BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to a heat exchanger for transferring heat from a heat source contained in tubes to an air stream, 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.
Generally, fins located between the tubes and secured to the outer surface of the tubes enhance heat transfer from the coolant to the air stream.
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.
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 further improve heat transfer in a heater core without increasing its package size.
SUMMARY OF THE INVENTION
A heat exchanger for an automotive vehicle includes two headers, first tubes for carrying fluid between the headers, and second tubes for carrying engine coolant between the headers and staggered with respect to the first tubes. Each tube is inclined relative to an air stream entering the heat exchanger.
The heater core provides improved performance over a current production heater core by up to five percent without increasing fin density or changing tube geometry. The heater core realizes an increase of about five percent in heat transfer surface area without increasing the size of the heater core.
An increase in turbulence of the air stream flowing through the heater core improves heat transfer performance of the heater core.
Design enhancements include offsetting the second row of tubes to increase impingement effect on tube surface and redirection of the air through the core face. Additionally, both the first and second tube rows may be inclined or angled relative to the air stream to increase the heat transfer surface area of the tube and to enhance impingement of the air on the tubes and fins. Both the first and second rows of tubes are angled in relation to the incoming flow of air up to 20 degrees. The optimal angle modeled in the simulations is about 15 degrees to maximize both the surface area for heat transfer and turbulence to the air flow through the core.
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.
DESCRIPTION OF THE DRAWINGS
The invention will be more readily understood by reference to the following description, taken with the accompanying drawings, in which:
FIG. 1A is an end view showing a prior art arrangement of a single row of parallel, flat tubes for a heater core arranged parallel to the air flow;
FIG. 1B is an end view of a single row of parallel, flat tubes for a heat exchanger inclined relative to the air flow;
FIG. 2A is an end view showing a prior art arrangement of two rows of parallel, flat tubes in a heater core arranged in-line and parallel to the air flow;
FIG. 2B is an end view showing two rows of parallel, flat tubes of a heat exchanger arranged parallel to the air flow, with the second row offset or staggered with respect to the first row of tubes.
FIG. 2C is an end view showing two rows of parallel, flat tubes of a heat exchanger inclined relative to the air flow
FIG. 3B is a top view of an alternate heat exchanger;
FIG. 3B is a top view of a heat exchanger;
FIG. 3C is a top view of an alternate heat exchanger;
FIG. 4 is a cross section taken at plane 4-4 in FIG. 3A;
FIG. 5 is a cross section taken at plane 4-4 in FIG. 3A showing an alternate arrangement of tubes;
FIG. 6 is a cross section taken at plane 4-4 in FIG. 3A showing another arrangement of tubes;
FIG. 7 is a cross section taken at plane 4-4 in FIG. 3A showing another arrangement in which the tubes are angled in first and second directions; and
FIGS. 8A, 8B and 8C show folded tubes whose surfaces are joined and sealed along at least one longitudinal seam.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings, there is illustrated in FIG. 1A a single row of parallel, flat, thin-walled tubes 12 for use in a heater core, the tubes being arranged parallel to the air stream 13.
FIG. 1B shows a single row of parallel, flat, thin-walled tubes 14 for a heater core, the tubes being inclined relative to the air stream 13. In the heater core, tubes 12, 14 carry hydraulic engine coolant along the tubes, and air passes over the outer surface of the tubes. Each tube 14 has a height, which extends between flat surfaces 15; a depth, which extends laterally between the leading edge 16 and trailing edge 17; and a length, which extends along the tube, normal to the plane of the page.
FIG. 2B illustrates two rows of flat, thin-walled tubes 18, 20 for use in a heater core, wherein the tubes of one row are staggered relative to the tubes of the other row and all the tubes are mutually parallel and parallel to the air stream 14.
FIG. 2C shows two rows of parallel, flat, thin-walled tubes 22, 24 for a heater core, wherein the tubes of the second row 24 are staggered relative to the tubes of the first row 22 and all the tubes are mutually parallel and inclined relative to the air stream 14 at an angle A, which may be as large as about 20 degrees.
The heater core 26 illustrated in FIG. 3A includes a housing 28 containing tubes organized in a first bank of tubes 30, which extends longitudinally between headers 31, 32, and a second bank of tubes 33, which extend longitudinally between headers 32, 34. Header 31, which is partitioned from header 34 by a short cross baffle 35, is formed with an inlet 36. Header 34 is formed with an outlet 37. Tubes 30 carry hydraulic engine coolant at relatively high temperature from inlet 36 and header 31 to return to return header 32. Tubes 33 carry the coolant from header 32 to header 34 and the outlet 37. Heat is transferred from the engine coolant to the air stream 13, which flows into the passenger compartment of a vehicle.
Alternatively the tubes 30, 33 may be organized in a first bank comprising the tubes of the first row 22 and a second bank comprising the tubes of the second row 24.
FIG. 3B demonstrates an alternative, in which a second bank of tubes 24 carries relatively high temperature engine coolant from an inlet 48 between a header 42 and a return header 44. A first bank of tubes 22 returns the engine coolant to header 42 and outlet 40. Header 42 is partitioned with a long longitudinal baffle 50.
FIG. 3C demonstrates an alternative, in which tubes 22, 24 carry coolant from inlet 52, between headers 54, 56 and through the outlet 58.
FIG. 4 shows the tubes arranged as shown in FIG. 2B with a first row 18 and a second row 20, each row parallel with respect to the air stream 13, the second row 20 being offset or staggered such that the leading edge 16 of each tube of the second row 24 is aligned with a space 60 between successive tubes of the first row 18.
FIG. 5 shows that the tubes are arranged with a first row 22 and a second row 24, each row inclined with respect to the air stream 13, the second row 24 aligned such that the leading edge 16 of each tube of the second row 24 is aligned with a tube of the first row 22.
FIG. 6 shows that the tubes are arranged as shown in FIG. 2C with a first row 22 and a second row 24, each row inclined with respect to the air stream 13, the second row 24 offset or staggered such that the leading edge 16 of each tube of the second row 24 is aligned with a space 60 between successive tubes of the first row 22.
FIG. 7 shows that the tubes of the second row 62 may be directed in another direction from the tubes of the first row 22, each tube 22, 62 being inclined at an angle A with respect to the air stream, the second row 24 being offset or staggered such that the leading edge 16 of each tube of the second row 62 being aligned with a space 60 between successive tubes of the first row 22.
In another embodiment, the tubes may be arranged in the heater core 26 as shown in FIG. 1B with a single row 16 but no second row, each tube 16 being inclined at an angle A with respect to the air stream 14.
The tubes may be welded along a longitudinal seam or brazed along the seam. Alternatively, as shown in FIG. 8A, the tubes may be folded from sheet stock and brazed or welded at overlapping, longitudinal seams 66, 68.
FIG. 8B illustrates a tube folded from sheet stock and brazed or welded at overlapping seams 70, 71, 72. The flat surfaces 15 are formed with beads 74, 75, 76.
FIG. 8C illustrates a clenched tube folded from sheet stock and brazed or welded at an overlapping seam 78. The flat surfaces 15 are formed with beads 80, 81, 82, 83, 84.
Inclining the tubes with respect to the air stream 14 and staggering the tubes enhances turbulence of the air flow through the heater core 26 and increase the impingement effect on the surfaces of the tubes by redirecting the air at the face of the heater core. Inclining the tubes with respect to the air stream 13 and staggering the tubes improves the rate of heat transfer in the heater core.
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.
Patent Application
20100116481
