March 13, 2006—Air Squared’s new scroll expander is designed for expansion generators used to convert waste heat energy from the exhaust gases or liquid cooling systems of internal combustion engines, fuel cells, solar collectors and similar devices, the company says.
With an expansion ratio of 4.6:1 and displacement of 12 cc/rev., the patented scroll expander is rated up to 1 kW, based on a maximum inlet pressure of 13.5 bar/200 psig. A magnetic coupling eliminates any leakage path for the working fluid, allowing the scroll to be used with many different types of refrigerant gases. Oilless and lubricated models of the scroll allow design flexibility, with the lubricated version running at 80% efficiency and the oil-free version at 70%.
The rotary scroll design provides quiet, balanced, pulse-free operation with a noise level of just 50 dBa. The operating element of a scroll compressor is made up of two identical involutes which form right- and left-hand components.
One scroll is indexed or phased 180 degrees with respect to the other to allow the scrolls to mesh. This indexing creates crescent shaped gas pockets, bounded by the involutes and base plates of both scrolls.
In operation, one scroll remains fixed; the other is attached to an eccentric that drives a generator shaft. As the moving scroll orbits around the fixed scroll, the tiny pockets formed by the meshed scrolls at the center follow the spiral outward and enlarge in size. The expander inlet is at the center of the scrolls. The entering gas is trapped in two diametrically opposed gas pockets and expands as the pockets move toward the periphery, where the discharge port is located. No valves are needed, which reduces noise and improves the durability of the unit, says Air Squared.
Air Squared is a consulting firm specializing in air compressors, specifically scroll compressors, pumps and expanders. For more on the company, visit its Web site.
