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چكيده انگليسي :

Design and Manufacturing of a Free Piston Stirling Engine Ali Behjatian ali beh83@me iut ac ir October 7th 2009 Department of Mechanical Engineering Isfahan University of Technology Isfahan 84156 8311 IranDegree M Sc Language FarsiAhamad Saboonchi ahmadsab@cc iut ac irAbstractThe capabilities and unique features of the Stirling engines have made them suitable for a wide range ofapplications Although these engines compared to internal combustion engines have less specific power their structures are simpler and it makes them more reliable for long term missions The structures of freepiston Stirling engines are simpler and by use of non contact seals the friction between piston and cylinderwill be minimized The Longer life high efficiency and possibility for use of any source of energy in freepiston Stirling engines make it possible to utilize them in solar energy convertors and today a number ofNASA spacecrafts utilize them to produce electricity for spacecrafts In the present work using the lineardynamic analysis a free piston Stirling engine is designed After determination of principal dimensions of theengine a finite element analysis is used to design the piston and displacer flexure bearings All engines partswere manufactured by conventional machine tools and flexure bearings could be manufactured by electricdischarge machines After assembling the engine parts and initial tests the actual operating frequency of theengine was measured The operating frequency of the engine could be obtained by measuring the frequencyof the output electrical current of alternator The actual measured frequency of the engine is about 43Hz andit is possible to increase the operating frequency to 60Hz by changing the mass of piston and displacer According to the assumptions of isothermal analysis it is necessary to develop a numerical multi dimensional analysis to get a better understanding of the engine operation In this Thesis using FLUENTcode a 2 D unsteady axis symmetric model is presented The motion of piston and displacer boundaries isproduced with the aid of user defined functions UDF in FLUENT and the grid is updating in each time stepby layering method Since we are using layering method we should consider an appropriate time step size foriterations In this Problem time step size is constant but it is possible to consider variable time step size toreduce the computational time To reduce the computational time the initial temperatures of working fluid invarious zones are set manually These initial temperatures have great effect in achieving to quasi steadycondition The initial pressure is 1 MPa and initial velocities are considered zero At the end of each timestep a user defined function is executed and calculates the average pressures and volumes of working spaces The output cyclic power could be obtained from p v diagram The output power calculated by CFD analysisis about 10 watts but the isothermal analysis estimates an output power about 30 watts It is obvious that thedifference between calculated power outputs is related to poor operation of heat exchangers and we canincrease the actual power output to about 40 watts by optimizing the heat exchangers and increasing thecharge pressure The velocity profile in regenerator gap shows that the maximum velocity in high frequencyoscillating flows compared to fully developed steady flows does not occur in centerline and it occurs nearthe walls This phenomenon that called Richardson effect increases the pressure drop in oscillating flows andit should be considered in designing Stirling engines Key WordsStirling Engine Free Piston Stirling Engine Manufacturing CFD analysis

بهجتيان، علي

طراحي و ساخت يك موتور استرلينگ پيستون آزاد مولد برق

شبيه سازي عددي , ياتاقان هاي منعطف , مدل ايزوترمال