Condensing Heat Exchanger for Gas Furnaces

Abstract

A condensing heat exchanger (100, 100a) is disclosed that includes a pair of opposing half shells (145, 145a) connected together. The half shells (145, 145a) define an inlet (111) at one end and at least one outlet (112, 113) at an opposing end of the heat exchanger. The pair of opposing half shells (145, 145a) also defines a central axis (133). Each half shell (145, 145a) includes a plurality of elongated angled beads (117, 117a, 119) that extend inwardly towards the other half shell. The elongated angled beads (117, 117a, 119) of each half shell (145, 145a) extend traversely across the central axis (133) at an angle θ with respect to the central axis (133). The beads of one half shell (145, 145a) also extend traversely across one or more beads of the other half shell. The half shells (145, 145a) form two side channels (121, 121a, 122, 122a) for collecting condensate disposed opposite the plurality of elongated angled beads (117, 117a, 119) from one another and between the inlet (111) and at least one outlet (112, 113).

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application is a non-provisional patent application claiming priority under 35 USC §119(e) to U.S. Provisional Patent Application Ser. No. 61/247,328 filed on Sep. 30, 2009.

BACKGROUND

1. Technical Field

This disclosure relates to heat exchangers. More specifically, this disclosure relates to heat exchangers for gas furnaces in which water vapor present as a combustion gas product in flue gas is condensed and the latent heat of vaporization is transferred to another medium, such as air of an interior space. Still more specifically, this disclosure relates to enhanced internal flow barriers within condensing heat exchangers for improved heat transfer.

2. Description of the Related Art

Condensing heat exchangers are typically plate-type heat exchangers made from two opposing halves or half shells. Heat is transferred from the inside, between the half shells, to the exterior of the heat exchanger. The external fluid is air; the internal fluid is flue gas from hydrocarbon gas combustion (e.g., natural gas), which includes carbon dioxide and water vapor. One purpose of condensing heat exchangers is to condense the water vapor to liquid water thereby releasing the latent heat of vaporization of the water in the flue gas and the transfer this latent heat, along with other heat, to the air disposed the outside the heat exchanger.

Typically, the internal designs of condensing heat exchangers include barriers to flow which force the flue gas to travel through a tortuous path inside the heat exchanger before exiting the heat exchanger. The barriers cause the flow to change direction slightly or dramatically, which is intended to increase the total flow path length and residence time inside the heat exchanger, and increase contact between the flue gas and the interior walls of the heat exchanger. In current designs, the barriers to flow are often referred to as beads. Matching beads are disposed in each opposing half of the heat exchanger and the matching beads meet in a center plane dividing the two heat exchanger halves to form a barrier disposed normal or perpendicular to the general flue gas flow direction. The flue gas flow is diverted around the beads to the ends of the opposing beads and continues to flow through the heat exchanger through the path of least resistance. Typically, two paths of least resistance are created in the form of two channels extending along the top and bottom of the heat exchanger. As a result, a large portion of the flue gas bypasses the circuitous pattern created by the bead pattern.

FIGS. 1-4 are side views of a currently available condensing heat exchanger 10. The heat exchanger 10 includes a flue gas inlet 11 and a pair of gas outlets 12, 13. The internal flue gas directional flow is indicated by the arrows 14-16. The heat exchanger 10 features a plurality of beads 17, 18, 19 disposed normally to the flow direction 14-16. Channels 21, 22 are created by the ends 17′, 18′, 19′ of the beads 17, 18, 19 where the gas flow can bypass the circuitous path created by the beads 17, 18, 19. The eyelets 32 are used to hold the two half-shells of the heat exchanger 10 together.

FIG. 2 is a computational fluid dynamics (CFD) model of condensing heat exchanger of FIG. 1 which illustrates flue gas velocities. The darker areas 20 in the middle or core of the exchanger 10 indicate low flow rates and the lighter areas in the outer channels 21, 22 and inside the inlet 11 indicate higher flow rates. The white areas 17a, 18a, 19a indicate areas where the beads 17, 18, 19 of each half shell meet thereby creating a barrier to flow. Based on the higher flow rates at the inlet 11 and the lower flow rates in the middle or core 20 of the exchanger 10 downstream of the inlet 11 and between the channels 21, 22, the vast majority of the flue gas follows the initial circuitous paths shown at 23, 24 but then passes along the outer channels 21, 22 as opposed to the middle areas 20 of the heat exchanger 10.

FIG. 3 is another CFD model of the prior art condensing heat exchanger 10 of FIG. 1 which illustrates locations where water vapor condensation occurs and the relative amounts of condensation. The darker areas 20 in the middle of the exchanger between the outer channels 21, 22 experience little or no condensation. Significant amount of condensation occurs at the areas 25, 26 of the channels 21, 22 disposed toward the outlets 12, 13 and in the areas 27-31 disposed closer to the inlet 11. As seen in FIG. 3, the vast majority of the surface area in the middle 20 of the condensing heat exchanger 10 produces little or no condensation.

FIG. 4 is yet another CFD model of the prior art condensing heat exchanger 10 of FIG. 1 which illustrates surface temperatures. The darker areas toward the middle 20 and outlets 12, 13 are the coldest with the lighter areas disposed in the channels 21, 22 and towards the inlet 11 along the initial flow paths 23, 24 the hottest. FIG. 4 illustrates that the large area 20 in the core of the heat exchanger 10 has low wall temperatures and therefore it has high potential for condensation. However, FIG. 3 illustrates very little condensation occurring in the middle 20 downstream more than about ⅓ of the distance from the inlet 11. The velocity profiles of FIG. 2 indicate that there is little flow through the core areas 20 of the heat exchanger 10 and therefore condensation in the middle areas 20 is not possible.

SUMMARY OF THE DISCLOSURE

In satisfaction of these needs, an improved condensing heat exchanger is disclosed that comprises a pair of opposing half shells connected together. The half shells define an inlet at one end and at least one outlet at an opposing end of the heat exchanger. The pair of opposing half shells also defines a central axis. Each half shell comprises a plurality of elongated angled beads that extend inwardly towards the other half shell. The elongated angled beads of each half shell extend traversely across the central axis at an angle θ with respect to the central axis. The beads of one half shell also extend traversely across one or more beads of the other half shell. The half shells form two side channels for collecting condensate disposed opposite the plurality of elongated angled beads from one another and between the inlet and at least one outlet.

A method of reducing the size of a condensing heat exchanger as described above is also disclosed. The method comprises providing elongated angled beads in the opposing half shells that extend across the central core areas of the half shells between the side channels of the heat exchanger. The elongated angled beads of one half shell are not in matching registry with the elongated angled beads of the other half shell. Further, the elongated angled beads of one half shell extend traversely across the elongated angled beads of the other half shell. By incorporating these design features, the size of the heat exchanger can be reduced as a result of the improved efficiency.

Other advantages and features will be apparent from the following detailed description when read in conjunction with the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the disclosed methods and apparatuses, reference should be made to the embodiments illustrated in greater detail in the accompanying drawings, wherein:

FIG. 1 is a side plan view of a prior art condensing heat exchanger;

FIG. 2 is a computational fluid dynamics (CFD) model of the heat exchanger shown in FIG. 1 illustrating relative flue gas velocities through the heat exchanger;

FIG. 3 is a computational fluid dynamics (CFD) model of the heat exchanger shown in FIG. 1 illustrating areas where water vapor condenses and the relative amounts of condensation;

FIG. 4 is a computational fluid dynamics (CFD) model of the heat exchanger shown in FIG. 1 illustrating interior wall temperatures;

FIG. 5 is a side view of a disclosed condensing heat exchanger;

FIG. 6 is a computational fluid dynamics (CFD) model of a heat exchanger like that shown in FIG. 5, except the beads have flat upper surfaces, and illustrating relative flue gas velocities through the heat exchanger;

FIG. 7 is another computational fluid dynamics (CFD) model of the heat exchanger shown in FIG. 5 with beads having arced upper surfaces thereby reducing the proximity of intersecting beads to one another and illustrating relative flue gas velocities through the heat exchanger resulting in an improved flow distribution over the embodiment illustrated in FIG. 6;

FIG. 8 is a computational fluid dynamics (CFD) model of the heat exchanger shown in FIG. 7 illustrating areas where water vapor condenses and the relative amounts of condensation;

FIG. 9 is a computational fluid dynamics (CFD) model of the heat exchanger shown in FIGS. 7-8 illustrating interior wall temperatures;

FIG. 10 is a sectional view of a half shell equipped with arced beads disposed next to a mirror image of the half shell illustrating the arcing of the beads away from the centerlines of the half shells; and

FIG. 11 is a sectional view of a half shell equipped with non-arced beads disposed next to a mirror image of the half shell illustrating top surfaces of the beads extending along the centerlines of the half shells.

It should be understood that the drawings are not necessarily to scale and that the disclosed embodiments are sometimes illustrated diagrammatically and in partial views. In certain instances, details which are not necessary for an understanding of the disclosed methods and apparatuses or which render other details difficult to perceive may have been omitted. It should be understood, of course, that this disclosure is not limited to the particular embodiments illustrated herein.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

As shown in FIGS. 2-3, it must be concluded that the core areas 20 of the heat exchanger 10 are largely ineffective and improvements are therefore desirable. Further, it would also be desirable to have lower pressure drop to reduce the power needed to flow the flue gas through the heat exchanger. It would also be desirable to reduce the size of such heat exchangers thereby reducing the direct costs of the heat exchangers as well as the overall weight of the heat exchangers and associated parts.

Improved heat exchangers 100, 100a are illustrated in FIGS. 5-9. Components or elements that are analogous to those illustrated in FIGS. 1-4 will be labeled with the analogous reference numerals but include an additional 1-prefix, e.g., the inlet 111 (FIGS. 5-9) as opposed to the inlet 11 (FIGS. 1-4).

Instead of the conventional beads 17-19 of FIG. 1 that are normal or perpendicular to the gas flow 114-116, or that extend only partially across the flow path like the beads 18 of FIG. 1, the majority of disclosed beads 117, 119 of FIGS. 5-9 are angled with respect to the gas flow 114-116 or a central axis 133 and extend substantially across the heat exchangers 100, 100a leaving opposing side channels 121, 122 for the collection of condensed water. In the embodiments 100, 100a illustrated in FIGS. 5-9, the angle θ (FIG. 5) of the beads 117, 119 relative to the axis 133 is about 40°, however the angle θ can vary greatly depending upon the size of the heat exchanger 100, 100a, the flue gas flow rate, temperature and pressure, and the temperature, pressure and flow rate of the outer medium, which is typically indoor air or an indoor air flow. While the embodiments 100, 100a illustrated in FIGS. 5-9 employ an angle θ of about 40°, θ can range from about 20° to about 70°. The angle θ of about 40° of the beads 117, 119 with respect to the central axis 133 was determined by creating CFD models of heat exchangers with different angles. The eyelets 132 are used to connect opposing half shells 145 (FIG. 10) or 145a (FIG. 11) of the heat exchangers 100, 100a together.

FIGS. 6-7 are CFD models illustrating relative flow rates. Comparing FIGS. 6-7 with FIG. 2, the middle or core areas 120a (FIG. 6), 120 (FIG. 7) are substantially lighter than the corresponding core areas 20 of FIG. 2. Thus, the core areas 120a, 120 of the heat exchangers 100a, 100 experience substantially more flow than the core areas 20 of the conventional heat exchanger 10. The angle θ of the beads 117, 119 with respect to the flow path 114-116 and intersecting arrangement of the beads 117, 119 of the two half shells 145, 145a permit internal flow across the beads 117, 119 without causing most of the flow to be diverted to the opposing outer channels 121, 122. Specifically, in contrast to FIG. 2, the internal flow across the beads 117, 119 is not substantially barred as it is in the conventional heat exchanger 10 of FIGS. 1-4 wherein beads 17-19 of the opposing half shells that overlie each other.

By angling the beads 117, 119 at angle θ and having the beads 117, 119 of opposing half shells cross each other as opposed to overlying each other, the beads 117, 119 do not create a barrier to flow over the full length of the beads 117, 119. As a result, flue gas can more easily pass over the center core areas 120a, 120 of the heat exchangers 100a, 100 so that the center core areas 120a, 120 are better utilized for overall heat transfer. The angled beads 117, 119 permit the heat exchangers 100a, 100 to be smaller while accomplishing the same or higher efficiency than the prior art heat exchanger 10, depending on the height or width H (FIG. 5) selected for the new design 100a, 100. The flue gas is forced to flow from side 135, 135a to side 136, 136a and vice versa as flue gas passes over the beads 117, 119 between the inlet 111 and outlets 112, 113.

By allowing the flue gas to flow more freely through the center core areas 120a, 120 of the heat exchangers 100a, 100, the peak velocities 123a, 124a, 123, 124 near the inlets 111 are substantially reduced as compared to the high velocities along the initial flow paths 23, 24 as illustrated in FIG. 2 for the conventional exchanger 10. It will be noted that the velocities at 123, 124 for the heat exchanger 100 (FIG. 7) are even lower than those shown at 123a, 124a for the heat exchanger 100a due to the presence of the arc beads 117, 119 which will be discussed below in connection with FIGS. 10 and 11. As a result, the improved flow rate distribution illustrated in FIGS. 6-7 provides a reduced pressure drop across the heat exchangers 100a, 100 in comparison to the flow rates illustrated in FIG. 2, where the bulk of the flow proceeds through the outer channels 21, 22. While the flow rates through the channels 121a, 122a, 121, 122 in FIGS. 6-7 respectively remain substantial, the flow rates through the channels 121a, 122a, 121, 122 are substantially less than the flow rates through the channels 21, 22 of the prior art exchanger 10 as more gas flow is directed toward the central core areas 120a, 120 of the disclosed exchangers 100, 100a. Specifically, holding the operating conditions constant, the pressure drop across the heat exchanger 100 (FIGS. 7-9) is about ⅓ of the pressure drop across the conventional heat exchanger 10 The heat exchanger 100a also provides a reduced pressure drop vis-à-vis a heat exchanger 10.

FIG. 8 is a CFD model of the condensing heat exchanger 100 illustrating where water vapor condensation occurs. The area 137 near the inlet 111 experiences little or no water condensation. However, substantial amounts of water condensation occur in the middle areas 120 downstream of the second eyelets 132. Additional water condensation occurs in about two thirds of the lengths of the channels 121, 122. In contrast, the prior art heat exchanger 10 has fewer and smaller areas 25-31 where water condensation occurs. The comparison of FIGS. 3 and 8 clearly establish that the heat exchanger 100 is substantially more efficient than the prior art heat exchanger 10 of FIGS. 1-4.

FIG. 9 is a CFD model of the heat exchanger 100 illustrating surface temperature distribution. The area 137 near the inlet 111 is the hottest but the temperatures decrease substantially downstream of the first eyelet 132. FIG. 9 illustrates a more consistent distribution of temperature from the top channel 121 to the bottom channel 122 of the heat exchanger 100. This corresponds to the velocity pattern illustrated in FIG. 7. The lower peak velocities of the heat exchanger 100 in comparison to the higher peak velocities of the current heat exchanger 10 provides a greater amount flow through the central core area 120. As a result, the surface temperatures are more uniform along the length of the heat exchanger 100 as illustrated in FIG. 9.

As illustrated in FIG. 10, the beads 117 of each half shell 145 are preferably arced away from the opposing half shell 145. FIG. 11 illustrates non-arced beads 117a of a half shell 145a. FIGS. 10 and 11 are not sectional views, but mirror images of one half shell 145 for purposes of illustrating how the beads 117 of the heat exchanger 100 of FIGS. 5 and 7-9 are arced away from the center line 139. Because the arced, crossed beads 117 of one half shell 145 do not engage beads 117 of a corresponding half shell 145, the upper surfaces 138 of the arced beads 117 are exposed to the internal flue gas flow, which increases the proportion of usable surface area of each bead 117. The beads 119 that pass through the eyelets 132 do not need to be arced they are spaced apart from the beads 117, 119 of the other opposing half shell. The arced configuration provides a lower overall pressure drop, and more of the gas will flow through the core 120 of the heat exchanger 100. Variations of the distance that the centers of the beads 117 are raised will affect the performance. It is shown in CFD modeling that a gradual reduction in the distance to the center plane 139 from the beads 117 closest to the inlet to those closest to the outlets 112, 113 provides a slight increase in performance.

Side channels 121, 122 are created by the ends of the beads 117, 119 to permit easy extraction of the condensate. However, in contrast to the prior art design 10, the center core areas 120 of the heat exchanger 100 remain fully open so that the gas flow is not inhibited by the water collecting in the outer channels 121, 122.

Returning to FIG. 5, the vertical beads 141, 142 in the inlet region 137 of each half shell are off-set from the vertical beads 141, 142 of the corresponding opposing half shell. The offset design for the vertical beads 141, 142 permits the flue gas to flow over the top of the vertical beads 141, 142 and the vertical beads 141, 142 force the flue gas to flow from side 135 to side 136 and vice versa, which enhances contact with the interior core surfaces 120, 120a of the heat exchangers 100, 100a. Additional vertical beads 141, 142 can be added for increased heat transfer performance. The round inlet 111 end has a defined radius R. The radius R was optimized for efficiency performance and for manufacturability. A smaller radius R may be desirable for performance, and a larger radius R may be desirable for manufacturability. As the half shells 145, 145a become smaller in size, the need for eyelets 132 is reduced. Through CFD modeling, it has been shown that different placements of the eyelets 132 and the use of fewer eyelets 132 will improve the heat exchanger performance.

The performance of the heat exchangers 100, 100a may increase the overall furnace efficiency over the current production heat exchanger 10, at a reduced size thereby making a more efficiency gas furnace at a lower cost for materials.

As a result, the heat exchanger 100 illustrated in FIGS. 5 and 7-11 provide increased efficiency (e.g., about 15% or more), reduced pressure (by about 60% or more), and a reduced height H (by about 30% or more).

While only certain embodiments have been set forth, alternatives and modifications will be apparent from the above description to those skilled in the art. These and other alternatives are considered equivalents and within the spirit and scope of this disclosure and the appended claims.

Claims

1. A condensing heat exchanger (100, 100a) comprising:

a pair of opposing half shells (145, 145a) connected together, the half shells (145, 145a) defining an inlet (111) at one end and at least one outlet (112, 113) at an opposing end, the pair of opposing half shells (145, 145a) also defining a central axis (133),

each half shell (145, 145a) comprising a plurality of elongated angled beads (117, 119) that extend inwardly towards the other half shell (145, 145a), the elongated angled beads (117, 119) of each half shell (145, 145a) extending traversely across the central axis (133) at an angle θ with respect to the central axis (133), the beads (117, 119) of one half shell (145, 145a) extending traversely across one or more beads (117, 117a, 119) of the other half shell (145, 145a).

2. The condensing heat exchanger (100, 100a) of claim 1 wherein the half shells (145, 145a) form two side channels (121, 121a, 122, 122a) for collecting condensate disposed opposite the plurality of elongated angled beads (117, 117a, 119) from one another and between the inlet (111) and at least one outlet (112, 113).

3. The condensing heat exchanger (100, 100a) of claim 1 wherein each half shell (145, 145a) further comprises at least one perpendicular bead (141, 142) disposed in close proximity to the inlet (111).

4. The condensing heat exchanger (100, 100a) of claim 3 wherein the perpendicular beads (141, 142) of the half shells (145, 145a) are offset from one another.

5. The condensing heat exchanger (100, 100a) of claim 4 wherein each half shell (145, 145a) comprises from about two to about four perpendicular beads (141, 142) disposed in close proximity to the inlet (111).

6. The condensing heat exchanger (100, 100a) of claim 3 wherein the perpendicular beads (141, 142) do not extend across the central axis (133).

7. The condensing heat exchanger (100, 100a) of claim 1 wherein the elongated angled beads (117, 117a, 119) each comprise an elongated outer surface (138), the elongated outer surfaces (138) of at least some of the elongated angled beads (117, 117a, 119) being arced inwardly away from the opposing half shell (145, 145a) for increasing flow along the central axis (133).

8. The condensing heat exchanger (100, 100a) of claim 1 wherein the elongated angled beads (117, 117a, 119) each comprise two opposite ends (117′, 119′) with an elongated outer surface extending between the opposite ends (117′, 119′),

the elongated outer surfaces (138) of at least some of the elongated angled beads (117, 117a, 119) being arced inwardly away from the opposing half shell (145, 145a) between the two opposite ends (117′, 119′) so the two opposite ends (117′, 119′) are disposed closer to the opposing half shell (145, 145a) than a remainder of the arced outer surface (138) extending between the two opposite ends (117′, 119′).

9. The condensing heat exchanger (100, 100a) of claim 1 wherein θ ranges from about 20° to about 70°.

10. The condensing heat exchanger (100, 100a) of claim 1 wherein θ is about 40°.

11. The condensing heat exchanger (100, 100a) of claim 1 wherein the inlet (111) is co-axial with the central axis (133) and the heat exchanger (100, 100a) comprises two outlets (112, 113) disposed opposite the central axis (133) from each other.

12. The condensing heat exchanger (100, 100a) of claim 1 wherein the elongated angled beads (117, 117a, 119) of one half shell (145, 145a) are disposed of perpendicularly to the elongated angled beads (117, 117a, 119) of the other half shell (145, 145a).

13. A condensing heat exchanger (100, 100a) comprising:

a pair of opposing half shells (145, 145a) connected together, the half shells (145, 145a) defining an inlet (111) at one end and at least one outlet (112, 113) at an opposing end, the pair of opposing half shells (145, 145a) also defining a central axis (133),

each half shell (145, 145a) comprising a plurality of elongated angled beads (117, 117a, 119) that extend inwardly towards the other half shell, the elongated angled beads (117, 117a, 119) of each half shell (145, 145a) extending traversely across the central axis (133) at an angle θ with respect to the central axis (133), the beads of one half shell (145, 145a) extending traversely across one or more beads (117, 117a, 119, 119a) of the other half shell (145, 145a),

the elongated angled beads (117, 117a, 119) each comprising an elongated outer surface (138), the elongated outer surfaces (138) of at least some of the elongated angled beads (117, 117a, 119) being arced inwardly away from the opposing half shell (145, 145a) for increasing flow along the central axis (133),

the half shells (145, 145a) forming two side channels (121, 121a, 122, 122a) for collecting condensate disposed opposite the plurality of elongated angled beads (117, 117a, 119) from one another and between the inlet (111) and at least one outlet (112, 113).

14. The condensing heat exchanger (100, 100a) of claim 13 wherein each half shell (145, 145a) further comprises at least one perpendicular bead (141, 142) disposed in close proximity to the inlet (111).

15. The condensing heat exchanger (100, 100a) of claim 14 wherein the perpendicular beads (141, 142) of the half shells (145, 145a) are offset from one another.

16. The condensing heat exchanger (100, 100a) of claim 13 wherein θ ranges from about 20° to about 70°.

17. The condensing heat exchanger (100, 100a) of claim 12 wherein the elongated angled beads (117, 117a, 119) of one half shell (145, 145a) are disposed of perpendicularly to the elongated angled beads (117, 117a, 119) of the other half shell (145, 145a).

18. A method of reducing a size of a condensing heat exchanger (100, 100a) that comprises a pair of opposing half shells (145, 145a) connected together, the half shells (145, 145a) defining an inlet (111) at one end and at least one outlet (112, 113) at an opposing end, the pair of opposing half shells (145, 145a) also defining a central axis (133), the half shells (145, 145a) forming two side channels (121, 121a, 122, 122a) for collecting condensate disposed opposite the central core areas (120, 120a) of the two half shells (145, 145a), the method comprising:

providing elongated angled beads (117, 117a, 119) in the opposing half shells (145, 145a) that extend across the central core areas (120, 120a) of the half shells (145, 145a) between the side channels (121, 121a, 122, 122a), the elongated angled beads (117, 117a, 119) of one half shell (145, 145a) extending traversely across the elongated angled beads (117, 117a, 119) of the other half shell (145, 145a).

19. The method of claim 18 further comprising increasing flow across central core areas (120) of the opposing half shells (145) by arcing an elongated outer surface of at least some of the elongated angled beads (117) inwardly away from the opposing half shell (145) to increase space between the elongated angled beads (117, 119) of the two opposing half shells (145) and for increasing flow along the central axis (133) of the condensing heat exchanger (100).

20. The method of claim 17 wherein the elongated angled beads (117, 117a, 119) of each half shell (145, 145a) extending traversely across the central axis (133) at an angle θ with respect to the central axis (133), and wherein θ ranges from about 20° to about 70°.