Sheet metal pipe geometry for minimum pressure drop in a heat exchanger

Abstract

A heat exchanger joint between a pipe and a header wall defines an endless transition for conveying the heat exchange medium closely over a control surface of a radius or a chamfer between the interior surface and the pipe to reduce turbulence and pressure loss. The radiused or chamfered flow control surface expands radially as it opens axially into the interior surface of the header wall.

Description

FIELD OF THE INVENTION

This invention relates to automotive heat exchangers in general, and specifically to a liquid flow heat exchanger, such as a radiator, with a novel in tank structure for reducing the pressure drop caused by flow turning losses.

BACKGROUND OF THE INVENTION

Automotive heat exchangers that use a pumped, liquid heat exchange medium, as opposed to a compressed gaseous/liquid heat exchange medium, include radiators and heaters. Typically, these include two elongated manifolds or header tanks, one on each side of the heat exchanger, with a central core consisting of a plurality of evenly spaced, flattened flow tubes and interleaved corrugated air fins running between the two tanks. Each tank is generally box shaped, with parallel side walls, a back wall joining the side walls, two axially opposed ends, and an open area opposite the back wall, which is eventually closed off when it is fixed leak tight to one side of the core. Each header tank distributes pumped liquid to or from the flow tubes in the core, and is in turn filled or drained by an inlet or outlet pipe opening into the header tank at a discrete location. In typical radiators, the inlet or outlet pipe to the header tank is oriented both transversely to the length of the tank and to the flow tubes. Coolant flow entering the inlet pipe must, therefore, turn through a substantial angle toward the two ends of the tank before as well as turning substantially again to flow out of the tank interior and into the flow tubes. The converse is true for coolant exiting the return tank through the outlet pipe. An example of a recent radiator with molded plastic, box shaped header tanks may be seen in U.S. Pat. No. 5,762,130, which is fairly typical in its basic flow configuration, apart from being a U flow design, with the inlet and outlet pipe located on one tank. The orientation of the pipes relative to the tank walls and flow tubes is as described above, however. A metal design is shown in U.S. Pat. No. 6,283,200 wherein the end of the inlet pipe is flared outwardly to reduce the pressure loss.

The design of a radiator or any cross flow heat exchanger with a liquid medium flowing in one direction through flow tubes, and with air blown perpendicularly across the flow tubes, is a compromise between heat exchange efficiency between the two flowing media, and the pressure or pumping losses of the two media. For example, it is well known that decreasing the flow passage cross sectional area will present relatively more surface area of the fluid medium within the flow passage to the air blowing over the flow tube, increasing the heat transfer efficiency from fluid to air. A tube that is smaller on the inside is also thinner on the outside, and so presents less obstruction the air blown over the outside of it, decreasing the air side pressure loss through the core. However, a thinner flow tube creates more fluid pressure loss through the tube, end to end. Some compromise can generally be found between airside pressure drop, tube thickness, and liquid (coolant) pressure drop. However, the ability to reduce total coolant pressure loss (pumping loss) elsewhere in the heat exchanger would allow the use of thinner tubes in general, which would be very positive, considering that thinner tubes also decrease air side pressure loss.

One source of coolant pressure drop through the heat exchanger that has not received a great deal of attention in the prior art is turbulence or “turning” losses that occur at the transition between the pipe opening and the enclosed interior of the header tank. That is, since the inlet pipe typically enters through a tank side wall, and not the tank back wall, it is oriented transversely to the flow tubes, as well, and must change direction both to reach the opposite ends of the tank and in order to flow into the tubes. The turning transition is not a great source of pressure loss when the interior volume of the tanks is large, since a large interior volume can act as a large pressure reservoir to “absorb” and distribute coolant to the flow tubes. As available underhood space shrinks, however, radiator header tanks become smaller, and the parallel sidewalls become closer. Flow exiting the opening of the inlet pipe (through the first side wall) impinges on the proximate, opposed second side wall, creating turbulence and pressure loss before it can be distributed toward the opposite ends of the tank and into the flow tubes.

The other liquid medium heat exchanger typically found in an automobile, the heater core, has a similar cross flow configuration, but faces a different problem. There, the inlet pipe generally opens through the back wall of the header tank, in line with, rather than perpendicular to, the flow tubes. The flow thus impinges directly onto the ends of the nearest aligned flow tubes, rather than against a sidewall of the tank, which would theoretically be positive, in terms of direct flow into the tubes with minimal pressure loss. However, the fact that the ends of the nearest tubes are in line with the inlet pipe is a detriment, because the force of the impinging flow against the near tube ends causes erosion and damage. Therefore, it has been proposed in several heater core designs to place a protective tent or baffle like structure between the inlet pipe opening and the ends of the nearest aligned flow tubes. These act as a road block, in effect, interrupting the flow at that point, rather than smoothing it out, and would actually increase total coolant pressure drop across the core. This is an acceptable price in that context, however, since it is considered necessary to protect the otherwise eroded tubes. Another solution is shown in U.S. Pat. No. 6,116,335 to Beamer et al wherein a flow turning structure is molded into the inlet header tank opposite to the inlet pipe.

Design of tanks and manifolds in automotive heat exchangers such as radiators involves tradeoffs between the conflicting requirements of minimizing coolant pressure drop and packaging space. Market trends are simultaneously driving down the allowable tank size and pressure drop. This problem is further compounded when internal oil coolers or baffles are required that partially block the inlet/outlet pipes.

Plate type oil coolers are frequently incorporated in radiator tanks to provide engine and transmission oil cooling. Due to packaging constraints, it is common for oil coolers to straddle the coolant inlet/outlet pipes. This flow blockage increases coolant pressure drop and creates local regions of high coolant velocity that can cause erosion corrosion of the oil cooler. In a typical cross flow radiator, the tanks and oil cooler represent 50% of the total coolant pressure drop. The penalty due to the oil cooler blockage is 35-40% of the tank pressure drop (˜20% of total pressure drop).

Since the pipe diameters are specified by the vehicle manufacture, the most common method used to limit the oil cooler coolant pressure drop penalty is the spacing (stand off height) of the oil cooler from the inside tank wall. Typically it is not practical to reduce the pressure drop penalty below the levels described above because the increased stand off height required will reduce the size of oil cooler that can be installed in the tank, or a larger tank must be used with increased packaging space, mass, and cost penalties.

For sheet metal tanks and pipes, the internal juncture between the pipe and tank is typically sharp edged. Due to the joint design, the pipe is frequently extended into the tank to allow secure clinching of the pipe to the tank. Both the sharp edge and pipe extension act to increase coolant pressure drop.

SUMMARY OF THE INVENTION AND ADVANTAGES

The subject invention provides a radiator header tank to pipe joint that reduces coolant pressure drop by reducing turning losses at the transition between the pipe and the header tank wall.

The heat exchanger assembly of the subject invention is distinguished by a transition between the header wall and the pipe extending transition completely around the opening to present an expanding flow control surface between from the header wall to the pipe for conveying the heat exchange medium closely over the control surface between the tank interior and the pipe to reduce turbulence and pressure loss at the transition between the tank interior the said pipe.

This invention provides a transition to significantly reduce the oil cooler pressure drop penalty and/or reduce the size of the tank. A method of determining the required feature size and practical designs are provided for integrally molded or fabricated sheet metal tanks. Several configurations are shown that incorporate an internal radius or chamfer to eliminate the pipe extension inside the tank.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 is a fragmentary view of a heat exchanger showing a header tank and heat exchanger core;

FIG. 2 is an interior perspective view of the heat exchanger header tank of FIG. 1;

FIG. 3 is schematic showing the flow pattern for a sharp edged pipe to header joint of the prior art;

FIG. 4 is schematic showing the flow pattern for a chamfered header to pipe transition of the subject invention;

FIG. 5 is a schematic view comparing the radius and chamfered joints of the subject invention; and

FIG. 6 is a perspective view of a header tank incorporating an oil cooler facing an inlet configured in accordance with FIG. 4;

FIG. 7 is a plot of the chamfer/radius size versus the pressure drop for a given inlet diameter;

FIG. 8 is a plot of the taper angle versus pressure drop with a given chamber angle and pipe size;

FIG. 9 is a plot of chamfer versus pressure drop for various pipe diameters and stand off heights;

FIG. 10 is a plot of radius versus pressure drop for a given pipe size and various stand-off heights;

FIGS. 11 through 16 show various pipe to header joints constructed in accordance with the subject invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A heat exchanger assembly constructed in accordance with the subject invention is generally shown at 20 in FIGS. 1 and 2. The assembly 20 includes a core comprising a plurality of flow tubes 22 having heat exchange fins 24 extending therebetween. A header tank 26 distributes a flowing liquid heat exchange medium to and from the flow tubes 22 and presents a header wall 28 with an interior surface. A pipe 30 is disposed in an opening through the header wall 28.

A joint extends between the pipe 30 and the header wall 28 to define an endless transition completely around the opening to present an expanding flow control surface between the pipe 30 and the interior surface 32 of the header wall 28 for conveying the heat exchange medium closely over the control surface between the interior surface and the pipe 30 to reduce turbulence and pressure loss at the transition between the interior surface and the pipe 30.

A typical pipe to header wall joint is shown in FIG. 3 wherein a sharp edged corner is presented annularly about the opening into the header wall 28. The pipe is formed in a cylindrical shape to define entry flow into the header as cylindrical. However, it is to be understood that the cylindrical pipe could be flattened into an oval, elliptical, or other shape at the joint. The joint of the subject invention presents an expanding flow control surface with a rounded radius 32 or a straight or conical shaped chamfer 34 as illustrated in FIG. 4. The use of a chamfer 34 is slightly more effective than the radius 32 due to increased entrance flow area for the same size pipe flow area as shown in FIG. 5.

The typical pipe/tank juncture is a sharp edged corner as illustrated in FIG. 3. The limiting entrance flow area into the pipe is a cylinder. This invention replaces the sharp corner with a radius or chamfer to increase entrance flow area and facilitate turning of the flow into the pipe. Flow streamlines for both sharp and chamfered geometry's are shown in FIGS. 3 and 4. Use of a chamfer is slightly more effective than a radius due to increased entrance flow area for the same size feature as shown in FIGS. 5 and 7. The optimum chamfer angle was found to be 45° as shown in FIG. 8.

Based on CFD simulation and prototype testing it was found that the effect of radius/chamfer size is similar through out the practical range of pipe and standoff sizes. A radius/chamfer of 2.0 mm yields approximately 50% of the total savings possible as shown in FIGS. 9 and 10. Therefore this invention claims the use of a radius or 30/60° chamfer equal to or greater than 2.0 mm.

Accordingly, the pipe 30 is cylindrical about an axis and the flow control surface expands radially as it opens axially into the interior surface 32 of the header wall 28, it expanding through a radius or through a cone shaped chamfer. The header wall 28 presents a planar disk-like portion immediately adjacent to and extending radially from the opening in the header wall 28 to define the interior surface 32 in a radial plane. In all cases, the control surface blends into the planar disk-like portion to present a smooth transition of the control surface from the pipe 30 into the interior surface 32 of the header wall 28. It is important that the control surface blend into the planar interior surface 32 to present a smooth transition of the control surface from the pipe 30 into the interior surface 32 of the header wall 28. As alluded to above, the control surface may extend through a radius 32 or through a cone to define a chamfer 34.

Referring to FIG. 6, the pipe 30 is integrally formed of plastic material with the header wall 28 define the chamfered control surface 34 that expands to the radial plane of the interior surface 32 of the header wall 28. An oil cooler 36 is disposed opposite to the pipe 30. The chamfer 34 significantly reduces the pressure drop caused by the imposition of the oil cooler 36.

Referring to FIGS. 11-16, the header wall 28 defines the control surface and the control surface expands from a cylindrical collar 40 to the radial plane of the interior surface 32. Said another way, the header wall 28 extends through a transition control surface into a cylindrical collar 40, which receives the pipe 30.

In the FIGS. 11 and 12, the pipe 30 extends within the opening of the collar 40 and terminates in an annular edge 38. The header wall 28 extends into the axially extending collar 40 to surround and engage the pipe 30. The pipe 30 includes a bead 42 abutting the open end of the collar 40.

Accordance with the invention, the pipe 30 has an end which terminates in spaced relationship to the radial plane in the header wall 28.

In FIGS. 13-16, the pipe 30 is disposed about the exterior of the collar 40.

In FIG. 13, the pipe 30 is flared 48 outwardly into a flare to engage the exterior of the collar 40 defining the control surface.

In FIGS. 14 and 15, the pipe 30 includes an enlarged end 50 defining a shoulder 52 for surrounding and engaging the exterior of the collar 40 with the shoulder 52 abutting the collar 40. The only difference in FIG. 15 is that the pipe 30 and the collar 40 are forced radially into one another to create a mechanically overlapping connection in the axial direction.

In FIG. 16, the pipe 30 and the collar 40 include mating undulations 54 extending annularly thereabout for locking the pipe 30 to the collar 40 to create a mechanically overlapping connection in the axial direction.

It is to be understood that the various embodiments may employ the radius 32 shown in FIGS. 12-14 and 16 or the chamfer 34 shown in FIGS. 11 and 15 and that either may be used with the various species of FIGS. 11-16. The joint may be formed with a radiused or chamfered flange and may be secured by fixturing, staking, tack weld, or spin welding, prior to final bonding. The pipe 30 end may be expanded to engage the outside surface of the collar or flange 40 as illustrated in FIGS. 11-12. A feature can be added to the end of the pipe 30 to provide lead in.

The pipe 30 and the header wall 28 may be molded of an organic polymeric material (plastic) or formed of sheet metal, when of metal, the pipe 30 may be secured to the tank 26 prior to brazing by expanding the collar 40 into the pipe 30. Alternately, as illustrated in FIGS. 13-16, the pipe 30 can be a press fit on to the collar 40, or can be shrunk onto the collar 40. Either the collar 40 or the pipe 30 can be tapered to control the press fit characteristics. The collar 40 can be expanded into the pipe 30 or the pipe 30 shrunk on to the collar 40. The bead 42 may be formed into the pipe 30 and the collar expanded into the bead 42. All configurations allow the use of an unclad pipe 30 and externally clad tank 26. All configurations are designed to allow brazing of the pipe 30 and collar. Typically clad material is used for the tank 26 body and bare material for the pipe 30, but either or both parts can be clad. Alternately, a separate source of braze material can be used such as a braze ring or braze paste. Some of the configurations could also be spin welded. In the case of plastics, the pipe 30 may be mechanically attached or bonded to the collar 40, as by an adhesive, fusion or spin welding or integrally molded.

The collar 40 and the pipe 30 may be bonded together by brazing, soldering, welding or an adhesive, depending upon the composition of the components. In addition, the pipe 30 may be secured prior to bonding to the collar 40 by fixturing, a press fit, e.g., expanding or shrinking, staking, forming undulations, etc. In order to facilitate assembly, the pipe 30 and/or collar 40 may include a lead-in such as a taper, or the locating bead 42 or shoulder 52.

Obviously, many modifications and variations of the present invention are possible in light of the above teachings. The invention may be practiced otherwise than as specifically described within the scope of the appended claims.

Claims

1. A heat exchanger assembly comprising;

a plurality of flow tubes,

a header tank for distributing a flowing liquid heat exchange medium to and from said flow tubes and presenting a header wall with an interior surface,

a pipe disposed in an opening through said header wall, and

a transition by extending said header wall into said pipe around said opening to present an expanding flow control surface between said pipe and said interior surface of said header wall for conveying the heat exchange medium closely over said control surface between said interior surface and said pipe to reduce turbulence and pressure loss at said transition between said interior surface and said pipe.

2. An assembly as set forth in claim 1 wherein said flow control surface is internal with said header wall and expands radially as it opens axially into said interior surface of said header wall.

3. An assembly as set forth in claim 2 wherein said flow control surface extends in a circle about an axis for defining a collar for receiving said pipe.

4. An assembly as set forth in claim 2 wherein said control surface extends through a radius.

5. An assembly as set forth in claim 2 wherein said control surface extends through a cone to define a chamfer.

6. An assembly as set forth in claim 2 wherein said pipe and said header wall comprise an organic polymeric material.

7. An assembly as set forth in claim 2 wherein said pipe and said header wall comprise metal.

8. An assembly as set forth in claim 3 wherein said pipe terminates in spaced relationship to the plane of said header wall.

9. An assembly as set forth in claim 3 wherein said pipe includes a bead abutting said collar.

10. An assembly as set forth in claim 3 wherein said collar and said pipe are bonded together.

11. An assembly as set forth in claim 10 wherein said pipe is secured prior to bonding to said collar.

12. An assembly as set forth in claim 3 wherein said pipe is flared outwardly and engages the exterior of said collar defining said control surface.

13. An assembly as set forth in claim 12 wherein said pipe includes an enlarged end defining a shoulder for surrounding and engaging the exterior of said collar with said shoulder abutting said collar.

14. An assembly as set forth in claim 12 wherein said pipe and said collar include mating undulations extending annularly thereabout for locking said pipe to said collar.

15. An assembly as set forth in claim 4 wherein said control surface presents a smooth transition from said pipe into said interior surface of said header wall with a radius or a 30° to 60° chamfer equal to or greater than 2.0 mm

16. An assembly as set forth in claim 5 wherein said control surface presents a smooth transition from said pipe into said interior surface of said header wall with a radius or a 30 to 60 chamfer equal to or greater than 2.0 mm.