PRIORITY CLAIM

[0001] This application claims the benefit of United States Provisional Application No. 62/958,385, filed on January 8, 2020.

TECHNICAL FIELD

[0002] This disclosure relates to a heat exchanger device. The heat exchanger may be used in a heating, ventilation, and air conditioning (HVAC) chiller system, for example.

BACKGROUND

[0003] Refrigerant loops are known to include a compressor, a condenser, an expansion device, and an evaporator. The compressor compresses the fluid, which then travels to a condenser, which in turn cools and condenses the fluid. The refrigerant then goes to an expansion device, which decreases the pressure of the fluid, and to the evaporator, where the fluid is vaporized, completing a refrigeration cycle. Heat exchangers are used to transfer heat between two or more fluids, and may be used in the condenser or evaporator, for example.

SUMMARY

[0004] A plate heat exchanger according to an exemplary aspect of the present disclosure includes, among other things, a plate having a metal surface, the plate is arranged in a flow of fluid. A plurality of carbon nanotubes are arranged on the metal surface, and the carbon nanotubes are configured to exchange heat with the fluid.

[0005] In a further embodiment, the metal surface is curved.

[0006] In a further embodiment, the metal surface is flat. [0007] In a further embodiment, each of the carbon nanotubes has at least one end bonded to the metal surface.

[0008] In a further embodiment, the plurality of carbon nanotubes have a variety of diameters, lengths and densities from a controlled manufacturing process.

[0009] In a further embodiment, the plurality of carbon nanotubes are deposited on the metal surface within a designated deposition area.

[0010] In a further embodiment, the plurality of carbon nanotubes have a varying density within the deposition area.

[0011] In a further embodiment, the carbon nanotubes have a first density on a first side of the deposition area, and a second density on a second side of the deposition area, the second density is lower than the first density.

[0012] In a further embodiment, a fluid inlet and a fluid outlet are arranged adjacent the first side of the deposition area.

[0013] In a further embodiment, the plurality of carbon nanotubes have a diameter between about 10 and 100 nanometers.

[0014] In a further embodiment, the plate is one of a plurality of plates arranged between a top plate and a back plate, the plurality of plates separating a plurality of chambers.

[0015] In a further embodiment, each of the plurality of plates has a plurality of carbon nanotubes.

[0016] In a further embodiment, the plate heat exchanger is used in a heating, ventilation, and air conditioning (HVAC) chiller system.

[0017] A refrigerant system according to an exemplary aspect of the present disclosure includes, among other things, a heat exchanger arranged along a fluid flow path, wherein the heat exchanger has a plate having a metal surface, and the plate is arranged in a flow of fluid. A plurality of carbon nanotubes are arranged on the metal surface, and the carbon nanotubes are configured to exchange heat with the fluid.

[0018] In a further embodiment, the heat exchanger is arranged upstream of a compressor.

[0019] In a further embodiment, the heat exchanger is arranged downstream of a compressor.

[0020] In a further embodiment, the fluid is present in both a liquid and a vapor form in the heat exchanger.

[0021] In a further embodiment, each of the carbon nanotubes has at least one end bonded to the metal surface.

[0022] In a further embodiment, the plurality of carbon nanotubes have a variety of diameters, lengths and densities.

[0023] In a further embodiment, the plurality of carbon nanotubes have a diameter between about 10 and 100 nanometers.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 schematically illustrates a refrigerant system.

[0025] Figure 2 schematically illustrates an example plate heat exchanger for use in a refrigerant system.

[0026] Figure 3 schematically illustrates an example plate for a plate heat exchanger.

[0027] Figure 4 schematically illustrates another example plate for a plate heat exchanger.

[0028] Figure 5 schematically illustrates an example carbon nanotube geometry for a plate heat exchanger. [0029] Figure 6 illustrates example carbon nanotube geometries for a plate heat exchanger.

DETAILED DESCRIPTION

[0030] Figure 1 illustrates a refrigerant system 10. The refrigerant system 10 includes a main refrigerant loop, or circuit, 12 in communication with a compressor 14, a condenser 16, an evaporator 18, and an expansion device 20. This refrigerant system 10 may be used in a chiller, for example. In that example, a cooling tower may be in fluid communication with the condenser 16. While a particular example of the refrigerant system 10 is shown, this application extends to other refrigerant system configurations, including configurations that do not include a chiller. For instance, the main refrigerant loop 12 can include an economizer downstream of the condenser 16 and upstream of the expansion device 20.

[0031] Figure 2 schematically illustrates an example plate heat exchanger 22. The plate heat exchanger may be used in the condenser 16 or evaporator 18, for example. The heat exchanger 22 is used to transfer heat between two or more fluids. In one example, the heat exchanger 22 transfers heat between refrigerant and water or refrigerant and air, for example. The heat exchanger 22 has a plurality of plates 28 separating a plurality of chambers 24. The plates 28 may be metallic. In a further embodiment, the plates 28 may be a thin corrugated metal, for example. A first fluid 26 and a second fluid 30 flow through the plates 28 and chambers 24. The fluids 26, 30 pass through the plates 28 and chambers 24 via connecting pipes 32, 34, 36, 38. In the illustrated example, the pipe 32 provides an inlet for the fluid 30, while pipe 34 provides a return flow path. The pipe 36 provides an inlet for the fluid 26, while pipe 38 provides a return flow path. [0032] In the illustrated example, the fluid 30 is a cold fluid, and the fluid 26 is a hot fluid. The fluids 26, 30 flow through the pipes 32, 34, 36, 38 and through alternating chambers 24. For example, the hot fluid 26 flows through chambers 24A while the cold fluid 30 flows through chambers 24B. Heat transfers from the hot fluid 26 to the cold fluid 30 through the plates 28 as the fluids 26, 30 flow through alternating chambers 24A, 24B, respectively. The plates 28 may be arranged between a top plate 40 and a back plate 42. In some examples, a sensor 44 is arranged at the back plate 42.

[0033] Figure 3 schematically illustrates an example plate 28 for a plate heat exchanger 22. The plate 28 has a portion 50 between the pipes 32, 34, 36, 38. The portion 50 corresponds to a heat exchanger zone, in which heat is transferred between the fluids 26, 30 and the plate 28. The portion 50 of the plate 28 may be flat or curved, for example. A plurality of carbon nanotubes are arranged on the portion 50. In some examples, the portion 50 covers the entire area of the plate 28, while in other examples, the portion 50 is small relative to the area of the plate 28. In one example, the portion 50 covers at least half of the area of the plate 28. In some examples, one or more plate 28 in the heat exchanger 28 has a carbon nanotube portion 50, while in other examples, all of the plates 28 have a carbon nanotube portion 50. The carbon nanotubes increase the area of the heat exchange surface of the plates 28, which improves efficiency. The carbon nanotubes are shown and described more fully herein.

[0034] Figure 4 schematically illustrates another example plate 128 for a plate heat exchanger 22. To the extent not otherwise described or shown, the plate 128 corresponds to the plate 28 of Figure 3, with like parts having reference numerals preappended with a “1.” In this example, a density of carbon nanotubes varies across the portion 150. In the illustrated view, fluid 130 flows between the pipes 132 and 134 across the portion 150 of the plate 128. The carbon nanotubes are arranged more densely on a first side 152 of the portion 150 than on a second side 154. A more dense carbon nanotube area provides a larger heat exchange area than a less dense carbon nanotube area. Although the figure shows two densities at sides 152, 154, the density of carbon nanotubes may be a gradient across some or all of the portion 150. In this example, the density is varied over the portion 150 to optimize the fluid flow 130 across the plate 150. The density may be tunable based on heat exchanger requirements at different locations. In some examples, the carbon nanotubes 160 are arranged on only part of the portion 150. The carbon nanotube arrangement may vary across different plates 128 within the heat exchanger 22, in some examples.

[0035] Figure 5 schematically illustrates an example carbon nanotube geometry for a plate heat exchanger 22. A plurality of carbon nanotubes 60 extend from the portion 50 of the plate 28. The carbon nanotubes 60 each have one end 62 that is bonded or constrained to the portion 50 of the plate 28. The nanotubes 60 may be synthesized directly on the plate 28, or may be bonded to the surface of the plate 28. Each of the carbon nanotubes 60 has a diameter D and length L. The carbon nanotubes 60 may have differing lengths and diameters across the portion 50. The length L and diameter D of the nanotubes 60 may be varied. For example, the length L may be longer for areas where there is a larger space between adjacent plates 28.

[0036] Figure 6 illustrates example carbon nanotube geometries for a plate heat exchanger 22. This example shows several different nanotube diameters D. The diameters of the nanotubes may be between about 10 and 100 nm, for example. One example diameter Di is about 18.7 nanometers. Another example diameter D2 is about 26.8 nm. Another example diameter D3 is about 44.6 nm, and a fourth example diameter D4 is about 87.7 nm. Different nanotubes 60 may have different diameters on the same plate 28. In other embodiments, all of the nanotubes 60 on the plate 28 may have the same diameter. The size of the nanotubes 60 can change the heat exchange area, and thus alter the efficiency of the heat exchanger 22. In some examples, the nanotubes 60 are multiwalled carbon nanotubes. The carbon nanotubes may have a variety of diameters, lengths and densities from a controlled manufacturing process. [0037] The disclosed plate heat exchanger 22 may improve heat exchange efficiency by increasing the effective heat transfer area and optimizing the flow pattern in the chambers 24. The carbon nanotubes 60 act as fins on the heat exchanger plates 28, increasing the heat exchange area between the plate 28 and the fluid 26, 30. The carbon nanotubes 60 may reduce the drag between the solid plate 28 and the fluids 26, 30, which may reduce the pressure drop across the heat exchanger 22. In some heat exchangers 22, two phase flow is present, and at least one of the fluids 26, 30 is present in a liquid and vapor form. In these examples, the carbon nanotubes 60 may increase turbulent flow to avoid vapor and liquid separation, which may improve heat transfer distribution. The position, density, and size of the carbon nanotubes 60 may allow for optimization of flow distribution of the fluids 26, 30 across the plates 28.

[0038] For a condenser application, the CNTs 60 form a hydrophobic layer on the heat exchanger solid surface. When the gas condenses within the heat exchanger, the formed liquid cannot stay on the heat exchanger surface and will be pushed away by the pressure. This may prevent a liquid thermal barrier forming between the heat exchanger solid surface and the gas and ensures the heat exchanger solid surface always exchanges energy was the gas directly. Such an arrangement may improve condenser efficiency.

[0039] Terms such “generally,” “about,” and “substantially” are not intended to be boundary less terms, and should be interpreted consistent with the way one skilled in the art would interpret those terms.

[0040] Although the different examples have the specific components shown in the illustrations, embodiments of this disclosure are not limited to those particular combinations. It is possible to use some of the components or features from one of the examples in combination with features or components from another one of the examples.

[0041] One of ordinary skill in this art would understand that the above-described embodiments are exemplary and non-limiting. That is, modifications of this disclosure would come within the scope of the claims. Accordingly, the following claims should be studied to determine their true scope and content.