Thesis Defense - Erphan Safdari (MSME)

Erphan Safdari – M.Sc. in Mechanical Engineering

Prof. Mehmet Arık - Advisor

Asst. Prof. Altuğ Melik Başol – Co-Advisor

Date: 10.07.2025

Time: 09:00

Location: AB1 245

“An Investigation into Thermal and Optical Characteristics of Blue Light Emitting Diodes and White Light Conversion”

Prof. Mehmet Arık, Özyeğin University

Asst. Prof. Altuğ Melik Başol, Özyeğin University

Assoc. Prof. Özgür Ertunç, Özyeğin University

Asst. Prof. Ramazan Ünal, Özyeğin University

Prof. Sedat Nizamoğlu, Koç University

Abstract:

The evolution of lighting technologies has progressed from primitive fire-based sources to advanced solid-state devices, with Light-Emitting Diodes (LEDs) emerging as a cornerstone of modern illumination due to their energy efficiency and versatility. However, the performance and longevity of LEDs are critically dependent on effective thermal management, as excessive heat generation can degrade efficiency and lead to premature failure. This study investigates the thermal and optical performance of blue and white LED packages under various configurations, including bare LEDs, painted LEDs, and optically transparent fluid immersed LEDs, using both experimental and computational approaches. A comprehensive analysis of heat dissipation mechanisms is conducted, focusing on convective heat transfer coefficients, Nusselt (Nu), Rayleigh (Ra), and Prandtl (Pr) numbers. 

Experimental measurements of junction temperature, fluid temperature, and heat transfer rates are validated with computational fluid dynamics (CFD) simulations, demonstrating a good agreement. The study highlights the impact of surface modifications, such as high-emissivity paint, on thermal performance, revealing significant enhancements in convective heat transfer. Additionally, new correlations for small-scale surface natural convection heat transfer (< 1 mm) to predict the Nusselt number are proposed, tailored for millimetric-scale heating surfaces, addressing gaps in existing literature. These correlations are derived from empirical data and simulations, offering improved accuracy for small-scale electronic cooling applications. 

The findings underscore the importance of optimizing thermal management strategies for LEDs, particularly in high-power applications. The study contributes to the advancement of LED technology by providing insights into heat dissipation mechanisms and proposing practical solutions for enhancing optical and thermal performance for the added benefits of reliability.

Bio:

Erphan Safdari graduated from the University of Isfahan (Shahreza Campus) in Mechanical Engineering in 2021. He conducted molecular dynamics studies of silicon and carbon nanotubes. In September 2022, he joined Özyeğin University as a Master’s candidate in Mechanical Engineering under the supervision of Dr. Mehmet Arık and Dr. Altuğ Melik Başol. Since then, he has served as a Research Assistant at EVATEG (2022-2025), where he has developed coupled thermal–optical models and experiments. At EVATEG, he has worked on projects including passive liquid cooling of LEDs, nanofluid heat-transfer enhancement, microscale Nusselt–Ra–Pr correlations for millimetric chip cooling, and thermo-optical characterization of phosphor-converted LEDs. His research interests consist of thermal management in photonic systems, nanofluid heat transfer, and thermo-optical coupling in LED devices.