Person: ARIK, Mehmet
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Mehmet
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ARIK
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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.ArticlePublication Open Access Investigation of combined optical and thermal effects on phosphor converted light-emitting diodes with liquid immersion cooling(SPIE, 2018) Kahvecioğlu, Halil İbrahim; Tamdoğan, E.; Arık, Mehmet; Mechanical Engineering; ARIK, Mehmet; Kahvecioğlu, Halil İbrahimThe inclusion of phosphor into a high brightness light-emitting diode (LED) package is a complicated task since LEDs are encapsulated with a phosphor and epoxy mixture to convert blue photons to white light. Moreover, this common practice may cause high temperatures and fractures in the gold wire bonds of the chip or solder balls due to local heating and thermal stresses leading to device failures. Furthermore, at elevated junction temperatures, the light conversion efficiency of the phosphor reduces and decreases the overall optical efficiency of an LED. Although, remote phosphor technique has been already applied to LED systems, the high power requirements have needed better performing methods. Thus, an immersion liquid cooled remote phosphor-coated system has been proposed and experimentally and computationally investigated. First, a set of experiments was performed, which includes the combined effects coming from both optical and thermal improvements with the proposed liquid cooled remote phosphor-coated technique, where the total light extraction enhancement was obtained in excess of 25%. Then, the same problem has been computationally studied for investigation of solely optical enhancements, which has shown that remote phosphor-coated LED package with a liquid coolant of suitable refractive index at the optical path has enhanced the overall lumen performance about 13%, whereas the rest of the improvements of 12% were due to thermal enhancements.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.ArticlePublication Metadata only An Eulerian multiphase frost model based on heat transfer measurements(Elsevier, 2023-12-01) Saygın, Alper; Başol, Altuğ Melik; Arık, Mehmet; Mechanical Engineering; BAŞOL, Altuğ Melik; ARIK, Mehmet; Saygın, AlperIn this paper, a laminar numerical model is developed to predict frost formation over a horizontal cold flat surface. An Eulerian-Eulerian multiphase approach is followed to model humid air and ice phases separately. Frost accumulation on the cold surface is modeled with an empirical mass source term. Model constants were tuned in a systematic way using experimental heat flux and frost thickness data. A velocity dependent model constant is introduced into the mass source term. The heat flux rise observed experimentally at the initial stages of the frosting could be captured with the use of the velocity dependent model constant and the addition of this term considerably improved the accuracy of the frost model at the initial stages of frosting. It was also observed that the selected particle diameter for the solid ice phase has a considerable effect on the velocity profile over the frost layer. This requires tuning of the velocity dependent model constant parameters according to the selected ice particle diameter. The developed numerical model was tested with three different frost thermal conductivity models. Using the thermal conductivity of solid ice for the frost thermal conductivity resulted in the most accurate prediction at the early stages of the frost growth process indicating a rather column-wise vertical growth of ice crystals with very low lateral branching. However, the overprediction of the numerical heat flux with the thermal conductivity of solid ice points out a decrease in the thermal conductivity of the newly added frost layers indicating a more pronounced lateral branching of ice crystals within the frost layer. The effect of the diffusion coefficient of the water vapor in humid air on frosting is also investigated. An artificial increase in the diffusion coefficient improved the accuracy of the heat flux prediction of the model at the initial stages of frosting which might indicate an eddy-driven enhanced mixing in the boundary layer which might not be captured in the laminar flow model. Finally, the developed numerical model is also tested on another scenario with the surface temperature held at -30 °C. Detailed analysis of the numerical simulations showed a more porous frost layer with the surface temperature at -30 °C as compared to the frost porosity formed on the surface at -20 °C.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%.ArticlePublication Metadata only Natural convection immersion cooling with enhanced optical performance of light-emitting diode systems(2015-10-15) Tamdoğan, Enes; Arık, Mehmet; Mechanical Engineering; ARIK, Mehmet; TAMDOĞAN, Enes; Tamdoğan, EnesElectronics driven at high currents may experience local hot spots, which may cause thermal degradation or even catastrophic failures. This common problem occurs at light-emitting diode (LED) chips and it is not easily observed by end-users. Driving over 700 mA over a 1 mm2 chip is expected to generate local temperature gradients. In addition, bonding failures at manufacturing or during operation (cracks, delamination, etc.) may also lead to local hot spots. Therefore, possible hot spots over an LED chip have turned attention to direct cooling with dielectric liquids comprises the current study. Computational and experimental studies have been performed to understand the impact of conduction and alternatively convection with various dielectric fluids to abate local hot spots in a multichip LED light engine. To capture the local temperature distributions over the LED light engine with a dome in the domain especially over the LED chip; first, computational models have been built with a commercial computational fluid dynamics (CFD) software. Later, attention has been turned into experimental validation by using a multichip high brightness LED (HB LED) light engine. An optothermal evaluation has been made at single and multiphase heat transfer modes with dielectric fluids (LS5252, HFE7000, and silicone oil, etc.) to compare with a series of CFD models and experimental studies. While multiphase liquid-cooled LED system has a better cooling performance but lower optical extraction, single-phase liquid-cooled LED system has shown a reasonable thermal performance with a 15% enhancement at light extraction.ArticlePublication Metadata only A computational and experimental investigation of synthetic jets for cooling of electronics(The American Society of Mechanical Engineers, 2015-06-01) Arık, Mehmet; Utturkar, Y. V.; Mechanical Engineering; ARIK, MehmetSeamless advancements in electronics industry resulted in high performance computing. These innovations lead to smaller electronics systems with higher heat fluxes than ever. However, shrinking nature of real estate for thermal management has created a need for more effective and compact cooling solutions. Novel cooling techniques have been of interest to solve the demand. One such technology that functions with the principle of creating vortex rings is called synthetic jets. These jets are mesoscale devices operating as zero-net-mass-flux principle by ingesting and ejection of high velocity working fluid from a single opening. These devices produce periodic jet streams, which may have peak velocities over 20 times greater than conventional, comparable size fan velocities. These jets enhance heat transfer in both natural and forced convection significantly over bare and extended surfaces. Recognizing the heat transfer physics over surfaces require a fundamental understanding of the flow physics caused by microfluid motion. A comprehensive computational and experimental study has been performed to understand the flow physics of a synthetic jet. Computational study has been performed via FLUENT commercial software, while the experimental study has been performed by using laser Doppler anemometry (LDA). Since synthetic jets are typical sine-wave excited between 20 and 60 V range, they have an orifice peak velocity of over 60 m/s, resulting in a Reynolds number of over 2000. Computational fluid dynamics (CFD) predictions on the vortex dipole location fall within 10% of the experimental measurement uncertainty band.ArticlePublication Metadata only Numerical and experimental analysis of a heat-pipe-embedded printed circuit board for solid state lighting applications(Taylor & Francis, 2019-01-02) Salem, Thamer Khalif; Khosroshahi, F. S.; Arık, Mehmet; Hamdan, M. O.; Budakli, M.; Mechanical Engineering; ARIK, Mehmet; Salem, Thamer KhalifThermal management is one of the main issues for electronics cooling especially for tightly packaged PCBs that experience local heat generation. Thus, theoretical and experimental investigations have been conducted to predict thermal performance of a novel heat-pipe-embedded-PCB. First, plain heat-pipe is experimentally tested under various inclination angles and validated by theoretical and numerical calculations. Flattened heat-pipes have been embedded into PCB prototypes made of polymer and aluminum and have been tested for similar experimental parameters; they have shown a decrease in compared with conventional heat pipe. Accordingly, reduction of approximately 50% is achieved for both embedded PCB prototypes.ArticlePublication Metadata only Heat transfer impact of synthetic jets for air-cooled array of fins(ASME, 2015-10-13) Li, R.; Gerstler, W. D.; Arık, Mehmet; Vanderploeg, B.; Mechanical Engineering; ARIK, MehmetFree convection air cooling from a vertically placed heat sink is enhanced by upward concurrent pulsated air flow generated by mesoscale synthetic jets. The cooling enhancement is experimentally studied. An enhancement factor is introduced and defined as the ratio of convection heat transfer coefficients for jet-on (enhanced convection) to jet-off (natural convection) cooling conditions. To obtain the two coefficients, heat transfer by radiation is excluded. A high-resolution infrared (IR) camera is used to capture detailed local temperature distribution on the heat sink surface under both cooling conditions. Analysis is carried out to obtain local convection heat transfer coefficients based on measured local surface temperatures. The enhancement of convectional cooling by synthetic jets can be then quantified both locally and globally for the entire heat sink. Two categories of thermal tests are conducted. First, tests are conducted with a single jet to investigate the effects of jet placement and orifice size on cooling enhancement, while multiple jets are tested to understand how cooling performance changes with the number of jets. It is found that the cooling enhancement is considerably sensitive to jet placement. Jet flow directly blowing on fins provides more significant enhancement than blowing through the channel between fins. When using one jet, the enhancement ranges from 1.6 to 1.9 times. When multiple jets are used, the heat transfer enhancement increases from 3.3 times for using three jets to 4.8 times for using five jets. However, for practical thermal designs, increasing the number of jets increases the power consumption. Hence, a new parameter, “jet impact factor (JIF),” is defined to quantify the enhancement contribution per jet. JIF is found to change with the number of jets. For example, the four-jet configuration shows higher JIF due to higher contribution per jet than both three-jet and five-jet configurations.ArticlePublication Metadata only Thermal performance of a light emitting diode light engine for a multipurpose automotive exterior lighting system with competing board technologies(ASME, 2017-06-12) Uras, Umut Zeynep; Arık, Mehmet; Tamdoğan, Enes; 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 replacing old-fashioned incandescent and halogen systems. LEDs are preferable for automobile lighting applications due to its numerous advantages such as low power consumption and precise optical control. Although these solid state lighting (SSL) products offer unique advantages, 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 (PCBs) are utilized for both driver electronic components and LEDs. In fact, this approach will be a leading trend for advanced internet of things applications embedded LED systems in the near future. Therefore, automotive lighting systems are already facing with tight-packaging issues. To evaluate thermal issues, a hybrid study of experimental and computational models is developed to determine the local temperature distribution on both sides of a three-purpose automotive light engine for three different PCB approaches having different materials but the same geometry. Both results showed that FR4 PCB has a temperature gradient (TMaxBoard to TAmbient) of over 63 °C. Moreover, a number of local hotspots occurred over FR4 PCB due to low thermal conductivity. Later, a metal core PCB is investigated to abate local hot spots. A further study has been performed with an advanced heat spreader board 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 the advanced vapor chamber substrate is observed. In addition to superior thermal performance, a significant amount of lumen extraction in excess of 15% is measured, and a higher reliability rate is expected.