• Title/Summary/Keyword: temperature and diameter effect

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An experimental study and new correlations of viscosity of ethylene glycol-water based nanofluid at various temperatures and different solid concentrations

  • Bidgoli, Mahmood Rabani;Kolahchi, Reza;Karimi, Mohammad Saeed
    • Structural Engineering and Mechanics
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    • v.58 no.1
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    • pp.93-102
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    • 2016
  • This article presents an experimental study on the effect of temperature and solid volume fraction of nanoparticles on the dynamic viscosity for the CuO/EG-water nanofluid. Nanoparticles with diameter of 40 nm are used in the present study to prepare nanofluid by two-step method. A "Brookfield viscometer" has been used to measure the dynamic viscosity of nanofluid with solid volume fraction up to 2% at the temperature range between 20 to $60^{\circ}C$. The findings have shown that dynamic viscosity of nanofluid increases with increasing particle volume fraction and decreasing temperature. Nine different correlations are developed on experimental data point to predict the relative dynamic viscosity of nanofluid at different temperatures. To make sure of accuracy of the proposed correlations, margin of deviation is presented at the end of this study. The results show excellent agreement between experimental data and those obtained through the correlations.

Evaluzation of Model equation Predicting Roll Force and Roll Power during Hot Rolling (열간압연중 압연하중 및 압연동력 예측 모델)

  • 곽우진;황상무
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 1999.08a
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    • pp.308-312
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    • 1999
  • Developed the model equations which calculate roll force, roll power during hot rolling in real time. The variables which mainly effect on the roll force, roll power are shape factor, reduction, roll diameter, roll velocity, strip inlet temperature, carbon content of strip and strip-roll contact friction coefficient. Among these variables roll diameter, roll velocity, inlet temperature, carbon content and friction coefficient can be excluded in interpolated model equation by introducing equation of die force(F'), power(p') of the frictionless uniform plane strain compression which can be calculated without iteration. At the case of coulomb friction coefficient of 0.3, we evaluated coefficient of polynomial equations of {{{{ { F} over {F' } }}}}, {{{{ { Pf} over {Pd }, { Pd} over {P' } }}}} from the result of finite element analysis using interpolation. It was found that the change of values of {{{{ { F} over {F' }, { P} over {P' } }}}} with the friction coefficient tend to straight line which slope depend only on shape factor. With these properties, developed model equations could be extended to other values of coulomb friction coefficient. To verify developed roll force, roll power model equation we compared the results from these model equation with the results from these model equation with the results from finite element analysis in factory process condition.

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The influence of V, Cu on the Bauschinger effect in API steel (고강도 API 강의 바우싱거 효과에 미치는 V, Cu의 영향)

  • Park J. S.;Kim D. W.;Chang Y. W.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2005.10a
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    • pp.336-339
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    • 2005
  • API steel is used for line-pipe to transport the oil and natural gas. As the recent trends in the development of API steel are towards the use of larger diameter and thicker plate, many researches have been studied to achieve higher strength, higher toughness and lower yield ratio in API steel. However, the strength of API steel after pipe forming is changed depend on the competition of the Bauschinger effect and work hardening. So, the purpose of this study is to investigate the influence on the Bauschinger effect for API steel by addition of V and Cu which are formed the precipitations for higher strength in API steel. The results are that the addition of V considered as a ferrite stabilizer and Cu considered as a austenite stabilizer decreases and increases the Bauschinger effect for API steel respectively.

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An Experimental Study on the Flow Motion of the Working Fluid in Miniature Thermosyphons (미세 서모사이폰 내의 작동유체의 유동에 대한 실험적 연구)

  • Oh, K.Y.;Kim, K.N.;Jang, J.H.
    • Proceedings of the KSME Conference
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    • 2000.04b
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    • pp.341-346
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    • 2000
  • This experimental study investigated the flow motion of the working fluid for various diameters of miniature thermosyphons and the performance characteristics for the various amount of the working fluid. The temperatures of condenser surface were measured and visual observations were conducted. The test results show that some fluid condensed in the tube diameters of 0.18cm and 0.22cm is not returned to the evaporator section due to capillary effect so that large temperature gradients are measured. To enhance returning the working fluid, one copper wire of 0.5mm diameter was inserted and the test results show good performance. When the liquid charge was less than 10% in volume dry-out was occurred fur the thermosyphons of the inner diameter of 1.8mm and 2.2mm.

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An Experimental Study on the Heat Transfer Characteristics of High-Temperature Cylindrical Heat Pipes (고온 원관형 히트파이프의 열전달 특성에 관한 실험 연구)

  • 박수용;부준홍
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.16 no.1
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    • pp.70-76
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    • 2004
  • High-temperature cylindrical sodium/stainless-steel heat pipes were manufactured and tested for transient as well as steady states. Total length of the heat pipe was 1 m and the diameter was 25.4 mm. Screen meshes of 3 different sizes were used to estimate the effect of mesh size on the thermal performance of the heat pipe. The minimum thermal resistance achieved was as low as 0.02$^{\circ}C$/W for the maximum thormal load of 2 ㎾. The average heat transfer coefficient in the evaporator was about 2,000 ㎾/$m^2$K and those in the condenser region were up to 5 times higher.

Thermometry in Hyperthermia induced by Ultrasound A Phantom study (초음파를 이용한 온열료법시 온도분포에 관한 연구)

  • Park, Charn-Il;Koh, Kyeong-Whan;Ha, Sung-Whan
    • Radiation Oncology Journal
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    • v.2 no.1
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    • pp.21-23
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    • 1984
  • Temperature homogeniety and stationary temperature is the most important thermometric considerations for the clinical use of hyperthermia. A thermal mapping was done in a phantom with thermocouple during hyperthermia which was induced by 1.0MHz,$0.7\~0.8watts/cm^2$ ultrasound and unfocused 2.5cm-diameter transducer. The results were as follows 1. Effective heating range$(42.5^{|circ}C\pm0.5^{\circ}C)$ were obtained 3cm in width and 4cm in depth from surface of phantom and temperature distribution was relatively uniform. 2. There was little heating effect more than 2cm away from transducer axis and more than 5cm in depth. 3. There was hot spots(more than $43^{\circ}C$) in $2.0\pm0.5cm$ depth from transducer along tranducer axis.

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Effect of Processing Factors on Critical Current Density in Bi2212/Ag Wires

  • Kim, Sang-Cheol;Ha, Dong-Woo;Oh, Sang-Soo;Han, Il-Yong;Ha, Hong-Soo;Sohn, Ho-Sang
    • Proceedings of the Korean Powder Metallurgy Institute Conference
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    • 2006.09b
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    • pp.1243-1244
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    • 2006
  • Five kinds of double stacked 385 (55 x7) filamentary Bi2212/Ag round wires and 55 filamentary tapes with different Ag ratios (silver area/superconductor area) have been fabricated via PIT method, and the effects of Ag ratio and processing factors on critical current density were studied. The effects of the maximum temperature and average filament diameter on critical current density were also studied. The wire of 0.74 mm diameter having Ag ratio 3.7 showed critical current density of $2,218\;A/mm^2$ at 4.2 K, 0 T.

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An Experimental Study on the Combustion Phenomena in Porous Media (다공질 내부의 연소현상에 대한 실험적 연구)

  • Lee, Yong-Il;Sin, Hyeon-Dong
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.20 no.1
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    • pp.321-327
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    • 1996
  • Experiments were performed on the laminar premixed flame stabilized in a porous medium to know whether the flame downstream of the combustor exists or not. In previous theoretical studies, a stable flame has been predicted in the downstream region of the combustor, but it has never been observed in experiments. In this study, a stable downstream flame could be obtained for the lower burning velocity through circumferential heating by a blue flame positioned outside the periphery of the specially devised combustor. The existence of the stable downstream flame was confirmed by a direct photography of soot line, and temperature measurements. The effect of combustor diameter to flame stability was also considered. As the diameter of the combustor increases, the lean flammability limit was extended.

A Characteristic study of SiC Nanowires by RF-Sputtering (RF-Sputtering 법에 의한 SiC 나노와이어의 특성연구)

  • Jeong, Chang-Gu;Kim, Tae-Gyu
    • Journal of the Korean Society for Heat Treatment
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    • v.23 no.6
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    • pp.344-349
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    • 2010
  • Silicon carbide nanowires were grown by heat treatment of the films at $1200^{\circ}C$ after amorphous SiC thin films were deposited on graphite substrate by radio frequency magnetron sputtering at $600^{\circ}C$. It was confirmed that SiC nanowires with the diameter of 20-60 nm and length of about 50nm were grown from Field Emission Scanning Election Microscope (FE-SEM) and Transmission Election Microscope (TEM) observation. The diameter of nanowires was increased as heat treatment time is increased. The nanowires were identified to ${\beta}$-SiC single crystalline from X-Ray Diffraction(XRD) analysis. It was observed from this study that deposition temperature of samples was critical to the crystallization of nanowires. On the other hand, the effect of deposition time was insignificant.

자발적 상분리법과 수열합성법을 이용한 ZnO계 일차원 나노구조의 수직 합성법 연구

  • Jo, Hyeong-Gyun;Kim, Dong-Chan;Bae, Yeong-Suk
    • Proceedings of the Materials Research Society of Korea Conference
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    • 2009.11a
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    • pp.5.2-5.2
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    • 2009
  • From 10 years ago, the development of nano-devices endeavored to achieve reconstruction of information technology (IT) and nano technology (NT) industry. Among the many materials for the IT and NT industry, zinc oxide (ZnO) is a very promising candidate material for the research of nano-device development. Nano-structures of ZnO-based materials were grown easily via various methods and it attracts huge attention because of their superior electrical and optical properties for optoelectronic devices. Recently, among the various growth methods, MOCVD has attracted considerable attention because it is suitable process with benefits such as large area growth, vertical alignment, and accurate doping for nano-device fabrication. However, ZnO based nanowires grown by MOCVD process were had the principal problems of 1st interfacial layers between substrate and nanowire, 2nd a broad diameter (about 100 nm), and 3rd high density, and 4th critical evaporation temperature of Zinc precursors. In particular, the growth of high performance nanowire for high efficiency nano-devices must be formed at high temperature growth, but zinc precursors were evaporated at high temperature.These problems should be repaired for materialization of ultra high performance quantum devices with quantum effect. For this reason, we firstly proposed the growth method of vertical aligned slim MgZnO nanowires (< 10 nm) without interfacial layers using self-phase separation by introduced Mg at critical evaporation temperature of Zinc precursors ($500^{\circ}C$). Here, the self-phase separation was reported that MgO-rich and the ZnO-rich phases were spontaneously formed by additionally introduced Mg precursors. In the growth of nanowires, the nanowires were only grown on the wurzite single crystal seeds as ZnO-rich phases with relatively low Mg composition (~36 at %). In this study, we investigated the microstructural behaviors of self-phase separation with increasing the Mg fluxes in the growth of MZO NWs, in order to secure drastic control engineering of density,diameter, and shape of nanowires.

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