2007

Solid insulation exposed to voltage is degraded by electrical tree process. And the degradation of the insulation is accelerated by voltage application. For this experimental, specimen of electrical tree model is made by XLPE (cross-linked polyethylene). And the size of the specimen is $7^*5^*7mm^3$. Distance between needle and plane is 2 mm. Voltages applied to acceleration test are ranged 12 to 15 kV. And distribution characteristic of degraded stage is studied too. By PD detecting and data processing, discharge data was acquired from PD detecting system (Biddle instrument). The system presents statistical distribution of phase resolved. Moreover, the processing time of electrical tree is recorded to know the speed of degradation according to voltage. Finally, it's used PD classification by ANFIS method.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.464-465
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• 2007

Solid insulation exposed to voltage is degraded by electrical tree process. And the degradation of the insulation is accelerated by voltage application. For this experimental, specimen of electrical tree model is made by XLPE (cross-linked polyethylene). And the size of the specimen is $7*5*7\;mm^3$. Distance of needle and plane is 2 mm. Voltages applied for acceleration test are 12 kV to 15 kV. And distribution characteristic of degraded stage is studied too. As a PD detecting and data process, discharge data acquire from PD detecting system (Biddle instrument). The system presents statistical distribution as phase resolved. Moreover the processing time of electrical tree is recorded to know the speed of degradation according to voltage.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.10a
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• pp.231-235
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• 2005

Most tissue engineering strategies for creating functional replacement tissues or organs rely on the application of temporary three-dimensional scaffolds to guide the proliferation and spread of seeded cells in vitro and in vivo. Scaffolds should be satisfied following requirements; macrostructure to promote cell proliferation, pore interconnectivity, pore size ranging from 200 to $400{\mu}m$, surface chemistry and mechanical properties. Rapid prototyping techniques have often been used as an useful process that fabricates scaffolds with complex structures. In this study, a new process to fabricate a three-dimensional scaffolds using bio-compatible polymer has been developed. It employs a highly accurate three-dimensional positioning system with pressure-controlled syringe to deposit biopolymer structures. The pressure-activated microsyringe is equipped with fine-bore nozzles of various inner-diameters. In order to examine relationships between line width and process parameters such as nozzle height, applied pressure, and speed of needle, experiments were carried out. Based on the experimental results, three-dimensional scaffold was fabricated using the apparatus. It shows the validity of the proposed process.

• Korean Journal of Pharmacognosy
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• v.5 no.3
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• pp.159-166
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• 1974

The Yellow needle crystal was isolated from Atractylis Rhizoma, having mp $124{\sim}126^{\circ}C$(decomp.), the chemical composition $C_{16}H_{21}N_{3}O_{6}$, and its m.w. 251. The pharmacological actions of this alkaloid were studied by various psycopharmacological experiments. 1) In order to see the effect of this Atractylis(=At.) alkaloid on gross general behaviors in mice, a behavioral analysis experiment was adapted. The occurrence number of sleep and lying in At. alkaloidal animals with the doses 10mg/kg or 20mg/kg was increased but the number of jumping, exploration, rearing and defecation was significantly decreased than those of placebo. 2) The effect of the At. alkaloid on unlearned emotional behaviors of mice was studied with an open-field method. The At. alkaloidal groups with the doses 20mg/kg or 30mg/kg showed less often the frequency of locomotion than that of placebo. 3) To know the effect of the At. alkaloid on the learning, a standard water maze experiment and conditioned avoidance response were conducted. As compared to placebo control, the aquisition rate of the maze learning in the alkaloidal mice with the dose of 10mg/kg or 20mg/kg was significantly impaired and the speed of swimming was also signficantly delayed. In the conditioned avoidance response, the extinction performances of the alkaloidal rats with doses of 20mg/kg or 30mg/kg did not differ significantly than that of placebo.