Heat exchanger with long and short fins

1. Field of the Invention

This invention relates generally to a heat exchanger for transferring heat to an air stream from a heat source flowing in tubes, and, in particular, to a heater core in the passenger compartment of an automotive vehicle.

2. Description of the Prior Art

Conventionally, the tubes, which carry engine coolant through the heater core of an automotive vehicle, are arranged parallel to the stream of air that passes through the heater core. The heater core usually includes one or two rows of tubes, the second row being in-line and parallel to the first row.

It has long been understood that the heat transfer rate is much larger for turbulent flow than for laminar flow. Increasing turbulence of the air stream through the heater core is beneficial to the convection heat transfer rate and improves the overall performance of the heat exchanger. It is also more effective to increase the heat transfer on the air-side to improve the heat exchanger, as this is the more restrictive side compared to the rate of heat transferred from the fluid flowing inside the tube.

Generally, fins located between the tubes are secured to the outer surface of the tubes to enhance heat transfer from the coolant to the air stream. In order to induce turbulence in the air stream, fins on the outer surface of the tubes are usually mutually staggered and offset, but the tubes are aligned parallel to the air stream.

A need exists in the industry for techniques that improve heat transfer in a heater core without increasing its package size.

A heat exchanger includes two headers and tubes secured to and extending between the headers, each tube including a wall formed with a leading surface, a trailing surface and lateral surfaces extending between the headers and interconnecting the leading and trailing surfaces, a passage enclosed by the wall for carrying fluid between the headers, and long and short fins formed integrally with and extending outward from the wall.

The heat exchanger increases the heat transfer surface area and reduces the complexity and number of components compared to a conventional heat exchanger having the same package space requirements.

The heat exchanger increases turbulence of the air flow through the exchanger by changing the heater core tube geometry in contact with the air flow, thereby increasing the convection heat transfer rate and improving the overall performance of the heat exchanger.

The integral extruded tube-fin process improves the structural integrity of the relationship between the tube and fins, and minimizes the number and complexity of the manufacturing process steps.

The scope of applicability of the preferred embodiment will become apparent from the following detailed description, claims and drawings. It should be understood, that the description and specific examples, although indicating preferred embodiments of the invention, are given by way of illustration only. Various changes and modifications to the described embodiments and examples will become apparent to those skilled in the art.

The invention will be more readily understood by reference to the following description, taken with the accompanying drawings, in which:

FIG. 1 is a top view showing two rows of tubes assembled in a header plate;

FIG. 2 is top view of a tube showing the arrangement of short and long fins; and

FIG. 3 is a side view of a heater core showing the tubes assembled in headers with tanks installed.

Referring now to the drawings, there is illustrated in FIG. 1 a header plate 10 for a heater core having a first row 12 and a second row 14 of flat, thin-walled tubes 16 arranged parallel to an air stream 18 as it enters the first row.

Each tube 16 includes a passage 17 that carries hydraulic engine coolant along the tube length between tanks 20 , 22 located at opposite ends of the tubes. Each tube 16 has a height, which extends between flat lateral surfaces 26 , 28 of the tube wall 24 ; a depth, which extends laterally between the leading surface 30 and trailing surface 32 ; and a length, which extends along the tube, perpendicular to the plane of the page and between the tanks 20 , 22 .

Each tube of the second row 12 is aligned with a tube of the first row. The lateral outer surfaces 26 , 28 of each tube of the first row 10 are arranged parallel to the corresponding lateral outer surfaces of a tube of the second row 12 and substantially parallel to the air stream 18 entering the first row.

FIG. 2 shows that each tube is formed with long fins 36 and short fins 38 extending outward and substantially perpendicular to the lateral surfaces 26 , 28 of the tube wall 24 and the arcuate leading surface 30 and trailing surface 32 . A long fin 36 is located between consecutive short fins 38 along the lateral surfaces 26 , 28 of the tube wall 24 . Preferably three short fins 40 and two long fins 42 extend outward from the arcuate leading and trailing surfaces 30 , 32 . The long and short fins 36 , 38 of consecutive tubes 16 are mutually aligned creating a flow path in which air flow between consecutive tubes is turbulent.

Preferably the tubes 16 and fins 36 , 38 , 40 , 42 are extruded such that the fins are formed integrally with the walls 24 without a separating space or a joint required to connect the fins to the outer surfaces of the walls.

FIG. 3 shows a tube 16 extending between tanks 20 , 22 and secured, preferably by brazing, to collars 48 formed on header plates 10 , 50 and enclosing the end of the tube 16 . The brazed connection seals the headers 10 , 50 and tubes against leakage of the engine coolant carried in the tubes. The space 52 between the short and long fins 36 , 38 of consecutive tubes 16 provide a space in which the air stream passes in direction 54 over the tubes and fins carrying convected heat from the engine coolant in the tubes to the air stream.

In accordance with the provisions of the patent statutes, the preferred embodiment has been described. However, it should be noted that the alternate embodiments can be practiced otherwise than as specifically illustrated and described.