• Title/Summary/Keyword: Temperature Gradient

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Second-order velocity and temperature in pulse tube refrigerators (맥동관냉동기의 2차속도와 온도)

  • Lee, H.J.;Chae, W.B.;Jeong, E.S.
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.9 no.2
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    • pp.239-248
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    • 1997
  • Steady components and unsteady components of second-order velocity and temperature within pulse tube refrigerators were obtained. Second-order solutions were obtained from the first-order solutions of continuity, momentum and energy equations, assuming that the amplitude of the piston motion is small. The axial temperature gradient was considered in the analysis. The flow direction of the streaming was consistent with previous experimental observations. Effects of axial temperature gradient on secondary flow and second-order temperature were shown.

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NUMERICAL SIMULATION ON CONTROL OF HUMIDITY AND AIR TEMPERATURE IN THE GRADIENT BIOME (환경경도 바이옴 내의 온도 및 습도 제어 시뮬레이션)

  • Jeong, S.M.
    • Journal of computational fluids engineering
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    • v.21 no.2
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    • pp.32-39
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    • 2016
  • The Gradient Biome is a unique and large greenhouse(length 200 m, width 50 m, height:40 m) in which the elements of the weather, such as temperature and humidity, are controlled and reproduced in such a way as to create a continuous gradient from the tropical to frigid zones along specified longitudinal or transvers lines on the earth. One of the main purposes of the Gradient Biome is to observe the possible responses of the ecosystems (mainly plants), which are to be corresponding to each test climate and be introduced in the Biome, to the expected global warming. As one of the expected responses is the shift of the ecosystem(s) toward the region of suitable environment, there should be no artificial obstacles, which can prevent the shift, inside the facility. However, it is important but not so easy to find the ways of how the temperature and humidity in the Biome could be reproduced since the environmental variables tends to be homogeneous. In this paper, numerical simulations were carried out to find the effective control methods for air temperature and humidity inside the real scale Biome. One of the contributed solvers of OpenFOAM, which is an open source physics simulation code, was modified and used for the simulations.

A high-order gradient model for wave propagation analysis of porous FG nanoplates

  • Shahsavari, Davood;Karami, Behrouz;Li, Li
    • Steel and Composite Structures
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    • v.29 no.1
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    • pp.53-66
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    • 2018
  • A high-order nonlocal strain gradient model is developed for wave propagation analysis of porous FG nanoplates resting on a gradient hybrid foundation in thermal environment, for the first time. Material properties are assumed to be temperature-dependent and graded in the nanoplate thickness direction. To consider the thermal effects, uniform, linear, nonlinear, exponential, and sinusoidal temperature distributions are considered for temperature-dependent FG material properties. On the basis of the refined-higher order shear deformation plate theory (R-HSDT) in conjunction with the bi-Helmholtz nonlocal strain gradient theory (B-H NSGT), Hamilton's principle is used to derive the equations of wave motion. Then the dispersion relation between frequency and wave number is solved analytically. The influences of various parameters (such as temperature rise, volume fraction index, porosity volume fraction, lower and higher order nonlocal parameters, material characteristic parameter, foundations components, and wave number) on the wave propagation behaviors of porous FG nanoplates are investigated in detail.

Temperature Reduction of Concrete Pavement Using Glass Bead Materials

  • Pancar, Erhan Burak;Akpinar, Muhammet Vefa
    • International Journal of Concrete Structures and Materials
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    • v.10 no.1
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    • pp.39-46
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    • 2016
  • In this study, different proportions of glass beads used for road marking were added into the concrete samples to reduce the temperature gradient through the concrete pavement thickness. It is well known that decreasing the temperature gradient reduces the risk of thermal cracking and increases the service life of concrete pavement. The extent of alkali-silica reaction (ASR) produced with partial replacement of fine aggregate by glass bead was investigated and compressive strength of concrete samples with different proportion of glass bead in their mix designs were measured in this study. Ideal results were obtained with less than 0.850 mm diameter size glass beads were used (19 % by total weight of aggregate) for C30/37 class concrete. Top and bottom surface temperatures of two different C30/37 strength class concrete slabs with and without glass beads were measured. It was identified that, using glass bead in concrete mix design, reduces the temperature differences between top and bottom surfaces of concrete pavement. The study presented herein provides important results on the necessity of regulating concrete road mix design specifications according to regions and climates to reduce the temperature gradient values which are very important in concrete road design.

Bubble-driven Convective Flow in the Liquid with Temperature Gradient (온도구배가 있는 액체 내에서 기포가 유발하는 대류유동)

  • Bae, Dae-Seok;Kim, Jeong-Soo
    • Journal of the Korean Society of Propulsion Engineers
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    • v.15 no.4
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    • pp.65-72
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    • 2011
  • Numerical simulation has been performed to investigate the bubbly flow in the liquid with vertical temperature gradient. The objective of this study is to establish an accurate numerical prediction program of gas-liquid two-phase flows in a vertical temperature gradient condition, whose mathematical model is formulated by the Eulerian-Lagrangian model. The present numerical results reveal the temperature mixing mechanism and the fluid dynamical characteristics induced by the bubbly flow in the liquid with stratified temperature. The effects of bubble radius, void fraction, and gas flow rate on bubble-driven convective flow are considered, too.

Temperature Gradient for Tire Pavement Noise Measurement

  • Yeo, Woon-Ho
    • The Journal of the Acoustical Society of Korea
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    • v.20 no.1E
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    • pp.3-6
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    • 2001
  • Sound pressure level (SPL) measurements were performed on a controlled test track vehicle coast-by runs of a passenger vehicle with six different sets of tires across a range of temperatures. A small but significant reduction of noise level with positive temperature increases was observed for some tires. The temperature gradient of the different tires at 80㎞/h ranged from -0.07 to + 0.01 dB/℃. Frequency analysis of the tire noise identified that noise content in the range of 1,300 to 1,900Hz was particularly sensitive to temperature changes. Differences in SPL due to speed and tire type were much greater than that due to temperature.

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An Experimental Study on the Lift-off Characteristics of the Triple Flame with Concentration Gradient (농도구배가 삼지화염의 부상특성에 미치는 영향에 관한 실험적 연구)

  • Seo, Jeong-Il;Kim, Nam-Il;Oh, Kwang-Chul;Shin, Hyun-Dong
    • 한국연소학회:학술대회논문집
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    • 2004.06a
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    • pp.7-14
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    • 2004
  • The lift-off characteristics of the triple flame have been studied experimentally with various mean velocities and concentration gradients using a multi-slot burner, which can control the concentration gradient and the mean velocity independently, Lift-off height, axial maximum velocity, flame temperature, and some other characteristics were examined for methane and propane flame, It was found that minimum values of the lift-off heights exist at a certain concentration gradient for constant mean velocity, and this result implies that the propagation velocity has a maximum value at this condition, OH radical distribution was measured with LIF method and velocity variation along streamline was measured with PlV system. In addition maximum temperature along streamline was measured with CARS system. The intensity of the diffusion flame affects on the propagation velocity of triple flame in the region of very weak concentration gradient.

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The experimental study on the Characteristics of the Moxa-Combustion in the input period of indirect moxibustion (간접구(間接灸)의 제품별(製品別) 입열기(入熱期) 연소특성(燃燒特性)에 관한 연구(硏究))

  • Ha, Chi-Hong;Cho, Myung-Rae;Chae, Woo-Seok;Park, Young-Bae
    • Journal of Acupuncture Research
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    • v.17 no.1
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    • pp.89-105
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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 input 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 input period ARIRANG had the longest combustion time followed by PUNG, JANG in a descending order but these were not acknowledged to have significant difference each other. 2. In the peak temperature of the input period, PUNG had the highest temperature followed by ARIRANG, 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. 3. In the average temperature, during the input 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. 4. In the maximum gradient temperature, during the input period, PUNG had the highest temperature followed by ARIRANG, 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. 5. In the average gradient temperature, during the input period, PUNG had the highest temperature followed by ARIRANG, 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. 6. In the moxa-combustion calorie rate, during the input period, JANG had the highest temperature followed by ARIRANG, PUNG in a descending order. ARIRANG and PUNG were acknowledged to have significant difference with JANG. ARIRANG and PUNG however were not acknowledged to have difference each other.

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Experimental Study on the Thermodynamic Characteristics of Commercial Small-size Moxa Combustion (상용 소형 쑥뜸의 열역학적 특성에 대한 실험적 연구)

  • Lee Geon-Mok;Hwang Yoo-Jin;Lee Gun-Hyee
    • Journal of Acupuncture Research
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    • v.18 no.6
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    • pp.171-187
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    • 2001
  • Objective : Moxibustion has been proved efficacious for many diseases, but isn't widespread in the clinics due to a danger of skin burning, the smoke produced while burning a moxa combustion and so on. Therefore, another type of moxa that can be resolved these troubles is required. To improve the effect of moxibustion and develop the new thermal stimulating treatment, the performance of commercial moxibustion widely used are studied systematically and found out quantitatively. Methods : We have selected two types (small-size moxa A(sMA), small-size moxa B (sMB)) among small-size moxaes used widely in the clinic. We examined combustion time, various temperatures, temperature gradient in each period during a combustion of moxa. Results : 1. The combustion time in the preheating period appeared somewhat longer in sMA than in sMB. 2, The combustion time in the heating period appeared longer in sMA by 26% than in sMB. 3. The average temperature in the heating period was $37.6{\sim}37.8^{\circ}C\;in\;sMA\;and\;36.2{\sim}36.8^{\circ}C$ in sMB and the maximum temperature measured at a center of contact surface in sMA was $48.6^{\circ}C$, higher by over $2.8^{\circ}C$ than that of sMB moxibustion. 4. The average ascending temperature gradient in the heating period was $0.08{\sim}0.1^{\circ}C/sec$ in both moxaes, and the average ascending temperature gradient of heating period in sMB appeared larger. The maximum ascending temperature gradient appeared higher in sMB, and the time reaching maximum ascending temperature gradient appeared much earlier in sMA than in sMB. 5. The combustion time in the retaining period was around 100 sec in sMA and around 275 sec in sMB. 6. The average temperature in the retaining period was $42.2{\sim}46.0^{\circ}C\;in\;sMA\;and\;39.3{\sim}41.4^{\circ}C/sec$ in sMB. The minimum temperature in the retaining period was over $38.80^{\circ}C$ in sMA but just $34.7^{\circ}C$ in sMB. 7. The average descending temperature gradient in sMA was $-0.050{\sim}0.067^{\circ}C/sec$ and in sMB was $-0.030{\sim}0.037^{\circ}C/sec$ 8. The combustion time in the cooling period appeared longer over two times in sMA than in sMB, and the time which the cooling period (minimum temperature) finished at appeared later in sMB by 55 sec. 9. We classified the combustion process that the measured temperature rose over body heat($37^{\circ}C$) into the effective combustion period. The effective combustion time was 233.3 sec in sMA and 300.4 sec in sMB respectively, and was longer by about 29% in sMB. The average temperature and maximum temperature in the effective combustion time appeared higher in sMA. The time taken until the maximum temperature was reached was 225.1 sec in sMA and 244.5 sec in sMB, faster by about 20 sec in sMA. The maximum ascending temperature gradient during the effective combustion period appeared larger about 1.4 times in sMB, but the time when the maximum ascending temperature gradient happened was faster in sMA. Conclusion : It appears that sMB, compared with sMA, is proper if necessary to apply the long time and weak stimulus, because of the gentle stimulus during the relatively longer time. In contrast, sMA that the symmetrical combustion happened is proper if necessary to apply the short time and strong stimulus.

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Numerical simulation of slit wall effect on the Taylor vortex flow with radial temperature gradient

  • Liu, Dong;Chao, Chang-qing;Zhu, Fang-neng;Han, Xi-qiang;Tang, Cheng
    • International Journal of Fluid Machinery and Systems
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    • v.8 no.4
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    • pp.304-310
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    • 2015
  • Numerical simulation was applied to investigate the Taylor vortex flow inside the concentric cylinders with a constant radial temperature gradient. The reliability of numerical simulation method was verified by the experimental results of PIV. The radial velocity and temperature distribution in plain and 12-slit model at different axial locations were compared, and the heat flux distributions along the inner cylinder wall at different work conditions were obtained. In the plain model, the average surface heat flux of inner cylinder increased with the inner cylinder rotation speed. In slit model, the slit wall significantly changed the distribution of flow field and temperature in the annulus gap, and the radial flow was strengthen obviously, which promoted the heat transfer process at the same working condition.