C. M. Johnson, P. H. Riley and C. R. Saha

1. Investigation of thermo-acoustically Driven Linear Alternator C. M. Johnson, P. H. Riley and C. R. Saha Introduction Thermo-acoustic impedance ; Equivalent input impedance; Thermo-acoustic engine converts thermal energy into sound energy by transferring heat between the working media (gas) and a porous solid structure stack. This sound energy could be used to drive a linear alternator to generate electricity and also power a thermo-acoustic refrigerator. Where, • This paper presents a standing wave thermo-acoustic prototype which has been built and tested with the linear alternator. • A simplified theoretical model of a linear alternator driven by a standing wave thermo-acoustic engine is introduced. • The model is validated against experimental results obtained from a prototype standing wave thermo-acoustic engine. Vductis the total volume of the thermo-acoustic duct, Sc is the area of generator, VR is the volume of the regenerator section and α is the propagation constant Mechanical Quality factor ; Where, Thermo-acoustic linear Alternator The device consists of five basic elements such as a regenerator (stack), hot (HHX) and cold heat exchanger (AHX) facing both ends of the stack, stove fitted on the top of the hot tube and the alpine SPR-17S electromagnetic loudspeaker acts as a linear alternator connected at the back end of the AHX. An air cooled car radiator was used for AHX and an LPG burner was used for heat input into the engine. Model verification • The impedance response of the alternator was measured with and without heat to understand the thermo-acoustic strength. • Thermo-acoustic effect increases the input impedance and shifts the resonant frequency downwards. • The measured mechanical quality factor (Qms) for hot and cold cases are 4 and 3.5 . • The measured results agrees well with the theoretical model. Conclusions • A simple theoretical model of thermo-acoustically driven linear alternator has been developed and verified with real device. • Measured results shows that significant mechanical loss present in the system which prevent the self-oscillation of the system. Tested prototype of standing wave thermo-acoustic electromagnetic generator Electrical circuit model of the thermo-acoustic electromagnetic generator • The thermo-acoustic generator consists of electrical, mechanical and acoustic components. It is easier to put the acoustic and mechanical components into a single electrical circuits using lumped electrical components. • Electromagnetic Linear Alternator can be represented as coil internal resistance (R0), coil inductance (L0) associated with source voltage (V) and the load resistance (RL). • Acoustic components can be represented by an equivalent impedance (ZTA ) and force source (FTA ) and mechanical components can be represented by a second order mass (m), damper (Rm) and spring constant (1/k) model. Measured hot and cold impedance response of Alternator with duct Force on voice coil; Generated Voltage; Where, B is the constant flux density in the coil, l is the effective length of the coil, u is the relative velocity between magnet and coil. Measured and calculated results for hot Case Measured and calculated results for cold Case Acknowledgement The Score project www.score.uk.com is funded by EPSRC, the UK Engineering and Physical Research Council. Thanks to the Score partners, Universities of Manchester, QMUL, City London and the charity Practical Action. Equivalent electrical circuit of the thermo-acoustic electromagnetic generator