The Design of Small Solar Thermal Dish Stirling 500 W Stand Alone in Thailand.

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The Design of Small Solar Thermal Dish Stirling 500 W Stand Alone in Thailand.ISEC 2007

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The Design of Small Solar Thermal Dish Stirling 500 W Stand Alone in Thailand.

  1. 1. The Design of Small Solar Thermal Dish Stirling 500 W Stand Alone in Thailand. Eng’r. Suravut, Snidvongs*1 and Dr. Sirinuch, Chindaruksa*2 *1 Vice President, Asian Renewable Energy Development and Promotion Foundation, Bangkok, 10400, Thailand , airscan@cscoms.com, PhD Students, School of Renewable Energy Technology (SERT), Naresuan University, Pitsanulok, THAILAND. *2 Physic Department, Faculty of Science, Naraesuan University, Pitsanulok, THAILAND.Abstract This can be rearranged as Thailand has the average insolation of 550 W/m2daily average which is quite low when compare to the P/(pfVo) = constant (2)existing system such as SES or Solo, which designed = 0.015their system for 1000 W/m2, but do not require 1000W/m2 to operate. Operating the Solar Dish Stirling The equation was found by Bale to bewith medium insolation the system must design with approximately true for all types and sizes of Stirlingproper conditions, such as Increase Dish Diameter, Engines for which data were available including free-Minimum Power to track the dish, Reduce Piston and piston machines and those with crank mechanism. InDrive mechanism friction. most instances the engines operated at temperatures of A purpose of this research is to design a Small 650 ºC and cooler temperatures of 30 ºC [2].Solar Thermal Dish Stirling 500 W Stand Alone The size of the engine cylinder required may thenSystem that can operate with lower insolation such as be computed from the Beale number. There is someThailand conditions. evidence that the Beale number is conservative for large engine. Furthermore, in such a high capital cost1. Introduction application, a sophisticated design with adequate Insolation in Thailand is varying between in 450 cooling might be expected. Therefore perhaps it wouldto 550 W/m2 daily whole year round, and the average be reasonable to double the value of the constant invalue is at 550 W/m2 daily over the year. equation (2) from 0.015 to 0.03. Finally, it is To operate the Solar Dish Stirling with medium advantageous at this stage to recall, from the aspect ofinsolation the system must design to operate with seal, bearing, and piston-ring wear, the attractions ofproper conditions, such as increasing dish diameter, an ‘over square’ engine, i.e. a large bore and shortreduce power to track dish structure, reduce piston and stroke.drive mechanism friction. From Beale equation considers only the speed, The rotary drive mechanism seems to be lower volume, mean pressure, and constant. All thosefriction than other mechanism such as gear drive, and information can let us find the stroke and pistonwhisper tech swash plate system [1]. diameter.In this research the author will design a Small For the design data we must give the expectedSolar Thermal Dish Stirling 500 W stand alone power output, desire speed, and mean pressure, for theSystem that can operate with lower insolation such as example 550 W, 20 hertz (1200 RPM), 1 MPa. For aThailand conditions. square engine the piston and stroke ratio usually we use 1 from equation 1.2. Solar Stirling Engine Design The preliminary Stirling Engines designs usually Stroke = Duse the Beale number concept (1). The power output of Vo = ¶ / 4 D2 x D (3)many Stirling Engines conformed approximately to the P/(pfVo) = 0.03simple equation: Vo = P/(0.03pf) (4) D = (4P/(0.03¶pf))1/3 (5) P = 0.015pfVo (1) = (4*550/(0.03*¶*10*20)) 1/3 D = 4.89 cmWhere P = engine power (watts), Stroke = 4.89 cm p = mean cycle pressure (bar), f = cycle frequency or engine speed (hertz), Beale equation can give roughly diameter and Vo = displacement of power piston (cm3) stroke of power and displacement piston. BealeCopyright© 2007 by the Japan Society of Mechanical equation cannot give more details on the differenceEngineers. All rights reserved. size of power and displacement piston. 1
  2. 2. The Schmidt analysis equation was published by a pure sinusoidal reciprocating motion having a 90Gustav Schmidt of the German Polytechnic Institute of degree phase difference between the adjacent pistons.Praque in 1871 [3] in which he obtained closed formsolutions of these equations for the special case ofsinusoidal volume variations of the working spaces.Schmidt and Simple analysis can give us moreaccurate and give the difference size of power piston,displacement piston, heater area, cooler area, andregenerator size. The calculation used the math labprogram from Dr. Urieli [4]. p = MR (Vc/Tk + Vk/Tk + (Vrln(Th/Tk))/(Th-Tk) + Vh/Th + Vc/Th)-1 (6)Where p = Mean Pressure bar M = Mass R = Gas Constant Figure 2 Compound Gamma type Stirling engine Vc = Compression Space Volume Source: By author Vr = Regenerator Space Volume Vh = Heater Space Volume The advantages of Rotary Drive Mechanism Vk = Cooler Space Volume Stirling engine are that it is easy staring, smooth Th = Heater Temperature, K running, and has good low end torque. Rotary Drive Tk = Cooler Temperature, K Mechanism works well for applying the generator at the top of a Stirling engine. It easy to installed at the From Schmidt equations it can give the volume of focal point of a parabolic reflector.heater and compression volume by this we can get the This Solar Stirling engine was first tested with 700size of the power and displacer piston. Schmidt W x 4 electric heaters 1 ф 220 V, adjustable power,equations give us more accurate piston size. and final tested with real solar insolation in Bangkok, In this prototype engine the author decided to use Thailand at AREF.4 cylinders gamma type Stirling Engine with internal This Solar Stirling engine was designed by author,regenerator, Figure 1. This type of engine has the namely “Siam Solar Stirling Engine III”. Don Boscoadvantage of having separate cylinders out weight. Technical School has meanwhile supported theGamma type engine can also be compounded into a fabrication work on the Dish Structure, Stirling Enginecompact multiple cylinder configuration, as shown in components, Tracking mechanism and assembly theFigure 2. engine. The author and his staff have then continued to do the testing. All tests were done at AREF, Bangkok in Thailand. 3. Solar Stirling Engine Specification The Solar Stirling engine was designed as the following Table 1: Table 1 Solar Stirling Engine Specification Type Gamma Acting Double Driver Mechanism Negative Rotary Working Gas Air Figure 1 Diagram of a simple displacer type gamma Expansion space Temp 650 C (+/- 5 C) engine. Source: www.ent.ohio.edu/~urieli/stirling/engines Compression space Temp 40 – 50 C (+/- 5 C) Ambient Temperature 40 C (+/-5 C) This engine is enabling an extremely high specific Thermal Efficiency 60 %power output. The four cylinders are interconnected Power Control Variable Pressure(daisy chain), so that the expansion space of one No. of Cylinders 4cylinder is connected to the compression space of the Means Pressure 0.5 MPaadjacent cylinder via a series connected heater, Maximum Pressure 1 Mparegenerator and cooler. The pistons are typically driven Power Piston Diameter, mm. 48by a negative swash-plate (Rotary Drum), resulting in Stroke, mm. 40 2
  3. 3. Power Displacement, cc. 72 x 4 Displacer Diameter, mm. 42 Displacer Length, mm. 150 Heater surface area, cm2 11.40 Cooler surface area, cm2 29.12 Regenerator surface area, cm2 161.60 Expansion swept, cm3 340.00 Compression swept, cm3 220.80 Speed, rpm 500 – 1200 Regenerator Type Tube Cooling type Ethyl glycol Electric heater 220 V 700 x 4 W Mechanical Output Power 215 W @ 20 psi Mechanical Output Power 550 W @ 80 psiSource : By Author4. Rotary Drive Mechanisms The four pistons gamma type Stirling engine, aredaisy chained together with negative Swash Plate(Rotary), Figure 3. This is done by driving the Figure 3 Swash Plate Type 2 (Rotary)displacer via linear drive rods which are attached to the Source : By Authortop of power pistons. The rods pass through a sealedbulkhead and the displacer cylinders are ported topower piston cylinders that are phased behind them90°. This allows an engine that only requires one crankthrough per piston where other Stirling engine requirestwo. The bronze bushing sealed bulkhead was replacedwith guide bearing with rubber seal, and replace theMitter gear with Rotary Drum. This could callNegative Swash plate. It also added more bearing anduniversal joint. The rotation, Clock-wise or counterclock-wise, can be done by adjust a little phase angle,positive or negative, different. This engine stands a height of 60 cm. The surfacearea of the heating side is 11.40 cm2. The total weightwhen mostly made of aluminum casting is around 20kgs. The working piston diameter is 4.8 cm, therestrictor piston diameter is 5.00 cm, and the stroke is4.00 cm. The engine was designed with pressured airas working fluid at an operating pressure of up to 1MPa (147 Psi). The method of heating it arbitrarysince it is a Striling engine, but the prototype washeated with 700 x 4 W electric heater, adjustablepower, each cylinder the engine produces 130 Wmechanical work. The maximum heat input is 2800 W which is more Figure 4 Swash Plate Type 2 (Rotary)than the estimated heat input from the concentrating Source : By Authordish, 2,000 W at solar insolation 550 W/m2, averagedaily Thailand insolation. The engine was circulating 5. Calculation resultswith Ethyl Glycol to cool the engine. The engine isestimated to have the thermal efficiency of 60 % and 5.1 Engine datamechanical efficiency of 30 %. Comp clearance vols 4.0 cm3 The engine starts running at 200 °C and produces Comp swept vols 72.0 cm3550 W power output when near the max temperature Exp clearance vols 3.0 cm3of 650 °C. The ideal speed is approximately 1200 rpm Exp swept vols 69.0 cm3and the torque output is 10.4 Nm. Expansion phase angle advance 90.0 deg 3
  4. 4. 5.2 Annular heat exchanger Cooler data 5.9 Heater Simple analysisVoid vols 137.22 cm3 Average Reynolds number 1841.00Free flow area 0.13 cm2 Maximum Reynolds number 3323.90Wetted area 3.43 cm2 Heat transfer coefficient 202.79 W/m2*KHydraulic diameter 16.00 mm Heater wall/gas temperatures Twh 923.00 KCooler length 10.50 cm Tgh 892.00 K5.3 Tubular regenerator housing with stacked wire 5.10 Cooler Simple analysismesh matrix Average Reynolds number 4110.70Matrix porosity 0.160 Maximum Reynolds number 7135.40Matrix wire dia 0.130 mm Heat transfer coefficient 38.94 W/m2*KHydraulic dia 0.024 mm Heater wall/gas temperatures Twh 313.00 KTotal wetted area 0.0542 m2 Tgh 374.50 KRegenerator length 148.0 mmVoid vols 0.24 cm3 5.11 Converged heater and cooler mean temperatures heater wall/gas temperatures Twh 923.00 K5.4 Annular gap heat exchanger heater data Th 892.00 KVoid vols 21.44 cm3 cooler wall/gas temperatures Twk 313.00 KFree flow area 0.02 cm2 Tk 374.50 KWetted area 2.86 cm2Hydraulic dia 3.00 mm 5.12 Regenerator Simple AnalysisHeater length 10.00 cm Average Reynolds number 18.1005.5 Operating parameters Maximum Reynolds number 32.800Gas Type Air Stanton number (Average Re) 0.203Mean pressure 4,200 kPa Number of transfer units 2,487.000Cold sink temperature 313.0 K Regenerator effectiveness 1.000Hot source temperature 923.0 K Regenerator net enthalpy loss 0.500 WEffective regenerator temperature 546.1 K Regenerator wall heat leakage 13.900 WOperating frequency 20.0 HzPressure phase angle beta 18.0 deg 5.13 Pressure Drop Simple AnalysisTotal mass of gas 0.991 gms Pressure drop available work loss 26,946.7 W Actual power from simple analysis -26,848.8 W5.6 Schmidt Analysis Actual heat power in from simple 193.9 WWork 5.067 J analysisPower 101.3 W Actual efficiency from simple -13,845.0 %Qexp 7.667 J analysisQcom -2.600 JIndicated efficiency 0.661 6. Dish specifications5.7 Ideal Adiabatic Analysis Table 2. Dish SpecificationHeat transferred to the cooler -59.73 W Dish Type ParabolicNet heat transferred to the regenerator 0.00 W Structure Type Space TrussHeat transferred to the heater 160.67 W Dish Diameter, m 2.50Total power output 101.34 W Dish Focus, m 1.56Thermal efficiency 0.631 Depth. m 0.25 Total height, m 3.205.8 Simple Analysis Aperture area, m2 4.90Heat transferred to the cooler -82.11 W Reflective, % 90Net heat transferred to the regenerator 0.00 W Power at receiver, W 2,000Heat transferred to the heater 179.48 W Tracking sensor H bridge LEDTotal power output 97.85 WThermal efficiency 0.545 Tracking power, W 10 x 2 Source : By Author 4
  5. 5. 9. Conclusions The “Siam Solar Stirling Engine System III (SSES III) prototype” was designed to meet Thailand’s weather environment (such as humidity, solar insolation, soft land, and wind load, etc.). The Dish structure and Solar Stirling engine components were fabricated by the Don Bosco Technical School under the author’s supervision. The system is now under testing for reliability and endurance. Figure 3 shows the SSESIII. This engine stands aFigure 5 Parabolic Dish Structure at AREF, Bangkok, height of 60 cm. The surface area of the heating side isThailand. Basic engineering and calculation for steel 11.40 cm2. The total weight when mostly made ofstructure and foundation was created by the author. aluminum casting is around 20 kgs. The workingSteel fabrication work was built by the Don Bosco piston diameter is 4.8 cm, the restrictor piston diameterTechnical School. Erection and Installation work was is 5.00 cm, and the stroke is 4.00 cm. The engine wasalso created by the author and the AREF staffs as well designed with pressured air as working fluid at anas controllers system, Solar Tracker mechanism, the operating pressure of up to 0.5 MPa (72 Psi). Thecircuit design and assembly work. method of heating it arbitrary since it is a StrilingSource : By author engine, but the prototype was heated with 700 x 4 W electric heaters, adjustable power, each cylinder the Delta Truss Support Structure made from steel. engine produces 130 W mechanical work. TheThe Delta Ring attached to the top of Delta Truss maximum heat input is 2,800 W which is more thanSupport Column. The dish structure made from GRP, the estimated heat input from the concentrating dish,12 panels. The acrylic mirror was glued to the GRP 2,000 W at solar insolation 550 W/m2, daily averagedish. The reflector attach to the Delta Ring with Thailand solar insolation. The engine was circulatingadjustable screw. The Solar Stirling engine install at with Ethyl Glycol to cool the engine. The engine isthe center of focus point. The temperature at the focus estimated to have the total efficiency of 31 %. Theis around 650 °C. engine starts running at 200 °C and produces 550 W power output when near the max temperature of 6507. Performance °C. The ideal speed is approximately 1200 rpm and the torque output is 10.4 Nm. Table 3 Solar Stirling Engine Performance SSESIII can be rotate Clock-wise or counter Cost USD 1,280.00 clock-wise by adjust a little phase angle, positive or Mean Time Between Fail (hrs) 18,000 negative, different. Maintenance Time (hrs) 3,500 The Negative Swash Plate Drive Mechanism Torque (N-m) 10.4 (Rotary Drive), all piston rods install with guide Thermal Eff. % 60 bearing on both side to reduce the friction. This type of Mechanical Eff. % 31 Mechanism needs very accurate workmanship toSource : By Author make. It is very quite during the operation. The Stirling engine can be rotate clockwise or counter clockwise by8. Results adjust a little phase angle, positive or negative, different. The maintenance time are high, 18,000 hrs. Figure 6 show the friction test for this rotary Rotary Drive Friction Test mechanism. 12 As the weight of Rotary drum is in balance so this 10 type of mechanism create much lower vibration than V other system. This type of Drive Mechanism has fewer 8 A parts than Daisy Chain Gear Drive but complicate to 6 W make. The cost of the system is medium high. The 4 friction is about 6.1 W. The engine torque 10.4 N-m is quite good. Thermal efficiency is 60 %. and 2 Mechanical Efficiency is 31 %. The Rotary Drive - Mechanism can be improved mechanical efficiency up 500 700 900 1100 1300 1500 1700 1900 to 31 %. SSESIII required power to track only 10 x 2 W. Figure 6 Daisy Chain Rotary, Friction Test By increasing dish diameter, reduce power to Source : By Author track, enlarge displacer piston, reduce friction for drive 5
  6. 6. mechanism, and reduce power piston friction make theSSESIII operate with Thailand conditions. Friction of Stirling engine may not have directeffect to the insolation, but if the Stirling engine hasless friction, Stirling engine will require less power toovercome the friction. This will gain the performanceof the Stirling engine up. Thus, with mediuminsolation as Thailand, average 550 W/m2 daily,Stirling engine could perform better.ACKNOWLEDGMENTSThis research was prepared by Mr. SuravutSNIDVONGS, Vice President, Asian RenewableEnergy Development and Promotion Foundation, EITmember, a PhD Student, School of Renewable EnergyTechnology, Naraesuan University, Pitsanulok,Thailand. The author would like to acknowledge theassistance and guidance of Asian Renewable EnergyDevelopment and Promotion Foundation Dr. Sub.Lt.Prapas Limpabandhu Deputy Minister of ForeignAffair, Mr. Sutas AROONPAIROJ and staffs, theEngineering Institute of Thailand members whoprovided a critical review of this research through itsvarious stages, including Asist. Prof. Dr. Sirinuch,Chindaruksa, Physic Department, Faculty of ScienceNaraesuan University, as Advisor, Dr. Vichit,Yamboonrung, Assoc. Prof. Dr. WattanapongRakwichien, Asist. Prof. Dr. MathaneeSanugansermsri, as Co-Advisor and the NaraesuanUniversity Staffs, Pitsanulok, Thailand. Especially theDon Bosco Technical School staffs for theirfabrication and construction work on the prototype.Finally, the author would like to thank the numerousindustries to provide information for this research.References[1] Suravut, Snidvongs, The comparison fordifferent type of drive mechanism for small solarstirling engine 500 w in Thailand, 2007. ISEC 2007,24-26 September, 2007. Tokyo, JAPAN.[2] Ronald J. Steele, The Stirling Steele Enginedrawing, 1994. U.S.A[3] G.Walker, Stirling Engines, ClaarendonPress, Oxford, 1980, p.73.[4] Schmidt G 1871 The Theory of Lehmann’sCalorimetric Machine Z. ver. Dtsch. Ing. 15 part[5] http://www.ent.ohio.edu/~ureli/stirling/[6] Chris Newton, Team Solaris, Final Design,Fall 2003. 6

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