طراحي و بهينه سازي پره هاي داخلي طولي در جريان آرام داخل لوله توسط تئوري ساختاري

چكيده انگليسي :

Constructal Design and Optimization of Internal Longitudinal Fins at Internal Laminar Flows Jalal Darabi j darabi@me iut ac ir 25 April 2011 Department of Mechanical Engineering Isfahan University of Technology Isfahan 84156 83111 IranDegree M Sc Language FarsiSupervisor M R Salimpour salimpour@cc iut ac irAbstractThis research is devoted to geometrical optimization of internal longitudinal fins based on constructal theory These fins are extended inward from the pipe perimeter to a prescribed radius R L and would have an optimallength L which have been determined analytically by means of constructal theory The effective parameters ofthe current study are the ratio between the high conductivity and low conductivity k the relative amount ofhigh conductivity material and the number of sectors of the disc shaped body N Constructal theory anddesign serves as a reminder that flow systems that must be designed configured must be treated as malleable i e as morphing structures that are as free to change as possible Configurations that are postulated assumed based on past practice handbooks and rules of thumb are not necessarily the best The only rule of thumb worthremembering is that geometry must not be taken for granted In fact geometry is a result not an assumption Itis geometry that endows the flow system with the ability to serve its purpose in spite of the constraints Thefield of heat transfer has demonstrated for many years how the principle of generating flow geometry works First and foremost this principle is one about objective the need to make things compact to use the availablespace to the maximum The oldest and best documented subfield of heat transfer where the generation ofgeometry is documented is the geometric optimization of fins Our strategy is to start from the smallest scale e g the optimized elemental volume The first challenge is to understand the functioning of elemental systems and to optimize their performance subject to their own smallest scale space constraints Next is the challenge toassemble and optimize the relative positions of a number of elemental systems into a larger and fixed space Theresulting flow system is a first construct This procedure can be continued toward stepwise larger scales in stepsof aggregation combined with optimization under global constraints For a round tube with two thermalboundary conditions i e constant heat flux and constant temperature the optimization length L and also thecorresponding thickness of fins for a known material ratio DNL R 2 are determined parametricallywhich ensures maximum heat transfer and thermal efficiency In analytic solution two different velocityprofiles are assumed while the flow regime is considered to be laminar In addition dominancy of conductionheat transfer between fins and convection in the core of pipe is the main assumptions of this research Finally our analytical results are verified with numerical results obtained from commercial software Fluent In thenumerical simulation the following criteria are used to find the optimized fin aspect ratios For constant heatflux boundary condition the maximum temperature at the surface shall be minimal For constant temperatureboundary condition the amount of transferred heat to the fluid is measured and a case in which this amount ismaximum is considered as optimum fin aspect ratio KeywordsConstructal theory Longitudinal fin Optimization Laminar flow Internal fin

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طراحي و بهينه سازي پره هاي داخلي طولي در جريان آرام داخل لوله توسط تئوري ساختاري

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