The Thermo Acoustic Engine by Marvin McEntire


by Marvin McEntire

At the beginning of my time in the Navy in the Sixties, I was selected to be a sonar technician and learn electronics and the physics of sound. Until recently, I have spent my time with aerospace, the Air Force and NASA.

The Navy taught me some physics of sound for the sonar work. The Air Force upgraded my knowledge of electronics. NASA taught me the instrumentation of rockets. Along with that I received a bachelor degree in English and learned to write, though not well. No writer that I know is satisfied with his or her own writing.

With all of the technical excitement that I have experienced in my life, comparing the ground-shaking test of the Space Shuttle solid rocket motor in northern Utah where I worked, to the silent movement of a thermo acoustic engine recently, is very significant to me.

I used sound from the sonar system of a large Navy destroyer to hunt submarines. But this new thermo acoustic engine is the greatest marvel I have ever seen and feel it a privilege to have built three of them. They truly use an internal sound to cause heat to migrate in one direction within the sound tube. Instantaneous interruption of that heat migration is the key, which allows the device to be used as an engine rather than its other good use as a silent refrigerator.

Thermoacoustic experimenters have known for about ten years that as a stack (like the stainless wool) in a tube is heated at one end, it begins to sing because of the temperature gradient (hot to cold).

That sound has the effect of transporting the heat toward the open end of the tube (streaming). In our engine, heat is applied with the alcohol burner at the precise inner edge of the stack. The latent heat of the stack is transported toward the heat source and on through the air in the tube toward the piston of the power cylinder, leaving just a narrow band of heat on the stack. Excess heat is dissipated through the large copper plumbing part joining the sound and power tubes

As the piston closes in toward the sound tube, blowing air into it, the movement of that air runs temporary interference on the sound waves by (Doppler Effect). This action slows the effect of the heat streaming, causing the heated edge to temporarily widen, thus a fast pressure rise due to more heated area on the stainless wool.

Rising pressure has already begun pushing the piston back on its return stroke. Consequently, with increased pressure and wind not blowing in, the higher heat streaming is back, narrowing the band of heat on the edge of the stack, dropping pressure so the flywheel can carry the piston back in toward the sound tube again by inertia.

I had a kind scientist from Los Alamos try to explain this to me in his scientific terms. He totally lost me. Maybe I have totally lost you, but if you would like to dive into their explanations, look up thermoacoustics+Los Alamos on any search engine. They explain the mechanism of heat streaming. (The bucket brigade effect)

Technically, the World is truly on the cusp of such a great revolution in energy use and production, we may look back at previous centuries and call them "The Dirty Years".

Of course everyone's quality of life will improve with cleaner air and cheaper power. World leaders who are recognizing this new cleaner, higher standard of living are already making plans to let the poor bedraggled people have more government benefits to get them through their last miserable years.

After seeing first hand some of the many devices that will make life easier, my forecast is bright. See my website: Hybrid Engine Design at www.angelfire.com/ut2/texubaco/  There you may find links to some other websites where you will learn elementary thermo acoustic physics, Stirling engines, fusion and other energy subjects.

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