• Title, Summary, Keyword: Temperature gradient

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Numerical Study of Radial Temperature Gradient Effect on Taylor Vortices (반경방향으로의 온도구배가 Taylor Vortex에 미치는 영향에 대한 수치적 연구)

  • Kang, Chang-Woo;Yang, Kyung-Soo;Yoon, Dong-Hyeog
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.33 no.11
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    • pp.900-908
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    • 2009
  • Numerical simulation has been carried out to investigate the influence of radial temperature gradient on the Taylor Vortex flow. Varying the Grashof number, we study the detailed flow and temperature fields. The current numerical results show good agreement with the experimental results currently available. It turns out that wavy spiral vortices are generated by increasing temperature gradient. We classify flow patterns for various Grashof numbers based on the characteristics of flow fields and spiral vortices. The correlation between Grashof number with wave number shows that the spiral angle and size of Taylor vortices increase with increasing temperature gradient. Temperature gradient does not have a great influence on the heat transfer rate of the cylinder surfaces.

A study on the Effective Utilization of Temperature Logging Data for Calculating Geothermal Gradient (지온경사 산출을 위한 효율적인 온도검층자료 이용방법 연구)

  • 김형찬
    • Economic and Environmental Geology
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    • v.32 no.5
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    • pp.503-517
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    • 1999
  • The purpose of this study is to verfify a more effecive techique for calculating geothermal gradient. this study examines 370 data of temperature-logging having been collected since 1985. The daya are divided into three different grades grades according to the type of temperature-depth plots: 204 data show typical linear gradient (Grade A); 126 data do not explicitily show the gradient becase of various external effects such as water flow (Grade B); and the rest 40 data do not show the gradient at all (Grade D). The new technique for calculating geothermal gradient is to be required to use Greade-B data more effctiviely. This new technique includes (1) calculating the independer depth of atmospheric temperature in the earth; (2) drawing a distribution map of subsurface tempurature by using the distribution map of subsurface temperature by using Grade-A data at the independent depth; and (3) recalculating geothermal gradient of Grade-B data by using the distrbution map of subsurface temperature, borehole depth, and bottom temperature of Grade-B data by using the distribution map of subsurface temperature, borehole depth, and bottom temperature of Grade-B data. As a result, 330 data-both Grade-A and Grade-B data--can be used to draw a distribution map of hot spradient. The map clearly distinguishes anomaly areas, and helps interpret their relations to the distribution of hot springs, geology, geological structures, and geophysical anomaly areas. These new results reveal that the average of geothermal in south Korea is 25.6$^{\circ}C$/km, when calculated to the Kriging method.

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Effect of temperature gradient on track-bridge interaction

  • Kumar, Rakesh;Upadhyay, Akhil
    • Interaction and multiscale mechanics
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    • v.5 no.1
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    • pp.1-12
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    • 2012
  • Considerable longitudinal rail forces and displacements may develop in continuous welded rail (CWR) track on long-span bridges due to temperature variations. The track stability may be disturbed due to excessive relative displacements between the sleepers and ballast bed and the accompanied reduction in frictional resistance. For high-speed tracks, however, solving these problems by installing rail expansion devices in the track is not an attractive solution as these devices may cause a local disturbance of the vertical track stiffness and track geometry which will require intensive maintenance. With reference to temperature, two actions are considered by the bridge loading standards, the uniform variation in the rail and deck temperature and the temperature gradient in deck. Generally, the effect of temperature gradient has been disregarded in the interaction analysis. This paper mainly deals with the effect of temperature gradient on the track-bridge interaction with respect to the support reaction, rail stresses and stability. The study presented in this paper was not mentioned in the related codes so far.

Detection of Mutated DNA Fragment by the Heteroduplex Analysis at the Temperature Gradient Gel (온도 기울기(temperature gradient) 젤에서 Heteroduplex Analysis 기법을 이용한 돌연변이 DNA의 검출)

  • 조용석;구미자;박귀근;박영서;강종백
    • Environmental Mutagens and Carcinogens
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    • v.18 no.2
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    • pp.83-88
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    • 1998
  • To detect the mutation in a given sequence, there are variety of methods developed by use of the gel electrophoresis. One of the methods, TGGE (Temperature Gradient Gel Electrophoresis), is a popular technique because it can detect mutations in DNA fragment with ease and at low cost. This study used 200 bp BamHI-digested DNA fragment containing the human $\varepsilon$-globin promoter which was mutated[$\varepsilon$ F1*(-141), GATA- I*(-163), and GATA-1* & $\varepsilon$F1]. This BamHI-digested DNA fragment was directly used to detect the mutated DNA fragment on 50% denaturant gel with temperature gradient of 45$^{\circ}C$ through $53^{\circ}C$. In agreement with the theoretical result of MELTSCAN program (Brossette and Wallet, 1994) the mobilities of mutated DNA fragments were shown to be nearly distinguished on the temperature gradient gel. In contrast to the above result the heteroduplex analysis under the temperature gradient condition was shown to detect the mutated DNA fragments through the heteroduplex formation between strands of mutated DNA and wild-type DNA.

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Theoretical and Simulation Study of Thermo-Osmosis of Liquid in Microchannel (마이크로 채널 내 액체에서의 열삼투현상에 대한 이론 및 시뮬레이션 연구)

  • Han, Min-Sub
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.29 no.1
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    • pp.131-138
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    • 2005
  • Thermo-osmosis of liquids in a microscale channel is investigated by theoretical and simulation study. From the basic set of conservation equations, the temperature and velocity distributions are derived in the function of the given temperatures and pressure gradient. The pressure gradient for a given temperature gradient is then obtained by the molecular simulation. It is shown that the temperature gradient tangential to the surface induces the pressure gradient and thus the flow in the interfacial region between the liquid and channel surface. The thermo-osmotic flow is proportional to the applied temperature gradient, and the factor of proportionality depends on temperature and intermolecular potential. The origin and characteristics of the phenomenon are discussed in molecular details.

An experimental and numerical study on temperature gradient and thermal stress of CFST truss girders under solar radiation

  • Peng, Guihan;Nakamura, Shozo;Zhu, Xinqun;Wu, Qingxiong;Wang, Hailiang
    • Computers and Concrete
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    • v.20 no.5
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    • pp.605-616
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    • 2017
  • Concrete filled steel tubular (CFST) composite girder is a new type of structures for bridge constructions. The existing design codes cannot be used to predict the thermal stress in the CFST truss girder structures under solar radiation. This study is to develop the temperature gradient curves for predicting thermal stress of the structure based on field and laboratory monitoring data. An in-field testing had been carried out on Ganhaizi Bridge for over two months. Thermal couples were installed at the cross section of the CFST truss girder and the continuous data was collected every 30 minutes. A typical temperature gradient mode was then extracted by comparing temperature distributions at different times. To further verify the temperature gradient mode and investigate the evolution of temperature fields, an outdoor experiment was conducted on a 1:8 scale bridge model, which was installed with both thermal couples and strain gauges. The main factors including solar radiation and ambient temperature on the different positions were studied. Laboratory results were consistent with that from the in-field data and temperature gradient curves were obtained from the in-field and laboratory data. The relationship between the strain difference at top and bottom surfaces of the concrete deck and its corresponding temperature change was also obtained and a method based on curve fitting was proposed to predict the thermal strain under elevated temperature. The thermal stress model for CFST composite girder was derived. By the proposed model, the thermal stress was obtained from the temperature gradient curves. The results using the proposed model were agreed well with that by finite element modelling.

Effect of Mold Dimensions on Temperature Distribution of Die during Plasma Activated Sintering (플라즈마 활성 소결에 있어서 다이스의 온도분포에 미치는 몰드 크기의 영향)

  • Lee Gil-Geun;Park IK-Min
    • Journal of Korean Powder Metallurgy Institute
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    • v.11 no.5
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    • pp.363-368
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    • 2004
  • In the present study, the focus is on the analysis of the effect of the mold dimensions on the temperature distribution of a die during plasma activated sintering. The temperature distribution of a cylindrical mold with various dimensions was measured using K-type thermocouples. The temperature homogeneity of the die was studied based on the direction and dimensions of the die. A temperature gradient existed in the radial direction of the die during the plasma activated sintering. Also, the magnitude of the temperature gradient was increased with increasing sintering temperature. In the longitudinal direction, however, there was no temperature gradient. The temperature gradient of the die in the radial direction strongly depended on a ratio of die volume to punch area.

Characteristic Changes of the Hydrated Sodium Silicate Depending on Heat Treatment Temperature (수화된 규산소다의 열처리 온도에 따른 물성변화)

  • Kong, Yang-Pyo;Cho, Ho-Yeon;Suhr, Dong-Soo
    • Journal of the Korean Ceramic Society
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    • v.45 no.3
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    • pp.185-189
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    • 2008
  • In order to fabricate porous ceramics, hydrated sodium silicate was synthesized by hydrothermal reaction using anhydrous sodium silicate. The microstructural and the structural characteristics of the expanded ceramics were observed depending on heat treatment temperature (550, 600, 650, $700^{\circ}C$) and then the effect of these characteristics on the compressive strength and the temperature gradient was investigated. As the heat treatment temperature was increased, the compressive strength was decreased from $0.717KN/cm^2\;(550^{\circ}C)\;to\;0.166KN/cm^2\;(700^{\circ}C)$. The temperature gradient was increased with increasing the experimental temperature regardless of the heat treatment temperature. The temperature gradient of the expanded ceramics which was heat treated at $650^{\circ}C\;was\;300^{\circ}C$. The bulk specific gravity, porosity, pore size, pore characteristics and wall thickness were varied depending on heat treatment temperature, and the compressive strength and the temperature gradient were governed by the complex effects of these factors.

Thermophoresis in Dense Gases: a Study by Born-Green- Yvon Equation

  • Han Minsub
    • Journal of Mechanical Science and Technology
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    • v.19 no.4
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    • pp.1027-1035
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    • 2005
  • Thermophoresis in dense gases is studied by using a multi-scale approach and Born- Yvon­Green (BYG) equation. The problem of a particle movement in an ambient dense gas under temperature gradient is divided into inter and outer ones. The pressure gradient in the inner region is obtained from the solutions of BYG equation. The velocity profile is derived from the conservation equations and calculated using the pressure gradient, which provides the particle velocity in the outer problem. It is shown that the temperature gradient applied to the quiescent ambient gas induces some pressure gradient and thus flow tangential to the particle surface in the interfacial region. The mechanism that induces the flow may be the dominant source of the thermophretic particle movement in dense gases. It is also shown that the particle velocity has a nonlinear relationship with the applied temperature gradient and decreases with increasing temperature.

Effect of Temperature Gradient on the Defects of Nd;YAG Single Crystal Grown by Czochralski Method (융액인상법에 의한 Nd;YAG 단결정 성장시 온도구배의 변화에 따른 결함거동)

  • 김한태;배소익;이상호;정수진
    • Journal of the Korean Ceramic Society
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    • v.34 no.10
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    • pp.1015-1020
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    • 1997
  • In the Nd;YAG crystal growth by Czochralski method, the relationship between the core formation and the solid-liquid interface was observed by controlling the temperature gradient in the furnace. When the crystal was grown along<111> direction, defects and core area were reduced as the temperature gradient increased. The optimum temperature gradient was found to be higher than 4$0^{\circ}C$/cm. The Nd3+ concentration analysis by ICP-Mass showed that the segregation coefficient was about 20% higher in the core region than core-free region, where the segregation coefficients of core region and core-free region were 0.22 and 0.18, respectively.

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