• Title/Summary/Keyword: Heat conduction

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Measurement of Critical Heat Flux Using the Transient Inverse Heat Conduction Method in Spray cooling (비정상 열전도 역산법에 의한 분무냉각 임계열유속(CHF)의 측정에 관한 연구)

  • Kim, Yeung Chan
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.40 no.10
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    • pp.653-658
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    • 2016
  • A study on the measurement of critical heat flux using the transient inverse heat conduction method in spray cooling was performed. The inverse heat conduction method estimates the surface heat flux or temperature using a measured interior temperature history. The effects of the measuring time interval and location of temperature measurement on the measurement of critical heat flux were primarily investigated. The following results were obtained. The estimated critical heat flux decreased as the time interval of temperature measurement increased. Meanwhile, the effect of measurement location on critical heat flux was not significant. It was also found, from the experimental results, that the critical superheat increased as the measurement location of thermocouple neared the heat transfer surface.

A Study on the Influence Affect of Thermal Sensation in Korean and Japanes to Sit Directly on a Heated Floor (바닥난방시 바닥 접촉면에 의한 한국인과 일본인의 온열감 반응에 대한 비교 연구)

  • Choi, Young-Sik
    • Journal of the Korean Society of Industry Convergence
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    • v.5 no.1
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    • pp.81-89
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    • 2002
  • The objective of this paper is to clarify the combined effect of heat conduction, air temperature and thermal radiation on the person seated on the floor under operation of floor heating system. Experiments were conducted for summer seasons under 8 kinds of condition: combinations of air temperature $20^{\circ}C$, $22.5^{\circ}C$ and floor temperature $20^{\circ}C$, $22.5^{\circ}C$, $30^{\circ}C$, $35^{\circ}C$ and $40^{\circ}C$ under still air. Japanese and Koreans were adopted as subjects. To evaluate the effect of conduction operative temperature modified by heat conduction was derived from the human heat balance equation. New weighting coefficients were estimated from the modified operative temperature and modified mean skin temperature. As for thermal sensation the modified operative temperature more significantly correlated to that sensation each heat transfer processes. As the floor temperature is higher, the human conduction heat gain from floor increase and the dry heat from the human body decrease.

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MHD SIMULATIONS OF A MOVING SUB CLUMP WITH HEAT CONDUCTION

  • ASAI NAOKI;FUKUDA NAOYA;MATSUMOTO RYOJI
    • Journal of The Korean Astronomical Society
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    • v.37 no.5
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    • pp.575-578
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    • 2004
  • High resolution observations of cluster of galaxies by Chandra have revealed the existence of an X-ray emitting comet-like galaxy C153 in the core of cluster of galaxies A2125. The galaxy C153 moving fast in the cluster core has a distinct X-ray tail on one side, obviously due to ram pressure stripping, since the galaxy C153 crossed the central region of A2125. The X-ray emitting plasma in the tail is substantially cooler than the ambient plasma. We present results of two-dimensional magnetohydrodynamic simulations of the time evolution of a sub clump like C153 moving in magnetized intergalactic matter. Anisotropic heat conduction is included. We found that the magnetic fields are essential for the existence of the cool X-ray tail, because in non-magnetized plasma the cooler sub clump tail is heated up by isotropic heat conduction from the hot ambient plasma and does not form such a comet-like tail.

An Application of Time Discontinuous Finite Element Method for Heat Conduction Problems (열전도 방정식의 시간 불연속 유한요소법 적용)

  • Kim, Chi-Kyung
    • Journal of the Korean Society of Safety
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    • v.23 no.3
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    • pp.87-92
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    • 2008
  • A finite element method which is discontinuous in time is developed for the solution of the classical parabolic model of heat conduction problems. The approximations are continuous with respect to the space variables for each fixed time, but they admit discontinuities with respect to the time variable at each time step. The method is superior to other well-known approaches to these problems in that it allows a wider range of moving boundary value problems to be dealt with, such as are encountered in complex engineering operations like ground freezing. The method is applied to one-dimensional and two-dimensional heat conduction problems in this paper, although it could be extended to more higher dimensional problems. Several example problems are discussed and illustrated, and comparisons are made with analytical approaches where these can also be used.

Wall Heat Conduction and Convection Heat Transfer from a Cylinder in Cross Flow (원형 실린더 주위의 전도-대류 열전달)

  • 이상봉;이억수;김시영
    • Journal of Ocean Engineering and Technology
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    • v.15 no.3
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    • pp.1-8
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    • 2001
  • With uniform heat generation within the wall of the cylinder placed in a cross flow, heat flows by conduction in the circumferential direction due to the asymmetric nature of the fluid flow around the perimeter of the cylinder. The circumferential heat flow affects the wall temperature distribution to such an extent that in some cases significantly different results may be obtained for geometrically similar surfaces. In the present investigation, the effects of circumferential wall heat conduction on local convective heat transfer is investigated for the case of forced convection around horizontal cylinder in cross flow of air. Two-dimensional temperature distribution $T_w$/(${\gamma}$,${\theta}$) is presented through the numerical analysis. The one-dimensional and two-dimensional solutions are in good agreement with experimental results of local heat transfer coefficients.

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REDUCED DIFFERENTIAL TRANSFORM FOR THERMAL STRESS ANALYSIS UNDER 2-D HYPERBOLIC HEAT CONDUCTION MODEL WITH LASER HEAT SOURCE

  • SUTAR, CHANDRASHEKHAR S.;CHAUDHARI, KAMINI K.
    • Journal of the Korean Society for Industrial and Applied Mathematics
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    • v.25 no.2
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    • pp.54-65
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    • 2021
  • In this study, a two-dimensional thermoelastic problem under hyperbolic heat conduction theory with an internal heat source is considered. The general solution for the temperature field, stress components and displacement field are obtained using the reduced differential transform method. The stress and displacement components are obtained using the thermal stress function in the reduced differential transform domain. All the solutions are obtained in the form of power series. The special case with a time-dependent laser heat source has been considered. The problem is considered for homogeneous material with finite rectangular cross-section heated with a non-Gaussian temporal profile. The effect of the heat source on all the characteristics of a material is discussed numerically and graphically for magnesium material taking a pulse duration of 0.2 ps. This study provides a powerful tool for finding the solution to the thermoelastic problem with less computational work as compared to other methods. The result obtained in the study may be useful for the investigation of thermal characteristics in engineering and industrial applications.

Calibration of Thermistors for Precision Temperature Measurements (정밀온도측정을 위한 서미스터 교정)

  • Gam, Kee-Sool;Kim, Yong-Gyoo;Yang, In-Seok
    • Journal of Sensor Science and Technology
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    • v.20 no.5
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    • pp.329-335
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    • 2011
  • We demonstrated that high-stability thermistors can be calibrated with an uncertainty less than 1 mK, if the error due to the heat conduction is minimized. We first investigated the effect of the self-heating of typical thermistor probes to see how accurate we need to determine the effect of self-heating. We, then, calibrated thermistors and fitted the results using various modeling equations. We found out that the heat conduction is an important factor in achieving the calibration uncertainty under 1 mK for thermistors when the diameter of the probe is as thick as 10 mm. Therefore, we controlled the room temperature within $0.5^{\circ}C$ to minimize the heat conduction error during the calibration. The calibration with an uncertainty below 1 mK was possible when the stabilization time for each calibration was long enough to obtain a good thermal equilibrium.

Characteristics on the Non-Steady Heal Transfer of the STS 304 Hollow Cylinder (STS 304 중공 원통의 비정상 열전달 특성)

  • Lee, Sang-Chul;Kim, Young-Geun;Shim, Kyu-Jin;Bae, Kang-Youl;Chung, Han-Shik;Jeong, Hyo-Min
    • Proceedings of the KSME Conference
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    • 2004.04a
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    • pp.1552-1557
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    • 2004
  • This paper introduced about characteristics on the non-steady heat transfer of STS 304 hollow cylinder, 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 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 in varied with temperature, the temperature distributions became in steady state after 15 minutes. Therefore, a numerical analysis of the non steady state heat transfer will has to apply that conductivity varied with temperature.

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Modeling of Fin-Tube Heat Exchanger (핀-관 열교환기의 모델링)

  • 박희용;이관수;박동규
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.13 no.5
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    • pp.952-961
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    • 1989
  • The purpose of this study is to investigate the behavior of operational and design factors on the performance characteristics of a horizontal fin-tube heat exchanger under phase change conditions for refrigerant. The flow and heat transfer in the heat exchanger are simulated numerically taking into account the variations of heat transfer coefficients, thermodynamic and flow properties of refrigerant, and the axial heat conduction in the tube wall. As the results of this study, it was found that the annular flow model was more reasonable physically than the homogeneous one for the two phase flow of refrigerant and axial heat conduction of tube wall did not have a great influence on the analysis. The effects of refrigerant pressure, mass flow rate of air, diameter of tube and the number of fins per unit length of tube were also discussed.

An Inverse Analysis of Two-Dimensional Heat Conduction Problem Using Regular and Modified Conjugate Gradient Method (표준공액구배법과 수정공액구배법을 이용한 2차원 열전도 문제의 역해석)

  • Choi, Eui-Rak;Kim, Woo-Seung
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.22 no.12
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    • pp.1715-1725
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    • 1998
  • A two-dimensional transient inverse heat conduction problem involving the estimation of the unknown location, ($X^*$, $Y^*$), and timewise varying unknown strength, $G({\tau})$, of a line heat source embedded inside a rectangular bar with insulated boundaries has been solved simultaneously. The regular conjugate gradient method, RCGM and the modified conjugate gradient method, MCGM with adjoint equation, are used alternately to estimate the unknown strength $G({\tau})$ of the source term, while the parameter estimation approach is used to estimate the unknown location ($X^*$, $Y^*$) of the line heat source. The alternate use of the regular and the modified conjugate gradient methods alleviates the convergence difficulties encountered at the initial and final times (i.e ${\tau}=0$ and ${\tau}={\tau}_f$), hence stabilizes the computation and fastens the convergence of the solution. In order to examine the effectiveness of this approach under severe test conditions, the unknown strength $G({\tau})$ is chosen in the form of rectangular, triangular and sinusoidal functions.