The disclosure relates to heat exchangers, in general, and more particularly, to a recuperator employing an additively manufactured porous metal.
Transferring energy or heat from one fluid stream to another is something common to a variety of industries. A heat exchanger is used for transferring heat between fluids. A recuperator is a type of heat exchanger that is usually fitted in the exhaust hot gases of a gas turbine engine to pre-heat compressed air prior to entry into the combustor to reduce fuel consumption and increase efficiency.
In a first aspect, a porous heat exchanger includes a core comprising a single piece component extending axially. The core defines a first air inlet for a first fluid, a first air outlet for the first fluid, a second air inlet for a second fluid, and a second air outlet for the second fluid flow. The first fluid flows into the core from the first air inlet through a first fluid channel and flows out of the core through the first air outlet, and the second fluid flows into the core from the second air inlet through a second fluid channel and flows out of the core through the second air outlet. The core also includes a plurality of solid material sheets having a length that extends in the axial direction, and a plurality of porous material sheets having a length that extends in the axial direction, the porous material sheets disposed alternately with the plurality of solid material sheets so each porous material sheet has an adjacent solid material sheet on each side defining one of the first fluid channel for a flow of the first fluid or the second fluid channel for a flow of the second fluid. Heat transfer occurs between the first fluid in the first fluid channel and the second fluid in the second fluid channel.
In a second aspect, a modular additively manufactured porous heat exchanger includes a plurality of additively manufactured porous heat exchangers arranged so that an outlet of a first heat exchanger is in fluid communication with the inlet of a second heat exchanger.
In a third aspect, a porous heat exchanger includes a plurality of flow channels stacked in a stackwise direction to define a heat exchanger core. Each flow channel includes a first sheet, a porous flow layer formed as one-piece with the first sheet, a second sheet formed as one-piece with the porous flow layer, the second sheet also forming the first sheet of an adjacent flow channel, a hot flow path inlet and a hot flow path outlet each in fluid communication with a first portion of the plurality of flow channels, and a cold flow path inlet and a cold flow path outlet each in fluid communication with each cannel of the plurality of flow channels that are not part of the first portion of the plurality of flow channels.
In a fourth aspect, a method of producing a heat exchanger includes forming a plurality of flow channels by a forming a plurality of flow channels by a 3D printer employing a continuous additive manufacturing process in one-piece. The flow channels are stacked in a stackwise direction. The 3D printer settings are adjusted to create an open-cell porous structure, each flow channel including a first sheet, a porous flow layer formed as one-piece with the first sheet, a second sheet formed as one-piece with the porous flow layer, the second sheet also forming the first sheet of an adjacent flow channel, a hot flow path inlet and a hot flow path outlet each in fluid communication with a first portion of the plurality of flow channels, and a cold flow path inlet and a cold flow path outlet each in fluid communication with each channel of the plurality of flow channels that are not part of the first portion of the plurality of flow channels.
To easily identify the discussion of any particular element or act, the most significant digit or digits in a reference number refer to the figure number in which that element is first introduced.
Micro Gas Turbines are small combustion gas turbines with power outputs ranging from approximately 30 kW to over 200 kW. These gas turbines are generally inefficient. A recuperator may be used to boost the efficiency of these machines by utilizing some of the waste heat from the gas turbine to pre-heat air before it enters the compressor.
In general, effective heat transfer requires maximizing surface area per unit of volume as heat exchanged is directly proportional to a total surface area of the heat exchanger. Typical recuperators employ thin, wavy corrugated fin sheets to increase surface area. Another concept to increase surface area in a recuperator is to use open pore metal foams.
Both of these solutions present significant challenges and limitations. Manufacturing such metal foams or fins places significant limitations on the possible design or layout of the recuperator. Additionally, the area augmenting feature, whether it be a metal foam or fin, must be in perfect contact with the flow channels to avoid decreases in performance. This requires a number of high precision weld or braze joints. Any failure of these braze or weld joints results in the decreased thermal efficiency along with the possibility of leaks.
Porous materials may be used in heat exchangers to increase surface area. Metal foams having a certain amount of porosity have been previously used in heat exchanger technology. The metal foams are generally created by injecting gas into a still-molten metal liquid. As the metal cools, the voids are left resulting in a foam. However, metal foams present many challenges. One such problem is creating metal foams of consistent quality with defined parameters.
With the advent of additive manufacturing, the ability to print porous metals is being developed. The issues described above using metal foams may be remedied by employing additive manufacturing to create uniform porous metals with predictable porosities that can be tuned to suit the application. The present inventors recognize that by utilizing additive manufacturing the porous surfaces of the heat exchanger may be printed integral with the solid flow channels.
Additive Manufacturing of components includes a wide range of materials and process techniques such as powder bed methods. Powder bed methods include selective laser melting (SLM), Selective Laser Sintering, and electron beam melting which use a laser as the power source to fuse the powdered material by aiming the laser automatically at points in space defined by a 3D model, binding the material together to create a solid structure. Binder jetting is another AM process in which a printhead selectively deposits a liquid binding agent onto a layer of powdered material to fuse the material together, creating the solid structure.
Starting on the left side of
The heat exchanger 200 comprises a core that is a single piece. The single-piece component includes both solid and porous portions. Additive manufacturing methods may be employed to produce the single piece component. The core extends axially having a first end 210 and a second end 212 that defines a fluid passageway, the fluid passageway extending between the first end 210 and the second end 212 on an interior of the core. A fluid flows from the first end 210 through the fluid passageway to the second end 212 or from the second end 212 through the fluid passageway to the first end 210. The fluid may comprise a flow of air of varying temperatures. However, in some embodiments, the fluid may also be a liquid.
The heat exchanger 200 includes a plurality of material sheets stacked in a stackwise direction of that define a plurality of flow channels. The stacked material sheets are formed as one piece so that one single contiguous component is produced. The plurality of material sheets alternate between a solid sheet 214 and a porous flow layer 216. Thus, the porous flow layer 216 has an adjacent solid sheet 214 on both sides so that a flow channel is created. A fluid may flow into the flow channel through an inlet, flow through the flow channel created within the porous flow layer 216, and flow out through an outlet.
As shown in
As stated above, the heat exchanger 200, shown in
For example,
The heat exchanger 300 of
A porous material, as defined for the purposes of this disclosure, includes an open-cell pore structure such that there are no enclosed pockets within the material. Thus, the open-cell pore structure of the porous flow layer 216, 316 allows a fluid flow to pass uninterrupted through the porous material from the first end 210 to the second end 212. The porous flow layer 316 as shown in
In an embodiment, the porous material comprises a metallic material such as a nickel-based alloy or a stainless steel. In a further embodiment, the porous flow layer 216, 316 may include a ceramic material, such as silicon carbide. While ceramic materials are poor heat conductors, an advantage of utilizing ceramic materials in the heat exchanger 200, 300 as compared to metallic materials is that the overall weight of the heat exchanger 200, 300 would be much less than a heat exchanger that comprises only a metallic metal. As a heat exchanger, such as the recuperator 212 in
In an embodiment, as shown in
In an embodiment, the heat exchanger 200, 300, 400 may be a modular heat exchanger such that it comprises a plurality of single piece heat exchangers 200, 300, 400 so that the outlet of a first heat exchanger is in fluid communication with the inlet of a second heat exchanger. One advantage to having a series of repeated heat exchanger sections is that if one section, or single piece heat exchanger fails, (i.e., an inlet section to a heat exchanger typically experiences a failure first due to the stress the material experiences having an extremely hot fluid entering the heat exchanger) only the section experiencing the failure can be removed and replaced.
Additive manufacturing of porous materials allows the creation of a uniform porous flow layer 216, 316. These porous materials have a more predictable porosity than that of metal foams, for example, and thus can be tuned to suit the application. The chart 700, shown in
In an embodiment, the porous flow layer 216, 316 comprises a plurality of additively manufactured layers, the layers comprising a plurality of adjacent unit cells wherein each unit cell includes a lattice structure so that the pores are in fluid communication with one another. An embodiment of a unit cell comprising a lattice structure may be seen in
A method of producing a porous heat exchanger is also presented. The method includes the steps of forming a plurality of flow channels by a 3D printer employing a continuous additive manufacturing process in one-piece, the flow channels stacked in a stackwise direction. Each of the flow channels may be arranged as previously described. In contrast to forming the porous flow layer 216, 316 of the flow channels 302 utilizing a unit cell porous structure as discussed above, the porous flow layer 216, 316 may be formed by adjusting the laser settings on the 3D printer to create a porous open-cell structure.
An additively manufactured heat exchanger enables the ability to create a uniform ultra-high surface area flow layer comprising a porous material. By decreasing porosity, surface area may be increased, improving heat transfer and the efficiency of the heat exchanger. A porous flow layer comprising a lattice structure forms a particularly large surface area. An embodiment of an additively manufactured porous heat exchanger comprises a ceramic material porous material. While ceramic materials decrease the heat transfer ability of the heat exchanger as compared to a metallic heat exchanger, the ceramic heat exchanger allows inlet temperatures to increase beyond what is possible now and provides a lower weight option.