Date: Dec 15, 2009 Author: Joan M. Zimmermann Source: MDA (
click here to go to the source)
by Joan M. Zimmermann/jzimmermann@nttc.edu
A small device that uses sound to directly move heat could make refrigeration less costly and far more efficient, support cryogenic cooling applications for sensors, and improve the safety of MRI units. The technology, developed by CryoWave Advanced Technology, Inc., uses no moving parts and relies on a principle known as thermoacoustic cooling—a notion that dates back to 1887, when Lord Rayleigh suggested it might be possible to pump heat with sound.
CryoWave's work in thermoacoustic cooling has been aided by Phase I and II SBIR contracts from MDA, which funded the company's work to develop recuperative cryocoolers for surveillance and interceptor systems.
CryoWave's MDA-funded work on pressure-expansion and pressure-controlling technology—which the company has termed thermoacoustic expansion technology (TAET)—has taken the form of a miniature cryocooler that employs high-energy acoustic waves, generated with no moving parts, to produce efficient cooling over a wide range of temperatures with different gases.
Pros of design
The company developed a miniature thermoacoustic expander (MTAE) for MDA applications in infrared surveillance and interceptor systems. In contrast to Joule-Thompson expanders, which work over narrow temperature ranges, the MTAE was designed to cool efficiently over a wide range of temperatures. CryoWave's expansion device uses pressurized inflow gas to produce high-energy acoustic waves, converting energy to heat that is expelled from the system (hence, cooling).
In part due to the lack of moving parts, CryoWave's MTAE is also more efficient than a Joule-Thompson cooler, and competitive to its cousin, the Turbo-Brayton cooler, and thus offers high reliability, greater simplicity of its structure, and lower manufacturing costs, according to CryoWave President Dr. Zhimin Hu, who invented this technology.
The technology also can be used in energy-recovery processes, to "recycle" energy that might otherwise be wasted in the heating and cooling cycles of engines and refrigerators. MDA has committed to a Phase III project with CryoWave, pending its finishing touches on a prototype device.
In the past, conventional cooling technologies have relied on complex machinery and ozone-depleting coolants. Although coolants such as Freon have since been replaced by chemicals friendlier to the environment, refrigeration mechanisms still tend to be big and bulky, relying on inefficient expansion devices, especially when used in industrial-scale settings. In space applications, more sophisticated cryocooling schemes have been designed, but they can be limited by either prohibitive cost or narrow applications.
Applications aplenty:
Many potential thermoacoustic applications have been recognized since Lord Rayleigh's work in the 1880s; thermoacoustic hot air engines and refrigerators have long been objects of theoretical inquiry and engineering curiosity. In more recent decades, researchers also have targeted niche applications in small- and medium-scale cryocooling, such as for infrared sensors on satellites. When developed to a larger scale, the technology can become vastly more practical for air-conditioning in homes, commercial buildings, vehicles, and other cooling and heating applications.
CryoWave researchers also foresee grand new applications for thermoacoustic expansion technologies. While the company is perfecting its prototype, its leaders are envisioning a full line of products, such as thermoacoustic expanders, pressure regulators, coolers, and expansion valves which enable energy savings, increase production efficiencies and reduce costs for a variety of industrial processes. The large-scale prototype of thermoacoustic expansion devices developed for the oil and gas industry is also available in demonstration.
CryoWave also is poised to provide technical services for customers to identify the feasibility of TAET in their processes, revamp their systems, and assess the economic return of adapting the new technology, in order to extract its greatest potential. There are many applications for thermoacoustic expansion technology including cooling for infrared sensors in space and military missions, cryogenic refrigeration in general, and for industrial gas liquefaction.
In the medical field, TAET devices could some day be used to cool MRI magnets and integrated lab-on-chip bioprocessing systems. For open MRI units, the strong electrical fields are produced by magnets that are made superconductive through the use of liquid helium as well as immersion in liquid nitrogen. This design also carries a hazard: if superconductivity is lost, energy is released in the form of heat, which quickly turns liquid back into gas, displacing oxygen and causing burns. Thus MRI units must be accompanied by a complex safety system and a continuous monitoring scheme.
Supercooling MRI magnets with a thermoacoustic system would eliminate this hazard. TAET also has the potential to revolutionize offshore gas productions and conversion, where it could extend the capabilities of platform-based petroleum-processing from shallow to deep-water operations. Without complex moving parts, small, streamlined thermoacoustic expansion valves could better withstand deep-water pressures, regulate production pressure, and cool down low-dew-point components in natural gas to liquid at the subsea wellhead or platform, to reduce dew point and dehydrate gas stream before it is delivered through offshore pipelines. TAET could also be used to remove water from gas and oil that is procured from ocean sources, and to efficiently produce liquid hydrogen for fuel cells.
