Optimum composition of gas mixture in a novel chimney-based LED bulb

The performance and lifetime of a LED bulb are highly sensitive to its operating temperature. Due to size and shape constraints, thermal management of LED bulb is challenging. This paper presented a combined numerical, analytical, and experimental study on the thermal-fluid flow and optimization of a novel chimney-based LED bulb. A CFD model considering both natural convection and radiation heat transfer was established and validated by experiment. An analytical model based on thermal resistance analysis was developed and verified against the CFD model. Compared to conventional LED bulbs, the advantage of the chimney-based LED bulb is that it can utilize the lampshade surface for heat dissipation in addition to the conventional role for light guide. To improve natural convection inside the chimney-based LED bulb, a gas mixture was introduced in the bulb and its composition was optimized by using the analytical model. It was found that the temperature rise of a LED bulb filled with the optimum gas mixture (a mixture of 74% helium and 26% xenon) was 30.7% lower than that filled with air at the same power input. The optimized gas mixture and the optimization method may be extended to other applications for natural convection in enclosures.