# Patent

## Title
Heat exchanger flow balancing system

## Abstract

The heat exchanger flow balancing system serves to substantially equalize fluid flow through essentially identical diameter heat exchanger tubes in a heat exchanger having a single inlet plenum, a single outlet plenum, and a series of equal diameter heat exchanger tubes extending therebetween. In one embodiment, a series of different diameter orifices are provided at the inlet end of each of the tubes, with those tubes farther from the single larger diameter inlet pipe to the plenum generally having smaller orifices. In another embodiment, each of the tubes is provided with a conical nozzle at its inlet end, with those tubes farther from the single inlet pipe to the plenum generally having smaller diameter nozzles. The effect is to substantially equalize fluid flow through all of the heat exchanger tubes, thus increasing the efficiency of the heat exchanger.

## Background
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to devices for handling pneumatic flow, and particularly to a heat exchanger flow balancing system incorporating means for controlling the pneumatic flow through each of the multiple tubes of a heat exchanger in order to create substantially equal flow through each tube.
2. Description of the Related Art
Heat exchangers, also known as radiators in many applications, are used in a wide variety of applications including stationary and vehicle heating and air conditioning systems, engine supercharging and turbocharging intercooler systems, power generation, and other mechanical and pneumatic systems of various types. The heat exchangers manufactured for these systems are generally relatively simply constructed, with their heat exchanging tubes all being cut from the same stock material to have the same diameters and wall thicknesses. Generally, a single header or entry plenum is provided, with this plenum having a single relatively large diameter inlet with a relatively large number of equal diameter heat exchanger tubes extending to an outlet plenum with its single large diameter outlet or exhaust tube. The inlet and outlet tubes may connect to their respective plenums at either end of the plenum or at some point at or near the center of the plenum, or perhaps at some other location on the plenum depending upon manufacturing considerations, physical constraints for the intended installation, and perhaps other factors.
The problem with such equal tube diameter heat exchangers is that the fluid flow varies to each of the individual tubes, depending upon the distance of the tube inlet from the larger single intake tube of the plenum (and perhaps other factors as well, such as any changes in direction of airflow from the inlet tube to the individual heat exchanger tubes). Much the same problem can occur at the outlet plenum as well. This can result in significant variation in the fluid flow through the heat exchanger tubes located at some distance from the large intake tube, in comparison to those heat exchanger tubes having their inlets adjacent to the inflow from the single large intake tube. The result is that the heat exchanger is far less efficient than it might otherwise be, if the fluid flow were at least close to equal through each of the individual heat exchanger tubes.
Innumerable heat exchanger and radiator configurations have been developed in the past, as noted further above. An example of such is found in German Patent Publication No. 2,209,684 published on Sep. 13, 1973 to Karl Heinkel Apparatebau KG. This reference describes a heat exchanger having a two-way flow path contained within a single plenum, with the two flow directions separated by an internal wall. A series of tubes extend from the inlet side of the plenum, with these tubes contained concentrically within larger diameter tubes. Fluid flowing into the inlet side and through the smaller diameter tubes leaves the smaller tubes at their open distal ends, flowing into the surrounding larger diameter tubes and returning to the outlet side of the plenum.
Thus, a heat exchanger flow balancing system addressing the aforementioned problems is desired.
SUMMARY OF THE INVENTION
The heat exchanger flow balancing system is adapted for use in heat exchangers constructed with tubes of equal diameter extending between the inlet and outlet plenums, where the inlet and/or outlet plenum(s) do not distribute the fluid flow equally to all of the tubes. The flow balancing system serves to substantially equalize fluid flow through all of the tubes, thus substantially equalizing heat exchange between the tubes to increase the efficiency of the device.
Two examples of embodiments are provided and described, but should not be construed in a limiting sense. A first embodiment of a heat exchanger flow balancing system restricts the diameter of the inlet opening to various tubes, with the inlet opening being smaller for those tubes located farther from the single inlet tube or pipe of the plenum to substantially balance the flow in the tubes. A second embodiment of a heat exchanger flow balancing system accomplishes the flow equalization by means of a series of conical inlets, or nozzles, between each of the heat exchanger tubes and the plenum, with the inlet or nozzle opening being smaller for those tubes located farther from the single inlet tube or pipe of the plenum to substantially balance the flow in the tubes.
While the drawings depict heat exchangers having an intake plenum with a single large diameter delivery tube located substantially at the center of the plenum and with its axis normal to the axes of the smaller heat exchanger tubes, it will be seen that the heat exchanger flow balancing system may be configured for heat exchangers having their inlet or delivery tubes located in other positions relative to the plenum, e.g., at one end thereof, etc. The heat exchanger flow balancing system may be configured for installation at the outlet ends of the heat exchanger tubes, as well.
These and other features of the present invention will become readily apparent upon further review of the following specification and drawings.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a partial perspective view of a heat exchanger incorporating a first embodiment of the heat exchanger flow balancing system according to the present invention.
FIG. 2 is a perspective view in section along line 2-2 of the heat exchanger incorporating the heat exchanger flow balancing system of FIG. 1, illustrating further details thereof.
FIGS. 3A through 3F are a series of elevation views in section through six of the tubes of the heat exchanger of FIGS. 1 and 2, illustrating the different diameter restrictions incorporated with each to equalize the pneumatic flow through the tubes.
FIG. 4 is a partial perspective view of a heat exchanger incorporating a second embodiment of the heat exchanger flow balancing system according to the present invention.
FIG. 5 is a perspective view in section along line 5-5 of the heat exchanger incorporating the heat exchanger flow balancing system of FIG. 4, illustrating further details thereof.
FIGS. 6A through 6F are a series of elevation views in section through six of the tubes of the heat exchanger of FIGS. 4 and 5, illustrating the different conical restrictions incorporated with each to equalize the pneumatic flow through the tubes.
FIG. 7 is a graph illustrating the uncorrected flow through a heat exchanger and the corrected flows respectively through the heat exchanger for the first and the second embodiments of the heat exchanger flow balancing system according to the present invention.



Unless otherwise indicated, similar reference characters denote corresponding features consistently throughout the attached drawings.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The heat exchanger flow balancing system includes, for example, various embodiments, each providing for the equalization or substantial equalization of flow through the various tubes of the heat exchanger. The equalizing of the flow through the tubes results in relatively greater efficiency of the heat exchanger, as all of the tubes have substantially equal flow and thus substantially equal heat transfer with the surrounding environment.
FIGS. 1 through 3F illustrate a first embodiment of a heat exchanger flow balancing system, with FIG. 1 illustrating a heat exchanger 10 incorporating the first embodiment. The heat exchanger 10 has a first plenum or header 12a and an opposite second plenum or header 12b (shown in broken lines) with a plurality of substantially equal diameter heat exchanger tubes 14a through 14s extending therebetween. It will be understood that the nineteen heat exchanger tubes 14a through 14s are exemplary, and that more or fewer such tubes may be provided. Each of the two plenums 12a and 12b has a first end, respectively 16a and 16b, an opposite second end, respectively 18a and 18b, and a tube wall, respectively 20a and 20b, with the series of heat exchanger tubes 14a through 14s extending between the two tube walls 20a and 20b. A first transfer pipe 22a extends generally medially from the first plenum 12a, and a second transfer pipe 22b extends generally medially from the second plenum 12b. Fluid flow through the heat exchanger 10 may be in either direction, with the first transfer pipe 22a and plenum 12a serving as an inlet pipe and plenum, or as the outlet pipe and plenum, depending upon the connection of the heat exchanger 10 to the remainder of the heat exchanger system.
In FIG. 2, the interior of the tube wall 20a of the first plenum 12a is shown clearly in the perspective view in section along line 2-2 of FIG. 1, with the heat exchanger tubes 14a through 14s extending therefrom to the opposite second plenum 12b. The junctures of the ends of the substantially equal diameter tubes 14a through 14s are shown in broken line circles of equal diameter along the tube wall 20a of the first plenum 12a in FIG. 2. However, a series of flow restriction orifices 24a through 24s of varying diameters are shown within the broken line circles designating the tube ends. FIGS. 3A through 3F provide cross-sectional elevation views through various tubes and their flow restriction orifices, to illustrate concepts of the heat exchanger 10. The orifices 24a through 24s may be integral with the tube wall 20a of the plenum 12a, e.g., formed by punching or otherwise forming holes or passages through the tube wall 20a, or alternatively by welding or otherwise adding a disc of material across larger passages formed for each of the heat exchanger tubes, or across the ends of the tubes, with the discs having calibrated flow restriction orifices formed therethrough.
The orifices 24a through 24s vary in diameter from smallest orifices 24a and 24s at the extreme ends 16a and 18a of the plenum 12a, generally as shown in FIG. 3F, to largest orifices 24i and 24k immediately to the sides of the central transfer pipe 22a, generally as shown in FIG. 3B. This is because fluid flowing into or out of the plenum 12a through the transfer pipe 22a will generally have a relatively large radial velocity component relative to the tubes as it flows along the length or span of the plenum 12a, i.e., the fluid will tend to flow across the openings to the tubes rather than directly into the tubes. The exception is of course at the ends of the plenum, where the fluid is constrained by the plenum ends 16a and 18a. The corresponding tubes 14a and 14s would thus allow significantly greater flow than the tubes further inboard. Accordingly, the smallest diameter flow restriction orifices 24a and 24s are provided for tubes 14a and 14s to substantially equalize their flow relative to other tubes of the heat exchanger 10.
The greatest radial velocity component is typically generated closest to the center of the plenum 12a, close to the transfer pipe 22a. Accordingly, the largest diameter orifices 24i and 24k are located at the entrances to the corresponding tubes 14i and 14k, generally as shown in the cross-sectional view of FIG. 3B. However, it will be seen that the tube 14j located between the two tubes 14i and 14k, has its opening essentially concentric with the center of the transfer pipe 22a. The fluid at this location essentially “splits” to flow in opposite directions through the length of the plenum 12a, with little radial velocity component directly along the center of the transfer pipe 22a. Thus, the central tube 14j will have relatively high flow and a correspondingly small orifice 24j is installed at the opening thereto, generally as shown in FIG. 3A. The orifice 24j may be about the same diameter as the two extreme end orifices 24a and 24s, or perhaps only slightly larger, depending upon the measured or calculated flow, for example.
The other orifices have intermediate diameters between the relatively smallest diameters of the two end orifices 24a and 24s and the relatively largest diameters of the two orifices 24i and 24k, with the diameters changing incrementally, or changing based on the radial velocity at the corresponding orifice, between smallest and largest orifices, to substantially balance the flow in the tubes. Thus, typically the diameter of the orifice 24b is larger than the diameter of the orifice 24a, the orifice 24c is slightly larger in diameter than the diameter of the orifice 24b, etc., with the diameter of the orifice 24i being slightly larger than the diameter of the orifice 24h and the orifice 24i having a diameter substantially equal to the inner diameter of the tube 14i, and the diameter of the tube 14i being substantially equal to the diameter of the other tubes 14a through 14s, for that matter. Similarly, the orifices 24l to 24r gradually decrease in diameter between the relatively largest diameter of the orifice 24k and the relatively smallest diameter of the orifice 24s. For example, FIG. 3C illustrates an intermediate orifice 24g or 24m for tube 14g or 14m, FIG. 3D illustrates a somewhat smaller diameter intermediate orifice 24e or 24o for the corresponding tubes 14e or 14o, and FIG. 3E illustrates an even smaller diameter intermediate orifice 24c or 24q for corresponding tubes 14c or 14q. Other orifices not shown in FIGS. 3A-3F have diameters that fall between those depicted in FIGS. 3A through 3F in a relative order, for example.
FIGS. 4 through 6F provide illustrations of a second embodiment of a heat exchanger flow balancing system. FIGS. 4 and 5 illustrate a heat exchanger 110. The heat exchanger 110 includes first and second plenums 112a and 112b, with the plenums having first and second ends and tube walls 116a, 118a, and 120a for the first plenum 112a and 116b, 118b, and 120b for the second plenum 112b. First and second transfer pipes, respectively 122a and 122b, extend from the medial areas of the two corresponding plenums 112a and 112b. A plurality of heat exchanger tubes 114a through 114s extend between the two tube walls 120a and 120b of the two plenums 112a and 112b, similar to those in the first embodiment heat exchanger 10.
The heat exchanger embodiment 110 differs from the earlier discussed embodiment 10 in the configuration of the flow restrictors. In the embodiment of the heat exchanger 110 of FIGS. 4 through 6F, the flow restrictors include a plurality of nozzles that include conical nozzles, respectively nozzles 124a through 124s, disposed between the corresponding tubes 114a through 114s and the tube wall 120a. Each of the nozzles 124a through 124s has a minor diameter 126 equal to the diameter of the corresponding tube 114a through 114s to which it is attached, such as shown in FIGS. 6A through 6F. However, the major diameter of the nozzles 124a through 124s varies depending upon the required flow restriction to substantially equalize or equalize the flow through each of the tubes 114a through 114s. 
FIGS. 6A through 6G provide a series of cross-sectional views to illustrate examples of the different major diameters and corresponding conical angles of the nozzles 124a through 124s, relative to each other. FIG. 6A illustrates the very narrow conical nozzle configuration 124j that would be installed between the tube wall 120a and the central heat exchanger tube 114j. This configuration is analogous to the orifice 24j of FIG. 3A. As this tube 114j allows nearly the maximum flow due to its location at the transfer pipe 122a and the lack of any significant radial flow vector at this location, the conical shape of the nozzle 124j is quite narrow, and is very nearly cylindrical, for example. FIG. 6B provides a cross-sectional view of the widest major diameter conical nozzle 124i or 124k that would be installed with the corresponding tubes 114i and 114k immediately adjacent to the inlet of the transfer pipe 122a. This relatively wide conical shape is analogous to the largest orifices 24i and 24k, as shown in FIG. 3B. FIG. 6C illustrates a conical nozzle 124g or 124m having a slightly smaller major diameter, analogous to the orifice 24g or 24m of FIG. 3C. FIG. 6D illustrates an intermediate conical nozzle 124e or 124o, analogous to the intermediate orifices 24e, 24o of FIG. 3D. FIG. 6E illustrates an even narrower conical nozzle 124c, 124q analogous to the orifices 24c and 24q of FIG. 3E. Finally, FIG. 6F illustrates a cross-sectional view in which the nozzle 124a or 124s has no or substantially no conical taper whatsoever, i.e., the major diameter where it joins the tube wall 120a is the same or substantially the same as the internal diameter of the tube 114a, 114s. This is analogous to the smallest orifice 24a or 24s provided for the pipes 14a and 14s as shown in FIG. 3F of the drawings.
Referring to FIG. 7, tests have been performed using an experimental prototype, to determine the equalization of flow provided by the different diameter orifices or conical nozzles installed in embodiments of heat exchangers of a heat exchanger flow balancing system. FIG. 7 provides a graph 200 illustrating the results of this testing. The lower portion of the graph 200 includes a representation of a tube wall 202 having a plurality of different diameter flow restrictions 204a through 204q installed therewith. This presentation has two fewer tubes and restrictors than the embodiments of FIGS. 1 through 6F for clarity in FIG. 7, but the principle of flow balancing remains substantially the same. The flow restrictions may include the orifices of the embodiment of the heat exchanger 10 of FIGS. 1 through 3F, or the conical nozzles of the embodiment of the heat exchanger 110 of FIGS. 4 through 6F, for example.
The graph 200 represents testing performed upon a plenum (or header) wherein the transfer pipe (e.g., inlet pipe) is installed at the center of the elongate header or plenum, with the central orifice 204i positioned at the center of the header. The legend at the top of the graph 200 indicates that the solid black line 206 represents a standard flow pattern in a conventional header tube (or plenum and tube) assembly, without varying the inlet orifices of the tubes. It can be seen that the solid line 206 on the graph 200 reaches maximum flow rates at the extreme ends of the plenum or header, through the end tubes and orifices 204a and 204q. Minimal flow rates are achieved through the orifices 204f, 204g, 204k, and 204l to each side of the central transfer pipe at the center of the header or plenum, with the difference in flow rates being on the order of about five times less through the unmodified orifices 204f, 204g, 204k, and 204l in comparison to the unmodified orifices 204a and 204q at the extreme ends of the header or plenum, for example.
Results following installation of flow restriction orifices as in the embodiment of FIGS. 1 through 3F are shown by the uniformly dashed line 208 on the graph 200. It will be seen that placement of restrictor orifices, as described above, results in a considerable smoothing out of the flow curve, thus showing a relatively significant gain in equalizing or substantially equalizing the flow rates through all of the heat exchanger tubes. The difference in flow rates as shown by the dashed line 208 is only about fifteen percent, approximately, for example.
In the graph 200, the alternating long and short dashed line 210 represents the flow rates following installation of a series of conical restrictor nozzles, as described above in the embodiment of FIGS. 4 through 6F. Once again, the flow rates have been very nearly equalized or substantially equalized throughout all of the heat exchanger tubes, with the difference in maximum and minimum flow rates being only approximately fifteen percent, for example. Further adjustment of orifice or nozzle diameters may result in further equalization of flow in the tubes, but the results achieved from the test, as illustrated in the graph 200, indicate a relative sufficiency for practical purposes.
Numerous variations on the above-described heat exchanger configurations may be provided while still making use of either (or perhaps both) of the flow modification orifices or nozzles described further above. For example, the heat exchanger may have its transfer pipe (inlet or outlet) located at or close to one end of the plenum or header. In such a case, the mirror image installation of restrictors to each side of the transfer pipe typically may not be applicable, but the restrictors may decrease in diameter toward the most distant heat exchanger tube. Moreover, while the restrictors have been described as being installed at the inlet plenum ends of the tubes, the term “transfer pipe” is intended to include either an inlet pipe or an outlet pipe, and should therefore not be construed in a limiting sense. In certain circumstances, the restrictors (orifices or nozzles) may be installed at the outlet ends of the heat exchanger tubes, or some combination of inlet end and outlet end installations may be carried out, for example. In any event, the installation of such orifice or nozzle restrictors in embodiments of heat exchangers, in a manner similar to the described embodiments, can significantly improve the average flow through such heat exchangers, and can thereby significantly increase heat exchanger efficiencies.
It is to be understood that the present invention is not limited to the embodiments described above, but encompasses any and all embodiments within the scope of the following claims.

## Claims

1. A heat exchanger flow balancing system, comprising:
a first plenum having a first end, a second end opposite the first end, and a tube wall, wherein the first plenum extends between the first and second ends thereof along a first direction;
a first transfer pipe communicating with the first plenum, wherein the first transfer pipe extends along a second direction orthogonal to the first direction;
a second plenum spaced apart from the first plenum, the second plenum having a first end, a second end opposite the first end, and a tube wall, wherein the second plenum extends between the first and second ends thereof along the first direction;
a second transfer pipe communicating with the second plenum, wherein the second transfer pipe extends along the second direction;
a plurality of tubes extending between the tube wall of the first plenum and the tube wall of the second plenum, each of the tubes being of equal diameter to one another, the first plenum communicating with the second plenum by the plurality of tubes extending therebetween, wherein each said tube extends along a third direction orthogonal to the first and second directions; and
a flow restriction disposed at a juncture of each of the tubes with the first plenum, where smallest diameter restrictions are located at a juncture nearest the first transfer pipe and at each juncture farthest from the first transfer pipe, where diameters of the flow restrictions of the remaining junctures of the remaining transfer pipes decreases from the restriction at the juncture nearest first transfer pipe to each of the junctures farthest from the first transfer pipe.

2. The heat exchanger flow balancing system according to claim 1, wherein the flow restrictions comprise restrictor orifices formed in the tube wall.

3. The heat exchanger flow balancing system according to claim 1, wherein the flow restrictions comprise conical nozzles disposed between the tube wall and the tubes.

4. The heat exchanger flow balancing system according to claim 3, wherein each of the conical nozzles has a minor diameter equal to the tube diameter and a major diameter at the juncture of each corresponding tube with the first plenum.

5. The heat exchanger flow balancing system according to claim 1, wherein at least the first transfer pipe is disposed medially with the first plenum.

6. The heat exchanger flow balancing system according to claim 1, wherein the first plenum is an inlet plenum.

7. The heat exchanger flow balancing system according to claim 1, wherein the first plenum is an outlet plenum.

8. A heat exchanger flow balancing system, comprising:
a first plenum having a first end, a second end opposite the first end, and a tube wall, wherein the first plenum extends between the first and second ends thereof along a first direction;
a first transfer pipe communicating with the first plenum, wherein the first transfer pipe extends along a second direction orthogonal to the first direction;
a second plenum spaced apart from the first plenum, the second plenum having a first end, a second end opposite the first end, and a tube wall, wherein the second plenum extends between the first and second ends thereof along the first direction;
a second transfer pipe communicating with the second plenum, wherein the second transfer pipe extends along the second direction;
a plurality of tubes extending between the tube wall of the first plenum and the tube wall of the second plenum, each of the tubes being of equal diameter to one another, the first plenum communicating with the second plenum by the plurality of tubes extending therebetween, wherein each said tube extends along a third direction orthogonal to the first and second directions; and
a restrictor orifice disposed in the tube wall at a juncture of each of the tubes with the first plenum, where smallest diameter restrictor orifices are located at a juncture nearest the first transfer pipe and at each juncture farthest from the first transfer pipe, where diameters of the restrictor orifices of the remaining junctures of the remaining transfer pipes decreases from the restrictor orifice at the juncture nearest first transfer pipe to each of the junctures farthest from the first transfer pipe.

9. The heat exchanger flow balancing system according to claim 8, wherein at least the first transfer pipe is disposed medially with the first plenum.

10. The heat exchanger flow balancing system according to claim 8, wherein the first plenum is an inlet plenum.

11. The heat exchanger flow balancing system according to claim 8, wherein the first plenum is an outlet plenum.

12. A heat exchanger flow balancing system, comprising:
a first plenum having a first end and a second end opposite the first end, wherein the first plenum extends between the first and second ends thereof along a first direction;
a first transfer pipe communicating with the first plenum, wherein the first transfer pipe extends along a second direction orthogonal to the first direction;
a second plenum spaced apart from the first plenum, the second plenum having a first end and a second end opposite the first end, wherein the second plenum extends between the first and second ends thereof along the first direction;
a second transfer pipe communicating with the second plenum, wherein the second transfer pipe extends along the second direction;
a plurality of tubes extending between the first plenum and the second plenum, each of the tubes being of equal diameter to one another, the first plenum communicating with the second plenum by the plurality of tubes extending therebetween, wherein each said tube extends along a third direction orthogonal to the first and second directions; and
a nozzle disposed at a juncture of each of the tubes with the first plenum, where smallest diameter nozzles are located at a juncture nearest the first transfer pipe and at each juncture farthest from the first transfer pipe, where diameters of the nozzles of the remaining junctures of the remaining transfer pipes decreases from the nozzle at the juncture nearest first transfer pipe to each of the junctures farthest from the first transfer pipe.

13. The heat exchanger flow balancing system according to claim 12, wherein the nozzles comprise conical nozzles having a minor diameter equal to the tube diameter and a major diameter at the juncture of each corresponding tube with the first plenum.

14. The heat exchanger flow balancing system according to claim 12, wherein at least the first transfer pipe is disposed medially with the first plenum.

15. The heat exchanger flow balancing system according to claim 12, wherein the first plenum is an inlet plenum.

16. The heat exchanger flow balancing system according to claim 12, wherein the first plenum is an outlet plenum.