• Proceedings of the KSME Conference
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• 2000.04b
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• pp.385-391
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• 2000

An analysis of the heat transfer in a PDP ventilation chamber has been conducted to investigate the required heat curve and temperature uniformity of the panels. Firstly, experiment in a test chamber has been carried out and compared with the unsteady 3D numerical simulation. Reasonable agreement was found, which suggested that the employed numerical model had its credibility in an actual PDP ventilation process. On this ground, tact-type heating/cooling system was analyzed. The panel temperature was more uniform in the $40^{\circ}C$ tact-type system than in the $80^{\circ}C$ one. Comparison of full simulation of a cart and simplified simulation of one panel shows the panel pitch, which is closely related to a production rate, can be also predicted.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.225-226
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• 2006

As the technique of high-speed end-milling is widely adopted to machining field. The investigation for microscopic precision of workpiece is necessary for machinability evolution. The environmental pollution has become a big problem in industry and many researcher have investigated in order to preserve the environment. The environmentally conscious machining and technology have more important position in machining process. In the milling process, the cutting fluid has greatly bad influence on the environment. The damaged layer affect mold life and machine parts in machining. In this study, the cutting force, the surface roughness, micro hardness and residual stress is evaluated according to machining environment. Finally, it is obtained that the characteristics of damaged layer in environmentally conscious machining is better than that in conventional machining using cutting fluid.

• Journal of the Korean Society of Propulsion Engineers
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• v.16 no.6
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• pp.73-78
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• 2012

The ignition characteristics of liquid rocket engine thrust chambers which have been developed by domestic technology were analyzed through hot-firing tests. Thrust chambers used in hot-firing tests have different characteristics in terms of the injector for ignition, film cooling method and the position of the oxidizer inlet. Also, these thrust chambers used their respective startup sequences. Analysis results showed that according to temperature profiles of the oxidizer manifold, low frequency fluctuation was appeared in ignition area. This low frequency fluctuation didn't give rise to violent malfunction of the thrust chamber, but the continuous observation as a concern parameter in the side of interfaces with engine system and launch vehicle should be demanded.

• Proceedings of the Korean Nuclear Society Conference
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• 1998.05a
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• pp.357-362
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• 1998

PWR 정지시 일차계통 수화학 제어의 주요대상은 계통표면에 침적된 부식생성물의 주성분인 비화학양론적 니켈(코발트)페라이트로서, 산성-환원 단계에서 용존수소에 의해 Ni$^{\circ}$ (또는 Co$^{\circ}$)로 환원되고 산성-산화 단계에서 용존산소에 의해 Ni$^{2+}$ (또는 CO$^{2+}$)로 산화되어 이온교환기에 의해 제거된다 본 연구에서는, 니켈 및 코발트 산화물의 25~300 $^{\circ}C$ 환원 또는 산화반응 시 표준자유에너지의 변화 및 용존수소 또는 용존산소의 요구농도를 계산하여, 원자로 정지시 일차계통수 용존 기체의 제어조건을 고찰하였다. 산성-환원 단계의 냉각재 온도인 300~82$^{\circ}C$ 범위에서 용존수소가 충분할 경우 열역학적으로 $^{58}$ Co(또는 $^{60}$Co)Fe$_2$O$_4$$\longrightarrow$Co의 역반응이 억제되므로서 노심외 계통부위 침적이 감소될 수 있기 때문에, 용존수소를 온도에 따라 요구농도 곡선 위로 약간 높게 유지하는 것보다 25~50 cc/kg-$H_2O$로 유지하는 방식이 바람직한 반면, 용존산소를 제공하는 과산화수소 농도가) 2.7 ppm일 때 NiFe$_2$O$_4$$\longrightarrow$Ni$_2$O$_4$(+$\alpha$-Fe$_2$O$_3$) 반응이 일어날 수 있기 때문에, 산성-산화 단계에서는 과산화수소의 냉각재 농도를 이보다 낮게 유지하는 것이 바람직하다.

• The Journal of the Korea institute of electronic communication sciences
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• v.15 no.2
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• pp.253-258
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• 2020

Petrochemical industry complex in Korea always has high riskiness due to explosive and inflammable gases. To prevent these explosion, most facility of petrochemical industry complex requires the performance of explosive proof. The control panel, which is used as explosive proof, has been used the air injection method by manually from outside to constantly keep the temperature and pressure between inside and outside of the panel. In this paper, we propose the automatic temperature controller, which performs automatic heating and cooling according to temperature inside the panel in order to control temperature automatically.

• Aerospace Engineering and Technology
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• v.5 no.2
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• pp.134-142
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• 2006

Sub-cooling of cryogenic propellant by helium injection is one of the most effective methods for suppressing bulk boiling and keeping sub-cooled liquid oxygen before rocket launch. In order to design the cooling system, understanding of the limitations of heat and mass transfer is required. In this paper, an analytical model for the helium injection system is presented. This model's main feature is the representation of bubbling system using finite-rate heat transfer and instantaneous mass transfer concept. With this simplified approach, the effect of helium injection to liquid oxygen system under several circumstances is examined. Experimental results along with simulations of single bubble rising in liquid oxygen and bubbling system are presented with various helium injection flow rates, and with change of oxygen chamber pressure.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 1999.11a
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• pp.516-519
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• 1999

스위칭 전원에 사용되는 Mn-Zn 페라이트에 대항하는 고성능화의 요구에 부응하기 위해 그 중요한 요인이 되는 기수가 다른 Mn 산화물에 착목하여 그것들을 이용 제작한 Mn-Zn 페라이트의 자기특성 및 결정구조를 정밀하게 조사함과 동시에 그것들의 상관성을 검토하였다. Mn-Zn 페라이트의 소성 분위기의 변경방식은 소성개시에서 종료시까지 질소 분위기, 냉각시부터 질소분위기로 변경, 소성 개시에서 종료시까지 대기중 소성 세가지를 실험하였고, 소성 온도는 115$0^{\circ}C$, 120$0^{\circ}C$, 125$0^{\circ}C$ 130$0^{\circ}C$ 135$0^{\circ}C$ 및 140$0^{\circ}C$의 6종류의 시료를 제작하였다. 이 결과는 Mn-Zn 페라이트의 소성 분위기 및 온도 최적화는 승온 및 온도 유지 단계에서는 대기중으로, 냉각단계에서는 질소가스 분위기로 치환한 것과 소성 온도는 120$0^{\circ}C$ 이다. 이 분위기에서 Mn-Zn 페라이트를 가수를 다르게 하여 시료의 투자율 및 주파수 특성, 코아로스 주파수 의존성, 코아로스 주파수로 나눈값의 주파수 의존성, 스피넬 구조(311)의 면에서의 회절픽, 자화의 온도 의존성을 분석하였다. 이 결과는 Mn$_3$O$_4$를 출발원료로 사용한 Mn-Zn 페라이트가 투자율 및 한계 주파수 모두 뛰어난 특성을 나타내었다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.1
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• pp.88-98
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• 2016

The Korean summer is hot and humid, and air-conditioners consume considerable amounts of electricity. In such cases, the simultaneous use of indirect evaporative coolers may help reduce the sensible heat and save electricity. In this study, heat transfer and pressure drop characteristics of indirect or regenerative evaporative coolers made from plastic/paper are investigated. The results showed that heat and mass transfer model based on the ${\epsilon}-NTU$ method predicted the indirect evaporation efficiencies, cooling capacities and pressure drops adequately. Both for indirect or regenerative evaporative cooler, the indirect evaporation efficiency increased with increasing dry channel inlet temperature or relative humidity. The indirect evaporation efficiency of the regenerative evaporative cooler was larger than that of the indirect evaporative cooler.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.3
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• pp.347-355
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• 2001

A heat transfer analysis in a ventilation chamber of Plasma Display Panel(PDP) has been conducted. The process requirement is to precisely follow prescribed temperature trajectory while maintaining temperature uniformity for each panel. Firstly, experiment in a test chamber has been carried out and the results are compared with the unsteady 3D numerical data. Reasonable agreement was found, which suggested that the employed numerical model had its credibility in actual PDP ventilation processes. On this ground, a tact-type heating/cooling system was analyzed. The panel temperature in the 40$^{\circ}C$ tact-type system was more uniform than that in the 80$^{\circ}C$ one. For improving the uniformity of panel temperature, relocation of ventilation head to the rear part and inlet flow control are required. Comparison of full simulation of a cart and simplified simulation of one panel indicates the optimized panel pitch can also be predicted.

• Tribology and Lubricants
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• v.39 no.4
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• pp.123-132
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• 2023

In this study, the expansion, stress, and operating clearance of bearing elements during operation are observed using the inner/outer ring temperature test data of a 3.0×10⁶ DN-class roller bearing. The operating clearance characteristics of inner-/outer-ring cooling (IORC) bearings are compared to those of inner-ring cooling (IRC) bearings. For IRC bearings, the thermal expansion of the outer ring is the most important factor in clearance variation. As a result, the operating clearance is less than the initial clearance of 61 ㎛, and the operating clearance decreases to 0.5 ㎛ at 25,500 rpm. Conversely, the temperature of the outer ring of IORC bearings is lower than that of IRC bearings, so the operating clearance is kept smaller. When the coolant flow rate to the outer ring is approximately 1.5 to 2.0 L/min, the temperature difference between the inner and outer rings is minimized and the operating clearance is maintained at a significantly lower level than IRC bearings. Small operating clearances are expected to be effective in reducing cage slip and skid damage in roller bearings. The results and analysis procedures of this study can be utilized to design of bearing clearance, lubricant flow rate, and assembled interference in the early design stage of aerospace roller bearings.