4949

4652

كارشناسي ارشد

تبديل انرژي

اصفهان: دانشگاه صنعتي اصفهان، دانشكده مكانيك

1388

دوازده،99ص: مصور، جدول،نمودار

ص.ع. به: فارسي و انگليسي

احمد رضا عظيميان

ابراهيم شيراني

28/10/88

علي اكبر عالم رجبي، محسن ثقفيان

مهندسي مكانيك

ID4652

به فارسي و انگليسي: قابل رويت در نسخه ديجيتال

Slip flow and Temperature Jump in Different Cross Section Micro channels Massoud Massoudi Farid m masoudifarid@me iut ac ir 2009 06 02 Department of Mechanical Engineering Isfahan University of Technology Isfahan 84156 83111 IranDegree M Sc Language FarsiDr A R Azimian azimian@cc iut ac irDr E Shirani eshirani@ictp itAbstractRarefied gas flow and heat transfer in the rectangular trapezoidal elliptical and circular micro channelsare investigated numerically in the slip flow regime A control volume based numerical method is used tosolve the Navier Stokes and energy equations with velocity slip and temperature jump conditions at thewalls Effect of various parameters such as Reynolds number from 0 1 to 1 channel aspect ratio from0 2 to 1 and Knudsen number less than 0 1 on the velocity pressure and temperature fields wereexamined Also variation of parameters such as hydrodynamic and thermal entrance length frictionfactor Nusselt number efficiency and thermal resistance of micro channels with different cross sectionsare studied too Comparison of the results with no slip and no jump condition showed that in the entranceregion of all cross sections a very large reduction in the friction factor and Nusselt number are obtained This reduction is due to the rarefaction effects There is a finite asymptotic value for the friction factorand Nusselt number at the channel inlet This asymptotic limit is observed for any geometry at any valueof Reynolds number As it is evaluated at a location where fluid is about to enter the channel andtherefore there is no recognition of the geometry and Reynolds number yet In this region when the no slip boundary condition is applied strong pressure gradients that exist near the walls causes the maximumvelocities to be found near the walls rather than in the channel core as would normally be expected Butthe slip condition reduces the amount of pressure generated as a result of the slowing down of the fluidparticles at the wall and therefore the maximum velocities near the walls decrease As flow approachesthe fully developed region the maximum velocities are found in the channel core which is due toreduction of the pressure gradients in the cross section Applying temperature jump at the wall reducesthe heat transfer rates and therefore lowers the fluid temperature as compared to the no slip no jumpconditions The best efficiency in these cross sections is for a elliptical cross section at the Re 0 3 Kn 0 1 and 1 3 whit the maximum heat transfer rates and minimum pressure reduction Key wordsSlip flow Temperature jump Rarefaction Rectangular micro channel Trapezoidal micro channel Elliptical micro channel Circular micro channel Entrance region Friction coefficient Heat transfer coefficient

احمد رضا عظيميان

ابراهيم شيراني

علي اكبر عالم رجبي، محسن ثقفيان