Thesis Defense - Ceren Cengiz (MSME)

Ceren Cengiz – M.Sc. Mechanical Engineering

Prof. Mehmet Arık – Advisor

Date: 31.05.2022

Time: 15:30

Location:  AB1 408

AN EXPERIMENTAL AND NUMERICAL INVESTIGATION OF IMMERSION COOLED BLUE LED COMBINED WITH YAG:Ce PHOSPHOR FOR THERMAL, ELECTRICAL AND OPTICAL PERFORMANCE

Thesis Committee:

Prof. Dr. Mehmet Arık Özyeğin University

Prof. Dr. Murat Uysal, Özyeğin University

Asst. Prof. Dr. Altuğ Başol, Özyeğin University

Assoc.  Prof.  Dr. Sedat Nizamoğlu, Koç University

Asst. Prof. Dr. Ramazan Ünal, Özyeğin University

Abstract:

In the new age of illumination, light emitting diodes (LEDs) have been proven to be the most efficient alternative to conventional light sources. Yet, in comparison to the other lighting systems, LEDs can function at a lower maximum operating temperature while junction temperature (Tj) and heat generation in the phosphor layer are among the main factors dictating their lifespan, reliability, and luminance performance. Thermal concerns in high power LEDs are important not only because of the dramatic failure of the chip, but also lowered performance in terms of light characteristics. Considering the thermal, electrical, and optical concerns with current LED devices, this study focused on the accurate thermal characterization of LEDs through experimental and computational measurements and proposed a novel immersion cooling technique combined with YAG:Ce to improve the performance of Pc-LED light systems. Based on the outcomes of the extensive literature review for experimental Tj measurement techniques, a more accurate and time efficient forward voltage method (FVM) is studied for thermal and optical characterization of bare and phosphor coated LED chips under operation. Following that an immersion cooling technique that directly targets heat generation zones is suggested and a preparation method for an immersion cooled LED package with dispersed phosphor particles is introduced. Effectiveness of the immersion cooling technique is acknowledged and image processing of particle-based investigation of phosphor has revealed that in the presence of blue light, 10-fold increase in particle velocity can be observed. Two-phase flow analysis is also conducted computationally by utilizing a discrete phase model in ANSYS Fluent environment by comparing the impact of different heat generation rates and particle sizes. It was observed that depending on the particle size and position, individual phosphor particles can follow a different trajectory that can affect the probability of obtaining white light emission.

Bio: 

Ceren Cengiz obtained her B.Sc. in Mechanical Engineering from Ozyegin University in 2019. Currently, she is pursuing the M.Sc. degree at Ozyegin University, focusing on thermal management and performance improvements of photonic devices.