Patent Publication Number: US-2021190441-A1

Title: Additively manufactured spiral diamond heat exchanger

Description:
FOREIGN PRIORITY 
     This application claims priority to European Patent Application No. 19461621.5 filed Dec. 23, 2019, the entire contents of which is incorporated herein by reference. 
     FIELD 
     The present invention described herein relates to a heat exchanger with a spiral diamond core which is suitable for printing by additive manufacturing techniques. 
     BACKGROUND 
     Heat exchangers comprising a diamond channel core improve on conventional plate-fin heat exchangers due to the fact that all internal core faces are primary transfer surfaces. A diamond channel core is suitable for counter flow and parallel flow type heat exchangers. This core type is relatively simple to print by additive manufacturing (AM) techniques. However, it can be difficult to print the entire heat exchanger because the diamond channel core requires a complex manifold which is difficult to print. Printing issues arise because a design must meet face orientation restrictions specific to AM technology. When there are limitations to the printing of the heat exchanger, either complex distribution tanks or internal core turnround structures must be designed to compensate for this to allow for proper fluid distribution. It would therefore be useful to provide a diamond core that overcomes these problems by providing attachments to tanks and ports that are suitable for AM. 
     SUMMARY 
     According to a first aspect there is a provided a method for forming a heat exchanger. The method comprises forming a central channel and a core section. Forming the central channel comprises forming a channel that runs along a longitudinal axis. A division is formed in the central channel such that the central channel is divided into a first section and a second section, wherein the first section is in fluid communication with a first inlet of the central channel and the second section is in fluid communication with a second inlet of the central channel. Forming the core section comprises forming a first spiral channel and a second spiral channel. The first end of the first spiral channel is in fluid communication with the first section of the central channel. The first spiral channel has a diamond cross-section and the first spiral channel spirals in the plane perpendicular to the longitudinal axis of the central channel. The first end of the second spiral channel is in fluid communication with the second section. The second spiral channel has a diamond cross-section and the second spiral channel spirals in the plane perpendicular to the longitudinal axis of the central channel. The second spiral channel is stacked on top of the first spiral channel such that the core has a diamond lattice cross-section. 
     Optionally there is provided at least one layer of first spiral channels and at least one layer of second spiral channels, and the at least one layer of the first spiral channels and the at least one layer of the second spiral channels alternate with each other. 
     Optionally, the at least one layer of first spiral channels is configured such that a first end of the at least one layer of first spiral channel is in fluid communication with the first section, and the at least one layer of second spiral channels is configured such that a first end of the at least one layer of second spiral channels is in fluid communication with the second section. 
     Optionally, the method may further comprise forming a first external tank and a second external tank, wherein the at least one layer of first spiral channels is configured such that a second end of the at least one layer of first spiral channel is in fluid communication with the first tank, and the at least one layer of second spiral channels is configured such that a second end of the at least one layer of second spiral channels is in fluid communication with the second tank. Optionally, the first external tank has an outlet, and the second external tank has an outlet. 
     Optionally, all surfaces of the first spiral channel and second spiral channel are primary heat transfer surfaces. 
     Optionally, a diamond spiral heat exchanger may be formed by any of the previously described methods. 
     According to a second aspect there is provided a diamond spiral heat exchanger that comprises a central channel and a core section. The central channel has a longitudinal axis and the central channel is divided into a first section and a second section. The first section is in fluid communication with a first inlet of the central channel and the second section is in fluid communication with a second inlet of the central channel. The core section comprises a first spiral channel and a second spiral channel. The first end of the first spiral channel is configured to be in fluid communication with the first section. The first spiral channel has a diamond cross-section and the first spiral channel spirals in a plane perpendicular to the longitudinal axis of the central channel. The first end of the second spiral channel is configured to be in fluid communication with the second section. The second spiral channel has a diamond cross-section, and the second spiral channel is configured to spiral in a plane perpendicular to the longitudinal axis of the central channel. The second spiral channel is configured to be stacked on top of the first spiral channel such that the core has a diamond lattice cross-section. 
     Optionally there is provided at least one layer of first spiral channels and at least one layer of second spiral channels, and the at least one layer of the first spiral channels and the at least one layer of the second spiral channels alternate with each other. 
     Optionally, the at least one layer of first spiral channels is configured such that a first end of the at least one layer of first spiral channel is in fluid communication with the first section, and the at least one layer of second spiral channels is configured such that a first end of the at least one layer of second spiral channels is in fluid communication with the second section. 
     Optionally, the diamond spiral heat exchanger further includes a first external tank and a second external tank, wherein the at least one layer of first spiral channels is configured such that a second end of the at least one layer of first spiral channel is in fluid communication with the first tank, and the at least one layer of second spiral channels is configured such that a second end of the at least one layer of second spiral channels is in fluid communication with the second tank. Optionally, the first external tank has an outlet and the second external tank has an outlet. 
     Optionally, all surfaces of the first spiral channel and second spiral channel are primary heat transfer surfaces. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a heat exchanger with a spiral core 
         FIG. 2  shows a cross section of a spiral diamond heat exchanger 
         FIG. 3 a    shows spiral parallel flow in a spiral diamond heat exchanger 
         FIG. 3 b    shows counter flow in a spiral diamond heat exchanger 
         FIG. 4  shows a manifold of a spiral diamond heat exchanger 
         FIG. 5  shows a manifold of a spiral diamond heat exchanger with duct ports 
         FIG. 6  shows a spiral diamond heat exchanger printed by additive manufacturing techniques 
         FIG. 7  shows a method for removing powder residue from a spiral diamond heat exchanger 
     
    
    
     DETAILED DESCRIPTION 
     An exemplary heat exchanger  10  with a spiral core is described herein and depicted in  FIGS. 1, 2 and 3 . The core  2  of the heat exchanger  10  comprises a central channel  1  that runs through the centre of the heat exchanger  10 . The central channel  1  runs along a longitudinal axis L. The central channel has a first inlet  1   a  and a second inlet  1   b . The heat exchanger comprises a first single channel  11  and a second single channel  12 . Each of the channels  11 ,  12  have a diamond cross-section. Each of the spiral channels  11 ,  12  are in fluid communication with the central channel  1 . Each of the spiral channels are configured to spiral along a plane P perpendicular to the longitudinal axis L of the central channel  1 .  FIG. 1  shows the heat exchanger from the perspective of looking down the longitudinal axis L of the central channel  1 . 
     The central channel is divided into first and second sections  7   a ,  7   b , wherein the first section  7   a  is in fluid communication with the first inlet  1   a  and the second section  7   b  is in fluid communication with the second inlet  1   b . The first section  7   a  is in fluid communication with the first end of the first spiral channel  11 . The second section  7   b  is in fluid communication with the first end of the second spiral channel  12 . 
     The second spiral channel  12  is stacked on top of the first spiral channel  11  so that the cross-section of the core  2  forms a diamond lattice, as shown in  FIG. 2 . All surfaces of the first and second spiral channels  11 ,  12  can be primary heat transfer surfaces. 
     As shown in  FIG. 2 , the heat exchanger  10  can comprise at least one layer of first spiral channels  11  and at least one layer of second spiral channels  12 . The at least one layer of first spiral channels  11  and the at least one layer of second spiral channels  12  are stacked along the longitudinal axis L of the central channel  1  so that they alternate with each other. The first ends of the at least one layer of first spiral channels  11  are in fluid communication with the first section  7   a . The first ends of the at least one layer of second spiral channels  12  are in fluid communication with the second section  7   b . The at least one layer of first spiral channels  11  and the at least one layer of second spiral channels  12  are configured so that the core  2  has a diamond lattice cross-section. That is, a cross-sectional view of the heat exchanger  10 , wherein the longitudinal axis L of the central channel is exposed, will show the core  2  with a diamond lattice cross-section. The diamond lattice cross-section is formed by the walls of the at least one layer of first spiral channels  11  and the at least one layer of second spiral channels  12 . 
     The first section  7   a  is configured to distribute a first fluid to the at least one layer of first spiral channels  11  and the second section  7   b  is configured to distribute a second fluid to the at least one layer of second spiral channels  12 . Heat can therefore be exchanged between the fluids across the walls of the spiral channels  11 ,  12 . 
     As shown in  FIG. 3 , the at least one layer of first spiral channels  11  have a second end that terminates in a first tank  3   a . The at least one layer of second spiral channel  12  have a second end that terminates in a second tank  3   b.    
     As shown in  FIG. 2 , the first section  7   a  receives the first fluid from a first inlet  1   a  and the second section  7   b  receives the second fluid from a second inlet  1   b . The tanks  3   a  and  3   b  have outlets  4   a  and  4   b  respectively (only outlet  4   a  is shown in  FIG. 2 ). 
     An advantage of the above described heat exchangers is that they are easy to produce by additive manufacturing techniques. The design of the heat exchanger core can be easily scaled up by changing the length of the spirals or the number of layers. 
     By altering the number of layers and the spiral length of the first and second spiral channels  11  and  12 , the performance of the heat exchanger  10  can be easily altered. Increasing the number of layers results in a reduction in the pressure and an improvement in heat transfer. Increasing the spiral length results in an improvement in heat transfer and an increase in the pressure drop. 
     A further benefit is that the tubular shape of the heat exchanger core reduces stress compared to a conventional core. 
     The above described heat exchangers are suitable for use in two flow configurations: spiral counter flow and spiral parallel flow (both shown in  FIG. 3 ). Spiral parallel flow is shown in  FIG. 3 a    wherein the first section  7   a  receives the first fluid and the second section  7   b  receives the second fluid. The first fluid flows in a clockwise direction through the at least layer of first spiral channels  11  towards the tank  3   a . The second fluid flows in a clockwise direction through the at least one layer of second spiral channels  12  towards the tank  3   b.    
       FIG. 3 b    shows spiral counter flow, wherein section  3   a  receives the first fluid and tank  7   b  receives the second fluid. The first fluid flows in an anti-clockwise direction through the at least one layer of second spiral channels  12  towards tank  7   a , and the second fluid flows in a clockwise direction through the at least one layer of first spiral channels  11  towards the second section  3   b . The external tanks can therefore be used as fluid inlets or outlets depending on the flow configuration. The in/out ports to the heat exchanger can be attached depending on the requirements. 
     The placement of the first inlet  1   a  and second inlet  1   b  and the first outlet  4   a  and second outlet  4   b  can be easily changed depending on the interface requirements.  FIG. 4  shows one manifold configuration where the first inlet  1   a , and the first and second outlets  4   a ,  4   b  are on one end of the heat exchanger  10 , and the second inlet  1   b  is on the opposite end of the heat exchanger  10 . 
       FIG. 5  shows another manifold configuration wherein the outlets  4   a ,  4   b  are formed on a side face of the manifold, the first inlet port  1   a  is formed on one end the manifold, and the second inlet port  1   b  is connected on a second end of the manifold, wherein the first end is opposite the second end. Duct attachments can be attached to the first and second inlets  1   a ,  1   b  and first and second outlets  4   a ,  4   b.    
     The spiral diamond core as well as the attachments, including the tanks, distribution channels and pressure relief valves (PRVs) can easily be made suitable for Additive Manufacturing technology.  FIG. 6  shows how a spiral diamond heat exchanger can be easily printed from the bottom up. The alignment of the diamond spiral layers is printing friendly. Furthermore, in the examples described herein, there is no need to design complex manifolds to distribute the fluids. 
     Another aspect of the invention relates to a method to overcoming problems related to powder residue in heat exchanger. Powder residue can be left in the channels after the heat exchanger has been by additive manufacturing. The proposed method described herein involves rotating the heat exchanger around the axis of the central channel  1  in order to move powder from the internal sections of the coils up to the tank.  FIG. 7  shows the heat exchanger being rotated around the axis of the central channel. 
     Although this disclosure has been described in terms of preferred examples, it should be understood that these examples are illustrative only and that the claims are not limited to those examples. Those skilled in the art will be able to make modifications and alternatives in view of the disclosure which are contemplated as falling within the scope of the appended claims.