Testing of an integrated wood-fired cooking stove and thermo-acoustic engine-generator unit

Ron Dennis Paul Riley Prof Keith Pullen

City University University 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 2010. 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:

1 Produces 100W of electricity for up to 4 hours per day

2 Boils 3l of water in 15 minutes

3 Reaches 50% of full power in 20 minutes

4 Reduces wood consumption by 20%, compared to traditional stoves, to less than 1.4kg/hr

5 Has 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 chamber12 x 20 x 20cm

HHX duct

Wood Air

Hotplates

Testing Set-up

SlidingJoint

Test Results

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

Test Results

Test Results

Test Results

Test Results

Summary of Test Results

    

 

Heat componentHeat component Heat energy in kW % Consumption

Input from wood at 2.0 kg/hrInput from wood at 2.0 kg/hr 8.6 100

      

Losses in combustion chamber and ductsLosses in combustion chamber and ducts 1.29 15

Heat content of gases into HHXHeat content of gases into HHX 7.29  

Heat content of gases at exit of HHXHeat content of gases at exit of HHX 3.48  

Heat transferred in HHXHeat transferred in HHX 3.81 44.4

Heat to cooling waterHeat to cooling water 1.43  

Power producedPower produced 0.0029 0.034

Heat at exit of hotplateHeat at exit of hotplate 3.05  

Heat transferred in hotplateHeat transferred in hotplate 0.43 5.0

Heat to cooking potsHeat to cooking pots 0.24 2.80

Heat to flue gasHeat to flue gas 3.05 35.6

TOTALTOTAL   100

Conclusions

1 The maximum power achieved at ambient pressure of 2.9W is considerably below the potential output

2 Leakage accounts for a considerable loss. Slide 11 suggests eliminating leakage could increase power by a factor of x 3

3 Another significant source of loss is likely to be in tight bends and rough internal joints in the pipe loops and this is being rectified

4 Slide 13 suggests that power output could be further doubled by operating at 1 bar

5 Cooking 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 350o C. Cooking can also be improved by placing the hot-plates in series rather than parallel