• Journal of the Korean Society of Propulsion Engineers
• /
• v.15 no.6
• /
• pp.47-55
• /
• 2011

The present paper deals with numerical analysis to investigate the effect of rounded tube on the pressure drop and heat transfer in a compact tubular heat exchanger designed for high temperature and high pressure system. The pressure drop and heat transfer in the tubular heat exchanger greatly depend on the location of rounded tubes. The effect of locations of the rounded tubes was also analyzed. Three different locations which were tube inlet, tube outlet, and inlet&outlet were considered. In this paper, the tube with a rounded inlet&outlet showed the minimum pressure drop with decreased heat transfer while the tube with a rounded outlet showed better characteristics of pressure drop and heat transfer compared with the results of original model.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2012.02a
• /
• pp.569-569
• /
• 2012

탄소나노튜브(carbon nanotubes)의 우수한 전기적, 물리적 특성으로 인해 트랜지스터, 태양전지, 고감도 센서, 나노 섬유, 고분자-탄소나노튜브 고기능 복합체 등 다양한 분야에서 이를 응용하려는 노력이 활발히 진행되고 있다. 흥미롭게도 탄소나노튜브는 구조적인 특성 (직경, 밀도, 벽의 수)에 따라 각기 다른 비표면적, 열 전도성, 전기 전도성, 접촉각, 전계방출 특성을 지닌다고 보고되고 있다. 따라서 다양한 분야의 응용을 위해서는 구조적인 특성 제어가 핵심적인 요소라고 할 수 있다. 본 연구에서는 열화학기상증착법(thermal chemical vapor deposition)을 이용하여 수직 정렬된 탄소나노튜브를 합성 하였다. 합성과정에서 압력의 변화가 탄소나노튜브의 밀도와 길이에 큰 영향을 미친다는 것을 확인하였고, 이러한 현상을 이해하기 위해 두 가지의 가능성을 고려하였다. 첫째는 압력의 변화에 따른 촉매의 형성 변화 가능성이며, 둘째는 탄화수소가스의 유입양의 변화에 따른 영향이다. 분석 결과, 동일한 압력에서 탄화수소가스의 부분압을 변화시켜 실험한 결과로부터 탄화수소의 유입양의 변화가 합성된 탄소나노튜브의 밀도에 큰 영향을 미치고 밀도가 높은 경우 길이가 긴 탄소나노튜브가 합성되는 것을 확인할 수 있었다.

• Nuclear industry
• /
• v.6 no.10 s.44
• /
• pp.67-69
• /
• 1986

Pickering원전 1, 2호기의 압력튜브교체는 순조롭게 진행중인데, Ontario Hydro사에서는 이 폐기튜브를 어떻게 처리하고 있는지에 대해 설명한 P. J. Armstrong씨와 T. J. Carter씨의 글을 소개한다.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.43 no.8
• /
• pp.684-691
• /
• 2015

A sudden increase in combustion pressure is observed in the ducted rocket combustion test equipped with pipe shaped and converging nozzle exhaust tubes. This study aims to understand the physical mechanism of abrupt change in combustion pressure using thermal choking in the exhaust tube. Results confirmed that the thermal choking of the flow inside the exhaust tube was responsible for the sudden increase in combustion pressure. Also, high pressure exponent of solid propellants is critical sensitive to the occurrence of thermal choking exhaust pipe. Additionally, numerical simulation showed that the sudden increase in combustion pressure was less possible in diverging pipe because thermal choking is more reluctant to occur.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.38 no.7
• /
• pp.601-605
• /
• 2014

Porous conductors are known to demonstrate excellent electrical, mechanical, and chemical resistance. These porous conductors demonstrated potential applications in various fields such as electrodes for supercapacitors, flexible heaters, catalytic electrodes, and sorbents. In this study, we described a pressure sensitive device using conductive and porous sponges. With an extremely simple "dipping and drying" process using a single-walled carbon nanotube (SWCNT) solution, we produced conductive sponges with sheet resistance of < $30k{\Omega}/sq$. These carbon nanotube sponges can be deformed into any shape elastically and repeatedly compressed to large strains without collapse. The pressure sensors developed from these sponges demonstrated high resistance change under pressure of up to a half of their initial resistance.

• Proceedings of the KSR Conference
• /
• 2010.06a
• /
• pp.139-150
• /
• 2010

Recently, full-scale research about a passenger tube train system is being progressed as a next-generation transportation system in Korea in light of global green technology. The Korea Railroad Research Institute (KRRI) has commenced official research on the construction of a tube train system. In this paper, we studied various parameters of the tube train system such as the internal tube pressure, blockage ratio, and operating speed through computational analysis with a symmetric and elongated vehicle. This study was about the aerodynamic characteristics of a tube train that operated under standard atmospheric pressure (open field system, viz., ground) and in various internal tube environments (varying internal tube pressure, blockage ratio, and operating speed) with the same shape and operating speed. Under these conditions, the internal tube pressure was calculated when the energy efficiency had the same value as that of the open field train depending on various combinations of the operating speed and blockage ratio (the P-D relation). In addition, the dependence of the relation between the internal tube pressure and the blockage ratio (the P-${\beta}$ relation) was shown. Besides, the dependence of the relation between the total drag and the operating speed depending on various combinations of the blockage ratio and internal tube pressure (the D-V relation) was shown. Also, we compared the total (aerodynamic) drag of a train in the open field with the total drag of a train inside a tube. Then, we calculated the limit speed of the tube train, i.e., the maximum speed, for various internal tube pressures (the V-P relation) and the critical speed that leads to shock waves under various blockage ratios, which is related to the efficiency of the tube train (the critical V-${\beta}$ relation). Those results provide guidelines for the initial design and construction of a tube train system.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.35 no.5
• /
• pp.517-524
• /
• 2011

A vortex tube is a device that can separate small particles from a compressed gas or separate a compressed gas into hot and cold flows. We experimentally analyzed the energy-separation characteristics of a vortex tube with a diameter of 10 mm. We measured the energy-separation characteristics of the vortex tube for different inlet air pressures, orifice diameters, and tube lengths. The orifice diameter and inlet pressure are important for the vortex tube design and operation. The tube length has a small effect on the energy-separation performance. Maximum energy separation occurs for a vortex tube with Dc = 0.7 D and L = 16 D.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.16 no.6
• /
• pp.1056-1063
• /
• 1992

Burst pressure of right circular tube is predicted using analytic method, and asymptotic instability pressure of circular tube with roundness defect is found using FEM. Burst tests of nearly right circular tube specimens are carried out and predictions are compared with burst pressures and their accuracy is discussed. It is confirmed that FEM is useful for prediction of burst pressure.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.41 no.3
• /
• pp.187-192
• /
• 2017

This paper presents an ongoing study to develop a novel pressure sensor by means of a Nano Carbon Piezoresistive Composite (NCPC). The sensor was fabricated using the 3D printing process. We designed a miniaturized cantilever-type sensor electrode to improve the pressure sensing performance and utilized a 3D printer to build a small-sized body. The sensor electrode was made of 2 wt％ MWCNT/epoxy piezoresistive nano-composite, and the sensor body was encapsulated with a pipe plug cap for easy installation to any pressure system. The piezoresistivity responses of the sensor were converted into stable voltage outputs by using a signal processing system, which is similar to a conventional foil strain gauge. We evaluated the pressure-sensing performances using a pressure calibrator in the lab environment. The 3D-printed cantilever electrode pressure sensor showed linear voltage outputs of up to 16,500 KPa, which is a 200％ improvement in the pressure sensing range when compared with the bulk-type electrode used in our previous work.

• Journal of the Korea Institute of Military Science and Technology
• /
• v.3 no.2
• /
• pp.250-258
• /
• 2000

본 논문에서는 soot을 배출하는 층류 확산 화염에 대한 음향 가진(acoustic excitation) 효과에 대해 연구하였다. 최근의 연구결과는 soot 배출 화염에 음향 가진을 작용시키면 radiation은 증가하고 soot 배출은 감소한다는 사실을 밝혀주었다. 음향 속도(acoustic velocity)는 음향 압력(acoustic pressure)과 900 상(phase) 차이가 있기 때문에 acoustic driver를 장착한 유리 튜브 내부의 축방향으로 soot을 배출하는 아세틸렌 확산 화염을 이동시킴으로서 soot 배출 감소에 대한 음향 속도와 음향 압력의 상대적인 중요도를 밝혀낼 수 있다. Soot을 배출하는 아세틸렌 화염에 soot 배출이 멈출 때까지 음향 가진을 작용시키고 유리 튜브 안의 최대 압력 위치에서 음향 압력을 측정하며, 화염 위치의 음향 속도와 음향압력은 운동량 방정식과 파동 방정식을 통해 계산된다. 실험 결과 음향 속도가 최대이고 음향 압력이 최소인 위치에서 보다 음향 속도가 최소이고 음향 압력이 최대인 위치에서 훨씬 더 큰 acoustic power가 필요함을 보여주었다. Soot 배출을 멈추는데 필요한 음향 속도의 크기는 유리 튜브의 축방향에 대해 거의 일정한 반면 음향 압력의 크기는 상당한 변화가 있었다. 이러한 결과는 Soot 배출의 감소가 주로 음향 속도에 의한 것임을 강하게 시사한다고 할 수 있다. 또한 연료의 유량이 증가함에 따라 soot 배출을 억제하는데 필요한 acoustic power도 증가한다는 사실을 확인 할 수 있었다.