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나노유체를 이용한 평판형 태양열 집열기의 효율에 관한 연구
이승현(Seung-Hyun Lee),이승윤(Seoung Youn Lee),장석필(Seok Pil Jang) 대한기계학회 2012 대한기계학회 춘추학술대회 Vol.2012 No.11
In this paper, an analytical study is conducted to assess the efficiency of a flat-plate solar collector using the nanofluids. We obtain a simplified analytical solution for the flat-plate solar collector by assuming the wavelength-independent extinction coefficient and spectral intensity, and then a dimensionless temperature distribution in the flat-plate solar collector is obtained using the extinction coefficient of single wall carbon nanohorn (SWCNH) nanofluids. Finally, we show the effect of volume fraction, heat loss magnitude and collector depth on the dimensionless temperature distributions and evaluate the efficiency of the nanofluid-based flat-plate solar collector according to the particle concentrations.
나노유체 : 화학적 환원법의 혼합방법이 주석 나노유체의 입자 크기에 미치는 영향
장석필 ( Seok Pil Jang ),이승윤 ( Seoung Youn Lee ),이승현 ( Seung Hyun Lee ),김상훈 ( Sang Hoon Kim ) 한국액체미립화학회 2012 한국액체미립화학회 학술강연회 논문집 Vol.2012 No.-
being changing as alternative materials instead of tin-lead solder ball as following development of ecofriendly industry. However, one of the adverse effect of this change is tin-alloys have higher melting temperature (232oC) compared with tin-lead (~183oC). For this reason, electronic assembly has disadvantages such as warpage, electrical energy consumption, thermal stress and thermal cracking. Therefore studies of lowering meting temperature of tin are intensively investigating as a fundamental study of reducing tin-alloys melting temperature. In previous researches, the melting temperature of nanoparticle is non-linearly decreased with decreasing particle size which is the most dominant effect to determine the melting temperature1). Therefore decreasing the size of particle is core parameter to reduce the melting temperature of tin nanoparticle. Furthermore, to use these lead-free tin nano solder ball practically in industrial part, cost problem should be accompany with the investigation of lead-free solder ball. So, not only decreasing of the particle size but also improving of the production efficiency has to be considered. In this paper, tin nanoparticles are synthesized by chemical reduction method in ethylene glycol using stirrer and ultra-sonic wave bath respectively. Tin (II) acetate, Sodium borohidride and Polyvinylpyrrolidone (PVP) are used as precursors, reducting agents and surfactants respectively. Transmission electron microscopy (TEM) and particle size analyzer (PSA) are used to characterize particle size, shape and distribution of Sn particle and surfactant. Fig. 1, 2 show the well-made Sn nanoparticle manufactured with stirring method and ultra-sonic energy respectively. The stirring method and ultra-sonic energy method both well manufactured 45 ± 5 nm and 10 ± 5 nm average diameters sized tin nanoparticle respectively. The using of ultra-sonic energy is able to make much smaller sized tin nanoparticle than the using of stirrer and it has alternative advantages. As follows, Benefits of using ultrasonic energy are large quantity production due to shorten manufacturing time that only 5 minute and better dispersion stability. While the stirring method need at least two or more hours for one case of experiment. Fig.3 shows the manufacturing time effect on the particle size with ultra-sonic energy. Except for the time problem, the main prohibited problem to manufacture large quantity of Sn nanoparticle is dispersing of surfactant. It was identified that the suspension stability of surfactant effect on particle size and dispersing of surfactant is not easy in bulky amount of base fluid2). By so using of ultrasonic energy comparatively solved these problems not only prohibit aggregation of surfactant during reacting but also easily control large quantity of experimental specimens. Fig.4 shows the 0.01 vol. % of the optimum volume fraction of Tin (II) acetate respect on decreasing of the particle size. Additionally, the using of ultrasonic energy is helpful to reduce 80% of the integrating watt which is 25kWh and 125kWh for using of ultrasonic energy and using of stirrer respectively for each experiment.
다공성재를 통과하는 압축성 유체의 압력강하에 관한 실험적 연구
서민교(Min Kyo Seo),김도헌(Do Hun Kim),서찬우(Chan Woo Seo),이승윤(Seoung Youn Lee),장석필(Seok Pil Jang),구자예(Jaye Koo) 대한기계학회 2013 大韓機械學會論文集B Vol.37 No.8
동축형 전단 분사기의 액적분포 균일도 및 혼합성능을 개선하기 위해 고안한 액체로켓 엔진용 동축형 다공성 분사기의 개발에 앞서 다공성재를 분사기에 적용하기 위해 다공성재를 통과하는 압축성 유체의 압력강하 특성을 파악하였다. Non-Darcy 유동의 압력강하는 점성력과 관성력으로 인한 손실을 포함하는 Forchheimer 방정식을 이용하여 도출할 수 있으며, 이 때 다공성재의 형상인자인 투과율과 관성력의 영향을 나타내는 Ergun 상수를 이용하여 다공성재를 통과하는 압축성 유체의 압력강하를 예측할 수 있다. 본 연구에서는 다공성재의 압력강하 특성을 나타내는 투과율와 Ergun 상수를 작동유체의 압력강하에 대한 함수로 나타내었으며, 최종적으로 이를 일반화하여 pore의 크기에 따라 압력강하를 예측할 수 있는 관계식을 도출하였다. This study proposes the characteristics of the pressure drop in a compressible fluid through porous media for application to a porous injector in a liquid rocket engine in order to improve the uniformity of the drop size distribution and the mixing performance of shear coaxial injectors. The fluid through the porous media is a Non-Darcy flow that shows a Nonlinear relation between the pressure drop and the velocity at high speed and high mass flow rate. The pressure drop of the Non-Darcy flow can be derived using the Forchheimer equation that includes the losses of viscous and inertia resistance. The permeability and Ergun coefficient represented as a function of the pressure drop and pore size can be applied to the porous injector, where the fluid through the porous media is compressible. A generalized correlation between the pressure drop in relation to the pore size was derived.