PERFORMANCE EVALUATION OF THERMOACOUSTIC ENGINE USING DIFFERENT GASES

1. PERFORMANCE EVALUATION OF THERMOACOUSTIC ENGINE USING DIFFERENT GASES A.H. Ibrahim1*, M. M. Emam1, Hosny Omar1, Karim Addas1 and EhabAbdel-Rahman1,2+ 1The American University in Cairo, School of Sciences and Engineering, Department of Physics, 11835 New Cairo, Egypt. 2The American University in Cairo, School of Sciences and Engineering, Youssef Jameel Science and Technology Research Center (YJSTRC), 11835 New Cairo, Egypt. *On Leave from Mechanical Power Department, Faculty of Engineering, Cairo University, Giza, Egypt.

2. Thermoacoustic engines (TAE) are devices that convert heat into useful acoustic work. • TAE operate with pressurized mixture of gases. • Selection of TAE gas define its efficiency, dimensions, and operating conditions. • TAE acoustic work suffer losses in higher harmonics. • Hysteresis is a main characteristic of the TAE transient operation profile. Abstract

3. Thermoacoustic engines (TAE) advantages: • Environment-friendly • Simple device with few or no moving parts • Easy maintenance – low cost • Can exploit waste heat and/or solar energy • Suitable for linear-alternator power converters • TAE performance is characterized by: • Onset temperature difference • Pressure ratio • Power output • Conversion efficiency (first and second law based) • Frequency of the output wave Introduction

4. The study discusses • Factors for selection of a working gas • Harmonic dissertation in the output wave for different gases • Transient profiles and hysteresis loops for different gases Objectives

5. Apparatus

6. Apparatus Electric heater Input Cooling water Resonator Pressure sensor Oscilloscope

7. Apparatus • Mixtures of Air and Helium was used • Pressure is atmospheric • 3 different stack pore hydraulic diameters were used • 200 cell per in2 • 400 cell per in2 • 600 cell per in2

8. Apparatus

9. Analysis • Onset temperature was detected from a full engine cycle (startup – steady operation – shut down). • Power was calculated from 2 microphone method calculations. • Pressures at various points were analyzed into many harmonics by numerical fitting to the function: • * In our case, only the first 5 terms were considered (n = 0 to 4)

10. Analysis • Working gas should have: • high speed of sound  (power density speed of sound) • Low specific heat ratio  (causes lower Tonset) • Low Prandtl No. ()  (higher gas-stack thermal interactions) • suitable thermal conductivity(lower conduction losses ) (higher gas-stack thermal interactions) • Leak tight  (easy to seal)

11. Analysis

12. Results 481K 4.24 W

13. Results • 80% air – 20% He • 400 cpsi stack

14. Results • 80% air – 20% He • 400 cpsi stack

15. Results

16. Results

17. Results Results are in good agreement with those of (Swift 1992)* *G. W. Swift, analysis and performance of a large thermoacoustic engine, J. acous. Soc. Am.92(3):1551-63 (1992)

18. Results Transient operation *600 cpsi

19. Results

20. Results • The hysteresis loop gets narrower with the increase of Helium. • Suggested reason  • increase of thermal conductivity causes faster temperature uniformity. • Temperature uniformity causes properties to be the same during both startup and shutdown.

21. Summary • Gas selection is critical to the performance of a thermoacoustic engine . • Preferred gas properties cannot be achieved simultaneously. • Power output is related to the gas components. • Pressure of the first harmonic is related, only, to the fundamental pressure squared. • Hysteresis is present in thermoacoustic engines, and depends on gas thermal conductivity