Influence of dome phosphor particle concentration on mid-power LED thermal resistance

The modern white mid-power LEDs usually contain phosphor particles encapsulated in silicone dome material. The particles convert the blue light emitted from the epitaxial layer and play significant role in thermal processes of LED packages. In this paper the influence of the phosphor particles concentration and effect of sedimentation on thermal resistance and junction temperature of mid-power LEDs are investigated. Thermal transient measurements, thermal imaging and finite element simulations are used. It is shown that the sedimentation of phosphor particles has an impact on both thermal resistance and junction temperature of mid- power LEDs. General trends for phosphor particles concentration effect on thermal properties of a mid-power LED are determined

Experimental study on a simple Ranque-Hilsch vortex tube

The Ranque-Hilsch vortex tube is a device by which cold gas can be generated using compressed gas. To understand the cooling mechanism of this device, it is necessary to know the pressure, temperature, and velocity distributions inside the tube. In order to investigate this, a simple vortex tube is built and nitrogen is used as its working fluid. A special Pitot tube is used for the measurement of the pressure and velocity. This Pitot tube consists of a capillary which has only one hole in the cylinder wall. With this Pilot tube, the pressure and velocity fields inside the tube were measured. In the same way, the temperature field was measured with a thermocouple. The results of three different entrance conditions are compared here. With the measurements results, the analysis based on the two thermodynamic laws has been made. It is found that rounding off the entrance has influence on the performance of the vortex tube. The secondary circulation gas flow inside the vortex tube can be enhanced and enlarged, the performance of the Ranque-Hilsch vortex tube improved. (C) 2004 Elsevier Ltd. All rights reserved