DESIGN, ANALYSIS OF MEMS BASED GAS TURBINE FOR EFFECTIVE POWER GENERATION USING ANSYS PACAKAGE.

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1 International Journal of ISSN Systems and Technologies Vol.3, No.1, pp IJST KLEF 2010 DESIGN, ANALYSIS OF MEMS BASED GAS TURBINE FOR EFFECTIVE POWER GENERATION USING ANSYS PACAKAGE. Dr.A.Srinath 1 Ch.Pavan Kumar 2 S.Veera Reddy 3 1 Professor, School of Mechanical & Civil Sciences, K.L.College of Engineering, Vaddeswaram , A.P, India. 2,3 IV Year B.Tech, School of Mechanical & Civil Sciences, K.L.College of Engineering, Vaddeswaram , A.P, India. ABSTRACT: Generation of power is still a major issue of concern as there is a continuous and tremendous increase in the power requirements, but an efficient mechanism which can generate a higher yield of power with a minimal requirement of input resources is also a current necessity as we are running short of the conventional energy resources; to meet this requirement we have no option but to look forward towards the MEMS approach of design for a gas turbine used in power generation as usage of MEMS in gas turbines shall utilize a very minimal input of around a 100 microns of airfoil spans when compared to around mm airfoil spans of a conventional gas turbine and also yield a power output of around Watts which around 1 million times the power output of a conventional gas turbine power plant. 1. INTRODUCTION: The interest for smaller-size engines started in the early the 1990 s in order to develop the few hundred pound thrust range for small aircraft and missiles and in the kw size for distributed power production (popularly known as micro turbines ). More recently, interest has developed in even smaller size machines, 1-10 kw, several of which are marketed commercially. The technology is development of micromachining capability based on semiconductor manufacturing techniques. This enables the fabrication of complex small parts and assemblies devices with dimensions in the 1-10,000 μm size range with submicron precision. Such parts are produced with photo lithographically- 65

2 Dr.A.Srinath defined features and many can be made simultaneously, offering the promise of low production cost in large-scale production. Such assemblies are known in the US as micro-electricalmechanical systems (MEMS) and have been the subject of thousands of publications over the last two decades. In Japan and Europe, devices of this type are known as Microsystems, a term which may encompass a wider variety of fabrication approaches. The proliferation of small, portable electronics computers, digital assistants, cell phones, GPS receivers, etc. requires compact energy supplies. Increasingly, these electronics demand energy supplies whose energy and power density exceed that of the best batteries available today. These small, and in some cases very small, mobile systems require increasingly compact power and propulsion. Hydrocarbon fuels burned in air have times the energy density of the best current lithium chemistry-based batteries, so that fuelled systems need only be modestly efficient to compete well with batteries. MEMS gas turbine is one of the better solutions in compact power supply units with high power density. About MEMS: MEMS (Micro Electro Mechanical Systems) allows the complex electromechanical systems to be manufactured using batch fabrication techniques, decreasing the cost and increasing the reliability of the sensors and actuators to equal those of integrated circuits. 66

3 Design, Analysis The MEMS is the batch-fabricated integrated micro scale system which: 1. Converts physical stimuli, events, and parameters to electrical, mechanical, and optical signals and vice versa. 2. Performs actuation, sensing and other functions. 3. Comprise control (intelligence, decision-making, evolutionary learning, adaptation, selforganization, etc.), diagnostics, signal processing, and data acquisition features Basically, MEMS is a system that consists of microstructures, micro sensors, microelectronics, and micro actuators Microstructure builds the framework of the system, micro sensor detects signals, microelectronics processes the signals and gives commands to the micro actuator to react to these signals. 2. ADVANTAGES OF MEMS: MEMS are widely used in making compact power supply devices (gas turbine), biotechnology (for making DNA& monitoring blood pressure), electronics (for the development of high frequency circuits such as inductors and tunable capacitors), MEMS allows the complex electromechanical systems to be manufactured using batch fabrication techniques, decreasing the cost and increasing the reliability of the sensors and actuators to equal those of integrated circuits, active suspension systems for automobiles. 3. MATERIALS USED FOR FABRICATION IN MEMS: The available materials are Silicon Silicon carbide Titanium Titanium alloys Nickel based alloys General Design considerations for MEMS Gas Turbine: There are various factors which dictate the gas turbine design they are Thermodynamic Mechanical scaling Structural 67

4 Dr.A.Srinath 4. THERMODYNAMIC CONSIDERATIONS: Thermal power systems encompass a multitude of technical Disciplines. The architecture of the overall system is determined by thermodynamics while the design of the system s components is influenced by fluid and structural mechanics and by material, electrical and fabrication concerns. The physical constraints on the design of the mechanical and electrical components are often different at micro scale than at more familiar sizes so that the optimal component and system designs are different as well. 5. MECHANICAL SCALING: While the thermodynamics are invariant down to this scale, the mechanics are not. The fluid mechanics, for example, are scale-dependent. One aspect is that viscous forces are more important at small scale. Pressure ratios of 2:1 to 4:1 per stage imply turbo machinery tip Mach numbers that are in the high subsonic or supersonic range. Airfoil chords on the order of a millimeter imply that a device with room temperature inflow, such as a compressor, will operate at Reynolds numbers in the tens of thousands. With higher gas temperatures, turbines of similar size will operate at a Reynolds number of a few thousand. These are small values compared to the range of large-scale turbo machinery and viscous losses will be concomitantly larger. 6. STUCTURAL DESIGN CONSIDERATIONS: Structural design of a MEMS gas turbine has many of the same considerations as the design of large machines: basic engine layout is set by rotor dynamic considerations, centrifugal stress is due to the primary rotor load, stress concentrations must be avoided, and hot section life is the creep- and oxidation is limited. Some large concerns of engines do not exist at micron scale. For example, the micro vanes are of great strength, so that the bending is not a factor of concern; thermal stress from temperature gradients is not important at these sizes; maintenance is not a design issue; and fasteners do not exist here so the engineering details involved with bolting, static sealing, etc. do not exist. Ni based super alloys Ti alloys Micro SiC Micro Si Centrifugal Stress in MPa Thermal Stress in MPa 2.7X X X X10-3 Stiffness MPa/Kgm Max Temp(Life Limit) in o C 1000 (creep) 300(strength) 1500(oxidation) 600(creep) 68

5 Design, Analysis Design of MEMS gas turbine: The different components present in the Gas turbine unit are Compressor Combustion chamber Turbine Heat exchanger The design of turbine is primarily focused in this work and the necessary components of turbine are designed. Components present and their specifications are 1. Rotor 2. Stator Blades are present on the stator as well as rotor with an aerofoil shape. The stator blades are used to guide the flow on to the rotor. The rotor blades convert the heat energy in to mechanical energy which in turn is converted in to electrical energy. N o of blades on stator: 23 No of blades on rotor: 17 Turbine design: Vr1=Vf1 V1 U1=Vw1 Vf2=V2 Vr2 U2 69

6 Dr.A.Srinath V 1 = velocity of jet at inlet U 1 = blade (or) tangential velocity at in let V r1 =relative velocity at inlet V w1 =whirl velocity at inlet =guide blade angle at out let (or) jet angle at in let = blade angle at inlet V 2 = velocity of jet at out let U 2 = blade velocity at out let V w2 =whirl velocity at out let V r2 = relative velocity at out let = blade angle at out let = jet angle at out let 7. Data from literature survey: Radial inward flow turbine the outlet is radial =90, Vw2 =0 Relative velocity at rotor tip is radial =90 0, V = r1 V w1, Vr 1= V f1 Rotor inlet diameter =8.2mm Rotor outlet diameter =4.4mm Stator inlet diameter =10.5mm Stator outlet diameter r =8.5mm Number of blades on stator =23 Number of blades on rotor =17 Speed of the turbine =2, 00,000rpm From inlet velocity triangle: For best output should lies between 60to80 U 1= V w1 = D 1 N/60 = ( X8.2 X10-3 X )/60 U 1= m/sec = 67 0 V 1 = U 1 /sin 70

7 Design, Analysis = 85.87/sin67 =93.28 m/sec V f1 = V r1 =V 1 cos =93.28 cos67=36.45 m/sec Assuming that There is not much change in flow velocity V f1 =V f2 =36.45 m/sec Outlet velocity triangle: U 2 = ( D 2 N)/60 = ( X 4.2 X 10-3 X )/60 = m/sec V f2 =V f1 =36.45 m/sec =tan -1 (43.98/36.45) = V r2 = (U 2 2+V 2 f2 ) =57.12 m/sec Based on the inlet condition: = (P 1 / (RT 1 )) P 1 =1.1 bar T 1 =27 0 = ((1.1 X 100)/ (0.287 X 295)) Flow rate Q= ( X D X B X V f1 ) = ( X 8.2 X 10-3 X 2X10-3 X 36.45) = m 3 /sec Mass flow rate = Q =1.3 X (1.877X10-3 ) =2.44X10-3 kg/sec Power developed = Q (V w1 U 1 +V w2 U 2 ) =2.44X10-3 X =18 Watts Force = QV w1 = (2.44 X 10-3 X 85.87) = 0.2 N 71

8 Dr.A.Srinath Turbine shaft Stator vanes Rotor vanes Thermal and structural analysis tabulation 3-D view of turbine Angle(θ) Stress max (N/mm 2 ) Stress min Displacement (N/mm 2 ) (mm) e X e X e X e X e X e X e X e X Thermal &structural analysis: From the above table it can be inferred that the designed vane is safest to be used at an impact angle of 67 0 as it has both the max. and min. stress at the lowest levels at this angle, apart from displacement being at an optimal value, which can be regained after each impact. The schematic ANSYS figures for the 67 0 impact and its stress, thermal analysis are given below, followed with the schematic of 66 0 at which stress, displacements are very high, which is correlated with the failure as can be seen in fig However this data and results need to be optimized using various optimization techniques, which is a part of the future scope of the current work along with the flow visualization that can be extended. 72

9 Design, Analysis Structural analysis of vane in ANSYS showing the stress & deflection respectively at 67 0 of impact Thermal analysis of vane showing stress distribution in the vane at 1200k temperature Failed vane at 66 0 due to excessive stresses Conclusions: The MEMS based gas turbine which has been analyzed and designed as per the fundamentals and using ANSYS package is obtained, which can be utilized for a maximum power generation capacity of 18 Watts, at 2,00,000 rpm speed of the rotor. Numerous such turbines can function simultaneously and can generate as much power as required, with minimal effort, cost and wastage. References: Journal / Conference Papers: 1. X.C.Shan et al,design, fabrication and characterization of an air-driven micro turbine device, International MEMS Conference 2006, Journal of Physics: Conference Series 34 (2006)

10 Dr.A.Srinath 2. A.H. Epstein, Millimeter-scale MEMS gas turbine engines, in Proc. of ASME Turbo Expo Power for Land, Sea and Air, USA (2003) pp K. Isomura, S. Tanaka, S. Togo, H. Kanebako, M. Murayama, N. Saji, F. Sato and M. Esashi, Development of micro machined gas turbine engine for portable power generation, JSME International Journal Series B, 47 (2004) S. Tanaka, K. Isomura, S. Togo and M. Esashi, Turbo test rig with hydro-inertia air bearings for a palmtop gas turbine, J. Micromech. Microeng. 14 (2004) E.S. Piekos, Numerical simulation of gas-lubricated journal bearings for micro-fabricated machines, Doctoral thesis, MIT, M. Hara, S. Tanaka and M. Esashi, Rotational infrared polarization modulator using a MEMS-based air turbine, J. Micromech. Microeng, 13(2003) Books and Monographs: MILLIMETER-SCALE, MEMS GAS TURBINE ENGINES, Alan H. Epstein (MIT) GAS TURBINE THEORY BY H.H SARVANAMUTHU, ROGERS GAS TURBINE ENGINEERING HAND BOOK BY M.P.BOYCE Design, fabrication and characterization of an air-driven micro turbine device X. C. SHAN, QIDE ZHANG, YAOFENG SUN, ZHENFENG WANG 74