Enhanced thermal performance of high flux led systems with two-phase immersion cooling

Abstract

Considering significant worldwide use of electricity for general lighting, the implementation of energy efficient technologies is highlighted in many platforms with the use of light emitting diodes (LEDs). Because of its environmentally friendly nature, LEDs offer a promising solution to minimize inefficient use of energy as the demanding operating conditions pose new challenges. Reduction of lumen output, shorter lifetime and degradation of light characteristics with increasing package temperatures are critical issues that need to be addressed with innovative solutions. Especially in high power LEDs exposed to raised heat fluxes, standard cooling methods fail to remove the dissipated heat effectively. Recently, immersion cooling of LEDs with suspended phosphor particles in a dielectric liquid has been offered as a viable option to dissipate a vast amount of heat, ensuring a uniform distribution of temperature, and removal of local hot spots in a high brightness LED package. Therefore, understanding the fluid flow and particle motion due to natural convection in the package is crucial to improve thermal and optical design of an LED system. Temperature distribution and light extraction of a package can be considerably affected by material characteristics, flow regime and flow direction. In this study, the impact of different heat generation rates of an LED package is investigated considering natural convection currents and corresponding phosphor particle trajectories inside a fluid domain. A discrete phase model of a high-power white LED package is created in order to keep track of individual particles interacting with the carrier fluid and heat flow in a closed LED system. Current findings provide good basis for smart control of phosphor particles to maximize thermal and optical performance of both RGB and white LED packages.