performance evaluation of thermoacoustic engine using different gases

Performance evaluation of thermoacoustic engine using different gases

A.H. Ibrahim, M. M. Emam,Hosny Omar, K. Addas, E. Abdel-Rahman

PERFORMANCE EVALUATION OF THERMOACOUSTIC ENGINE USING

DIFFERENT GASES

A.H. Ibrahim1*, M. M. Emam1, Hosny Omar1, Karim Addas1 and Ehab Abdel-Rahman1,2+

1The American University in Cairo, School of Sciences and Engineering, Department ofPhysics, 11835 New Cairo, Egypt.

2The American University in Cairo, School of Sciences and Engineering, Youssef JameelScience and Technology Research Center (YJSTRC), 11835 New Cairo, Egypt.

*On Leave from Mechanical Power Department, Faculty of Engineering, Cairo University,Giza, Egypt.



Abstract

- 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.



Introduction

- 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



Objectives

- 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



145 mm295 mm

595 mm

930 mm

Three-channel DC amplifier

Mic # 1 Mic # 2 Mic # 3

Mic # 4

Three-channel DC amplifierData-acquisition

TC1 TC2 TC3 TC5TC4

Computer

Voltage divider

AC power supply

Cold-side heat

exchanger

TH Tc

Stack

Apparatus



ResonatorCooling waterElectric heater Input

Pressure sensor Oscilloscope

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

Apparatus



Apparatus



- 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)

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)

Analysis



Analysis



481K

4.24 W

Results



• 80% air – 20% He• 400 cpsi stack

Results



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



Results



ResultsResults 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)



ResultsTransient operation*600 cpsi



Results



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.



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

performance evaluation of thermoacoustic engine using different gases

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