Numerıcal ınvestıgatıon of lamınar forced convectıon and entropy generatıon of fe3o4/water nanofluıds ın dıfferent crosssectıoned channel geometrıes

In this study, forced convection of nanofluid flow in various channel geometries with a hydraulic diameter of 16 mm and length of 1.5 m under laminar flow condition has been investigated numerically. Constant heat flux of 6 kW/m2 has been applied on to the surfaces of the channels. Fe3O4/water nanofluid has been used in the analyses to enhance the convective heat transfer of the base fluid. Analyses have been performed for Reynolds numbers between 500≤Re≤2000, and for volume concentrations of nanoparticles between 1% and 5% in cylindrical, square, rectangle, and triangle cross-sectioned channel geometries. The finite volume discretization method has been used to solve the governing equations. The effects of some parameters; Reynolds number, nanoparticle volume fractions, channel geometries on the average Nusselt number, Darcy friction factor and entropy generation have been investigated in detail. The results indicate that nanofluid offers further convective heat transfer enhancement according to base fluid and cylindrical cross-sectioned channel gives the best heat transfer performance among other cross-sectioned channel geometries. Using water as a working fluid, cylindrical cross-sectioned channel geometry gives the highest heat transfer rate among other channel geometries, whereas triangle one gives the lowest. Cylindrical cross-sectioned channel geometry offers up to 77.6% enhancement compared to triangle cross-sectioned channel geometry for the same hydraulic diameter and same heat flux. However, triangle cross-sectioned channel geometry has highest convective heat transfer increment ratio (4.12%) for changing working fluid as water to nanofluid. Also, some new Nu correlations based on the channel geometries and nanoparticle volume fractions were proposed in the present study

Sessiz Helikopter Tasarım ve Analizi için İzlenen Adımlar ve Yöntemler

Günümüzde askeri ve sivil havacılık başta olmak üzere birçok alanda kullanılmakta olan helikopterlerin gürültü karakteristikleri oldukça karmaşık olup, birçok fiziksel sebeplerden kaynaklanabilmektedir. Bu bildiride, bir lisans bitirme projesi olarak yapılmakta olan " Sessiz Helikopter Tasarım ve Analizi Projesi " kapsamında yapılan literatür araştırması ile birlikte ön çalışmalarda belirlenen tasarım ve analiz adımları anlatılmaktadır. Özellikle, helikopterler için sesin tanımı, gürültü kaynakları ve gürültü azaltma yöntemleri özetlenip anlatılmaktadır. ABSTRACT Noise characteristics of helicopters that are used in many areas, especially, in military and civil aeronautics, are very complex and they can arise from many physical causes. In this paper, the literature review is performed and the design and analysis steps in the initial phases of this project titled " Design and Analysis of a Quiet Helicopter Project " as part of a senior design project are presented. Specifically, definition of sound, sources of noise, noise reduction methods are summarized and described

Experimental investigation on thermo hydraulic performance of ferronanofluid flow in a dimpled tube under magnetic field effect

Active and passive techniques have been utilized together to enhance heat transfer in this study. The ferronanofluid, magnetic field, and dimpled tube have not been utilized together in the literature so far. Regarding this issue, this investigation is the first experimental study to specify the effect of use of these three effects simultaneously. The concept of this study is to determine the thermo-hydraulic performance of Fe3O4/H2O flow inside a dimpled tube under magnetic field effect. Constant and uniform heat flux of 4500 W/m2 has been applied on the surface of the tube. The work aims to gain data in the range of laminar flow (1131≤ Re≤2102) in the dimpled tube. Dimple geometry with pitch ratio of P/d = 3.75, magnetic field (B = 0.03 ≤ T ≤ 0.16), and nanoparticle volume fraction of 1.0% are the base variables. The results showed that Nusselt number increases with increasing Reynolds number and magnetic field intensity. The highest increase in Nusselt number is obtained as 115.31% compared with the distilled water flow in the smooth tube for the case of magnetic field intensity of 0.3 T. The highest Performance Evaluation Criteria value is also determined as 1.44 for the case of ferronanofluid flow in dimpled tube at Re = 1131 in absence of magnetic field