• Solar Energy
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• v.5 no.2
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• pp.77-83
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• 1985

An analysis is performed to investigate the influence of the buoyancy force and the thickness variation of melting layer in the containment that is filled with phase-change Material surrounding a cylindrical heating tube during melting process. The phase-change material is assumed to be initially solid at its phase-change temperature and the remaining solid at any given time is still at the phase-change temperature and neglecting the effect of heat transfer occuring within the solid. At the start of melting process, the thickness of melting layer is assumed to be a stefan-problem and after the starting process, the change of temperature and velocity is calculated using a two dimensional finite difference method. The governing equations for velocity and temperature are solved by a finite difference method which used SIMPLE (Semi Implicit Method Pressure linked Equations) algorithm. Results are presented for a wide range of Granshof number and in accordance with the time increment and it is founded that two dimensional fluid flow occurred by natural convection decreases the velocity of melting process at the bottom of container. The larger the radius of heating tube, the higher heat transfer is occurred in the melting layer.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.6
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• pp.749-757
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• 1999

Holographic interferornetric tomography can provide reconstruction of instantaneous three dimensional gross flow fields. The technique however confronts ill-posed reconstruction problems in practical applications. Experimental data are usually limited in projection and angular scanning when a field is captured instantaneously or under the obstruction of test models and test section enclosures. An algorithm, based on a series expansion method, has been developed to improve the reconstruction under the ill-posed conditions. A three-dimensional natural convection flow around two interacting isothermal cubes is experimentally investigated. The flow can provide a challenging reconstruction problem and lend itself to accurate numerical solution for comparison. The refractive index fields at two horizontal sections of the thermal plume with and without an opaque object are reconstructed at a limited view angle of 80" The experimental reconstructions are then compared with those from numerical calculation and thermocouple thermometry. It confirms that the technique is applicable to reconstruction of reasonably complex, three-dimensional flow fields.elds.

• Solar Energy
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• v.6 no.2
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• pp.43-53
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• 1986

The objective of this study is to report on the characterics of convective flow and heat transfer during metling process in order to provide design information for thermal energy storage systems which use phase change material. In present study, flow and heat transfer characteristics of the Phase Change Material in the Open Top Model (O.T.M) and in the Closed Top Model (C.T.M) were studied numerically by the control volume formulation using the algebraic non-orthogonal coordinate transformation. For the calculation procedure, the physical properties of fluid are assumed to be constant except density which is linely dependent on temperature in the bouyancy term of momentum equations. At start of melting process, the thickness of melting layer is assumed from the Stefan Problem assumption. The heat transfer results of Open Top Model and Closed Top Model are compared with the parameters of Grashof number and aspect ratio. It was found that heat transfer phenomena in melted region was greatly affected by buoyancy-driven natural convection and the melting distance of Open Top Model at the upper region is greater than that of Closed Top Model.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.8 no.3
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• pp.437-450
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• 1996

A set of stability equations is formulated for natural convection flows adjacent to a vertical isothermal surface melting in cold pure water. It takes account of the nonparallelism of the base flows. The melting rate is regarded as a blowing velocity at the ice surface. The numerical solutions of the linear stability equations which constitute a two-point boundary value problem are accurately obtained for various values of the density extremum parameter $R=(T_m-T_{\infty})/(T_0-T_{\infty})$ in the range $0.3{\leq}R{\leq}0.6$, by using a computer code COLNEW. The blowing effects on the base flow becomes more significant as ambient temperature ($T_{\infty}$) increases to $T_{\infty}=10^{\circ}C$. The maximum decrease of heat transfer rate is about 6.4 percent. The stability results show that the melting at surface causes the critical Grashof number $G^*$ and the maximum frequency of disturbances to decrease. In comparision with the results for the conventional parallel flow model, the nonparallel flow model has a higher critical Grashof number but has lower amplification rates of disturbances than does the parallel flow model. The spatial amplification contours exhibit that the selective frequency $B_0$ of the nonparallel flow model is higher than that of the parallel flow model and that the effects of melting are rather small. The present study also indicates that the selective frequency $B_0$ can be easily predicted by the value of the frequency parameter $B^*$ at $G^*$, which comes from the neutral stability results of the nonparallel flow model.

• Journal of Energy Engineering
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• v.24 no.1
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• pp.78-87
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• 2015

Focusing effect of a metallic layer in a severe accident depending on the aspect ratios and cooling conditions of top plate and side wall was investigated. Experiments were carried out for Rayleigh numbers and aspect ratio in the range of $8.49{\times}10^7{\sim}5.43{\times}10^9$, 0.135~0.541 respectively. In order to achieve high Rayleigh numbers, the heat transfer experiments were replaced by mass transfer experiments based on the heat and mass transfer analogy. A sulfuric acid-copper sulfate ($H_2SO4-CuSO_4$) electroplating system was adopted as the mass transfer system. The experimental results agreed well with the Rayleigh-Benard natural convection correlations of Dropkin and Somerscales and Globe and Dropkin. When compared with the standard Rayleigh-Benard problem, the cooling by the side wall is even higher than the top. For a shorter height, the interaction between the heated and cooled plumes increases due to decrease of the height. Thus, the heat transfer increases.