AUC researchers devised a thermoacoustic heat engine to convert thermal energy into electricity

Addressing the issue of insufficiency of energy resources in the world and in Egypt in particular, a press conference was held today at The American University in Cairo, where a team of researchers at The American University in Cairo announced the development of a thermoacoustic heat engine to convert thermal energy into acoustic, or sound, energy, to eventually produce electricity. The team includes Ehab Abdel Rahman, associate dean of graduate studies and research at the School of Sciences and Engineering and director of the Yousef Jameel Science and Technology Research Center, along with Hosny Omar, professor of physics; Karim Addas, assistant professor of physics; Abdel Maged Ibrahim and Ahmed Abdel Rahman, two postdoctoral fellows and 10 graduate students. “Half of the increase in global energy use goes to generating electricity to satisfy rising domestic needs of lighting, communication, refrigeration and water supply,” said Abdel Rahman. “The increase in energy demand will be met with declining fossil fuel production, which makes the need for controlling the rising demand for fossil fuels, for enhancing geographic and fuel-supply diversity, and for alleviating climate-destabilizing emissions more critical than ever.” 

Thermoacoustic phenomenon was first discovered in the 19^th century by glass blowers, who found that sound could be generated by heating glass tube at one end. It was until 1985 when John Wheatley and G.W Swift designed and built the first thermoacoustic device. There are two types of thermoacoustic devices: a heat engine (sometimes called prime mover), where heat is converted to acoustic energy, and a heat pump or cooler, where sound can pump heat up a temperature gradient.

Because they have few or no moving parts, they require little maintenance, and are highly reliable and inexpensive to produce. “These features make them attractive for applications in remote or portable power generation,” said Abdel-Rahman, noting that in many countries such as Egypt, there is a need to generate electricity in remote areas that are not supplied by the main grid. “If this need can be met with a form of renewable energy, such as wind and solar energy, this would reduce the need for fossil fuels, and ensure a regular and reliable supply of electricity.”

Typically, Abdel-Rahman added, generators are used to provide electricity during power outages, especially on farms; and in off-grid areas, where there is no built-in power source available, such as on construction sites and camping trips. Conventional generators require gasoline, or fossil fuel, which is an expensive, non-renewable source of energy, and produces harmful gas emissions, contributing to air pollution and climate change. The thermoacoustic heat engine produced by AUC researchers, however, operates in an environmentally friendly medium using air or noble gas.

One of the biggest challenges in today’s modern world is to generate energy at a competitive cost, which is what the thermoacoustic heat engine aims to do. “The engine uses simple materials that have no special requirements (glass for the solar concentrator and iron tubes for the thermoacoustic heat engine), are commercially available in large quantities and are relatively cheap,” explained Abdel-Rahman. “The main constraint in advancing renewable energy over the last few decades has been cost effectiveness. Average costs of energy produced by our engine are much cheaper than other similar technologies. ”

Additionally, the engine performs at the highest efficiency rate available. According to thermodynamics laws, there is a limit on the thermal efficiency of all heat engines. “Even the best engine won’t be able to convert 100 percent of its input heat,” said Abdel-Rahman, adding that the limiting factors are the temperature at which the heat enters the engine and the temperature of the environment into which the engine exhausts its waste heat. This limiting value is called the Carnot cycle efficiency. “No heat-converting device or engine, no matter what its construction is, can exceed this efficiency; it represents the maximum efficiency value for any engine cycle,” said Abdel Rahman. “The thermoacoustic engine can perform up to the full Carnot efficiency.”

The innovative medium can run on solar heat, or can be used in combined heat and power applications, which convert industrial waste heat into electrical energy. Because it has no moving parts, the engine has a long life span and can operate on higher temperatures, thus allowing the Carnot efficiency to be higher. “This would represent a national solution to Egypt’s energy problem” said Abdel-Rahman, emphasizing the need to move from extensive use of fossil fuels to renewable energy sources. “Fossil fuels take millions of years to form, and reserves are being depleted at a much faster rate than new ones are being made, not to mention the harmful emission of toxic gasses into the atmosphere as a result of burning fossil fuels,” he said. “It is imperative to move toward renewable energy sources in order to help meet growing energy needs and to counter global environmental challenges.