Patent Application
20070017664
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.
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.
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.
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:
A heat exchanger assembly constructed in accordance with the subject invention is generally shown at 20 in
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
The typical pipe/tank juncture is a sharp edged corner as illustrated in
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
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
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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
In
In
In
It is to be understood that the various embodiments may employ the radius 32 shown 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
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.
