• 한국초전도ㆍ저온공학회논문지
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• 제4권2호
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• pp.68-72
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• 2002

This work investigates the transient cooling characteristics of an Infrared (IR) detector cryochamber, which has a critical effect on the cooling load. The current thermal modeling considers the conduction heat transfer through a cold well. the gaseous conduction due to outgassing. and the radiation heat transfer. The transient cooling Performance. i.e. the penetration depth and cooling load, is determined using a finite difference method. It is found that the penetration depth increases as the bore conductivity increases. Gaseous conduction and radiation hardly affect the penetration depth. The transient cooling load increases as the bore conductivity increases. The effects of gaseous conduction and radiation on transient heat transfer are weak at initial stages of cooling. However, their effects become significant as the cooling Process Proceeds.

• Structural Engineering and Mechanics
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• 제4권1호
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• pp.61-72
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• 1996

The time-stepping boundary element method has been so far applied by the authors to transient heat conduction in isotropic solids as well as in orthotropic solids. In this paper, attempt is made to extend the method to 2-D transient heat conduction in arbitrarily anisotropic solids. The resulting boundary integral equation is discretized by means of the boundary element with quadratic interpolation. The final system of equations thus obtained is solved by advancing the time step from the given initial state to the final state. Through numerical compuation of a few examples the potential usefulness of the proposed method is demonstrated.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1987년도 정기총회 및 창립40주년기념 학술대회 학회본부
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• pp.283-285
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• 1987

Transient conduction current (I - t characteristics) were measured in thin PPMMA (plasma-polymerized methyl methacrylate) films over the temperature range $60^{\circ}C-140^{\circ}C$ and the applied voltage range 3V - 30V. The current, which increased with temperature rise at constant applied voltage, showed less absorption current (current decay with time) at higher temperature region compared with those at lower temperature region. And the current, which increased with applied voltage rise at the constant temperature, showed less absorption current at higher voltage compared with those at lower voltage. The electric field current density characteristic curves were abtained from the conduction current values were after applying voltage for 30 minutes. And transient conduction currents were analyzed with high field conduction theories.

• 한국자동차공학회논문집
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• 제11권5호
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• pp.29-36
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• 2003

Exhaust manifolds suffer from serious temperature variation during the thermal fatigue test. The spatial distribution of temperature changes at each moment. Because transient flow can not be simulated during the long period of temperature change, the simulation can not be performed by conjugate heat transfer analysis. In this study, a new procedure for transient thermal analysis is established by decoupling fluid-solid analysis. The procedure consists of (1) transient CFD calculation (2 cycles), (2) mapping heat transfer coefficient to the inner surface of solid mesh as a boundary condition of heat conduction analysis and (3) transient heat conduction analysis in the long period (30 min). The realistic temperature change can be predicted by this procedure.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1376-1381
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• 2004

Understanding the thermal conductivity and heat transfer processes in superlattice structures is critical for the development of thermoelectric materials and optoelectronic devices based on quantum structures. $Chen^{(1)}$ developed ballistic diffusive equation(BDE) for alternatives of the Boltzmann equation that can be applied to the complex geometrical situation. In this study, a simulation code based on BDE is developed and applied to the 1-dimensional transient heat conduction across a thin film and transient 2-dimensional heat conduction across the film with heater. The obtained results are compared to the results of the $Chen^{(1)}$ and Yang and $Chen^{(1)}$. Finally, steady 2-dimensional heat conduction in the quantum dot superlattice are solved to obtain the equivalent thermal conductivity of the lattice and also compared with the experimental data from $Borca-Tasciuc^{(2)}$.

• 설비공학논문집
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• 제11권5호
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• pp.561-569
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• 1999

The effects of longitudinal heat conduction on the performance of heat transfer surfaces are investigated by using a single-blow method. In the transient testing method for determining the heat transfer characteristics, exponential inlet temperature variations are made by using screen-mesh heater with small time constant and low frontal velocities of the test section, and the experimentally determined inlet temperature profile is used as the inlet fluid temperature condition. The effects of longitudinal heat conduction are negligible only if $\gamma^\act<0.05\;and \;N_{tu}\le3$ and should be considered if $N_{tu}\le3$ The test results ate compared with the existing theoretical and experimental data and the validity of this technique is confirmed by the good agreement.

• Journal of Advanced Marine Engineering and Technology
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• 제15권3호
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• pp.57-65
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• 1991

The quenching of steels by water is one of the important problems in engineering for the applications of heat treatment or continuous casting process, but the fundamental researches by the theoretical approaches have not been satisfactorily improved yet. The very rapid cooling problems by the thermal conduction including the latent heat of phase transformation in steel and the transient boiling heat transfer of water on the surface of the steel covering from $850^{\circ}C$ to $20^{\circ}C$ are the key problems of heat treatment. The present quenching experiments are performed for the cylindrical specimens of carbon steel, S45C of diameters (12-30). Nonlinear transient heat conduction and transient boiling heat transfer problem of water on the surface of specimens is analyzed by the numerical method of inverse heat conduction problem. The conditions for the calculation are that the initial temperature of specimens is $820^{\circ}C$ and the cooling water in bath are $20^{\circ}C$,$40^{\circ}C$,$60^{\circ}C$,$80^{\circ}C$,$95^{\circ}C$ with no agitation.

• 오토저널
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• 제9권4호
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• pp.69-76
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• 1987

A conjugate conduction-convection analysis has been made for a plate fin which exchanges heat with its fluid environment by forced convection. The analysis is based on a one- dimensional model for the plate fin whereby the transient heat conduction equation for the fin is solved simultaneously with the conservation equations for mass, momentum, and energy in the fluid boundary layer adjacent to the fin. The forced convection heat transfer coefficient is not specified in advance but is one the results of the numerical solutions. Numerical results of the overall heat transfer rate, the local heat transfer coefficient, the local heat flux, the fin efficiency and the fin surface temperature distribution for Pr=0.7 are presented for a wide range of operating conditions.

• 대한기계학회논문집
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• 제7권4호
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• pp.417-424
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• 1983

This paper presents two methods of obtaining approximate analytic solutions for the temperature distributions and heat flow to two-dimensional transient heat conduction problems in a finite strip with constant thermal properties using the Heat Balance Integral. The methods introduced in this study are as follows; one using the Heat Balance Integral only, and the other successively using the Heat Balance Integral and an exact analytic method. Both methods are applicable to a large number of the two-dimensional unsteady conduction problems in finite regions such as extended surfaces with uniform thickness, but in this paper only solutions for the unsteady problems in a finite strip with boundary condition at the base expressed in terms of step function are provided as an illustration. Results obtained by both methods are compared with those by the exact two-dimensional transient analysis. It is found that both approximate methods generate small time solutions, which can not be obtained easily by any exact analytic method for small values of Fourier numbers. In the case of applying the successive use of the Heat Balance Integral and Laplace transforms, the analysis shows good agreement with the exact solutions for any Fourier number in the range of Biot numbers less than 0.5.

• 대한설비공학회지:설비저널
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• 제3권3호
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• pp.185-190
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• 1974

Floor panel heating system is popular in Korea as dwelling house heating system. There are two methods for keeping floor surface warm. One method is delivering warm air under the floor such as Roman Hypocaust and Korean traditional Ondol. The other method is imbedding hot water pipes into the concrete floor slab. This paper gives basic equations for steady and transient solutions of heat conduction from hurried pipes. For steady-state solution, fin Efficiency Method and Sink and Source Method were introduced. Sink and Source Method is applied to transient state and basic solution is given in the form of Exponential Integral Function. Numerical solutions can be solved easily by digital computer from these equations.