Browsing by Author "Manay, Eyuphan"

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Analysis of Mixed Convection Heat Transfer of Nanofluids in a Minichannel for Aiding and Opposing Flow Conditions
(Springer, 2019) Manay, Eyuphan; Mandev, Emre; Temiz, Resul Onder
In this study, mixed convection heat transfer characteristics of nanofluid flow in a circular minichannel were investigated experimentally. The effects of the particle volume ratio (0, 0.25, and 0.75%) and Reynolds number (200-60) on heat transfer by mixed convection were investigated for aiding and opposing flow conditions. Water and water based SiO2 nanofluids were used as working fluid in a minichannel with a diameter of 1.9 mm, and constant heat flux was applied to the outer surface of the minichannel. Temperature-dependent thermophysical properties such as thermal conductivity and viscosity, obtained by experimental measurements, were used in heat transfer calculations. Pressure based numerical computations for all experimental cases were also made by using single phase approach. The results were analyzed separately for aiding flow condition in which secondary flows originating from natural convection are in the same direction with the forced flow, and for opposing flow condition in which secondary flows are in the opposite direction with forced flow. For detailed analysis of mixed convection heat transfer, temperature contours and velocity profiles were obtained by the numerical computations which were compared and validated with the experimental results. According to the data obtained, it was determined that the addition of nanoparticles into the pure water increased the Nusselt number by around 21-64% for the aiding flow, and 18-58% for the opposing flow. The heat transfer in the aiding flow was observed to be minimum 4% and maximum 16% higher in comparison with the opposing flow condition. It was concluded that the direction of secondary flows significantly affects heat transfer.
CFD Simulation and Experimental Analysis of Cooling Performance for Thermoelectric Cooler with Liquid Cooling Heat Sink
(Springer, 2024) Muratcobanoglu, Burak; Mandev, Emre; Ceviz, Mehmet Akif; Manay, Eyuphan; Afshari, Faraz
Thermoelectric coolers are preferred in many areas because of their simple mechanism and no need for a refrigerant. In this study, an air-to-water mini thermoelectric cooler system was designed and produced. Experiments were performed by placing different numbers of thermoelectric modules on the liquid-cooling heat sink and applying different voltages. The cooling capacity and COP values of the system under different operating conditions were analyzed and discussed. In addition, the effect of fluid flow rate on system performance and temperature difference between inlet and outlet sections has been presented. The heat transfer and flow behavior of the fluid in the liquid-cooling heat sink were determined using CFD simulation methods. Moreover, the heat loss from the system was tried to be reduced by using extra foam insulation and the results were compared with single foam and the effect of the insulation on the temperature drop inside cooler was discussed. At 0.011 kg s-1 mass flow rate and 12 V voltage conditions, when the number of TE modules is increased from 1 to 3 in the TE cooler, a maximum increase of 35% in cooling load is obtained. Also, if the cases with 3 TE modules and 0.011 kg s-1 flow rate are compared in terms of cooling load, 12 V has 80% higher cooling load than 4 V. According to the numerical results, flow structures that negatively affect the heat transfer interactions and reduce the cooling performance of the TE cooler have been determined in the liquid-cooled heat exchanger. Additionally, a significant decrease in the temperature of the cooling chamber has also been achieved with additional insulation.
Combined Free and Forced Convection of Nanofluids in Minichannels with Different Diameters
(Begell House inc, 2022) Akyurek, Eda Feyza; Ceylan, Murat; Manay, Eyuphan; Sahin, Bayram
In this study, mixed convection heat transfer properties of nanofluids in minichannels were investigated by dispersing SiO2 nanopaticles into pure water. In the study, nanofluids prepared in three different volumetric ratios of 0.25%, 0.75%, and 1.25% were investigated experimentally under laminar conditions in circular horizontal minichannels with diameters of 1.21 mm, 1.5 mm, and 1.9 mm. For the minichannels with the diameters of 1.21 mm, 1.5 mm, and 1.9 mm, increasing the particle volume ratio from 0.25% to 1.25% provided a heat transfer enhancement compared to water by about 11-31%, 7-29%, and 9-27%, respectively. Increasing the minichannel diameter from 1.21 mm to 1.5 mm and from 1.5 mm to 1.9 mm caused an enhancement of the Nusselt number in the range of 6.9-13.9% and 3.3-9.3%, respectively. Summarizing the results, the natural convection/forced convection ratio and natural convection effect on total heat transfer increased at a constant Grashof number value when the volumetric ratio of nanoparticles increased. In contrast to the particle volumetric ratio, an increase in the minichannel diameter was found to reduce the natural convection/forced convection ratio and the natural convection effects on total heat transfer at a constant Grashof number value.
Comparison of the Energy and Economic Performance of a LEED Certified Educational Building Located in a Cold Climate Region with the National Standard
(Gazi Univ, Fac Engineering Architecture, 2025) Celik, Ali; Manay, Eyuphan; Sahin, Bayram
Purpose: The purpose of this study; To ensure the creation of new national standards and regulations in line with international norms and standards, where energy is prioritized, and which includes criteria that will make a positive contribution to the environment without the need for foreign certification. Theory and Methods: With the methods of this study; 1. Finding the primary energy consumption and emission values of the LEED certified reference building, 2. Evaluation of the energy performance of the reference building after use, 3. Conducting energy modeling and determining the energy consumption and emission values for the reference building if it is designed according to national standards, 4. Energy and emission data for both cases are evaluated for the reference building. Results: The additional costs incurred for a LEED certified building, especially those aimed at reducing energy consumption, can finance themselves in a very short time. Therefore, although measures that increase energy efficiency and reduce carbon emissions have additional costs, they provide continuous savings throughout the life of the building. For this reason, it is necessary to evaluate the expenditures on measures to increase energy efficiency not as an economic cost but as an investment with high medium and long-term returns. Conclusion: This work; It also shows that LEED certification assessment tools will not give the same results for different climate zones. For this reason, it is emphasized that countries should determine their green building priorities.
Computational Fluid Dynamics Simulation and Experimental Investigation of a Thermoelectric System for Predicting Influence of Applied Voltage and Cooling Water on Cooling Performance
(Emerald Group Publishing Ltd, 2023) Ceviz, Mehmet Akif; Afshari, Faraz; Muratcobanoglu, Burak; Ceylan, Murat; Manay, Eyuphan
Purpose The purpose of this paper is to experimentally and numerically investigate the cooling performance of the air-to-water thermoelectric cooling system under different working conditions. Design/methodology/approach An air-to-water thermoelectric cooling system was designed and manufactured according to the principle of discrete binary thermoelectric Peltier modules, and the thermal performance, heat transfer rate and average COP values were examined at different cooling water temperatures and voltages applied. Additionally, numerical simulations were performed by computational fluid dynamics approach to investigate the temperature distribution and airflow structure inside the cooling chamber. Findings Analyses were performed using experimental tests and numerical methods. It was concluded that, by decreasing the cooling water temperature from 20 to 5 degrees C, the average COP increases about 36%. The voltage analysis showed that the efficiency of the system does not always increase as the voltage rises; more importantly, the optimum voltage is different and depends on whether it is desired to increase COP or increase the cooling rate. Originality/value In the studies published in the field of thermoelectric cooling systems, little attention has been paid to the voltage applied and its relationship to other operating conditions. In most cases, the tests are performed at a constant voltage. In this study, several options, including applied voltage and cooling water temperature, were considered simultaneously and their effects on performance have been tested. It was found that under such studies, optimization work should be done to evaluate maximum performance in different working conditions.
Dairesel Bir Mikrokanalda SiO2 Nanoakışkanların Isı Transferi ve Basınç Düşümü Karakteristiklerinin İncelenmesi
(2019) Sahın, Bayram; Manay, Eyuphan; Mandev, Emre
Endüstriyel uygulamalarda ısı transferinin artırılması sıkça karşılaşılan ve sürekli geliştirme ihtiyacı duyulan bir mühendislik problemidir. Son yıllarda ısı transferi iyileştirmesinde sıklıkla kullanılan bir yöntem de nanoakışkan kullanımıdır. İş yapan akışkan içerisine nanometre boyutlarında partiküllerin eklenmesi, akışkanın ısı transferi performansını artıran bir uygulamadır. Bu çalışmada, sabit ısı akısı sınır şartlarında, 700 μm çapında dairesel bir mikrokanalda SiO2-saf su nanoakışkanlarının ısıl performansları ve basınç düşümleri deneysel olarak incelenmiştir. Çalışmada %0.2, %0.4, %0.8 ve %1.2 hacimsel orandaki nanoakışkanlar, saf suya 15 nm partikül çapında SiO2 nanopartikülleri ilave edilerek hazırlanmıştır. Sıcaklık, debi ve basınç ölçümleriyle ısı taşınım katsayısı, Nusselt sayısı, basınç düşümü ve sürtünme faktörü değerleri belirlenmiştir. Ayrıca ısıl performans ve basınç düşümü analizleri için gerekli olan ısıl iletkenlik ve viskozite özellikleri deneysel olarak saptanmıştır. Çalışma sonucunda Nusselt sayısının Reynolds sayısı ve partikülün hacimsel oranındaki artışla arttığı gözlenmiştir. Nanoakışkan kullanımıyla maksimum ısı transferi artışı Re = 2160 civarında ve %1.2 hacimsel oranda saf suya göre yaklaşık % 20 civarında olmuştur. Yüksek Reynolds sayılarında tüm akışkanların sürtünme faktörü değerleri birbirine çok yakın iken, Reynolds sayısı azaldıkça hacimsel partikül oranının sürtünme faktörün üzerindeki etkisi daha belirgin hale gelmiştir. Bütün hacimsel oranlarda nanoakışkanların sürtünme faktörü değerinin saf su sürtünme faktörü değerinden yüksek olduğu belirlenmiştir.
Desalination Performance Evaluation of a Solar Still Enhanced by Thermoelectric Modules
(Pergamon-Elsevier Science Ltd, 2024) Mandev, Emre; Muratcobanoglu, Burak; Manay, Eyuphan; Sahin, Bayram
Water scarcity is a pressing global issue, as a significant portion of the world's water resources remain salty and unsuitable for human consumption. Solar desalination has emerged as a sustainable solution to address this challenge, utilizing solar energy for water decontamination and purification. This study explores the enhancement of solar stills through the integration of thermoelectric (TE) modules, focusing on their impact on desalination performance. The optimal saltwater levels, TE module performance, and the efficiency of the system are identified in this investigation. The results of this study reveal that the integration of TE unit into solar still systems leads to a substantial increase in water production, achieving an impressive 35% improvement in productivity compared to conventional solar stills. The TE modules act as efficient cooling agents, accelerating the condensation process within the system. This improvement has substantial implications for addressing water scarcity in arid regions and providing an eco-friendly solution for freshwater production. By harnessing solar energy and advanced TE technology, the findings of this study underscore the potential of TE-enhanced solar desalination systems in providing sustainable and reliable sources of fresh water, even in areas with limited access to traditional water resources. The successful integration of TE modules into solar stills suggests a promising avenue for future research and development. Further exploration of these systems, optimization of TE module parameters, and increased utilization of renewable energy sources are all steps that can be taken to improve water production efficiency and contribute to water resource sustainability.
The Effect of Microchannel Height on Performance of Nanofluids
(Pergamon-Elsevier Science Ltd, 2016) Manay, Eyuphan; Sahin, Bayram
In this study, the effects of microchannel height and particle volume fraction of nanofluids on heat transfer and pressure drop characteristics are investigated experimentally. Nano sized TiO2 particles with an average diameter of 25 nm have been dispersed into the deionized water in five different particle volume fractions of 0.25%, 0.5%, 1.0%, 1.5% and 2.0%. The forced convective heat transfer experiments of nanofluids have been conducted in a microchannel, which has four different heights of 200, 300, 400 and 500 gm. A constant heat flux of 80 kW/m(2) has been applied to the bottom wall of the microchannel, and the experiments have been carried out under steady state and laminar flow conditions. The results have been presented with respect to convection heat transfer coefficient and pressure drop. An increase in the microchannel height decreased the heat transfer rate and enhanced the pressure drop. It is concluded that nano sized TiO2 particles in the base fluid have provided higher heat transfer and have not caused an excessive increase in pressure drop with respect to pure water. Convection heat transfer coefficient has also increased with an increase in the volume fraction. (C) 2015 Elsevier Ltd. All rights reserved.
Effects of Surface Roughness in Multiple Microchannels on Mixed Convective Heat Transfer
(Pergamon-Elsevier Science Ltd, 2022) Mandev, Emre; Manay, Eyuphan
The most widely used type of heat transfer in applications is convection heat transfer, and both natural and forced convection modes have an effect in total heat transfer to a certain extent, whether any of these modes is neglected or not. In this study, the contribution of natural and forced convection effects to total heat transfer in rectangular microchannels was investigated experimentally for determining the effect of manufacturing process -induced surface roughness in multiple microchannels fabricated using stainless steel material. The experiments were conducted with microchannel heat sinks having three different surface roughness values of 1.1 mu m, 1.8 mu m, and 3.0 mu m, three microchannel widths of 300 mu m, 500 mu m and 700 mu m and two heights of 300 mu m and 450 mu m. During the manufacturing process, surface roughness values were controlled by changing electro-erosion fabrication parameters, and detailed surface maps were generated for the microchannel heat sinks. In the ex-periments using pure water as the working fluid, constant heat flux was applied to the bottom surface of the microchannel heat sink. The experiments were conducted in the range of 10-80 Reynolds numbers to ensure mixed convection conditions. In conclusion, it was determined that surface roughness had a significant effect on mixed convective heat transfer. An increase in surface roughness from 1.1 mu m to 1.8 mu m in microchannel heat sinks with cross-sections of 300 mu m x 300 mu m, 700 mu m x 300 mu m, 300 mu m x 450 mu m, and 700 mu m x 450 mu m s led to an increase of about 24 %, 19 %, 17 %, and 13 %, respectively, in the Nusselt number. Likewise, the increase in surface roughness from 1.8 mu m to 3.0 mu m resulted in an increase of 17 %, 15 %, 14 %, and 10 %, respectively, in the Nusselt number in the same channel cross-sections. In general, an increase in hydraulic diameter led to a reduction in the effect of surface roughness on overall heat transfer. For a constant microchannel width and height, the effect of surface roughness on mixed convection could be observed only with the increase in the Grashof number. Among the eighteen microchannel heat sinks with different geometric parameters, the best heat transfer results were obtained for the smallest microchannel cross-section of 300 mu m x 300 mu m and the highest roughness value of 3.0 mu m.
Entropy Generation of Nanofluid Flow in a Microchannel Heat Sink
(Elsevier, 2018) Manay, Eyuphan; Akyurek, Eda Feyza; Sahin, Bayram
Present study aims to investigate the effects of the presence of nano sized TiO2 particles in the base fluid on entropy generation rate in a microchannel heat sink. Pure water was chosen as base fluid, and TiO2 particles were suspended into the pure water in five different particle volume fractions of 0.25%, 0.5%, 1.0%, 1.5% and 2.0%. Under laminar, steady state flow and constant heat flux boundary conditions, thermal, frictional, total entropy generation rates and entropy generation number ratios of nanofluids were experimentally analyzed in microchannel flow for different channel heights of 200 mm, 300 mm, 400 mm and 500 mm. It was observed that frictional and total entropy generation rates increased as thermal entropy generation rate were decreasing with an increase in particle volume fraction. In microchannel flows, thermal entropy generation could be neglected due to its too low rate smaller than 1.10e-07 in total entropy generation. Higher channel heights caused higher thermal entropy generation rates, and increasing channel height yielded an increase from 30% to 52% in thermal entropy generation. When channel height decreased, an increase of 66%-98% in frictional entropy generation was obtained. Adding TiO2 nanoparticles into the base fluid caused thermal entropy generation to decrease about 1.8%-32.4%, frictional entropy generation to increase about 3.3%-21.6%. (C) 2018 The Authors. Published by Elsevier B.V.
Experimental Analysis for Heat Transfer of Nanofluid with Wire Coil Turbulators in a Concentric Tube Heat Exchanger
(Elsevier Science Bv, 2018) Akyurek, Eda Feyza; Gelis, Kadir; Sahin, Bayram; Manay, Eyuphan
Nanofluids are a novel class of heat transfer suspensions of metallic or nonmetallic nanopowders with a size of less than 100 nm in base fluids and they can increase heat transfer potential of the base fluids in various applications. In the last decade, nanofluids have become an intensive research topic because of their improved thermal properties and possible heat transfer applications. For comparison, an experiment using water as the working fluid in the heat exchanger without wire coils was also performed. Turbulent forced convection heat transfer and pressure drop characteristics of Al2O3-water nanofluids in a concentric tube heat exchanger with and without wire coil turbulators were experimentally investigated in this research. Experiments effected particle volume concentrations of 0.4-0.8 to 1.2-1.6 vol% in the Reynolds number range from 4000 to 20,000. Two turbulators with the pitches of 25 mm and 39 mm were used. The average Nusselt number increased with increasing the Reynolds number and particle concentrations. Moreover, the pressure drop of the Al2O3-water nanofluid showed nearly equal to that of pure water at the same Reynolds number range. As a result, nanofluids with lower particle concentrations did not show an important influence on pressure drop change. Nonetheless, when the wire coils used in the heat exchanger, it increased pressure drop as well as the heat transfer coefficient. (C) 2018 The Authors. Published by Elsevier B.V.
Experimental and Numerical Study on Air-to Thermoelectric Cooling System Using Novel Surface-Modified Fe3O4 Nanoparticles
(Springer Heidelberg, 2023) Afshari, Faraz; Mandev, Emre; Rahimpour, Shabnam; Muratcobanoglu, Burak; Sahin, Bayram; Manay, Eyuphan; Teimuri-Mofrad, Reza
Peltier cooling systems are usually smaller, more portable, and relatively simpler to operate compared to conventional vapor compression cooling systems. For this reason, Peltier cooling systems are widely recommended for use in the field of cooling applications and refrigerators. These cooling systems have relatively low efficiency despite extensive operation. To solve this problem, a Peltier cooling system operated with advanced nanofluid is proposed in this study. In this cooling system, water-based Fe3O4 nanofluids were used to cool the Peltier. In order to obtain high stability in these nanofluids, the nanoparticles were synthesized chemically with surface modification processes (Fe3O4@SiO2@(CH2)(3)IM). By designing and manufacturing an air-to-nanofluid cooling system, the performance of Peltier cooling system was evaluated and compared to the conventional air-to-water system. The nanofluids were prepared in three different volume concentrations as 0.2%, 0.5% and 1.0% and then were examined at different working conditions. This research has been analyzed using both experimental and numerical methods. Temperature measurements and experimental COP evaluations were made in the cooling chamber. The flow structure and temperature distribution in spiral heat exchanger were closely surveyed and discussed in detail. According to the results obtained, nanofluid volumetric concentrations, inlet temperatures and mass flow rates had a significant effect on the cooling performance of the Peltier systems. It was observed that COP values decreased over time in all experiments and approach zero gradually.
Experimental Evaluation and Optimization of the Heat Pipes Integrated Thermoelectric Generator using Response Surface Methodology
(Pergamon-Elsevier Science Ltd, 2025) Muratcobanoglu, Burak; Akyurek, Eda Feyza; Manay, Eyuphan
In this study, integration of heat pipes with thermoelectric generators is proposed for the recovery of waste heat. Heat energy is transferred from a heat source to thermoelectric elements via heat pipes, enabling energy conversion. To dissipate excess heat from the system after conversion, additional heat pipes are positioned on the cold sides of thermoelectric elements. Cooling of the condenser sections of these heat pipes is facilitated using air flow provided by a fan. A novel approach in this study involves the innovative integration of heat pipes with thermoelectric generators. This integration provides a new pathway for optimizing waste heat recovery systems by combining advanced thermal management techniques with thermoelectric technology. Experiments conducted at different power inputs (12-42 W) and air velocities (0.4, 0.8, 1.2 m/s) determine the performance of the thermoelectric generator. Furthermore, a power usage efficiency analysis was conducted to discuss the applicability of the proposed method in electronics. At low air velocities, values below the ideal value of 1 were achieved. Experimental data were analyzed using response surface methodology to assess the impact of varying input parameters on the power output and efficiency of the thermoelectric generator. Optimization studies highlighted the importance of effectively cooling the cold side of thermoelectric elements. The highest power output and efficiency are achieved under conditions of 42 W power input, 1.2 m/s air velocity, and use of 4 heat sinks, yielding approximately 0.8 W and 2 %, respectively. Furthermore, the response surface methodology analysis indicated that the most significant effect on system outputs was the power input. Moreover, the results of this study lay the groundwork for future strategic advancements in thermoelectric generators, enhancing their role in sustainable energy solutions.
Experimental Investigation of Heat Transfer and Pressure Drop Characteristics of Al2O3-Water Nanofluid
(Elsevier Science Inc, 2013) Sahin, Bayram; Gultekin, Gul Gedik; Manay, Eyuphan; Karagoz, Sendogan
In this study, the steady state turbulent convective heat transfer and pressure drop characteristics of Al2O3-water nanofluid inside a circular tube were investigated experimentally. The effects of the volume fraction and Reynolds number were determined under constant heat flux. The results of the heat transfer and pressure drop characteristics with respect to appropriate variables were presented. It was observed that the heat transfer increased with the increase of Reynolds number. The heat transfer increased with an increase in the volume concentration With the exception of the particle volume concentrations of 2 and 4 vol.%. The highest heat transfer enhancement was achieved at Re = 8000 and Phi = 0.005. (c) 2013 Elsevier Inc. All rights reserved.
Experimental Investigation of Mixed Convection Heat Transfer of Ferrite-Based Nanofluids in Multiple Microchannels
(Springer, 2019) Manay, Eyuphan
The objective of this study is to experimentally investigate the mixed convection heat transfer characteristics of ferrite-based (Fe2O3.NiO) nanofluids in multiple microchannel heat sinks. Two rectangular cross-sectioned microchannel heat sinks having two different heights of H=1mm and 1.8mm and a width of 300m were used. Ferrite-based nanoparticles were suspended into the pure water at two different volumetric ratios of 0.25 and 0.5%, and experiments were performed for both pure water and nanofluids. Constant heat flux was applied to the bottom wall of the microchannels by the cartridge heaters placed in heat sinks. Ferrite-based nanofluids were prepared by the two-step method, and the average size of the particles was below 20nm. The thermal conductivity and viscosity values of all fluids used in the present study were measured in a temperature range of 20-60 degrees C. Increasing the channel height from 1 to 1.8mm caused an increase in the Nusselt number about 9.4-10.7, 9.9-13.9 and 5.8-11.7% for the pure water, the 0.25 vol.% Fe2O3.NiO-water nanofluid and the 0.5 vol.% Fe2O3.NiO-water nanofluid, respectively. The addition of Fe2O3.NiO nanoparticles into the base fluid further increased the natural convection effects compared to pure water. The effects of the natural convection heat transfer in H=1.8mm were more dominant than those of H=1mm at the same Grashof number values.
Experimental Investigation of Mixed Convection Heat Transfer of Nanofluids in a Circular Microchannel with Different Inclination Angles
(Springer, 2019) Manay, Eyuphan; Mandev, Emre
In this study, the characteristics of mixed convection heat transfer of nanofluids in circular microchannels with 500m diameter were investigated experimentally. In the study, water and water-based SiO2 nanofluids were used as the working fluid, and volumetric particle ratios of the nanofluids were selected as 0.2 and 0.4%. The thermal conductivity and viscosity characterizations of all fluids were performed in the temperature range of 20-60 degrees C, and the characteristics related to the temperature obtained from the measurements were used in calculations. The effect of the microchannel inclination angle and particle volumetric ratio on the mixed convection heat transfer characteristics was investigated. Upon examining the results, it was revealed that the range of 13-35% of the total heat transfer was generated by the natural convection effects. Increasing the inclination angle of the test section provided an enhancement between 4 and 13% in the total heat transfer. Furthermore, the increase in the volumetric particle ratio increased both forced convection heat transfer and the natural convection heat transfer components. Adding nanosized SiO2 particles into the water caused the total heat transfer to increase from 12 to 14% for 0.2vol% and from 29 to 32% for 0.4vol%.
Experimental Optimization and Investigation of Compressor Cooling Fan in an Air-To Heat Pump
(Begell House Inc, 2020) Afshari, Faraz; Sahin, Bayram; Khanlari, Ataollah; Manay, Eyuphan
Heat pumps are seen as a highly efficient promising technology for space heating and cooling. Their efficiency has been widely studied for different types of heat pumps operating with various energy sources including air, ground, and water. However, different components of the heat pump need to be closely investigated to improve the performance of the system. This study surveys the effects of compressor cooling fan, to evaluate how a heat pump system behaves at different fan speeds. Refrigerant R134a has been used as a circulating fluid in the system. The results obtained from detailed experiments are analyzed to optimize the performance of the entire system using a compressor cooling fan, considering COP, P-h diagrams, efficiency, and thermodynamic properties. It is concluded that cooling the compressor has a remarkable effect on the thermodynamic state of refrigerant which leads to a positive influence not only on the compressor efficiency but also on the entire heat pump unit.
An Experimental Study on Heat Transfer and Pressure Drop of CuO-Water Nanofluid
(Hindawi Ltd, 2015) Sahin, Bayram; Manay, Eyuphan; Akyurek, Eda Feyza
Heat transfer and pressure drop characteristics of water based CuO nanofluid inside a horizontal tube were investigated experimentally. The upper limitation of the particle volume fraction with respect to heat transfer performance was also found. CuO-water nanofluids with volume fractions of 0.5%, 1%, 2%, and 4% were prepared by dispersing the CuO nanoparticles with an average diameter of 33 nm into deionised water. Experiments were carried out under the steady-state, constant heat flux, and turbulent flow regime conditions. The variations of the average Nusselt number and the friction factor with the Reynolds number were presented. For all given particle volume concentrations, heat transfer enhancements were calculated. It was concluded that the particle volume concentrations higher than 1% vol. were not appropriate with respect to the heat transfer performance of the CuO-water nanofluid. No heat transfer enhancement was observed at Re - 4.000. The highest heat transfer enhancement was achieved at Re = 16.000 and phi = 0.005.
Farklı İmalat Yöntemleri İle Elde Edilen Mikrokanalların Metrolojik Karakterizasyonu
(2021) Sahın, Bayram; Ateş, İbrahim; Manay, Eyuphan
Mikro imalat teknolojilerindeki gelişmeler yüksek hassasiyetli, düşük maliyetli ve yüksek performansa sahip mikro sistemlerin imalatın olanaklı hale getirmiştir. Mikrokanallar, mikro sistemlerin temel bileşenlerinden biri olarak mikroelektromekanik, kimyasal ve biyolojik cihazlar gibi mikro ve nano akışkan uygulamalarında yaygın olarak kullanılmaktadır. Mikrokanalların malzemesine, boyutsal imalat hassasiyetine, yüzey yapısına, istenen mekanik ve termal özelliklerine bağlı olarak çeşitli mikro imalat yöntemleri geliştirilmiştir. Genel olarak, bu imalat yöntemlerinin hassas mekanik imalat, silikon temelli imalat ve polimer işleme teknolojilerine dayandığı söylenebilir. Ancak, mikro ölçekli imalatlarda istenen hassasiyet ve kaliteye ulaşabilmek için bu imalat tekniklerinde birtakım değişiklikler yapmak gerekir. Çoğu imalat yönteminde aynı prosesi kullanarak hem makro hem de mikro ölçekte istenen özelliklerde ürün elde etmek mümkün değildir. Bu çalışmada, farklı ısı transferi ve akış prosesinde kullanılmak üzere farklı imalat metotları ile elde edilen mikrokanallı ısı alıcıların boyut ve yüzey karakteristikleri karşılaştırılmıştır. Mikrokanallı ısı alıcılar, litografi, hassas mekanik işleme, lazer tabanlı imalat yöntemleri, elektroerozyonla işleme yöntemleri kullanılarak üretilmişlerdir. Elde edilen mikrokanalların metrolojik işlemleri optik mikroskop ve optik profilometre ile yapılmıştır. İmalat yöntemleri, her bir mikrokanal için aynı imalat toleransının yakalanabilmesi, mikrokanalların dikdörtgen kesitli profile sahip olması, mikrokanal tabanında radyüs oluşumu, yüzey pürüzlülük değerinin kontrol edilebilmesi ve yüzeyin homojen bir pürüzlülük dağılımına sahip olması açısından değerlendirilmiştir. Bu kriterleri en iyi sağlayan yöntemin dalma elektroerozyonla üretilen mikrokanallı ısı alıcılar olduğu görülmüştür.
Heat Transfer and Pressure Drop of Nanofluids in a Microchannel Heat Sink
(Taylor & Francis Inc, 2017) Manay, Eyuphan; Sahin, Bayram
The aim of this study is to determine the upper limitations of the particle volume fraction for heat transfer performance of TiO2-water nanofluids in microchannels. Nanofluids were prepared by the addition of TiO2 metallic nanoparticles into distilled water chosen as base fluid at five different volumetric ratios (0.25%, 0.5%, 1.0%, 1.5%, and 2.0%). The effects of the Reynolds number (100-750) and particle volume fraction at constant microchannel height (200 mu m) on heat transfer and pressure drop characteristics were analyzed experimentally. Adding metallic oxide particles with nano dimensions into the base fluid did not cause excessive increase of friction coefficient but provided higher heat transfer than that of pure water. It was also observed that water-TiO2 nanofluid increased heat transfer up to 2.0 vol%, but heat transfer decreased after 2.0 vol%. Furthermore, the thermal resistance was calculated and it was seen that adding nanoparticles with an average diameter smaller than 25 nm into the base fluid caused the thermal resistance to decrease.