book_cover_big.gifOf all forms of energy that of electricity is perhaps the most utile. One reason is the ease of transportation through a relative simple and vast infrastructure (power grid). Burning fossil fuels generates a large portion of the world’s electrical power. Heat applied in the boilers of power plants is used to generate steam and the steam drives subsequently turbines and the actual generator. The whole of this approach is particular geared towards mass volume electricity production. A typical size of a power plant these days is 2000 MW.

However, there are situations where it is beneficial to work at a much smaller scale to convert heat in electricity. For instance, the cooling of powerful processor chips in a computer. The microprocessor can dissipate up to and sometimes even more than 100 Watts of heat. The idea is now to turn that waste heat into electricity for re-use. There are several ways that that can be done for example through the use of Peltier[1] elements. But here I would like to focus on a method that is researched at the university of Utah. Professor Orest Symko studies methods to convert (waste) heat into electricity through an intermediate step namely through the generation of …… sound.

For this to work there are needed two types of devices. The first one is called a thermo-acoustic device. This device transforms heat into sound. A simple version is a tube in which there is a kind of a sieve or metal screen that can be heated by a flame or other heat sources such as the microprocessor chip. By air expansion in contact with hot parts and contractions when air comes in contact with cold parts a sound is generated in the pipe in a similar fashion as it is done in a flute or an organ pipe. Quite intense sound levels of 120 dB[2] or more can be generated in relatively small devices (dimensions a few cm’s). Once sound (basically pressure variations) is generated, it can be converted by an piezo-electric device[3]  in electricity. The situation has some similarity with that of the heat engines in power plants described above,  where heat is converted into steam under pressure and then used to generate electricity.

[1] A Peltier element is a device that upon current passage will cool at one location and heat at the other location.[2] Sound intensity of a rock and roll concert or a plane at 100 m distance.[3] A material that has piezo-electrical properties converts mechanical pressure variations in electrical energy.