• Title/Summary/Keyword: Thermal Transport

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Molecular Dynamics Simulations for Transport Coefficients of Liquid Argon : New Approaches

  • Lee, Song-Hi;Park, Dong-Kue;Kang, Dae-Bok
    • Bulletin of the Korean Chemical Society
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    • v.24 no.2
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    • pp.178-182
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    • 2003
  • The stress and the heat-flux auto-correlation functions in the Green-Kubo formulas for shear viscosity and thermal conductivity have non-decaying long-time tails. This problem can be overcome by improving the statistical accuracy by N (number of particles) times, considering the stress and the heat-flux of the system as properties of each particle. The mean square stress and the heat-flux displacements in the Einstein formulas for shear viscosity and thermal conductivity are non linear functions of time since the quantities in the mean square stress and the heat-flux displacements are not continuous under periodic boundary conditions. An alternative to these quantities is to integrate the stress and the heat-flux with respect to time, but the resulting mean square stress and heat-flux displacements are still not linear versus time. This problem can be also overcome by improving the statistical accuracy. The results for transport coefficients of liquid argon obtained are discussed.

Molecular Dynamics Simulation Study of Transport Properties of Diatomic Gases

  • Lee, Song Hi;Kim, Jahun
    • Bulletin of the Korean Chemical Society
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    • v.35 no.12
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    • pp.3527-3531
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    • 2014
  • In this paper, we report thermodynamic and transport properties (diffusion coefficient, viscosity, and thermal conductivity) of diatomic gases ($H_2$, $N_2$, $O_2$, and $Cl_2$) at 273.15 K and 1.00 atm by performing molecular dynamics simulations using Lennard-Jones intermolecular potential and modified Green-Kubo formulas. The results of self-diffusion coefficients of diatomic gases obtained from velocity auto-correlation functions by Green-Kubo relation are in good agreement with those obtained from mean square displacements by Einstein relation. While the results for viscosities of diatomic gases obtained from stress auto-correlation functions underestimate the experimental results, those for thermal conductivities obtained from heat flux auto-correlation functions overestimate the experimental data except $H_2$.

Modeling of Heat Transfer Equations for Estimation of Temperature Variations Inside the Oil Transport Pipe Line (원유 수송관 내부의 온도 변화 예측 을 위한 열전달 방정식의 모델링)

  • Jin, J.J.;Chung, H.T.;Bae, J.S.;Lee, S.O.
    • 한국전산유체공학회:학술대회논문집
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    • 2008.03b
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    • pp.300-303
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    • 2008
  • In the present study, the simple form of the heat transfer equation were suggested to estimate the temperature variation inside the oil pipe in order to determine the thickness of the insulating materials to retain the working oils below the critical temperature. The conservation of the thermal energy at arbitrary time were modeled to one dimensional unsteady equation with the empirical formula or data. The calculating results for non-insulation case showed that the temperature were very sensitive to the thermal convection by the velocity of the external wind. For insulation case, the insulation material which has higher density and specific heat, lower thermal conductivity should be chosen with more brighter coloring outside the pipe in order to retain the working oils below the critical temperature.

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Molecular Dynamics Simulation Study of the Transport Properties of Liquid Argon: The Green-Kubo Formula Revisited

  • Lee, Song-Hi
    • Bulletin of the Korean Chemical Society
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    • v.28 no.8
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    • pp.1371-1374
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    • 2007
  • The velocity auto-correlation (VAC) function of liquid argon in the Green-Kubo formula decays quickly within 5 ps to give a well-defined diffusion coefficient because the velocity is the property of each individual particle, whereas the stress (SAC) and heat-flux auto-correlation (HFAC) functions for shear viscosity and thermal conductivity have non-decaying, long-time tails because the stress and heat-flux appear as system properties. This problem can be overcome through N (number of particles)-fold improvement in the statistical accuracy, by considering the stress and the heat-flux of the system as properties of each particle and by deriving new Green-Kubo formulas for shear viscosity and thermal conductivity. The results obtained for the transport coefficients of liquid argon obtained are discussed.

A New Mechanism for Enhanced Beat Transport of Nanofluid (나노유체의 열전도도 향상에 관한 새로운 메커니즘)

  • Lee Dong-Geun;Kim Jae-Won
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.30 no.6 s.249
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    • pp.560-567
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    • 2006
  • Although various conjectures have been proposed to explain abnormal increase in thermal conductivity of nanofluids, the detailed mechanism could not be understood and explained yet. The main reason is primarily due to the lack of knowledge on the most fundamental factor governing the mechanisms such as Brownian motion, liquid layering, phonon transport, surface chemical effects and agglomeration. By applying surface complexation model for the measurement data of hydrodynamic size, zeta potential, and thermal conductivity, we have shown that sulfate charge state is mainly responsible for the increase in the present condition and may be the factor incorporating all the mechanisms as well. Moreover, we propose a new model including concepts of fractal and interfacial layer. The properties such as thickness and thermal conductivity of the layer are estimated from the surface charge states and the concept of electrical double layer. With this, we could demonstrate the pH dependences of the layer properties and eventually of the effective thermal conductivity of the nanofluid.

Effect of Porosity Characteristics of Hollow Composite Yarns to the Comfort Property of the Fabrics for the High Emotional Garment (중공 복합사 직물의 기공도 특성이 고감성 의류용 직물의 쾌적특성에 미치는 영향)

  • Kim, Hyun Ah;Kim, Young Soo;Kim, Seung Jin
    • Textile Coloration and Finishing
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    • v.26 no.3
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    • pp.218-229
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    • 2014
  • The wearing comfort of garment is governed by two kinds of characteristics such as moisture and thermal transport properties and mechanical properties of fabrics. The porosity influenced by yarn and fabric structural parameters is known as main factor for wearing comfort of garment related to the moisture and thermal transport properties. This study investigated effect of porosity of composite yarns to the moisture and thermal comfort properties of composite fabrics made of hollow composite DTY and ATY yarns. The theoretical porosity and pore size were inversely proportional to cover factor of fabric, but cover factor was not correlated with experimental pore size. The wicking property of hydrophobic PET filament fabric showed inferior result irrespective of porosity, pore size and cover factor. The drying rate was superior at composite fabrics with high pore size and low cover factor, and pore size was dominant factor for drying property. On the other hand, thermal conductivity of composite fabric was mainly influenced by cover factor and not influenced by porosity. Air permeability was influenced by both porosity and cover factor and was highly increased with increasing porosity and decreasing fabric cover factor.

Prediction of Transport Properties for Transporting Captured CO2. 2. Thermal Conductivity (수송조건 내 포집 이산화탄소의 전달물성 예측. 2. 열전도계수)

  • Lee, Won Jun;Yun, Rin
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.29 no.5
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    • pp.213-219
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    • 2017
  • This study investigated the thermal conductivity of $CO_2$ gas mixtures in order to ascertain the effects of particular impurities in $CO_2$ in pipeline transportation. We predicted the thermal conductivity of three $CO_2$ gas mixtures ($CO_2+N_2$, $CO_2+H_2S$, and $CO_2+CH_4$) by utilizing three different methods : Chung et al., TRAPP, and the REFPROP model. We validated predictions by comparing the estimated results with 216 experimental data for $CO_2+CH_4$, $CO_2+N_2$, and $CO_2+C_2H_6$. Following $CO_2$ transportation conditions, we observed that the model developed by Chung et al. showed the lowest mean deviation of 3.07%. Further investigations were carried out on the thermal conductivity of $CO_2$ gas mixtures based on the Chung et al. model including the effects of the operation parameters of pressure, temperature, and mole fraction of impurities.

Effect of accelerational perturbations on physical vapor transport crystal growth under microgravity environments

  • Choi, Jeong-Gil;Lee, Kyong-Hwan;Kwon, Moo-Hyun;Kim, Geug-Tae
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.16 no.5
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    • pp.203-209
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    • 2006
  • For $P_B=50,\;{\Delta}T=10K$, Ar=5, Pr=2.36, Le=0.015, Pe=1.26, Cv=1.11, the intensity of solutal convection (solutal Grashof number $Grs=3.44x10^4$) is greater than that of thermal convection (thermal Grashof number $Grt=1.81x10^3$) by one order of magnitude, which is based on the solutally buoyancy-driven convection due to the disparity in the molecular weights of the component A($Hg_2Cl_2$) and B(He). With increasing the partial pressure of component B from 10 up to 200 Torr, the rate is decreased exponentially. The convective transport decreases with lower g level and is changed to the diffusive mode at 0.1 $g_0$. In other words, for regions in which the g level is 0.1 $g_0$ or less, the diffusion-driven convection results in a parabolic velocity profile and a recirculating cell is not likely to occur. Therefore a gravitational acceleration level of less than 0.1 $g_0$ can be adequate to ensure purely diffusive transport.

DEVELOPMENT OF INTERFACIAL AREA TRANSPORT EQUATION

  • ISHII MAMORU;KIM SEUNGJIN;KELLY JOSEPH
    • Nuclear Engineering and Technology
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    • v.37 no.6
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    • pp.525-536
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    • 2005
  • The interfacial area transport equation dynamically models the changes in interfacial structures along the flow field by mechanistically modeling the creation and destruction of dispersed phase. Hence, when employed in the numerical thermal-hydraulic system analysis codes, it eliminates artificial bifurcations stemming from the use of the static flow regime transition criteria. Accounting for the substantial differences in the transport mechanism for various sizes of bubbles, the transport equation is formulated for two characteristic groups of bubbles. The group 1 equation describes the transport of small-dispersed bubbles, whereas the group 2 equation describes the transport of large cap, slug or chum-turbulent bubbles. To evaluate the feasibility and reliability of interfacial area transport equation available at present, it is benchmarked by an extensive database established in various two-phase flow configurations spanning from bubbly to chum-turbulent flow regimes. The geometrical effect in interfacial area transport is examined by the data acquired in vertical fir-water two-phase flow through round pipes of various sizes and a confined flow duct, and by those acquired In vertical co-current downward air-water two-phase flow through round pipes of two different sizes.

Effect of temperature gradient on junction magnetoresistance of magnetic tunnel junction devices

  • No, Seong-Cheol;Park, Min-Gyu;Lee, Yeo-Reum
    • Proceeding of EDISON Challenge
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    • 2014.03a
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    • pp.495-497
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    • 2014
  • Combining the quantum transport theory with new field of Spin Caloritronics, we investigate on the influence of thermal gradient on the magneto tunnel junction structure under various circumstances. The results indicate enhancement in performance of spintronic device is possible using thermal energy.

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