A compact microchannel LNG heat exchanger and preparation method thereof

Abstract

The present invention discloses a compact microchannel LNG heat exchanger and a preparation method thereof. The heat exchanger includes a heat exchanger body, and a plurality of cold fluid channels and hot fluid channels are arranged alternately and at intervals in the vertical direction. The two ends of the cold fluid channel are respectively connected to the cold fluid inlet and the cold fluid outlet, and the two ends of the hot fluid channel are respectively connected to the hot fluid inlet and the hot fluid outlet. The cold fluid channel includes a first diverter channel, a cold side heat exchange channel and a first confluence channel. The hot fluid channel includes a second diverter channel, a heat measurement heat exchange channel and a second confluence channel. The present invention adopts a countercurrent arrangement, and a large temperature difference stress is not generated at both ends of the heat exchanger. Diverter and confluence channel sections are respectively arranged after the fluid inlet and before the fluid outlet. The fluid flows through the diverter channel, and the diverter channel makes the flow distribution more uniform, so that the medium temperature is evenly distributed. The preparation method adopts additive manufacturing technology for one-piece molding, and the material utilization rate is high, which ensures the stability and efficiency of the heat exchanger operation.

Description

Technical Field

[0001] The present invention relates to an LNG heat exchanger and a preparation method thereof, and in particular to a compact microchannel LNG heat exchanger based on additive manufacturing and a preparation method thereof. Background Art

[0002] With the rapid increase in demand for natural gas (NG) and the development of the liquefied natural gas (LNG) industry chain, a complete industrial system has been gradually formed from production, storage, transportation, shipping to receiving, regasification, cold utilization, peak load regulation, etc., and the application of offshore LNG floating storage and regasification units (FSRU) is becoming more and more widespread. Before transporting liquefied natural gas (LNG) to the terminal, it is necessary to regasify the LNG at a temperature of about -163°C into gaseous NG at about 5°C. The LNG regasification process is carried out in the LNG heat exchanger, through which the heat of the heat source is transferred to the LNG, and the LNG absorbs heat and vaporizes into a gaseous state. Among the existing LNG heat exchangers, the advantages of compact microchannel heat exchangers are very consistent with the characteristics of floating storage and regasification units (FSRUs), so compact microchannel heat exchangers have been increasingly widely used in LNG floating storage and regasification units.

[0003] The core structure of the microchannel heat exchanger is complex, with a large number of long and thin channels inside. The flow direction of the channels is changeable and the cross-sectional geometry of the channels is irregular. The processing is difficult and the process requirements are high. At present, the core of the microchannel heat exchanger is generally made by chemically corroding metal plates to engrave grooves, and then the plate bundles are welded and bonded by diffusion welding. For the current chemical corrosion grooving process, only channels with simple cross-sectional shapes such as rectangles or semicircles and single channel flow arrangements can be prepared, while channels with complex cross-sections and variable flow arrangements that require more efficient heat exchange and stronger load-bearing cannot be prepared; the stability of channel precision control is poor; chemical corrosion liquid waste causes great pollution to the environment, and the cost of waste liquid treatment is high; the process is cumbersome and the production cycle is long. On the other hand, during the diffusion welding process, it is necessary to reasonably control the pressing force, the reducing atmosphere in the furnace, and the temperature in the furnace to ensure that the interface between the etched plates is tightly fitted during the welding process, no oxidation occurs, and all contact surfaces are completely diffused and melted into a whole. However, in the actual product manufacturing process, it is impossible to achieve defect-free welding of multiple plate bundles. There is a problem of incomplete welding inside the plate bundle, which is prone to deformation and cracking, affecting the flow direction and flow rate of the medium, and even leakage. The residual welding stress inside the core limits the working pressure of the heat exchanger, shortens the service life of the heat exchanger, and seriously reduces the heat exchange efficiency of the heat exchanger as well as the working safety and reliability of the product. Summary of the invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a compact microchannel LNG heat exchanger based on additive manufacturing to improve heat exchange efficiency and carrying capacity; the second purpose of the present invention is to provide a method for preparing the above-mentioned compact microchannel LNG heat exchanger.

[0005] Technical solution: A compact microchannel LNG heat exchanger of the present invention comprises a heat exchanger body, wherein a plurality of cold fluid channels and hot fluid channels are arranged alternately and at intervals in the vertical direction; the two ends of the cold fluid channel are respectively connected to the cold fluid inlet and the cold fluid outlet, and the two ends of the hot fluid channel are respectively connected to the hot fluid inlet and the hot fluid outlet, the cold fluid inlet and the hot fluid outlet are at one end of the heat exchanger body, and the cold fluid outlet and the hot fluid inlet are at the other end of the heat exchanger body, and the cold and hot fluids flow from the inlet to the outlet respectively and exchange heat in the heat exchanger body; the cold fluid channel comprises a first diverter channel, a cold side heat exchange channel and a first confluence channel which are connected in sequence and located in the same plane from the inlet to the outlet; the hot fluid channel comprises a second diverter channel, a hot side heat exchange channel and a second confluence channel which are connected in sequence and located in the same plane from the inlet to the outlet.

[0006] Furthermore, the cold fluid inlet and the cold fluid outlet are both cylindrical channels, and the axes of the cold fluid inlet and the cold fluid outlet are both located on the middle longitudinal section of the heat exchanger body; the cold fluid inlet and the cold fluid outlet are symmetrically arranged with respect to the middle transverse section of the heat exchanger body; the opening of the cold fluid inlet connected to the external pipeline is arranged above the heat exchanger body, and the opening of the cold fluid outlet connected to the external pipeline is arranged below the heat exchanger body; the cold fluid inlet has a first opening connected to the first branch flow channel along the longitudinal direction, and the cold fluid outlet has a second opening connected to the first confluence flow channel along the longitudinal direction. The hot fluid inlet and the hot fluid outlet are both composed of two groups of cylindrical channels symmetrically arranged along the longitudinal section of the heat exchanger body, the axis of the hot fluid inlet is in the same plane as the axis of the cold fluid outlet, and the axis of the hot fluid outlet is in the same plane as the axis of the cold fluid inlet; the hot fluid inlet and the hot fluid outlet are symmetrically arranged with respect to the middle transverse section of the heat exchanger body; the opening for the hot fluid inlet to communicate with the external pipeline is arranged above the heat exchanger body, and the opening for the hot fluid outlet to communicate with the external pipeline is arranged below the heat exchanger body; the hot fluid inlet is provided with a third opening connected to the second branch flow channel along the longitudinal direction, and the hot fluid outlet is provided with a fourth opening connected to the second confluence flow channel along the longitudinal direction. In the above scheme, the heat exchanger is arranged in countercurrent as a whole, the cold fluid inlet and the hot fluid outlet are at one end of the heat exchanger; the cold fluid outlet and the hot fluid inlet are at the other end of the heat exchanger; the inlets and outlets of the hot and cold fluids are both cylindrical channels inside the heat exchanger, and compared with the traditional heat exchanger using the inlet and outlet of the head, it can avoid the stress concentration at the welding point between the head and the heat exchange core.

[0007] Further, the first diverter channel extends from the first opening of the cold fluid inlet to both sides of the heat exchanger body, and a plurality of channel walls for dividing the channel are arranged in the first diverter channel; the first converging channel shrinks from both sides of the heat exchanger body to the second opening of the cold fluid outlet along the flow direction, and a plurality of channel walls for dividing the channel are arranged in the first converging channel; the structure of the first converging channel is the same as that of the first diverter channel, and is symmetrical about the middle cross section of the heat exchanger body. The second diverter channel extends from the third opening of the two groups of hot fluid inlets to both sides of the heat exchanger body, and converges at the middle longitudinal section of the heat exchanger body; a plurality of channel walls for dividing the channel are arranged in the second diverter channel; the second converging channel shrinks from both sides of the heat exchanger body to the fourth opening of the two groups of hot fluid outlets along the flow direction, and a plurality of channel walls for dividing the channel are arranged in the second converging channel; the structure of the second converging channel is the same as that of the second diverter channel, and is symmetrical about the middle cross section of the heat exchanger body. The cross section of the channel wall is rectangular. In the actual arrangement process, the lower part of the first diverter channel corresponds to the second confluence channel, the lower part of the cold side heat exchange channel corresponds to the hot side heat exchange channel, the lower part of the first confluence channel corresponds to the second diverter channel, the first diverter channel and the second confluence channel are arranged alternately in the longitudinal direction and are independent of each other; the first confluence channel and the second diverter channel are arranged alternately in the longitudinal direction and are independent of each other, the first diverter channel and the first confluence channel correspond to the cold side heat exchange channel, the second diverter channel and the second confluence channel correspond to the hot side heat exchange channel, and the cold fluid channel and the hot fluid channel are arranged alternately in the longitudinal direction in the corresponding order. The cold fluid and the hot fluid enter from both ends of the heat exchanger body at the same time, move from top to bottom in opposite directions, and exchange heat in the heat exchanger body.

[0008] Further, a first transition channel is provided between the first flow branch channel and the cold side heat exchange channel and between the cold side heat exchange channel and the first converging channel, and a flow channel wall parallel to the axial direction of the heat exchanger body is provided in the first transition channel, one end of which is respectively connected to the flow channel walls in the first flow branch channel and the first converging channel, and the other end leaves a gap with the two ends of the cold side heat exchange channel. A second transition channel is provided between the second flow branch channel and the hot side heat exchange channel and between the hot side heat exchange channel and the second converging channel, and a flow channel wall parallel to the axial direction of the heat exchanger body is provided in the second transition channel, one end of which is respectively connected to the flow channel walls in the second flow branch channel and the second converging channel, and the other end leaves a gap with the two ends of the hot side heat exchange channel. The setting of the gap can ensure that the fluid to be exchanged with heat and the fluid that has completed heat exchange can run smoothly in the heat exchanger. The width of the gap ranges from 5 to 10 mm. The fluid that has been diverted enters the transition channel from the diversion channel, and the direction of the fluid velocity is adjusted to be parallel to the heat exchange channel. The fluid that has completed heat exchange enters the transition channel from the heat exchange channel. The fluid is separated by the channel wall, and the velocity direction remains parallel to the heat exchange channel.

[0009] Furthermore, regularly arranged channel walls are provided in the diversion channel and the transition channel. The channel walls can increase the bearing capacity of the channel and can also play a dual role of internal support and collapse prevention during the 3D printing process.

[0010] Furthermore, the cold side heat exchange channel is composed of multiple groups of first channels located in the same plane, the arrangement direction of the first channels is perpendicular to the flow direction of the cold fluid, and the first channels are composed of two upper and lower pipes with semi-elliptical cross-sections arranged opposite to each other. An intermediate thin plate can be further arranged to separate the upper and lower small channels, which can significantly increase the heat exchange area per unit volume of the core. At the same time, when performing the additive manufacturing process, the semi-elliptical channel and the intermediate thin plate have a high support capacity to avoid collapse.

[0011] Furthermore, the hot side heat exchange channel is composed of multiple groups of second channels located in the same plane, the arrangement direction of the second channels is perpendicular to the flow direction of the hot fluid, the second channels are composed of pipes with a semicircular cross-section shape, and the cross-sections of the second channels adjacent to each other are arranged in reverse. Due to the high manufacturing freedom of additive manufacturing technology, the adjacent channels to each other can be arranged in reverse, reducing the distance between the two channels, so that more heat exchange channels can be arranged in the core of the same volume, increasing the heat exchange area and improving the heat exchange efficiency.

[0012] The present invention further protects a method for preparing a compact microchannel LNG heat exchanger, which is prepared by a laser selective melting additive manufacturing method. The material of the heat exchanger body is 316L stainless steel metal powder, and the heat transfer coefficient is controlled to be 5000~6000 W / m 2 ·K, the control limit bearing capacity is 18~20 MPa. Additive manufacturing technology, commonly known as 3D printing, is based on the idea of ​​layered manufacturing and CAD three-dimensional model files. It uses laser to quickly and completely melt the selected material powder. The material powder quickly cools and solidifies, and is stacked layer by layer to finally form a three-dimensional object. The heat exchange core prepared by additive manufacturing technology has a high material utilization rate. Compared with the chemical etching process, it does not need to discard a large amount of raw materials, saves the waste liquid treatment link, avoids the pollution of chemical waste liquid to the environment, and saves costs; the heat exchanger is integrally formed, there is no welding interface in the heat exchanger, and the sealing is good. It effectively overcomes the deformation and cracking problems of traditional heat exchanger plates during welding, eliminates the deformation stress during welding, and greatly improves the working pressure and service life of the heat exchanger; the manufacturing freedom is high, and the heat exchanger with complex channel cross-section shapes and variable channel flow arrangements can be prepared, thereby greatly increasing the heat exchange area and improving the heat exchange efficiency.

[0013] The working principle of the present invention is: the cold fluid and the hot fluid are respectively introduced into the heat exchanger body through their respective inlets, and the running process of the cold fluid in the heat exchanger is the cold fluid inlet, the first branch flow channel section, the first transition flow channel section, the cold side heat exchange channel section, the first transition flow channel section, the first confluence flow channel section and the cold fluid outlet; the running process of the hot fluid in the heat exchanger is the hot fluid inlet, the second branch flow channel section, the second transition flow channel section, the hot side heat exchange channel section, the second transition flow channel section, the second confluence flow channel section and the hot fluid outlet; the cold and hot fluids are independent of each other during the flow process, and due to the structure of alternating arrangement at intervals, heat exchange can be achieved at various positions.

[0014] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) The present invention adopts a countercurrent arrangement, and no large temperature difference stress is generated at both ends of the heat exchanger. A split-and-joint flow channel section is respectively arranged after the fluid inlet and before the fluid outlet. The fluid flows through the split flow channel, which makes the flow distribution more uniform, thereby making the medium temperature distribution uniform, further enhancing the heat exchange, avoiding the gas gap in the flow channel caused by the absence of a split structure or uneven flow distribution, hindering the heat transfer, and incomplete LNG vaporization; the fluid flows through the joining flow channel, and the joining flow channel gradually converges the fluid that has completed the heat exchange symmetrically to the middle along the flow direction. The changes in the velocity, pressure and flow of the fluid are gentle and orderly, and the steady flow channel smoothly transitions to the fluid outlet, avoiding increasing the pressure drop, blocking the heat exchanger, and even causing the heat exchange system to fail. The system is shut down in an emergency, ensuring the stability and efficiency of the heat exchanger operation; (2) The heat exchanger provided by the present invention is formed in one piece using additive manufacturing technology, with high material utilization rate. Compared with the chemical etching process, it does not need to discard a large amount of raw materials, saves the waste liquid treatment link, avoids the pollution of the environment by chemical waste liquid, and saves costs; there is no welding interface in the core, and the sealing is good, which effectively overcomes the deformation and cracking problems of traditional heat exchanger plates during welding, eliminates the deformation stress during welding, avoids the leakage of working medium, and greatly improves the working pressure and service life of the heat exchanger. The working pressure can reach up to 20MPa; the manufacturing freedom is high, and the heat exchange area density per unit volume reaches 2000m 2 / m 3 , greatly improving the heat exchange efficiency; (3) The present invention sets a transition channel, and the direction of the fluid velocity is adjusted to be parallel to the heat exchange channel, so that the speed and pressure of the fluid entering the heat exchange core are stable, the pressure drop is reduced, and the heat exchange efficiency and the operation stability of the heat exchanger are improved. The fluid that has completed the heat exchange enters the transition channel from the heat exchange channel, and the speed direction remains parallel to the heat exchange channel, avoiding the fluid from coming out of the tiny heat exchange channel. The speed, pressure, and volume change sharply, thereby causing excessive fluid pressure drop and blocking the heat exchanger, ensuring the stability of the heat exchanger operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0016] Figure 2 is a cross-sectional view of the cold fluid inlet end of the heat exchanger of the present invention;

[0017] Figure 3 is a cross-sectional view of the cold fluid outlet end of the heat exchanger of the present invention;

[0018] Figure 4 This is a schematic diagram of the overall structure of the cold fluid channel of the present invention;

[0019] Figure 5 It is a schematic diagram of the structure of the first flow diversion channel of the present invention;

[0020] Figure 6 It is a schematic diagram of the structure of the first converging flow channel of the present invention;

[0021] Figure 7 It is a schematic structural diagram of the thermal fluid channel of the present invention;

[0022] Figure 8 It is a schematic diagram of the structure of the second flow diversion channel of the present invention;

[0023] Fig. 9 It is a schematic diagram of the structure of the second converging flow channel of the present invention;

[0024] Fig.10 It is a partial schematic cross-sectional view of the cold-side heat exchange channel and the hot-side heat exchange channel of the present invention. DETAILED DESCRIPTION

[0025] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0026] Take the heat exchange between cold fluid LNG and hot fluid R290 as an example.

[0027] The flow of the cold fluid LNG in the heat exchanger is cold fluid inlet 4, first branch flow channel 21, first transition flow channel 24, cold side heat exchange channel 22, first transition flow channel 24, first confluence flow channel 23, and cold fluid outlet 5; the flow of the hot fluid R290 in the heat exchanger is hot flow channel inlet 6, second branch flow channel 31, second transition flow channel 34, hot side heat exchange channel 32, second transition flow channel 34, second confluence flow channel 33, and hot fluid outlet 7; the cold and hot fluids are independent of each other during the flow process.

[0028] The heat exchanger in this embodiment is formed by laser selective melting additive manufacturing technology, and the metal powder is 316L stainless steel. The total heat transfer coefficient exceeds 6000 W / m 2·K, the ultimate bearing capacity reaches 20 MPa; 316L stainless steel has good corrosion resistance and pressure bearing capacity; at the same time, when the medium is heat exchanged, there is no thermal resistance caused by solder, which enhances the heat exchange capacity of the compact microchannel LNG heat exchanger.

[0029] See also Figure 1-10 The compact microchannel LNG heat exchanger shown includes a heat exchanger body 1, which is a rounded cube structure. The heat exchanger body 1 is provided with a plurality of cold fluid channels 2 and hot fluid channels 3 arranged alternately and spaced in the vertical direction; the two ends of the cold fluid channel 2 are respectively connected to the cold fluid inlet 4 and the cold fluid outlet 5, and the two ends of the hot fluid channel 3 are respectively connected to the hot fluid inlet 6 and the hot fluid outlet 7. The cold fluid inlet 4 and the hot fluid outlet 7 are at one end of the heat exchanger body 1, and the cold fluid outlet 5 and the hot fluid inlet 6 are at the other end of the heat exchanger body 1. The cold and hot fluids flow from the inlet to the outlet respectively and exchange heat in the heat exchanger body 1. The shape and size of the fluid outlet on the same side are the same as the fluid inlet. At any end of the heat exchanger, the fluids on both sides enter and exit from the upper and lower sides of the heat exchanger respectively without interfering with each other, which is convenient for arranging pipes connected to the inlet and outlet of the heat exchanger.

[0030] See also Figure 2 The cold fluid inlet 4 is a cylindrical channel with a diameter of 60 mm. The axis of the cylinder is located on the middle longitudinal section of the heat exchanger body and is parallel to the middle transverse section of the heat exchanger body. The cold fluid inlet 4 is longitudinally provided with a first opening 41 connected to the first branch flow channel 21; the hot fluid outlet 7 is composed of two cylindrical channels of the same size and symmetrically arranged along the middle longitudinal section of the heat exchanger. The diameter of the two cylindrical channels is 40 mm, and their axes are in the same plane as the axis of the cold fluid inlet 4. The hot fluid outlet 7 is longitudinally provided with a fourth opening 71 connected to the second converging flow channel 33. See Figure 3The cold fluid outlet 5 is a cylindrical channel with a diameter of 60 mm. The axis of the cylinder is located on the middle longitudinal section of the heat exchanger body and is parallel to the middle transverse section of the heat exchanger body. The cold fluid inlet 4 and the cold fluid outlet 5 are symmetrically arranged with respect to the middle transverse section of the heat exchanger body 1. The cold fluid outlet 5 is longitudinally provided with a second opening 51 connected to the first converging flow channel 23; the hot fluid inlet 6 is composed of two cylindrical channels of the same size and symmetrically arranged along the middle longitudinal section of the heat exchanger. The diameter of the two cylindrical channels is 40 mm, its axis is in the same plane as the axis of the cold fluid outlet 5, the hot fluid inlet 6 is longitudinally provided with a third opening 61 connected to the second branch flow channel 31; the opening of the cold fluid inlet 4 connected to the external pipeline is arranged above the heat exchanger body 1, and the opening of the cold fluid outlet 5 connected to the external pipeline is arranged below the heat exchanger body 1; the opening of the hot fluid inlet 6 connected to the external pipeline is arranged above the heat exchanger body 1, and the opening of the hot fluid outlet 7 connected to the external pipeline is arranged below the heat exchanger body 1; the cold fluid LNG with a pressure of 10MPa is vertically injected from the top surface of the cylinder, the first opening 41 is semicircular, and the cold fluid LNG enters the cold fluid channel 2 from the first opening 41; the flow rate is 3.5 m 3 / h hot fluid R290 is vertically injected from the top surface of the cylinder, the third opening 61 is semicircular, and after heat exchange, the hot fluid R290 is discharged from the opening into the third opening 61 into the hot fluid channel 3 and discharged from the heat exchanger vertically from the cylindrical outlet.

[0031] See also Figure 4-6The first branch flow channel 21 is arranged after the cold fluid inlet 4 and before the first transition flow channel 24. The first branch flow channel 21 is provided with regularly distributed flow channel walls 8, and the cross section of the flow channel wall 8 is rectangular. The first opening 41 is a semicircular arc opening, and the corresponding central angle is 180 degrees. The semicircular arc is divided into four parts according to the angle. The first branch flow channel 21 is divided into four channels, that is, the central angle of each arc is 45 degrees, and three flow channel walls 8 are arranged; the branch flow channel is divided into five sections along the axial length of the heat exchanger. After each section, each flow channel is divided into two, that is, a flow channel wall 8 is added at the midpoint of the width of the flow channel, and the total width of the branch flow channel increases linearly. After five sections, the branch flow channel is expanded to 32 channels, and the total width of the branch flow channel is expanded to the total lateral width of the cold side heat exchange channel 23. The cold fluid LNG enters the diverter channel from the semicircular opening and is evenly divided into 4 parts. After each distance it flows, it is evenly divided into two by the channel wall 8. In the last section of the first diverter channel 21, the LNG is evenly divided into 32 parts. The first diverter channel expands symmetrically along the flow direction to both sides of the heat exchanger body 1. The overall shape is similar to a fan, which can evenly distribute the flow and temperature of LNG laterally, improve the heat exchange efficiency, and avoid incomplete vaporization caused by uneven distribution of LNG; realize the smooth and orderly changes in the speed, pressure and flow of LNG, reduce the pressure drop, and ensure the stability and efficiency of the heat exchanger operation. The first converging channel 23 is arranged before the cold fluid outlet 5 and after the first transition channel 24. The structural form of the first converging channel 23 is the same as that of the first diverter channel 21, and the two are symmetrical about the cross-section of the heat exchanger. LNG heated and vaporized into NG enters the confluence flow channel from the first transition flow channel 24, with a total of 32 channels. After each flow of a certain distance, the flow channel wall 8 between two adjacent flow channels is interrupted, and the two adjacent flow channels are merged into one. At the same time, the total width of the first confluence flow channel 23 decreases linearly. In the last section of the first confluence flow channel 23, the first confluence flow channel 23 is finally merged into four large channels, and the NG in the flow channel is also merged into four streams accordingly, and finally discharged into the cold fluid outlet 5 through the second opening 51. The first confluence flow channel shrinks symmetrically toward the middle along the flow direction, and the overall shape is similar to a fan, so that the changes in the speed, pressure and flow of NG are smooth and orderly, avoiding blocking the heat exchanger, thereby causing the heat exchange system to stop, and ensuring the stability and efficiency of the heat exchanger operation.

[0032] See also Figure 7-9The second flow branch channel 31 is arranged after the hot fluid inlet 6 and before the second transition channel 34. The hot fluid inlet 6 is composed of two cylindrical channels symmetrically distributed with respect to the longitudinal section of the heat exchanger. Correspondingly, the second flow branch channel 31 includes two sub-flow branch channels symmetrically distributed with respect to the longitudinal section of the heat exchanger, and the two sub-flow branch channels converge at the middle longitudinal section. Regularly distributed flow channel walls 8 are arranged in the sub-flow branch channels, and the cross section of the flow channel wall 8 is rectangular. The third opening 61 of the sub-dividing flow channel is a semicircular opening with a corresponding central angle of 180 degrees. The semicircular arc is divided into four parts according to the angle, and the sub-dividing flow channel is divided into four channels, that is, the central angle of each arc is 45 degrees, and three channel walls 8 are set; the sub-dividing flow channel is divided into four sections along the axial length of the heat exchanger, and each channel is divided into two after each section, that is, a channel wall 8 is added at the midpoint of the width of the channel, and the total width of the sub-dividing flow channel increases linearly at the same time. After four sections, the sub-dividing flow channel is expanded to 16 channels, and the total width of the sub-dividing flow channel is expanded to half of the total lateral width of the heat exchange channel 32 on the hot side; the two sub-dividing flow channels converge in their last section, and the entire second diverting flow channel 31 is expanded to a total of 32 channels, and its total width is expanded to the total lateral width of the heat exchange channel 32 on the hot side. The hot fluid R290 enters the sub-dividing flow channel from the third opening 61 and is evenly divided into 4 parts. After each distance it flows, it is evenly divided into two parts by the flow channel wall 8. In the last section of the sub-dividing flow channel, R290 is evenly divided into 16 parts. After the two sub-dividing flow channels merge, R290 is evenly divided into 32 parts in total. The sub-dividing flow channel expands symmetrically to both sides along the flow direction. The overall shape is similar to a fan, which can evenly distribute the flow and temperature of R290 laterally, improve the heat exchange efficiency, and avoid insufficient heat transfer of R290 due to uneven distribution of R290, thereby causing incomplete vaporization of LNG. Under the action of the diverting flow channel, the speed, pressure and flow of R290 change slowly and orderly, and can continuously and stably transfer heat to LNG, ensuring the stability and efficiency of the heat exchanger operation. The second converging flow channel 10 is arranged before the hot fluid outlet 7 and after the second transition flow channel 34. The structure of the second converging flow channel 33 is the same as that of the second branch flow channel 31, and the two are symmetrical about the cross section of the heat exchanger. After completing the heat exchange, R290 enters the second converging flow channel 33 from the second transition flow channel 34. There are 32 flow channels in total. With the middle longitudinal section as the boundary, 16 flow channels on the left and right lead to the two sub-converging channels on the left and right respectively. Every time R290 flows through a certain distance, the flow channel wall 8 in the two adjacent flow channels is interrupted, and the two adjacent flow channels are merged into one. At the same time, the total width of the second converging flow channel 33 decreases linearly. In the last section of the second converging flow channel 33, the second converging flow channel 33 is finally merged into 4 large channels, and the R290 in the flow channel is also merged into 4 streams accordingly, and finally discharged into the hot fluid outlet 7 through the fourth opening 71.The second converging flow channel 33 shrinks symmetrically toward the middle along the flow direction, and the overall shape is similar to a fan, so that the speed, pressure and flow rate of R290 can change smoothly and orderly, avoiding clogging of the heat exchanger, thereby causing the heat exchange system to stop, and ensuring the stability and efficiency of the heat exchanger operation.

[0033] At the end where the cold fluid inlet 4 of the heat exchanger is located, the first branch flow channel 21 and the second converging flow channel 33 are arranged alternately in the longitudinal direction, are independent of each other, and correspond one-to-one with the longitudinal positions of the cold side heat exchange channel 22 and the hot side heat exchange channel 32. At the end where the cold fluid outlet 5 of the heat exchanger is located, the first converging flow channel 23 and the second branch flow channel 31 are arranged alternately in the longitudinal direction, are independent of each other, and correspond one-to-one with the longitudinal positions of the cold side heat exchange channel 22 and the hot side heat exchange channel 32. The structure and arrangement of the branch and converging flow channels on both the cold and hot sides can increase the overlap area of ​​the two adjacent layers in the longitudinal direction, thereby performing a certain amount of heat exchange and increasing the effective heat exchange volume of the heat exchanger.

[0034] like Figure 4 As shown, a first transition channel 24 is provided between the first branch channel 21 and the cold side heat exchange channel 22 and between the cold side heat exchange channel 22 and the first converging channel 23. A channel wall 8 parallel to the axial direction of the heat exchanger is provided in the first transition channel 24, which is connected to the channel wall 8 in the branch and converging channels one by one. The first transition channel 24 is divided into 32 channels by the channel wall 8. The channel wall 8 does not extend to the cold side heat exchange channel 22, and there is a gap between the cold side heat exchange channel 22, and the gap width is 8 mm; see Figure 7 A second transition channel 34 is provided between the second branch channel 31 and the hot side heat exchange channel 32 and between the hot side heat exchange channel 32 and the second converging channel 33. A channel wall 8 parallel to the axial direction of the heat exchanger is provided in the second transition channel 34, which is connected with the channel wall 8 in the branch and converging channels one by one. The second transition channel 34 is divided into 32 channels by the channel wall 8. The channel wall 8 does not extend to the hot side heat exchange channel 32, and there is a gap between the channel wall 8 and the hot side heat exchange channel 32, and the gap width is 8 mm.

[0035] See also Fig.10 The cold side heat exchange channel 22 is composed of multiple groups of first channels 221 located in the same plane. The arrangement direction of the first channel 211 is perpendicular to the flow direction of the cold fluid. The first channel 221 is composed of two upper and lower semi-elliptical pipes arranged opposite to each other. The long axis of the semi-ellipse is 2mm and the short axis is 1mm. An intermediate thin plate is set between the two to separate the upper and lower small channels. The thickness of the intermediate thin plate is 0.4 mm. Compared with the elliptical channel with the same long and short axes, the combination of two semi-elliptical channels of unit length and the intermediate thin plate increases the heat exchange area by 2a mm 2 (a is the major axis length of the ellipse), which can significantly increase the heat exchange area per unit volume of the core. The heat exchange area per unit volume on the cold fluid side reaches 1100m 2 / m3 At the same time, when the additive manufacturing process is carried out, the semi-elliptical channel and the middle thin plate have a high supporting capacity and can avoid collapse; the hot side heat exchange channel 32 is composed of multiple groups of second channels 321 located in the same plane, and the arrangement direction of the second channel 321 is perpendicular to the flow direction of the hot fluid. The second channel 321 is composed of pipes with a semicircular cross-sectional shape, and the cross-sections of the second channels 321 adjacent to each other are arranged inverted. The radius of the semicircle is 0.75mm, the lateral distance between the centers of the two cross-sections is 0.18mm, and the thinnest wall thickness between the cross-sections is 0.415mm. Due to the high manufacturing freedom of additive manufacturing technology, the adjacent channels in the transverse direction can be arranged inverted, reducing the distance between the two channels, so that more heat exchange channels can be arranged in the core of the same volume, increasing the heat exchange area and improving the heat exchange efficiency.

Claims

1. A compact microchannel LNG heat exchanger, characterized in that: The invention comprises a heat exchanger body (1), wherein a plurality of cold fluid channels (2) and hot fluid channels (3) are arranged alternately and at intervals in a vertical direction; the two ends of the cold fluid channel (2) are respectively connected to a cold fluid inlet (4) and a cold fluid outlet (5), and the two ends of the hot fluid channel (3) are respectively connected to a hot fluid inlet (6) and a hot fluid outlet (7); the cold fluid inlet (4) and the hot fluid outlet (7) are located at one end of the heat exchanger body (1), and the cold fluid outlet (5) and the hot fluid inlet (6) are located at the other end of the heat exchanger body (1); the cold and hot fluids flow from the inlet to the outlet respectively and exchange heat in the heat exchanger body (1); the cold fluid channel (2) comprises, from the inlet to the outlet, a first flow branch channel (21), a cold side heat exchange channel ( 22) and a first converging flow channel (23); the hot fluid channel (3) comprises, from the inlet to the outlet, a second branch flow channel (31), a hot side heat exchange channel (32) and a second converging flow channel (33) which are sequentially connected and located in the same plane; the first branch flow channel (21) expands from the first opening (41) of the cold fluid inlet to both sides of the heat exchanger body (1), and a plurality of flow channel walls (8) for dividing the channel are arranged in the first branch flow channel (21); the first converging flow channel (23) contracts from both sides of the heat exchanger body (1) to the second opening (51) of the cold fluid outlet along the flow direction, and a plurality of flow channel walls (8) for dividing the channel are arranged in the first converging flow channel (23); the structure of the first converging flow channel (23) is the same as that of the first branch flow channel (21), and is symmetrical with respect to the middle cross-section of the heat exchanger body (1).

2. The compact microchannel LNG heat exchanger according to claim 1, characterized in that: The cold fluid inlet (4) and the cold fluid outlet (5) are both cylindrical channels, and the axes of the cold fluid inlet (4) and the cold fluid outlet (5) are both located on the middle longitudinal section of the heat exchanger body (1); the cold fluid inlet (4) and the cold fluid outlet (5) are symmetrically arranged with respect to the middle transverse section of the heat exchanger body (1); the opening of the cold fluid inlet (4) connected to the external pipeline is arranged above the heat exchanger body (1), and the opening of the cold fluid outlet (5) connected to the external pipeline is arranged below the heat exchanger body (1); the cold fluid inlet (4) is provided with a first opening (41) connected to the first branch flow channel (21) along the longitudinal direction, and the cold fluid outlet (5) is provided with a second opening (51) connected to the first converging flow channel (23) along the longitudinal direction.

3. The compact microchannel LNG heat exchanger according to claim 2 is characterized in that: The hot fluid inlet (6) and the hot fluid outlet (7) are both composed of two groups of cylindrical channels symmetrically arranged along the longitudinal section of the heat exchanger body (1); the axis of the hot fluid inlet (6) and the axis of the cold fluid outlet (5) are in the same plane, and the axis of the hot fluid outlet (7) and the axis of the cold fluid inlet (4) are in the same plane; the hot fluid inlet (6) and the hot fluid outlet (7) are symmetrically arranged with respect to the middle transverse section of the heat exchanger body (1); the opening of the hot fluid inlet (6) connected to the external pipeline is arranged above the heat exchanger body (1), and the opening of the hot fluid outlet (7) connected to the external pipeline is arranged below the heat exchanger body (1); the hot fluid inlet (6) is provided with a third opening (61) connected to the second branch flow channel (31) along the longitudinal direction, and the hot fluid outlet (7) is provided with a fourth opening (71) connected to the second converging flow channel (33) along the longitudinal direction.

4. The compact microchannel LNG heat exchanger according to claim 1, characterized in that: The second branch flow channel (31) extends from the third opening (61) of the two groups of hot fluid inlets to the two sides of the heat exchanger body (1) and converges at the middle longitudinal section of the heat exchanger body (1); a plurality of flow channel walls (8) for dividing the channels are arranged in the second branch flow channel (31); the second converging flow channel (33) contracts along the flow direction from the two sides of the heat exchanger body (1) to the fourth opening (71) of the two groups of hot fluid outlets, and a plurality of flow channel walls (8) for dividing the channels are arranged in the second converging flow channel (33); the structure of the second converging flow channel (33) is the same as that of the second branch flow channel (31) and is symmetrical with respect to the middle transverse section of the heat exchanger body (1).

5. The compact microchannel LNG heat exchanger according to claim 1, characterized in that: A first transition channel (24) is provided between the first branch channel (21) and the cold side heat exchange channel (22) and between the cold side heat exchange channel (22) and the first converging channel (23). A channel wall (8) parallel to the axis of the heat exchanger body (1) is provided in the first transition channel (24), one end of which is respectively connected to the channel walls in the first branch channel (21) and the first converging channel (23), and the other end leaves a gap with the two ends of the cold side heat exchange channel (22).

6. The compact microchannel LNG heat exchanger according to claim 1, characterized in that: A second transition channel (34) is provided between the second branch channel (31) and the hot side heat exchange channel (32) and between the hot side heat exchange channel (32) and the second converging channel (33); a channel wall (8) parallel to the axis of the heat exchanger body (1) is provided in the second transition channel (34); one end of the channel wall (8) is respectively connected to the channel walls in the second branch channel (31) and the second converging channel (33); and the other end leaves a gap with both ends of the hot side heat exchange channel (32).

7. The compact microchannel LNG heat exchanger according to claim 1 or 5, characterized in that: The cold side heat exchange channel (22) is composed of a plurality of groups of first channels (221) located in the same plane, the arrangement direction of the first channels (221) is perpendicular to the flow direction of the cold fluid, and the first channels (221) are composed of two upper and lower pipes with semi-elliptical cross-sections arranged opposite to each other.

8. The compact microchannel LNG heat exchanger according to claim 1 or 6, characterized in that: The hot side heat exchange channel (32) is composed of a plurality of groups of second channels (321) located in the same plane, the arrangement direction of the second channels (321) is perpendicular to the flow direction of the hot fluid, the second channels (321) are composed of pipes with a semicircular cross-sectional shape, and the cross-sections of the second channels (321) adjacent to each other in the transverse direction are arranged inverted.

9. A method for preparing the compact microchannel LNG heat exchanger according to claim 1, characterized in that: The heat exchanger body is made of 316L stainless steel powder using laser selective melting additive manufacturing method, and the heat transfer coefficient is controlled to be 5000-6000W / m 2 ·K, the control limit bearing capacity is 18~20MPa.

Images