1. Field of the Invention
The present invention relates generally to heat exchangers, and more particularly, to a heat exchanger for use in an automotive air conditioning system.
2. Description of the Prior Art
One prior art embodiment of a heat exchanger as described in Japanese Patent Application Publication No. 2-154986 is essentially illustrated in FIGS. 1 and 2. As shown in the figures, a heat exchanger such as a condenser 100 includes a plurality of adjacent, essentially flat tubes 100 having oval cross-sections and open ends which allow refrigerant fluid to flow therethrough. A plurality of corrugated outer fin units 120 are fixedly disposed between adjacent tubes 110. Cylindrical header pipes 130 and 140 having closed ends are disposed perpendicular to flat tubes 110. Flat tubes 110 having open ends are fixedly and hermetically connected to the inside of header pipes 130 and 140, so as to communicate with the hollow interiors of header pipes 130 and 140.
Inlet pipe 131 has an open end which is fixedly and hermetically connected to the outside of an upper portion of header pipe 130. The other open end of inlet pipe 131 is linked to an outlet of an element (not shown) positioned upstream with respect to condenser 100. The element may be, for example, a compressor. Outlet pipe 141 also has an open end which is fixedly and hermetically connected to the outside of a lower portion of header pipe 140. The other open end of outlet pipe 141 is linked to an inlet of an element (not shown) positioned downstream with respect to condenser 100. This element could be, for example, a receiver.
With reference to FIG. 2, each flat tube 110 includes flat tube member 111 and a plurality of partition walls 112. Partition walls 112 are integrally formed along an inner surface of flat tube member 111. Partition walls 112 extend longitudinally along the length of flat tube member 111 so as to divide the interior hollow portion of flat tube member 111 into a plurality of rectangular parallelepiped hollow regions 113 and a pair of semicylindrical hollow regions 114 which are located at the lateral ends of flat tube member 111. Hollow regions 113 and 114 extend in parallel directions with respect to one another. As discussed below, the hollow regions extend transversely relative to a flow direction "A" of the air. The air flows along the exterior surface of the flat tube 110.
During operation of a refrigerant circuit which includes condenser 100, the discharged refrigerant gas from a compressor is directed into the hollow interior of header pipe 130 via inlet pipe 131. The refrigerant gas directed into the hollow interior of header pipe 130 flows through the hollow interior of header pipe 130 toward its lower end. The refrigerant gas flowing through the hollow interior of header pipe 130 concurrently flows into each of the hollow regions 113 and 114 of each of flat tubes 110. The gas then longitudinally flows through each of hollow regions 113 and 114 of each of the flat tubes 110 from the right to the left sides (in FIG. 1). The refrigerant gas exchanges heat with air passing along corrugated fins 120 so as to be liquefied. The flow direction of the air passing along corrugated fins 120 is shown by large arrow "A" in FIG. 2. Accordingly, the air laterally passes along an exterior surface of flat tubes 110. Finally the refrigerant flows out from each of the hollow regions 113 and 114 of each of flat tubes 110. The liquefied refrigerant flowing out from each of hollow regions 113 and 114 of each flat tube 110 joins together at the hollow interior of header pipe 140, and flows through the hollow interior of header pipe 140 toward a lower end of header pipe 140. The liquefied refrigerant flowing through the hollow interior of header pipe 140 is conducted to the receiver via outlet pipe 141.
In this prior art embodiment, the integral formation of the partition walls 112 prevents expansion of flat tube members 111 caused by the pressure force of the refrigerant. Further, the area of the contact surface between the refrigerant and the flat tube 110 is increased so that a heat exchange efficiency of condenser 100 is improved.
FIG. 3 essentially illustrates one of a plurality of identical flat tubes 210 which form a part of a condenser (not shown) as described in U.S. Pat. No. 4,998,580. As shown in the figure, flat tube 210 includes flat tube member 211 and corrugated inner fin 212. Inner fin 212 is fixedly disposed along the entire interior length of the hollow portion of flat tube member 211. Corrugated inner fin 212 includes a plurality of ridges 212a which longitudinally extend along the length of flat tube member 211. Adjacent ridges 212a are fixedly connected to upper and lower inner surfaces of flat tube member 211, respectively, so as to define a plurality of hollow regions 213. The hollow regions have a lateral cross section which is defined by the generally sine curve shape of fin 212, in the interior hollow portion of flat tube member 211. Hollow regions 213 are aligned with one another in a parallel relationship. Hollow regions 213 are oriented to extend transversely to the flow direction "A" of the air. The air passes along the exterior surface of the flat tube 210.
In this prior art embodiment, the attachment of the separately formed corrugated inner fin 212 to flat tube member 211 effectively prevents the expansion of flat tube member 211 caused by the pressure of the refrigerant, without unnecessarily increasing the thickness of flat tube member 211. Furthermore, the heat exchangeability of the condenser is improved because the refrigerant contacts a surface of corrugated inner fin 212 which conducts the heat to flat tube member 211.
In the prior art embodiments, the amount of heat exchange between the refrigerant and the air at the upstream side (relative to the air flow) the flat tube is large, while the amount of heat exchange between the refrigerant and the air at the downstream side (relative to air flow) region of the flat tube is small. This difference results because the refrigerant flows only longitudinally through each of the hollow portions of the flat tube; that is, the refrigerant does not disperse in the lateral direction when it flows through the interior hollow space of the flat tube. Therefore, the amount of heat exchange between the refrigerant flowing through the interior hollow space of the flat tube and the air laterally passing along the exterior surface of the flat tube is gradually decreased in the direction from the upstream side (relative to the air flow) region of the flat tube to the downstream side (relative to the air flow) region of the flat tube. Accordingly, the heat exchange efficiency of the condenser is not sufficiently improved by the divided construction.