BACKGROUND

The present invention relates to header ducts and, more particularly, to internal topography of header ducts.

A header duct is a component shaped to distribute fluid from a source to a component attached to the header duct outlet. In some instances, the header duct forms a manifold whereby fluid from a single source is distributed among multiple outlets.

For example,FIG. 1Adepicts prior art duct10that distributes fluid received through inlet12to first outlet14aand second outlet14b. Duct10includes inlet portion16, transition portion18, and outlet portion20. Inlet portion16extends from inlet12to transition portion18, and outlet portion20extends from transition portion18to first and second outlets14a,14b. Transition portion18extends between inlet portion16and outlet portion20and is encompassed by bend22, which permits an inlet plane containing inlet12to be angularly offset with respect to an outlet plane containing first outlet14aand second outlet14b. Furthermore, transition portion18has walls forming a distribution of cross-sectional areas that transition from a circular cross-sectional area that is continuous with inlet portion16to a rectangular cross-sectional area that is continuous with outlet portion20.

FIG. 1Bis a cross-sectional view of duct10taken along line1B-1B inFIG. 1Ain which line1B-1B is coincident with center point24of inlet12.FIGS. 1C, 1D, and 1Eare additional cross-sectional views taken along lines1C-1C,1D-1D, and1E-1E shown inFIG. 1B, respectively. As generally shown byFIGS. 1B, 1C, 1D and 1E, transition portion18has walls that are generally characterized by a simple, monotonic transition between the circular cross-section of inlet12to the rectangular cross-section of outlet portion20. Headers such as duct10are designed using computer-aided-design (CAD) or a CAD-driven process in which designers are primarily concerned with the physical constraints of duct10.

While duct10provides outlets14aand14bwith fluid from inlet12, headers designed with such CAD-driven processes fail to consider the fluid flow dynamics within duct10and result in unnecessarily high pressure loss through the duct due to flow separation regions, which create a region of turbulent flow and effectively reduce the cross-sectional area of duct10near the separation region. For instance, as shown inFIG. 1B, flow separation region26results from bend28along outside radius duct wall30, and flow separation region27region results from bend28along inside radius duct wall31. Consequently, flow lines32a,32b, and32care diverted away from regions26and27, increasing the pressure loss and reducing flow uniformity through duct10.

Increased pressure loss and reduced flow uniformity decrease performance of components (e.g., one or more heat exchangers) which utilize fluid delivered through first outlet14aand second outlet14b. The total pressure loss through a system must not exceed the driving pressure by some margin in order to achieve a design flow rate through the system. For example, header duct10may supply one or more heat exchangers connected to first outlet14aand second outlet14b. Increased pressure loss in header duct10limits the allowable pressure loss through the heat exchangers and, thus, limits the overall size or passage geometry of the heat exchangers. Moreover, non-uniform flow distributions through duct10concentrate flow through some passages of the heat exchanger and reduce flow through other heat exchanger passages, thereby reducing the efficiency of the heat exchanger as well as creating unnecessary pressure losses due to the concentrated flow passages.

Accordingly, because duct manufactures continue to seek improved header duct performance, a need exists for a header duct that further eliminates or reduces pressure losses due to flow separation and improves flow uniformity.

SUMMARY

A header duct includes an inlet portion having a planar inlet, an outlet portion having multiple planar outlets, and a transition portion extending continuously from the inlet portion to the outlet portion and defining a bend, making the outlets non-parallel with the inlet. The transition portion further includes internal topography defining a non-monotonic cross-sectional area distribution between the inlet and outlet portions.

In a further embodiment of the header duct, the internal topography of the transition portion may define a bulbous, intermediate region and a protrusion along an inside radius of the bend. The bulbous region has a larger cross-sectional area than a cross-sectional area of the inlet measured along a first intermediate plane parallel to and offset from the inlet. The bulbous region further includes a convex curvature adjacent the inlet portion that smoothly transitions to a concave curvature within the bulbous region along a second intermediate plane perpendicular to the first intermediate plane and intersecting the inlet. Lateral walls of the bulbous region further include a concave curvature that converges towards a lateral dimension of the outlets.

A method of forming a header duct includes forming an inlet portion that extends from a circular inlet, forming an outlet portion with a plurality of rectangular outlets, and forming a transition portion joining the inlet portion to the outlet portion. Forming the transition portion includes forming internal topography that defines a non-monotonic cross-sectional area distribution between the inlet portion and the outlet portion. The method can further include forming a bulbous region defined by the internal topography that extends laterally away from a plane intersecting a center point of the inlet and extending perpendicularly away from the inlet along a longitudinal direction of the outlets.

