FIELD OF THE DISCLOSURE
The present disclosure generally relates to heat exchangers, and more particularly, to asymmetric dimple tubes for use with heat exchangers as applied to gas furnaces.
BACKGROUND OF THE DISCLOSURE
Heat exchangers are commonly known in the art of gas heating and typically used in conjunction with gas furnaces to provide heat to residential and commercial buildings. A typical gas furnace includes a burner which heats gases and supplies the heated gases into an inlet and through a tube of an associated heat exchanger. The tube of a heat exchanger generally provides one or more bends and passes through which the heated flue gases may travel. The heated gases traveling through the bends and passes emit radiation in the form of heat that is transferred through the walls of the tube. One or more fans are used to continuously move air over the surfaces of the heat exchanger tube so as to warm the air using the heat emitted through the heat exchanger tube. Vents and ducts channel the heated air into the interior spaces or rooms within the residential or commercial building. The heated air which eventually cools after some circulation is fed back toward the heat exchanger via the fans to be reheated and recirculated back into the rooms. The flue gases within the heat exchanger never reach the interior spaces of the home or building, and exhausted gases are safely discharged to an exterior of the home or building by induction blowers, or the like.
In residential applications, gas furnaces with such heat exchanger structures have been installed in confined spaces, such as the basement, of the home. In commercial applications, similar furnace and heat exchanger structures have been installed as roof-top units in order to save more valuable floor space. Heat exchangers of both applications share the common goal of transferring as much heat as possible from the heated flue gases into the surrounding air. Moreover, it is well known in the art that the efficiency of a heat exchanger to transfer heat is enhanced by slowing the flow of the heated gases through the passes of the heat exchangers and increasing turbulence thereof.
One existing approach to cause such turbulence uses baffles that are provided within the passes of the heat exchanger tube. Baffles disposed directly in the path of flue gases serve to cause turbulence and hinder the gas flow, and further, to increase the overall transfer of heat to the surrounding air. However, the physical nature of baffles allows substantial vibration and thus noise from within the passes of a particular heat exchanger tube. Furthermore, installing baffles into a heat exchanger tube adds several steps to the manufacturing and assembly thereof, and thus, adds to the overall costs to fabricate same.
Another approach to enhance the efficiency of heat transfer employs the flattening of certain sections of the heat exchanger tube so as to narrow the flow path. While such deformations cause a desired disturbance in the flow of gases therethrough, these deformations also cause inconsistencies in the overall cross-sectional width of the heat exchanger tube. More specifically, flattened sections tend to have wider cross-sections, or cross-sections with widths which extend beyond that of those sections of the tube that are not flattened. Such inconsistencies cause low spots, which in particular arrangements, may trap condensation and complicate any necessary draining.
Still further developments in the prior art provide a heat exchanger or dimple tube 10 having an inlet 12 and an outlet 13, as shown for example in FIGS. 1-4. The dimple tube 10 of FIG. 1 includes one bend 14 which defines a first pass 16 through which a premixed combustion gas is received and a second pass 17 through which the heated flue gases are discharged. As shown in FIG. 1, two linear sets or rows of dimples 18, 19 are evenly spaced and distributed along the length of the second pass 17 of the heat exchanger 10. The two rows of dimples 18, 19 are configured to directly correspond to one another and form opposing dimple pairs 18, 19, which at least partially constrict the passageway of the second pass 17 at distinct points. Moreover, the dimple pairs 18, 19 are configured to enable longer circulation of the heated gas within the second pass 17 and to cause more heat to transfer from the heated gas to the air surrounding the heat exchanger 10.
Each dimple pair 18, 19 consists of two dimples 18, 19 that are indented into opposing surfaces of the second pass 17 to restrict gas flow. Additionally, each dimple 18, 19 is symmetric in that it forms a converging upstream section 20 and a diverging downstream section 21 of equal lengths. The midpoint between the upstream and the downstream section 20, 21, or the merge point 22, has the smallest cross-sectional area, and thus, represents the most constrictive portion of the second pass 17. Such dimple tubes 10 overcome many of the deficiencies associated with heat exchangers with baffles by facilitating assemblies thereof and minimizing fabrication costs. Dimple tubes 10 also overcome many of the aforementioned deficiencies associated with heat exchangers with flattened sections by providing a generally circular cross-section and eliminating low points.
As demonstrated in FIGS. 2 and 3, the flow of flue gases passing the narrow merge point 22 of the dimple pair 18, 19 accelerates while the pressure thereof decreases. After exiting the merge point 22 and while in the diverging downstream section 21 the flue gases decrease in velocity and the pressure thereof is recovered. At the diverging downstream section 21 of the dimple pair 18, 19, however, a vortex and separation of the gases occur. Although the vortex enhances heat transfer, which is desirable, separation generates a significant loss of flow and a substantial pressure drop in the overall heat exchanger tube 10, which is undesirable. Accordingly, currently existing dimple tube 10 configurations provide adequate heat transfer but at a high cost of flow and pressure loss. Some modifications to overcome the pressure loss may employ smaller diameter and/or double dimple tubes which may not be effectively incorporated into all applications.
Therefore, there is a need for a more efficient heat exchanger which overcomes all of the deficiencies of the prior art. Moreover, there is a need for a heat exchanger with a tube structure that is quieter, increases heat transfer and substantially reduces losses in gas flow as well as losses in overall gas pressure. Furthermore, there is a need for a heat exchanger configuration that is easier and less costly to manufacture or assemble. There is also a need to provide a more efficient heat exchanger that is adaptable to both residential and commercial applications.
SUMMARY OF THE DISCLOSURE
In accordance with one aspect of the disclosure, a heat exchanger tube for a gas furnace is provided. The heat exchanger tube may extend between an inlet and an outlet so as to form a passageway therethrough for receiving a combustion gas. The heat exchanger tube may also include one or more asymmetric dimple pairs disposed between the inlet and the outlet. Each asymmetric dimple pair may include a first dimple and an opposing second dimple. The first and second dimples may be configured to at least partially constrict flow of gas therethrough. Each dimple may be configured to form an upstream section, a downstream section and a merge point.
In accordance with another aspect of the disclosure, another heat exchanger tube for a gas furnace is provided. The heat exchanger tube may include an inlet and an outlet which forms a passageway therethrough for receiving a combustion gas. The heat exchanger tube may also include at least two rows of asymmetric dimples that are disposed along opposing sides of the heat exchanger tube so as to form a plurality of dimple pairs. Each dimple pair may be configured to at least partially constrict flow of gas therethrough. Each dimple pair may also be configured to form an upstream section, a downstream section and a merge point. The upstream section may be shorter in length than the downstream section.
In accordance with yet another aspect of the disclosure, a heating and cooling system is provided. The heating and cooling system may include a ventilation duct, at least one blower or fan as well as at least one heat exchanger tube disposed within the ventilation duct and proximate to the fan. The ventilation duct may be configured to communicate external air with an interior space of a home or building. The fan may be configured to draw the external air through the ventilation duct and toward the interior space. The heat exchanger tube may be configured to receive a heated combustion gas therethrough and heat the external air supplied by the fan. The heat exchanger tube may include a plurality of asymmetric dimple pairs that are at least partially disposed along a length of the heat exchanger tube. Each asymmetric dimple pair may include two opposing dimples that are configured to at least partially constrict flow of gas therethrough. Furthermore, each asymmetric dimple may form an upstream section, a downstream section and a merge point wherein, the upstream section is shorter in length than the downstream section.
These and other aspects of this disclosure will become more readily apparent upon reading the following detailed description when taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a symmetric dimple tube as used in a prior art heat exchanger;
FIG. 2 is a partial perspective view of the symmetric dimple tube of FIG. 1 illustrating the velocity of gas flowing therethrough;
FIG. 3 is another partial perspective view of the symmetric dimple tube of FIG. 1 illustrating the pressure of gas flowing therethrough;
FIG. 4 is another partial perspective view of the symmetric dimple tube of FIG. 1 illustrating the heat transfer properties through the surface thereof;
FIG. 5 is a perspective view of an exemplary configuration of a heating and cooling system;
FIG. 6 is a perspective view of an asymmetric dimple tube constructed in accordance with the teachings of the disclosure;
FIG. 7 is a partial perspective view of the asymmetric dimple tube of FIG. 6;
FIG. 8 is a cross-sectional view of the asymmetric dimple tube of FIG. 6;
FIG. 9 is another partial perspective view of the asymmetric dimple tube of FIG. 6 illustrating the velocity of gas flowing therethrough;
FIG. 10 is another partial perspective view of the asymmetric dimple tube of FIG. 6 illustrating the pressure of gas flowing therethrough;
FIG. 11 is another partial perspective view of the asymmetric dimple tube of FIG. 6 illustrating the heat transfer properties through the surface thereof; and
FIG. 12 graphically illustrates the heat transfer and pressure drop characteristics of the asymmetric dimple tube of FIG. 6 as compared to those of the symmetric dimple tube of FIG. 1.
While the present disclosure is susceptible to various modifications and alternative constructions, certain illustrative embodiments thereof have been shown in the drawings and will be described below in detail. It should be understood, however, that there is no intention to be limited to the specific forms disclosed, but on the contrary, the intention is to cover all modifications, alternative constructions, and equivalents falling with the spirit and scope of the present disclosure.
DETAILED DESCRIPTION
Referring to the drawings and with particular reference to FIG. 5, an exemplary asymmetric dimple tube of a heat exchanger is provided and referred to as reference number 110. It is understood that the teachings of the disclosure may be used to construct asymmetric dimple tubes above and beyond those specifically disclosed below. One of ordinary skill in the art will readily understand that the following are only exemplary embodiments.
As schematically shown in FIG. 5, an exemplary heat exchanger or asymmetric dimple tube 110 is provided as applied to, for example, a heating and/or cooling system 200 of a commercial building, or the like. The heat exchanger 110 may typically provide a passageway through which heated gases from a burner 202, or the like, are received. The heat exchanger 110 may be configured to emit the heat carried by the heated gases through the surfaces of the heat exchanger 110 and into the air surrounding the heat exchanger 110. The heated air surrounding the heat exchanger 110 may be directed into the rooms of a building or similar interior spaces 204 using fans 206 and associated ventilation ducts 208, or the like. Exhausted flue gases may be safely isolated from the surrounding air and discharged to an exterior of the building using an induction blower 210, or the like.
Referring now to FIG. 6, the heat exchanger or asymmetric dimple tube 110 may include an inlet 112, an outlet 113 and one or more bends 114 disposed therebetween so as to form two or more passes 116, 117. The first pass 116 may be configured to receive a premixed combustion gas through the inlet 112 to be routed through the bend 114. The second pass 117 may be configured to receive and discharge the heated flue gases through the outlet 113. In order to optimize the efficiency of heat transfer, or to improve the ability of the heat exchanger 110 to transfer heat, the heat exchanger 110 may be configured to partially reduce the flow of gas and/or to cause turbulence. Deformations in the form of dimples 118, 119, or the like, may be used to cause such turbulence.
As shown in the embodiment of FIG. 6, two linear sets or rows of dimples 118, 119 may be evenly spaced and distributed along the length of the second pass 117 of the heat exchanger 110. Specifically, the two rows of dimples 118, 119 may be configured to directly correspond to one another and form opposing dimple pairs 118, 119, which at least partially constrict the passageway of the second pass 117 at distinct points. Moreover, the dimple pairs 118, 119 may be configured to enable longer circulation of the heated gas within the second pass 117 and to cause more heat to transfer from the gas to the air surrounding the heat exchanger 110. In alternative embodiments, a particular pass 116, 117 of a heat exchanger 110 may include only one row of dimples 118, or more than two rows of dimples 118, 119. In still further alternatives, each set of dimples 118, 119 may be distributed nonlinearly or spirally along the length of one or more passes 116, 117.
Referring now to FIGS. 7 and 8, each dimple pair 118, 119 may include two opposing dimples 118, 119 that are indented into opposing sides of the second pass 117. Each dimple pair 118, 119 may be configured to form a converging upstream section 120, a diverging downstream section 121 as well as a merge point 122 disposed between the upstream and downstream sections 120, 121. The dimple pair 118, 119 may be configured such that the merge point 122 has the smallest cross-sectional area, and thus, the most constrictive portion of the second pass 117. As compared with the prior art embodiments of FIGS. 1-4, the dimples 118, 119 of the heat exchanger tube 110 may be asymmetric in that the upstream and downstream sections 120, 121 have unequal lengths. For example, as shown in the exemplary embodiment of FIG. 7, the upstream section 120 may be configured to have a length Lu that is shorter than the length Ld of the downstream section 121. The ratio of the upstream length Lu to the downstream length Ld may be dependent upon various factors, such as the cross-sectional diameter of the second pass 117, internal and external flow rates, tube operating points, and the like. In the particular embodiment of FIG. 7, for example, the upstream length Lu may be substantially shorter than the length of the downstream section Ld. Such a configuration may significantly improve the efficiency of heat transfer and compensate for losses in gas flow or pressure as heated gases travel past the merge point 122 and through the downstream section 121.
Turning now to FIGS. 9 and 10, modeled characteristics of gas flow within an exemplary dimple pair 118, 119 are provided. More specifically, the embodiment of FIG. 9 may graphically illustrate the changes in velocity of a gas as it flows into the converging upstream section 120, through the merge point 122 and as it exits the diverging downstream section 121. The distribution of the gas flow through the asymmetric dimple tube 110 may be indicated by the velocity vectors shown. The embodiment of FIG. 10 may similarly illustrate changes in pressure as gas flows through the merge point 122, wherein darker areas may indicate higher pressures and lighter areas may indicate lower pressures.
As compared to the analogous illustrations of FIGS. 2 and 3 of the symmetric dimple tube 10 of the prior art, the longer downstream section 121 of the asymmetric dimple tube 110 of FIGS. 9 and 10 may provide a more conservative expanding angle. In doing so, separations in the gas flow exiting the merge point 122 of the asymmetric dimple pair 118, 119 may be significantly reduced. For instance, gas exiting the merge point 22 of the symmetric dimple pair 18, 19 of FIG. 2 may be unevenly distributed and significantly separated. Specifically, gas exiting the symmetric dimple pair 18, 19 may tend to accumulate along the inner surfaces thereof and cause a substantial separation at its midsection. In contrast, as shown by the velocity vectors of FIG. 9, gas exiting the merge point 122 of an asymmetric dimple pair 118, 119 may be more evenly distributed throughout the cross-section thereof with significantly less separations.
Minimizing such separations in gas flow may also serve to minimize dead zones as well as pressure loss, as demonstrated by FIGS. 3 and 10. For example, the drop in pressure as gas flows from the upstream section 20 to the downstream section 21 of the symmetric dimple pair 18, 19 of FIG. 3 may be shown to be far greater than the pressure drop through the asymmetric dimple pair 118, 119 of FIG. 10. More specifically, the higher pressures, or darker tones, which originate at the upstream section 20 of the symmetric dimple pair 18, 19 of FIG. 3 may not be recovered at the downstream section 21 thereof, whereas the higher pressures which originate at the upstream section 120 of the asymmetric dimple pair 118, 119 of FIG. 10 are essentially recovered at its respective downstream section 121. Accordingly, extending the length of the downstream section 121 of a dimple pair 118, 119 may increase heat transfer efficiency by minimizing separations in gas flow, and further, by reducing substantial losses in gas pressure.
Referring now to FIGS. 11 and 12, heat transfer characteristics of the asymmetric dimple tube 110 of FIGS. 9 and 10 are provided. Moreover, the embodiment of FIG. 11 may graphically illustrate the efficiency of heat transfer at different surface locations of the asymmetric dimple tube 110, wherein darker tones may represent higher magnitudes of heat transfer, or a higher heat transfer coefficient. For instance, as compared to the symmetric dimple pair 18, 19 of FIG. 4, the surfaces of the asymmetric dimple pair 118, 119 of FIG. 11 may be shown to have more darker areas, and therefore, greater efficiency of heat transfer overall. Further analyses may be provided by FIG. 12 which more quantitatively compares the heat transfer characteristics of symmetric dimple tubes 10 with those of asymmetric dimple tubes 110. For example, as compared to the symmetric dimple tube 10 of FIGS. 2-4, the asymmetric dimple tube 110 of FIGS. 9-11 may be shown to have approximately 12% less pressure drop, which may further translate into a heat transfer coefficient that is approximately 3% greater overall.
Based on the foregoing, it can be seen that the present disclosure may provide a heat exchanger that requires minimal modifications to current methods for manufacturing heat exchangers while overcoming several drawbacks associated with prior art configurations. More specifically, the present disclosure provides more efficient transfer of heat by significantly reducing losses in gas flow as well as minimizing overall pressure loss.
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.
Patent Application
20120006512
