Showing papers on "Stefan number published in 1997"
TL;DR: In this article, a framework for understanding low Weber number deposition in terms of similarity laws and experimentation is presented, based on experiments from the highly viscous limit to the inertia-dominated limit, correlations are given for the spreading velocity, spreading time scales, post-spreading oscillation amplitudes and oscillation damping time scales.
Abstract: Low Weber number deposition of small molten droplets on cold targets is of importance in certain dropwise buildup processes, but at this time, critical elements are absent from our theoretical understanding of the deposition process, and prediction from basic principles is not possible. This paper lays down a framework for understanding low Weber number deposition in terms of similarity laws and experimentation. Based on experiments from the highly viscous limit to the inertia-dominated limit, correlations are given for the spreading velocity, spreading time scales, post-spreading oscillation amplitudes, and oscillation damping time scales. Molten droplets are arrested, and their final solid shape determined, by contact line freezing. In homologous deposition, where the drop and the target are of the same material, the spreading factor is determined principally by the Stefan number, the dimensionless parameter which measures the temperature difference between the fusion point and the target temperature. Some concluding remarks are offered on what needs to be done to accurately compute such deposition processes.
350 citations
TL;DR: In this paper, the transient behavior of the crust at the upper and lower surfaces and the effect of crust formation on the turbulent natural convection process in the melt layer is investigated theoretically.
Abstract: The phenomenon of turbulent natural convection in a horizontal heat-generating melt layer with solidification taking place at the cooled upper and lower boundaries is investigated theoretically. The objective is to determine the transient behavior of the crust at the upper and lower surfaces and the effect of crust formation on the turbulent natural convection process in the melt layer. Various surface temperatures, latent heats, and the heat source strengths are considered along with the effects of the Stefan number and Rayleigh number. Special attention is given to the interaction between the melt pool heat transfer and the crust dynamics. Numerical results are presented for the transient crust thickness, transient temperature distribution, eddy heat transport, and the heat transfer characteristics at the solid liquid interface during the freezing process. The present study provides basic information needed to predict the transient behavior of a melt pool in a reactor lower head following a severe core-meltdown accident.
7 citations
TL;DR: In this article, a conduction based model for solving the phase change heat transfer problem around a vertical cylinder submersed in a phase change medium is presented. But, the model is based on the average control volume technique and the ADI approach and the results show the effects of the variation of the Biot number, Stefan number, inlet fluid temperature and the ratio of the outer to the inner tube radius on the solidified mass fraction, NTU, effectiveness and the time for complete solidification.
Abstract: This paper presents a conduction based model for solving the phase change heat transfer problem around a vertical cylinder submersed in the phase change medium. The energy equation is coupled to the flow problem by an energy balance. The system of equations is solved numerically by using the average control volume technique and the ADI approach. The results show the effects of the variation of the Biot number, Stefan number, the inlet fluid temperature and the ratio of the outer to the inner tube radius on the solidified mass fraction, NTU, effectiveness and the time for complete solidification.
5 citations
27 Jul 1997
TL;DR: In this article, the effects of the inner wall temperature variation within cylindrical or spherical capsules were analyzed and simple approximate equations were presented, which facilitates designing of the practical capsule bed LHTES systems.
Abstract: Melting and solidification of a phase change material (PCM) in a capsule is of practical importance in latent heat thermal energy storage (LHTES) systems which are considered to be very promising to reduce a peak demand of electricity in the summer season. Two melting modes are involved in melting in capsules. One is close-contact melting between the solid bulk and the capsule wall, and another is natural convection melting in the liquid region. Close-contact melting processes for a single enclosure have been solved using several numerical methods (e.g. Saitoh and Kato (1994)). However, there is no theoretical solution considering the inner wall temperature variation within cylindrical or spherical capsules. In this report close-contact melting heat transfer characteristics including melt flow in the liquid film under inner wall temperature distribution were analysed and simple approximate equations are presented, which facilitates designing of the practical capsule bed LHTES systems. The effects of the Stefan number and variable temperature profile etc., were clarified in detail. The melting velocity of the solid bulk under various conditions was also studied theoretically. In addition the effects of variable inner wall temperature on molten mass fraction were investigated.
3 citations