Thermoacoustic devices have the potential to provide electricity from waste heat to more efficiently use energy resources and to provide new access to electricity for millions of persons around the world. The international SCORE (Stove for Cooking and Refrigeration) research team is studying, designing, testing, and disseminating a biomass cook stove that generates electricity using thermoacoustics. The device captures heat from a small cook stove, uses the thermoacoustic effect to transfer the energy to acoustical sound waves that are captured by a linear alternator and turned into electricity. This study highlights research to characterize and improve the efficiency of heat captured in the SCORE stove.
The SCORE stove prototype, named Demo2, had a measured loss of 45\% in the process of capturing heat from a biomass fire to create an acoustic wave (Riley and Saha, 2010). This research used commercially available Computational Fluid Dynamics software to characterize the physical phenomena occurring inside the Demo2 unit. The simulation model was comprised of all components used in a thermoacoustic device including heat exchangers and regenerator. The thermoacoustic effect itself was not simulated, however. The simulation first derived the steady state temperature and flow fields, given boundary conditions extrapolated from observed experimental data. Secondly, an acoustic wave was induced over the steady state temperature solution to observe the impact on heat transfer. Finally, a simulation was run to calculate pressure transmission loss due to geometry.
Simulations predicted heat capture and transfer from the biomass fire's exhaust gases to the working air inside the unit. The amount of heat captured was low and therefore it is recommended that design of the hot heat exchanger should be altered to boost heat transfer. Results indicate that during stove operation absent of acoustics, radiation is the dominant mode of transferring heat. Surfaces closest in space and parallel to receiving surfaces had the highest heat flux. Simulations modeling acoustics showed convection during all portions of the sound wave to be greater the mode of heat transfer. It is recommended that heat exchanger geometry should be altered to expand the hottest sections of temperature distribution over the hot heat exchanger to improve both radiation at startup and convection during acoustic operation. Conduction in the air should be neglected at all times. Transmission pressure loss simulations for the acoustic wave due to geometry exceed 25%.