بررسي جريان آشوبناك و انتقال حرارت در مجراي با خم هاي متوالي در حالات پايا و ناپايا

چكيده انگليسي :

Analysis of chaotic flow and heat transfer in a duct with successive bends for steady and unsteady states Zahra Habibi z habibi@me iut ac ir Date of Submission June 7 2015 Department of Mechanical Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language FarsiSupervisor Ebrahim Shirani eshirani@cc iut ac ir Mohammad Reza Salimpour Salimpour@cc iut ac irAbstract Mixing heat transfer and the related issues are of important and basic topics One of the new methodsof achieving favorable mixing and heat transfer enhancemanet in the laminar flow regime is generatingchaotic advection flow which is creating chaotic particle trajectories in the laminar flow regime In thepresent study numerical simulation of chaotic heat transfer in laminar flow in a twisted duct is consideredin FLUENT software Two velocities in the steady and pulsating states in tow thermal boundary conditionsof constant wall temperature and constant heat flux are applied in the square cross section duct with threesuccessive bends in macro dimensions Each bend is 90 degrees curved duct The angle between thecurvature planes of two successive bends is also 90 degrees Simulations are performed for the Reynoldsnumbers range 200 Re 800 velocity amplitude ratios the ratio of the peak oscillatory velocity componentto the mean flow velocity 1 3 Womersley numbers 6 17 and wall temperatures 310 Tw K 360 The appearance of homoclinic and heteroclinic connections in the secondary flow structures are the signs ofchaos The more chaos in the flow represents mixing enhancement and since investigation of secondaryflow structures is a qualitative criterion of chaos vorticity vector method which describes stretching andengulfment of flow is used to give a quantitative criterion of chaos Also secondary flow structures arecompared in the absence and presence of heat Heat transfer quantity is discussed by analysis of secondaryflow structures temperature profiles and contours qualitatively and by calculation of Nusselt andRichardson numbers quantitative value of heat transfer and buoyancy forces effects respectively quantitatively in two thermal boundary condition Results confirm each other When the Reynolds numberand wall temperature increases in the steady flow homoclinic and heteroclinic connections develop and itimproves mixing and heat transfer enhancement In the pulsating flow in small and moderate values ofWomersly numbers 6 10 increasing Reynolds number wall temperature and velocity component ratio create a more favorable condition for mixing and heat transfer enhancement It is observed that incrementof Reynolds number in the steady flow and increment of Reynolds and Womersly numbers in the pulsatingflow decrease heating homogeneity and system efficiency from the energy consumption viewpoint In bothsteady and pulsating flow heating homogeneity improves by increscent wall temperature Heat transfer andheating homogeneity improves for 2 compared to steady state flow It is also observed that buoyancyforces have an important role in heating homogeneity occurrence It is concluded from comparing results oftwo thermal boundary conditions that in constant wall temperature condition more chaos mixing andconsequently heat transfer enhancement and heating homogeneity is achieved compared to constant heatflux condition with almost the same energy consumption quantity Pulsation energy consumption is higherthan the energy needed for increasing Reynolds number of the steady flow to match the same heat transferenhancement However a better heating homogenization is obtained in the pulsating flow which is not thecase in the steady flow Keywords Mixing Heat transfer enhancement Chaotic advection Secondary flow structure Vorticity vector Twisted duct Homogeneous heat transfer

حبيبي، زهرا

بررسي جريان آشوبناك و انتقال حرارت در مجراي با خم هاي متوالي در حالات پايا و ناپايا

اختلاط , افزايش انتقال حرارت , همرفت آشوبناك , ساختار جريان ثانويه , بردار گردابه , مجراي پيچدار , انتقال حرارت همگن