Localized radiative energy transfer from a plasmonic bow-tie nanoantenna to a magnetic thin film stack

Localized radiative energy transfer from a near-field emitter to a magnetic thin film structure is investigated. A magnetic thin film stack is placed in the near-field of the plasmonic nanoantenna to utilize the evanescent mode coupling between the nanoantenna and magnetic thin film stack. A bow-tie nano-optical antenna is excited with a tightly focused beam of light to improve near-field radiative energy transfer from the antenna to the magnetic thin film structure. A tightly focused incident optical beam with a wide angular spectrum is formulated using Richards-Wolf vector field equations. Radiative energy transfer is investigated using a frequency domain 3-D finite element method solution of Maxwell’s equations. Localized radiative energy transfer between the near-field emitter and the magnetic thin film structure is quantified for a given optical laser power at various distances between the near-field emitter and magnetic thin film

Pressure drop across micro-pin heat sinks under boiling conditions

Two-phase pressure drop was studied in four different micro pin fin heat sinks. Micro pin fin heat sinks used in the current studies were operated under boiling conditions using water and R-123 as working fluids. It was observed that once boiling was initiated severe temperature fluctuations and flow oscillations were recorded for three of the micro pin fin heat sinks, which was characterized as unstable boiling. Pressure drop signals were presented just before and after the unstable boiling conditions. Flow images and FFT (fast Fourier Transform) profiles of pressure signals were used to explain experimental results and unstable nature in flow boiling observed in the three of the devices. Stable boiling conditions where the temperature and pressure drop had a steady and stable profile could be only obtained from one micro pin fin heat sink at high mass velocities. The two-phase pressure drop in this hydrofoil-based micro pin fin heat sink has been investigated using R-123 as the working fluid. Two-phase frictional multipliers have been obtained over mass fluxes from 976 to 2349 kg/m2. It has been found that the two-phase frictional multiplier is strongly dependent on flow pattern. The theoretical prediction using Martinelli parameter based on the laminar fluid and laminar gas flow represented the experimental data fairly well for the spray-annular flow. For the bubbly and wavy-intermittent flow, however, large deviations from the experimental data were recorded. The Martinelli parameter was used successfully to determine the flow patterns, which were bubbly, wavy-intermittent, and spray-annular flow in the current study

Thermoelectric-coupled hydrodynamic cavitation energy harvesting system

The ever growing energy demand has led to the advent of different energy harvesting systems. This study investigates the performance of a thermoelectric coupled hydrodynamic cavitation system as an energy harvesting device. The effect of changing the working fluid from water to Titania-water nanofluid on the heat generation of the cavitation system is discussed in this study and also the coupling of the cavitation system with one of the micro thermoelectric generators in the literature is included. At the end, the device performance is quantified by comparing its power generation with the required power for the daily used miniature electrical devices

Changing bubble dynamics in subcooled boiling with TiO₂ nanoparticles on a platinum wire

Bubble dynamics in pool boiling provides a suitable platform for researchers to understand the mechanisms of subcooled boiling heat transfer. Besides, the effects of nanoparticles on this phenomenon have not been fully understood yet. In this study, the effect of TiO2 nanoparticles (with two weight fractions, 0.002% and 0.005%) mixed in de-ionized water during subcooled pool boiling on a thin platinum wire with a diameter of 250 μm was experimentally investigated for working bulk fluid temperatures between 30 and 50 °C at atmospheric pressure, and new bubble dynamics phenomena were reported. Applied heat fluxes varied from onset of nucleate boiling point to higher heat fluxes up to nucleation jet flow. The experiments were visualized with a high speed camera system, and acquired videos and images were utilized for analysing prevalent phenomena, such as bubble-bubble and nucleation site-bubble interactions, surface tension and Marangoni convection, structural disjoining pressure, pinning and nanoparticles deposition effects as well as the main mechanisms. In general, migration, coalescence, leaping and detaching were recorded for nanofluids with weight fractions of 0.002 wt% and 0.005 wt%, while oscillation, dancing and stick processes were exclusively observed only in nanofluids with a weight fraction of 0.005 wt%. The images, results, and related discussion provide new knowledge and physics for pool boiling phenomena on platinum fine wires in the presence of nanoparticles

On Bubble Dynamics in Subcooled Nucleate Boiling on a Platinum Wire

While much attention has been given to the phenomenon of boiling, the underlying physics and mechanisms are still not fully understood due to its complicated and illusive nature. In this study, an experimental investigation of subcooled pool boiling of de-ionized (DI) water, at a bulk temperature of 30 °C and atmospheric pressure, was performed on a platinum wire with a diameter of 250 μm, starting from the onset of nucleate boiling (ONB) point and rising to higher heat fluxes. A high speed camera system was utilized for visualization. Images of bubbles growth, migration, coalescence, leaping and detachment were recorded. Each of these events was investigated separately, and a comprehensive discussion undertaken. High speed camera images were analyzed by taking the most important parameters, such as surface tension, bubble-bubble interactions, nucleation site-bubble interactions, Marangoni convection and accumulation of non-condensable gases inside the bubbles. Lower applied heat fluxes led to bubble nucleation from the nucleation sites and slow growth of bubbles to a certain diameter, which were ready to migrate along the wire. Increasing the heat flux made the bubbles grow faster and favored coalescence, leaping and detaching that be observed one after another due to an increase in the temperature gradient and perturbation of the temperature field near the nucleation sites. Another important mechanism considered was the momentum of the non-condensable gases inside the bubbles, especially while the bubble tail disappeared and the bubble shrank whilst stopping near an immobile bubble or near the nucleation sites

Upcycled graphene nanoplatelets integrated fiber-based Janus membranes for enhanced solar-driven interfacial steam generation †

The increasing demand for drinking water and environmental concerns related to fossil fuels have given rise to the use of solar energy in water desalination. Solar-driven interfacial steam generation is a promising method for water purification, particularly in remote areas. Janus membranes, featuring bilayer hydrophobic/hydrophilic structures, offer high functionality and have attracted significant interest in this field. This study explores the integration of novel graphene nanoplatelets (GNP) derived from waste tire pyrolysis through upcycling as a photothermal source in Janus membranes. The membranes consist of polyacrylonitrile (PAN) nanofibrous membranes for water supply and polymethyl methacrylate (PMMA)/graphene nanoplatelets (GNP) nanofibrous membranes for light harvesting. The effects of GNP content and layer thicknesses on photothermal activity, water transport, and overall evaporation rate were analyzed experimentally and numerically. The results showed that a decrease in membrane thickness led to a 19% to 63% enhancement in evaporation rate, highlighting the importance of optimizing membrane design for efficient water desalination

Investigation of Single Air Bubble Dynamics and the Effect of Nanoparticles in Rectangular Minichannels

Bubble dynamics and understanding related mechanisms based on force analysis are necessary for better understanding two-phase flow phenomena in small channels. To address this subject, experiments were conducted with injected single air bubbles into rectangular minichannels containing flows of pure water, pure ethanol and TiO2-nanoparticle-based nanofluids, which had a nanoparticle mass fraction of 0.005 wt% for both water and ethanol base fluids. For a range of fluid flow rates, bubble movement and temperature profiles were captured along the channel using high-speed and infrared (IR) cameras, respectively. Upon heating, when using nanofluids, deposition of TiO2 nanoparticles occurred. The results in the channels with cross sectional dimensions of 2 mm × 4 mm and heated length of 7 cm were compared with their counterparts on plain surfaces. Heat fluxes were applied by means of a tantalum film heater on the outer surface of the channel. Bubble dynamics and forces acting on the bubbles were quantitatively analyzed in relation to the fluid type, heat flux, flow rate and deposition. This study highlights the effects of TiO2-nanoparticles (dispersed in two different base fluids) on single-bubble dynamics in minichannels. The nanoparticle deposition was found to have a retarding effect on the bubble movement and led to a more elliptical shape rather than a spherical bubble shape. The bubble behavior is comprehensively assessed in the light of the visualization data and acting forces

Öğretmen Mesleki Öğrenmesinin Yordayıcıları Olarak Öğretmen Öz Yeterliği ve Bireysel Akademik İyimserlik: Bir Yapısal Eşitlik Modellemesi

The purpose of this study is to investigate the relationship between teacher self-efficacy, individual academic optimism and teacher professional learning. A total of 300 teachers employed in primary and secondary schools located in the center of Karabuk province participated in this quantitative study designed as correlational research. The data of the current study were gathered through the Teacher Professional Learning Scale, Teacher Self-Efficacy Scale and Academic Optimism of Individual Teacher Scale. A Pearson Product Moment Correlation Coefficient was calculated to detect the relationships among variables of the study, and a path analysis was performed to indicate the direct predictive power of teacher self-efficacy on individual academic optimism and teacher professional learning, the direct predictive power of individual academic optimism on teacher professional learning and also the indirect predictive power of teacher self-efficacy on teacher professional learning through individual academic optimism. Results revealed that the dependent and independent variables of the study correlated to each other positively and significantly, and that teacher self-efficacy predicted individual academic optimism and teacher professional learning positively and significantly, and also that individual academic optimism predicted teacher professional learning positively and significantly. Finally, results illustrated that individual academic optimism predicted positively and indirectly teacher professional learning through individual academic optimism. The results of the current study supported the conceptual model built on the relationship between teacher self-efficacy, individual academic optimism, and teacher professional learning, the three being crucial for teacher development.Bu araştırmanın amacı, öğretmen öz yeterliği, bireysel akademik iyimserlik ve öğretmen mesleki öğrenmesi arasındaki ilişkilerin ortaya konmasıdır. İlişkisel tarama modelinde kurgulanan bu araştırmaya Karabük ili merkezinde bulunan ilk ve ortaokullarda görev yapan toplam 300 öğretmen katılmıştır. Araştırma verilerinin toplanmasında, “Öğretmen Mesleki Öğrenme Ölçeği”, “Öğretmen Öz Yeterlik Ölçeği” ve “Bireysel Akademik İyimserlik Ölçeği” kullanılmıştır. Değişkenler arasındaki ilişkileri belirlemek amacıyla Pearson Momentler Çarpım Korelasyon Katsayısı hesaplanmış; öğretmen öz yeterliğinin ve bireysel akademik iyimserliğin öğretmen mesleki öğrenmesi üzerindeki doğrudan yordayıcılık gücü ile öğretmen öz yeterliğinin bireysel akademik iyimserlik üzerinden öğretmen mesleki öğrenmesi üzerindeki dolaylı yordayıcılık gücünü sınamak için de yol (path) analizi kullanılmıştır. Sonuçlar, araştırmanın bağımlı ve bağımsız değişkenleri arasında pozitif yönde anlamlı ilişkilerin bulunduğunu, öğretmen öz yeterliğinin bireysel akademik iyimserliği ve öğretmen mesleki öğrenmesini pozitif yönde ve anlamlı bir biçimde yordadığını, bireysel akademik iyimserliğin öğretmen mesleki öğrenmesini pozitif yönde ve anlamlı bir biçimde yordadığını göstermektedir. Bununla birlikte mevcut araştırmada, öğretmen öz yeterliğinin bireysel akademik iyimserlik üzerinden öğretmen mesleki öğrenmesi üzerinde dolaylı yordayıcılık gücüne sahip olduğu belirlenmiştir. Mevcut araştırmanın sonuçları, öğretmenlerin gelişiminde önemli değişkenler arasında yer alan öğretmen mesleki öğrenmesi, öğretmen öz yeterliği ve bireysel akademik iyimserlik ilişkilerine yönelik kurulan teorik modeli istatistiksel olarak desteklemiştir

Flow boiling in microchannels: Fundamentals and applications

The rapid advances in performance and miniaturization of electronics and high power devices resulted in huge heat flux values that need to be dissipated effectively. The average heat flux in computer chips is expected to reach 2–4.5 MW/m2 with local hot spots 12–45 MW/m2 while in IGBT modules, the heat flux at the chip level can reach 6.5–50 MW/m2. Flow boiling in microchannels is one of the most promising cooling methods for these and similar devices due to the capability of achieving very high heat transfer rates with small variations in the surface temperature. However, several fundamental issues are still not understood and this hinders the transition from laboratory research to commercial applications. The present paper starts with a discussion of the possible applications of flow boiling in microchannels in order to highlight the challenges in the thermal management for each application. In this part, the different integrated systems using microchannels were also compared. The comparison demonstrated that miniature cooling systems with a liquid pump were found to be more efficient than miniature vapour compression refrigeration systems. The paper then presents experimental research on flow boiling in single tubes and rectangular multichannels to discuss the following fundamental issues: (1) the definition of microchannel, (2) flow patterns and heat transfer mechanisms, (3) flow instability and reversal and their effect on heat transfer rates, (4) effect of channel surface characteristics and (5) prediction of critical heat flux. Areas where more research is needed were clearly mentioned. In addition, correlations for the prediction of the flow pattern transition boundaries and heat transfer coefficients in small to mini/micro diameter tubes were developed recently by the authors and presented in this paper

Penil septal hematom: Nadir bir olgu sunumu

Hematoma associated with penile trauma, usually associated with a penile fracture involving a disruption in the integrity of tunica albuginea, is among the frequent causes of a penile mass. In this report, the authors present a 70-year-old patient with intercorporeal penile septal hematoma without a rupture of tunica albuginea following a traumatic event. Relevant imaging features are conclusive for an accurate diagnosis, particularly in cases with atypical clinical presentation, as was in the presented case.Penil travmaya bağlı olarak gelişen ve çoğu kez tunika albuginea’nın bütünlüğünde bir bozulmanın ve hematom oluşumunun eşlik ettiği klinik tablo en sık görülen penil kitle nedenidir. Bu yazıda, travma sonucu gelişen ve tunika albuginea’da bir rüptürün sözkonusu olmadığı 70 yaşındaki bir interkorporeal penil septal hematom olgusu sunulmaktadır. Sunulan olguda olduğu gibi, özellikle atipik bir kliniğin sözkonusu olduğu olgularda doğru tanı konulabilmesi için görüntüleme bulguları önem taşımaktadır