Showing papers on "Stefan number published in 2001"

Experimental study on melting in a rectangular enclosure heated below with discrete heat sources

Abstract: The melting process of n-octadecane in a rectangular cavity with three discrete protruding heat sources on its bottom surface was studied experimentally. It was observed that the experimental process, for the geometric arrangement in this paper, is neither a fixed melting nor a contact melting, but one in which fixed melting and contact melting take place alternatively. The effects of Stefan number, initial subcooling and aspect ratio on the melting process are reported. The larger the Stefan number, the more frequently the contact melting may occur, so does the aspect ratio. The initial subcooling plays a role only in early stage. As the melting process proceeds, its effect on the melting process becomes less.

Comparison of Asymptotic Solutions of a Phase-Field Model to a Sharp-Interface Model

Abstract: A one-dimensional directional solidification problem is considered for the purpose of analyzing the relationship between the solution resulting from a phase-field model to that from a sharp-interface model. The solidification problem is posed within a finite domain, rather than an infinite extent, as in classical Stefan problems. An asymptotic analysis based upon a small Stefan number is performed on the sharp-interface model. In the phase-field case, the small Stefan number expansion is coupled with a small interface-thickness boundary layer expansion. This approach enables us to develop analytical solutions to the phase-field model. The results show agreement at leading order between the two models for the location of the solidification front and the temperature profiles in the solid and liquid phases. However, due to the nonzero interface thickness in the phase-field model, corrections to the sharp-interface location and temperature profiles develop. These corrections result from the conduction of late...

Numerical solutions of Stefan problem in annuli by enthalpy method and heat balance integral method

Abstract: A novel enthalpy formulation is applied to the Stefan problem in annuli and is compared with the heat balance integral method (HBIM). The methods are applied to inward and outward solidification in cylindrical geometry, and the results are combined to give numerical solutions in annuli. It is found that the enthalpy method gives comparable accuracy with the HBIM except for small Stefan number, and is more efficient and flexible. Copyright © 2001 John Wiley & Sons, Ltd.

氷水スラリーと温空気との直接接触熱交換による放冷に関する基礎研究 : 熱工学 , 内燃機関 , 動力など

Abstract: This paper has dealt with direct contact heat exchange characteristics between ice water slurry (average ice particle diameter : 3.10 mm) and hot air bubbles. The hot air bubbles ascending in the layer fluidized the ice water slurry layer, and the bubbles were cooled down directly by the ice water slurry. The following results were obtained from the experiment. In case of ice water slurry layer, the hot air bubbles fluidized the layer in earlier stage and heat exchange performance was higher than using only ice particles layer. The maximum temperature efficiency increased as Reynolds number Re increased because fluid in the layer became active and kept at the fixed value in the region of Re >__=900. Dehumidity efficiency increased as modified Stefan number and Re increased since the heat capacity of inlet air and heat transfer coefficient increased. Some empirical correlations for temperature efficiency, dehumidity efficiency and the completion time of latent cold heat release were derived in terms of various nondimensional parameters.

Heat storage characteristics of latent-heat microcapsule slurry using hot air bubbles by direct-contact heat exchange

Abstract: This study deals with the heat storage characteristics of latent-heat microcapsule slurry consisting of a mixture of fine microcapsules packed with latent-heat storage material and water. The heat storage operation for the latent-heat microcapsules was carried out by the direct-contact heat exchange method using hot air bubbles. The latent-heat microcapsule consisted of n-paraffin as a core latent-heat storage material and melamine resin as a coating substance. The relationship between the completion time of latent-heat storage and some parameters was examined experimentally. The nondimensional correlation equations for temperature efficiency, the completion time period of the latent-heat storage process and variation in the enthalpy of air through the microcapsule slurry layer were derived in terms of the ratio of microcapsule slurry layer height to microcapsule diameter, Reynolds number for airflow, Stefan number and modified Stefan number for absolute humidity of flowing air.