This invention relates to brazed plate heat exchangers, and more particularly to brazed plate heat exchangers wherein one of the working fluids passing through the heat exchanger has a pressure greater than 1000 psi, such as in heat exchanger used in transcritical cooling systems.
Brazed plate heat exchangers are commonly used for oil coolers and to a lesser extent are known for use in refrigeration systems. Because of their compactness, such heat exchangers are desirable for use in systems having a limited installation envelope, such as in vehicular applications. One drawback to conventional brazed plate heat exchangers is that their construction does not lend itself to high pressure applications where, for example, the operating pressures can be 1000 psi to 2000 psi or greater and the burst pressure requirements can be in the range of around 4000 psi to around 6000 psi. In this regard, conventional brazed plate heat exchangers are typically limited to less than 1000 psi. This has prevented the use of such heat exchangers in high pressure systems, such as for example, transcritical cooling systems that use a refrigerant such as carbon dioxide (CO2).
Increasing environmental concerns over the use of many conventional refrigerants such as CFCl2 and, to a lesser extent HFC134a, has led to consideration of transcritical CO2 systems for use in vehicular applications, heat pumps, water heaters, and refrigeration systems. For one, the CO2 utilized as a refrigerant in such systems could be claimed from the atmosphere or from waste products of other industrial processes at the outset with the result that if it were to leak from the system back to the atmosphere, there would be no net increase in atmospheric CO2 content. Moreover, while CO2 is undesirable from the standpoint of a greenhouse effect, it does not affect the ozone layer and would not cause an increase in the greenhouse effect since there would be no net increase in the atmospheric CO2 content as a result of the leakage.
It is the principle object of the invention to provide a new and improved brazed plate heat exchanger that can be used with high pressure working fluids, such as supercritical CO2.
According to one aspect of the invention a brazed plate heat exchanger is provided for transferring heat between a first fluid and a second fluid, wherein the first fluid is pressurized to greater than 1000 psi. The brazed plate heat exchanger includes a plurality of plate pairs to define flow paths for the first fluid, a plurality of turbulator plates interleaved between the plate pairs to define flow paths for the second fluid, each of the turbulator plates sandwiched between the plate pairs to provide structural support thereto, and reinforcements extending between each of the plate pairs. Each plate pair encloses a plurality of flow channels extending from a first inlet opening to a first outlet opening, with each of the flow channels having a hydraulic diameter less than 1 mm. The plate pairs are arranged as a stack with the first inlet openings being aligned with each other to define a first inlet manifold for distributing the first fluid to the flow channels, and the second openings aligned with each other to define a first outlet manifold for collecting the first fluid from the flow channels. The reinforcements are aligned with the first inlet and outlet openings and define the first inlet and outlet manifolds between the plate pairs.
In one aspect of the invention, the reinforcements are a plurality of washers interleaved between the plate pairs. In a further aspect, the first inlet and outlet openings are circular openings and each of the washers includes an annular step that is received in a corresponding one of the first inlet and outlet openings.
According to one aspect of the invention, pairs of channeled plates are sandwiched between the plates of each of the plate pairs, with grooves extending through each of the channeled plates to define the flow channels with the grooves of the other channeled plate of the pair.
In one aspect, the plates of each of the plate pairs are drawn-cup plates, and one of the plates of each of the plate pairs is dimpled to define the flow channels.
According to one aspect, the first inlet and outlet openings are circular openings, and the reinforcements include a cylindrical inlet header tube extending through the first inlet openings with an outer surface of the inlet header tube brazed to a surrounding periphery of the inlet openings in each of the plates of each of the plate pairs, and a cylindrical outlet header tube extending through the first outlet openings with an outer surface of the outlet header tube brazed to a surrounding periphery of the outlet openings in each of the plates of each of the plate pairs. In a further aspect, each of the header tubes includes a plurality of slots, with each of the slots aligned with the flow channels of a corresponding plate pair.
In one aspect, each of the plate pairs further includes a pair of sealed openings extending through the plate pair, with one of the pair of sealed openings in each of the plate pairs being aligned with the one of the pair of sealed openings in the adjacent plate pairs to define a second inlet manifold to distribute the second fluid to the flow paths for the second fluid, and the other of the pair of sealed openings in each of the plate pairs being aligned with the other of the pair of sealed openings in the adjacent plate pairs to define a second outlet manifold to collect the second fluid from the flow paths for the second fluid.
In one aspect of the invention, the brazed plate heat exchanger further includes a top plate defining an upper exterior of the heat exchanger, a turbulator plate sandwiched between the top plate and an upper-most one of the plate pairs to define flow channels for the second fluid and provide structural support to the plate pairs, a bottom plate defining a lower exterior of the heat exchanger, and a turbulator plate sandwiched between the bottom plate and a lower-most one of the plate pairs to define flow channels for the second fluid and provide structural support to the plate pairs.
According to one aspect of the invention, a brazed plate heat exchanger is provided for transferring heat between a first fluid and a second fluid, with the first fluid being pressurized to greater than 1000 psi. The brazed plate heat exchanger includes a plurality of flat plate subassemblies, a plurality of turbulator plates interleaved between the subassemblies to define flow paths for the second fluid, the turbulator plates sandwiched between the subassemblies to provide structural support thereto, and a plurality of solid washers interleaved between the subassemblies to provide structural support thereto. Each of the subassemblies includes a pair of outer flat plates and a pair of channeled plates sandwiched between the outer plates, with each of the plates having an inlet opening and an outlet opening spaced from the inlet opening. The inlet openings are aligned with each other to define a first inlet manifold, and the outlet openings aligned with each other to define a first outlet manifold. Each of the channeled plates includes a plurality of grooves that cooperate with the grooves of the other channeled plate of the pair to define a plurality of flow channels for the first fluid extending between the inlet openings to the outlet openings of the pair. The washers are aligned with the inlet and outlet openings, with the washers that are aligned with the inlet openings defining the first inlet manifold between the subassemblies, and the washers that are aligned with the outlet openings defining the first outlet manifold between the subassemblies.
In one aspect, the inlet and outlet openings in the outer plates are circular openings and each of the washers includes an annular step that is received in a corresponding one of the inlet and outlet openings in the outer plates without extending through the outer plate.
According to one aspect, the grooves in one of the channeled plates of each pair extend longitudinally between the inlet and outlet openings, and the grooves in the other channeled plate of the pair extend transverse to the grooves in the one of the channeled plates.
In one aspect of the invention, each of the subassemblies further includes a pair of sealed openings extending through the subassembly. One of the pair of sealed openings in each of the subassemblies is aligned with the one of the pair of sealed openings in the adjacent subassemblies to define a second inlet manifold to distribute the second fluid to the flow paths for the second fluid, and the other of the pair of sealed openings in each of the subassemblies being aligned with the other of the pair of sealed openings in the adjacent subassemblies to define a second outlet manifold to collect the second fluid from the flow paths for the second fluid. According to a further aspect, the brazed plate heat exchanger further includes a plurality of spacer plates interleaved between the subassemblies, with each of the spacer plates sandwiched between an adjacent pair of the subassemblies and surrounding the turbulator plate and the washers sandwiched between the adjacent pair to enclose a flow space for the second fluid.
According to one aspect of the invention, the brazed plate heat exchanger further includes a top plate defining an upper exterior of the heat exchanger, a turbulator plate sandwiched between the top plate and an upper-most one of the subassemblies to define flow channels for the second fluid and provide structural support to the subassemblies, a bottom plate defining a lower exterior of the heat exchanger, and a turbulator plate sandwiched between the bottom plate and a lower-most one of the subassemblies to define flow channels for the second fluid and provide structural support to the subassemblies.
In one aspect of the invention, each of the turbulator plates is a lanced and offset fin.
According to another aspect of the invention, a transcritical cooling system is provided and includes a working fluid flow loop, a compressor connected to the working fluid flow loop to receive the working fluid therefrom and to compress the working fluid to a supercritical pressure for delivery back to the working fluid flow loop, and a brazed plate heat exchanger connected to the working fluid flow loop to receive the working fluid therefrom and return the working fluid thereto. The brazed plate heat exchanger includes a plurality of brazed, stacked plate subassemblies that define high pressure flow paths for the working fluid. The brazed plate subassemblies are interleaved with another set of flow paths for another fluid to transfer heat between the working fluid and the other fluid.
In one aspect, each of the subassemblies comprise a pair of mating drawn-cup plates.
According to one aspect, each of the subassemblies comprises a pair of outer flat plates and a pair of channeled plates sandwiched between the outer flat plates.
Other features, aspects, objects, and advantages of the invention will become apparent from a complete reading of the Specification, including the appended drawings and claims.
With reference to
Having described a typical operating environment for heat exchangers embodying the present invention, a more detailed description will now be provided for one preferred embodiment of the heat exchangers.
As seen in
Each of the channel plates 42, 44 include a plurality of grooves 54 that extend through the thickness of the associated plate 42, 44, as best seen in
Preferably, each of the flow channels 56 has a hydraulic diameter less than 0.04″ or 1 mm, and the channels 54 are spaced a sufficient distance from each other so that when the plates 38, 40, 42, and 44 are brazed together to form the subassembly 36, there is sufficient brazed surface area to provide the structural support to withstand the high pressure force within the flow channels 56 which is limited by the small hydraulic diameter. In this regard, as one possible construction for the illustrated embodiment, each of the plates 38, 40, 42, and 44 could be made from 0.028″ thick aluminum with a suitable amount of braze material clad on both sides of each of the plates 38, 40, 42, and 44, and each of the grooves 54 having a width W equal to 0.030″ and a spacing S between adjacent grooves 54 equal to 0.060″ in each of the plates 42 and 44. It should be understood, that the dimensions and spacing required for the grooves 54 will depend upon a number of factors, including but not limited to, the particular material chosen for the plates 38, 40, 42, and 44, the thickness of each of the plates 38, 40, 42, and 44, the operating and burst pressure of the first fluid 32, and the pattern of the grooves 54 in each of the plates 42 and 44. Furthermore, it should be appreciated that while in the illustrated embodiment, each of the plates 38, 40, 42, and 44 have the same thickness, in some applications it may be desirable for the thickness among the plates to vary.
The heat exchanger 30 further includes a plurality of turbulator plates 58 (only two partially shown in
Reinforcements 62, in the form of a plurality of washers 64, are aligned with the inlet and outlet openings 46 and 48 and interleaved between the subassemblies 36 to provide structural support thereto, with the washers 64 that are aligned with the inlet openings 46 defining the inlet manifold 50 between the subassemblies 36, and the washers 64 that are aligned with the outlet openings 48 defining the outlet manifold 52 between the subassemblies 36. As seen in
Each of the subassemblies 36 further includes a pair of elongated sealed openings 66 and 68 extending through the subassembly 36, with the opening 66 in each of the subassemblies being aligned with the sealed openings 66 in the adjacent subassemblies 36 to define a second inlet manifold 70 to distribute the second fluid 34 to the flow paths 60, and the other sealed opening 68 in each of the subassemblies 36 being aligned with the other sealed openings 68 in the adjacent subassemblies 36 to define a second outlet manifold 72 to collect the second fluid 34 from the flow path 60. The sealed openings 66 and 68 are defined by individual openings 74 and 76, respectively, formed in each of the plates 38, 40, 42, and 44 that are sealed by the mating flat surfaces surrounding the openings 74, 76 when the plates 38, 40, 42 and 44 are brazed together.
As best seen in
The heat exchanger 30 also includes a top plate 84 defining an upper exterior of the heat exchanger 30 and a bottom plate 86 defining a lower exterior of the heat exchanger 30. As best seen in
Turning now to
Preferably, each of the plates 120 and 122 includes a peripheral rim or lip 128 that is angled slightly outward so that the plates 120 and 122 and subassemblies 36 can be nested together in the assembled state to form the heat exchanger 30. This assists in the assembly and brazing of the heat exchanger 30 and increases the strength of each of the subassemblies 36. It should also be appreciated that each of the top plate 84 and bottom plate 86 has a similar rim 128 that can be nested with the rims of the subassemblies during assembly.
As in the embodiment of
As best seen in
It should also be appreciated that the plates shown in
With reference to
Preferably, the heat exchangers 30 will be assembled and then brazed as an assembled unit, with a constant clamping force being applied the stack of the plates during the brazing process so as to assure the quality of the braze, particularly at the mating surfaces of the plates.
It should be appreciated that the capacity of the heat exchangers 30 can be relatively simply adjusted by adding or subtracting the number of subassemblies 36.