• Title/Summary/Keyword: Temperature Gradient

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Experimental Study of the Axial Slit Wall and Radial Temperature Gradient Effect on Taylor-Couette Flow (Taylor-Couette 유동에서 축방향 홈과 반경방향 온도구배의 영향에 대한 실험적 연구)

  • Lee, Sang-Hyuk;Kim, Hyoung-Bum
    • Journal of the Korean Society of Visualization
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    • v.6 no.2
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    • pp.33-38
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    • 2008
  • The effect of the radial temperature gradient and the presence of slits in the wall of outer of two cylinders involved in creating a Taylor-Couette flow was investigated by measuring the velocity field inside the gap. The slits were azimuthally located along the inner wall of the outer cylinder and the number of slits used in this study was 18. The radius ratio and aspect ratio of the models were 0.825 and 48, respectively. The heating film wrapped around the inner cylinder was used for generating the constant heat flux and we ensured the constant temperature condition at the outer space of the outer cylinder. The velocity fields were measured by using the PIV(particle image velocimetry) method. The refractive index matching method was applied to remove image distortion. The results were compared with plain wall configuration of Taylor-Couette flow. From the results, the presence of slits in the wall of outer cylinder and temperature gradient increased the flow instability.

Thermal Stress at the Junction of Skirt to Head in Hot Pressure Vessel (고온 수직형 압력용기 Skirt 부의 열응력에 관한 연구)

  • 한명수;한종만;조용관
    • Journal of Welding and Joining
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    • v.16 no.2
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    • pp.111-121
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    • 1998
  • It is well recognized that a excessive temperature gradient from the junction of head to skirt in axial direction in a hot pressure vessel can cause unpredicted high thermal stress at the junction and/or in axial direction of a skirt. this thermal stress resulting from axial thermal gradient may be a major cause of unsoundness of structural integrity. In case of cyclic operation of hot pressure vessels, the thermal stress becomes one of the primary design consideration because of the possibility of fracture as a result of cyclic thermal fatigue and progressively incremental plastic deformation. To perform thermal stress analysis of the junction and cylindrical skirt of a vessel, or, at least, to inspect quantitatively the magnitude and effect of thermal stress, the temperature profile of the vessel and skirt must be known. This paper demonstrated the temperature distribution and thermal stress analysis for the junction of skirt to head using F.E. analysis. Effect of air pocket in crotch space was quantitatively investigated to minimize the temperature gradient causing the thermal stress in axial direction. Effect of the skirt height on thermal stresses was also studied. Analysis results were compared with theoretical formulas to verify th applicability to the strength calculation in design field.

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The experimental study on the Characteristics of the Moxa-Combustion in the retaining period of indirect moxibustion (간접구(間接灸)의 제품별(製品別) 보온기(保溫期) 연소특성(燃燒特性)에 관한 연구(硏究))

  • Yoon, Jung-Sun;Cho, Myung-Rae;Yoon, Yeo-Chung;Park, Young-Bae
    • Journal of Acupuncture Research
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    • v.17 no.1
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    • pp.75-88
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    • 2000
  • In order to obtain the clinical data on the different effects of the three different methods of indirect moxibustion, moxa-combustion time, peak temperature, average temperature, maximum gradient temperature, average gradient temperature, and moxa-combustion calorie rate of the retaining period in ARIRANG, JANG, PUNG were measured through this experiment. The results of the experiment were as follows : 1. In the combustion time, during the retaining period ARIRANG had the longest combustion time followed by PUNG, JANG in a descending order. ARIRANG and JANG were acknowledged to have significant difference with PUNG. ARIRANG and JANG however were not acknowledged to have difference each other. 2. In the average temperature, during the retaining period, PUNG had the highest temperature followed by JANG, ARIRANG in a descending order. ARIRANG and JANG were acknowledged to have significant difference with PUNG. ARIRANG and JANG however were not acknowledged to have difference each other. 3. In the maximum gradient temperature, during the retaining period, PUNG had the highest temperature followed by JANG, ARIRANG in a descending order. JANG and PUNG were acknowledged to have significant difference with ARIRANG. JANG and PUNG however were not acknowledged to have difference each other. 4. In the average gradient temperature, during the retaining period, JANG had the highest temperature followed by ARIRANG, PUNG in a descending order. ARIRANG and JANG were acknowledged to have significant difference with PUNG. ARIRANG and JANG however were not acknowledged to have difference each other. 5. In the moxa-combustion calorie rate, during the retaining period, PUNG had the highest temperature, ARIRANG, JANG were founded in error limits. ARIRANG and JANG were acknowledged to have significant difference with PUNG. ARIRANG and JANG however were not acknowledged to have difference each other.

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Thermal field of large-diameter concrete filled steel tubular members under solar radiation

  • Yang, Daigeng;Chen, Guorong;Ding, Xiaofei;Xu, Juncai
    • Computers and Concrete
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    • v.26 no.4
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    • pp.343-350
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    • 2020
  • Concrete-filled steel tubular (CFST) members have been widely used in engineering, and their tube diameters have become larger and larger. But there is no research on the thermal field of large-diameter CFST structure. These studies focused on the thermal field of the large-diameter CFST structure under solar radiation. The environmental factors and the actual placement position were considered, and the finite element model (FEM) of the thermal field of CFST members under solar radiation (SR) was established. Then the FEM was verified by practical experiments. The most unfavorable temperature gradient model in the cross-section was proposed. The testing results showed that the temperature field of the large-diameter CFST member section was non-linearly distributed due to the influence of SR. The temperature field results of CFST members with different pipe diameters indicated that the larger the core concrete diameter was, the slower the central temperature changed, and there was a significant temperature difference between the center and the boundary. Based on the numerical model, the most unfavorable temperature gradient model in the section was proposed. The model showed that the temperature difference around the center of the circle is small, and the boundary temperature difference is significant. The maximum temperature difference is 15.22℃, which appeared in the southern boundary area of the specimen. Therefore, it is necessary to consider the influence of SR on the thermal field of the member for large-diameter CFST members in actual engineering, which causes a large temperature gradient in the member.

An optimal control in cement kiln heat-up (시멘트 소성로 가열 단계에서의 최적 제어)

  • 김송호;이광순;이원규
    • 제어로봇시스템학회:학술대회논문집
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    • 1986.10a
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    • pp.468-470
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    • 1986
  • An optimal control in heat-up operation was formulated for minimizing the quadratic performance criterion which is a function of temperature, temperature gradient in the wall and fuel flow rate. For optimal control law computations mathematical model was simplified with assumptions and then linearized by use of orthogonal collocation in radial direction. Effects of weighting function assigned to temperature and temperature gradient and final time were compared with industrial data.

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Experimental analysis of thermal gradient in concrete box girder bridges and effects of polyurethane insulation in thermal loads reduction

  • Raeesi, Farzad;Heydari, Sajad;Veladi, Hedayat
    • Structural Engineering and Mechanics
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    • v.83 no.5
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    • pp.645-654
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    • 2022
  • Environmental thermal loads such as vertical and lateral temperature gradients are significant factors that must be taken into account when designing the bridge. Different models have been developed and used by countries for simulating thermal gradients in bridge codes. In most of the codes only vertical temperature gradients are considered, such as Iranian Standard Loads for Bridge code (ISLB), which only considers the vertical gradient for bridge design proposes. On the other hand, the vertical gradient profile specified in ISLB, has many lacks due to the diversity of climate in Iran, and only one vertical gradient profile is defined for whole Iran. This paper aims to get the both vertical and lateral gradient loads for the concrete box girder using experimental analysis in the capital of Iran, Tehran. To fulfill this aim, thermocouples are installed in experimental concrete segment and temperatures in different location of the segment are recorded. A three dimensional finite element model of concrete box-girder bridge is constructed to study the effects of thermal loads. Results of investigation proved that the effects of thermal loads are not negligible, and must be considered in design processes. Moreover, a solution for reducing the negative effects of thermal gradients in bridges is proposed. Results of the simulation show that using one layer polyurethane insulation can significantly reduce the thermal gradients and thermal stresses.

Dendrite Arm Spacing and Carbide Morphology with Thermal Gradient and Solidification Rate in Directionally Solidified Ni-Base Superalloy (일방향 초내열합금에서 응고속도 및 온도구배 따른 수지상간격 및 탄화물 형상 변화)

  • Son, S.D.;Kim, Y.H.;Choi, G.S.;Lee, J.H.;Seo, S.M.;Jo, C.Y.
    • Journal of Korea Foundry Society
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    • v.27 no.2
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    • pp.77-82
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    • 2007
  • The effects of thermal gradient and solidification rate on the dendrite arm spacing and carbide morphology were investigated in directionally solidified Ni-base superalloy, CM 247LC. Thermal gradient was controlled by changing the position of the cold chamber and the furnace set temperature. The interface morphology changed from the planar to dendritic as increasing solidification rate. It was found that the dendrite spacing decreased as increasing the thermal gradient as well as the solidification rate. Also, as increasing solidification rate, carbide morphology changed from blocky shape to script and spotty shapes.

Spalling of heated high performance concrete due to thermal and hygric gradients

  • Zhang, Binsheng;Cullen, Martin;Kilpatrick, Tony
    • Advances in concrete construction
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    • v.4 no.1
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    • pp.1-14
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    • 2016
  • In this study, high performance concrete beams and prisms with high content of PFA were heated to various temperatures up to $450^{\circ}C$ at heating rates of $1^{\circ}C/min$, $3^{\circ}C/min$ and $10^{\circ}C/min$. The thermal gradient was found to increase first with the heating time until a peak value was reached and then decrease until the thermal equilibrium was reached, measured as $115^{\circ}C$, $240^{\circ}C$ and $268^{\circ}C$ for the three heating rates. Spalling occurred on some specimens when the heating temperature was over $400^{\circ}C$ for heating rates of $3^{\circ}C/min$ and $10^{\circ}C/min$. The hygric gradient was found to reach its maximum when the thermal gradient reached its peak. This study indicates that spalling of HPC could happen when the heating temperature was high enough, and both thermal and hygric gradients reached their maxima.

A Study on the Characteristics of Cylinder Wake Placed in Thermally Stratified Flow (I) (열성층유동장에 놓인 원주후류의 특성에 대한 연구 (1))

  • 김경천;정양범;김상기
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.18 no.3
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    • pp.690-700
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    • 1994
  • The effects of thermal stratification on the flow of a stratified fluid past a circular cylinder were examined in a wind tunnel. In order to produce strong thermal stratifications, a compact heat exchanger type variable electric heater is employed. Linear temperature gradient of up to $250^{\circ}C/m$ can be well sustained. The velocity and temperature profiles in the cylinder wake with a strong thermal gradient of $200^{\circ}C/m$ were measured and the smoke wire flow visualization method was used to investigate the wake characteristics. It is found that the temperature field effects as an active contaminant, so that the mean velocity and temperature profiles can not sustain their symmetricity about the wake centerline when such a strong thermal gradient is superimposed. It is evident that the turbulent mixing in the upper half section is stronger than that of the lower half of the wake in a stably stratified flow.

Nondestructive Estimation of Average Wood Moisture Content Using Surface Temperature Rise by Radiation Heating and Moisture Gradient

  • Lee, Hyoung-Woo;Kim, Byung-Nam
    • Journal of the Korean Wood Science and Technology
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    • v.27 no.4
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    • pp.38-42
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    • 1999
  • Average moisture content of 30mm-thick Korean red pine(Pinus densiflora) was estimated nondestructively and continuously using surface temperature rise by radiation heating and moisture gradient profile in wood. The surface temperature rises increased as surface moisture contents decreased and good relationships were found between surface moisture contents and surface temperature rises at three different feed speeds of 10, 20 and 30 m/min. Average moisture content could be described as a function of surface moisture content and wood thickness.

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