US20080141708A1

US20080141708A1 - Space-Saving Multichannel Heat Exchanger

Info

Publication number: US20080141708A1
Application number: US12/040,724
Authority: US
Inventors: Charles B. Obosu; Dan R. Burdette; Jeffrey N. Nichols; Peter J. Breiding
Original assignee: Johnson Controls Technology Co
Current assignee: Johnson Controls Technology Co
Priority date: 2006-11-22
Filing date: 2008-02-29
Publication date: 2008-06-19
Also published as: KR20090096601A; US20080141525A1; KR20090096600A; WO2008064238A1; US7757753B2; WO2008064251A3; WO2008064257A3; WO2008064243A1; KR101568200B1; US20080148760A1; US7677057B2; US7980094B2; US20080142203A1; WO2008064251A2; KR101518205B1; WO2008064257A2; US20090288440A1

Abstract

A multichannel heat exchanger is provided that may be used in any suitable application, such as air conditioning, refrigeration, heat pump, and similar systems. The heat exchanger provides for enhanced thermal exchange density within reduced envelope dimensions. Multichannel tubes may be oriented such that their major width is generally in a vertical plane, but such that their edges are inclined with respect to the vertical. The resulting envelope dimensions are reduced. Moreover, liquid condensate that may collect on the heat exchangers (e.g., when used as evaporators) may be channeled toward lower edges of the multichannel tubes along which the condensate flows for evacuation and collection.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority from and the benefit of U.S. Provisional Application Ser. No. 60/867,043, entitled MICROCHANNEL HEAT EXCHANGER APPLICATIONS, filed Nov. 22, 2006, U.S. Provisional Application Ser. No. 60/882,033, entitled MICROCHANNEL HEAT EXCHANGER APPLICATIONS, filed Dec. 27, 2006, and U.S. Provisional Application Ser. No. 60/909,598, entitled MICROCHANNEL COIL HEADER, filed Apr. 2, 2007, which are hereby incorporated by reference.

BACKGROUND

The invention relates generally to space-saving multichannel heat exchangers.
Heat exchangers are used many fields. For example, heat exchangers of various types and configurations are used in heating, ventilation, air conditioning, and refrigeration (HVAC&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. Fins may be positioned between the tubes to facilitate heat transfer between refrigerant contained within the tube flow channels and external air passing over the tubes. Multichannel heat exchangers may be used in small tonnage systems, such as residential systems, or in large tonnage systems, such as industrial chiller systems.
In general, in HVAC&R applications, heat exchangers transfer heat by circulating a refrigerant through a cycle of evaporation and condensation. In many systems, the refrigerant changes phases while flowing through heat exchangers in which evaporation and condensation occur. For example, the refrigerant may enter an evaporator heat exchanger as a liquid and exit as a vapor. In another example, the refrigerant may enter a condenser heat exchanger as a vapor and exit as a liquid. In a typical building heating and cooling application, one of the heat exchangers is placed in a building and the other outside the building. Whether the inside or outside heat exchanger functions as an evaporator (tending to cool an air stream) or as a condenser (tending to heat an air stream) depends upon whether the system is functioning in heating or cooling mode. Many air conditioning systems, for example only function in cooling mode, with an inside evaporator and an outside condenser. Heat pumps, on the other hand, may function in cooling or heating mode, reversing the function of the heat exchangers in the different modes.
In many applications, space constraints are placed on the equipment, whether placed inside or outside of a building or other enclosure to be heated or cooled. Higher thermal exchange densities, which may be thought of as energy exchange rate per unit volume, have been achieved by altering the design of the heat exchangers and components themselves, such as by using multichannel tubes rather then conventional hollow tubing. Improvements have also been made by wrapping the heat exchanger around other equipment, such as a compressor, expansion device, and so forth, and then drawing air through a central volume partially surrounded by the heat exchanger. However, further reductions in size and increases in thermal exchange density are needed.
Another issue with conventional multichannel heat exchangers is their tendency to hold condensate between the tubes (and cooling fins). Due to the relatively small interstices between these elements, water tends to collect and reduces the thermal transfer capabilities by closing flow paths for air. This is particularly problematic for heat exchangers functioning as evaporators outside (i.e., in a heat pump operating in heat pump mode). Condensate can freeze when outside temperatures drop, and while the condensate may be defrosted by various means, it typically does not clear and will simply refreeze, significantly reducing the effectiveness of the system.

SUMMARY

In accordance with aspects of the invention, a heat exchanger is presented. The heat exchanger includes a first manifold, a second manifold, and a plurality of multichannel tubes in fluid communication with the manifolds. The multichannel tubes include a plurality of generally parallel flow paths. The multichannel tubes also include an acute angle bend between the first and second manifolds.
In accordance with further aspects of the invention, a heat exchanger and a system including a heat exchanger are presented. The heat exchanger includes a first manifold, a second manifold, and a plurality of multichannel tubes in fluid communication with the manifolds. Each of the tubes includes generally parallel flow paths extending through the tubes generally parallel to a longitudinal axis of the tube. The first manifold is disposed in an upper position, the second manifold is disposed in a lower position, and the tubes are disposed with their longitudinal axis at an acute angle with respect to vertical to permit condensate to flow down an edge of the tubes towards the second manifold during operation.

DRAWINGS

FIG. 1 is a perspective view of an exemplary residential air conditioning or heat pump system of the type that might employ a heat exchanger.
FIG. 2 is a partially exploded view of the outside unit of the system of FIG. 1, with an upper assembly lifted to expose certain of the system components, including a heat exchanger.
FIG. 3 is a perspective view of an exemplary commercial or industrial HVAC&R system that employs a chiller and air handlers to cool a building and that may also employ heat exchangers.
FIG. 4 is a diagrammatical overview of an exemplary air conditioning system which may employ one or more heat exchangers.
FIG. 5 is a diagrammatical overview of an exemplary heat pump system which may employ one or more heat exchangers.
FIG. 6 is a perspective view of an exemplary heat exchanger.
FIG. 7 is a detailed exploded view of a portion of a heat exchanger illustrating component parts including a manifold and multichannel tubes.
FIG. 8 is a perspective view of a heat exchanger in accordance with certain embodiments of the invention designed to permit greater density for heat extraction within an available envelope, and to allow for the draining of condensate from the heat exchanger.
FIG. 9 is a side elevational view of the arrangement of FIG. 8 illustrating how condensate is allowed to drain in the arrangement.
FIG. 10 is a perspective view of an additional space-saving heat exchanger including a pair of opposite bends.
FIG. 11 is a perspective view of a further alternative embodiment of a space-saving heat exchanger in which a single acute angle bend is formed.

DETAILED DESCRIPTION

FIGS. 1-3 depict exemplary applications for heat exchangers. Such systems, in general, may be applied in a range of settings, both within the HVAC&R field and outside of that field. In presently contemplated applications, however, heat exchanges 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. Moreover, the heat exchanges may be used in industrial applications, where appropriate, for basic refrigeration and heating of various fluids. FIG. 1 illustrates a residential heating and cooling system. In general, a residence, designated by the letter R, will be equipped with an outdoor unit OU that is operatively coupled to an indoor unit IU. The outdoor unit is typically situated adjacent to a side of the residence and is covered by a shroud to protect the system components and to prevent leaves and other contaminants from entering the unit. The indoor unit may be positioned in a utility room, an attic, a basement, and so forth. The outdoor unit is coupled to the indoor unit by refrigerant conduits RC that transfer primarily liquid refrigerant in one direction and primarily vaporized refrigerant in an opposite direction.
When the system shown in FIG. 1 is operating as an air conditioner, a coil in the outdoor unit serves as a condenser for recondensing vaporized refrigerant flowing from indoor unit IU to outdoor unit OU via one of the refrigerant conduits. In these applications, a coil of the indoor unit, designated by the reference characters IC, serves as an evaporator coil. The evaporator coil receives liquid refrigerant (which may be expanded by an expansion device described below) and evaporates the refrigerant before returning it to the outdoor unit.
The outdoor unit draws in environmental air through sides as indicated by the arrows directed to the sides of unit OU, forces the air through the outer unit coil 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 coil 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 coil IC, and is then circulated through the residence by means of ductwork D, as indicated by the arrows in FIG. 1. The overall system operates to maintain a desired temperature as set by a thermostat T. 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. 1 operates as a heat pump, the roles of the coils are simply reversed. That is, the coil of the outdoor unit will serve as an evaporator to evaporate refrigerant and thereby cool air entering the outdoor unit as the air passes over the outdoor unit coil. Indoor coil IC will receive a stream of air blown over it and will heat the air by condensing a refrigerant.
FIG. 2 illustrates a partially exploded view of one of the units shown in FIG. 1, in this case outdoor unit OU. In general, the unit may be thought of as including an upper assembly UA made up of a shroud, a fan assembly, a fan drive motor, and so forth. In the illustration of FIG. 2, the fan and fan drive motor are not visible because they are hidden by the surrounding shroud. An outdoor coil OC is housed within this shroud and is generally deposed to surround or at least partially surround other system components, such as a compressor, an expansion device, a control circuit.
FIG. 3 illustrates another exemplary application, in this case an HVAC&R system for building environmental management. A building BL is cooled by a system that includes a chiller CH, which is typically disposed on or near the building, or in an equipment room or basement. Chiller CH is an air-cooled device that implements a refrigeration cycle to cool water. The water is circulated to a building through water conduits WC. The water conduits are routed to air handlers AH at individual floors or sections of the building. The air handlers are also coupled to ductwork DU that is adapted to blow air from an outside intake OI.
Chiller CH, which includes heat exchangers for both evaporating and condensing a refrigerant as described above, cools water that is circulated to the air handlers. Air blown over additional coils that receive the water in the air handlers causes the water to increase in temperature and the circulated air to decrease in temperature. The cooled air is then routed to various locations in the building via additional ductwork. Ultimately, distribution of the air is routed to diffusers that deliver the cooled air to offices, apartments, hallways, and any other interior spaces within the building. In many applications, thermostats or other command devices (not shown in FIG. 3) will serve to control the flow of air through and from the individual air handlers and ductwork to maintain desired temperatures at various locations in the structure.
FIG. 4 illustrates an air conditioning system 10, which uses multichannel tubes. Refrigerant flows through the system within closed refrigeration loop 12. 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 10 includes control devices 14 that enable system 10 to cool an environment to a prescribed temperature.
System 10 cools an environment by cycling refrigerant within closed refrigeration loop 12 through a condenser 16, a compressor 18, an expansion device 20, and an evaporator 22. The refrigerant enters condenser 16 as a high pressure and temperature vapor and flows through the multichannel tubes of condenser 16. A fan 24, which is driven by a motor 26, draws air across the multichannel tubes. The fan may push or pull air across the tubes. Heat transfers from the refrigerant vapor to the air producing heated air 28 and causing the refrigerant vapor to condense into a liquid. The liquid refrigerant then flows into an expansion device 20 where the refrigerant expands to become a low pressure and temperature liquid. Typically, expansion device 20 will be a thermal expansion valve (TXV); however, in other 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 20, the refrigerant enters evaporator 22 and flows through the evaporator multichannel tubes. A fan 30, which is driven by a motor 32, draws air across the multichannel tubes. Heat transfers from the air to the refrigerant liquid producing cooled air 34 and causing the refrigerant liquid to boil into a vapor.
The refrigerant then flows to compressor 18 as a low pressure and temperature vapor. Compressor 18 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 18 is driven by a motor 36 that receives power from a variable speed drive (VSD) or a direct AC or DC power source. In one embodiment, motor 36 receives fixed line voltage and frequency from an AC power source although in some 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 18 as a high temperature and pressure vapor that is ready to enter the condenser and begin the refrigeration cycle again.
The operation of the refrigeration cycle is governed by control devices 14, which include control circuitry 38, an input device 40, and a temperature sensor 42. Control circuitry 38 is coupled to motors 26, 32, and 36 that drive condenser fan 24, evaporator fan 30, and compressor 18, respectively. The control circuitry uses information received from input device 40 and sensor 42 to determine when to operate the motors 26, 32, and 36 that drive the air conditioning system. In some 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, 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 42 determines the ambient air temperature and provides the temperature to control circuitry 38. Control circuitry 38 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 38 may turn on motors 26, 32, and 36 to run air conditioning system 10. The control circuitry may execute hardware or software control algorithms to regulate the air conditioning system. In some 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.
In system 10, the configuration of heat exchangers serving as either the condenser or the evaporator, or both, may follow the teachings of the present discussion. That is, to reduce the size or simply to increase the thermal exchange capacity of the heat exchanger for a given available envelope size, one or more of the heat exchangers may be bent, repeatedly bent, inclined or a combination thereof as described with respect to FIGS. 8-11.
FIG. 5 illustrates a heat pump system 44 that uses multichannel tubes. Because the heat pump may be used for both heating and cooling, refrigerant flows through a reversible refrigeration/heating loop 46. The refrigerant may be any fluid that absorbs and extracts heat. The heating and cooling operations are regulated by control devices 48.
Heat pump system 44 includes an outside coil 50 and an inside coil 52 that both operate as heat exchangers. As noted above, the coils may function either as an evaporator or a condenser depending on the heat pump operation mode. For example, when heat pump system 44 is operating in cooling (or “AC”) mode, outside coil 50 functions as a condenser, releasing heat to the outside air, while inside coil 52 functions as an evaporator, absorbing heat from the inside air. When the heat pump system 44 is operating in heating mode, outside coil 50 functions as an evaporator, absorbing heat from the outside air, while inside coil 52 functions as a condenser, releasing heat to the inside air. A reversing valve 54 is positioned on reversible loop 46 between the coils to control the direction of refrigerant flow and thereby to switch the heat pump between heating mode and cooling mode.
Heat pump system 44 also includes two metering devices 56 and 58 for decreasing the pressure and temperature of the refrigerant before it enters the evaporator. The metering devices also act to regulate refrigerant flow into the evaporator so the amount of refrigerant entering the evaporator is approximately equal to the amount of refrigerant exiting the evaporator. The metering device 56 or 58 used depends on the heat pump operation mode. For example, when heat pump system 44 is operating in cooling mode, refrigerant bypasses metering device 56 and flows through metering device 58 before entering the inside coil 52, which acts as an evaporator. When heat pump system 44 is operating in heating mode, refrigerant bypasses metering device 58 and flows through metering device 56 before entering outside coil 50, which acts as an evaporator. In other 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 coil 50 in heating mode and inside coil 52 in cooling mode, as a low temperature and pressure liquid. Some vapor refrigerant may be present as a result of the expansion process that occurs in the metering device 56 or 58. 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 passing over 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 54 and into compressor 60. Compressor 60 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 the compressor, 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 coil 50 (acting as a condenser). A fan 62, which is powered by a motor 64, draws air over the multichannel tubes containing refrigerant vapor. The fan may be replaced by a pump which 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 coil 52 (acting as a condenser). A fan 66, which is powered by a motor 68, draws air over 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 (56 in heating mode and 58 in cooling mode) and returns to the evaporator (outside coil 50 in heating mode and inside coil 52 in cooling mode) where the process begins again.
In both heating and cooling modes, a motor 70 drives compressor 60 and circulates refrigerant through reversible refrigeration/heating loop 46. 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 the motor 70 is controlled by control circuitry 72. Control circuitry 72 receives information from an input device 74 and sensors 76, 78, and 80 and uses the information to control the operation of the heat pump system 44 in both cooling mode and heating mode. For example, in cooling mode, the input device provides a temperature set point to control circuitry 72. Sensor 80 measures the ambient indoor air temperature and provides it to control circuitry 72. Control circuitry 72 then compares the air temperature to the temperature set point and engages compressor motor 70 and fan motors 64 and 68 to run the cooling system if the air temperature is above the temperature set point. In heating mode, control circuitry 72 compares the air temperature from sensor 80 to the temperature set point from input device 74 and engages motors 64, 68, and 70 to run the heating system if the air temperature is below the temperature set point.
Control circuitry 72 also uses information received from the input device 74 to switch the heat pump system 44 between heating mode and cooling mode. For example, if the input device is set to cooling mode, control circuitry 72 will send a signal to a solenoid 82 to place reversing valve 54 in air conditioning position 84. Consequently, the refrigerant will flow through the reversible loop 46 as follows: the refrigerant exits compressor 60, is condensed in outside coil 50, is expanded by metering device 58, and is evaporated by inside coil 52. If the input device is set to heating mode, control circuitry 72 will send a signal to solenoid 82 to place reversing valve 54 in heat pump position 86. Consequently, the refrigerant will flow through the reversible loop 46 as follows: the refrigerant exits compressor 60, is condensed in inside coil 52, is expanded by metering device 56, and is evaporated by outside coil 50.
The control circuitry may execute hardware or software control algorithms to regulate the heat pump system 44. In some 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 system 44 is operating in heating mode. When the outdoor temperature approaches freezing, moisture in the outside air that is directed over outside coil 50 may condense and freeze on the coil. Sensor 76 measures the outside air temperature, and sensor 78 measures the temperature of the outside coil 50. These sensors provide the temperature information to the control circuitry which determines when to initiate a defrost cycle. For example, if either of the sensors 76 or 78 provides a temperature below freezing to the control circuitry, system 44 may be placed in defrost mode. In defrost mode, solenoid 82 is actuated to place reversing valve 54 in air conditioning position 84, and motor 64 is shut off to discontinue air flow over the multichannels. System 44 then operates in cooling mode until the increased temperature and pressure refrigerant flowing through the outside coil defrosts the coil 50. Once sensor 78 detects that coil 50 is defrosted, control circuitry 72 returns reversing valve 54 to heat pump position 86. The defrost cycle can be set to occur at many different time and temperature combinations.
In heat pump system 44, one or both of the heat exchangers may be configured to follow the teachings of the present discussion. That is, to reduce the size, to provide enhanced thermal exchange capacity of the heat exchanger for a given available envelope size, or to promote clearing of condensate, one or more of the heat exchangers may be bent, repeatedly bent, inclined or a combination thereof as described with respect to FIGS. 8-11.
Moreover, the techniques described below allow for more effectively clearing condensate from the heat exchangers. Such techniques are believed to be particularly useful for clearing defrosted condensate from an outside heat exchanger functioning as an evaporator with a heat pump system operating in heat pump mode.
FIG. 6 is a perspective view of an exemplary multichannel heat exchanger for use in air conditioning or refrigeration system 10, or in the heat pump system 44. The heat exchanger includes a first manifold 88, in this case positioned in a lower position, and a second manifold 90, in an upper position. The manifolds are hollow tubes, such as made from aluminum alloy, although other materials may be employed. A series of multichannel tubes 92 extend between the manifolds and are in fluid communication with the manifolds such that fluid can flow from one of the manifolds to the other through the tubes. In a presently contemplated embodiment, the tubes are also made of an aluminum alloy and are sealed at passages where they contact the manifolds. Fins 94 are disposed between adjacent tubes, and may be held in place by any suitable joining technique, such as brazing. In the illustrated embodiment, the fins are generally serpentine in shape, being formed by crimping or bending a continuous ribbon or tape of material. One or more inlets 98 are in fluid communication with manifold 88 for receiving refrigerant flow, while one or more outlets 100 are formed for allowing refrigerant to exit.
The heat exchanger may be a single-pass heat exchanger, or may provide multiple passes for refrigerant flow with separation baffles in the manifolds. The inlet of the heat exchanger may be provided in a lower position or a higher position, depending upon the desired direction of flow of refrigerant. In certain embodiments of the present invention, the orientation of the heat exchanger may be altered, with the manifolds being provided in generally vertical orientations. Baffles (not shown) may be included in one or both of the manifolds to appropriately separate and channel flow. This is intended where the heat exchanger will be designed for multiple passes of refrigerant.
FIG. 7 illustrates certain components of the heat exchanger of FIG. 6 in a somewhat more detailed exploded view. Each manifold (manifold 88 being shown in FIG. 7) is a tubular structure, each open end of which is closed by a cap 102. Openings or apertures 104 are formed in the manifolds, such as by conventional piercing operations. Multichannel tubes 92 have a generally flat shape with a width along which a series of openings (not separately shown) extend in a generally parallel fashion. The openings form parallel pathways for refrigerant flow, and are generally arranged in the plane of the respective tube. The planes, corresponding to the width of the tubes are oriented generally perpendicular to the axis of the manifold, such that the tubes are fitted within apertures 104 provided in the manifold. Fins 94 are disposed between adjacent pairs of the multichannel tubes.
Various arrangements allow for disposing the heat exchangers in a way intended to provide enhanced thermal exchange density for an available envelope size. In one presently contemplated embodiment, illustrated generally in FIG. 8, a heat exchanger, designated by reference numeral 106, is inclined with respect to the vertical, with multichannel tubes 92 being oriented generally at an acute angle with respect to the vertical. That is, the heat exchanger leans in one direction from the vertical by an acute angle, although multichannel tubes 92 extend generally up-and-down. Manifolds 88 and 90 are arranged in upper and lower positions at either end of tubes 92. Multichannel tubes 92 are arranged such that the planes of their widths are oriented generally vertically, presenting upper and lower edges. Condensate (and liquid from melted ice) can flow down the lower edges of the tubes.
The heat exchanger, when operating as an evaporator, will tend to condense vapor from surrounding air that is drawn through the heat exchanger, as generally indicated by arrow 107. This condensate will collect, as indicated at reference numeral 108. Due to the generally vertical orientation of the planes of the tubes (and the angling of the tubes from vertical), the condensate will be caused to drip down an edge of each tube toward a recipient or pan 110. The pan may have sides 112, and similar sides may be provided around the entire periphery of the pan (two sides being removed in the figure for clarity). The pan generally has a length A and height B sufficient to collect all dripping condensate and to hold the condensate until it can be evacuated, such as by a drain line (not shown). A filter 114 may be positioned on one side of the heat exchanger, particularly where the heat exchanger is used to cool fresh intake air (e.g., as an inside evaporator in a system working in air condition mode).
FIG. 9 represents a side elevation of the arrangement shown in FIG. 8. The heat exchanger is inclined to allow condensate 108 to drip down the edges of the multichannel tubes. The horizontal axis is generally designated by reference letter D, with the vertical axis being represented by letter E. An acute angle C is formed between the plane of the heat exchanger and the vertical axis. The particular angle of incline may be determined by the relative adherence of the condensate droplets to the multichannel tubes, such that the droplets will tend to stay attached to the tube edges and to drain down the tubes to recipient 110. Another angle F of inlets 98 also may be defined and that may be a function of the angle of incline C. The condensate, then, will tend to exit from spaces between the tubes and fins (not shown in FIG. 9) and to collect on lower edge 116 of tubes 92 to form a generally continuous flow as indicated by arrow 118. Collected condensate 120 in recipient 110 may then be drained any suitable means, such as a drain line (not shown).
It should also be noted that the arrangement of FIG. 9 allows the heat exchanger to be mounted in an available envelope size that is reduced as compared to an envelope in which a vertical heat exchanger would be mounted. The overall height of the envelope, designated by dimension G in FIG. 9 is therefore reduced, providing enhanced thermal exchange capacity within the reduced envelope dimension.
FIGS. 10 and 11 illustrate additional multichannel heat exchanger configurations intended to allow for a higher thermal exchange density or reduced envelope size, or both. In the embodiment illustrated in FIG. 10, for example, a generally serpentine-shaped heat exchanger 122 is formed beginning with a slab of the type illustrated in the previous figures. That is, manifolds 88 and 90 are provided with a plurality of multichannel tubes 92 extending therebetween, and fins 94 disposed between the tubes. As before, the tubes are in fluid communication with both manifolds such that refrigerant can flow through the manifolds and the tubes, in a single or multiple passes. Bends 124 and 126 are formed, however, to reduce the overall envelope dimensions of the heat exchanger. A first bend 124 is formed that is generally concave on the right-hand side of the illustration, and convex on an opposite side. Bend 26 is in an opposite direction. It may be noted that the bends formed in the tubes are in directions generally parallel to the planes of the tubes described above. That is, an axis of each bend (not separately represented in FIG. 10) extends generally perpendicular to the plane of the width of the tubes.
Reference numeral 128 in FIG. 10 indicates the available envelope size for the heat exchanger. In particular, dimension H represents the curvature of the bend 124, while dimension J represents the curvature of bend 126. These oppositely oriented bends reduce the overall height of the heat exchanger, designated by dimension K. Width L is maintained constant, while depth M is somewhat greater than this dimension would be if the heat exchanger were provided in a planar slab, owing to the curvature H and J of the bends. Moreover, a variable in configuration of the serpentine heat exchanger is dimension N which generally represents the distance between the apexes of bends 124 and 126. By adjusting these dimensional parameters, more relative surface area for heating or cooling can be provided in a reduced height for the overall structure. The configuration illustrated in FIG. 10 could be modified by the inclusion of a series of bends (i.e., three or more), which in accordance with present embodiments may be of alternating orientation.
FIG. 11 represents a further exemplary configuration of a space-saving heat exchanger in accordance with aspects of the present technique. In this embodiment, however, the heat exchanger, designated by reference numeral 130, includes a single bend 132 which forms an acute angle P. That is, the heat exchanger is bent around an angle greater than 90°. The curvature of this bend, indicated generally by reference character Q will determine the overall envelope dimensions, along with the width S, height V, and depth W. The illustrated embodiment includes an inlet 98 and an outlet 100 disposed on the same manifold 88. Consequently, the fluid flows to manifold 90 in one direction and returns to manifold 88 in an opposite direction. A baffle 134 is disposed within manifold 88 to separate the inlet and outlet flow. Although FIG. 11 illustrates a multiple-pass heat exchanger, with the inlet and outlet disposed on the same manifold, the embodiment illustrated in FIG. 11 may be employed in heat exchangers with inlets and outlets disposed on separate manifolds. Any of the embodiments illustrated in FIGS. 6-11 may be employed with heat exchangers configured for single-pass or multiple-pass.
For both heat exchangers illustrated in FIGS. 10 and 11, it should also be noted that the angling of the multichannel tubes with respect to the vertical, and the general alignment of the width of the tubes in parallel vertical planes, allows for collection and flow of liquid condensate along outer edges of the multichannel tubes. This condensate flow may be promoted along these edges, and allowed to collect in a recipient of the type illustrated in FIG. 8.
The heat exchanger configurations described herein may find application in a variety of heat exchangers and HVAC&R systems containing heat exchangers. However, the configurations are particularly well-suited to heat exchangers used in confined spaces or environments where high levels of condensation may occur. Furthermore, the configurations allowing drainage of condensate are particularly well-suited for clearing defrosted condensate from an outside heat exchanger functioning as an evaporator with a heat pump system operating in heat pump mode. The configurations may be applied to heat exchangers with any number of inlets and outlets that may be disposed on the same manifold or disposed on separate inlet and outlet manifolds. The heat exchanger configurations are intended to allow high thermal density to be achieved within small envelope dimensions and improve system efficiency by draining condensate from the tubes.
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 unless otherwise specified in the appended claims.
While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. 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. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation specific decisions must 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.

Claims

1. A multichannel heat exchanger comprising:

a first manifold;

a second manifold; and

a plurality of multichannel tubes in fluid communication with the first and second manifolds and including a plurality of generally parallel flow paths extending therethrough, wherein the multichannel tubes include an acute angle bend between the first and second manifolds.

2. The heat exchanger of claim 1, wherein the multichannel tubes include a single bend between the manifolds.

3. The heat exchanger of claim 1, wherein the heat exchanger is configured to fit within available envelope dimensions in a system, and wherein the manifolds are configured to be disposed at one end of the envelope and a rear side of the bend is configured to be disposed at an opposite end of the envelope.

4. The heat exchanger of claim 1, comprising a plurality of fins extending between the first and second manifolds and disposed intermediate adjacent multichannel tubes.

5. The heat exchanger of claim 1, wherein the heat exchanger is a single pass heat exchanger.

6. The heat exchanger of claim 1, wherein the heat exchanger is a multiple pass heat exchanger.

7. A multichannel heat exchanger comprising:

a first manifold;

a second manifold; and

a plurality of multichannel tubes in fluid communication with the first and second manifolds, each of the plurality of tubes having generally parallel flow paths extending therethrough and disposed generally in a plane, wherein the multichannel tubes include a first bend in a first direction generally parallel to the planes of the tubes and a second bend in a second direction opposite from the first direction between the first and second manifolds.

8. The heat exchanger of claim 7, wherein the multichannel tubes include only two bends between the manifolds.

9. The heat exchanger of claim 7, wherein the heat exchanger is configured to fit within available envelope dimensions in a system, and wherein the first bend is configured to be disposed at one side of the envelope and the second bend is configured to be disposed at an opposite end of the envelope.

10. The heat exchanger of claim 7, comprising a plurality of fins extending between the first and second manifolds and disposed intermediate adjacent multichannel tubes.

11. The heat exchanger of claim 7, wherein the heat exchanger is a single pass heat exchanger.

12. The heat exchanger of claim 7, wherein the heat exchanger is a multiple pass heat exchanger.

13. A multichannel heat exchanger comprising:

a first manifold;

a second manifold; and

a plurality of multichannel tubes in fluid communication with the first and second manifolds, each of the plurality of tubes having generally parallel flow paths extending therethrough generally parallel to a longitudinal axis thereof;

wherein the first manifold is disposed in an upper position, the second manifold is disposed in a lower position, and the multichannel tubes are disposed with their longitudinal axis at an acute angle with respect to vertical to permit condensate to flow down an edge of the multichannel tubes towards the second manifold during operation.

14. The heat exchanger of claim 13, wherein the heat exchanger is a multiple pass heat exchanger.

15. The heat exchanger of claim 13, comprising a recipient disposed below the second manifold to collect condensate.

16. A heating, ventilating, air conditioning or refrigeration system comprising:

a compressor configured to compress a gaseous refrigerant;

a condenser configured to receive and to condense the compressed refrigerant;

an expansion device configured to reduce pressure of the condensed refrigerant; and

an evaporator configured to evaporate the refrigerant prior to returning the refrigerant to the compressor;

wherein at least one of the condenser and the evaporator includes a heat exchanger having a first manifold, a second manifold, and a plurality of multichannel tubes in fluid communication with the first and second manifolds, each of the plurality of tubes having generally parallel flow paths extending therethrough generally parallel to a longitudinal axis thereof, wherein the first manifold is disposed in an upper position, the second manifold is disposed in a lower position, and the multichannel tubes are disposed with their longitudinal axis at an acute angle with respect to vertical to permit condensate to flow down edges of the multichannel tubes towards the second manifold during operation.

17. The system of claim 16, wherein the system is configured to operate in heat pump mode including a defrost cycle in which ice is melted by a flow of refrigerant through the heat exchanger, and water resulting from melting of the ice flows down the edges of the multichannel tubes.

18. The system of claim 17, comprising a recipient disposed below the second manifold to collect condensate.

19. A heating, ventilating, air conditioning or refrigeration system comprising:

a compressor configured to compress a gaseous refrigerant;

a condenser configured to receive and to condense the compressed refrigerant;

at least one expansion device configured to reduce pressure of the condensed refrigerant;

an evaporator configured to evaporate the refrigerant prior to returning the refrigerant to the compressor; and

a reversing valve configured to reverse a direction of flow of refrigerant within the system to establish a cooling mode and a heat pump mode of operation;

20. The system of claim 19, wherein the system is configured to perform a defrost operation in which ice is melted from the heat exchanger by a flow of refrigerant through the heat exchanger, and water resulting from melting of the ice flows down the edges of the multichannel tubes.