Patent Publication Number: US-2012031601-A1

Title: Multichannel tubes with deformable webs

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from and the benefit of U.S. Provisional Application Ser. No. 61/370,316, entitled “MULTICHANNEL TUBES WITH DEFORMABLE WEBS”, filed Aug. 3, 2010, which is hereby incorporated by reference. 
    
    
     BACKGROUND 
     The invention relates generally to multichannel tubes with deformable webs, and more particularly, to multichannel tubes that may be employed in plate fin heat exchangers. 
     Heat exchangers are used in heating, ventilation, air conditioning, and refrigeration (HVAC&amp;R) systems. Multichannel heat exchangers generally include multichannel tubes for flowing refrigerant through the heat exchanger. Each multichannel tube may contain several individual flow channels. As a fluid, such as refrigerant, flows through the flow channels, the fluid may exchange heat with an external fluid, such as air, flowing between the multichannel tubes. Multichannel tubes may be used heat exchangers of small tonnage systems, such as residential systems, or in large tonnage systems, such as industrial chiller systems. Further, multichannel tubes may be used in other heating and/or cooling devices, such as radiators. 
     Fins are positioned between the multichannel tubes to facilitate heat transfer between the refrigerant contained within the tubes and the external air passing over the tubes. Typically, multichannel heat exchangers include corrugated sets of fins that are placed in between and parallel to adjacent tubes. The crests of the fins may be brazed or otherwise joined to the adjacent tubes. However, due to the relatively small interstices between the crests, water may tend to collect on the fins, thereby reducing thermal transfer capabilities by closing flow paths for air. This may be particularly problematic for heat exchangers, such as heat pumps, functioning as evaporators in an outdoor location. 
     Plate fins, extending generally transverse to tubes, may be used instead of corrugated fins to inhibit condensate collection. Plate fin heat exchangers are typically assembled by inserting the tubes through openings in the fins and then outwardly expanding the tubes. A bullet, or similar object, may be inserted within the tubes to expand the tubes into the fins. However, the multiple individual flow channels within the multichannel tubes may make assembly using a bullet or other expansion tool problematic. 
     SUMMARY 
     The present invention relates to a heat exchanger tube that includes a top wall, a bottom wall disposed generally opposite from the top wall and separated by a height of the heat exchanger tube, and a pair of sidewalls extending between the top and bottom walls and separated by a width of the heat exchanger tube. At least one of the pair of sidewalls has a chamfered edge configured to deform in response to hydraulic expansion of the heat exchanger tube to produce a curved and generally symmetrical sidewall. The heat exchanger tube also includes a plurality of deformable webs spaced across the width and extending between the top wall and the bottom wall to form a plurality of generally parallel flow paths therebetween. The deformable webs are configured to deform in response to the hydraulic expansion of the heat exchanger tube to increase the height of the heat exchanger tube. 
     The present invention also relates to a heat exchanger that includes a top wall, a bottom wall disposed generally opposite from the top wall and separated by a height of the heat exchanger tube, and a pair of sidewalls extending between the top and bottom walls and separated by a width of the heat exchanger tube. Each of the sidewalls has a chamfered edge. The heat exchanger tube also includes a plurality of deformable webs spaced across the width, slanted in a common direction across the width with respect to the bottom wall and the top wall, and extending between the top wall and the bottom wall to form a plurality of generally parallel flow paths therebetween. The deformable webs are configured to deform in response to the hydraulic expansion of the heat exchanger tube to increase the height of the heat exchanger tube. 
     The present invention further relates to a method for assembling a heat exchanger. The method includes inserting a multichannel tube through a plurality of openings each disposed on a sheet of thermally conductive material and hydraulically expanding the multichannel tube to deform internal webs defining a plurality of generally parallel flow paths within the multichannel tube, to expand the multichannel tube into the plurality of openings, and to deform chamfered edges of the multichannel tube to produce curved and generally symmetrical sidewalls. 
    
    
     
       DRAWINGS 
         FIG. 1  is an illustration of an exemplary embodiment of a commercial or industrial HVAC&amp;R system that employs plate fin heat exchangers. 
         FIG. 2  is an illustration of an exemplary embodiment of a residential HVAC&amp;R system that employs plate fin heat exchangers. 
         FIG. 3  is an exploded view of the outdoor unit shown in  FIG. 2 . 
         FIG. 4  is a diagrammatical overview of an exemplary air conditioning system that may employ one or more plate fin heat exchangers. 
         FIG. 5  is a diagrammatical over of an exemplary heat pump system that may employ one or more plate fin heat exchangers. 
         FIG. 6  is a perspective view of an exemplary embodiment of a plate fin heat exchanger containing multichannel tubes with deformable webs. 
         FIG. 7  is a partially exploded view of a portion of the heat exchanger of  FIG. 6 . 
         FIG. 8  is a cross-sectional view of an embodiment of multichannel tube with deformable webs prior to hydraulic expansion. 
         FIG. 9  is a cross-sectional view of the multichannel tube of  FIG. 8  inserted through a plate fin prior to hydraulic expansion. 
         FIG. 10  is a cross-sectional view of the multichannel tube and plate fin of  FIG. 9  after hydraulic expansion. 
         FIG. 11  is a cross-sectional view of an embodiment of multichannel tube with deformable webs and chamfered edges prior to hydraulic expansion. 
         FIG. 12  is a cross-sectional view of the multichannel tube of  FIG. 11  after hydraulic expansion. 
         FIG. 13  is a cross-sectional view of another embodiment of multichannel tube with deformable webs and chamfered edges prior to hydraulic expansion. 
         FIG. 14  is a flow chart of an embodiment of a method for assembling a heat exchanger. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure is directed to multichannel tubes that can be expanded to assemble the multichannel tubes within plate fin heat exchangers. The multichannel tubes each include several generally parallel flow paths, which extend along the length of the multichannel tubes. The flow paths are separated from one another by deformable webs that are designed to deform upon pressurization of the tube. As used herein, the term “deformable webs” includes webs designed to change in shape, geometry, width, and/or height in response to a change in pressure. The deformable webs are slanted in a common direction along the width of the multichannel tubes to produce flow paths of a generally parallelogram shape. The edges of the multichannel tubes may be chamfered to inhibit deflection of the sidewalls during hydraulic expansion. In certain embodiments, the chamfered edges may be designed to produce curved and generally symmetrical sidewalls upon hydraulic expansion. 
     The multichannel tubes may be expanded by directing a high pressure fluid, such as gas or oil, through the tubes. As the fluid pressurizes the tubes, the walls of the tubes may expand outward to increase the outer dimension of the tubes, allowing the tubes to be press fit within fin openings encircling the tubes. During pressurization, the deformable webs, which extend between the tube walls, may deform to allow the tubes to expand. For example, the webs may stretch, shift positions, and/or change shape. According to certain embodiments, the deformable webs may be designed to straighten, or become less slanted, upon expansion of the tubes. As a result of the pressurization, the top and bottom walls may move in opposite lateral directions, which may cause deflection of the sidewalls. Accordingly, in certain embodiments, one or more of the sidewalls may be chamfered to inhibit and/or reduce deflection of the sidewalls upon hydraulic expansion. 
       FIGS. 1 and 2  depict exemplary applications for plate fin heat exchangers. Plate fin heat exchangers may be employed in a range of settings, both within the HVAC&amp;R field and outside of that field. In presently contemplated applications, however, plate fin heat exchangers may be used in residential, commercial, light industrial, industrial, and in any other application for heating or cooling a volume or enclosure, such as a residence, building, structure, and so forth. Although described below in the context of a multichannel tubes for evaporators and/or condensers, in other embodiments, the multichannel tubes disclosed herein may be used in other types of heat exchangers, such as radiators, among others. 
       FIG. 1  illustrates an exemplary application; in this case an HVAC&amp;R system for building environmental management that may employ heat exchangers. A building  10  is cooled by a system that includes a chiller  12  and a boiler  14 . As shown, chiller  12  is disposed on the roof of building  10  and boiler  14  is located in the basement; however, the chiller and boiler may be located in other equipment rooms or areas next to the building. Chiller  12  is an air cooled or water cooled device that implements a refrigeration cycle to cool water. Chiller  12  may be a stand-alone unit or may be part of a single package unit containing other equipment, such as a blower and/or integrated air handler. Boiler  14  is a closed vessel that includes a furnace to heat water. The water from chiller  12  and boiler  14  is circulated through building  10  by water conduits  16 . Water conduits  16  are routed to air handlers  18 , located on individual floors and within sections of building  10 . 
     Air handlers  18  are coupled to ductwork  20  that is adapted to distribute air between the air handlers. In certain embodiments, the ductwork may receive air from an outside intake (not shown). Air handlers  18  include heat exchangers that circulate cold water from chiller  12  and hot water from boiler  14  to provide heated or cooled air. Fans, within air handlers  18 , draw air through the heat exchangers and direct the conditioned air to environments within building  10 , such as rooms, apartments, or offices, to maintain the environments at a designated temperature. A control device  22 , shown here as including a thermostat, may be used to designate the temperature of the conditioned air. Control device  22  also may be used to control the flow of air through and from air handlers  18 . Other devices may, of course, be included in the system, such as control valves that regulate the flow of water and pressure and/or temperature transducers or switches that sense the temperatures and pressures of the water, the air, and so forth. Moreover, control devices may include computer systems that are integrated with or separate from other building control or monitoring systems, and even systems that are remote from the building. 
       FIG. 2  illustrates a residential heating and cooling system. In general, a residence  24  will include refrigerant conduits  26  that operatively couple an indoor unit  28  to an outdoor unit  30 . Indoor unit  28  may be positioned in a utility room, an attic, a basement, and so forth. Outdoor unit  30  is typically situated adjacent to a side of residence  24  and is covered by a shroud to protect the system components and to prevent leaves and other contaminants from entering the unit. Refrigerant conduits  26  transfer refrigerant between indoor unit  28  and outdoor unit  30 , typically transferring primarily liquid refrigerant in one direction and primarily vaporized refrigerant in an opposite direction. 
     When the system shown in  FIG. 2  is operating as an air conditioner, a heat exchanger in outdoor unit  30  serves as a condenser for recondensing vaporized refrigerant flowing from indoor unit  28  to outdoor unit  30  via one of the refrigerant conduits  26 . In these applications, a heat exchanger of the indoor unit, designated by the reference numeral  32 , serves as an evaporator. Indoor unit  32  receives liquid refrigerant (which may be expanded by an expansion device, not shown) and evaporates the refrigerant before returning it to outdoor unit  30 . 
     Outdoor unit  30  draws in environmental air through its sides as indicated by the arrows directed to the sides of the unit, forces the air through the outer unit heat exchanger by a means of a fan (not shown), and expels the air as indicated by the arrows above the outdoor unit. When operating as an air conditioner, the air is heated by the condenser heat exchanger within the outdoor unit and exits the top of the unit at a temperature higher than it entered the sides. Air is blown over indoor heat exchanger  32  and is then circulated through residence  24  by means of ductwork  20 , as indicated by the arrows entering and exiting ductwork  20 . The overall system operates to maintain a desired temperature as set by thermostat  22 . When the temperature sensed inside the residence is higher than the set point on the thermostat (plus a small amount), the air conditioner will become operative to refrigerate additional air for circulation through the residence. When the temperature reaches the set point (minus a small amount), the unit will stop the refrigeration cycle temporarily. 
     When the unit in  FIG. 2  operates as a heat pump, the roles of the heat exchangers are reversed. That is, the heat exchanger of outdoor unit  30  will serve as an evaporator to evaporate refrigerant and thereby cool air entering outdoor unit  30  as the air passes over the outdoor unit heat exchanger. Indoor heat exchanger  32  will receive a stream of air blown over it and will heat the air by condensing a refrigerant. 
       FIG. 3  illustrates a partially exploded view of one of the units shown in  FIG. 2 , in this case, outdoor unit  30 . Unit  30  includes a shroud  34  that surrounds the sides of unit  30  to protect the system components. Adjacent to shroud  34  is a heat exchanger  36 . A cover  38  encloses a top portion of heat exchanger  36 . Foam  40  is disposed between cover  38  and heat exchanger  36 . A fan  42  is located within an opening of cover  38  and is powered by a motor  44 . A wire way  46  may be used to connect motor  44  to a power source. A fan guard  48  fits within cover  38  and is disposed above the fan to prevent objects from entering the fan. 
     Heat exchanger  36  is mounted on a base pan  50 . Base pan  50  provides a mounting surface and structure for the internal components of unit  30 . A compressor  52  is disposed within the center of unit  30  and is connected to another unit within the HVAC&amp;R system, for example an indoor unit, by connections  54  and  56  that connect to conduits circulating refrigerant within the HVAC&amp;R system. A control box  58  houses the control circuitry for outdoor unit  30  and is protected by a cover  60 . A panel  62  may be used to mount control box  58  to unit  30 . 
     Refrigerant enters unit  30  through vapor connection  54  and flows through a conduit  64  into compressor  52 . The vapor may be received from the indoor unit (not shown). After undergoing compression in compressor  52 , the refrigerant exits compressor  52  through a conduit  66  and enters heat exchanger  36  through inlet  68 . Inlet  68  directs the refrigerant into a header or manifold  70 . From manifold  70 , the refrigerant flows through heat exchanger  36  to a header or manifold  72 . From header  72  the refrigerant flows back through heat exchanger  36  and exits through an outlet  74  disposed on header  70 . After exiting heat exchanger  36 , the refrigerant flows through conduit  76  to liquid connection  56  to return to the indoor unit where the process may begin again. 
       FIG. 4  illustrates an air conditioning system  78 , which may employ plate fin heat exchangers. Refrigerant flows through system  78  within closed refrigeration loop  80 . The refrigerant may be any fluid that absorbs and extracts heat. For example, the refrigerant may be hydrofluorocarbon (HFC) based R-410A, R-407, or R-134a, or it may be carbon dioxide (R-744A) or ammonia (R-717). Air conditioning system  78  includes control devices  82  that enable the system to cool an environment to a prescribed temperature. 
     System  78  cools an environment by cycling refrigerant within closed refrigeration loop  80  through a condenser  84 , a compressor  86 , an expansion device  88 , and an evaporator  90 . The refrigerant enters condenser  84  as a high pressure and temperature vapor and flows through the multichannel tubes of the condenser. A fan  92 , which is driven by a motor  94 , draws air across the multichannel tubes. The fan may push or pull air across the tubes. As the air flows across the tubes, heat transfers from the refrigerant vapor to the air, producing heated air  96  and causing the refrigerant vapor to condense into a liquid. The liquid refrigerant then flows into an expansion device  88  where the refrigerant expands to become a low pressure and temperature liquid. Typically, expansion device  88  will be a thermal expansion valve (TXV); however, according to other exemplary embodiments, the expansion device may be an orifice or a capillary tube. After the refrigerant exits the expansion device, some vapor refrigerant may be present in addition to the liquid refrigerant. 
     From expansion device  88 , the refrigerant enters evaporator  90  and flows through the evaporator multichannel tubes. A fan  98 , which is driven by a motor  100 , draws air across the multichannel tubes. As the air flows across the tubes, heat transfers from the air to the refrigerant liquid, producing cooled air  102  and causing the refrigerant liquid to boil into a vapor. According to certain embodiments, the fan may be replaced by a pump that draws fluid across the multichannel tubes. 
     The refrigerant then flows to compressor  86  as a low pressure and temperature vapor. Compressor  86  reduces the volume available for the refrigerant vapor, consequently, increasing the pressure and temperature of the vapor refrigerant. The compressor may be any suitable compressor such as a screw compressor, reciprocating compressor, rotary compressor, swing link compressor, scroll compressor, or turbine compressor. Compressor  86  is driven by a motor  104  that receives power from a variable speed drive (VSD) or a direct AC or DC power source. According to an exemplary embodiment, motor  104  receives fixed line voltage and frequency from an AC power source although in certain applications the motor may be driven by a variable voltage or frequency drive. The motor may be a switched reluctance (SR) motor, an induction motor, an electronically commutated permanent magnet motor (ECM), or any other suitable motor type. The refrigerant exits compressor  86  as a high temperature and pressure vapor that is ready to enter the condenser and begin the refrigeration cycle again. 
     The control devices  82 , which include control circuitry  106 , an input device  108 , and a temperature sensor  110 , govern the operation of the refrigeration cycle. Control circuitry  106  is coupled to the motors  94 ,  100 , and  104  that drive condenser fan  92 , evaporator fan  98 , and compressor  86 , respectively. Control circuitry  106  uses information received from input device  108  and sensor  110  to determine when to operate the motors  94 ,  100 , and  104  that drive the air conditioning system. In certain applications, the input device may be a conventional thermostat. However, the input device is not limited to thermostats, and more generally, any source of a fixed or changing set point may be employed. These may include local or remote command devices, computer systems and processors, and mechanical, electrical and electromechanical devices that manually or automatically set a temperature-related signal that the system receives. For example, in a residential air conditioning system, the input device may be a programmable 24-volt thermostat that provides a temperature set point to the control circuitry. 
     Sensor  110  determines the ambient air temperature and provides the temperature to control circuitry  106 . Control circuitry  106  then compares the temperature received from the sensor to the temperature set point received from the input device. If the temperature is higher than the set point, control circuitry  106  may turn on motors  94 ,  100 , and  104  to run air conditioning system  78 . The control circuitry may execute hardware or software control algorithms to regulate the air conditioning system. According to exemplary embodiments, the control circuitry may include an analog to digital (A/D) converter, a microprocessor, a non-volatile memory, and an interface board. Other devices may, of course, be included in the system, such as additional pressure and/or temperature transducers or switches that sense temperatures and pressures of the refrigerant, the heat exchangers, the inlet and outlet air, and so forth. 
       FIG. 5  illustrates a heat pump system  112  that may employ plate fin heat exchangers. Because the heat pump may be used for both heating and cooling, refrigerant flows through a reversible refrigeration/heating loop  114 . The refrigerant may be any fluid that absorbs and extracts heat. The heating and cooling operations are regulated by control devices  116 . 
     Heat pump system  112  includes an outside heat exchanger  118  and an inside heat exchanger  120  that both operate as heat exchangers. Each heat exchanger may function as an evaporator or a condenser depending on the heat pump operation mode. For example, when heat pump system  112  is operating in cooling (or “AC”) mode, outside heat exchanger  118  functions as a condenser, releasing heat to the outside air, while inside heat exchanger  120  functions as an evaporator, absorbing heat from the inside air. When heat pump system  112  is operating in heating mode, outside heat exchanger  118  functions as an evaporator, absorbing heat from the outside air, while inside heat exchanger  120  functions as a condenser, releasing heat to the inside air. A reversing valve  122  is positioned on reversible loop  114  between the heat exchangers to control the direction of refrigerant flow and thereby to switch the heat pump between heating mode and cooling mode. 
     Heat pump system  112  also includes two metering devices  124  and  126  for decreasing the pressure and temperature of the refrigerant before it enters the evaporator. The metering devices also regulate the refrigerant flow entering the evaporator so that the amount of refrigerant entering the evaporator equals, or approximately equals, the amount of refrigerant exiting the evaporator. The metering device used depends on the heat pump operation mode. For example, when heat pump system  112  is operating in cooling mode, refrigerant bypasses metering device  124  and flows through metering device  126  before entering inside heat exchanger  120 , which acts as an evaporator. In another example, when heat pump system  112  is operating in heating mode, refrigerant bypasses metering device  126  and flows through metering device  124  before entering outside heat exchanger  118 , which acts as an evaporator. According to other exemplary embodiments, a single metering device may be used for both heating mode and cooling mode. The metering devices typically are thermal expansion valves (TXV), but also may be orifices or capillary tubes. 
     The refrigerant enters the evaporator, which is outside heat exchanger  118  in heating mode and inside heat exchanger  120  in cooling mode, as a low temperature and pressure liquid. Some vapor refrigerant also may be present as a result of the expansion process that occurs in metering device  124  or  126 . The refrigerant flows through multichannel tubes in the evaporator and absorbs heat from the air changing the refrigerant into a vapor. In cooling mode, the indoor air flowing across the multichannel tubes also may be dehumidified. The moisture from the air may condense on the outer surface of the multichannel tubes and consequently be removed from the air. 
     After exiting the evaporator, the refrigerant passes through reversing valve  122  and into a compressor  128 . Compressor  128  decreases the volume of the refrigerant vapor, thereby, increasing the temperature and pressure of the vapor. The compressor may be any suitable compressor such as a screw compressor, reciprocating compressor, rotary compressor, swing link compressor, scroll compressor, or turbine compressor. 
     From compressor  128 , the increased temperature and pressure vapor refrigerant flows into a condenser, the location of which is determined by the heat pump mode. In cooling mode, the refrigerant flows into outside heat exchanger  118  (acting as a condenser). A fan  130 , which is powered by a motor  132 , draws air across the multichannel tubes containing refrigerant vapor. According to certain exemplary embodiments, the fan may be replaced by a pump that draws fluid across the multichannel tubes. The heat from the refrigerant is transferred to the outside air causing the refrigerant to condense into a liquid. In heating mode, the refrigerant flows into inside heat exchanger  120  (acting as a condenser). A fan  134 , which is powered by a motor  136 , draws air across the multichannel tubes containing refrigerant vapor. The heat from the refrigerant is transferred to the inside air causing the refrigerant to condense into a liquid. 
     After exiting the condenser, the refrigerant flows through the metering device ( 124  in heating mode and  126  in cooling mode) and returns to the evaporator (outside heat exchanger  118  in heating mode and inside heat exchanger  120  in cooling mode) where the process begins again. 
     In both heating and cooling modes, a motor  138  drives compressor  128  and circulates refrigerant through reversible refrigeration/heating loop  114 . The motor may receive power either directly from an AC or DC power source or from a variable speed drive (VSD). The motor may be a switched reluctance (SR) motor, an induction motor, an electronically commutated permanent magnet motor (ECM), or any other suitable motor type. 
     The operation of motor  138  is controlled by control circuitry  140 . Control circuitry  140  receives information from an input device  142  and sensors  144 ,  146 , and  148  and uses the information to control the operation of heat pump system  112  in both cooling mode and heating mode. For example, in cooling mode, input device  142  provides a temperature set point to control circuitry  140 . Sensor  148  measures the ambient indoor air temperature and provides it to control circuitry  140 . Control circuitry  140  then compares the air temperature to the temperature set point and engages compressor motor  138  and fan motors  132  and  136  to run the cooling system if the air temperature is above the temperature set point. In heating mode, control circuitry  140  compares the air temperature from sensor  148  to the temperature set point from input device  142  and engages motors  132 ,  136 , and  138  to run the heating system if the air temperature is below the temperature set point. 
     Control circuitry  140  also uses information received from input device  142  to switch heat pump system  112  between heating mode and cooling mode. For example, if input device  142  is set to cooling mode, control circuitry  140  will send a signal to a solenoid  150  to place reversing valve  122  in an air conditioning position  152 . Consequently, the refrigerant will flow through reversible loop  114  as follows: the refrigerant exits compressor  128 , is condensed in outside heat exchanger  118 , is expanded by metering device  126 , and is evaporated by inside heat exchanger  120 . If the input device is set to heating mode, control circuitry  140  will send a signal to solenoid  150  to place reversing valve  122  in a heat pump position  154 . Consequently, the refrigerant will flow through the reversible loop  114  as follows: the refrigerant exits compressor  128 , is condensed in inside heat exchanger  120 , is expanded by metering device  124 , and is evaporated by outside heat exchanger  118 . 
     The control circuitry may execute hardware or software control algorithms to regulate heat pump system  112 . According to exemplary embodiments, the control circuitry may include an analog to digital (A/D) converter, a microprocessor, a non-volatile memory, and an interface board. 
     The control circuitry also may initiate a defrost cycle when the system is operating in heating mode. When the outdoor temperature approaches freezing, moisture in the outside air that is directed over outside heat exchanger  118  may condense and freeze on the heat exchanger. Sensor  144  measures the outside air temperature, and sensor  146  measures the temperature of outside heat exchanger  118 . These sensors provide the temperature information to the control circuitry which determines when to initiate a defrost cycle. For example, if either sensor  144  or  146  provides a temperature below freezing to the control circuitry, system  112  may be placed in defrost mode. In defrost mode, solenoid  150  is actuated to place reversing valve  122  in air conditioning position  152 , and motor  132  is shut off to discontinue airflow over the multichannel tubes. System  112  then operates in cooling mode until the increased temperature and pressure refrigerant flowing through outside heat exchanger  80  defrosts the heat exchanger. Once sensor  146  detects that heat exchanger  118  is defrosted, control circuitry  140  returns the reversing valve  122  to heat pump position  154 . As will be appreciated by those skilled in the art, the defrost cycle can be set to occur at many different time and temperature combinations. 
       FIG. 6  is a perspective view of an exemplary heat exchanger that may be used in air conditioning system  78 , shown in  FIG. 4 , or heat pump system  112 , shown in  FIG. 5 . The exemplary heat exchanger may be a condenser  84 , an evaporator  90 , an outside heat exchanger  118 , or an inside heat exchanger  120 , as shown in  FIGS. 4 and 5 . It should be noted that in similar or other systems, the heat exchanger might be used as part of a chiller or in any other heat exchanging application. The heat exchanger includes manifolds  70  and  72  that are connected by multichannel tubes  164 . Although 30 tubes are shown in  FIG. 6 , the number of tubes may vary. The manifolds and tubes may be constructed of aluminum or any other material that promotes good heat transfer. Refrigerant flows from manifold  70  through a set of first tubes  166  to manifold  72 . The refrigerant then returns to manifold  70  in an opposite direction through a set of second tubes  168 . The first tubes may be of identical construction to the second tubes, or the first tubes may vary from the second tubes by properties such as construction material, shape, internal flow paths, size, and the like. According to certain exemplary embodiments, the heat exchanger may be rotated approximately 90 degrees so that the multichannel tubes run vertically between a top manifold and a bottom manifold. Furthermore, the heat exchanger may be inclined at an angle relative to the vertical. Although the multichannel tubes are depicted as having an elongated and oblong shape, the tubes may be any shape, such as tubes with a cross-section in the form of a rectangle, square, circle, oval, ellipse, triangle, trapezoid, or parallelogram. It should also be noted that the heat exchanger may be provided in a single plane or slab, or may include bends, corners, contours, and so forth. Moreover, although a two-pass heat exchanger is depicted, the multichannel tubes may be employed in single or multi-pass heat exchangers. 
     Refrigerant enters heat exchanger  36  through inlet  68  and exits heat exchanger  36  through outlet  74 . Although  FIG. 6  depicts the inlet at the top of the manifold and the outlet at the bottom of the manifold, the inlet and outlet positions may be interchanged so that the fluid enters at the bottom and exits at the top. The fluid also may enter and exit the manifold from multiple inlets and outlets positioned on bottom, side, or top surfaces of the manifold. Baffles  170  separate the inlet and outlet portions of manifold  70 . Although a double baffle  170  is illustrated, any number of one or more baffles may be employed to create separation of the inlet and outlet portions. It should also be noted that according to other exemplary embodiments, the inlet and outlet might be contained on separate manifolds, eliminating the need for a baffle. 
     Plate fins  172  are located around multichannel tubes  164  to promote the transfer of heat between the tubes and the environment. According to an exemplary embodiment, the fins are plate fins constructed of aluminum and are interference fit to the tubes, and disposed generally perpendicular to the flow of refrigerant. However, according to other exemplary embodiments, the fins may be made of other materials that facilitate heat transfer and may extend at varying angles with respect to the flow of the refrigerant. The fins may include surface features and formations such as louvers, raised lances, corrugations, ribs, and combinations thereof. Further, in certain embodiments, the fins may include spacers and/or collars for spacing the fins. 
     When an external fluid, such as air, flows across multichannel tubes  164 , as generally indicated by airflow  174 , heat transfer occurs between the refrigerant flowing within tubes  164  and the external fluid. Although the external fluid is shown here as air, other fluids may be used. As the external fluid flows across the tubes, heat is transferred to and from the tubes to the external fluid. For example, in a condenser, the external fluid is generally cooler than the fluid flowing within the multichannel tubes. As the external fluid contacts a multichannel tube, heat is transferred from the refrigerant within the multichannel tube to the external fluid. Consequently, the external fluid is heated as it passes over the multichannel tubes and the refrigerant flowing within the multichannel tubes is cooled. In an evaporator, the external fluid generally has a temperature higher than the refrigerant flowing within the multichannel tubes. Consequently, as the external fluid contacts the leading edge of the multichannel tubes, heat is transferred from the external fluid to the refrigerant flowing in the tubes to heat the refrigerant. The external fluid leaving the multichannel tubes is then cooled because the heat has been transferred to the refrigerant. In certain embodiments, a portion of the external fluid may condense and collect on the tubes and/or fins. 
       FIG. 7  illustrates certain components of the heat exchanger of  FIG. 6  in a somewhat more detailed and exploded view. Each manifold (manifold  70  being shown in  FIG. 7 ) is a tubular structure with open ends that are closed by a cap  178 . Openings, or apertures,  180  are formed in the manifolds, such as by conventional piercing or machining operations. Multichannel tubes  164  may then be inserted into openings  180  in a generally parallel fashion. Ends  182  of the tubes are inserted into openings  180  so that fluid may flow from the manifold into flow paths  184  within the tubes. Flow paths  184  may extend along the length  186  of each multichannel tube  164  to allow the refrigerant to flow through the tube  164  between manifolds  70  and  72 . 
     Prior to or after insertion into manifold  70 , tubes  164  may be inserted through openings  188  within fins  172  to promote heat transfer between an external fluid, such as air or water, and the refrigerant flowing within the tubes. Openings  188  encircle cross sections of tubes  164  and are disposed generally transverse to the longitudinal axis of the tubes. Collars  190  encircle openings  188  for receiving tubes  164  and may extend generally parallel to the length of the tubes. In certain embodiments, collars  190  may space adjacent fins  172  from on another. Fins  172  may be constructed of aluminum, aluminum alloy, copper, or the like. In certain embodiments, fins  172  may include metal sheets with openings  188  and collars  190  formed by stamping, punching, or other suitable manufacturing method. 
     After ends  182  are inserted into openings  180  of manifolds  70  and  72 , the tubes  164  and manifolds  70  and  72  may be brazed, or otherwise joined to hold the components together. For example, a torch brazing process may be used to secure the manifolds  70  and  72  to the tube ends. Hydraulic pressure may then be employed to expand tubes  164  into fin openings  188 . For example, a fluid, such as a gas or oil, may be directed through tubes  164  to pressurize and expand the tubes  164 . Openings  188  may have an inner diameter that is slightly larger than the outer diameter of tubes  164 . When internal pressure is applied to the tubes, deformable webs within the tubes  164  allow the tubes to expand to pressure fit tubes  164  into openings  188 , as described further below with respect to  FIGS. 9 and 10 . According to certain embodiments, the expansion of tubes  164  into openings  188  may decrease the thermal contact resistance between the tubes and fins, thereby increasing the heat transfer between the fins and tubes. 
       FIG. 8  is a cross-sectional view through one of the multichannel tubes  164  prior to hydraulic expansion. Before hydraulic expansion, multichannel tube  164  has outer dimensions that are smaller than the dimensions of fin openings  188  ( FIG. 7 ), which may facilitate insertion of multichannel tube  164  through fins  172 . For example, a width  196  and a height  198  of multichannel tube  164  may be slightly smaller than a corresponding width  238  and height  240  of fin opening  188 , shown in  FIG. 9 . According to certain embodiments, width  196  may be approximately 15 to 20 millimeters, and all subranges therebetween, or more specifically, width  196  may be approximately 18 millimeters. Further, in certain embodiments, height  198  may be approximately 0.5 to 3 millimeters, and all subranges therebetween, or more specifically, height  198  may be approximately 1.3 millimeters. 
     Width  196  extends between sidewalls  200  and  202 . According to certain embodiments, sidewalls  200  and  202  each may have a thickness  204  designed to withstand pressures produced by refrigerant flowing through multichannel tube  164 . According to certain embodiments, thickness  204  may be approximately 0.3 to 0.5 millimeters, and all subranges therebetween, or more specifically, thickness  204  may be approximately 0.4 millimeters. Height  198  extends between top and bottom walls  206  and  208 , respectively, which also may have a thickness  210  designed to withstand pressures produced by refrigerant flowing through multichannel tube  164 . According to certain embodiments, thickness  210  may be approximately 0.24 to 0.26 millimeters, or more specifically, 0.25 millimeters. 
     The thicknesses  204  and  210  of the tube walls  200 ,  202 ,  206 , and  208  may ensure that the multichannel tube  164  is able to withstand high pressures without bursting and/or developing leaks. According to certain embodiments, multichannel tube  164  may be designed to withstand pressures of at least approximately 1,950 to 2,000 psi without bursting. However, in other embodiments, the pressures may vary depending on factors such as the type of heat exchanger, the type of refrigeration cycle, and/or the type of refrigerant, among others. Further, in certain embodiments, the thicknesses  204  and  210  and/or the tube dimensions  196  and  198  may vary depending on factors such as the material of construction, the type of heat exchanger, and/or the number of flow paths  184 , among others. 
     Multichannel tube  164  includes internal webs  214  that extend between top and bottom walls  206  and  208  to divide the interior of multichannel tube  164  into multiple flow paths  184 . According to certain embodiments, multichannel tube  164  may be extruded and webs  214  may be formed during the extrusion process. Although eleven flow paths  184  are shown in  FIG. 8 , in other embodiments, the number of flow paths may vary. Webs  214  also extend between the top and bottom walls  206  and  208  along the entire length  186  ( FIG. 7 ) of multichannel tube  164  to produce independent and separate flow paths  184  though multichannel tube  164 . In other words, refrigerant may flow through multichannel tube  164  from one manifold  70  to the other manifold  72  ( FIG. 6 ) within a single flow path  184 , without intermixing with refrigerant flowing through the other flow paths  184 . Further, multichannel tube  164  may have a generally uniform cross section throughout the entire length  186 . 
     Webs  214  have a height  212  that corresponds to the distance between top and bottom walls  206  and  208 . According to certain embodiments, height  212  may be approximately 0.8 millimeters. Each web  214  also has a thickness  216 , which in certain embodiments, may be approximately 0.1 to 0.3 millimeters, or more specifically, approximately 0.21 millimeters. However, in other embodiments, web thickness  216  may vary depending on factors such as the number of webs  216  included within multichannel tube  164 , the dimensions of multichannel tube  164 , and the material of construction of multichannel tube  164 , among others. 
     The web thickness  216  may be designed to allow the webs  214  to deform at a pressure that is lower than the burst pressure of multichannel tube  164 , but higher than the operating pressure of the multichannel tube. According to certain embodiments, the burst strength may be at least approximately three times greater than the operating pressure. Further, the web shape may be designed to produce flow paths  184  of a desired shape after deformation of the webs  214 . In certain embodiments, webs  214  may be designed to deform at pressures that are approximately 20 to 80 percent of the burst pressure of multichannel tube  164 , and all subranges therebetween. More specifically, webs  214  may be designed to deform at pressures that are approximately 30 to 60 percent of the burst pressure, or even more specifically, at pressures that are approximately 50 percent of the burst pressure. For example, in embodiments where the operating pressure may be approximately 600 to 700 psi and the burst pressure may be approximately 1,950 to 2,000 psi, webs  214  may be designed to perform at pressures of approximately 1,000 to 1,500 psi. In another example, where multichannel tubes  164  are designed to be used in a lower pressure heat exchanger, such as a radiator, the operating pressure may be approximately 5 to 15 psi and the burst pressure of the tubes may be approximately 50 to 75 psi. In these embodiments, the webs  214  may be designed to deform at a pressure of approximately 25 to 40 psi. 
     As shown in  FIG. 8 , webs  214  are slanted in the same direction and are generally parallel to one another. In particular, webs  214  are slanted at an angle  218  with respect to bottom wall  208 . According to certain embodiments, angle  218  may be less than approximately 45 degrees. Further, in certain embodiments, angle  218  may be approximately 38 to 42 degrees, or more specifically, approximately 40 degrees. However, in other embodiments, the degree of angle  218  may vary. Webs  214  extend between top and bottom walls  206  and  208  to produce flow paths  184 A of a parallelogram shape. In the embodiment shown in  FIG. 8 , flow paths  184 A are defined by a pair of rounded corners  220  disposed opposite of one another, and a pair of angled corners  222  also disposed opposite of one another. The rounded corners have an inner radius  224 , which, in certain embodiments may be approximately 0.05 millimeters. However, in other embodiments, the size of inner radius  224  may vary. Further, in other embodiments, each of the corners  220  and  222  may be rounded or angled, or a combination thereof. The outermost webs  214  and the sidewalls  200  and  202  form outermost flow paths  184 B and  184 C. Each of the outermost flow paths  184 B and  184 C may be formed by one web  214  and one of the sidewalls  200  or  202 . Accordingly, the outer walls of flow path  184 B and  184 C have a curvature defined by interior walls  226  of sidewalls  200  and  202 . 
     Each of the webs  214  includes an upper portion  228  that is adjacent to top wall  206 , and a lower portion  230  that is adjacent to bottom wall  208 . During hydraulic expansion, the upper and lower portions  228  and  230  move in generally opposite directions to straighten webs  214 . In particular, upper portions  228  of webs  214  may move towards sidewall  200 , while lower portions  230  of webs may move towards sidewall  202 . Accordingly, webs  214  may straighten during hydraulic expansion to produce generally square flow paths, as described further below with respect to  FIGS. 9 and 10 . 
       FIGS. 9 and 10  show multichannel tube  164  inserted within a plate fin  172 . In particular,  FIG. 9  shows multichannel tube  164  inserted within opening  188  of fin  172  prior to hydraulic expansion, and  FIG. 10  shows multichannel tube  164  pressure fit within fin  172  after hydraulic expansion. As shown in  FIG. 9 , opening  188  has a width  238  and a height  240 , which are slightly larger than the width  196  and height  198  ( FIG. 8 ) of tube  164 . Accordingly, gaps  242  and  244  exist between multichannel tube  164  and fin  172 . According to certain embodiments, gaps  242  and  244  may be approximately 0.25 millimeters. 
     During hydraulic expansion, the outer dimensions of multichannel tube  164  may increase so that multichannel tube  164  fills opening  188 , as shown in  FIG. 10 . In particular, multichannel tube  164  may increase from a height  198  shown in  FIG. 8  to a height  256 , shown in  FIG. 10 . As can be seen by comparing  FIGS. 9 and 10 , during expansion, webs  214  may deform under the hydraulic pressure to allow multichannel tube  164  to expand. In particular, upper portions  228  may move toward sidewall  200 , while lower portions  230  move towards sidewall  202 , causing webs  214  to straighten. Further top wall  206  and bottom wall  208  may move laterally with respect to one another. As webs  214  straighten, the multichannel tube  164  may expand in height to fill opening  188 . In certain embodiments, webs  214  also may stretch and become thinner to allow multichannel tube  164  to increase in height. However, in other embodiments, the thickness of webs may remain relatively constant during hydraulic expansion. 
       FIG. 10  is a cross section of multichannel tube  164  within opening  188  of plate fin  172  after hydraulic expansion. As shown, multichannel tube  164  has an increased height  246 , which allows multichannel tube  164  to fill opening  188  and produces a pressure fit for multichannel tube  164  within fin  172 . After expansion, multichannel tube  164  more fully contacts fin  172 , which may increase the heat transfer between the fin and multichannel tubes during operation of the heat exchanger. Height  256  may be approximately equal to or just slightly larger than height  240  of opening  188 , as shown in  FIG. 9 . Accordingly, gaps  242  may no longer exist between opening  188  and top and bottom walls  206  and  208 . According to certain embodiments, height  246  may increase by approximately 0.25 to 0.5 millimeters as compared to height  198  of multichannel tube  164  prior to hydraulic expansion, as shown in  FIG. 8 . In certain embodiments, height  246  may be approximately 5 to 40 percent larger, and all subranges therebetween, than the height  198  of multichannel tube  164  prior to hydraulic expansion. Multichannel tube  164  also has a width  248 , which may be approximately equal to, slightly smaller than, or slightly larger than width  196  of multichannel tube  164  prior to hydraulic expansion. 
     As can be seen by comparing  FIGS. 9 and 10 , the slanted webs  214  have been deformed under hydraulic expansion to become generally straight webs  214  that extend between top and bottom walls  206  and  208 . In particular, upper portions  228  of webs  214  have moved towards sidewall  200 , and lower portions  230  of webs  214  have moved towards sidewall  202 . Accordingly, flow paths  184 A have changed from the generally parallelogram shape shown in  FIG. 9  to the generally square shape shown in  FIG. 10 . 
     Further, top wall  206  and bottom wall  208  have moved in opposite lateral directions to facilitate straightening of webs  214 . In particular, top wall  206  has moved towards sidewall  200  while bottom wall  208  has moved towards sidewall  202 . As a result of the lateral movement of sidewalls  200  and  202  and/or the straightening of webs  214 , sidewalls  200  and  202  have deflected in generally opposite vertical directions. The deflected sidewalls  200  and  202  include extended sections  247  that may extend vertically beyond the adjacent top wall  206  or bottom wall  208 . In certain embodiments, the contact between extended sections  247  and plate fin  172  may compress plate fin  172  and/or may push the adjacent top wall  206  or bottom wall  208  away from plate fin  172 . In certain embodiments, the contact between extended sections  247  and plate fin  172  may result in decreased and/or uneven contact between multichannel tube  164  and plate fin  172 , which may reduce the heat transfer between multichannel tube  164  and plate fin  172  during operation of the heat exchanger. The deflected sidewalls  200  and  202  also include slanted sections  249  that are separated from the perimeter of fin opening  188 , which may also reduce the heat transfer between multichannel tube  164  and plate fin  172 . According to certain embodiments, deflection of sidewalls  200  and  202  may be minimized or eliminated by including a chamfered edge along the sidewalls, as discussed further below with respect to  FIGS. 11 to 13 . 
     After expansion, webs  214  may extend from bottom wall  208  at an angle  250 , which in certain embodiments, may be approximately 70 to 130 degrees, and all subranges therebetween. According to certain embodiments, angle  250  may be approximately 90 degrees. Further, in another example, angle  250  may be less than or equal to approximately 75 degrees. However, in other embodiments, the degree of angle  250  may vary, depending on factors such as the expansion pressure, the burst pressure of the multichannel tube, the size of the multichannel tube, and the thickness of the webs, among others. As a result of the hydraulic expansion, webs  214  have increased to a height  252  while top and bottom walls  206  and  208  have expanded outward to produce the increased height  246  of multichannel tube  164 . According to certain embodiments, height  246  may be approximately 5 to 70 percent larger, and all subranges therebetween, than the height  212  of webs  214  prior to hydraulic expansion. The increased height  246  is achieved due to straightening and/or elongation of the webs. Accordingly, in certain embodiments, webs  214  also may have decreased to a thickness  254 . According to certain embodiments, thickness may be approximately 0 to 10 percent smaller, and all subranges therebetween, than the thickness  216  of webs  214  prior to hydraulic expansion. However, in other embodiments, thickness  254  may be approximately equal to the thickness  216  of webs  214  prior to hydraulic expansion. In these embodiments, the increase in height of multichannel tube  164  may be achieved solely by the straightening of the webs in response to hydraulic expansion. 
       FIGS. 11 and 12  depict another embodiment of a multichannel tube  164  that includes deformable webs  214 . The multichannel tube shown in  FIGS. 11 and 12  may be generally similar to the multichannel tube shown in  FIGS. 8 to 10 ; however, rather than having generally symmetrical curves, sidewalls  200  and  202  include chamfered edges  256 . Chamfered edges  256  include angled sections that connect the top or bottom wall to the curved profile of the sidewall. Chamfered edges  256  may inhibit the deflection of sidewalls  200  and  202 , as shown in  FIG. 10 . For example, chamfered edges  256  may provide room for sidewalls  200  and  202  to shift without extending vertically past the adjacent wall  206  or  208 . In certain embodiments, chamfered edges  256  may reduce and/or prevent the formation of extended sections  247  and/or slanted sections  249 , as shown in  FIG. 10 . In general, chamfered edges  256  may promote a curved and generally symmetrical shape of sidewalls  200  and  202  upon hydraulic expansion of tube  164 . The generally symmetrical shape of sidewalls  200  and  202  may promote relatively even contact between multichannel tube  164  and plate fin  172  upon hydraulic expansion, which, in turn, may provide increased heat transfer between plate fin  172  and multichannel tube  164 . As shown, sidewalls  200  and  202  each have one chamfered edge  256 . However, in other embodiments, sidewalls  200  and  202  each may have two chamfered edges  256  located opposite of one another on top and bottom walls  206  and  208 , as generally shown in  FIG. 13 . 
     Chamfered edge  256  may have a width  258 , which, in certain embodiments, may be approximately 1 millimeter. According to certain embodiments, width  258  may be approximately 1 to 10 percent of the total width  196  of multichannel tube  164 . Further, in certain embodiments, width  258  may be approximately 5 to 15 percent greater than width  204  of sidewalls  200  and  202 . Chamfered edge  256  may be disposed at an angle  260  with respect to top and bottom wall  206  and  208 . According to certain embodiments, angle  260  may be approximately 15 to 30 degrees, and all subranges therebetween. More specifically, angle  260  may be approximately 19 to 23 degrees, or even more specifically, may be approximately 21 degrees. 
       FIG. 12  depicts the multichannel tube of  FIG. 11  after hydraulic expansion. The multichannel tube of  FIG. 11  is generally similar to the multichannel tube shown in  FIG. 10  where the flow paths  184  have changed from a generally parallelogram shape to a generally square shape. However, rather than including slanted sections  249  on the sidewalls  200  and  202 , the sidewalls  200  and  202  have a generally symmetrical curve. In particular, during hydraulic expansion, the chamfered edges  256  may deform to produce the generally curved and symmetrical sidewalls  200  and  202 . According to certain embodiments, the curved sidewalls may provide increased contact between multichannel tube  164  and fins  172  after hydraulic expansion, which in turn may increase the heat transfer between multichannel tube  164  and fins  172 . 
       FIG. 13  depicts another embodiment of a multichannel tube with slanted webs  214 . In this embodiment, sidewalls  200  and  202  each have two chamfered edges  256  with one chamfered edge extending from top wall  206  and the other chamfered edge extending from bottom wall  208 . During hydraulic expansion, the chamfered edges  256  may allow sidewalls  200  and  202  to deform into a curved shape as shown in  FIG. 12 . As shown in  FIG. 13 , each of the chamfered edges  256  has a similar width  256  and extends from the top or bottom wall at a similar angle  260 . However, in other embodiments, the chamfered edges included within the same multichannel tube may have different widths and/or angles. 
       FIG. 14  is a flow chart of an embodiment of a method  280  that may be employed to assemble a heat exchanger. Method  280  may be used to assemble a heat exchanger that includes multichannel tubes  164  with chamfered edges  256  as shown in  FIGS. 11 to 13  and/or without chamfered edges as shown in  FIGS. 8 to 10 . Method  280  may use techniques described in the commonly assigned provisional patent application, entitled “Multichannel Heat Exchanger Fins,” by Jeffrey Lee Tucker et al., filed on Aug. 7, 2009, and assigned application Ser. No. 61/232,199, which is hereby incorporated by reference in its entirety for all purposes. 
     Method  280  may begin by inserting (block  282 ) the multichannel tubes through openings within the plate fins. For example, as shown in  FIG. 7 , tubes  164  may be inserted through openings  188  of fins  172 . The multichannel tubes may then be inserted (block  284 ) into the manifolds. For example, tube ends  182  may be inserted into openings  180  of manifolds  70  and  72 , as shown in  FIG. 7 . In certain embodiments, the ends of the tubes may first be inserted into one manifold, the tubes may then be inserted through the fins, and then the other ends of the tubes may be inserted into the other manifold. However, in other embodiments, the tubes may be inserted through the fins and then the tube ends may be inserted into both of the manifolds. Once the tubes are inserted into the fins and manifolds, the manifolds may be brazed (block  286 ) to the tubes. For example, in certain embodiments, a torch brazing system may be used to join the tubes and the manifolds. 
     The tubes may then be secured to the fins by hydraulically expanding (block  288 ) the tubes into the plate fins. For example, a hydraulic fluid such as refrigerant oil may be injected into a manifold to flow through the flow paths within the multichannel tubes. The fluid may then be pressurized to expand the tubes. After expansion of the tubes, the hydraulic fluid may be drained or removed from the heat exchanger. In certain embodiments, the fluid may be compatible with the refrigerant designed to be used within the heat exchanger, so that any fluid remaining after the expansion process may mix with the refrigerant. In other embodiments another type of fluid, such as a gas, may be used as a hydraulic fluid. According to certain embodiments, the hydraulic fluid may be polyalkylene glycol (PAG) oil or nitrogen gas, among others. 
     Various hydraulic expansion pressures may be employed depending on the specific design of the heat exchanger and the refrigerant intended to be used within the heat exchanger. In general, the hydraulic expansion pressures may be greater than the operating pressure of the heat exchanger, but less than the burst strength of the tubes. For example, in certain embodiments, the heat exchanger may be designed for a glycol refrigerant at an operating pressure of approximately 50 psi and the tubes may have a burst pressure of approximately 150 to 200 psi. In these embodiments, the hydraulic fluid may be pressurized to approximately 75 to 125 psi to expand the tubes. In another example where the heat exchanger is designed to use carbon dioxide as refrigerant at an operating pressure of approximately 1500 psi, the tubes may have a burst pressure of approximately 4500 to 7500 psi. In these embodiments, hydraulic pressures of approximately 2200 to 4000 psi may be employed to expand the tubes. However, in other embodiments, the pressures may vary. 
       FIGS. 8 through 13  depict embodiments of deformable webs that may be employed to allow hydraulic expansion of multichannel tubes. As may be appreciated, the dimensions are provided by way of example only, and are not intended to be limiting. For example, in other embodiments, the thicknesses, radii, widths, and heights described herein may vary. Further, in other embodiments the shape of the flow paths and/or the geometry of the webs  214  may vary. For example, in certain embodiments, deformable webs may be employed within a tube where the webs each curve in the same direction. 
     It should be noted that the present discussion makes use of the term “multichannel” tubes or “multichannel heat exchanger” to refer to arrangements in which heat transfer tubes include a plurality of flow paths between manifolds that distribute flow to and collect flow from the tubes. A number of other terms may be used in the art for similar arrangements. Such alternative terms might include “microchannel” and “microport.” The term “microchannel” sometimes carries the connotation of tubes having fluid passages on the order of a micrometer and less. However, in the present context such terms are not intended to have any particular higher or lower dimensional threshold. Rather, the term “multichannel” used to describe and claim embodiments herein is intended to cover all such sizes. Other terms sometimes used in the art include “parallel flow” and “brazed aluminum.” However, all such arrangements and structures are intended to be included within the scope of the term “multichannel.” In general, such “multichannel” tubes will include flow paths disposed along the width or in a plane of a generally flat, planar tube, although, again, the invention is not intended to be limited to any particular geometry. 
     While only certain features and embodiments of the invention have been illustrated and described, many modifications and changes may occur to those skilled in the art (e.g., variations in sizes, dimensions, structures, shapes, and proportions of the various elements, values of parameters (e.g., temperatures, pressures, etc.), mounting arrangements, use of materials, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter recited in the claims. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention. Furthermore, in an effort to provide a concise description of the exemplary embodiments, all features of an actual implementation may not have been described (i.e., those unrelated to the presently contemplated best mode of carrying out the invention, or those unrelated to enabling the claimed invention). It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation specific decisions may be made. Such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure, without undue experimentation.