Presentation on theme: "Score Stove Generating electricity in developing countries using thermo-acoustics powered by burning wood Bonjour Paris, Bonjour Madame et messieurs."— Presentation transcript:
1 Score StoveGenerating electricity in developing countries using thermo-acoustics powered by burning woodBonjour Paris, Bonjour Madame et messieurs.My name is Paul Riley Project Director for Score and work at the University of Nottingham, in the UK.Am pleased to be invited to give this paper to the Acoustics OK conference and share our experiences with such an accomplished audience.Paul H. Riley, Score Project Director Professor Mark JohnsonPartners: Universities of Manchester, QMUL, City London and the charity Practical Action.
2 Background In Poor Rural areas Score >2 Billion are without electricity and cook on an open fire Smoke is a real hazardScoreStove cooks, generates electricity and cooling€3M project3 years research2 years exploitationLarge volume manufacture after 2012Extended partnerships
3 Technical Challenges Cost Weight Power output Fuel Low cost is the main driverTarget = €30 per household delivered to capital city of country2 billion units at €3060 million units at €90WeightIn many areas hand carrying is the only optionTarget = 10 – 20 kgPower outputElectrical = 100We (from battery)Cooking = 1.6kWth full power 0.75 kW for simmeringFuelConsumption < 0.3 g/s (<2 logs per hour)Material initially wood. Looking at Dung and other bio-mass, LPG.
4 Options Internal combustion engine with bio-gasifier Expensive, high maintenance requirementThermo-piles with wood burning stoveExpensive, low efficiency, lack of robustnessBio-Fuel fed Stirling engineExpensive, maintenance may be an issueThermo-acoustic engineTravelling waveCurrently expensive, but options for cost reductionUnits have been developed in power rangeReasonable efficiencyStanding wavePotentially the lowest costPredicted efficiencies just acceptable.Lack of experimental data at the output power required.NB: Only low/ zero CO2 options are shown
5 Standing Wave TAE Fractional wavelength design Combustor Frequency determined by alternator, not duct length.Complex acoustic - LA matchingCombustorInitially wood burningHigh efficiencyLow emissionsWaste heat used for cookingHot Heat Exchanger (HHX) (1)500OC gas temperatureStackHeats and cools gas packetsProvides time lag at required frequency, eliminates displacer.Ambient Heat Exchanger (AHX) (2)80OC gas temperatureAmbient heat exchanger Water cooled, also used for cooking.
6 Power flow (pre-optimisation) Heat to cooking Hob = 1.6kWthHeat to Water (AHX) = 1.7kWthTAE heat input (HHX) = 2kWthAcoustic power = 300WaAlternator Loss = 150WthSystem losses = 0.8kWthStorage Battery loss = 50WthCombustion = 4.4kWthElectrical Output to devices = 100WeLaptop and light orTV, Radio and lightsCharge mobile phones
7 Optimisation of the design A non-trivial, multi- variable problem
8 Optimisation: Cost Paradox Low material content is key Smoke free stove Nepalese manufacture ~ £25Low labour costsExcludes profit and transportGas stove (LPG) in UK£14.99 includes:Local tax and transportProfit (manufacturer and retailer)Low material content is keyThin sectionsStrengthened by geometric shapeLeads to low weight design
9 Optimising the TA Geometry (Standing wave model) xhxcxLcbHot terminationHot h.e.StackLhbLhCold h.e.Cold ‘outlet’Hot bounceCold matchingzoneLc
10 Sensitivities in the TA model (for single set of base conditions) Pressure (at fixed drive ratio)FrequencyStack LengthStack Passage dia.
11 Optimisation: Cost Issues Optimisation examplesIncreased frequencyAlternator efficiencyThermo-acoustic efficiencyIncreased pressureMass of containmentPower output per volumeTAE topologyStanding wave less complex, (Hence lighter for given efficiency)Travelling wave more efficient (Hence less weight per Watt)Working gasAir is cheapestHelium allows higher frequency (hence lighter alternator and TAE)
12 Optimisation: Alternator Operation at higher frequency increases cost of electronics but dramatically reduces alternator cost.However, noise then becomes an issue.
13 Demo#0 DeltaEC Simulation -based on the commercially available parts Segments in DeltaEC simulationBounce volume : m x 0.175m square, length=8cmHot heat exchange: HX, Porosity=0.4, Length=10 cmStack: Honeycomb, Pore D=3.2 mm, L=8 cmAmbient heat exchange: AHX, Porosity=0.4, Length=2 cmTransition Cone, S1=0.01 m2 S2= m2, L=1.5 cmLoudspeakerDiaphragm D: 15 cm; E-Resistance R: 5.5 ohms;BL: T-m; Force factor K: N/mMechanical resistance: 3.07N-s/mThis “design” is based on the commercially available parts: metal honeycomb as stack, car radiator as CHX, loudspeaker as alternator.Air, Pm= 1 bar, f = 50 Hz612345Distribution of Re[p] and Im[U]Distribution of Edot and Hdot
14 Optimisation Issues: -Cross sectional area & Bounce volume The volumetric velocity lU1l at the diaphragm of LA is decided by its stroke and the area. To transport sufficient acoustic power to the LA, a high pressure amplitude lp1l is required. Therefore, a smaller (but still big enough for HHXs) cross sectional area if required for the engine. As shown in the left figure: 0.01 m2 is chosen for this Demo #0.In the resonator, the acoustic field is approximately a standing wave. The local acoustic impedance of stack (depends on the location) plays an important role in maximizing the energy conversion in the stack. The local impedance of the stack can be determined by the length of the bounce volume. 8 cm is given by the simulation.
15 Early Demonstrator#0 Off the shelf parts Ambient pressure Powered by Propane6kW heat inTubular Hot ExchangerStack3.2mm hole size100mm square120mm longCar radiator ambient exchangerLinear Alternator17cm loudspeaker with additional mass added
16 Demo#0 results Self resonant Cold Burner on Mass increasing to 500g Speaker electrically driven to characterise T/A ductMechanical Q measuredThiele Qms well definedEasy to measureSeparates T/A effect from rig and alternator lossesHHXHeat transfer mainly through radiationSignificant loss through stack from radiationLarge temperature profilePerceived noise increases above 40Hz, even when back of speaker enclosed.Mechanical issuesHHX crackingVibrationQms> 9Qms= 4.7Qms= 7.61Qms= 4.8Qms= 3.58Qms= 4.11Self resonant(power out condition)ColdBurner onMass increasing to 500g
17 AcknowledgementsThe Score project is funded by EPSRC, the UK Engineering and Physical Research Council.Thanks toProfessor Chris Lawn, Dr Catherine Gardner QMUL, Dr Zhibin Yu and Dr Ron Dennis for permission to use their slides, Dr. Scott Backhaus of LANL and Dr Zhibin Yu at Manchester for their support with the DeltaEC calculations, my Nottingham colleagues Professor Mark Johnson, Mr. Ian Dwyer and Mr. Chitta Saha and the Score partners, Dr Artur Jaworski University of Manchester, Dr Keith Pullen City University London, and Dr Teo Sanchez from Practical Action.
18 References  www.score.uk.com  The World Bank 2005, “Rural energy and development for two billion people: Meeting the challenge for rural energy and development (September)”