• Title/Summary/Keyword: Heat conduction

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A Study of the Heat Conduction Phenomena with a Phase Lag of Heat Flux (열유속 상지연이 존재하는 열전도 현상에 대한 연구)

  • Jin, Chang-Fu;Kim, Kyung-Kun;Chung, Han-Shik;Jeong, Hyo-Min;Choi, Du-Yeol;Choi, Soon-Ho
    • Journal of Advanced Marine Engineering and Technology
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    • v.32 no.5
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    • pp.684-690
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    • 2008
  • In most engineering applications related with the heat conduction phenomena, a conventional Fourier heat conduction equation has been successfully applied and it has supplied quite reasonable results. However, it is well known that the Fourier heat conduction equation is failed in the application to the extremely small space and short time, in other words, a nano-scale system and a pico-second time. In this study, non-Fourier effect was evaluated in the heat conduction by considering the concept of a phase lag model. The results show the existence of a heat wave, which means that the heat is transferred with a finite speed while an infinite speed of heat transfer is assumed in the conventional Fourier heat conduction. In addition, the copper and the gold are tested to evaluate the phase lag time between the heat flux and the temperature gradient. The results show that the gold has the heat wave speed faster than that of the copper consistent with the prediction based on an actual experiment.

Effect of Circumferential Wall Heat Conduction on Boundary Conditions for Convection Heat Transfer from a Circular Tube in Cross Flow (원관 주위의 대류 열전달에서 경계조건에 대한 원주방향 열전도의 영향)

  • 이상봉;이억수;김시영
    • Journal of Ocean Engineering and Technology
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    • v.15 no.2
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    • pp.39-45
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    • 2001
  • With uniform heat generation from the inner surface of the cylindrical heater placed in a cross flow boundary condition, heat flow that is conducted along the wall of the heater creates a non-isothermal surface temperature and non-uniform heat flux distribution. In the present investigation, the effects of circumferential wall heat conduction on convection heat transfer is investigated for the case of forced convection around horizontal circular tube in cross flow of air. The wall conduction number which can be deduced from the governing energy equation should be used to express the effect of circumferential wall heat conduction. It is demonstrated that the circumferential wall heat conduction influences local Nusselt numbers of one-dimensional and two-dimensional solutions.

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Comparative Analysis of the Parabolic and Hyperbolic Heat Conduction and the Damped Wave in a Finite Medium (유한한 평판에서 포물선형 및 쌍곡선형 열전도 방정식과 파동 방정식의 비교 해석)

  • Park, S.K.;Lee, Y.H.
    • Journal of Power System Engineering
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    • v.3 no.3
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    • pp.14-21
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    • 1999
  • The wave nature of heat conduction has been developed in situations involving extreme thermal gradients, very short times, or temperatures near absolute zero. Under the excitation of a periodic surface heating in a finite medium, the hyperbolic and parabolic heat conduction equations and the damped wave equations in heat flux are presented for comparative analysis by using the Green's function with the integral transform technique. The Kummer transformation is also utilized to accelerate the rate of convergence of these solutions. On the other hand, the temperature distributions are obtained through integration of the energy conservation law with respect to time. For hyperbolic heat conduction, the heat flux distribution does not exist throughout all the region in a finite medium within the range of very short times(${\xi}<{\eta}_l$). It is shown that due to the thermal relaxation time, the hyperbolic heat conduction equation has thermal wave characteristics as the damped wave equation has wave nature.

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Implementation and Experiments of Sparse Matrix Data Structure for Heat Conduction Equations

  • Kim, Jae-Gu;Lee, Ju-Hee;Park, Geun-Duk
    • Journal of the Korea Society of Computer and Information
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    • v.20 no.12
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    • pp.67-74
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    • 2015
  • The heat conduction equation, a type of a Poisson equation which can be applied in various areas of engineering is calculating its value with the iteration method in general. The equation which had difference discretization of the heat conduction equation is the simultaneous equation, and each line has the characteristic of expressing in sparse matrix of the equivalent number of none-zero elements with neighboring grids. In this paper, we propose a data structure for sparse matrix that can calculate the value faster with less memory use calculate the heat conduction equation. To verify whether the proposed data structure efficiently calculates the value compared to the other sparse matrix representations, we apply the representative iteration method, CG (Conjugate Gradient), and presents experiment results of time consumed to get values, calculation time of each step and relevant time consumption ratio, and memory usage amount. The results of this experiment could be used to estimate main elements of calculating the value of the general heat conduction equation, such as time consumed, the memory usage amount.

A Study of the Non-Fourier Heat Conduction Phenomena (비푸리에 열전도 현상에 관한 고찰)

  • Choi, Soon-Ho;Jin, Chang-Fu;Choi, Hyun-Kue;Yun, Seok-Hoon;Kim, Myoung-Hwan;Oh, Cheol
    • Proceedings of the Korean Society of Marine Engineers Conference
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    • pp.37-38
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    • 2005
  • Although the law of classical fourier heat conduction predicts the heat conduction phenomena occurred in most engineering fields with a good accuracy, it is also well-known that the conventional fourier law of a heat conduction has an application limit when the heating and cooling are periodic for a short duration or when the heat conduction is analyzed in the extremely low temperature region. This application limit of classical fourier law results from the fact that it assumed the infinite speed of a heat wave. In this study, we investigated the feasibility of whether the molecular dynamics could be used to calculate the speed of a heat wave through a solid. The calculated sound velocity showed a good agrement with the theoretical prediction qualitatively. From the calculated results, we confirmed that the same methodology can be applied the evaluation of the speed of a heat wave.

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Analytical solution of the Cattaneo - Vernotte equation (non-Fourier heat conduction)

  • Choi, Jae Hyuk;Yoon, Seok-Hun;Park, Seung Gyu;Choi, Soon-Ho
    • Journal of Advanced Marine Engineering and Technology
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    • v.40 no.5
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    • pp.389-396
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    • 2016
  • The theory of Fourier heat conduction predicts accurately the temperature profiles of a system in a non-equilibrium steady state. However, in the case of transient states at the nanoscale, its applicability is significantly limited. The limitation of the classical Fourier's theory was overcome by C. Cattaneo and P. Vernotte who developed the theory of non-Fourier heat conduction in 1958. Although this new theory has been used in various thermal science areas, it requires considerable mathematical skills for calculating analytical solutions. The aim of this study was the identification of a newer and a simpler type of solution for the hyperbolic partial differential equations of the non-Fourier heat conduction. This constitutes the first trial in a series of planned studies. By inspecting each term included in the proposed solution, the theoretical feasibility of the solution was achieved. The new analytical solution for the non-Fourier heat conduction is a simple exponential function that is compared to the existing data for justification. Although the proposed solution partially satisfies the Cattaneo-Vernotte equation, it cannot simulate a thermal wave behavior. However, the results of this study indicate that it is possible to obtain the theoretical solution of the Cattaneo-Vernotte equation by improving the form of the proposed solution.

NEW WEIGHTING COEFFICIENTS FOR CALCULATING MEAN SKIN TEMPERATURE IN RELATION TO THE POSTURE WITH CONSIDERATION TO HEAT CONDUCTION (열전도를 고려한 각 자세에 따른 평균 피부온의 산출)

  • Lee, Ju-Youn;MIYAMOTO, Seiichi;ISODA, Norio
    • Journal of the Ergonomics Society of Korea
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    • v.19 no.2
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    • pp.63-74
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    • 2000
  • This paper is to clarify a thermal physiological index that can account for the effects of local thermal environment. For this purpose two young female subjects exposing themselves to the above while sitting on a chair, sitting on the floor and lying on the floor were measured. These three representative postures accompanied the different contact surface areas, thereby the heat conduction rate between the floor and subject was quantitatively measured for each posture. It made the present study deal with the effect of heat conduction concerning the modified mean skin temperature and finally propose new weighting coefficients for the mean skin temperature calculation based on the Hardy & DuBois' formulas. In order to verify the proposed model, the experiment was carried out using a floor heating system. The comparison between the experimental result and prediction revealed that the proposed model should be about 10% more accurate than the conventional one in the case of lying on the floor which the heat conduction effect becomes important.

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A GN-based modified model for size-dependent coupled thermoelasticity analysis in nano scale, considering nonlocality in heat conduction and elasticity: An analytical solution for a nano beam with energy dissipation

  • Hosseini, Seyed Mahmoud
    • Structural Engineering and Mechanics
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    • v.73 no.3
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    • pp.287-302
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    • 2020
  • This investigation deals with a size-dependent coupled thermoelasticity analysis based on Green-Naghdi (GN) theory in nano scale using a new modified nonlocal model of heat conduction, which is based on the GN theory and nonlocal Eringen theory of elasticity. In the analysis based on the proposed model, the nonlocality is taken into account in both heat conduction and elasticity. The governing equations including the equations of motion and the energy balance equation are derived using the proposed model in a nano beam resonator. An analytical solution is proposed for the problem using the Laplace transform technique and Talbot technique for inversion to time domain. It is assumed that the nano beam is subjected to sinusoidal thermal shock loading, which is applied on the one of beam ends. The transient behaviors of fields' quantities such as lateral deflection and temperature are studied in detail. Also, the effects of small scale parameter on the dynamic behaviors of lateral deflection and temperature are obtained and assessed for the problem. The proposed GN-based model, analytical solution and data are verified and also compared with reported data obtained from GN coupled thermoelasticity analysis without considering the nonlocality in heat conduction in a nano beam.

The Effects of the STS 304 Hollow Cylinder Property Variations on the Non-Steady Heat Conduction (STS 304 중공 원통의 물성치 변화가 비정상 열전도에 미치는 영향)

  • Lee, S.C.;Choi, H.G.;Seo, J.S.;Jeong, H.M.;Chung, H.S.
    • Journal of Power System Engineering
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    • v.8 no.2
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    • pp.39-44
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    • 2004
  • The effects of the STS 304 hollow cylinder property variations on the non-steady heat conduction are considered in this paper. In the non steady state, the specific heat and conductivity are depended on the temperature variations, and these properties affect to the governing equation on heat conduction. But the most of numerical analysis on heat conduction is assumed to constant properties which is conductivity and specific heat. Assuming that the properties are reacted sensitively, the numerical results can have the difference of between constant properties with non constant properties. The main parameters are specific heat and conductivity. The temperature distributions of the STS 304 hollow cylinder became in steady state after 4 minutes in case of the constant properties. As the conductivity is varied with temperature, the temperature distributions became in steady state after 15 minutes. Therefore, a numerical analysis of the non steady state heat transfer is so important in case of varying temperature.

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Calculation of Heat Transfer Coefficients by Steady State Inverse Heat Conduction (정상상태의 열전달계수 예측을 위한 최적화기법의 열전도 역문제에 관한 연구)

  • 조종래;배원병;이부윤
    • Journal of Advanced Marine Engineering and Technology
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    • v.21 no.5
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    • pp.549-556
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    • 1997
  • The inverse heat conduction problems is the calculation of surface heat transfer coefficients by utilizing measured temperature. The numerical technique of finite element analysis and optimizition is introduced to calculate temperatures and heat transfer coefficients. The calculated heat transfer coefficients and temperature distribution are good agreement with the results of direct analysis. The inverse method has been applied to the control valve of nuclear power plant.

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