Advisor: Steve Alexander
The goal of this project was to create a thermoacoustic engine in order to learn about the creation of these devices as well how they can be best optimized. These devices can be made from much more easily available parts than many engines, can run on a variety of heat sources and can be designed so that they make use of no moving parts, which would make them ideal for many applications, were more known about how to optimize the efficiency of these engines. It is out hope that this project adds to the understanding of the design and the applications of thermacoustic engines.
This engine makes use of the thermoacoustic effect in order to produce electricity. In essence, this device is made up of three parts, a heat source, a heat sink, and a resonant tube. The heat source is the copper end cap, which is where thermal energy is put into the device. The heat sink is a section of copper tubing that has been filled with aluminum mesh and has copper and aluminum fins attached to the outside. The mesh allows for a large amount of the air flowing past it to transfer heat into this section of pipe and then out of the device, via the fins.
When air is heated at the heat source, it flows towards the heat sink, where it is cooled. As the air cools, it flows back towards area it had just vacated, at the heat source. In many ways, this is very similar to the way that convection works, with air rising and then falling as it cools, simply in the horizontal direction instead. These oscillations occur extremely quickly and the vibrations of the air movement create a sound wave, which is captured by the resonant tube.
Once this device creates sound, it is fairly simple to harness the energy of the sound. By placing a speaker at the end of the resonance tube, the sound can be converted into electricity, essentially doing the reverse of what a speaker typically does. In addition, this device uses an input sound. A small speaker, which produces a small input sound at a controllable frequency, is placed in between the heat source and heat sink. Adjusting this frequency allows for the engine to be tuned to run as efficiently as possible.