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Designer's Corner
By Design News Staff -- Design News, March 3, 1997
High-efficiency furnace
In experiments, hot combustion gases entered the secondary heat exchanger at 121F and exhaust air exited the furnace at 70F.
At the heart of this patented system is a secondary heat exchanger, a rotating wheel made from twin spirals of 0.002-inch-thick stainless steel. Burners inject a stream of hot gases into a primary heat exchanger formed by fire tubes, which conduct the combustion products to a hot collector located above the wheel. As gases flow through the wheel, waterin the gas stream condenses withinthe wheel. A power venting system then collects and expels the products of combustion.
The furnace's centrifugal fan forces air across the primary heat exchanger, and also drives air into a baffle that forces the air through the wheel. This airstream evaporates water from the rotating wheel, and also collects heat captured by the wheel. Half the wheel always lies in the furnace's combustion zone, half in its primary airflow zone. Ambient air directed through a buffer or "neutral" zone between the combustion area and primary zone purges the wheel of combustion gases. In experiments, the wheel enabled a non-condensing conventional furnace with 100,000 BTU burner input and 79,000 BTU output to achieve efficiencies in the high 90% range.
Each secondary heat exchanger is made from high-chrome 0.002-inch-thick stainless steel. Two continuous spirals of stainless, one crimped, one flat, wrap about a piece of 13/8 inch ID tubing to form the wheel. They create 400 cells/sq-inch of wheel area. The wheel's driven surface consists of as many as five wraps of flat stainless. In one prototype system, the inventor drives the wheel with a small gearmotor and a elastomer-faced traction wheel.
To add strength to the wheel, grooves are cut into the cold side of the wound stainless, and flat steel pieces inserted. High-temperature epoxy bonds the steel in place.
Coating the stainless with such materials as platinum and palladium effectively makes it a catalytic converter, and produces very significant reductions in emissions of NOx and other pollutants. The technology is available for license.
W.B. Astle, Jr., Astle Corp., 146 Old Farm Rd., Leominster, MA 01453, 508-534-0979.
Nitinol valve
Replacing the electromagnetic coil in a pneumatic valve with a nickel-titanium shape memory alloy (nitinol) cuts valve cost 60%. Why? Compared to a solenoid valve, the nitinol valve consumes less power; has virtually no audio, electrical, or magnetic emissions; can modulate flow proportionally; requires loose manufacturing tolerances; has fewer parts, and is smaller in size. It is also lightweight and non-magnetic.
How does it work? A heat-activated shape memory alloy wire functions as the valve actuator. It contracts when electrical power is applied, relaxes when power is removed. A compression spring holds the seal against the seat when power is off. When power is applied, the nitinol wire heats up and pulls the seal off the seat, allowing air to flow.
Curtis Coffee, Advanced Control Technologies, Inc., 8076 Woodland Dr., Indianapolis, IN 46278, 317-337-0100.
Locking key
Key rollover is a common problem in the high-frequency, high-inertia, stop/start applications of clutches/brakes. As key and keyway wear, the key eventually rolls over in the keyway channel, losing all torque transmission. Damage can require disassembly and replacement of shafts, bearings, and seals.
A patented locking system secures the clutch/brake output shaft in blind bores like those found in gear reducers. Screwing the locking bar into the shaft forces the key up a ramp to prevent backlash. The system is an integral feature of Air Champ® flange-mounted clutch/brakes.
Dave Amundson, Horton Industrial Products, Inc., 1170 15th Ave. S.E., Minneapolis, MN 55414, 612-378-6415.
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