Patent Publication Number: US-2021180888-A1

Title: Heat exchanger with varying surface roughness

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. provisional application Ser. No. 62/946,587 filed Dec. 11, 2019, the disclosure of which is hereby incorporated in its entirety by reference herein. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to a heat exchanger with varying surface roughness. 
     BACKGROUND 
     Heat exchangers can be used in a variety of applications to cool or heat associated components. In an automotive vehicle, heat exchangers can be found in the form of radiators, oil coolers, intercoolers, battery chillers, condensers, internal heat exchangers (IHXs), among others. Heat exchangers are also found in other non-vehicle applications, such as heating, ventilation, and air conditioning (HVAC) systems, appliances such as refrigerators, and the like. Heat exchangers typically include the passing of two fluids relative to one another, in which heat can exchange between the two fluids. For example, warm fluid can enter the heat exchanger and exits as a cooled fluid, by exchanging heat with a cold fluid that enters the heat exchanger and exits as a warmed fluid. 
     The two fluids can be separated by a solid patrician such as a tube, wall, or the like. The partition may have an intricate shape to direct the fluid from one specific area to another. The heat exchanger may include several partitions, and the respective temperatures of the two passing fluids may be different in various localized regions of the heat exchanger. 
     SUMMARY 
     According to one embodiment, a heat exchanger includes a tube configured to transfer a first fluid. The tube includes an outer surface configured to exchange heat with a second fluid as the second fluid flows over the outer surface of the tube, an inner surface defining an interior configured to contain and transfer the first fluid, and a plurality of surface features integrally formed as part of the inner surface, wherein the surface features extend radially inward toward the interior and are configured to increase a surface area of the inner surface to improve heat exchange between the tube and the first fluid. 
     In another embodiment, a 3D-printed heat exchanger includes a tube configured to transfer a first fluid. The tube includes an outer surface configured to contact a second fluid to transfer heat therewith, an inner surface defining an interior and configured to contain the first fluid therein, and a plurality of 3D-printed surface features formed therewith, wherein a first plurality of localized regions of the tube include the surface features, and a second plurality of localized regions of the tube do not include the surface features. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an automotive vehicle having a heat exchanger, in this case a radiator, according to an embodiment. 
         FIG. 2  is a front plan view of the radiator of  FIG. 1 , according to an embodiment. 
         FIG. 3  is a cross-sectional view of one of the tubes of the radiator, according to an embodiment. 
         FIG. 4  is cross-sectional view of one of the tubes of the radiator, according to another embodiment. 
         FIG. 5  is a cross-sectional view of a tube of another heat exchanger, such as a chiller, according to one embodiment. 
         FIG. 6  is a cross-sectional view of a tube of a heat exchanger, such as a chiller, according to another embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present disclosure are described herein. It is to be understood, however, that the disclosed embodiments are merely examples and other embodiments can take various and alternative forms. The figures are not necessarily to scale; some features could be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the embodiments. As those of ordinary skill in the art will understand, various features illustrated and described with reference to any one of the figures can be combined with features illustrated in one or more other figures to produce embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. Various combinations and modifications of the features consistent with the teachings of this disclosure, however, could be desired for particular applications or implementations. 
     In automotive vehicle settings, various heat exchangers can be used to cool or heat associated components. For example, radiators cool engine coolant, condensers cool HVAC fluid, engine oil coolers cool engine oil, chillers cool battery components, etc. Other heat exchangers are known. These heat exchangers can be mounted at various locations throughout the vehicle. Radiators are typically mounted at the front of the vehicle, directly behind the front grill, allowing the heat exchanger to take advantage of incoming ambient air to cool fluid in the radiator as the vehicle is being driven. 
       FIG. 1  illustrates a vehicle  10 , in this case an automotive passenger vehicle, with the location of the radiator shown at  20  according to an embodiment. Radiators are typically mounted at the front of the vehicle, directly behind the front grill  14 . This allows incoming air to flow across the tubes of the radiator as the vehicle is being driven. The passing of the ambient air across the tubes cools the coolant contained within the tubes. 
       FIG. 2  illustrates a front view of the radiator  20 , according to an embodiment. As explained above, the radiator is but one type of heat exchanger that the teachings of this disclosure can be applied to. The radiator  20  includes an inlet header tank  22 , an outlet header tank  24 , and a core  26  disposed between the inlet header tank  22  and the outlet header tank  24 . The inlet header tank  22  defines an inlet  28  through which fluid (e.g., engine coolant) enters the radiator  20 . The outlet header tank  24  defines an outlet  30  though which the coolant exits the radiator  20 . 
     The core  26  includes a plurality of tubes  32  and a plurality of fins  34  which extend between the inlet header tank  22  and the outlet header tank  24 . The tubes  32  fluidly connect the inlet  28  to the outlet  30 . The tubes  32  extend horizontally across the core  26  and in parallel fashion, with adjacent tubes  32  being connected by a row of the fins  34 . Engine coolant, which may be in either a liquid or gaseous phase, flows from the inlet header tank  22 , through the core  26 , and to the outlet header tank  24 . The core  26  cools the coolant flowing through the radiator  20 . More specifically, the coolant flows through the tubes  32 , and the fins  34  conduct or transfer heat from the coolant flowing through the tubes  32 . Heat transferred to the fins  34  is transferred to ambient air flowing through the radiator  20 . The ambient air can flow through the radiator  20  as supplied naturally when the vehicle is traveling, or via a fan (not shown). 
     The tubes  32  are typically manufactured by forming a thin piece or strip of metal, such as brass or aluminum. In one example, rollers bend the strip of metal into its flattened tube shape. The tube then runs through a vat of molten metal such as lead. As the tube exits the vat, it runs through water to cool and harden. A cutter cuts the tube to its desired length (e.g., the width of the radiator). The fins  34  are also manufactured by forming a thing piece or strip of metal, such as copper. In one embodiment, a machine shapes a narrow strip of copper into its alternating or sinusoidal shape. The tubes and fins can be stacked in alternating fashion, such as shown in  FIG. 2 . The stack of tubes and fins are then compressed together. If any tubes or fins become distorted or crooked during the process, they can be manually straightened out. Another metal sheet (e.g., brass) can be formed to shape to create the inlet and outlet header tanks, which can then be welded or soldered onto the sides of the stack. Inlet and outlet pipes are then welded into place. 
     This process can be timely, expensive, and prone to error that requires manual fixing. Moreover, the tubes and fins are formed form a very long, continuous sheet of metal, and are all formed in the same manner; thus, the tubes are intended to be uniform in size and shape throughout the entire core of the radiator. 
     Therefore, according to various embodiments described herein, a heat exchanger is manufactured by, for example, additive manufacturing (e.g., 3D printing of metal, 3D printing of synthetic material such as plastic, dust layering and binding, etc.) to include localized surface roughness to improve the heat exchange process. In one example, a tube that carries one of the fluids for the heat exchange process is manufactured to include surface roughness in particular, localized regions of the tube. Other areas of that tube, or other tubes in the heat exchanger, may be manufactured via additive manufacturing to not include such surface roughness. A customized heat distribution characteristic of the heat exchanger can thus be created via the additive manufacturing; further detail is provided below. 
       FIG. 3  illustrates a cross-section of a tube  40  of a heat exchanger. The tube  40  may be a tube of a radiator, such as the tubes  32  described with reference to  FIG. 2 . Alternatively, the tube  40  may be a tube of another heat exchanger, such as a battery chiller, an internal heat exchanger (IHX), evaporator, boiler, condenser, a heat exchanger of a refrigerator, [anything else worth listing?] and other types of heat exchanger. Unless otherwise noted, the tube  40  may also be a tube of a gas-to-gas heat exchanger, liquid-to-gas heat exchanger, or liquid-to-liquid heat exchanger. The tube  40  may be any fluid-carrying passageway in which heat is exchange between the fluid within the tube  40  and a second fluid passing around the outer surface of the tube  40 . In the embodiment illustrated in  FIG. 3 , the fluid being carried within the interior of the tube  40  may be a gas or liquid refrigerant or coolant, and ambient air may flow across or over the exterior of the tube  40 . 
     The tube  40  has an inner surface  42  and an outer surface  44 . The inner surface  42  defines a hollow interior  46  of the tube  40  configured to transfer a first fluid within the heat exchanger. At least a portion of the inner surface  42  of the tube  40  is manufactured (e.g., via 3D printing) to include surface features  48 . The surface features  48  may be a series of undulations, projections, peaks, corrugations, or the like. In the embodiment of  FIG. 3 , the surface features  48  include projections that extend radially inwardly toward a center of the interior  46 . 
     The surface features  48  are configured to increase or maximize the surface area of the inner surface  42  that contacts the fluid flowing within the interior  48 . In the illustrated embodiment, the surface features  48  project radially inwardly and have sharp peaks  50  located within the interior  46 . At least some of these peaks may be formed to have sharp, acute angles such as between 10-50 degrees, or more particularly between 20-30 degrees. 
     In some embodiments, only a portion of the inner surface  42  is provided with the surface features  48 . For example, the tube  40  may have a first end  52  and a second end  54  located at opposite width ends of the tube  40 . The inner surface  42  at the first end  52  may be formed with a smooth inner surface, while the second end  54  may be formed with the surface features  48 , as shown in  FIG. 3 . The surface features  48  may extend all the way around the second end  54 , and beyond a center point of the tube  40 , closer to the first end  52  than the second end  54 . In other words, the surface features  48  may be located in a majority of the inner surface  42 . The inner surface  42  at the first end  52  may be smooth, while the inner surface  42  at the second end  54  is volatile or rough due to the surface features  48 . The tube  40  may be specifically manufactured in this way to promote a desired flow characteristic and increase heat transfer at the second end  54  of the tube  40 . More heat transfer capability is provided at the second end  54  than the first end  52 , due to the increase of surface area of the inner surface  42  at the second end  54 . 
     Rather than, or in addition to, the inner surface  42  being provided with the surface features, the outer surface  44  can be provided with surface features.  FIG. 4  illustrates an embodiment in which the inner surface  42  is smooth and has no surface features, and the outer surface  44  is rough in regions provided with surface features  48 . In other words, the surface features  48  are now illustrated as extending outwardly from the outer surface  44 . Thus, the fluid (e.g., ambient air in this example) flowing over the outer surface  44  directly contacts the surface features  48 , instead of the embodiment of  FIG. 3  in which the fluid within the interior  46  of the tube  40  directly contacts the surface features  48 . The embodiment of  FIG. 4  may be chosen when manufacturing the heat exchanger to improve the heat exchange between the outer fluid (e.g., ambient air) and the outer surface  44  in regions where such improved heat exchange is desired. 
     In another embodiment not shown, both the inner surface  42  and outer surface  44  are provided with the surface features  48 . The surface features  48  may be provided at any location about or within the tube  40  to improve the localized heat transfer in that region of the tube  40 , depending on the heat distribution of the overall heat exchanger. 
     The surface features  48  may be manufactured so as to be non-uniform. For example, the surface features  48  may vary in peak-to-peak distance, valley-to-valley distance, width, height, depth, and the like. Additive manufacturing such as 3D printing provides the ability to easily vary these relative sizes amongst the surface features  48  to provide customized heat distribution characteristics of the heat exchanger. 
       FIG. 5  illustrates an embodiment of utilizing surface features in regions where the tube or fluid passage of a heat exchanger is curved, in that the tube extends along a curved path to define a corresponding curved flow path. In the embodiment of  FIG. 5 , an overhead cross-sectional view is provided of a tube  60 . The tube  60  may be part of any of the heat exchangers listed above, but in this embodiment is a tube of a batter chiller. The tube  60  may be S-shaped, having a turn in one direction and then a turn in an opposite direction. For example, from the perspective of the view of  FIG. 5 , as fluid flows from the bottom of the tube  60  to the top of the tube  60 , the fluid turns right along a first curve  62 , and then turns left along a second curve  64 . 
     The tube  60  has an inner surface  66 , and an outer surface  68 . At the first turn  62 , the inner surface  66  is provided with first surface features  70 . At the second turn  64 , the inner surface  66  is provided with second surface features  72 . The first and second surface features  70 ,  72  may be manufactured in the same manner as described above (e.g., 3D printing, etc.), with undulations, peaks, etc. with customized sizes, shapes, and orientations. 
     The surface features  70 ,  72  may be placed strategically along the curves of the tube  60  to maximize efficiency of heat exchange without significantly decreasing or disrupting the flow rate or pressure of the fluid within the tube  60 . For example, the first surface features  70  may be located along the inside of the first curve  62 , and the second surface features  72  may be located along the inside of the second curve  64 . In other words, at the first curve  62  of the tube  60 , the surface features are on the radially-inward inner surface of the tube  60 , e.g., the portion of the tube  60  that is closer to the center point of the first curve  62 . This would be the right-hand side of the inner surface  68  at the first curve  62 , as looking at the orientation of  FIG. 5 . As the tube  60  curves in an opposite direction at the second curve  64 , the first surface features  70  are no longer on that side of the tube  60 , but are on the opposite side of the tube  60 . In other words, at the second curve  64  of the tube  60 , the surface features are on the radially-inward inner surface of the tube  60 , e.g., the portion of the tube  60  that is closer to the center point of the second curve  64 . 
     Said another way, the first curve  62  is curved in a first direction, with an inside of the first curve defined by a first portion  81  of the inner surface  68 , and an outside of the first curve defined by an opposing second portion  82  of the inner surface  68 . The second curve  64  is curved in a second direction opposite the first direction, with an inside of the second curve  64  defined by a third portion  83  of the inner surface  68 , and an outside of the first curve defined by an opposing fourth portion  84  of the inner surface  68 . The surface features  70  may be located at the first portion  81 , and the surface features  72  may be located at the third portion  83  such that the surface features are provided along the inside of each curve  62 ,  64 . The second portion  82  and fourth portion  84  may be smooth, e.g., not provided with such surface features. The first portion  81  is located opposite the second portion  82  relative to a centerline of the tube  60 , and likewise the third portion  83  is located opposite the fourth portion  84  relative to the centerline. 
     In this embodiment, the surface features  70 ,  72  create a tube  60  with internal surface roughness that is greater on the inside of the curves of the tubes compared to the outside of the curves. The inner surface  68  at the inside of the curves  62 ,  64  may be provided with the respective surface features  70 ,  72 , while the inner surface  68  at the outside of the curves  62 ,  64  may not be provided with such surface features. In one embodiment, the inner surface  68  at the outside of the curves  62 ,  64  is smooth with no such surface features such as projections or the like extending toward the interior of the tube  60 . In another embodiment, the inner surface  68  at the outside of the curves  62 ,  64  is provided with surface features that are smaller in number or size than the surface features  70 ,  72  of the inner surface  68  at the inside of the curves  62 ,  64 . 
     These surface features  70 ,  72  may be manufactured via additive manufacturing, as described above. The manufacturing of the surface features  70 ,  72  via additive manufacturing provides the ability to tailor the surface roughness at a granular, micro level. This allows the heat exchanger to be tailored with surface features that increase the efficiency of the heat exchanger without decreasing the fluid flow or pressure. The surface features  70 ,  72  can be positioned in locations where heat exchange may be lacking, and thus additional surface area of the material of the tube  60  can increase the heat exchanged in those regions. 
     Rather than, or in addition to, the inner surface  68  being provided with the surface features, the outer surface  66  can be provided with surface features.  FIG. 6  illustrates an embodiment in which the inner surface  68  is smooth and has no surface features, and the outer surface  66  is rough in regions provided with surface features  70 ,  72 . In other words, the surface features  70 ,  72  are now illustrated as extending outwardly from the outer surface  66  at the respective curves  62 ,  64 . Thus, the fluid (e.g., ambient air, etc.) flowing over the outer surface  66  directly contacts the surface features  70 ,  72 , instead of the embodiment of  FIG. 5  in which the fluid within the interior of the tube  60  directly contacts the surface features  70 ,  72 . The embodiment of  FIG. 6  may be chosen when manufacturing the heat exchanger to improve the heat exchange between the outer fluid (e.g., ambient air) and the outer surface  66  in regions where such improved heat exchange is desired. 
     While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms encompassed by the claims. The words used in the specification are words of description rather than limitation, and it is understood that various changes can be made without departing from the spirit and scope of the disclosure. As previously described, the features of various embodiments can be combined to form further embodiments of the invention that may not be explicitly described or illustrated. While various embodiments could have been described as providing advantages or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those of ordinary skill in the art recognize that one or more features or characteristics can be compromised to achieve desired overall system attributes, which depend on the specific application and implementation. These attributes can include, but are not limited to cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. As such, to the extent any embodiments are described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics, these embodiments are not outside the scope of the disclosure and can be desirable for particular applications.