Using a non-contact sealing technique, a new compressor from Parker-Hannifin Corp. could offer the right combination of mechanical efficiency, durability, and performance required for fuel cells, demanding needs.

The compressor, employed on a new fuel cell-based scooter, could be twice as efficient and twice as durable as competing technologies, while offering the pressure and flow needed for such applications. Parker Hannifin engineers say that it could serve as a cathode air compressor or as a hydrogen recirculation pump on all kinds of fuel cells, both in vehicles and stationary power applications.

"The main players in the fuel cell arena have one of our units and are evaluating it now," notes Steven Knight, business unit manager for fuel cell systems at Parker Hannifin .

The fluid power giant adds that its new compressor could also serve in life sciences, semiconductor processing, medical device, and vacuum pump applications, and for pond aeration systems at golf courses.

"There are about 17,000 golf courses in the United States, each with an average of eight or nine water hazards that would benefit from aeration," Knight says.
Big market, big problem

Ultimately, however, engineers from Parker Hannifin foresee fuel cells as the big market for the new device, which is known as the Parker Univane Compressor. Fuel cells, they say, have a unique set of needs, including low power, low maintenance, pressures up to about 10 psi, and flow rates up to 20 cfm in the applications the company is targeting.

"The big problem was that conventional compressors ate up a significant amount of the power made by the fuel cell," notes Tom Edwards. He is president and founder of DynEco Corp , who developed the concept that Parker Hannifin now uses. "It became apparent that there wasn't any technology around that would do exactly what was needed," Edwards adds.
Non-contact sealing

To cut the power losses, DynEco developed the original design concepts for the Univane and licensed them to Parker Hannifin, which is refining the design for production volume manufacturing.

The Univane is said to offer greater mechanical efficiency and durability because it employs a non-contact sealing concept. The key parts of the device are its rotor and a single vane, both of which are constrained rotational mechanisms with independent bearings.

In essence, the unit operates in a manner similar to most conventional vane compressors, with two key exceptions: the rotor incorporates only a single slot for a vane, and that vane does not contact the housing while the rotor is spinning. Instead, it leaves an extremely thin air gap—approximately 1/1,000th of an inch—between itself and the inner diameter of the housing.

During Univane operation, air enters through a port on one side of the unit and is compressed by the front side of the vane. The vane's rear side, meanwhile, draws gas into the housing. Discharge gas is then dumped out through a reed valve similar to those used on conventional compressors.

Edwards says the compressor is able to provide sealing without contact for two key reasons: its leakage path is long, and the air gap is exceptionally small. "Gas leakage varies as the cube of the gap, so it's very important that the gap be as small as possible," he explains.

"The gap is so tiny that it looks like the vane is actually touching the housing, but there really isn't any contact," Knight adds.

Engineers say the unit offers greater mechanical efficiency because there are no frictional forces to sap power. Similarly, wear on the parts is less, they say, because rubbing is non-existent.

An additional benefit is cleanliness. Because there is no rubbing, there is less debris downstream, the company says.

Edwards adds that engineering teams have run one unit non-stop for 16,000 hours without maintenance. In contrast, conventional vane-type compressors typically need maintenance at 5,000-hour intervals.

Similarly, power draw is reduced dramatically when compared to conventional vane-type compressors. The new unit is said to operate between 10-12 W/cfm at 1 psi, whereas conventional units draw more than double at 25W under the same conditions, Knight says.
Pressure and flow

Equally important, the Univane offers the precise combination of pressure and flow needed for fuel cell applications. Knight says it can provide pressures of up to 10 psi at flow rates ranging from 1-20 cfm. That, he says, places it in a niche between conventional regenerative blower-type compressors, which offer high flow and very low pressure (less than 2 psi), and conventional piston-type compressors, which offer high pressures (more than 200 psi) along with low flows.

"We needed a compressor that would fit right in that sweet spot," Knight notes.
On the road

Parker Hannifin has been working with Vectrix Corp. (see the Design News story ) on incorporating the compressor into a scooter, which uses the fuel cell to power its batteries during travel. Because the Univane offers greater mechanical efficiency than competing regenerative blowers and piston-type compressors, engineers dramatically reduced the size of the on-board fuel cell module.

"This compressor was developed with the fuel cell market in mind, with the idea of driving the power efficiency and cleanliness," Knight says.

To stand up to the inevitable corrosion associated with the hydrogen on board the fuel cells, engineers at Parker Hannifin have developed a version of the compressor that employs a carbon rotor and ceramic ball bearings. That compressor can serve in hydrogen recirculation, while a separate version with conventional steel ball bearings serves as a cathode air compressor.
Other applications

While the fuel cell market continues to emerge, however, the Parker Hannifin business unit has targeted non-fuel cell applications for the Univane. Those uses include vacuum pumps for semiconductor processing and life science applications, as well as pond aeration.

The company claims that the device could help lower the cost of aerating golf course ponds by reducing power requirements, and could provide air flow to more of the so-called "air stones" that aerate the ponds.

Parker Hannifin plans to officially roll out the compressor in about six months and has not yet announced its cost.

For now, executives hope the non-fuel-cell applications will launch the technology while Parker Hannifin awaits the emergence of the fuel cell market. "We're hoping to start building some sales volume prior to the emergence of the fuel cell market," Knight says. "That way, we can use economies of scale to make this specialized technology cost effective."
New stuff

The unit's inventor, Tom Edwards, notes that its non-contact sealing technology can dramatically reduce energy usage, particularly in applications that employ fuel cells. "With even the tiniest amount of friction, it's surprising how much more electrical power you can end up using," he adds. "Because we've eliminated the friction, the user gets the best of all worlds. The parts won't wear out the way normal parts do, and it's more energy efficient because the parts aren't rubbing."