Solidification of Immiscible Alloys and Convective Effect

A model describing the microstructure formation in a directionally solidified immiscible alloy under the convective effect is presented. The microstructure evolution in a directionally solidified Al-Pb alloy is investigated. It is demonstrated that convective flows have great effects on the solidification of immiscible alloys. A convective flow against the solidification direction causes an increase in the nucleation rate while a convective flow along the solidification direction causes a decrease in the nucleation rate. The convective flows lead to a more uneven distribution of the minority phase droplets in the melt. It causes an increase in the size of the largest minority phase droplets and is against the obtaining of the immiscible alloys with a well dispersed microstructure.

THE INFLUENCE ON THE THERMAL RESISTANCE OF LED PACKAGING WITH DIFFERENT SUBMOUNT AND SURROUNDING CONDITIONS

A three-dimensional numerical model using the finite element method is proposed in the present study to accurately simulate the influences of the thermal resistance on the submount of an LED. In a system with adiabatic lateral boundaries, the internal thermal resistance of the submount is principally analyzed from the series connection effect of the spreading thermal resistance and one-dimensional material resistance. However, the total thermal resistance is used for analysis under various heat dissipating conditions due to the complex coupling relations among the material resistance, the spreading thermal resistance, and the external thermal resistance. A higher contact ratio between heat source and submount, a larger external convective effect, and dissipation of heat from the symmetrical axis of the submount will decrease the spreading thermal resistance.

An Appropriate Design in Dimensions of Submount with Extra-Low Thermal Resistance for High Power LED

A numerical simulation model to obtain the extra-low internal thermal resistance for submount of LED is presented. The 3-D numerical model for calculating thermal resistance is demonstrated on examining the aspect ratio of submount, the contact ratio between chip and submount, and the surrounding condition. According to the analysis by accurate numerical simulations of heat transfer; the appropriate dimensions for different conditions of ambient are determined. The thickness of submount should be over a specially designated value. Besides, a higher contact ratio between heat source and submount, a larger external convective effect, and the heat dissipated from symmetry axis of submount will decrease the spreading thermal resistance.