TWI839736B - Triply periodic minimal surface heat exchangers with equal or different characteristic diameters - Google Patents

Abstract

A Triply Periodic Minimal Surface (TPMS) structure is utilized and designed in a new structure of heat exchanger. This new TPMS heat exchanger main body is composed of a hot flow inlet, a hot flow exit, a cold flow inlet, a cold flow exit, and a TPMS structure forming two independent channels to allow these two fluid flow in a 3D corrugated structure channel without mixing together. Because of its complex geometry, it is made by either additive manufacturing technique or lost wax technique successfully. Therefore, this structure can be applied as a heat exchanger to enhance the heat transfer efficiency.

The heat transfer coefficient, fluid contact area and temperature difference are the most important factors for the heat exchanger rate; The TPMS structure can be controlled by the characteristic diameter of the two fluid pipelines, and by adjusting the same or two different characteristic diameters, the relative space volume and surface are of the two fluids can be adjusted, that is the new strategy for the efficiency of the heat exchanger to be further improved.

As the surface-to-volume ratio is increased by more than 2-3 times based on the TPMS structure, and due to its good structural characteristics, it is possible to design a relatively thinner tube thickness, minimized material to weight ratio and high strength-to-weight ratio, so the efficiency of the heat exchanger is greatly improved. Due to the inherent structural strengthening properties, the pressure (at the same temperature) that can be tolerated is much higher than that of traditional heat exchangers, while maintaining low weight and smaller volume.

According to the design requirements, the heat exchanger can define different shells and adopt different TPMS structures. Among all TPMS structures, five TPMS structures can be utilized for heat exchanger, names are Gyroid, Schwarz Primitive, Diamond, Lidinoid, and SplitP. For example, gyroid has two coupling volumes separated by Gyroid wall, that two coupling gyroid can be utilize for heat exchanger with closing the unwanted holes. This innovative design adopts the design method based on 3D printing, in which the hot flow channel and the cold flow channel maynot be on the same plane to form a design with a 90-degree, and one of the flow channels can also be further designed by two intersecting 90 degrees. It can be matched with the angle of special needs to achieve a highly flexible three-dimensional import and export orientation design, which is conducive to the deployment and full use of space.

Description

Design of three-dimensional minimum surface structure heat exchanger

Heat Exchanger Design

A heat exchanger is a system used to transfer heat between two or more fluids. Heat exchangers are used in cooling and heating processes. For example, the radiator of a car engine is a heat exchanger. The design of this heat exchanger is to circulate the refrigerant around the engine, heat it, and then flow to the radiator pipe structure of the water tank to exchange heat. The air flows through the radiator structure to discharge the engine waste heat into the atmosphere. The fluids can be separated by solid walls to prevent mixing, or they can be in direct contact. They are widely used in space heating, cooling, air conditioning, power plants, chemical plants, petrochemical plants, refineries, natural gas processing and sewage treatment.

Three-dimensional Triply Periodic Minimal Surface (TPMS)

A three-dimensional periodic minimal surface (TPMS) represents a periodic infinite structure with three independent directions and a surface with zero mean curvature. A three-dimensional periodic minimal surface (TPMS) is a biomimetic structure with many advantages in the fields of engineering and biomedicine. From the perspective of recreating itself in 3D, the continuous mean curvature of the minimal surface is zero, that is, the sum of the principal curvatures at each point is zero. So far, many TPMS structures have been discovered and studied, most of which are in the field of structure, and other fields are just beginning. This patent is based on the study of applying TPMS structures to heat exchangers.

Additive Manufacturing, or 3D Printing

The name Additive manufacturing (AM) refers to the manufacturing process by adding materials as continuous material deposition layer by layer; it is also called 3D printing, which is a synonym for additive manufacturing.

Additive manufacturing is the construction of 3D objects from computer-generated graphics (CAD) models or digital 3D models. The term "3D printing" can refer to various processes in which materials are deposited, connected or solidified under computer control to create 3D objects, where materials are added together (such as plastic, liquid or powder particles are fused together), usually layer by layer.

The history of heat exchangers (HEX) dates back to the 1880s, with their primary application being in the food and beverage industry. It is generally believed that the first documented patent for a plate heat exchanger was granted to Albrecht Dracke of Germany in 1878. However, the first modern and commercial use of heat exchangers can be found in the early 1900s. The classic example of a heat exchanger is found in an internal combustion engine, where a circulating fluid called the engine refrigerant flows through a radiator pipe structure, exchanging heat with air flowing through the radiator pipes, cooling the refrigerant and transferring heat to the incoming air.

Another example is a heat sink, which is a passive heat exchanger that transfers heat generated by electronic or mechanical equipment to a fluid medium, usually air or liquid coolant.

Heat exchangers affect the overall efficiency of a plant, and with the development of industry, the demand for more efficient and improved heat exchangers is increasing. The design of heat exchangers has been constantly improving for centuries. There are different types of heat exchangers, such as Shell & Tube, Plate, Plate & Frame, Plate & Shell, etc. Plate and Frame heat exchangers were widely used in the past because of their easy maintenance and high efficiency. But the basic design concept of all types of heat exchangers is the same.

Plate Heat Exchanger (PHE)

A plate heat exchanger (PHE) is a heat exchanger that uses metal plates to transfer heat between two fluids. It consists of a series of thin plates, two types of thin plates are staggered on a frame, and the space between each adjacent staggered plate is exposed to the same fluid. Compared with traditional heat exchangers, plate heat exchangers have a major advantage because the fluid flows spread out on the plates, so the fluid is exposed to a larger surface area. These thin plates have corrugated flow channels, which increases strength and helps promote turbulent flow. In order to obtain the correct liquid velocity and appropriate pressure drop, the thin plates can be placed in a series of channels.

Three-dimensional Triply Periodic Minimal Surface (TPMS) - To date, many TPMS structures have been discovered and are being studied. The surface described by Schwarz in 1865 was the first example of TPMS, followed by the surface described by his colleague Neovius in 1883. Alan Schoen (NASA scientist) described another 12 TPMS in 1970. TPMS, as a widely used lightweight material, has broken the limitations in addition to structure and can also be applied to many fields, such as sound absorption, battery electrodes, catalyst carriers and other technical fields.

Three-dimensional minimum surface structure heat exchanger design (TPMS Heat Exchanger Design)

The triple-periodic (i.e., three-dimensionally repeatedly extended) minimal surface (TPMS) structure (similar to a honeycomb structure) has a feature - that is, there is a pair (two groups) of 3D infinitely extended pipes that are not interconnected. Therefore, the feature of not being interconnected can be used to transform it into an innovative three-dimensional minimal surface structure heat exchanger design (TPMS Heat Exchanger Design) so that the hot fluid and the cold fluid will not mix together. The main feature of this creation is to apply the TPMS structure to the new field of heat exchanger design. This innovative design can be used in heat exchangers and thermal management equipment to achieve more efficient heat transfer.

Compared with the plate heat exchanger design, the TPMS heat exchanger has the following advantages:

(1) Due to the high structural strength of TPMS, it can withstand higher pressure than traditional heat exchangers at the same temperature.

(2) Due to the high curved surface characteristics of TPMS, its contact surface area is about twice that of a general plate heat exchanger;

(3) Due to the high curved surface characteristics of TPMS, the fluid is more likely to generate turbulence in the flow, which prevents the fluid from generating boundary layer growth in flat plate flow and the heat transfer coefficient decreases with length, reducing the overall heat transfer efficiency. That is, the TPMS heat exchanger can have a higher heat transfer coefficient.

(4) Due to the high structural strength of TPMS, under the same operating pressure requirement, the overall tube wall can be designed to be thinner, which can reduce thermal resistance and thus achieve greater heat transfer efficiency.

The above four points can more clearly demonstrate the outstanding characteristics of this invention's three-dimensional minimum surface structure heat exchanger (TPMS Heat Exchanger), which will have a heat transfer efficiency nearly 5 times higher than the previously so-called advanced plate heat exchanger, and has the potential to largely replace high heat transfer efficiency or high heat transfer devices in the future.

However, the innovative heat exchanger concept structure design of TPMS heat exchanger can only be realized through laminated manufacturing technology. For example, there are two coupling bodies separated by a structural wall in the Gyroid heat exchanger. The two cross structures can be designed into a heat exchanger by closing the unnecessary holes. These complex heat exchanger structures can currently be achieved by laminated manufacturing methods.

This invention is a new TPMS heat exchanger design as shown in Figure 1. This three-dimensional periodic minimum surface (TPMS) structure includes an inlet and an outlet for hot fluid and an inlet and an outlet for cold fluid. The two fluids in the TPMS structure inside the heat exchanger just become different flow channels that are 3D intertwined with each other but are independent and do not mix with each other. Therefore, the heat exchanger has the conditions to achieve heat transfer only through the tube wall. Since the fluid contact area, heat transfer coefficient and temperature difference are the most important factors in the heat exchange rate. The following is the governing equation (1) that describes the convective heat transfer phenomenon of a fluid: q = h _c ． A． ΔT (1)

Where q is ^the heat transfer per unit time (W/hr) ; A is the heat transfer surface area ( m2 ) ; ΔT is the temperature difference between the heat transfer surface and the fluid (℃) ; hc _is the convection heat transfer coefficient ( W/m2 ^℃ ).

Based on the calculation of convective heat transfer above, it is estimated that for a heat exchanger of approximately the same volume, the surface area of the new TPMS heat exchanger created by this invention is increased by about 2-3 times, and the heat transfer coefficient can be increased by about 2-3 times by replacing the laminar flow field with the turbulent flow field. In addition, the thickness can be reduced to reduce thermal resistance, so the newly created heat exchanger will have a heat transfer gain or efficiency increase of about 5-10 times.

The present invention emphasizes that the TPMS structure can be based on the characteristic diameter (Characteristic Diameter, d _C ) of the two fluid pipelines. By adjusting the characteristic diameters to be the same ( d _C1 = d _C2 ) or different ( d _C1 ≠ d _C2 ), the relative spatial size of the two fluids can be adjusted, that is, the efficiency of the heat exchanger can be further improved; generally, TPMS can increase the surface area ratio by more than 2-3 times compared with the plate heat exchanger under the same diameter, and due to its good structural characteristics, a relatively thinner tube wall thickness can be designed, the material weight is minimized, and the strength-to-weight ratio is high, thereby significantly improving the efficiency of the heat exchanger.

Due to the inherent structural reinforcement characteristics, the pressure that can be borne (at the same temperature) is much higher than that of traditional heat exchangers, while maintaining low weight and smaller volume. The heat exchanger can define different shells and adopt different TPMS structures according to design requirements. Among all TPMS structures, there are 5 TPMS structures that can be used for heat exchangers, namely Gyroid, Schwarz Primitive, Diamond, Lidinoid and SplitP.

100 : Main body of heat exchanger

101 : Inlet connector of hot fluid

102 : Exit connector of hot fluid

103 : Inlet connector of cold fluid

104 : Exit connector of cold fluid

105 : Inlet chamber of hot fluid

106 : Exit chamber of hot fluid

107 : Inlet chamber of cold fluid

108 : Exit chamber of cold fluid

110 : Gyroid structure

111 : Inlet passages of hot fluid channel

112 : Exit passages of hot fluid channel

113 : Inlet passages of cold fluid channel

114 : Exit passages of hot fluid channel

120 : Characteristic Diameter of Channel Hole

201 : Blockage plate in hot flow inlet

202 : Blockage plate in hot flow exit

203 : Blockage plate in cold flow inlet

204 : Blockage plate in cold flow exit

300 : Cone connector

301 : Pipe connector

302 : Cone transition to rectangle connector

Figure 1. is a cross-sectional diagram of a Gyroid (a type of three-dimensional minimal surface structure) heat exchanger design.

Figure 2(a) shows the cross section of the Gyroid structure with two channel holes of the same characteristic diameter, and Figure 2(b) shows the cross section of the Gyroid structure with two channel holes of different characteristic diameters.

Figure 3(a) shows that, like a general shell and tube heat exchanger, the heat fluid can enter the heat exchanger in opposite directions (Counter Flow) or in the same direction (Parallel Flow) as shown in Figure 3(b).

Figure 4. A Gyroid structure that can be used in a heat exchanger TPMS structure.

Figure 5. The second Schwarz Primitive structure that can be used for heat exchanger TPMS structure.

Figure 6. A triple diamond structure that can be used in a heat exchanger TPMS structure.

Figure 7. A four-lidinoid structure that can be used in a heat exchanger TPMS structure.

Figure 8. This is the fifth SplitP structure that can be used in the heat exchanger TPMS structure.

Figure 9(a) shows one of the heat exchanger TPMS structures. Gyroid has two coupling bodies separated by a structural wall. Figure 9(b) shows the orifice plugging plates 201, 202 that close the holes in the hot fluid direction, and the orifice plugging plates 203, 204 that close the holes in the cold fluid direction.

Figure 10. is a cross-sectional isometric view of a square-shaped TPMS applied to a heat exchanger, and a TPMS structure (Gyroid) heat exchanger with the smallest curved surface.

Figure 11. An isometric view of a TPMS Gyroid heat exchanger with two different channel hole characteristic diameters, and a square design Gyroid minimum surface structure heat exchanger.

Figure 12(a) is an isometric view of a cylindrical structure (Gyroid) minimum surface structure heat exchanger, and the top view of two cylindrical structure (Gyroid) heat exchangers with different hole sizes is shown in Figure 12(b).

Referring to FIG. 1, a cross-sectional diagram of the Gyroid heat exchanger design is shown. The design of the Gyroid minimum surface structure heat exchanger is similar to the external geometric shape of the traditional heat exchanger, but the internal structure is different, wherein the main heat exchanger structure is changed to an innovative TPMS structure. The heat exchanger body 100 is a structure 110 with a Gyroid inside. The heat exchanger body structure has two inlets and two outlet channels, namely, a hot fluid inlet connector 101 , a hot fluid outlet connector 102 , a cold fluid inlet connector 103 , and a cold fluid outlet connector 104. The two fluid apertures of the TPMS structure (Gyroid) are basically the same. In the operation of the heat exchanger, the fluid entering from the hot fluid inlet connector 101 first reaches a buffer chamber 105 , passes through the hot flow inlet channel 111 in the TPMS structure, and then flows into the hot fluid outlet steady flow chamber 106 in a diagonal direction after heat exchange in the adjacent cold flow inlet channel 112 of the TPMS structure, and finally flows out of the heat exchanger from the hot fluid outlet connector 102 ; the cold fluid flows in a similar manner, the fluid entering from the cold fluid inlet connector 103 first reaches a buffer chamber 107 , passes through the cold flow inlet channel 112 in the TPMS structure, and then flows into the cold fluid outlet steady flow chamber 108 in a diagonal direction after heat exchange in the adjacent hot flow inlet channel 111 of the TPMS structure. , and finally flows out of the heat exchanger from the cold fluid outlet connector 104 ; the TPMS structure of these two fluids in the heat exchanger just becomes different flow channels that are 3D intertwined with each other but are independent and do not mix with each other, so that the heat exchanger can achieve heat transfer only through the pipe wall.

Referring to FIG. 2 , another feature of the present invention is that the Gyroid structure can adjust the area size of the two independent flow channels during engineering design according to the actual need for heat dissipation. The area size can be determined by the characteristic diameter (Characteristic Diameter) 120 d _C1 and d _C2 of the two channel holes of the Gyroid structure. When d _C1 = d _C2 , as shown in FIG. 2 (a), the cross-sectional area size of the two independent flow channels is the same; when d _C1 ≠ d _C2 , as shown in FIG. 2 (b), two independent but different-sized flow channel spaces can be formed, which is beneficial to the needs of different flow sizes or different fluids (such as separate liquid and gas flow channels). The two-phase efficient heat exchanger can adopt two mixed volumes of different sizes. It can be clearly seen from the figure that one of the flow channels has a larger flow channel space with a large characteristic diameter d _C1 , while the other flow channel has a smaller flow channel space with a small characteristic diameter d _C2 .

As shown in FIG9(a), the TPMS structure heat exchanger has two separated coupling bodies, that is, two coupling structures can be used for the heat exchanger structure, but the unnecessary holes need to be closed; the plugging plates 201, 202 that close the holes in the direction of the hot fluid, and the plugging plates 203, 204 that close the holes in the direction of the cold fluid; the plugging plates on the four closed sides allow the heat exchanger design to guide the flow of the hot fluid and the cold fluid, but do not allow them to mix with each other inside, and the completely isolated flow path can only cause heat transfer from the adjacent wall surface. This is the necessary condition for the above-mentioned heat exchanger.

FIG. 10 is an isometric cross-sectional view of a TPMS heat exchanger, which has a square-designed structure (Gyroid) minimum curved surface structure heat exchanger, similar to FIG. 9 (a). The diameters of the two fluid channel holes of the TPMS structure (Gyroid) are basically the same. The same device is installed in the heat exchanger body shell in this embodiment, but the two different channel hole characteristic diameters ( d _C1 ≠ d _C2 ) in the diagonal fluid flow, and its cross-sectional shape is shown in FIG. 2 (b), and the rectangular cone transition circular tube 300 with different shapes at both ends. The two pairs of connecting circular tubes 301 can connect the inlet and outlet of the hot fluid and the inlet and outlet of the cold fluid.

FIG. 11 is an isometric cross-sectional view of a TPMS gyroid heat exchanger, which has a square heat exchanger body shell , and the interior is also a gyroid minimum curved surface heat exchanger, similar to FIG. 10 , installed in the heat exchanger body shell, providing two different channel hole characteristic diameters ( d _C1 ≠ d _C2 ) in the diagonal fluid flow, and its cross-sectional shape is shown in FIG. 2( b ), and its two pairs of connecting circular tubes 301 can connect the inlet and outlet of the hot fluid with the inlet and outlet of the cold fluid.

FIG12 is a cylindrical structure (Gyroid) minimum curved surface structure heat exchanger with a circular tube with different shapes at both ends transferred to a rectangular tube 302 and a circular tube-shaped inlet and outlet design transferred to a rectangular tube 300 , as shown in the isometric view of FIG12(a), and the cylindrical structure (Gyroid) heat exchanger with two different hole sizes inside is shown in the top view of FIG12(b). This embodiment further demonstrates a design method based on 3D printing, wherein the hot flow channel and the cold flow channel are not on the same plane, but are designed to cross 90 degrees, and one of the flow channels can also be further designed by two cross 90 degrees, which is to meet the special required angles and can achieve a highly flexible three-dimensional inlet and outlet orientation design structure, which helps to allocate space to increase the full use of corner space.

100: Main body of heat exchanger

101: Inlet connector of hot fluid

102: Exit connector of hot fluid

103: Inlet connector of cold fluid

104: Exit connector of cold fluid

105: Inlet chamber of hot fluid

106: Exit chamber of hot fluid

107: Inlet chamber of cold fluid

108: Exit chamber of cold fluid

110: Gyroid structure

111: Inlet passages of hot fluid channel

112: Exit passages of hot fluid channel

113: Inlet passages of cold fluid channel

114: Exit passages of hot fluid channel

Claims (6)

A newly designed three-dimensional minimal surface (TPMS) structure heat exchanger is characterized by: an outer shell, two pairs of heat exchanger inlets and outlets for hot fluid and cold fluid, and a three-dimensional minimal surface (TPMS) structure design in the outer shell, the structure is separated into two volume spaces, and a cold flow inlet and a cold flow outlet with a cold flow channel (volume space) can be provided, and a hot flow inlet and a hot flow outlet with a hot flow channel (volume space), and the cold flow and the hot flow flow along their respective volume path channels are separated by a 3D continuous wall of the TPMS structure and maintained The channel hole diameter can prevent mutual mixing. These two volume spaces and the outer shell form a special heat exchanger, and the connecting pipe design connects the external cold flow and hot flow pipelines to meet the customer's heat transfer needs between the same or different fluids, the same phase (Phase) or different phase fluids, and fluids of different temperatures. Its operation is similar to that of traditional parallel flow or counter-flow heat exchangers; because this new heat exchanger design provides perfect structural integrity, high induced turbulence and a larger contact surface area, its heat exchanger efficiency is greatly improved, and it has been verified according to experimental results. According to the three-dimensional minimum surface (TPMS) structure heat exchanger described in item 1 of the patent claim, it is characterized by a TPMS structure in which the internal cold fluid volume and hot fluid volume are the same fluid volume, that is, the channel hole characteristic diameters of the cold fluid volume and the hot fluid volume are the same, but not limited to the same channel hole characteristic diameter size, that is, the channel hole diameter size of the cold fluid volume and the hot fluid volume is the same or different, that is, the space size of the two fluid volumes can be the same or different. According to the first item of the patent application, the structure of the three-dimensional minimum curved surface (TPMS) structure heat exchanger can be composed of five three-dimensional infinite extension structures, such as Gyroid, Schwarz primitive, Diamond, Lidinoid, and SplitP. The channel hole shapes can include square, spherical, and cylindrical shapes, which are the main surface locations for heat transfer. According to the three-dimensional minimum surface (TPMS) structure heat exchanger described in item 1 of the patent claim, the TPMS structure is made by additive manufacturing (AM), but is not limited to the AM manufacturing process. Other manufacturing processes, such as lost foam casting process, policast process, wax casting, etc., can also provide TPMS structural parts. As described in the first item of the patent application, the three-dimensional minimum curved surface (TPMS) structure heat exchanger design can be easily changed in relative position and flow direction, and the design features that can be included are the design that the cold volume flow and the hot volume flow can have the same flow direction, cross flow direction and opposite flow direction. For example, the three-dimensional minimum curved surface (TPMS) structure heat exchanger design described in Item 1 of the patent application can be manufactured using a design method based on 3D printing, in which the hot flow channel and the cold flow channel may not be on the same plane, and may be designed to cross 90 degrees or at other angles, and one of the flow channels may be further designed to cross two 90 degrees or at other angles, which can be matched with special required angles to achieve a highly flexible three-dimensional inlet and outlet orientation design, which is conducive to the allocation and full use of space.