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United States Patent Application 20180023895
Kind Code A1
Kraft; Wayne Neal ;   et al. January 25, 2018

Enhanced Tubular Heat Exchanger

Abstract

A heating, ventilation, and/or air conditioning (HVAC) system may include a heat exchanger comprising at least one heat exchanger tube. The heat exchanger tube may include multiple passes: a first pass, a second pass having an elliptical portion with dimples disposed in the elliptical portion, and a third pass having an elliptical portion with dimples disposed in the elliptical portion. The first pass and the second pass may be connected in fluid communication by a first bend, and the second pass and the third pass may be connected in fluid communication by a second bend. The heat exchanger tube may be configured to promote heat transfer while also controlling a pressure drop across the heat exchanger tube.


Inventors: Kraft; Wayne Neal; (Tyler, TX) ; Tian; Qiao; (Tyler, TX) ; Wadia; Anosh Porus; (Tyler, TX)
Applicant:
Name City State Country Type

Trane International Inc.

Davidson

NC

US
Family ID: 1000002135304
Appl. No.: 15/217619
Filed: July 22, 2016


Current U.S. Class: 1/1
Current CPC Class: F28D 1/0478 20130101; F28F 1/006 20130101; F28D 2021/0024 20130101; F28F 13/12 20130101; F24H 3/087 20130101; F28F 1/426 20130101
International Class: F28D 1/047 20060101 F28D001/047; F24H 3/08 20060101 F24H003/08; F28F 13/12 20060101 F28F013/12; F28F 1/00 20060101 F28F001/00; F28F 1/42 20060101 F28F001/42

Claims



1. A heat exchanger, comprising: at least one heat exchanger tube, comprising: a first pass; a second pass; and a third pass; wherein at least a portion of the second pass and at least a portion of the third pass comprises an elliptical portion.

2. The heat exchanger of claim 1, wherein the second pass and the third pass do not overlap in a downstream direction with respect to the primary direction of an incoming airflow.

3. The heat exchanger of claim 2, wherein a longitudinal axis of a major diameter of the elliptical portions are aligned with the primary direction of the incoming airflow.

4. The heat exchanger of claim 1, wherein the elliptical portions comprise at least about a 10% reduction in a minor diameter of the elliptical portions.

5. The heat exchanger of claim 4, wherein the elliptical portion of the second pass and the elliptical portion of the third pass comprise substantially different reductions in minor diameter.

6. The heat exchanger of claim 1, wherein each of the second pass and the third pass comprises a plurality of dimples.

7. The heat exchanger of claim 6, wherein the dimples comprise spherical shaped indentions disposed along the elliptical portions of the second pass and the third pass, and wherein the dimples protrude inward along a lateral axis associated with a minor diameter of the elliptical portions.

8. The heat exchanger of claim 7, wherein the dimples are configured to locally accelerate a flow of fluid travelling through internal passages of the second pass and the third pass near the dimples.

9. The heat exchanger of claim 8, wherein the second pass comprises larger diameter dimples than the third pass.

10. The heat exchanger of claim 1, wherein the heat exchanger comprises a plurality of heat exchanger tubes.

11. The heat exchanger of claim 10, wherein the heat exchanger comprises a primary heat exchanger of a furnace.

12. A heating, ventilation and/or air conditioning (HVAC) system, comprising: a heat exchanger, comprising: at least one heat exchanger tube, comprising: a first pass; a second pass; and a third pass; wherein at least a portion of the second pass and at least a portion of the third pass comprises an elliptical portion.

13. The HVAC system of claim 13, wherein a longitudinal axis of a major diameter of the elliptical portions are aligned with the primary direction of the incoming airflow.

14. The HVAC system of claim 13, wherein the elliptical portions comprise at least about a 10% reduction in a minor diameter of the elliptical portions.

15. The HVAC system of claim 14, wherein the elliptical portion of the second pass and the elliptical portion of the third pass comprise substantially different reductions in minor diameter.

16. The HVAC system of claim 13, wherein each of the second pass and the third pass comprises a plurality of dimples.

17. The HVAC system of claim 16, wherein the dimples comprise spherical shaped indentions disposed along the elliptical portions of the second pass and the third pass, and wherein the dimples protrude inward along a lateral axis associated with a minor diameter of the elliptical portions.

18. The HVAC system of claim 17, wherein the second pass comprises larger diameter dimples than the third pass.

19. The HVAC system of claim 13, wherein the heat exchanger comprises a plurality of heat exchanger tubes.

20. The HVAC system of claim 19, wherein the heat exchanger comprises a primary heat exchanger of a furnace.

21. A method of operating a heating, ventilation, and/or air conditioning (HVAC) system, comprising: providing at least one heat exchanger tube in a heat exchanger of the HVAC system, the at least one heat exchanger tube comprising a first pass, a second pass, and a third pass, wherein at least a portion of the second pass and at least a portion of the third pass comprises an elliptical portion, and wherein each of the second pass and the third pass comprises a plurality of dimples; generating an airflow; contacting the at least one heat exchanger tube with the airflow; and promoting heat transfer between a fluid passing through an internal passage of the at least one heat exchanger tube and the airflow.

22. The method of claim 21, further comprising: locally accelerating a flow of fluid travelling through internal passages of the second pass and the third pass near the dimples to promote heat transfer the fluid and the airflow; and reducing a pressure drop across the heat exchanger.
Description



CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] Not applicable.

REFERENCE TO A MICROFICHE APPENDIX

[0003] Not applicable.

BACKGROUND

[0004] Heating, ventilation, and/or air conditioning (HVAC) systems used in commercial and residential applications often include a heat exchanger configured to promote heat transfer with a fluid carried within the heat exchanger and a fluid and/or airflow that contacts the heat exchanger to provide heating, cooling, and/or otherwise condition interior spaces. Because the amount of heat transfer between fluids affects overall system performance and efficiency, many heat exchangers are often designed for maximum heat transfer efficiency. Additionally, because heat exchangers are becoming more compact and less expensive, attempting to maximize heat transfer in a heat exchanger while reducing the size of a heat exchanger may often produce an undesirable pressure drop across the heat exchanger.

SUMMARY

[0005] In some embodiments of the disclosure, a heat exchanger is disclosed as comprising: at least one heat exchanger tube, comprising: a first pass; a second pass; and a third pass; wherein at least a portion of the second pass and at least a portion of the third pass comprises an elliptical portion.

[0006] In other embodiments of the disclosure, an HVAC system is disclosed as comprising: a heat exchanger, comprising: at least one heat exchanger tube, comprising: a first pass; a second pass; and a third pass; wherein at least a portion of the second pass and at least a portion of the third pass comprises an elliptical portion.

[0007] In yet other embodiments of the disclosure, a method of producing a fin and tube heat exchanger is disclosed as comprising: providing at least one heat exchanger tube in a heat exchanger of the HVAC system, the at least one heat exchanger tube comprising a first pass, a second pass, and a third pass, wherein at least a portion of the second pass and at least a portion of the third pass comprises an elliptical portion, and wherein each of the second pass and the third pass comprises a plurality of dimples; generating an airflow; contacting the at least one heat exchanger tube with the airflow; and promoting heat transfer between a fluid passing through an internal passage of the at least one heat exchanger tube and the airflow.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] For a more complete understanding of the present disclosure and the advantages thereof, reference is now made to the following brief description, taken in connection with the accompanying drawings and detailed description:

[0009] FIG. 1 is a schematic diagram of an HVAC system according to an embodiment of the disclosure;

[0010] FIG. 2 is a schematic diagram of air circulation paths of a structure conditioned by two HVAC systems of FIG. 1 according to an embodiment of the disclosure;

[0011] FIG. 3 is a schematic view of a furnace according to an embodiment of the disclosure;

[0012] FIG. 4A is an oblique side view of a heat exchanger tube according to an embodiment of the disclosure;

[0013] FIG. 4B is a partial cross-sectional view of the heat exchanger tube of FIG. 4A taken along cutting line 4B-4B of FIG. 4A according to an embodiment of the disclosure;

[0014] FIG. 4C is a cross-sectional view of the heat exchanger tube of FIG. 4A taken along cutting line 4C-4C of FIG. 4A according to an embodiment of the disclosure; and

[0015] FIG. 5 is a flowchart of a method of operating a heating, ventilation, and/or air conditioning (HVAC) system according to an embodiment of the disclosure.

DETAILED DESCRIPTION

[0016] Referring now to FIG. 1, a schematic diagram of an HVAC system 100 according to an embodiment of this disclosure is shown. HVAC system 100 comprises an indoor unit 102, an outdoor unit 104, and a system controller 106. In some embodiments, the system controller 106 may operate to control operation of the indoor unit 102 and/or the outdoor unit 104. As shown, the HVAC system 100 is a so-called heat pump system that may be selectively operated to implement one or more substantially closed thermodynamic refrigeration cycles to provide a cooling functionality and/or a heating functionality. In alternative embodiments, the HVAC system 100 may comprise a type of air-conditioning system that is not a heat pump system.

[0017] Indoor unit 102 comprises an indoor heat exchanger 108, an indoor fan 110, and an indoor metering device 112. Indoor heat exchanger 108 is a plate fin heat exchanger configured to allow heat exchange between refrigerant carried within internal tubing of the indoor heat exchanger 108 and fluids that contact the indoor heat exchanger 108 but that are kept segregated from the refrigerant. In other embodiments, indoor heat exchanger 108 may comprise a spine fin heat exchanger, a microchannel heat exchanger, or any other suitable type of heat exchanger.

[0018] The indoor fan 110 is a centrifugal blower comprising a blower housing, a blower impeller at least partially disposed within the blower housing, and a blower motor configured to selectively rotate the blower impeller. In other embodiments, the indoor fan 110 may comprise a mixed-flow fan and/or any other suitable type of fan. The indoor fan 110 is configured as a modulating and/or variable speed fan capable of being operated at many speeds over one or more ranges of speeds. In other embodiments, the indoor fan 110 may be configured as a multiple speed fan capable of being operated at a plurality of operating speeds by selectively electrically powering different ones of multiple electromagnetic windings of a motor of the indoor fan 110. In yet other embodiments, the indoor fan 110 may be a single speed fan.

[0019] The indoor metering device 112 is an electronically controlled motor driven electronic expansion valve (EEV). In alternative embodiments, the indoor metering device 112 may comprise a thermostatic expansion valve, a capillary tube assembly, and/or any other suitable metering device. The indoor metering device 112 may comprise and/or be associated with a refrigerant check valve and/or refrigerant bypass for use when a direction of refrigerant flow through the indoor metering device 112 is such that the indoor metering device 112 is not intended to meter or otherwise substantially restrict flow of the refrigerant through the indoor metering device 112.

[0020] Outdoor unit 104 comprises an outdoor heat exchanger 114, a compressor 116, an outdoor fan 118, an outdoor metering device 120, and a reversing valve 122. Outdoor heat exchanger 114 is a spine fin heat exchanger configured to allow heat exchange between refrigerant carried within internal passages of the outdoor heat exchanger 114 and fluids that contact the outdoor heat exchanger 114 but that are kept segregated from the refrigerant. In other embodiments, outdoor heat exchanger 114 may comprise a plate fin heat exchanger, a microchannel heat exchanger, or any other suitable type of heat exchanger.

[0021] The compressor 116 is a multiple speed scroll type compressor configured to selectively pump refrigerant at a plurality of mass flow rates. In alternative embodiments, the compressor 116 may comprise a modulating compressor capable of operation over one or more speed ranges, the compressor 116 may comprise a reciprocating type compressor, the compressor 116 may be a single speed compressor, and/or the compressor 116 may comprise any other suitable refrigerant compressor and/or refrigerant pump.

[0022] The outdoor fan 118 is an axial fan comprising a fan blade assembly and fan motor configured to selectively rotate the fan blade assembly. In other embodiments, the outdoor fan 118 may comprise a mixed-flow fan, a centrifugal blower, and/or any other suitable type of fan and/or blower. The outdoor fan 118 is configured as a modulating and/or variable speed fan capable of being operated at many speeds over one or more ranges of speeds. In other embodiments, the outdoor fan 118 may be configured as a multiple speed fan capable of being operated at a plurality of operating speeds by selectively electrically powering different ones of multiple electromagnetic windings of a motor of the outdoor fan 118. In yet other embodiments, the outdoor fan 118 may be a single speed fan.

[0023] The outdoor metering device 120 is a thermostatic expansion valve. In alternative embodiments, the outdoor metering device 120 may comprise an electronically controlled motor driven EEV, a capillary tube assembly, and/or any other suitable metering device. The outdoor metering device 120 may comprise and/or be associated with a refrigerant check valve and/or refrigerant bypass for use when a direction of refrigerant flow through the outdoor metering device 120 is such that the outdoor metering device 120 is not intended to meter or otherwise substantially restrict flow of the refrigerant through the outdoor metering device 120.

[0024] The reversing valve 122 is a so-called four-way reversing valve. The reversing valve 122 may be selectively controlled to alter a flowpath of refrigerant in the HVAC system 100 as described in greater detail below. The reversing valve 122 may comprise an electrical solenoid or other device configured to selectively move a component of the reversing valve 122 between operational positions.

[0025] The system controller 106 may comprise a touchscreen interface for displaying information and for receiving user inputs. The system controller 106 may display information related to the operation of the HVAC system 100 and may receive user inputs related to operation of the HVAC system 100. However, the system controller 106 may further be operable to display information and receive user inputs tangentially and/or unrelated to operation of the HVAC system 100. In some embodiments, the system controller 106 may comprise a temperature sensor and may further be configured to control heating and/or cooling of zones associated with the HVAC system 100. In some embodiments, the system controller 106 may be configured as a thermostat for controlling supply of conditioned air to zones associated with the HVAC system 100.

[0026] In some embodiments, the system controller 106 may selectively communicate with an indoor controller 124 of the indoor unit 102, with an outdoor controller 126 of the outdoor unit 104, and/or with other components of the HVAC system 100. In some embodiments, the system controller 106 may be configured for selective bidirectional communication over a communication bus 128. In some embodiments, portions of the communication bus 128 may comprise a three-wire connection suitable for communicating messages between the system controller 106 and one or more of the HVAC system 100 components configured for interfacing with the communication bus 128. Still further, the system controller 106 may be configured to selectively communicate with HVAC system 100 components and/or other device 130 via a communication network 132. In some embodiments, the communication network 132 may comprise a telephone network and the other device 130 may comprise a telephone. In some embodiments, the communication network 132 may comprise the Internet and the other device 130 may comprise a so-called smartphone and/or other Internet enabled mobile telecommunication device.

[0027] The indoor controller 124 may be carried by the indoor unit 102 and may be configured to receive information inputs, transmit information outputs, and otherwise communicate with the system controller 106, the outdoor controller 126, and/or any other device via the communication bus 128 and/or any other suitable medium of communication. In some embodiments, the indoor controller 124 may be configured to communicate with an indoor personality module 134, receive information related to a speed of the indoor fan 110, transmit a control output to an electric heat relay, transmit information regarding an indoor fan 110 volumetric flow-rate, communicate with and/or otherwise affect control over an air cleaner 136, and communicate with an indoor EEV controller 138. In some embodiments, the indoor controller 124 may be configured to communicate with an indoor fan controller 142 and/or otherwise affect control over operation of the indoor fan 110. In some embodiments, the indoor personality module 134, or any other suitable information storage device, may comprise information related to the identification and/or operation of the indoor unit 102 and/or a position of the outdoor metering device 120.

[0028] In some embodiments, the indoor EEV controller 138 may be configured to receive information regarding temperatures and pressures of the refrigerant in the indoor unit 102. More specifically, the indoor EEV controller 138 may be configured to receive information regarding temperatures and pressures of refrigerant entering, exiting, and/or within the indoor heat exchanger 108. Further, the indoor EEV controller 138 may be configured to communicate with the indoor metering device 112 and/or otherwise affect control over the indoor metering device 112.

[0029] The outdoor controller 126 may be carried by the outdoor unit 104 and may be configured to receive information inputs, transmit information outputs, and otherwise communicate with the system controller 106, the indoor controller 124, and/or any other device via the communication bus 128 and/or any other suitable medium of communication. In some embodiments, the outdoor controller 126 may be configured to communicate with an outdoor personality module 140 that may comprise information related to the identification and/or operation of the outdoor unit 104. In some embodiments, the outdoor controller 126 may be configured to receive information related to an ambient temperature associated with the outdoor unit 104, information related to a temperature of the outdoor heat exchanger 114, and/or information related to refrigerant temperatures and/or pressures of refrigerant entering, exiting, and/or within the outdoor heat exchanger 114 and/or the compressor 116. In some embodiments, the outdoor controller 126 may be configured to transmit information related to monitoring, communicating with, and/or otherwise affecting control over the outdoor fan 118, a compressor sump heater, a solenoid of the reversing valve 122, a relay associated with adjusting and/or monitoring a refrigerant charge of the HVAC system 100, a position of the indoor metering device 112, and/or a position of the outdoor metering device 120. The outdoor controller 126 may further be configured to communicate with a compressor drive controller 144 that is configured to electrically power and/or control the compressor 116.

[0030] The HVAC system 100 is shown configured for operating in a so-called cooling mode in which heat is absorbed by refrigerant at the indoor heat exchanger 108 and heat is rejected from the refrigerant at the outdoor heat exchanger 114. In some embodiments, the compressor 116 may be operated to compress refrigerant and pump the relatively high temperature and high pressure compressed refrigerant from the compressor 116 to the outdoor heat exchanger 114 through the reversing valve 122 and to the outdoor heat exchanger 114. As the refrigerant is passed through the outdoor heat exchanger 114, the outdoor fan 118 may be operated to move air into contact with the outdoor heat exchanger 114, thereby transferring heat from the refrigerant to the air surrounding the outdoor heat exchanger 114. The refrigerant may primarily comprise liquid phase refrigerant and the refrigerant may be pumped from the outdoor heat exchanger 114 to the indoor metering device 112 through and/or around the outdoor metering device 120 which does not substantially impede flow of the refrigerant in the cooling mode. The indoor metering device 112 may meter passage of the refrigerant through the indoor metering device 112 so that the refrigerant downstream of the indoor metering device 112 is at a lower pressure than the refrigerant upstream of the indoor metering device 112. The pressure differential across the indoor metering device 112 allows the refrigerant downstream of the indoor metering device 112 to expand and/or at least partially convert to a gaseous phase. The gaseous phase refrigerant may enter the indoor heat exchanger 108. As the refrigerant is passed through the indoor heat exchanger 108, the indoor fan 110 may be operated to move air into contact with the indoor heat exchanger 108, thereby transferring heat to the refrigerant from the air surrounding the indoor heat exchanger 108. The refrigerant may thereafter reenter the compressor 116 after passing through the reversing valve 122.

[0031] To operate the HVAC system 100 in the so-called heating mode, the reversing valve 122 may be controlled to alter the flowpath of the refrigerant, the indoor metering device 112 may be disabled and/or bypassed, and the outdoor metering device 120 may be enabled. In the heating mode, refrigerant may flow from the compressor 116 to the indoor heat exchanger 108 through the reversing valve 122, the refrigerant may be substantially unaffected by the indoor metering device 112, the refrigerant may experience a pressure differential across the outdoor metering device 120, the refrigerant may pass through the outdoor heat exchanger 114, and the refrigerant may reenter the compressor 116 after passing through the reversing valve 122. Most generally, operation of the HVAC system 100 in the heating mode reverses the roles of the indoor heat exchanger 108 and the outdoor heat exchanger 114 as compared to their operation in the cooling mode.

[0032] Referring now to FIG. 2, a schematic diagram of air circulation paths of a structure 250 conditioned by two HVAC systems 100 is shown. In this embodiment, the structure 250 is conceptualized as comprising a lower floor 222 and an upper floor 224. The lower floor 222 comprises zones 226, 228, and 230 while the upper floor 224 comprises zones 232, 234, and 236. The HVAC system 100 associated with the lower floor 222 is configured to circulate and/or condition air of lower zones 226, 228, and 230 while the HVAC system 100 associated with the upper floor 224 is configured to circulate and/or condition air of upper zones 232, 234, and 236.

[0033] In addition to the components of HVAC system 100 described above, in this embodiment, each HVAC system 100 further comprises a ventilator 146, a prefilter 148, a humidifier 150, and a bypass duct 152. The ventilator 146 may be operated to selectively exhaust circulating air to the environment and/or introduce environmental air into the circulating air. The prefilter 148 may generally comprise a filter media selected to catch and/or retain relatively large particulate matter prior to air exiting the prefilter 148 and entering the air cleaner 136. The humidifier 150 may be operated to adjust a humidity of the circulating air. The bypass duct 152 may be utilized to regulate air pressures within the ducts that form the circulating air flowpaths. In some embodiments, air flow through the bypass duct 152 may be regulated by a bypass damper 154 while air flow delivered to the zones 226, 228, 230, 232, 234, and 236 may be regulated by zone dampers 156.

[0034] Still further, each HVAC system 100 may further comprise a zone thermostat 158 and a zone sensor 160. In some embodiments, a zone thermostat 158 may communicate with the system controller 106 and may allow a user to control a temperature, humidity, and/or other environmental setting for the zone in which the zone thermostat 158 is located. Further, the zone thermostat 158 may communicate with the system controller 106 to provide temperature, humidity, and/or other environmental feedback regarding the zone in which the zone thermostat 158 is located. In some embodiments, a zone sensor 160 may communicate with the system controller 106 to provide temperature, humidity, and/or other environmental feedback regarding the zone in which the zone sensor 160 is located.

[0035] While HVAC systems 100 are shown as a so-called split system comprising an indoor unit 102 located separately from the outdoor unit 104, alternative embodiments of an HVAC system 100 may comprise a so-called package system in which one or more of the components of the indoor unit 102 and one or more of the components of the outdoor unit 104 are carried together in a common housing or package. The HVAC system 100 is shown as a so-called ducted system where the indoor unit 102 is located remote from the conditioned zones, thereby requiring air ducts to route the circulating air. However, in alternative embodiments, an HVAC system 100 may be configured as a non-ducted system in which the indoor unit 102 and/or multiple indoor units 102 associated with an outdoor unit 104 is located substantially in the space and/or zone to be conditioned by the respective indoor units 102, thereby not requiring air ducts to route the air conditioned by the indoor units 102.

[0036] Furthermore, the system controllers 106 may be configured for bidirectional communication with each other and may further be configured so that a user may, using any of the system controllers 106, monitor and/or control any of the HVAC system 100 components regardless of which zones the components may be associated. Further, each system controller 106, each zone thermostat 158, and each zone sensor 160 may comprise a humidity sensor. As such, it will be appreciated that structure 250 is equipped with a plurality of humidity sensors in a plurality of different locations. In some embodiments, a user may effectively select which of the plurality of humidity sensors is used to control operation of one or more of the HVAC systems 100. In some embodiments, the HVAC systems 100 may further comprise a furnace 170 configured to burn fuel such as, but not limited to, natural gas, heating oil, propane, and/or any other suitable fuel, to generate heat and/or provide heated air to at least one zone 226, 228, 230, 232, 234, 236 conditioned by an HVAC system 100.

[0037] Referring now to FIG. 3, a schematic view of a furnace 170 is shown according to an embodiment of the disclosure. The furnace 170 may comprise a furnace cabinet 172, a partition panel 173, a burner box 174 comprising at least one or more burners configured to at least partially combust an air-fuel mixture, a primary heat exchanger 176 comprising at least one or more heat exchanger tubes 177, a hot header 178, a secondary exchanger 180, a cold header 182, a draft inducer system 184 configured to draw the at least partially combusted air-fuel mixture from the burner box 174 through the above-described components before ejecting the at least partially combusted air-fuel mixture through an exhaust 186.

[0038] In operation, at least one burner of the burner box 174 may be configured to receive and combust an air-fuel mixture. In some cases, additional burners may be utilized to increase an overall heating capacity. The one or more heat exchanger tubes 177 of the primary heat exchanger 176 may be configured to receive hot gases produced by at least partially combusting the air-fuel mixture from the burner box 174 and/or each of the burners associated with the burner box 174. In some embodiments, each heat exchanger tube 177 may receive the hot gases produced by at least partially combusting the air-fuel mixture from an associated and/or dedicated burner of the burner box 174, so that multiple parallel air-fuel mixture flow paths may be formed through the heat exchanger tubes 177 of the primary heat exchanger 176. However, in other embodiments, the burners may feed at least one manifold configured to distribute the hot gases to a plurality of heat exchanger tubes 177 of the primary heat exchanger 176. The hot gases may flow through the heat exchanger tube 177 and/or the primary heat exchanger 176 to the hot header 178 that may then generally receive the flow of hot gases from the heat exchanger tube 177 and/or the primary heat exchanger 176. The hot gases are then passed from the hot header 178 through the secondary heat exchanger 180 and subsequently through the cold header 182. Further, the flow of the hot gases produced from at least partially combusting the air-fuel mixture may be provided by the draft inducer system 184 before ejecting the hot gases through the exhaust 186.

[0039] In some embodiments, the secondary heat exchanger 180 may generally comprise a fin and tube type heat exchanger that comprises a plurality of tubes connected in fluid communication with the hot header 178 and the cold header 182. The secondary heat exchanger 180 may also comprise a plurality of fins that may generally be connected to the secondary heat exchanger tubes along a finned portion of the secondary heat exchanger 180. Additionally, in some embodiments, each heat exchanger tube 177 of the primary heat exchanger 176 may comprise a plurality of U-shaped bends, so that each heat exchanger tube 177 passes multiple times across an interior space 188 of the furnace 170. The interior space 188 of the furnace 170 may be configured to receive an incoming airflow 190 generated by a blower of the furnace 170 and/or the indoor fan 110 of the indoor unit 102 so the incoming airflow 190 may conduct heat from at least one of the secondary heat exchanger 180 and the primary heat exchanger 176. Further, while furnace 170 is disclosed as a so-called high efficiency furnace 170 comprising at least one primary heat exchanger 176 and a secondary heat exchanger 180, alternative furnace 170 embodiments may be a so-called low efficiency furnace and comprise only the primary heat exchanger 176 with no secondary heat exchanger 180.

[0040] Referring now to FIGS. 4A-4C, an oblique side view, a partial cross-sectional view taken along cutting line 4B-4B, and a cross-sectional view taken along cutting line 4C-4C of a heat exchanger tube 200 are shown, respectively, according to an embodiment of the disclosure. In some embodiments, heat exchanger tube 200 may be substantially similar to heat exchanger tube 177 of FIG. 3. Heat exchanger tube 200 generally comprises a first pass 202, a second pass 204, and a third pass 206. The first pass 202 is coupled to the second pass 204 by a first bend 203, while the second pass 204 is coupled to the third pass 206 by a second bend 205 to form a continuous internal fluid flow path that extends from an inlet 201 associated with an opening of the first pass 202, through internal passages of each of the first pass 202, first bend 203, second pass 204, second bend 205, and third pass 206, to an outlet 207 associated with an opening of the third pass 206. It will be appreciated that the passes 202, 204, 206 generally comprise substantially straight tubes that are oriented substantially parallel to each other, such that the bends 203, 205 generally comprise 180 degree U-shaped bends. Additionally, each of the passes 202, 204, 206 and/or the bends 203, 205 extend across an airflow path, so that the airflow 190 may come into contact with each of the passes 202, 204, 206 and/or bends 203, 205 to promote heat transfer between a fluid and/or hot gases within the internal passages of the heat exchanger tube 200 and the incoming airflow 190.

[0041] The first pass 202 generally comprises a substantially straight, round tube that extends from the inlet 201 to the first bend 203. The first pass 202 also generally comprises no additional enhancements and/or features on the tube surface that are configured to enhance heat transfer. The first bend 203 and the second bend 205 also generally comprise substantially round tubes that are bent (i.e. via a mandrel and/or other tubing bending apparatus) to form 180 degree U-shaped bends. Each of the bends 203, 205 further comprise no additional enhancements and/or features on the tube surface that are configured to enhance heat transfer. However, in some embodiments, the process of forming the bends 203, 205 may result in a series of crimps, ripples, and/or consecutively compressed sections on an inner portion of the bends 203, 205 that may provide enhanced heat transfer properties as compared to a substantially smooth bends 203, 205 having no crimps, ripples, and/or consecutively compressed sections.

[0042] However, in some embodiments, the second pass 204 and the third pass 206, may comprise enhancements and/or features that further enhance heat transfer. Each of the second pass 204 and the third pass 206 comprises an elliptical portion 210, a transition 208 disposed at each end of the elliptical portion 210, and a plurality of dimples 212. Each of the transitions 208 comprises a portion of a pass 204, 206 that comprises a round shape on a first end and gradually and/or progressively transitions to an elliptical shape complementary to and/or substantially similar to the elliptical portions 210 on a second end that is adjacent to and/or abuts the elliptical portions 210 of each pass 204, 206. Accordingly, the transitions 208 of the second pass 204 comprise a complementary elliptical shape on the ends of the transitions 208 adjacent to the elliptical portion 210 of the second pass 204 and gradually transition to a complementary round shape at the ends adjacent to the bends 203, 205. Additionally, the transitions 208 of the third pass 206 comprise a complementary elliptical shape on the ends of the transitions 208 adjacent to the elliptical portion 210 of the third pass 206 and comprise a complementary round shape at the ends adjacent to the second bend 205 and the outlet 207.

[0043] As shown in FIG. 4B, the elliptical portions 210 of each of the second pass 204 and the third pass 206 generally comprise a longitudinal axis 214 and a lateral axis 216. The longitudinal axis 214 may be associated with a major (larger) diameter of the elliptical portions 210, while the lateral axis 216 may be associated with a minor (smaller) diameter of the elliptical portions 210. Accordingly, the geometries of the elliptical portions 210 may be parameterized by comprising a major diameter and a minor diameter, caused by a so-called "flattening" of the original round shape of the pass 204, 206. As such, in some embodiments, the elliptical portions 210 may comprise at least about a 10% reduction of the minor diameter along the lateral axis 216 as compared to the original diameter of the round tube. However, in other embodiments, the elliptical portions 210 may comprise at least about a 15% reduction, at least about a 20% reduction, at least about a 25% reduction, at least about a 30% reduction, at least about a 33% reduction, and/or at least about a 35% reduction of the minor diameter. For example, a round heat exchanger tube having a 1.5 inch diameter may comprise a 2.0 inch major diameter along the longitudinal axis 214 and a 1.0 inch minor diameter along the lateral axis 216. Accordingly, the reduction in minor diameter is (1-(1.0/1.5)).times.100=33% reduction in minor diameter.

[0044] In some embodiments, the longitudinal axis 214 may be aligned with a primary direction of the incoming airflow 190. As shown in FIG. 4C, the second pass 204 and the third pass 206 do not overlap in a downstream direction with respect to the primary direction of the incoming airflow 190, which may also reduce a pressure drop across the passes 202, 204, 206 of the heat exchanger tube 200. Additionally, by reducing the minor diameter of the elliptical portions 210 along the lateral axis 216, the elliptical portion 210 may provide less resistance to the incoming airflow 190. As such, the incoming airflow 190 may experience a reduced pressure drop as compared to a round tube. In some embodiments, each elliptical portion 210 of the second pass 204 and the third pass 206 may comprise substantially different reductions in minor diameter. In this embodiment, the elliptical portion 210 of the third pass 206 may comprise a greater reduction in the minor diameter with respect to the reduction in minor diameter of the elliptical portion 210 of the second pass 204. Thus, the third pass 206 comprises a more elliptical shape, such that the pressure drop is significantly reduced across the third pass 206 as compared to a round shaped tube. However, the pressure drop increase across the second pass 204 may be negligible due to the elliptical portion 210 of the second pass 204 as compared to the pressure drop that would occur if the third pass 206 and the second pass 204 comprised round shaped tubes.

[0045] In one exemplary embodiment, the first pass 202 may comprise a 1.5 inch diameter round tube, the elliptical portion 210 of the second pass 204 may comprise a 1.22 inch minor diameter and a 1.78 inch major diameter, and the elliptical portion 210 of the third pass 206 may comprise a 0.94 inch minor diameter and a 2.06 inch major diameter. Accordingly, the reduction in minor diameter of the elliptical portion 210 of the second pass 204 is 18.7%, while the reduction in minor diameter of the elliptical portion 210 of the third pass 206 is 37.3%. Thus, in some embodiments, the reduction in minor diameter of the elliptical portion 210 of the second pass 204 may comprise about half of the reduction of the minor diameter of the elliptical portion 210 of the third pass 206. However, in alternative embodiments, each elliptical portion 210 of the second pass 204 and the third pass 206 may comprise substantially similar reductions in minor diameter.

[0046] Still referring to FIGS. 4A-4C, the heat exchanger tube 200 may also comprise a plurality of dimples 212. The dimples 212 may generally comprise spherical shaped indentions that are disposed along the elliptical portions 210 of the second pass 204 and the third pass 206 and protrude inward along the lateral axis 216. Further, each dimple 212 may be disposed substantially opposite along the lateral axis 216 from a second dimple 212. The dimples 212 may disturb a flow and/or locally accelerate the flow of fluid and/or hot gases travelling through the internal passages of the second pass 204 and/or the third pass 206 near the dimples 212, disrupting a boundary layer that may form within the internal passages of the second pass 204 and the third pass 206. By disrupting the boundary layer, thereby causing a more turbulent flow of fluid and/or hot gases through the passes 204, 206, the dimples 212 may provide an increased heat transfer rate and/or promote additional heat transfer between the fluid and/or the hot gases passing through the passes 204, 206 and the incoming airflow 190.

[0047] In some embodiments, opposing dimples 212 may generally comprise a substantially similar diameter. However, in other embodiments, one opposing dimple 212 may comprise a larger diameter as compared to the dimple 212 disposed oppositely along the lateral axis 216. Because dimples 212 disposed oppositely protrude into the internal passage of the heat exchanger tube 200, the cross-sectional area of the heat exchanger tube 200 is greatly reduced at the apex of the opposing dimples 212. Alternatively, the dimples 212 may be alternating, still providing a reduction in the overall heat exchanger tube 200 cross sectional area. In some embodiments, the cross sectional area of the heat exchanger tube 200 may result in at least about a 95%, at least about an 85%, at least about a 75%, at least about a 65%, at least about a 50%, at least about a 35%, at least about a 30%, at least about a 25%, at least about a 20%, at least about a 15%, at least about a 10%, and/or at least about a 5% in overall cross sectional area of the heat exchanger tube 200, However, opposing dimples 212 and/or adjacently disposed alternating dimples 212 may even contact one another in certain embodiments. Accordingly, it is an object of the dimples 212 of the heat exchanger tube 200 to increase velocity through the internal passage of the heat exchanger tube 200 while increasing heat transfer and maintaining a manageable pressure drop though the heat exchanger tube 200.

[0048] In some embodiments, the dimples 212 may comprise a substantially similar diameter. However, in other embodiments, the dimples 212 may comprise varying and/or different diameters. For example, in some embodiments, the second pass 204 may comprise larger diameter dimples 212 than the dimples 212 of the third pass 206 to further enhance heat transfer, while the third pass 206 comprises smaller diameter dimples 212 to further promote a reduced pressure drop across the third pass 206 while also enhancing heat transfer properties of the third pass 206. Additionally, in some embodiments, the second pass 204 and the third pass 206 may comprise a substantially similar number of dimples 212. However, in other embodiments, the second pass 204 and the third pass 206 may comprise a different number of dimples 212. In this embodiment, each of the second pass 204 and the third pass 206 comprise two pairs of opposing dimples 212. Additionally, in some embodiments, the dimples 212 of the second pass 204 may be offset from the dimples 212 of the third pass 206 such that the dimples 212 of the second pass 204 may only partially overlap the dimples 212 of the third pass 206 in the downstream direction with respect to the primary direction of the incoming airflow 190. Accordingly, it is an object of the heat exchanger tube 200 to provide enhanced heat transfer while also controlling the pressure drop of the incoming airflow 190 across the heat exchanger tube 200.

[0049] It will be appreciated that in some embodiments, the heat exchanger tube 200 and/or the features of the passes 204, 206 of the heat exchanger tube 200 may be used in the indoor heat exchanger 108 and/or the outdoor heat exchanger 114. Further, the heat exchanger tube 200 may comprise a plurality of thin, plate-like fins disposed along the tubes. Still further, adjacently disposed heat exchanger tubes 200 may not overlap one another in the downstream direction with respect to a primary airflow direction across the heat exchanger tube 200. Additionally, the heat exchanger tube 200 may comprise elliptical portions 210 comprising fins and be void of fins on portions of the heat exchanger tube 200 where the dimples 212 are disposed. Further, in embodiments disclosed herein, the heat exchanger tube 200 may only comprise a second pass 204 and/or third pass 206 comprising an elliptical portion 210 and a plurality of dimples 212. Additionally, in some embodiments, the heat exchanger tube 200 may further comprise a plurality of second passes 204 and/or third passes 206. For example, in the case of a non-condensing furnace, the heat exchanger tube 200 may comprise four passes, where the first pass 202 comprises no dimples 212, and each of the second pass 204, the third pass 206, and a fourth pass (or second third pass 206) may comprise dimples 212. However, in other embodiments of a non-condensing furnace having four passes, only the third pass 206 and the fourth pass (second third pass 206) may comprise dimples. Further, in some embodiments, a plurality of second passes 204 and/or third passes 206 may be connected between two headers such that fluid flows through the internal passages of the passes 204, 206 in parallel. Accordingly, it will be appreciated that the features and/or geometries of the heat exchanger tube 200 described herein may be applied to any tube of a heat exchanger comprising multiple passes.

[0050] Referring now to FIG. 5, a flowchart of a method 300 of operating a heating, ventilation, and/or air conditioning (HVAC) system 100 is shown according to an embodiment of the disclosure. The method 300 may begin at block 302 by providing at least one heat exchanger tube 177, 200 in a heat exchanger 108, 114, 176 in the HVAC system 100. The method 300 may continue at block 304 by contacting the at least one heat exchanger tube 200 with an airflow 190. The method 300 may continue at block 306 by promoting heat transfer between a fluid passing through an internal passage of the at least one heat exchanger tube 200 and the airflow 190. In some embodiments, contacting the at least one heat exchanger tube 200 with an airflow 190 and/or promoting heat transfer between the fluid in the at least one heat exchanger tube 200 and the airflow 190 may also reduce a pressure drop across the at least one heat exchanger tube 200.

[0051] At least one embodiment is disclosed and variations, combinations, and/or modifications of the embodiment(s) and/or features of the embodiment(s) made by a person having ordinary skill in the art are within the scope of the disclosure. Alternative embodiments that result from combining, integrating, and/or omitting features of the embodiment(s) are also within the scope of the disclosure. Where numerical ranges or limitations are expressly stated, such express ranges or limitations should be understood to include iterative ranges or limitations of like magnitude falling within the expressly stated ranges or limitations (e.g., from about 1 to about 10 includes, 2, 3, 4, etc.; greater than 0.10 includes 0.11, 0.12, 0.13, etc.). For example, whenever a numerical range with a lower limit, R.sub.l, and an upper limit, R.sub.u, is disclosed, any number falling within the range is specifically disclosed. In particular, the following numbers within the range are specifically disclosed: R=R.sub.l+k*(R.sub.u-R.sub.l), wherein k is a variable ranging from 1 percent to 100 percent with a 1 percent increment, i.e., k is 1 percent, 2 percent, 3 percent, 4 percent, 5 percent, . . . , 50 percent, 51 percent, 52 percent, . . . , 95 percent, 96 percent, 97 percent, 98 percent, 99 percent, or 100 percent. Unless otherwise stated, the term "about" shall mean plus or minus 10 percent of the subsequent value. Moreover, any numerical range defined by two R numbers as defined in the above is also specifically disclosed. Use of the term "optionally" with respect to any element of a claim means that the element is required, or alternatively, the element is not required, both alternatives being within the scope of the claim. Use of broader terms such as comprises, includes, and having should be understood to provide support for narrower terms such as consisting of, consisting essentially of, and comprised substantially of. Accordingly, the scope of protection is not limited by the description set out above but is defined by the claims that follow, that scope including all equivalents of the subject matter of the claims. Each and every claim is incorporated as further disclosure into the specification and the claims are embodiment(s) of the present invention.

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