Person: ARIK, Mehmet
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Mehmet
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ARIK
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Conference ObjectPublication Metadata only Thermal and optical performance of eco-friendly silk fibroin proteins as a cavity encapsulation over LED systems(ASME, 2015) Yuruker, Sevket Umut; Arık, Mehmet; Tamdoğan, Enes; Melikov, R.; Nizamoğlu, Sedat; Press, D. A.; Durak, Ilkem; Mechanical Engineering; ARIK, Mehmet; TAMDOĞAN, Enes; Yuruker, Sevket Umut; Durak, Ilkem; Tamdoğan, EnesThe demand for high power LEDs for illumination applications is increasing. LED package encapsulation is one of most critical materials that affect the optical path of the generated light by LEDs, and may result in lumen degradation. A typical encapsulation material is a mixture of phosphor and a polymer based binder such as silicone. After LED chips are placed at the base of a cavity, phosphor particles are mixed with silicone and carefully placed into the cavity. One of the important technical challenges is to ensure a better thermal conductivity than 0.2 W/m-K of current materials for most of the traditional polymers in SSL applications. In this study, we investigated an unconventional material of the silk fibroin proteins for LED applications, and showed that this biomaterial provides thermal advantages leading to an order of magnitude higher thermal performance than conventional silicones. Silk fibroin is a natural protein and directly extracted from silk cocoons produced by Bombyx mori silkworm. Therefore, it presents a “green” material for photonic applications with its superior properties of biocompatibility and high optical transparency with a minimal absorption. Combining these properties with high thermal performance makes this biomaterial promising for future LED applications. An experimental and computational study to understand the optical and thermal performance is performed. A computational fluid dynamics study with a commercial CFD software was performed and an experimental set-up was developed to validate the computational findings to determine the thermal conductivity of the proposed material.ArticlePublication Metadata only On the individual droplet growth modeling and heat transfer analysis in dropwise condensation(IEEE, 2021-10) Azarifar, Mohammad; Budaklı, M.; Başol, Altuğ Melik; Arık, Mehmet; Mechanical Engineering; BAŞOL, Altuğ Melik; ARIK, Mehmet; Azarifar, MohammadThe low convective coefficient at condenser part of spreaders and vapor chambers due to film blanket blocking encourages utilizing dropwise condensation (DWC). Challenges exist in the experimental characterization of DWC, which includes dependency on numerous parameters and more importantly measurement difficulties due to low driving temperature differences. This highlights the necessity of accurate modeling of this complex process. The widely used macroscale modeling process of DWC, known as classical analytical modeling of DWC, typically combines state of the art droplet size distribution model with a simplified shape-factor based heat transfer analysis of a single droplet which contains major simplifications such as conduction-only through the bulk liquid, hemispheric droplet shape, and homogeneously distributed temperature over the entire droplet surface. Recent numerical approaches included effect of Marangoni convection and implanted realistic thermal boundary conditions on liquid-vapor interface and reported significant errors of classical modeling. Based on a novel dynamic numerical approach which incorporates surface tension, Marangoni convection, and active mass transfer at the liquid-vapor interface, droplet growth phenomenon has been modeled in this study. Notable differences of droplet growth and flow field have been observed resulted from dynamic growth modeling of the droplet as more than 70% heat transfer rate underestimation of quasi steady modeling in 1 mm droplets with contact angle of 150° is observed. Effect of shape change due to gravity on the heat and mass transfer analysis of individual droplets found to be negligible.Conference ObjectPublication Metadata only Effect of direct liquid cooling on light emitting diode local hot spots: Natural convection immersion cooling(Begell House Inc., 2014) Tamdoğan, Enes; Arık, Mehmet; Mechanical Engineering; ARIK, Mehmet; TAMDOĞAN, Enes; Tamdoğan, EnesThe increased popularity of solid state systems with the technological developments have led them to be a favorable choice for many lighting applications besides electronics. However, the development of denser high lumen packages has been accompanied by increasing heat fluxes at the LED chip and package levels. Especially, the chips driven at high currents may experience local hot spots, which may cause thermal degradation or even catastrophic failures. As the air cooling has been widely used over the years and significant advances have been made to manage increased heat fluxes. It has been recognized as very difficult to rely solely on it to have an efficient cooling in higher heat fluxes. Moreover, active cooling methods may provide necessary thermal performance but at the expense of high cost and energy consumption. Hence, an efficient cooling capability in high heat fluxes (100 W/cm2) can be accommodated through the use of immersion liquid cooling. Immersion cooling has been studied for electronics circuits since last several decades where the thermal capability of such cooling systems have proved several orders of magnitude higher heat fluxes capability due to phase change heat transfer. Thus, direct liquid cooling with the usage of fluorocarbon liquids, generally considered as the most suitable liquids, has been applied in the current study. The thermal and optical performances of a multi chip LED light engine has been investigated with a series of computational fluid dynamics models and experimental validation studies. Heat transfer mode has been kept at the single phase in dielectric fluids. Effect on the local temperatures, peak and dominant wavelength shifts with respect to temperatures, and impact on total lumen extraction has been presented. Finally, a close form first order correlation has been developed for total lumen extraction depending on driving current and chip temperature.Conference ObjectPublication Metadata only Direct liquid cooling of high flux LED systems: hot spot abatement(ASME, 2013) Tamdoğan, Enes; Arık, Mehmet; Doğruöz, M. B.; Mechanical Engineering; ARIK, Mehmet; TAMDOĞAN, Enes; Tamdoğan, EnesWith the recent advances in wide band gap device technology, solid-state lighting (SSL) has become favorable for many lighting applications due to energy savings, long life, green nature for environment, and exceptional color performance. Light emitting diodes (LED) as SSL devices have recently offered unique advantages for a wide range of commercial and residential applications. However, LED operation is strictly limited by temperature as its preferred chip junction temperature is below 100 °C. This is very similar to advanced electronics components with continuously increasing heat fluxes due to the expanding microprocessor power dissipation coupled with reduction in feature sizes. While in some of the applications standard cooling techniques cannot achieve an effective cooling performance due to physical limitations or poor heat transfer capabilities, development of novel cooling techniques is necessary. The emergence of LED hot spots has also turned attention to the cooling with dielectric liquids intimately in contact with the heat and photon dissipating surfaces, where elevated LED temperatures will adversely affect light extraction and reliability. In the interest of highly effective heat removal from LEDs with direct liquid cooling, the current paper starts with explaining the increasing thermal problems in electronics and also in lighting technologies followed by a brief overview of the state of the art for liquid cooling technologies. Then, attention will be turned into thermal consideration of approximately a 60W replacement LED light engine. A conjugate CFD model is deployed to determine local hot spots and to optimize the thermal resistance by varying multiple design parameters, boundary conditions, and the type of fluid. Detailed system level simulations also point out possible abatement techniques for local hot spots while keeping light extraction at maximum.Conference ObjectPublication Metadata only Effect of optical design on the thermal management for the smart tv led backlight systems(IEEE, 2014) Karslı, K.; Arık, Mehmet; Mechanical Engineering; ARIK, MehmetDue to recent advances in electronics, lighting and communication technologies, SMART Televisions (TV) have become more affordable, and are rapidly eplacing old-fashioned LCD (liquid crystal display) TV technologies. These TVs are nearly ten times thinner; they include much brighter displays, true-color ualities, at least two times faster refresh rates and smart communication features. While providing such advanced features, lighting has become a critical part of technology advancement. While the backlight unit consumes over 50% of total energy in TVs, light emitting diodes (LEDs) have rapidly replaced the conventional CCFL (Cold Cathode Fluorescent Lamp) based LCD backlight units due to their low energy consumption. The present study identifies the impact of optical solutions with high-power LEDs located at the corner of the backlight unit on the optical efficiency for an advanced TV system. Various optical designs are created and impacting metrics for novel LED backlight units are determined. A computational and experimental study has been performed to identify the optical-thermal interactions in a tight-space LED packaging for a slim TV. Optical modeling has been performed via Light Tools optical simulation software, while thermal modeling was performed via Icepak CFD software. Smart optical packaging resulted in an effective light distribution of minimum 75% brightness uniformity, with no MURA effect problem on the panel The thermal challenge was found to be immense; so a smart thermal packaging was vital. An experimental validation of computational models was also performed. While the target is obtaining a uniform light distribution generated by HB (high brightness) LEDs and reduction of cost by having fewer LEDs, optical structure is found to be very critical in terms of both optical efficiency and pattern design of the light guide plate (LGP), which is an essential part of slim LED TVs. The study is concluded with a detailed discussion of the impact on lum- nance uniformity and cost for advanced SMART TVs.Conference ObjectPublication Metadata only Developing a standard measurement and calculation procedure for high brightness LED junction temperature(2014) Arık, Mehmet; Kulkarni, K. S.; Royce, C.; Weaver, S.; Mechanical Engineering; ARIK, MehmetWhite light emitting diodes (LEDs) are appearing in general illumination applications. Clusters of such LEDs can replace an incandescent light bulb of equal luminosity on the merit of considerably low power consumption. However the optical performance and working life of these LED packages are strongly dependent on the temperature of the p-n junction of the LED. Hence it is very critical to determine the temperature of the junction. Three methods - forward voltage change, peak wavelength shift and infrared thermal imaging are employed to determine the junction temperature. Forward voltage change method is found to be the most accurate method (± 3 °C) for an optimized set of parameters. Analytical model is proposed for the thermal transient behavior of the LED junction and the predictions are compared with experimental results. A good agreement is observed between that of two experimental methods. Thermal resistance of the LED package is estimated analytically and experimentally. Experimental values show a larger variation than expected through material property variation.ArticlePublication Metadata only An experimental study of impinging synthetic jets for heat transfer augmentation(World Scientific Publishing Co, 2015-07) Ghaffari, Omidreza; Ikhlaq, Muhammad; Arık, Mehmet; Mechanical Engineering; ARIK, Mehmet; Ghaffari, Omidreza; Ikhlaq, MuhammadAccording to recent trends in the field of miniature electronics, the need for compact cooling solutions compatible with very thin profiles and small footprint areas is inevitable. Impinging synthetic jets are recognized as a promising technique for cooling miniature surfaces like laptops, tablets, smart phones and slim TV systems. Effect of jet to cooled surface spacing is crucial in cooling performance as well as predicting Nusselt number for such spacing. An experimental study has been performed to investigate the cooling performance of two different synthetic jets actuated with piezoelectric actuators cooling over a vertical surface. Results showed that a major degradation of heat transfer when jets are close to the surface is occurred. Slot synthetic jets showed a better performance in terms of coefficient of performance (COP) than semi-confined circular jets for small jet to surface spacing. Later, a correlation is proposed for predicting Nu number for a semi-confined circular synthetic jet accounting the effects of Re number (500≤Rej≤1150500≤Rej≤1150), jet-to-surface spacing (H∕D=2H∕D=2 and H∕D=4H∕D=4) and the stroke length (1.75≤L0∕D≤4.751.75≤L0∕D≤4.75 and L0∕H<2.5L0∕H<2.5). It is found that correlation can provide predictions with an R2R2 value of over 98%.Conference ObjectPublication Metadata only Thermal enhancement of an LED light engine for automotive exterior lighting with advanced heat spreader technology(ASME, 2016) Uras, Umut Zeynep; Tamdoğan, Enes; Arık, Mehmet; Mechanical Engineering; ARIK, Mehmet; TAMDOĞAN, Enes; Uras, Umut ZeynepIn recent years, light emitting diodes (LEDs) have become an attractive technology for general and automotive illumination systems. LEDs have been preferable for automobile lighting due to its numerous advantages such as long life, low power consumption, optical control and light quality as well as robustness for high vibration. Thermal management is one of the main issues due to severe ambient conditions and compact volume. Conventionally, tightly packaged double sided FR4 based printed circuit boards are utilized for both driver electronics components and LEDs. In fact, this approach will be a leading trend for advanced Internet of Things (IOT) applications in near future. A series of numerical models are developed to determine the local temperature distribution on both sides of a light engine. Results showed that FR4 PCB has a temperature gradient of over 63°C while the maximum temperature is 105°C. This causes a significant degradation of lifetime and lumen extraction as many LEDs are recommended to be operated below 100°C. In addition to FR4, Aluminum metal core and vapor chamber based advanced heat spreader substrates are developed to obtain thermal impact on the substrate due to a wide range of thermal conductivity of three boards. To mimic real application, two special flex circuits are developed for LEDs and driver circuit. 10 red and 6 amber LEDs at one flex-PCB, and driver components are populated on the other flex-PCB are mounted. Both flex circuits are attached each side of the substrate. Experimental results showed that the local hotspots occurred at FR4 PCB due to low thermal conductivity. Later, a metal core printed circuit board is investigated to minimalize local hot spots. High conductivity metal core PCB showed a 19.9% improvement over FR4 based board. A further study has been performed with an advanced heat spreader based on vapor chamber technology. Results showed that a thermal enhancement of 7.4% and 25.8% over Al metal core and FR4 based boards with an advanced vapor chamber substrate.Conference ObjectPublication Metadata only Effect of direct liquid cooling on the light emitting diode local hot spots? A computational and experimental study(Begell House Inc, 2014) Tamdoğan, Enes; Arık, Mehmet; Mechanical Engineering; ARIK, Mehmet; TAMDOĞAN, Enes; Tamdoğan, EnesThe increased popularity of solid state systems with the technological developments have led them to be a favorable choice for many lighting applications besides electronics. However, the development of denser high lumen packages has been accompanied by increasing heat fluxes at the LED chip and package levels. Especially, the chips driven at high currents may experience local hot spots, which may cause thermal degradation or even catastrophic failures. As the air cooling has been widely used over the years and significant advances have been made to manage increased heat fluxes. It has been recognized as very difficult to rely solely on it to have an efficient cooling in higher heat fluxes. Moreover, active cooling methods may provide necessary thermal performance but at the expense of high cost and energy consumption. Hence, an efficient cooling capability in high heat fluxes (100 W/cm2) can be accommodated through the use of immersion liquid cooling. Immersion cooling has been studied for electronics circuits since last several decades where the thermal capability of such cooling systems have proved several orders of magnitude higher heat fluxes capability due to phase change heat transfer. Thus, direct liquid cooling with the usage of fluorocarbon liquids, generally considered as the most suitable liquids, has been applied in the current study. The thermal and optical performances of a multi chip LED light engine has been investigated with a series of computational fluid dynamics models and experimental validation studies. Heat transfer mode has been kept at the single phase in dielectric fluids. Effect on the local temperatures, peak and dominant wavelength shifts with respect to temperatures, and impact on total lumen extraction has been presented. Finally, a close form first order correlation has been developed for total lumen extraction depending on driving current and chip temperature.ArticlePublication Metadata only Effect of phase change materials on the optical path of LEDs for opto-thermal enhancement(IEEE, 2023-05) Azarifar, M.; Arık, Mehmet; Xie, B.; Luo, X.; Mechanical Engineering; ARIK, MehmetA novel concept based on the encapsulation of transparent phase change materials (PCMs) into the optical packaging structure of light-emitting diodes (LEDs) is presented in this article. The concept was initiated by challenges of thermal management of photoluminescent particles in high-power optical systems. LEDs, white LEDs (WLEDs), and porous/network-based photoluminescent matrices can achieve improved thermal networks by embedding PCMs. In this article, paraffin is selected as a suitable PCM encapsulant, and aside from thermal perspectives, an unexpected optical benefit with melted paraffin after surface wetting of the chip was observed. Immersing an LED chip in a melted paraffin pool showed up to an 8% increase in light extraction efficiency and a 1.5% increase in power conversion efficiency (PCE). An accurate dynamic opto-electro-thermal monitoring of studied devices was used to support the proof of concept. This viable method can be integrated into current industrial packaging processes.