Patent Application
20190107343
This application relates generally to heat exchangers, and specifically to polymer heat exchangers.
Heating, ventilation, and air conditioning (HVAC) residential and rooftop systems typically use round tube plate fin (RTPF) or microchannel (MCHX) heat exchangers. These types of heat exchangers are not suitable for low Global Warming Potential (GWP), low pressure refrigerants, due to heat exchanger size and pressure drop constraints of these types of refrigerants. Also, the weight associated with metallic heat exchangers is a key concern in transport and aerospace applications. Polymers can be used to make heat exchangers that mitigate these shortcomings; however, polymer materials typically have low thermal conductivity.
In one embodiment, a heat exchanger includes a plurality of polymer tubes, each of the plurality of polymer tubes comprised of a functionally graded polymer composite, the functionally graded polymer composite comprising a polymer, and at least one filler material.
In a second embodiment, a heat exchanger wall includes a first side, and a second side opposite the first side, wherein the first side and the second side are comprised of a polymer composite, the polymer composite functionally graded across the heat exchanger wall from the first side to the second side.
In another embodiment, a method of making a heat exchanger includes creating functionally graded polymer plates comprising a polymer composite, and assembling the heat exchanger with the polymer plates.
Using polymers to make heat exchangers results in more versatile heat exchangers, but present unique challenges not presented by other materials. For instance, polymers are not thermally conductive. Filler materials can be mixed into polymer to increase the thermal conductivity, but the resulting polymer mixture's mechanical strength and permeability can be affected by the amount and type of filler used. Different parts or areas of heat exchangers have different thermal conductivity, permeability, and mechanical strength requirements. Thus, creating functionally graded composite polymers tailored to specific parts of heat exchangers addresses these varying needs.
Heat exchanger 10 can be a plate-and-frame heat exchanger, a shell-and-tube heat exchanger, or other appropriate heat exchanger configurations. For example, a plate-and-frame heat exchanger can be used for liquid/liquid or liquid/2-phase heat exchange purposes, has reduced weight, and can be used in a variety of applications, including commercial HVAC chillers, aerospace, and process industry applications. Likewise, a shell and tube heat exchanger, for example, can be used with liquid/liquid or liquid/2-phase heat exchange purposes, and applied in chiller, industrial, food and beverage, or marine applications among others.
In heat exchanger 10 of
In one embodiment, plates 12 are made of a functionally grade polymer composite comprised of a polymer and a filler material. In this embodiment, tubes 14 can be made of a metallic material, or also made of a polymer material. In this embodiment, the polymer composite filler content is varied from high to low within plates 12 of heat exchanger 10, depending on heating and structure needs. The functionally graded polymer composite is described in more detail with reference to
In another embodiment, walls 20 of tubes 14 are comprised of the functionally graded polymer composite material. In
Polymer composite 22 is graded in both axial and radial directions in wall 20. This balances conflicting needs: areas with higher filler 30 content in polymer composite 22 generally have improved thermal conductivity at the expense of mechanical strength and increased porosity. In contrast, areas with lower filler 30 content in polymer composite 22 generally have higher mechanical strength and lower thermal conductivity.
Polymer 28 can be a rigid thermoplastic polymer, an elastomeric polymer, or any other suitable polymer. Examples of suitable rigid thermoplastic polymers include polypropylene, polyamides such as nylon 6, nylon 6/6, nylon 6/12, nylon 11, or nylon 12, polyphthalamide, polyphenylene sulfide, liquid crystal polymers, polyethylene, polyether ether ether ketone, polyether ketone, or other suitable rigid thermoplastic polymers. Examples of suitable elastomeric polymers include ketone fluoroelastomers, polyvinylidene fluoride, polytetrafluoro ethylene, silicones, fluoro silicones, ethylene propylene diene monomer rubber, polyurethane, or other suitable elastomeric polymers. Additionally, co-polymers of these polymers can be used.
Filler 30 should be a material that increases thermal conductivity of polymer 28 when mixed to form polymer composite 22. Filler 30 can be, for example, graphite, graphene, boron nitride, carbon nanotubes, carbon fiber, silicon carbide, silicon nitride, metal (such as elemental copper or aluminum), or other suitable micron or nanoscale materials. Filler 30 can be comprised of more than one of these materials.
In
In step 32, functionally graded polymer composite plates are created. This can be accomplished with fused filament fabrication (FFF). FFF can be used to create structural aerospace parts that are tailored in shape. In a FFF process, filaments of a material (either polymer 28 or polymer composite 22) are melted (step 34), extruded (step 36), fused together (step 38), and solidified into a part with a specific shape (step 40).
In steps 34-36, polymer material, typically in filament form, is melted so that it can then be extruded through a tube, nozzle, or other die of desired shape or cross-section. Extrusion in step 36 can use a single nozzle or a plurality of nozzles loaded with the polymer material, depending on the desired shape. If multiple nozzles are used, then each extrusion nozzle can receive a polymer material that has a different percentage of filler material. For instance, a first extrusion nozzle can receive a neat polymer material, while a second polymer material can receive a composite polymer material (containing filler). Alternatively, each nozzle can receive a composite polymer material containing fillers of different composition and concentrations. This can be tailored depending on the type of heat exchanger being made, and the specific part being formed. If the part requires lower porosity and higher mechanical strength, then the polymer material can contain less filler. In contrast, if the part requires higher thermal conductivity, the polymer material can contain more filler.
Next, in steps 38-40, the extruded polymer material is fused together into the desired shape for the functionally grade polymer composite plate, or other heat exchanger part. The fused polymer strands are then solidified together in step 40, creating a final functionally graded polymer composite plate. Grading the polymer in a perpendicular direction (radial or axial) can be tailored by using multiple extrusion nozzles at once with loading of polymer composite 22 with differing filler 30 contents or different types of fiber 30.
Alternatively, step 32 can be accomplished with other manufacturing methods such as fused filament fabrication (FFF), selective laser sintering, injection molding and its derivatives (such as reaction injection molding), and other types of extrusion or co-extrusion. Depending on the type of polymer used, different methods may be suitable. For example, FFF is suitable for thermoplastics that have a reasonable melting point (e.g., less than about 250 degrees Celsius) and solidify quickly. The heat exchanger is completed in step 42, where the grade polymer plates or parts are assembled into a heat exchanger, for example, heat exchanger 10 of
A heat exchanger made from the method shown in
The method of
The following are non-exclusive descriptions of possible embodiments of the present invention.
A heat exchanger includes a plurality of polymer tubes, each of the plurality of polymer tubes comprised of a functionally graded polymer composite, the functionally graded polymer composite comprising a polymer, and at least one filler material.
The heat exchanger of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components:
The plurality of polymer tubes are configured to receive a first fluid flow stream.
The tubes pass through a plurality of fin plates.
The fin plates are made of a functionally graded polymer composite.
The plurality of fin plates are configured to receive a second fluid flow stream.
Each of the plurality of polymer tubes comprised of the polymer composite contains a gradient of the at least one filler material.
Each of the plurality of polymer tubes comprises a different concentration of the at least one filler material.
The polymer is selected from the group consisting of polypropylene, polyamides, polyphthalamide, polyphenylene sulfide, liquid crystal polymers, polyethylene, polyether ether ether ketone, polyether ketone, ketone fluoroelastomers, polyvinylidene fluoride, polytetrafluoro ethylene, silicones, fluorosilicones, ethylene propylene diene monomer rubber, and polyurethane.
The at least one filler material is selected from the group consisting of graphite, graphene, boron nitride, carbon nanotubes, carbon filler, silicon carbide, silicon nitride, metal, or metallic alloys.
A heat exchanger wall includes a first side, and a second side opposite the first side, wherein the first side and the second side are comprised of a polymer composite, the polymer composite functionally graded across the heat exchanger wall from the first side to the second side.
The heat exchanger wall of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components:
The polymer composite is comprised of a polymer and at least one filler material.
The at least one filler material comprises fibers, the fibers extending beyond the first side of the wall.
The polymer composite is functionally graded from a high concentration of the at least one filler material to a low concentration of the at least one filler material.
The polymer composite is functionally graded from a high concentration of the at least one filler material at a center part of the wall to a low concentration of filler material at an exterior part of the wall.
The polymer composite is functionally graded from a low concentration of the at least one filler material at a center part of the wall to a high concentration of the at least one filler material an exterior part of the wall.
The polymer composite is functionally graded from a high concentration of the at least one filler material to a low concentration of the at least one filler material along a flow path inside the wall.
A method of making a heat exchanger includes creating functionally graded polymer plates comprising a polymer composite, and assembling the heat exchanger with the polymer plates.
The method of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components:
Creating functionally graded polymer plates comprises the steps of melting filaments of a polymer material, extruding strands of the polymer material, fusing together the strands, and solidifying the strands of the polymer material into a part.
Extruding strands of the polymer material comprises using a plurality of extrusion nozzles loaded with the polymer material, and wherein each of the plurality of extrusion nozzles extrudes a different grade of the polymer material.
Creating functionally graded polymer plates comprises fused filament fabrication, selective laser sintering, or injection molding.
While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.
