• Title/Summary/Keyword: Heat conduction

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Numerical method of hyperbolic heat conduction equation with wave nature (파동특성을 갖는 쌍곡선형 열전도방정식에 관한 수치해법)

  • 조창주
    • Journal of Advanced Marine Engineering and Technology
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    • v.22 no.5
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    • pp.670-679
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    • 1998
  • The solution of hyperbolic equation with wave nature has sharp discontinuties in the medium at the wave front. Difficulties encounted in the numrtical solution of such problem in clude among oth-ers numerical oscillation and the representation of sharp discontinuities with good resolution at the wave front. In this work inviscid Burgers equation and modified heat conduction equation is intro-duced as hyperboic equation. These equations are caculated by numerical methods(explicit method MacCormack method Total Variation Diminishing(TVD) method) along various Courant numbers and numerical solutions are compared with the exact analytic solution. For inviscid Burgers equa-tion TVD method remains stable and produces high resolution at sharp wave front but for modified heat Conduction equation MacCormack method is recommmanded as numerical technique.

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A Direct Integration Approach for the Estimation of Time-Dependent Boundary Heat Flux

  • Kim, Sin;Kim, Min-Chan;Kim, Kyung-Youn
    • Journal of Mechanical Science and Technology
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    • v.16 no.10
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    • pp.1320-1326
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    • 2002
  • In a one-dimensional heat conduction domain with heated and insulated walls, an integral approach is proposed to estimate time-dependent boundary heat flux without internal measurements. It is assumed that the expression of the heat flux is not known a priori. Hence, the present inverse heat conduction problem is classified as a function estimation problem. The spatial temperature distribution is approximated as a third-order polynomial of position, whose four coefficients are determined from the heat fluxes and the temperatures at both ends at each measurement. After integrating the heat conduction equation over spatial and time domain, respectively, a simple and non-iterative recursive equation to estimate the time-dependent boundary heat flux is derived. Several examples are introduced to show the effectiveness of the present approach.

Evaluation Methods on ONDOL Thermal Environmental Index (온돌 온열환경지표 평가방법)

  • Kim, Sung-Jo
    • Journal of the Korean Society of Industry Convergence
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    • v.25 no.1
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    • pp.101-110
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    • 2022
  • For this purpose, the authors proposed and proved usefulness of the modified mean skin temperature which is integrated mean radiation temperature and the effect of floor contacted heat conduction. The mean radiation temperature is applied form factor between half cross-legged human body and surrounding wall of indoor. In addition the floor contacted heat conduction is applied heat transfer coefficient of half cross-legged human body. Eight Korean young men were targeted for the experiment. From the experiment the authors excerpted physiological reaction and psychological reaction in Ondol environment which is combined physiccal environmental factor of artificial climate chamber, air and floor temperature. As a result of the experiment it is confirmed that heat conduction has more impact than heat exchange from existing research for the heat exchange between half cross-legged human body and surrounding wall in Ondol thermal environment. Thereby, it is proved the effectiveness of the modified mean skin temperature which is added floor contacted temperature to the Ondol thermal environmental evaluation index.

The effect of wall heat conduction on local convection heat transfer from a cylinder in cross flow of air (원형 실린더 주위의 공기로 국소 대류 열전달에 대한 열전도의 영향)

  • 이승홍;이억수
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.10 no.4
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    • pp.440-448
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    • 1998
  • This paper considers the influence of circumferential wall heat conduction for the case of forced convection around a circular cylinder in cross flow of air. Keeping uniform heat generation from the inner surface of the cylinder in radial direction, heat is transferred by wall conduction in the circumferential direction due to the asymmetric nature of the temperature distribution of the cylinder and by convection around the perimeter of the cylinder. The wall conduction depends on conductivity of the cylinder and size of the cylinder radius and thickness and affects the local convective heat transfer rate significantly for geometrically similar surfaces and flow conditions. A nondimensional conjugation parameter K. (=k$_t$R/k$_w$b) has been used to characterize the effect of the circumferntial wall heat conduction. The small values of conjugation parameter K are found to be associated with large effect of wall conduction on the local convective heat transfer rate.

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Numerical Analysis on Longitudinal Heat Conduction in Printed Circuit Heat Exchanger (인쇄기판형 열교환기의 유동방향 전도열전달에 관한 수치해석 연구)

  • Oh, Dong-Wook;Kim, Young;Choi, Jun Seok;Yoon, Seok Ho
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.26 no.12
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    • pp.600-604
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    • 2014
  • Longitudinal heat conduction is known to be an important factor in the design of a printed circuit heat exchanger(PCHE) for cryogenic applications. Parasitic heat conduction through the heat exchanger frame needs to be considered because it is known to decrease the effectiveness of the heat exchanger. In this paper, a conjugate heat transfer problem in a simple counter-flow PCHE is analyzed by a computational fluid dynamics simulation. The effect of longitudinal conduction in a straight channel is compared with the theoretical effectiveness-NTU relationship that assumes a "thin" heat exchanger frame. The calculation results suggest that the theoretical model is valid in the present calculation conditions where NTU is < 13.

Frost Behavior on a One-Dimensional Fin Considering Heat Conduction of Heat Exchanger Fins (열교환기 휜의 열전도를 고려한 1차원 휜에서의 착상 거동)

  • Kim, Jung-Soo;Kang, Soo-Jin;Lee, Kwan-Soo
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.20 no.11
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    • pp.727-732
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    • 2008
  • This paper presents a mathematical model to predict the behavior of frost formed on an one-dimensional fin of heat exchanger, considering fin heat conduction under frosting conditions. The computational domain consists of air-side, the frost layer, and fin region, and they are coupled to the frost layer. The frost behavior is more accurately predicted with fin heat conduction considered (Case A) than with constant fin surface temperature assumed (Case B). The results indicate that for Case B, the frost thickness and heat transfer are overpredicted in most regions of the fin, as compared with those for Case A. In addition, for Case A, the maximum frost thickness varies little with the fin length variations, and the extension of the fin length after 30mm contributes insignificantly to heat transfer.

Phenomena of Hyperbolic Heat Conduction in the Hot Mold with an Inner Defect (내부결함이 있는 고온 금형에서의 쌍곡선형 열전도 현상)

  • Lee, Gwan-Su;Im, Gwang-Ok;Jo, Hyeong-Cheol;Kim, U-Seung
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.25 no.7
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    • pp.952-957
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    • 2001
  • In the glass forming process, the phenomena of hyperbolic heat conduction in the hot mold with an inner defect are studied analytically. It is shown that the temperature predicted by the parabolic model is underestimated compared to the one by the hyperbolic model. As the rmal wave is reflected from the area with defects and then arrives at the surface supplied by the heat flux, it is expected that there exists thermal shock in the materials. The area with defects is assumed to be adiabatic since its thermal conductivity is much lower compared to the one of the material. The results also indicate that the sudden temperature -jump in the mold surface can cause diverse problems such as glass defect (embryo mark, etc), oxidation of mold and coating, and change of material properties.

A Study on the Mechanical Behavior of Resistance Spot Welding by Finite Element Method (유한요소법에 의한 저항 점용접부의 역학적 특성에 관한 연구)

  • 방한서;주성민;방희선;차용훈;최병기
    • Journal of Welding and Joining
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    • v.17 no.5
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    • pp.77-82
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    • 1999
  • Resistance spot welding process is completed in very short time and there are many factors affecting on the generation of heat. It is difficult to control these experimental factors and monitor distribution of the temperature and stresses in the experimental analysis case. and too much time and expense are required for the experimental trials to fine proper welding condition. So numerical analyses have been attempted steadily, but most numerical analyses on the resistance spot welding are mainly focused on thermal behavior. Therefore, in this paper, the numerical analysis of mechanical behavior as well as heat conduction is carried out for the spot welding process. For this numerical analysis, axial symmetric computer program for the spot welding analysis by F.E.M. has been developed considering heat conduction and thermal elastic-plastic theory. Material properties depending on temperature such as density, heat conductivity, heat expansion coefficient, specific heat, yield stress, elastic modulus, and specific resistance are considered. Using the results of temperature distribution obtained from heat conduction analysis, the thermal elastic-plastic analysis is carried out to clarify mechanical behavior of spot welded specimen. In order to evaluate the effect of residual stresses, numerical analyses are carried out under tension-shear load in two cases respectively; one with residual stress, the other without residual stresses.

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A Numerical Method for One-dimensional Inverse Heat Conduction Problem Using Laplace Transform (라플라스 변환을 이용한 1차원 열전도의 수치해석)

  • Shin, Woon-Chul;Bae, Sin-Chul
    • Journal of the Korean Society of Safety
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    • v.22 no.4
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    • pp.13-19
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    • 2007
  • An numerical method to estimate thermal diffusivity has been developed for one-dimensional unsteady heat conduction problem, when the temperatures are know at two positions in a semi-infinite body. Using the closed form solution which has already derived an explicit solution for the inverse problem for one-dimensional transient heat conduction using Laplace transform technique, we first estimate the surface temperature. The thermal diffusivity can be estimated by using the estimated surface temperature and measured temperatures, which include some uncertainties. The estimated surface heat flux and thermal diffusivity are found to be in good agreement with those of the experimented conditions. This method will be extended to the simultaneous measurement of thermal diffusivity and thermal conductivity.