Abstract: A partition panel is made of two overlaying sheets of high density polyethylene or other plastic material which have been bonded together around a perimeter and at selected regions such that the partition panel contains bonded regions where the two sheets are bonded together and hollow regions where the two sheets are spaced apart from one another. The partition panel is preferably made by thermoforming.

Abstract: An axial flow fan comprising: a cental hub rotatable on an axis; and a plurality of blades extending from the hub, each of the blades comprising a root portion adjacent to the hub, and terminating in a tip portion, the root portions of the blades being approximately evenly spaced around the hub; wherein each of the blades exhibits a curvature from the root portion of the blade to the blade's tip portion, the curvature being in a plane that is perpendicular to the axis on which the fan rotates; and wherein the curvature differs between at least two of the blades, such that the distance between the tip portions of at least wo sets of adjacent blades is unequal. The invention therefore achieves the advantage of having uneven blade spacing near the tips while maintaining high solidity near the hub, where the blade spacing is even. Uneven blade spacing near the tips reduces noise. Having high solidity near the hub, where non-dimensional loading is highest, maintains higher dynamic performance.