Abstract: A method is provided for CO2 separation from a combined-cycle power plant with exhaust-gas recirculation and CO2 separation. The hot-gas flow is split into a recirculation flow and an exhaust-gas flow before the final turbine stage in the turbine. A first partial flow remains in the turbine and carries out expansion work in the conventional form, before its waste heat is dissipated, for example in a waste-heat boiler, and the gases are recirculated into the inlet flow of the gas turbine. A second partial flow is diverted before the final turbine stage, and emits its waste heat in an HRSG/heat exchanger, before CO2 is separated from the exhaust-gas flow at an increased pressure level.

Abstract: Among other things, there is shown embodiments of a feedgate for a paintball loader having vanes or paddles that permit supplying paintballs into the loader but limit or inhibit escape of paintballs from the loader through the supply hole. Embodiments can include a frame, which may be a single piece or multiple-piece structure, and an insert with flexible vanes or paddles. Embodiments can include a pivotable cap, and/or the insert can snap into the frame.

Abstract: A method is provided for operating a gas turbine in a power station in which limits of the operating concept, which provide limits for optimization of the power station operation in respect of efficiency, service life consumption, emissions and power provision to the grid system, are adapted during operation. In particular, temperature limits and compressor inlet guide vane position limits are varied as a function of the optimization aims. A gas turbine power station is also provided for carrying out the method.

Abstract: A run-of-the-river or ocean current turbine may comprise a hatch and a slanted block having protector ribs for directing water flow to a waterwheel. The hatch may be controlled by a plurality of Transgear™ gear assemblies for varying the amount of water flow to the waterwheel from extreme drought to flood conditions so that the waterwheel may turn at rated speeds and within a predetermined range. The Transgear gear assemblies may comprise an accumulator for accumulating a rough and a fine tuned waterwheel speed. The Transgear assemblies may comprise embodiments of power take-off switches for, for example, bi-directional or clockwise and counterclockwise waterwheel shaft rotation. The turbine may be aligned for top-feed, side-feed or bottom feed of water and may comprise a tail wing or first and second turbines facing in opposite directions to capture high and low tidal flow.

Abstract: The CWE Concepts are designed to extract the maximum possible wind energy passing through a given square footage area of influencing machine interface at given calculated velocities, to deliver that energy to two power take off shafts for end user's useful work (electrical power generation and other requirements). A multi-bucket “S” rotor, airfoils, baffles and cowling combined, utilize one hundred percent of that moving air volume most efficiently. Our strategies are to use smaller units, yielding more power than existing designs while being installed at much lower levels, urban friendly, less visible, nearly-enclosed rotating machinery, quieter, and safer for indigenous wildlife populations. We plan to market for commercial and residential customers, in turn providing HVAC and electrical power augmentation to utility companies—a reliable and robust addition to the national power grid. Our goals—reduce dependency on foreign oil and provide a clean alternative.

Abstract: A guide blade ring (1) arranged downstream of the fan in the bypass duct of a turbofan engine for untwisting the airflow generated by the fan includes guide stator vane support struts (3) integrated into the guide blade ring at regular intervals respectively in place of a guide stator vane, the guide stator vane support struts (3) having a larger thickness and chord length than the guide stator vanes (2). A flow channel (4), respectively defined between a suction side (7) of the guide stator vane support strut and a guide stator vane (2.1) adjacent thereto on the suction side, is expanded by a geometric modification of the guide stator vane (2.1) with respect to the remaining guide stator vanes (2) in accordance with the respective configuration of the guide stator vane support strut.

Abstract: A turbocharger having a turbine with a wastegate, and a compressor including a compressor housing, a compressor wheel, and a wastegate actuator. The turbine wheel includes blades defining an inlet. The compressor housing has an inlet wall leading to the inlet, and a shroud wall surrounding the blades. The actuator includes a base that is integral with the inlet wall, and an electric motor that is attached to the base. The shroud wall forms a first port that is in direct fluid communication with the actuator chamber, and the inlet wall forms a second port that is in direct fluid communication with the actuator chamber. Air from the first port to passes through the actuator housing and out the second port. This airflow convectively cools the working components of the actuator, while the connection of the motor to the inlet wall conductively cools the motor.

Abstract: An airflow shielding device is configured for being secured to fan and includes a first member, a second member, and a plurality of shielding pieces. The first member defines a first through opening. The second member defines a second through opening corresponding to the first through opening. The shielding pieces are rotatably secured between the first member and the second member and rotate between a closed position, where the shielding pieces cover the first through opening, and an open position, where the shielding pieces are located so that air can flow through the first and second through openings.

Abstract: An axial-flow turbine assembly that includes one or more features for enhancing the efficiency of the turbine's operation. In one embodiment, the turbine assembly includes a turbine rotor having blades that adjust their pitch angle in direct response to working fluid pressure on the blades themselves or other part(s) of the rotor. In other embodiments, the turbine assembly is deployable in an application, such as an oscillating water column system, in which the flow of working fluid varies over time, for example, as pressure driving the flow changes. In a first of these embodiments, the turbine assembly includes a valve that allows the pressure to build so that the flow is optimized for the turbine's operating parameters. In a second of these embodiments, one or more variable-admission nozzle and shutter assemblies are provided to control the flow through the turbine to optimize the flow relative to the turbine's operating parameters.

Abstract: A rotational axis multi-phased wind turbine power generating system is disclosed. A differential pressure is created by utilizing the prevailing wind, and air from the prevailing wind is directed into air blades for the creation of power. Optimally, the air blades directly utilize the prevailing wind in combination with the created differential pressure to create power. An adjustable air scoop, adjustable exit drag curtain or barrier, orienting systems, and air flow directing dampers are disclosed.

Abstract: An extraction unit for a steam turbine includes an end plate mounted downstream of a selected stage of a steam turbine, the end plate sealing the selected stage from the atmosphere, and an extraction pipe passing through the end plate for extracting steam from the selected stage.

Abstract: A compounded wind power generator includes a first tube, a second tube, a blocking member and an electricity-generating assembly. The first tube has a first end and a second end. The first end has an air inlet. The first tube forms a first air channel therein. The second tube is disposed in the first air channel of the first tube and forms a second air channel therein. The blocking member is connected between the first tube and the second tube and has a plurality of panels. Each of the panels has one end abutting against the second tube, and the end of each of the panels is capable of being disengaged from the second tube by wind. The electricity-generating assembly is disposed in the first air channel.

Abstract: A turbocharger system comprises a first relatively small turbocharger and a second relatively large turbocharger connected in series and an exhaust gas flow control valve. The exhaust control valve has an inlet port communicating with the exhaust gas flow upstream of the first turbine a first outlet port communicating with the exhaust flow downstream of said first turbine but upstream of said second turbine, and a second outlet port communicating with the exhaust flow downstream of said second turbine. The valve is operable to selectively permit or block flow through the first and second outlet ports.

Abstract: An energy conversion system, including a wave chamber, and a turbine wheel coupled to a shaft and fluidly coupled with the wave chamber. The energy conversion system may also include a first radial flow passage fluidly coupled with the wave chamber and the turbine wheel, and first vanes disposed at least partially in the first radial flow passage, each of the first vanes being compliantly mounted and pivotal between first and second positions, the first vanes being configured to allow a motive fluid to flow in a first radial direction through the first radial flow passage when the first vanes are in the first position, and the first vanes being configured to substantially prevent the motive fluid from flowing through the first radial flow passage in a second radial direction when the second vanes are in the second position.

Abstract: The present invention relates to a fresh gas system (1) for supplying an internal combustion engine (4) with fresh gas, in particular in a motor vehicle, having a charging device (8) for increasing the pressure of the fresh gas and having a swirl generator (12), which is arranged upstream of the charging device (8), for generating a swirl, which rotates about the main flow direction of the fresh gas, in the fresh gas, wherein the swirl generator (12) has guide blades (14) with adjustable angle of incidence. In order to be able to produce the fresh gas system (4) more cost-effectively, the swirl generator (12) has a flow guide body (13) on which the guide blades (14) are integrally formed and which, in order to adjust the angle of incidence of the guide blades (14), can be twisted with elastic deformation about the main flow direction starting from an undeformed initial position.

Abstract: The invention relates to an adjusting shaft arrangement (1) of a variable turbine geometry turbocharger or waste gate turbocharger having an adjusting shaft (2) which has a fastening section (3); having a lever (4) which is connected to the adjusting shaft (2) via the fastening section (3); having a sleeve (5) which is arranged on a base body (6) of the adjusting shaft (2); and having a seal (7) which is arranged in the region of the base body (6) between the sleeve (5) and the adjusting shaft (2); the main body (6) of the adjusting shaft (2) having a stepped outer contour; and the sleeve (5) having an inner contour with a stepped inner contour which complements the design of the base body (6).

Abstract: Provision of flow control arrangements which can be switched from high flow restriction to low flow restriction or vice versa are desirable. It is known to use switched vortex valves comprising a vortex chamber having a diverter portion which jets a through flow into either radial presentation to an outlet or tangential presentation with differential flow restrictions. Typically deflection is through cross flows presented from control ports as determined by mechanically actuated and controlled valves. Sensors are required to determine pressure differentials in order to actuate these moving part valves. By providing association between the control ports and an outlet path along with appropriate configuration and sizing of the flow regulators switching states can be provided through the cross flows presented via the flow regulators between the high and low through flow restriction. The flow regulators generally comprise orifice restrictors, diffusers/venturi arrangements or vortex throttles.

Abstract: A vertical-axis wind turbine for use with an electrical generator for producing power by converting the energy of wind currents into mechanical rotational energy which is then used to operate the electrical generator. In an embodiment, a rotor is responsive to wind currents by imparting rotation upon a central vertical shaft. Preferably, the rotor is designed with functional curved surfaces for efficient operation.

Abstract: Variable geometry turbine, in particular a gas turbine, comprising a housing (2, 22), a turbine rotor (4), a fluid inlet scroll (1) that surrounds the turbine rotor, a vaned nozzle interposed between the inlet scroll and the turbine rotor conceived to accelerate the flow of fluid, the nozzle comprising an axially adjustable ring (5, 25) conceived to vary the nozzle gap (3, 23) and having a wall (19) delimiting the nozzle gap, the wall having balance holes (6, 26, 26?) connecting the nozzle gap with a chamber (12) delimited by the housing and the ring, characterised in that the edges (16), formed by the holes with the surface (18) of the wall facing the nozzle gap, are rounded in the portion (17, 17?) located downstream the holes with respect to the fluid flow. Turbocharger and supercharged engine comprising the engine.

Abstract: A system and method provide a proactive mechanism to control pitching of the blades of a wind turbine to compensate for rotor imbalance during normal operation by pitching the blades individually or asymmetrically, based on turbulent wind gust measurements in front of the rotor, determined before it reaches the rotor blades.

Abstract: The present application provides a compressor for a gas turbine. The compressor may include a number of rotor wheels positioned about a compressor aft section having a low alloy material, a number of inlet guide vanes positioned about a compressor inlet section, and a wet compression system positioned about the compressor inlet section.

Abstract: To provide a turbofan jet engine for a supersonic aircraft, which enables a supersonic cruise with small additional drag due to engine installation while minimizing the jet noise at takeoff. In the turbofan jet engine, two fans, i.e., a front fan and an aft fan, are disposed, and an air inlet and an air outlet are provided on each of the front and aft fans, whereby at takeoff, air is introduced to each of the air inlets of the front and aft fans to drive the front and aft fans in parallel, and the air is then ejected from each of the outlets. On the other hand, during a supersonic cruise, an inlet of an aft fan duct is coupled to an outlet of a front fan duct, where external air is introduced only to an air inlet of the front fan duct and the air compressed through the front fan is fed to the aft fan duct and further compressed through the aft fan, and ejected from a nozzle, so that the front and aft fans are driven in series.

Abstract: A gas turbine includes a compressor, a turbine downstream of the compressor having stators, and a rotor connecting the compressor to the turbine. The rotor includes rotor cavities. A supply plenum containing a process by-product gas and a control valve is connected to at least one of the rotor cavities to supply the process by-product gas to at least one of the rotor cavities. A process for operating a gas turbine having a compressor and a turbine includes connecting the compressor to the turbine by a rotor, creating cavities in the rotor, and injecting a process by-product gas into at least one of the cavities. The process further includes regulating the flow of the process by-product gas into at least one of the cavities according to a pre-programmed parameter.

Abstract: The present invention broadly comprises a blade for a torque converter stator including a first blade segment connected to inner and outer circumferential sections of the stator and a second blade segment, separately formed from the first blade segment, and connected to the circumferential sections. In some aspects, the blade segments are: in contact along edges, overlapped, circumferentially misaligned, at least partially folded, stamped, or cast. Configurations of the blade segments can be selected to modify performance characteristics of the stator such as torque ratio, efficiency, and capacity. In some aspects, the blade segments are in a circumferential alignment, and the stator includes an alignment element operatively arranged to control the circumferential alignment, for example, in response to pressure from fluid in the stator upon the blade. In some aspects, the stator includes axial halves, separately formed and fixedly connected and the blade segments are connected to respective halves.

Abstract: A check valve of the flapper type structured for use in a self-primer pump is structured for attachment to the pump casing in a manner that facilitates servicing of the check valve, and includes securement means that are positioned external to the casing and a flapper that is located through an opening of the casing in a manner that enables the servicing of the valve without dropping the flapper or the hardware into the interior of the pump.

Abstract: A vertical axis wind turbine system includes a vertical shaft rotatably mounted about a vertical axis and an upper platen coupled to the vertical shaft. Vanes are coupled to the vertical shaft and extend downward from the upper platen. Each vane has a concave face and an opposing convex face. A lower platen is coupled to the vertical shaft and to each vane. The lower platen has an opening formed therein proximate to the concave face of each vane. A plenum is disposed below the vertical axis wind turbine and is rotatably mounted about the shaft for rotation about the vertical axis. The plenum includes a top portion disposed proximate to the lower platen and has an outlet port therein. The outlet port is in fluid communication with at least one of the lower platen openings. A plenum passage provides fluid communication between a plenum inlet and the outlet port.

Abstract: A turbine having an inflow housing is provided. The turbine includes an inlet for an inflowing working fluid, wherein the inlet can be closed by a quick closing valve, a plurality of control valves and at least two nozzle groups. The flow of the working fluid is controllable by the inlet into the nozzle groups via the control valves. Furthermore, the inlet can be connected via an inlet line to the first nozzle group, wherein the inlet line is guided through the primary control valve such that the flow of the working fluid along the inlet line can be controlled using the primary control valve. The secondary control valve connects the first nozzle group to the second nozzle group such that the flow of the working fluid from the first nozzle group into the second nozzle group may be controlled using the secondary control valve.

Abstract: A vertical axis multi-phased wind turbine power generating system is disclosed. An adjustable air scoop directs air from a first phase of the prevailing wind into an air turbine for efficient power generation. An exit section, which uses a second phase of the prevailing wind in combination with an optional and adjustable exit section drag curtain or barrier, provides for efficient re-entrainment of this first stage of power generating air back into the downstream prevailing wind. The adjustable air scoop and adjustable exit drag curtain or barrier, where utilized, is automatically rotated in a self correcting manner to be suitably and optimally oriented to the prevailing wind direction. The design provides for a second stage of power generation to be accomplished by additionally utilizing a portion of the second phase of prevailing wind to directly or indirectly drive the turbine in a second stage of power production.

Abstract: A wind turbine for use in generating electricity. The wind turbine includes a housing being secured atop a tower. A wheel is mounted within the housing and is rotatable about a horizontal axis when struck by winds passing over the front of housing. The wheel has a hub and a number of paddles radiating outwardly from the hub and above the housing. An electrical current generator is connected to the wheel so as to be powered thereby. A wind shield is mounted within the housing for selectively preventing winds passing over the front of the housing from reaching the wheel.

Abstract: A system for generating electricity from steam power, which includes a steam source communicated with a steam load, the steam load requiring steam at a load pressure lower than the steam source; a pressure reduction valve communicated between the steam source and the steam load, and adapted to reduce steam pressure to the load pressure; and a pressure reduction valve bypass circuit including a steam turbine for converting steam to electric power, the turbine being communicated with an electric power load to provide power to the load. The turbine is advantageously positioned vertically above a motor.

Abstract: An axial fan comprising an impeller provided with a supporting ring on which is disposed an adapter. Spindles are rotatably mounted in the supporting ring, and adjustable blades are connected to the spindles. A support is provided for each spindle and is comprised of a roller bearing that rests against an inner side of the supporting ring, and of a bushing that rests against an inner side of the adapter. A tubular nut is threaded onto the outer end of the spindle to fix it in the supporting ring.

Abstract: The present invention relates to a fresh gas system (1) for supplying an internal combustion engine (4) with fresh gas, in particular in a motor vehicle, having a charging device (8) for increasing the pressure of the fresh gas and having a swirl generator (12), which is arranged upstream of the charging device (8), for generating a swirl, which rotates about the main flow direction of the fresh gas, in the fresh gas, wherein the swirl generator (12) has guide blades (14) with adjustable angle of incidence. In order to be able to produce the fresh gas system (4) more cost-effectively, the swirl generator (12) has a flow guide body (13) on which the guide blades (14) are integrally formed and which, in order to adjust the angle of incidence of the guide blades (14), can be twisted with elastic deformation about the main flow direction starting from an undeformed initial position.

Abstract: A method and apparatus for providing ventilation to a selected structure. The apparatus may include various features such as flexible portions, rigid portions, and assembly portions. Further, various steps may be used to form the structure to achieve selected results, such as monolithic formation, inclusion of various positioning members, and the like.

Abstract: A fluid pump (10) includes a pumping chamber (14), an inlet (16) and an outlet (18) fluidly connected with the pumping chamber, and a passage (24) fluidly connected between the inlet and the outlet. Fluid flowing through the passage bypasses the pumping chamber. In one example, the fluid pump (10) pumps coolant within a vehicle cooling system between a heater core (23b) and a vehicle engine (23a).

Abstract: There is provided an adjustable vane turbine and turbine generator using the same, in which hydrodynamic properties are employed to adjust adjustable vanes automatically in response to flow condition such as the flow rate of the working fluid, thereby simplifying the system using the adjustable vanes and reducing cost. In the adjustable vane turbine, a turbine wheel is installed in a turbine housing and rotatably supported by a shaft, and a plurality of adjustable vanes are movably installed between the turbine housing and the turbine wheel, wherein each of the adjustable vanes includes an adjustable vane member having one end portion rotatably fixed to the turbine housing, a vane control element attached on one side of the adjustable vane member at a set angle, and a guide element attached on the other side of the adjustable vane member, the plurality of adjustable vanes being connected using links between neighboring vanes.

Abstract: A variable pitch stator vane stage, said vanes being moved by an automatically-centered rotary actuator ring. The casing carries a stationary coaxial annular rail projecting from its outside surface, and circumferentially spaced apart moving equipments are provided that are constrained to move along said rail, each moving equipment being coupled to the actuator ring via a radial guide arrangement.

Abstract: A variable stator vane assembly for a gas turbine engine including an actuation ring including an upper surface, a lower surface, a first side, a second side, and at least one recess that is defined between the upper surface, the lower surface, the first side, and the second side, a plurality of variable stator vanes, and a lever arm assembly coupled between the actuation ring and at least one of the variable stator vanes, the lever arm assembly including an articulating block inserted at least partially into the actuation ring recess such that the articulating block is movable in a first axis; and a lever arm coupled to the articulating block and at least one of the variable stator vanes such that the lever arm is movable in a second axis that is different than the first axis.

Abstract: A pre-whirl generating apparatus (26) is provided that employs deformable air deflecting vanes (46) adjacent the inlet (18) of a radial air compressor (12-22), which vanes (46) can be mechanically deformed to generate positive, neutral, or negative pre-whirl flow to the compressor. A minimum number of parts are used to position one or more thin, deformable vanes (46) in the intake channel (34) leading to the compressor inlet (18). In their undeformed position, the vanes (46) do not deflect the incoming air, thereby causing little or no flow restriction. To achieve the desired positive or negative pre-whirl of flow to the compressor (12-22), the trailing edge (62) of the vanes (46) are deflected transverse to the direction of flow in the channel (34) in either the positive or negative direction.

Abstract: A ventilation fan assembly (10) having a fan (22) mounted in a housing (12) and a shutter assembly (60). The housing has a square inlet portion (12C), a circular center portion (12E) and a conical outlet portion (12D) having rifling grooves (20). The shoulder (16) formed between the inlet portion and the center portion is radiused to reduce disruption of air flowing from the inlet portion to the center portion. The shape of the blades (32) of the propeller (28) is such that the axial velocity produced as the propeller rotates is essentially constant along the length of the blades. The shutter assembly has a large, radiused entrance and airfoil shaped blades which reduce air disruption. The blades have a flexible flap (68) along the trailing edges (64D) which form a seal between adjacent blades to prevent air from leaking from the housing through the shutter assembly.

Abstract: A wind power system is provided including at least one generator fan having a front face and a rear face. The system also includes a first wind capturing device positioned proximate to the front face. The wind capturing device can be configured to capture wind to create a first pressure proximate to the front face that is greater than a second pressure proximate to the rear face. The pressure difference causes the captured wind to flow across the at least one generator fan from the front face to the rear face.

Abstract: Water is first caused to flow through a first passage and rotate a first impeller. Rotation of the first impeller is linked to rotation of a second impeller, which is in fluid communication with a second, discrete passage. Vanes on the second impeller are constrained to move faster than vanes on the first impeller. Water is subsequently caused to flow through the second passage and to be more aggressively advanced by the second impeller.

Abstract: A pump particularly adapted for use in a closed fluid circuit, as within its housing a resiliently compressible chamber in contact with the fluid being conveyed by the pump so that any pressure change within the fluid caused by temperature variations can be volumetrically absorbed by compression or extension of the chamber.

Abstract: A circulator-pump-motor-unit which has two inlet ports and means to change the path of the hot water conveyed between these ports so that either the hot water system or the hydronic system gets heat.

Abstract: A ventilation fan assembly (10) having a fan (22) mounted in a housing (12) and a shutter assembly (60). The housing has a square inlet portion (12C), a circular center portion (12E) and a conical outlet portion (12D) having rifling grooves (20). The shoulder (16) formed between the inlet portion and the center portion is radiused to reduce disruption of air flowing from the inlet portion to the center portion. The shape of the blades (32) of the propeller (28) is such that the axial velocity produced as the propeller rotates is essentially constant along the length of the blades. The shutter assembly has a large, radiused entrance and airfoil shaped blades which reduce air disruption. The blades have a flexible flap (68) along the trailing edges (64D) which form a seal between adjacent blades to prevent air from leaking from the housing through the shutter assembly.

Abstract: Two stages of relatively rotatable guide vanes (22,24) are arranged in tandem. Shroud portions (42,46) on the vanes overlap in loose engagement, until an associated gas turbine engine starts operating. Gas loads then act on the downstream vane stage (24) and move it in a downstream direction until the opposing flanks of radially opposing lands (44,48) on respective shrouds (42,46) engage, whereupon, gas leakage via the overlap onto the turbine casing (40) is at least substantially reduced.

Abstract: A modular wind energy device for converting wind energy into mechanical energy, which includes a support structure configured for placement onto a support surface (36) and defining an axis of rotation (23) generally parallel thereto; one or more panemone type rotors (16) mounted onto the support structure for free rotation about the axis of rotation, having a pair of wing elements, of which, during rotation of the rotor in response to an airflow, at all times, one of the wing elements faces in an upstream direction and the other of the wing elements faces in a downstream direction; a power take off element associated with the one or more rotors; and shroud apparatus (10) for reducing resistance against the returning wing surfaces, and for directing the airflow toward the effective wing surfaces.

Abstract: A flow regulator for a water pump, comprising a control valve. The control valve is mounted on an inlet pipe of a water pump and has a chamber, housing a flat-shaped control plate, the upper part of which forms a piston plate, vertically gliding in an upper chamber. The upper chamber is connected with an outlet pipe. The control valve is exposed to water pressure in the outlet pipe, with the control plate driven downward by the water pressure, countered by two springs at two lateral sides of the control plate. The control plate thus has a varying vertical position according to the water pressure.

Abstract: An intake and exhaust damper assembly has a motor and fan assembly pivotally mounted for movement toward and away from a louvered rotatable blade damper.

Abstract: Nozzle control apparatus for an axial flow air turbine having an inlet nozzle for air entering the turbine and an associated turbine inlet housing for channeling air flowing to the inlet nozzle for at least partially blocking air flow from the turbine inlet housing to the turbine inlet nozzle. The nozzle control apparatus uses an axially movable annular slider member that is biased to its open position by an annular spring and is moved axially by bleed air pressure exerted on a portion of the annular slider member.

Abstract: A ventilation fan assembly (10) having a fan (22) mounted in a housing (12) and a shutter assembly (60). The housing has a square inlet portion (12C), a circular center portion (12E) and a conical outlet portion (12D) having rifling grooves (20). The shoulder (16) formed between the inlet portion and the center portion is radiused to reduce disruption of air flowing from the inlet portion to the center portion. The shape of the blades (32) of the propeller (28) is such that the axial velocity produced as the propeller rotates is essentially constant along the length of the blades. The shutter assembly has a large, radiused entrance and airfoil shaped blades which reduce air disruption. The blades have a flexible flap (68) along the trailing edges (64D) which form a seal between adjacent blades to prevent air from leaking from the housing through the shutter assembly.