The invention relates generally to an exhaust fan and more particularly to an axial-flow exhaust fan for use as a bilge blower in marine environments.
Two industrial forms of fans or blowers predominate, axial-flow fans and centrifugal, or radial-flow, fans. In centrifugal fans, air flows through the fan wheel in a mostly radially outward direction, while air flows in an axial-flow fan in an axial direction with almost no radial component.
Axial-flow fans operate by deflecting axially directed air on airfoils, or blades. This deflection causes the air flow to take on a helical flow pattern past the airfoils. This flow shape has two flow components, tangential velocity and axial velocity. Of the two flow components, the axial velocity is the more important component for moving air through the fan. Guide vanes positioned either upstream or downstream of the airfoils serve to translate the tangential velocity component of the air flow into the axial velocity component.
There are two methodologies for determining the size, dimensions, and number and positioning of blades for an axial-flow fan. One method is testing a first axial-flow fan design to ascertain the air volume and static pressure of the fan. Rarely does a first design meet the desired running parameters, and thus redesigning one or more times becomes necessary. Redesigning costs man-hours, and often the result is a fan which is larger than originally anticipated that runs at higher speeds and consumes more brake horsepower than needed. In addition, redesigning often leads to uneven and turbulent air flow and to the creation of stalling effects in certain parts of the blades.
A second methodology, which improves over the first methodology, is to design the axial-flow fan based upon desired outcome parameters as well as desired structural and design parameters. Such parameters may include high efficiency and low sound output over a wide range of operation, non-overloading brake horsepower, a steep pressure curve (little variation in air delivery), a large free delivery of air, large pressure safety margin, and compactness.
One problem experienced with conventional axial fans used in marine environments is that the fan housings are subjected to physical and thermal stresses which may alter the diameter of the housings.
The invention provides an axial-flow fan which includes a plurality of airfoils extending from a rotatable fan wheel hub, a motor engaged with the fan wheel hub through a shaft, and a housing into which the fan wheel hub and the motor are positioned. The housing has a circumference with a diameter and at least one supporting element surrounding the circumference of the housing. The supporting element inhibits variation in the diameter of the circumference of the housing.
The invention further provides a method of manufacturing an axial-flow fan. The method includes the steps of engaging a fan wheel hub with a motor through a shaft, mounting at least one straightening vane from an inner surface of a housing, positioning the fan wheel hub and the motor within the housing such that the motor is mounted on one of the straightening vanes, and surrounding the housing with at least one supporting element which inhibits variation in the diameter of the circumference of the housing.
With these and other objects, advantages and features of the invention that may become hereinafter apparent, the nature of the invention may be more clearly understood by reference to the following detailed description of the invention, the appended claims and to the several drawings attached herein.