WO2019183503A2

WO2019183503A2 - Heat exchangers and methods of manufacture thereof

Info

Publication number: WO2019183503A2
Application number: PCT/US2019/023631
Authority: WO
Inventors: Lance R. BROCKWAY; David C. Walther
Original assignee: Nelumbo Inc.
Priority date: 2018-03-22
Filing date: 2019-03-22
Publication date: 2019-09-26
Also published as: WO2019183503A3

Abstract

Designs of heat exchangers and components thereof are provided, and methods for their manufacture. The heat exchangers are designed to manage condensation and heat transfer effectiveness, which can minimize air side pressure drop and can be used to improve both refrigerant effectiveness and overall system performance. Flow rectification design features are also described.

Description

HEAT EXCHANGERS AND METHODS OF MANUFACTURE THEREOF

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

[01] This application claims the benefit of U.S. Provisional Application Nos.

62/646,859, filed March 22, 2018, and 62/646,863, filed March 22, 2018, both of which are incorporated herein by reference in their entireties.

FIELD OF THE INVENTION

[02] The invention relates to heat exchanger designs, in particular to manage

condensation and heat transfer effectiveness, and manufacturing methods to decouple these phenomena to enhance overall heat exchanger performance.

BACKGROUND

[03] Heat exchangers are built to minimize cost using current manufacturing techniques (such as extrusion, stamping, expanding, punching, and brazing) with legacy materials (such as aluminum, copper, and steel). While this combination of techniques and materials are used to both manage condensate and enhance heat transfer, there are manufacturing limitations. Unfortunately, condensate management and heat transfer effectiveness are often coupled and limited by cost effective fabrication methods and have thus capped heat exchanger improvements.

[04] Current air-coolant heat exchangers are made primarily from fin-tube designs. One type uses extruded round tubes with punched fins that are slid over the tubes. The tubes are then expanded to cause an interference fit with the fins or the fins are welded onto the tubes. This design is often limited to radially symmetric tubes, is manufacturing intensive, and is often made out of expensive and heavy materials such as copper, aluminum and steel. Another type of heat exchanger is composed of a series of parts that are brazed in a controlled atmosphere furnace and typically made out of aluminum alloys. These heat exchangers typically have vertical tubes that have bisymmetry, brazed into a prepunched manifold with corrugated flat clad fins designed for both heat transfer and condensate management. This brazed design is typically limited to clad aluminum alloys, is subject to accelerated corrosion failure, and has poor condensate management. This design does however have increased heat transfer effectiveness when compared to more traditional designs, lower manufacturing costs, and lower refrigerant charge which has a significant climate impact. [05] Improved heat exchanger designs and methods of manufacture are needed to decouple condensate management and heat transfer effectiveness, to enhance overall heat exchanger performance.

BRIEF SUMMARY OF THE INVENTION

[06] Provided herein is an improved heat exchanger that uses new designs to decouple condensate drainage and heat transfer surfaces, and methods of manufacture thereof.

[07] The heat exchangers described herein include integrated channels for water drainage within the tubes such that the fins can be reoptimized for heat transfer without the same regard for drainage. For example, one or more siphon-like channel(s) leverages surface tension to pull water from the fins into the tube channel(s) to enhance heat transfer on the fin surfaces and minimize air side pressure drop and blowoff

[08] Surprisingly, by more efficiently removing the water from the fins, the fin designs can be modified to more optimally conduct heat, minimize air pressure drop, and allow for new materials to be used to manufacture said heat exchangers.

[09] Intratubular design elements are described herein which improve refrigerant distribution, and that leverage design improvements to reduce the overall size and performance of heat exchangers operated in condensing and frosting conditions.

[10] Described herein are (a) design elements that can be integrated into traditionally simple design components, and (b) design features that improve performance via modifications to the drainage paths of heat exchangers, resulting in improvements in heat transfer efficiency, capacity, and improved operability of the components at the system level.

[11] In some embodiments, heat exchanger components described herein may be manufactured by layer-by-layer additive manufacturing techniques ( e.g ., 3D printing), extrusion, or extruded origami (e.g., pull a sheet and rotate or twist a die or the extrudate, optionally with heat treatment to seal folds).

[12] In one aspect, a tube is provided that includes one or more longitudinal concave liquid drainage channel in the direction of its length, wherein the tube is in thermal contact with a fin at a thermal contact point. In one embodiment, the fin includes

a gravitational potential minimum at the thermal contact point. In one embodiment, a drainage channel is in contact with the fin at a drainage channel contact point, and the fin includes a gravitational potential minimum at the drainage channel contact point. In some embodiments, the fin includes a sessile drop water contact angle less than about 90 degrees, less than about 80 degrees, less than about 70 degrees, less than about 60 degrees, less than about 50 degrees, less than about 40 degrees, or less than about 30 degrees. In one embodiment, the fin does not include holes or perforations.

[13] In another aspect, a tube is provided that includes one or more longitudinal concave liquid drainage channel in the direction of its length, manufactured by extrusion, extrusion followed by cold working, or extrusion plus grinding.

[14] In another aspect, a heat exchanger is provided that includes: one or more tube tha includes one or more longitudinal concave liquid drainage channel in the direction of its length; one or more fin in thermal contact with a tube at a thermal contact point; and inlet and exit lines or a manifold configured to allow flow of a working fluid through the inside of the tube(s), thereby transferring heat to a process fluid outside of the tube(s). In one embodiment, the fin(s) each include a gravitational potential minimum at the thermal contact point. In one embodiment, the fin(s) do not include holes or perforations. In some embodiments, the fin(s) include a sessile drop water contact angle less than about 90 degrees, less than about 80 degrees, less than about 70 degrees, less than about 60 degrees, less than about 50 degrees, less than about 40 degrees, or less than about 30 degrees. In some embodiments, the heat exchanger further includes a process fluid. For example, the process fluid may be humid air with relative humidity greater than about 5%, about 10%, about 15%, or about 20%. In some embodiments, the heat exchanger is manufactured using a controlled atmospheric brazing method or one or more additive manufacturing technique.

[15] In another embodiment, a heat exchanger is provided that includes internal drainage channels, which improve condensate removal in comparison to a heat exchanger that does not include internal drainage channels. In one embodiment, a majority of condensed liquid is drained from the heat exchanger through the internal channels rather than from the leading or trailing edge of the heat exchanger. In one embodiment, the heat exchanger further includes fins, wherein the heat exchanger exhibits improved blowoff properties in comparison to a heat exchanger that does not include internal drainage channels, wherein the improved blowoff properties include lower blowoff and/or higher velocity operation before blowoff, resulting in more greater heat transfer capacity per unit area, due to lower amount of condensate retention on fins. [16] In another aspect, a fin design is provided, which includes a convex surface, wherein the surface provides an increased effective surface area of more than about 1%, about 5%, about 10%, about 20%, about 30%, about 40%, about 50%, about 60%, about 70%, about 80%, about 90%, or about 100%, relative to a flat fin.

[17] In another aspect, a fluid conducting channel is provided that includes an integrated flow rectification component, wherein the flow rectification component includes a passive and/or or an active component at least partially contained within the fluid conducting channel, wherein the passive component promotes rectification of flow of a fluid in the channel to prevent backpressure from leading to a reversing flow direction. In one embodiment, a passive flow rectification component includes protuberances on an internal surface of the fluid conducting channel, thereby impacting flow of the fluid in the channel through resultant pressure, vorticity, or velocity driven fields. In another embodiment, an active component includes a floating block, a floating ball, a tethered block, a tethered ball, a cone, a reed valve, a check valve, or an active flow rectifier and an effective mating surface.

[18] In another aspect, a heat exchanger is provided that includes one or more fluid conducting channels as described herein.

[19] In another aspect, a fluid conducting apparatus is provided that includes a plurality of fluid conducting channels, wherein the fluid conducing device includes an integrated flow redistribution component. For example, the flow redistribution component may include an integrated section in which the contents of two or more fluid channels are in fluid connection and allowed to mix and redistribute. In one embodiment, the flow redistribution component includes the intersection of two or more fluid conducting channels, configured to allow the contents of the two or more channels to mix and redistribute. In one embodiment, the flow redistribution component includes one or more fluid conducting channels split or merged to increase or decrease the overall internal volume available for carrying fluid, thereby reducing or increasing the pressure drop and improving the overall fluid transport efficiency.

[20] In another aspect, a heat exchanger is provided that includes one or more fluid conducting as described herein.

[21] In another aspect, a heat exchanger is provided, wherein a fluid conducting channel, flow rectification component, or fluid conducing apparatus as described herein results in: improved drainage design; improved airflow; improved refrigerant flow and/or distribution; and/or lower corrosion rates and/or different failure mechanisms on environmental exposure, in comparison to a heat exchanger that does not comprise the fluid conducting channel, flow rectification component, or fluid conducting apparatus. In some

embodiments, a heat exchanger herein includes lower pressure drop; improved heat transfer; and/or improved refrigerant flow and/or distribution, in comparison to a heat exchanger that does not comprise a fluid conducting channel, flow rectification component, or fluid conducting apparatus as described herein.

[22] In another embodiment, a heat exchanger is provided that includes an integrated condensate collection manifold that maintains a siphon path including a contiguous liquid contact, thereby permitting the use of active pumps and/or drains and limiting bio-related fouling from standing liquid in comparison to a static condensation pan.

BRIEF DESCRIPTION OF THE DRAWINGS

[23] FIGS. 1A - 1C show embodiments of cross-sections of tubes with built in drainage pathways down the length of the tube (into the plane of the paper).

[24] FIGS. 2A - 2B show an embodiment of a convex fin connected to two tubes as depicted in Fig. 1 A.

[25] FIGS. 3A - 3B show an embodiment of a convex fin connected to two tubes as depicted in Fig. 1B.

[26] FIGS. 4A - 4B show an embodiment of a convex fin connected to two tubes as depicted in Fig. 1C.

[27] FIGS. 5A - 5B show an embodiment of an array of fins and tubes.

[28] FIGS. 6A - 6E shows an embodiment of a heat exchanger that includes features to enhance refrigerant flow and condensate drainage.

[29] FIG. 7A - 7B show embodiments of fin designs that may be used with a tube that has a symmetric center drainage channel.

[30] FIG. 8A - 8B show embodiments of fin designs that may be used with a tube that has an asymmetric center drainage channel.

[31] FIG. 9A - 9B show embodiments of fin designs that may be used with a tube that has a symmetric center with multiple drainage channels per tube.

[32] FIGS. 10A - 10C show cross-sections of embodiments of tubes with an air foil-like design to minimize the air-pressure drop as it flows in the positive x direction. [33] FIGS. 11A - 11C show an embodiment of a convex fin connected to embodiments of tube designs.

[34] FIGS. 12A - 12B show embodiments of fin designs that may be used with a tube that has a drainage channel that is shifted in the positive x axis toward the back of the fin.

[35] FIGS. 13A - 13C show embodiments of fin-tube assemblies in which the absolute z-minimum of the fin corresponds to a drainage channel of the microchannel tube.

[36] FIGS. 14A - 14B show embodiments of fin-tube assemblies in which the absolute z-minimum of the fin corresponds to a drainage channel of the microchannel tubes.

[37] FIGS. 15A - 15C show an embodiment of an array of fins and tubes in a single piece of corrugated material is bent such that it acts as multiple fins.

[38] FIG. 16 schematically depicts primary flow paths for condensate along the coil length in a heat exchanger.

[39] FIG. 17 schematically depicts a flow channel with integrated flow rectification features.

[40] FIGS. 18A - 18C show embodiments of tube manifold flow redistribution configurations.

[41] FIG. 19 shows an embodiment of a heat exchanger component that may operate as an evaporator.

[42] FIG. 20 shows an embodiment of an annular tube shape that may be produced using an extrusion process.

[43] FIGS. 21A - 21B show an embodiment of an integrated condensate collection system.

[44] FIG. 22 shows embodiments of asymmetric design features that may facilitate increased condensate drainage and the ability to withstand stresses due to frost and ice formation,

[45] FIGS. 23A - 23B show photographs of produced parts using additive

manufacturing that include different example channel geometries and heat transfer surface aspect ratios.

DETAILED DESCRIPTION

[46] Heat exchangers and components that provide improved refrigerant flow and/or distribution with improved properties are provided herein. [47] In some embodiments, the heat exchangers described herein exhibit improved drainage relative to traditional heat exchanger designs, due to inclusion of active design features, such as tube drainage channels, fin design coupled to drainage channel design, and/or primary condensate drainage paths that are not on the leading or trailing edge of the heat exchanger.

[48] In some embodiments, the heat exchangers described herein exhibit improved heat transfer, due to inclusion of active design features that increase fin surface area.

[49] In some embodiments, the heat exchangers described herein exhibit improved pressure profiles ( e.g ., reduced pressure drop, due to inclusion of active design features, such as airfoil tubes).

[50] In some embodiments, asymmetric designs are deployed. For example, larger diameter flow channels may be included at the base to account for the accumulation of condensate near the bottom of the heat exchanger. In some embodiments, asymmetric designs may be manufactured using additive manufacturing processes.

[51] In some embodiments, heat exchangers as described herein are produced using additive manufacturing techniques. Benefits of additive processes include, but are not limited to, reduced corrosion (e.g., plastic may be used instead of metal), more readily customizable designs, and integration of operational features.

[52] In some embodiments, inter and intra tube designs are provided that contain passive features for improved refrigerant flow and/or distribution. For example, a feature may include a modification to promote refrigerant pressure drop modulation or rectification. In some embodiments, larger diameter refrigerant channels may be provided across tubes to effectively use refrigerant and avoid phase transition effects. In another example, a passive feature may include a nanostructured coating material with wettability enhancement. For example, a fluid conducting channel may include a surface treatment that includes a nanostructured surface coating. In some embodiments, the nanostructured surface coating increases the amount of nucleation and/or condensation sites to promote the onset of boiling and/or condensation of an internal working fluid. In some embodiments, the

nanostructured surface coating affects the interaction of the fluid and the channel.

Nonlimiting examples of nanostructured surface coatings may be found in PCT Application Nos. WO2018/053452 and WO2018/053453, which are incorporated herein by reference in their entireties. [53] In some embodiments, a heat exchanger may include an integrated condensate collection manifold, which permits the use of active pumps / drains and limits bio-related fouling. For example, the condensate manifold, in fluid connection with a low pressure supply, would actively pull condensate from a unit.

[54] In some embodiments, asymmetric designs are deployed. In some embodiments, asymmetric designs may be manufactured using additive manufacturing processes.

[55] In some embodiments, a critical dimension of a heat exchanger or component thereof (for example, but not limited to, a flow channel, a fin, a pin, a radius of curvature, a drainage channel) is about 20 pm to about lmm in length, or less than about lmm, less than about 950 pm, less than about 900 pm, less than about 850 pm, less than about 800 pm, less than about 750 pm, less than about 700pm, less than about 650 pm, less than about 600 pm, less than about 550 pm, less than about 500 pm, less than about 450 pm , less than about 400 pm, less than about 350 pm, less than about 300 pm, less than about 250 pm, less than about 200 pm, less than about 150 pm, less than aboutlOO pm, less than about 50 pm. In some embodiments, the critical dimension is any of about 1 mm, 950 pm , 900 pm, 850 pm, 800 pm, 750 pm, 650 pm, 600 pm, 550 pm, 500 pm, 450 pm, 400 pm, 350 pm, 300 pm, 250 pm, 200 pm, 150 pm, 100 pm, 50 pm, to about 20 pm in length.

[56] In some embodiments, heat exchangers described herein provide more effective utilization of refrigerant, e.g., mass of refrigerant per watt of heat transfer capacity than a design that does not include features described herein.

Definitions

[57] Numeric ranges provided herein are inclusive of the numbers defining the range.

[58] “A,”“an” and“the” include plural references unless the context clearly dictates, thus the indefinite articles“a”,“an,”, and“the” as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean“at least one.”

[59] The phrase“and/or,” as used herein in the specification and in the claims, should be understood to mean“either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Other elements may optionally be present other than the elements specifically identified by the “and/or” clause, whether related or unrelated to those elements specifically identified unless clearly indicated to the contrary. Thus, as a non-limiting example, a reference to“A and/or B,” when used in conjunction with open-ended language such as“comprising” can refer, in one embodiment, to A without B (optionally including elements other than B); in another embodiment, to B without A (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.

[60] The term“about” as used herein when referring to a measurable value such as an amount, a temporal duration, and the like, is meant to encompass variations of ±20%,

±10%, ±5%, ±1%, or ±0.1% from the specified value, as such variations are appropriate to perform the disclosed methods.

[61] “Process fluid” refers to a liquid, gas or vapor that transmits energy to or from a working fluid. In the case of a vapor compression system, the process fluid is typically humid air.

[62] “Relative humidity” refers to the amount of water vapor present in air expressed as a percentage of the amount needed for saturation at the same temperature.

[63] “Working fluid” refers to a liquid or gas that absorbs or transmits energy from or to a process fluid. In the case of a vapor compression system, the working fluid is the refrigerant. In other systems, chilled water or glycol may be used as the working fluid.

[64] A“tube” or“microchannel tube” refers to a physical element comprising an internal channel or channels for transfer of working fluid and/or refrigerant.

[65] A“fin” refers to an elongated surface of a heat exchanger. Adding a fin to a heat exchanger increases the surface area through which heat transfer may occur to or from the environment, e.g., by increasing convection. In one example, a fin is a horizonal material that runs parallel to the airflow.

[66] “ Thermal contact” refers to intimate contact between two parts such that the contact resistance is not excessive.

[67] “ Gravitational potential minimum” refers to the lowest local point on a part.

[68] “ Sessile drop contact angle” refers to the contact angle formed between the liquid and substrate as measured through the liquid for a static drop on the surface.

[69] “Leading edge” in reference to a heat exchanger refers to the edge of the part which first comes into contact with the incoming fluid stream from which energy is to be transferred.

[70] “Trailing edge” in reference to a heat exchanger refers to the edge of the part which last comes into contact with the fluid stream from which energy is to be transferred. [71] “Blowoff’ refers to liquid condensate or condensate droplets which leave the part and are transferred downstream from the trailing edge of the part.

[72] “Effective surface area” or“effective fin area” refers to the surface area in contact with the fluid stream from which energy is to be transferred.

[73] “Flow modification” refers to a change in pressure, vorticity, and/or velocity of the fluid stream.

[74] “Flow rectification” refers to a net change in velocity of a dynamic fluid flow situation.

[75] “Flow redistribution” refers to a net change in the velocity field of the fluid flow.

[76] “ Coil” refers to a common name for a heat exchanger.

Exemplary Embodiments

[77] Figures 1A - 1C. Cross-sections of tubes are shown with built in drainage pathways down the length of the tube (into the paper plane). Fig. 1A shows an example of a tube that has two drainage channels in the center that can pull water from the attached fins down the length of the tube to a drain. The tube depicted has 10 channels inside for moving around refrigerant, although other numbers of channels may be deployed depending on the size and capacity of the unit. This example has bisymmetry and could easily be made by traditional manufacturing techniques such as extrusion, for example, using aluminum alloys. Fig. IB shows a tube that has 3 drainage channels, 2 on one side of the tube and 1 on the other, although other numbers of channels may be deployed depending on the size and capacity of the unit. In some embodiments, this tube design is useful when used with an asymmetric fin design (in the y axis) to pull more water off one side than the other. In this case, the refrigerant internal cavities may be smaller to achieve a more uniform distribution across the tubes. This asymmetric tube cannot be easily made with traditional manufacturing techniques. This tube type would be beneficial to lower thermal conductivity materials, typically found in additive manufacturing, due to the more uniform refrigerant distribution. Fig. 1C shows a tube that is similar to the tube depicted in Fig 1A, but allows for more drainage due to 4 drainage pathways per fin or for the controlled drainage based on an asymmetric fin (in the x axis) where the fin low point may not be centered or symmetrical. However, other numbers of drainage pathways may be deployed depending on the size and capacity of the unit. [78] Figures 2A - 2B. Fig. 2B is a view of the xy plane wherein a symmetric convex fin is connected to two tubes as depicted in Fig. 1A. Fig. 2A is a view in the yz plane of this fin tube assembly where an array of fins is shown between two tubes. Upon passing refrigerant through the tubes in the negative z direction and flowing humid air across the fins in the positive x direction, the air will be cooled and dehumidified as it passes through the fin array and transfers energy with the coolant. Condensate is removed from the air and condenses on the fin surface where it drains down from the high part (middle) of the fin towards the tubes, where it is gravitationally drained in the positive z direction via the water drainage pathways in the tube surface. When an amount of water condenses, the tube assembly reaches a steady state where there is a continuous stream of water flowing that creates a siphon of water through the water drainage pathways that can further accelerate water drainage.

[79] Figures 3A - 3B. Fig. 3B is a view of the xy plane wherein an offset convex fin is connected to two tubes as depicted in Fig. 3B in order to facilitate and promote increased fluid flow as compared to a flat fin. Fig. 3A is a view in the yz plane of this fin tube assembly where an array of fins is shown between two tubes. Upon passing refrigerant through the tubes in the negative z direction and flowing humid air across the fins in the positive x direction, the air will be cooled and dehumidified as it passes through the fin array and transfers energy with the coolant. Condensate is removed from the air and condenses on the fin surface where it drains down from the high part of the fin towards the tubes where it is gravitationally drained in the positive z direction via the water drainage pathways in the tube surface. Because there is likely to be more water drained in the negative y direction than in the positive y direction due to the offset convex fin, there are 2 drainage channels on one side of the fin and 1 drainage channel on the other, although different numbers of drainage channels may be deployed depending on the size and capacity of the unit, while retaining asymmetry as described herein. When an amount of water condenses, the tube assembly reaches a steady state where there is a continuous stream of water flowing that creates a siphon of water through the water drainage pathways that can further accelerate water drainage. This asymmetry can potentially create thermal gradients in the y plane and induce different air flow patterns.

[80] Figures 4A - 4B. Fig. 4B is a view of the xy plane wherein a pyramid embossed convex fin is connected to two tubes as depicted in Fig. 1C in order to increase fluid flow as compared to a flat fin. Fig. 4A is a view in the yz plane of this fin tube assembly where an array of fins is shown between two tubes. Upon passing refrigerant through the tubes in the negative z direction and flowing humid air across the fins in the positive x direction, the air will be cooled and dehumidified as it passes through the fin array and transfers energy with the coolant. Condensate is removed from the air and condenses on the fin surface where it drains down from the high part (tip of the pyramid) of the fin towards the tubes where it is gravitationally drained in the positive z direction via the water drainage pathways in the tube surface. This fin design drains both in the positive and negative x direction toward the tubes where 4 drainage pathways can aid with removing water. In various embodiments, different numbers of drainage channels may be deployed depending on the size and capacity of the unit, while retaining the geometry described herein. When an amount of water condenses, the tube assembly reaches a steady state where there is a continuous stream of water flowing that creates a siphon of water through the water drainage pathways that can further accelerate water drainage.

[81] Figures 5A - 5B. Fig. 5B shows the xy plane of an array of fins and tubes similar to that described in Figs. 2A-2B, 3A-3B, 4A-4B, 11A-11C, 13A-13C, and 14A-14C. Figs. 5A-5B depict an embodiment with multiple tubes in the array, wherein the top and the bottom of the array are connected to a manifold through which refrigerant can be added and removed. Fig. 5A shows the assembled heat exchanger consisting of fins, tubes, and a manifold. In this case, the refrigerant enters the bottom manifold (refrigerant inlet), flows through the tube channels, into the top manifold, and then exits the heat exchanger

(refrigerant outlet). Humid air flows in the positive x direction (into the plane of the paper) where it transfers heat with the refrigerant through the heat exchanger fins and tubes. As the humid air flows over the tubes, water condenses onto fin surfaces and gravitationally flows down the fin to the fluid drainage pathway in the tube. Here the water is gravitationally drained through that fluid drainage pathway along the tube wall. At equilibrium with substantial condensation, a siphon can be created through the drainage pathway that can accelerate the condensate removal further. The tube-fin design can be very simple and symmetric, as depicted in Figs. 5A-5B, or may be more complex, for example, utilizing the designs depicted in Figs. 2A-2B, 3A-3B, 4A-4B, 11A-11C, 13A-13C, and 14A-14C.

[82] Figures 6 A - 6D. A heat exchanger was designed to include many features to enhance refrigerant flow and condensate drainage. Computer-aided design drawings were created of this heat exchanger. This heat exchanger contains rectangular baffles in one of the heat exchanger manifolds (Fig. 6A), tubes with varying diameters to modulate refrigerant pressure drop across the inside of the heat exchanger (Figs. 6B and 6C), chevron shaped fins with a built in drainage path on the center of the fin such that the fluid can travel downward along the tube wall, such as depicted in Figs. 2A - 2B and Figs. 5A - 5B, with a simultaneous tilt along the exterior flow direction (Figs. 6B and 6D), and pin shaped baffles in a secondary manifold of the heat exchanger (Fig. 6C). This heat exchanger was manufactured using stereolithographic additive manufacturing.

[83] Figure 7A - 7B. Two example fin designs with their respective equations were chosen to represent variations in fin designs that could be used with a tube that has a symmetric center drainage channel, such as depicted in Fig. 1A. The fin shown in Fig. 7A is a simple parabola that has a minimum where the fin contacts the tube. The fin shown in Fig. 7B has a minimum in the middle of the tube at the contact point. These fin designs ensure that when paired with the proper draining tube (such as the tube depicted in Fig. 1A), there will be no or substantially no retained condensate on the fins. A simple inverted V design will function the same as or similarly to the parabola shown in Fig. 7A and both can be potentially manufactured, for example, using traditional controlled atmosphere brazing of aluminum heat exchangers. The periodic function fin shown in Fig. 7B would require additive manufacturing techniques, such as 3D printing. The parabolic fin shown in Fig. 7A has a surface area l.44x that of a flat fin, while the fin shown in Fig. 7B has a surface area l.20x that of a flat fin.

[84] Figures 8A - 8B. Two example fin designs with their respective equations were chosen to represent variations in fin designs that could be used with a tube that has an asymmetric center drainage channel, such as depicted in Fig. IB. The fin shown in Fig. 8A is a shifted, non-centered parabola that has minima where the fin contacts the tube. The fin shown in Fig. 8B has a single minimum at the center of the tube on one side at the contact point and 2 minima offset on the other. These fin designs ensure that when paired with the proper draining tube (such as the tube depicted in Fig. IB) that there will be no or substantially no retained condensate on the fins. A shifted inverted V design will function the same as or similarly to the parabola shown in Fig. 8A and both can be potentially manufactured, for example, using traditional controlled atmosphere brazing of aluminum heat exchangers. The periodic function fin shown in Fig. 8B would require additive manufacturing techniques, such as 3D printing. The parabolic fin shown in Fig. 8A has a surface area l.67x that of a flat fin, while the fin shown in Fig. 8B has a surface area l.20x that of a flat fin. [85] Figure 9A - 9B. Two example fin designs with their respective equations were chosen to represent variations in fin designs that could be used with a tube that has a symmetric center with multiple drainage channels per tube, such as depicted in Fig. 1C.

The fin shown in Fig. 9A is a 3D parabola that has minima where the fin contacts the tube in the corner extremities. The fin shown in Fig. 9B has 2 minima off center of the tube on one side at the tube contact point and 2 minima off center on the other side. These fin designs ensure that when paired with the proper draining tube (such as the tube depicted in Fig. 1C) that there will be no or substantially no retained condensate on the fins. An embossed pyramid design (similar to the design shown in Figs. 4A - 4B) will function the same or similarly to the parabola shown in Fig. 9A. The embossed pyramid can be potentially manufactured, for example, using traditional controlled atmosphere brazing of aluminum heat exchangers. The periodic function fin shown in Fig. 9B would require additive manufacturing techniques, such as 3D printing. The parabolic fin shown in Fig. 9A has a surface area 1.19c that of a flat fin while the fin shown in Fig. 9B has a surface area

1.16c that of a flat fin.

[86] Figures 10A - 10C. Cross-sections of tube designs are shown that include an air foil-like design to minimize the air-pressure drop as it flows in the positive x direction. Fig. 10A shows a tube that includes an annular refrigerant flow cavity. This example has bisymmetry and could be made, for example, using extrusion or additive manufacturing. Typically, the corrugated fins in controlled atmosphere brazing have a constant y dimension and would not attach properly to the tube. Additive manufacturing advantageously provides the ability to print a fin with a variable y dimension to take advantage of this type of design. Fig. 10B shows a tube that includes multiple cavities for refrigerant flow, thereby increasing the contact surface area and enhancing heat transfer. Like the tube shown in Fig.

IOA, a heat exchanger cannot be easily made with this tube using traditional manufacturing techniques. However, in some embodiments, extrusion or additive manufacturing techniques may be deployed. This tube type would be beneficial to lower thermal conductivity materials, typically found in additive manufacturing, due to the more uniform refrigerant distribution. Fig. 10C shows a tube that is similar to the tube shown in Fig.

IOB, but allows for more drainage due to inclusion of multiple ( e. g ., 2) drainage pathways per fin or for the controlled drainage for fins that have low points on the positive x axis end of the heat exchanger. As with the tubes depicted in Figs. 10A and 10B, extrusion or additive manufacturing techniques may be used to produce the tube shown in Fig. 10C. These drainage tubes work the same or similarly to those in the tubes depicted in Figs. 1A - 1C

[87] Figures 11A - 11C. Figs. 11B and 11C show views of the xy plane wherein a simple convex fin is connected to two tubes as shown in Fig. 10B and 10C, respectively. The xy plane images show tube based on an air foil design wherein the fin has a variable y dimension as a function of x. This unusual fin dimension necessitates the use of advanced manufacturing techniques, such as additive manufacturing, to properly utilize this tube geometry to aid with reduction in pressure drop. The design shown in Fig. 11B has drainage channels built into the tube to help remove condensate. The design shown in Fig. 11C does not have this drainage feature. Instead, a gap was left between the fin and the tube to act as a drainage path. This method, while functional, may be inferior due to condensate carryover in view of the lack of a drainage to create a siphon. Fig. 11A is a view in the yz plane of this fin tube assembly where an array of fins is depicted between two tubes. Upon passing refrigerant through the tubes in the negative z direction and flowing humid air across the fins in the positive x direction, the air will be cooled and dehumidified as it passes through the fin array and transfers energy with the coolant.

Condensate is removed from the air and condenses on the fin surface where it drains down from the high part (middle) of the fin towards the tubes, where it is gravitationally drained in the positive z direction.

[88] Figures 12A - 12B. Two example fin designs with their respective equations were chosen to represent variations in fin designs that could be used with a tube that has a drainage channel that is shifted in the positive x axis toward the back of the fin. The fin shown in Fig. 12A is a periodic function in both the x and y dimensions with 2 minima toward the exit of the heat exchanger. The fin shown in Fig. 12B also has minima at the same location, but it has a subtler curvature of minimize the pressure drop of air across the fins. These fin designs ensure that when paired with the proper draining tube that there will be no or substantially no retained condensate on the fins. These periodic function fins would require additive manufacturing techniques, such as 3D printing. These fins can be paired will with a drainage tube as shown in Figs. 11A - 11C to help optimize heat transfer and condensate management. The effective fin area, as compared to a flat fin, for the fin shown in Fig. 12A is 1.49. The effective fin area for the fin shown in Fig. 12B is 1.22.

[89] Figures 13A - 13C. The right side images are views of the xy plane. The fin-tube assemblies are designed such that the absolute z-minimum of the fin corresponds to a drainage channel of the microchannel tube. The fins are shown as contour plots with lighter shading indicating larger z (highest point with respect to gravity) and darker shading indicating smaller z (gravitational minimum). The 3d plots corresponding to their respective contour plots are shown on the left. These periodic functions are chosen as examples to show the versatility of the channel design, in particular by using advanced manufacturing techniques, such as 3D printing. The fins depicted in Figs. 13A - 13C are in the form of z = sinx + siny or z = sinx +xsiny. The exact equation of each fin design is described in preceding figures. These fins all have a symmetry line along y = 1.5p, in the middle of the fin.

[90] Figures 14A - 14B. The right-side images are views of the xy plane. The fin-tube assemblies are designed such that the absolute z-minimum of the fin corresponds to a drainage channel of the microchannel tubes. The fins are shown as contour plots with lighter shading indicating larger z (highest point with respect to gravity) and darker shading indicating smaller z (gravitational minimum). The 3d plots corresponding to their respective contour plots are shown on the left. The example shown in Fig. 14A has no level of symmetry, while the example shown in Fig. 14B has minimal symmetry. There are asymmetric fins with asymmetric tubes to ensure drainage at the minimums. These designs cannot easily be made with traditional manufacturing. Additive manufacturing is an option to execute designs with this type of complexity.

[91] Figures 15A - 15C. The heat exchanger depicted in Figs. 15A - 15C is similar to the heat exchanger depicted in Figs. 5A - 5B, but in this case the fins in the heat exchanger are a single piece of corrugated material that is bent in a way such that it acts as multiple fins in a heat exchanger (Fig. 15A). This fin type is typically adhered to the tube via controlled atmosphere brazing.

[92] Figure 16. Condensate primary flow paths along the coil length are schematically depicted.

[93] Figure 17. A flow channel with integrated flow rectification features is

schematically depicted.

[94] Figures 18A - 18C. Exemplar tube manifold flow redistribution configurations are shown. Typical heat exchangers contain only vertical tubes , as shown in the Fig. 18A.

(Fins are removed in these images for simplicity). If there is a phase change event inside of the tubes, a pressure change occurs that can affect refrigerant flow. If there is a flow or thermal gradient across the heat exchanger in the y direction, this design cannot accommodate for this imbalance in internal tube pressure, and heat transfer is thus adversely affected. The designs shown in Figs. 18B and 18C connect the tubes together in a matrix with pressure equalization tubes that are designed to compensate for refrigerant flow and/or thermal gradients across the yz plane of the heat exchanger by equilibrating flow in the y direction to allow for more uniform heat transfer across the exchanger. The heat exchanger shown in Fig. 18B has tubes orthogonal to the flow direction, providing minimal blow back through the tubes. This will provide a subtler pressure differential. This design can potentially be manufactured with traditional techniques, such as extrusion and brazing, potentially requiring some minor tube intersection manifolding. The design shown in Fig. 18C eliminates the vertical tubes in favor of refrigerant flow in both the y and z directions. The interfaces between the tubes are also at an angle. This can be beneficial if there is a phase change event as a pressure wave, which will be sent uniformly toward all tubes. This design provides more pressure wave compensation with an increased manufacturing complexity. Conversely, additional brazing joints, using traditional manufacturing, results in additional joints which are subject to failure and more difficulty in fin integration. This design would be more readily manufactured when utilizing more modern manufacturing techniques, such as additive manufacturing.

[95] Figure 19. An exemplar heat exchanger component is shown, depicted as operating as an evaporator, in which a refrigerant enters from the bottom manifold and exchanges heat with the surrounding process fluid that is passed through the exchanger. In the heat exchange process the refrigerant expands, which results in an increasing flow velocity through a straight channel. An expanding or bifurcating channel as depicted in Fig. 19 would result in an increased residence time for the refrigerant to exchange heat, thereby increasing the effectiveness of the system. This configuration is readily adapted to additive manufacturing techniques.

[96] Figure 20. A nonstandard annular tube shape that can be extruded is depicted. This design increases refrigerant contact area with the tube. While the tube can be made with traditional manufacturing techniques, additive manufacturing would be advantageous to build a heat exchanger from this tube, due to the variable fin width perpendicular to the flow direction as the process fluid moves in the positive x axis.

[97] Figures 21A - 21B. An example of an integrated condensate collection system is schematically depicted in Fig. 21A. The drainage path along the tube and manifold is also shown in Fig. 21B. This is a non-limiting example of a condensate collection device. Additive manufacturing makes possible the integration of the condensate drain features and the heat exchanger, simplifying the overall system design and reducing the overall footprint.

[98] Figure 22. A schematic diagram is provided that highlights some asymmetric design features, which can be considered for additive manufacturing and which would facilitate increased condensate drainage and the ability to withstand stresses due to frost and ice formation. The features highlighted in Fig. 22 would be challenging to fabricate using traditional means. However, they may be readily adapted through the use of additive manufacturing.

[99] Figures 23A - 23B. Photographs are provided of stereolithographically produced parts, which highlight different example channel geometries and heat transfer surface aspect ratios.

[100] The following examples are intended to illustrate, but not limit, the invention.

EXAMPLES

Example 1

[101] The heat exchanger depicted in Fig. 6, with design features from Figs. 2A - 2B and Fig. 5A - 5B, was attached to a wind tunnel with a 30% propylene glycol in water refrigerant loop attached to the threaded NPT fittings set at a temperature around 2 °C to 10 °C. As the refrigerant flowed through the heat exchanger, conditioned air at 20 °C to 30 °C and 30% to 60% relative humidity was passed through the fins at a velocity of about 1 m/s to 2 m/s. Heat was transferred through the heat exchanger from the working refrigerant loop into the air stream.

Example 2

[102] A condensate collection system, similar to the system shown in Figs. 21A - 21B, was assembled using PVC pipe and fittings and attached to the bottom of a heat exchanger manifold. The collection system was clamped onto the heat exchanger, creating a unitary piece. The heat exchanger was placed into a wind tunnel with a 30% propylene glycol in water refrigerant loop attached to the threaded NPT fittings set at a temperature around 2 °C to 10 °C. As the refrigerant flowed through the heat exchanger, conditioned air at 20 °C to 30 °C and 30% to 60% relative humidity was passed through the fins at a velocity of about 1 m/s to 2 m/s. As heat was transferred into the refrigerant and humidity was removed from the air, condensate gravitationally drained into the condensation collection system. The condensation collection device maintained a water drainage path and aided the condensation from the bottom of the heat exchanger.

Example 3.

[103] A part with several critical features required for additive manufacturing design is shown at a nominal depth that would be useful for heat exchanger designs as described herein. (Figs. 23A - 23B) Channel features which represent tubular structures and fin structures are shown.

[104] Although the foregoing invention has been described in some detail by way of illustration and examples for purposes of clarity of understanding, it will be apparent to those skilled in the art that certain changes and modifications may be practiced without departing from the spirit and scope of the invention which is delineated in the appended claims. Therefore, the description should not be construed as limiting the scope of the invention.

Claims

CLAIMS We claim:

1. A tube comprising a length, wherein the tube comprises one or more longitudinal concave liquid drainage channel in the direction of the length, wherein the tube is in thermal contact with a fin at a thermal contact point.

2. The tube according to claim 1, wherein the fin comprises a gravitational potential minimum at the thermal contact point.

3. The tube according to claim 2, wherein a drainage channel is in contact with the fin at a drainage channel contact point, and wherein the fin comprises a gravitational potential minimum at the drainage channel contact point.

4. The tube according to any of claims 1 to 3, wherein the fin comprises a sessile drop water contact angle less than about 90 degrees, less than about 70 degrees, or less than about 30 degrees.

5. The tube according to any of claims 1 to 4, wherein the fin does not comprise holes or perforations.

6. A tube comprising a length, wherein the tube comprises one or more longitudinal concave liquid drainage channel in the direction of the length, manufactured by extrusion, extrusion followed by cold working, or extrusion plus grinding.

7. A heat exchanger comprising: one or more tube comprising a length and comprising one or more longitudinal concave liquid drainage channel in the direction of the length;

one or more fin in thermal contact with a tube at a thermal contact point; and inlet and exit lines or a manifold configured to allow flow of a working fluid through the inside of the tube(s), thereby transferring heat to a process fluid outside of the tube(s).

8. The heat exchanger according to claim 7, wherein the fin(s) each comprises a gravitational potential minimum at the thermal contact point.

9. The heat exchanger according to claim 7 or 8, wherein the fin(s) do not comprise holes or perforations.

10. The heat exchanger according to any of claims 7 to 9, wherein the fin(s) comprise a sessile drop contact angle less than about 90 degrees, less than about 70 degrees, or less than about 30 degrees.

11. The heat exchanger according to any of claims 7 to 10, further comprising a process fluid, wherein the process fluid is humid air with relative humidity greater than about 5% or greater than about 20%.

12. The heat exchanger according to any of claims 7 to 11, wherein the heat exchanger is manufactured using a controlled atmospheric brazing method or one or more additive manufacturing technique.

13. A heat exchanger comprising internal drainage channels, wherein condensate removal is improved in the heat exchanger in comparison to a heat exchanger that does not comprise internal drainage channels.

14. The heat exchanger according to claim 13, wherein a majority of condensed liquid is drained from the heat exchanger through said internal channels rather than from the leading or trailing edge of the heat exchanger.

15. The heat exchanger according to claim 13, further comprising fins, wherein the heat exchanger comprises improved blowoff properties in comparison to a heat exchanger that does not comprise internal drainage channels, wherein said improved blowoff properties comprise lower blowoff and/or higher velocity operation before blowoff, resulting in more greater transfer capacity per unit area, due to lower amount of condensate retention on fins.

16. A fin design comprising a convex surface, wherein said surface provides an increased effective surface area of more than about 1%, about 5%, about 20%, about 50%, or about 100%, relative to a flat fin.

17. A fluid conducting channel, comprising an integrated flow rectification component, wherein the flow rectification component comprises a passive component at least partially contained within the fluid conducting channel, wherein the passive component promotes rectification of flow of a fluid in the channel to prevent backpressure from leading to a reversing flow direction.

18. The fluid conducting channel according to claim 17, wherein the flow rectification component comprises a passive component that comprises protuberances on an internal surface of the fluid conducting channel, thereby impacting flow of the fluid in the channel through resultant pressure, vorticity, or velocity driven fields.

19. A heat exchanger, comprising one or more fluid conducting channels according to any of claims 17 to 18.

20. A fluid conducting apparatus comprising a plurality of fluid conducting channels, wherein the fluid conducing device comprises an integrated flow redistribution component,

wherein the flow redistribution component comprises an integrated section in which the contents of two or more fluid channels are in fluid connection and allowed to mix and redistribute.

21. The fluid conducting apparatus according to claim 20, wherein the flow redistribution component comprises the intersection of two or more fluid conducting channels, configured to allow the contents of the two or more channels to mix and redistribute.

22. The fluid conducting apparatus according to claim 20, wherein the flow redistribution component comprises one or more fluid conducting channels split or merged to increase or decrease the overall internal volume available for carrying fluid, thereby reducing or increasing the pressure drop and improving the overall fluid transport efficiency.

23. A heat exchanger, comprising one or more fluid conducting apparatus according to any of claims 20 to 22.

24. A heat exchanger according to claim 19 or 23 wherein the fluid conducting channel, flow rectification component, or fluid conducing apparatus therein results in: a) improved drainage design;

b) improved airflow;

c) improved refrigerant flow and/or distribution; and/or d) lower corrosion rates and/or different failure mechanisms on environmental exposure

in comparison to a heat exchanger that does not comprise the fluid conducting channel, flow rectification component, or fluid conducting apparatus.

25. A heat exchanger according to any of claims 19, 23, or 24, comprising: e) lower pressure drop;

f) improved heat transfer; and/or

g) improved refrigerant flow and/or distribution, in comparison to a heat exchanger that does not comprise the fluid conducting channel, flow rectification component, or fluid conducting apparatus.

26. A heat exchanger comprising an integrated condensate collection manifold that maintains a siphon path comprising a contiguous liquid contact, thereby permitting the use of active pumps and/or drains and limiting bio-related fouling from standing liquid in comparison to a static condensation pan.