Abstract: A sound level reducing apparatus and method for reducing the outdoor sound level produced by a high efficiency gas furnace. The apparatus comprising a muffler having an internal length determined by an identified target pure tone frequency producing an undesirable sound level. The internal length may be optimized to reduce the sound level across a range of operational frequencies.

Abstract: A sound level reducing apparatus and method for reducing the outdoor sound level produced by a high efficiency gas furnace. The apparatus comprising a muffler having an internal length determined by an identified target pure tone frequency producing an undesirable sound level. The internal length may be optimized to reduce the sound level across a range of operational frequencies.

Abstract: Axial flow fan propellers are provided with a roughened portion along the trailing edge of the fan blades on the pressure side of the blade to minimize tonal acoustic emissions generated by laminar boundary layer vortex shedding. The roughened portion may be provided by trip surfaces formed in the blades, by strips of abrasive material adhered to the blades along the trailing edges, respectively, by parallel or cross-hatched serrations in the blades or by upturned or offset trailing edges of the blades. The height of the roughened portion should be about equal to the boundary layer thickness of air flowing over the blade surfaces during operation of the fan. The fan propellers are particularly advantageous in heat exchanger applications, such as residential air conditioning system condenser units.

Abstract: A device is provided for dampening compressor-induced vibration in an air conditioning system of the type having an indoor unit, an outdoor unit and a refrigerant conduit therebetween. The outdoor unit includes a compressor that is operable to circulate a vapor compression refrigerant through the conduit between the indoor and outdoor units. The device is comprised of a support member containing a section of refrigerant line. The support member is located beneath the outdoor unit and the refrigerant line section is interposed in a portion of the refrigerant conduit between said compressor and said indoor unit, such that the refrigerant flowing between the indoor unit and the compressor is routed through the line section in the outdoor unit support member.

Abstract: Axial flow fan propellers are provided with a roughened portion along the trailing edge of the fan blades on the pressure side of the blade to minimize tonal acoustic emissions generated by laminar boundary layer vortex shedding. The roughened portion may be provided by trip surfaces formed in the blades, by strips of abrasive material adhered to the blades along the trailing edges, respectively, by parallel or cross-hatched serrations in the blades or by upturned or offset trailing edges of the blades. The height of the roughened portion should be about equal to the boundary layer thickness of air flowing over the blade surfaces during operation of the fan. The fan propellers are particularly advantageous in heat exchanger applications, such as residential air conditioning system condenser units.

Abstract: Axial flow fan propellers are provided with a roughened portion along the trailing edge of the fan blades on the pressure side of the blade to minimize tonal acoustic emissions generated by laminar boundary layer vortex shedding. The roughened portion may be provided by trip surfaces formed in the blades, by strips of abrasive material adhered to the blades along the trailing edges, respectively, by parallel or cross-hatched serrations in the blades or by upturned or offset trailing edges of the blades. The height of the roughened portion should be about equal to the boundary layer thickness of air flowing over the blade surfaces during operation of the fan. The fan propellers are particularly advantageous in heat exchanger applications, such as residential air conditioning system condenser units.

Abstract: The leading edge of the jet engine nacelle is provided with structure to prevent the formation of ice particles at the inlet of the jet engine. The nacelle is split into leading and trailing chambers and there is a partition separating the chambers, the leading one of which includes the anti-icing apparatus. The leading chamber includes a double skin generally facing interiorly toward the jet engine and that double skin defines the nacelle therebetween which permits the passage of the hot gases which heat the outer skin from the inside thereof. Conduit means controllably pass hot exhaust gases from the jet engine to within the leading chamber from where they pass into a cell via a series of spaced apertures formed in the inner double skin. A series of spaced channels are formed between the inner and outer skins and connect the leading and trailing chambers.