Testing of an integrated wood-fired cooking stove and thermo-acoustic engine-generator unit Ron Dennis Paul RileyProf Keith Pullen City UniversityUniversity of Nottingham City University

Introduction City University has been responsible mainly for stove development This includes development of stoves to test thermo-acoustic engines (TAE) developed by other members of the SCORE group and carrying out the testing The first example of this was testing of a Kees deBlock prototype in November This is thought to be the World first TAE/ wood stove combination to produce electricity This paper describes the testing of a follow-up prototype, Demo 3, produced by Nottingham University

Aims of SCORE Project Develop a wood-fired cooking stove for domestic use that: 1Produces 100W of electricity for up to 4 hours per day 2Boils 3l of water in 15 minutes 3Reaches 50% of full power in 20 minutes 4Reduces wood consumption by 20%, compared to traditional stoves, to less than 1.4kg/hr 5Has low emissions

Design of TAE Heat Exchanger units Radiator Convolutions – Cold Side Convolutions – Hot Side

Assembly of TAE Unit – Cold Side Mesh Pack 185 x 180 x 15mm thick Ceramic cement seal around mesh Convolutions sealed at this end, open other end

Assembly of TAE – Hot Side Stainless steel duct Gas to cooking Gas from Combustion Chamber Convolutions sealed at each end with Ceramic Fibre Board

Stove Assembly Combustion chamber 12 x 20 x 20cm HHX duct WoodAir Hotplates

Testing Set-up Sliding Joint

Test Results Wood burn rate 2.0kg/hr; Moisture content 18%

Test Results

Summary of Test Results RESULTS TESTS 11 AND 12 Heat component Heat energy in kW% Consumption Input from wood at 2.0 kg/hr Losses in combustion chamber and ducts Heat content of gases into HHX 7.29 Heat content of gases at exit of HHX 3.48 Heat transferred in HHX Heat to cooling water 1.43 Power produced Heat at exit of hotplate 3.05 Heat transferred in hotplate Heat to cooking pots Heat to flue gas TOTAL 100

Conclusions 1The maximum power achieved at ambient pressure of 2.9W is considerably below the potential output 2Leakage accounts for a considerable loss. Slide 11 suggests eliminating leakage could increase power by a factor of x 3 3Another significant source of loss is likely to be in tight bends and rough internal joints in the pipe loops and this is being rectified 4Slide 13 suggests that power output could be further doubled by operating at 1 bar 5Cooking performance on this unit is inadequate. Analysis indicates the limiting factor is convection between the hot gas and inside of the hot-plate tubes. These are being replaced by aluminium heat sinks which are estimated to boil 3l of water in 27 minutes at an average gas temperature of 350 o C. Cooking can also be improved by placing the hot-plates in series rather than parallel