Falling film heat exchanger and film distribution head thereof

Abstract

The falling-film heat exchanger comprises a tube box and a barrel, a heat exchange tube is arranged in the barrel, the film distribution head comprises a liquid collecting hopper and a film distribution hopper which are vertically arranged in a spaced mode, the liquid collecting hopper and the film distribution hopper are each of a structure with a large upper portion, a small lower portion and an opening in the top, and the upper edge of the liquid collecting hopper is connected with the upper end of the heat exchange tube in a sealed mode; a downcomer is fixedly connected between the liquid collecting hopper and the film distributing hopper, the upper end of the downcomer is connected to the bottom of the liquid collecting hopper and communicated with an inner cavity of the liquid collecting hopper, the lower end of the downcomer is fixed to the bottom of the inner cavity of the film distributing hopper, and open grooves allowing liquid to flow into the inner cavity of the film distributing hopper are evenly formed in the circumferential face of the lower end of the downcomer. An annular flow guide inclined face is arranged on the outer edge of the top of the film distribution hopper and gradually inclines downwards from the film distribution hopper to the heat exchange pipe, and an annular gap is formed between the lower edge of the flow guide inclined face and the inner wall of the heat exchange pipe. After the liquid is distributed on the film distributing head, the liquid can smoothly form a film on the inner wall of the heat exchange tube through the liquid collecting hopper and the film distributing hopper, and the film forming uniformity is improved.

Description

Technical Field

[0001] This invention relates to a falling film heat exchanger and its film distribution head, belonging to the technical field of heat exchange equipment. Background Technology

[0002] The working principle of a falling film heat exchanger is that after the liquid enters the tube box, it forms a uniform thin film on the surface of the heat exchange tubes under the action of gravity after passing through the distributor. This film exchanges heat with the liquid outside the heat exchange tubes through the tube walls. Compared with conventional heat exchangers, falling film heat exchangers have a smaller liquid retention capacity, lower pressure loss, and the liquid forms a film, resulting in a larger contact area with the heat exchange tube surface, a generally higher heat transfer coefficient, and better heat exchange performance.

[0003] For falling film heat exchangers, uniform liquid film formation on the inner surface of the heat exchange tubes is crucial, as it significantly impacts the heat exchanger's performance. The process from liquid entering the heat exchanger to forming a film on the inner surface of the heat exchange tubes generally involves two steps: First, the liquid is distributed throughout the tube area by a liquid distributor within the tube box. Typically, this distributor uses a perforated plate or groove, with a suitable number and placement of holes to distribute the liquid across the entire tube area, allowing it to flow downwards along the inner wall of the heat exchange tubes to form a liquid film. However, the distribution effect of this type of distributor is difficult to guarantee, as it cannot evenly guide the liquid into the lower heat exchange tubes. Second, the distributed liquid forms a liquid film on the inner surface of the heat exchange tubes. Currently, this step often involves adding a grooved "falling film head" to the heat exchange tube head, allowing the liquid to overflow from the upper groove into the inner wall of the heat exchange tube, and then diffuse from the grooved area to the entire inner wall of the heat exchange tube. The uniformity and effectiveness of the liquid film formation are greatly affected by the number and area of ​​the grooves. In summary, the liquid distribution and film formation effect of existing falling film heat exchangers need to be improved. Summary of the Invention

[0004] The purpose of this invention is to provide a falling film heat exchanger to improve the uniformity and film-forming effect of liquid film formation in a falling film evaporator. This invention also provides a film-forming head in this falling film heat exchanger.

[0005] The falling film heat exchanger of the present invention adopts the following technical solution: A falling film heat exchanger includes a cylindrical body, a tube box is provided above the cylindrical body, a liquid distributor is provided inside the tube box, the tube box and the cylindrical body are connected by a tube sheet, a heat exchange tube is provided inside the cylindrical body, the top end of the heat exchange tube passes through the tube sheet in a sealed manner, the opening at the top end of the heat exchange tube forms a tube hole, and a film distribution head is provided inside the top end of the heat exchange tube. The film distribution head includes a liquid collecting hopper and a film distribution hopper arranged at intervals, both of which have a structure that is larger at the top and smaller at the bottom and open at the top, for collecting liquid... The upper edge of the hopper is sealed to the upper end of the heat exchange tube. A downcomer is fixedly connected between the liquid collecting hopper and the film distribution hopper. The upper end of the downcomer is connected to the bottom of the liquid collecting hopper and communicates with the inner cavity of the liquid collecting hopper. The lower end of the downcomer is fixed to the bottom of the inner cavity of the film distribution hopper. Grooves are evenly opened on the circumference of the lower end of the downcomer to allow liquid to flow into the inner cavity of the film distribution hopper. The outer edge of the top of the film distribution hopper is provided with an annular guide slope. The guide slope gradually slopes downward from the film distribution hopper to the heat exchange tube. There is an annular gap between the lower edge of the guide slope and the inner wall of the heat exchange tube.

[0006] The top of the heat exchange tube extends beyond the tube sheet, and the upper end of the liquid collecting hopper is provided with an outward-curved edge, which is engaged with the top of the heat exchange tube and fits against the outer wall of the heat exchange tube.

[0007] The downcomer has a vertically extending groove, and each downcomer has three or more grooves. The width of the annular gap between the guide slope and the inner wall of the heat exchange tube is 1-2 mm.

[0008] The liquid collecting hopper and the membrane hopper adopt a bowl-shaped, basin-shaped, conical, or hemispherical structure; the highest point of the downcomer is higher than the highest point of the guide slope, and the volume of the liquid collecting hopper is larger than that of the membrane hopper.

[0009] The liquid distributor includes an upper distributor and a lower distributor fixed inside a pipe box. The upper distributor and the lower distributor each include a horizontally arranged upper distribution plate and a lower distribution plate. The upper distribution plate has flow holes evenly distributed, and the lower distribution plate has distribution holes evenly distributed. The distribution holes are located below the flow holes and are offset from the flow holes. An overflow pipe is fixed on the upper surface of the lower distribution plate outside each distribution hole. Each overflow pipe has a sealing plate at its bottom. There are notches evenly distributed between the sealing plate and the edge of the distribution hole for liquid to pass through. The liquid passing through each notch flows into the membrane head below.

[0010] The top of the overflow pipe is provided with an overflow groove, which is evenly distributed around the circumference of the overflow pipe.

[0011] The upper and lower distributors adopt a trough structure or a plate structure. When the trough structure is adopted, the upper and lower trough walls are fixed to the outer periphery of the upper and lower distribution plates, respectively. The lower trough wall is fixedly attached to the inner wall of the pipe box, and the upper trough wall is located inside the lower trough wall and is fixedly connected to the lower trough wall by a ring plate. When the plate structure is adopted, the outer periphery of the upper and lower distribution plates is sealed and fixed to the inner wall of the pipe box.

[0012] There are three or four notches between each sealing plate and each distribution plate, each notch of each sealing plate corresponds to a pipe hole, and each pipe hole has three or four distribution holes above it.

[0013] The film distribution head of the falling film heat exchanger of the present invention adopts the following technical solution: A film distribution head of a falling film heat exchanger includes a liquid collecting hopper and a film distribution hopper arranged at intervals. Both the liquid collecting hopper and the film distribution hopper adopt a structure that is larger at the top and smaller at the bottom and open at the top. The upper edge of the liquid collecting hopper is sealed to the upper end of the heat exchange tube. A downcomer is fixedly connected between the liquid collecting hopper and the film distribution hopper. The upper end of the downcomer is connected to the bottom of the liquid collecting hopper and communicates with the inner cavity of the liquid collecting hopper. The lower end of the downcomer is fixed to the bottom of the inner cavity of the film distribution hopper. Grooves are evenly opened on the circumferential surface of the lower end of the downcomer to allow liquid to flow into the inner cavity of the film distribution hopper. An annular guide slope is provided on the outer edge of the top of the film distribution hopper. The guide slope gradually slopes downward from the film distribution hopper towards the heat exchange tube. There is an annular gap between the lower edge of the guide slope and the inner wall of the heat exchange tube.

[0014] The top of the heat exchange tube extends beyond the tube sheet, and the upper end of the liquid collecting hopper is provided with an outward-curved edge, which is engaged with the top of the heat exchange tube and fits against the outer wall of the heat exchange tube.

[0015] The downcomer has a vertically extending groove, and each downcomer has three or more grooves. The width of the annular gap between the guide slope and the inner wall of the heat exchange tube is 1-2 mm.

[0016] The liquid collecting hopper and the membrane hopper adopt a bowl-shaped, basin-shaped, conical, or hemispherical structure. The highest point of the downcomer is higher than the highest point of the guide slope, and the volume of the liquid collecting hopper is larger than that of the membrane hopper.

[0017] The beneficial effects of this invention are as follows: When the falling film heat exchanger of this invention is working, after the liquid enters the tube box, it is distributed by the liquid distributor and then enters the film distribution head inside the lower heat exchange tube. The liquid first concentrates at the bottom of the liquid collecting hopper, and then enters the lower film distribution hopper along the downcomer. After the liquid passes through the groove at the bottom of the downcomer, a certain liquid level is formed in the film distribution hopper, and finally it overflows evenly onto the guide slope at the upper edge of the film distribution hopper, and then enters the annular gap between the guide slope and the inner wall of the heat exchange tube, forming a film on the inner wall of the heat exchange tube. Because the liquid is subjected to a tangential force under the action of gravity after passing through the guide slope, the liquid is more likely to form a film after passing through the annular gap, and the film formation is also more uniform. The liquid enters the film distribution head at the top of each heat exchange tube, and with the liquid collecting hopper and film distribution hopper set above and below, the liquid can smoothly form a film on the inner wall of the heat exchange tube, thereby improving the film formation effect.

[0018] As a preferred option, the outward-curved edge at the top of the liquid collecting hopper can be easily engaged with the top of the heat exchange tube, making the installation of the film distribution head and the heat exchange tube more convenient.

[0019] As a preferred option, three or more slots are evenly arranged on the falling film tube to facilitate the uniform overflow of liquid onto the annular guide plate, thereby improving the uniformity of film distribution.

[0020] As a preferred embodiment, the liquid distributor comprises upper and lower stages, distributing the liquid entering the tube box twice. Since the flow holes are offset from the distribution holes, the liquid flows into the gap between the overflow pipes on the lower distribution plate. Because the overflow pipes are at a certain height relative to the upper surface of the distribution plate, when the liquid level flowing into the distribution plate reaches a certain height, it will flow evenly from the top of the overflow pipe into the interior of the overflow pipe, and then flow downwards along the gap between the sealing plate and the distribution holes into the film-forming head inside the heat exchange tube. Since the bottom of the overflow pipe has a sealing plate, and the gap between the sealing plate and the distribution holes forms a channel for the liquid to enter the tube holes, using the liquid distributor of this invention to distribute the liquid multiple times can make the liquid distribution into each heat exchange tube more uniform, improve the uniformity of liquid entering the heat exchange tube, and further improve the uniformity of film formation.

[0021] As a preferred option, an overflow groove is opened at the top of the overflow pipe to further increase the uniformity of liquid overflow into the overflow pipe.

[0022] As a preferred embodiment, there are three or four notches between an overflow pipe sealing plate and a pipe hole, forming three or four streams of fluid respectively. Each stream of fluid flows into a different heat exchange tube, and each heat exchange tube corresponds to three or four overflow pipes. A total of three or four streams of fluid enter the film distribution head from the circumference of the heat exchange tube, so that the amount of liquid entering the heat exchange tube is uniform. Attached Figure Description

[0023] Figure 1 This is an external schematic diagram of a falling film heat exchanger according to an embodiment of the present invention; Figure 2 yes Figure 1 A sectional view; Figure 3 yes Figure 2 A three-dimensional schematic diagram; Figure 4 yes Figure 2 Schematic diagram of the heat exchanger tube; Figure 5 yes Figure 2 Plan view of the heat exchanger tube; Figure 6 yes Figure 5 A magnified view of a portion of the image; Figure 7 yes Figure 2 Schematic diagram of the overflow pipe; Figure 8 This is a schematic diagram showing the positional arrangement of the first type of heat exchange tubes and distribution holes; Figure 9 yes Figure 8 A schematic diagram showing the positional arrangement of the distribution holes and their corresponding flow holes; Figure 10 yes Figure 8 Top view of the distribution hole in the center; Figure 11 This is a schematic diagram showing the arrangement of the second type of heat exchange tubes and distribution holes; Figure 12 yes Figure 11 A schematic diagram showing the positional arrangement of the distribution holes and their corresponding flow holes; Figure 13 yes Figure 11 Top view of the distribution hole in the center.

[0024] In the diagram: 1-Tube box, 2-Upper distributor, 3-Lower distributor, 4-Tube sheet, 5-Heat exchange tube, 6-Film distribution head, 6.1-Collection hopper, 6.2-Film distribution hopper, 6.3-Downcomer, 6.4-Guide slope, 6.5-Slot, 7-Pipe hole, 8-Distribution hole, 9-Flow hole, 10-Overflow pipe, 10.1-Sealing plate, 10.2-Notch, 10.3-Overflow groove, 11-Cylinder body. Detailed Implementation

[0025] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0026] like Figures 1 to 3 As shown, a falling film heat exchanger according to an embodiment of the present invention includes a cylindrical body 11, a tube box 1 above the cylindrical body, a liquid distributor inside the tube box 1, and a tube sheet 4 connecting the tube box 1 and the cylindrical body 11. A heat exchange tube 5 is disposed inside the cylindrical body 11, with its upper end sealingly passing through the tube sheet 4. The opening at the top of the heat exchange tube forms a tube hole 7. A film distribution head 6 is disposed inside the top of the heat exchange tube 5, and the structure of the film distribution head 6 is as follows... Figures 4 to 6As shown, the membrane head 6 includes a liquid collecting hopper 6.1 and a membrane distributing hopper 6.2 spaced apart vertically. Both the liquid collecting hopper 6.1 and the membrane distributing hopper 6.2 have a structure that is larger at the top and smaller at the bottom with an open top. The upper edge of the liquid collecting hopper 6.1 is sealed to the upper end of the heat exchange tube 5. The liquid collecting hopper 6.1 and the membrane distributing hopper 6.2 are connected by a downcomer 6.3. The upper end of the downcomer 6.3 is connected to the bottom of the liquid collecting hopper 6.1 and communicates with the inner cavity of the liquid collecting hopper 6.1. The lower end of the downcomer 6.3 is fixed to the bottom of the inner cavity of the membrane distributing hopper 6.2. Grooves 6.5 are evenly distributed on the circumference of the lower end of the downcomer 6.3 to allow liquid to flow into the inner cavity of the membrane distributing hopper 6.2. The shape and number of the grooves 6.5 can be set according to actual needs. Schematic, the grooves 6.5 can be long grooves extending vertically, and the number of grooves 6.5 on each downcomer 6.3 can be more than three. The top outer edge of the film-forming hopper 6.2 is provided with an annular guide slope 6.4, wherein the guide slope 6.4 gradually slopes downward from the edge of the film-forming hopper towards the inner wall of the heat exchange tube, and there is an annular gap between the lower edge of the guide slope 6.4 and the inner wall of the heat exchange tube 5. The width of the annular gap between the guide slope 6.4 and the inner wall of the heat exchange tube is 1-2 mm. The highest point of the downcomer 6.3 is higher than the highest point of the guide slope 6.4 to form a pressure difference, pushing the liquid to overflow to the slope and thus form a film. Exemplarily, the liquid collecting hopper 6.1 and the film-forming hopper 6.3 can adopt a bowl-shaped, basin-shaped, conical, or hemispherical structure, etc., and the volume of the liquid collecting hopper 6.1 is larger than that of the film-forming hopper 6.3. The upper end of the heat exchange tube 5 extends beyond the tube sheet 4, and the upper end of the liquid collecting hopper 6.1 is provided with an outwardly flared edge, which engages with the upper end of the heat exchange tube 5 and fits against the outer wall of the heat exchange tube 5.

[0027] The tube sheet 4 is a common type of tube sheet, mainly used to fix the heat exchange tubes 5 and connect the tube box 1 and the shell 11. The heat exchange tubes 5 are also common types of heat exchange tubes, fixed to the tube sheet 4 by expansion welding, with the top extending a certain height from the tube sheet 4 to house the film distribution head 6. The film distribution head 6 consists of three parts from top to bottom: the upper part is a liquid collecting hopper 6.1 with an outward-curving edge, mainly used to collect the liquid passing through the distribution holes 8 and fix the film distribution head 6 to the heat exchange tubes 5, and to concentrate the collected liquid in the middle position. In this embodiment, the liquid collecting hopper 6.1 adopts a "bowl-shaped" structure; the middle part is a downcomer 6.3 with a groove 6.5 at the bottom, used to transport the liquid collected by the liquid collecting hopper 6.1 to the lower part, and also serves to connect the upper and lower parts; the lower part is the film distribution hopper 6.2. In this embodiment, the film distribution hopper 6.2 adopts a "bowl-shaped" structure with a guide slope 6.4. The edge of the guide slope 6.4 forms a uniform annular gap of 1-2mm with the inner wall of the heat exchange tube 5. Of course, the shape of the film distribution hopper 6.2 is not limited to a "bowl" shape, as long as the liquid can overflow evenly and flow out along the guide slope. The height of the downcomer 6.3 is greater than the height of the guide slope 6.4 to form a pressure head, which pushes the liquid to overflow from the film distribution hopper 6.2 to the guide slope 6.4, thereby forming a film.

[0028] The liquid distributor includes an upper distributor 2 and a lower distributor 3 fixed inside a pipe box. The upper distributor 2 and the lower distributor 3 each include a horizontally arranged upper distribution plate and a lower distribution plate, respectively. Flow holes 9 are evenly distributed on the upper distribution plate, and distribution holes 8 are evenly distributed on the lower distribution plate. The distribution holes 8 are located below the flow holes 9 and are offset from them. For example, the arrangement can be as follows: Figure 9 and Figure 12 As shown. An overflow pipe 10 is fixed to the upper surface of the lower distribution plate outside each distribution hole 8. Each overflow pipe has a sealing plate 10.1 at its bottom. Notches 10.2 for liquid passage are evenly distributed between the sealing plate 10.1 and the edge of the distribution hole 8. Liquid passing through each notch 10.2 flows into the membrane head 6 below. An overflow groove is formed at the top of the overflow pipe, and the overflow grooves are evenly distributed circumferentially around the overflow pipe.

[0029] The tube box 1 in this invention is a common type of tube box, mainly serving to fix and support other components. A connecting pipe is located at the center of the top of the tube box 1, serving as the liquid inlet for the falling film heat exchanger. The upper and lower distributors adopt a trough-type or plate-type structure, such as... Figures 2 to 3 As shown, in this embodiment, both the upper distributor 2 and the lower distributor 3 are of a trough structure. The upper and lower distribution plates are respectively fixed to the outer periphery of an upper trough wall and a lower trough wall. The lower trough wall is fixedly attached to the inner wall of the pipe box, and the upper trough wall is located inside the lower trough wall and is fixedly connected to it by a ring plate. The upper distributor 2 has an overall shape resembling a "basin," located below the connecting pipe, and has a certain height. Its outer diameter is smaller than the inner diameter of the lower distributor 3. The specific height and diameter can be determined based on the flow area of ​​the connecting pipe. The total flow area of ​​the flow holes 9 on the upper distribution plate is not less than the flow area of ​​the connecting pipe. The outer diameter of the lower distributor 3 is equal to the inner diameter of the pipe box 1. In other embodiments, when the upper and lower distributors adopt a plate structure, the outer periphery of both the upper and lower distribution plates is sealed and fixed to the inner wall of the pipe box.

[0030] like Figure 10 and Figure 13 As shown, there are three or four notches between each sealing plate and each distribution plate. Each notch on each sealing plate corresponds to a pipe hole, and each pipe hole has three or four distribution holes above it. The position of the distribution holes 9 is mainly affected by the flow area of ​​the connecting pipe and the gap size of the flow holes 8. Specifically, the flow holes 8 on the distribution groove 2 should be staggered with the distribution holes 9 on the distribution plate 3, so that the liquid will not directly enter the distribution holes 8 after passing through the flow holes 9. The overflow pipe 10 is tightly connected to the distribution holes 9 and is higher than the distribution plate 3 to facilitate the formation of an overflow level; as Figure 10 and Figure 13As shown, the bottom sealing plate 10.1 of the overflow pipe 10 has three or four notches 10.2 at the intersection of the distribution hole 8 and the pipe hole 7, allowing the overflowing liquid to flow evenly and precisely to the corresponding heat exchange tube 5; the top of the overflow pipe 10 has an overflow groove 10.3 at the position corresponding to the notch 10.2 of the sealing plate, and the liquid overflows from the overflow groove 10.3 into the overflow pipe, and then flows to the pipe hole 7 below. Figure 8 As shown, the heat exchange tubes 5 are arranged with three notches between each sealing plate 10.1 and each tube hole 7, and each notch of each sealing plate 10.1 corresponds to one tube hole 7, as follows. Figure 8 As shown, each tube hole 7 has three distribution holes 8 above it. This arrangement is suitable for heat exchangers with tubes arranged at 30° and 60°. Figure 11 As shown, the heat exchange tubes 5 are arranged with four notches between each sealing plate 10.1 and each tube hole 7, and each notch of each sealing plate 10.1 corresponds to one tube hole 7, as follows. Figure 11 As shown, each tube hole 7 has four distribution holes 8 above it. This arrangement is suitable for heat exchangers with tubes arranged at 45° and 90°. These two arrangements are mainly due to the fact that heat exchange tubes are usually arranged very compactly, with only about 8-10 mm of spacing between the outer walls of the heat exchange tubes, which limits the arrangement of the distribution holes 8. The distribution holes 8 and the flow holes 9 need to be staggered in flow area to ensure that the liquid passing through the distribution holes 8 and the overflow pipe 10 achieve uniform overflow, thereby ensuring that the amount of liquid flowing into each heat exchange tube is equal.

[0031] In this embodiment, during operation of the falling film heat exchanger, liquid enters the tube box 1 through the connecting pipe at the top of the tube box 1 under the action of a pump or gravity. First, under the action of the upper distributor 2, it flows into the distribution plate 3 through the flow hole 9 at the bottom. Here, since the flow hole 9 is offset from the distribution hole 8, the liquid will flow into the gap between the overflow pipes 10 on the lower distribution plate. Because the overflow pipe 10 is at a certain height relative to the upper surface of the lower distribution plate, when the liquid level flowing into the lower distribution plate reaches a certain height, it will flow evenly from the overflow groove 10.3 at the top of the overflow pipe 10 into the interior of the overflow pipe 10, and along the gap 10.2 between the sealing plate 10.1 and the distribution hole 8, it is divided into 3 or 4 evenly flowing streams into the upper part of the fabric head 6. Here, each fabric head... The liquid collecting hopper 6.1 at the top of the membrane head 6 will receive the three or four streams of liquid flowing down from the three or four overflow pipes 10, and concentrate these three or four streams of liquid to the center position. Then, through the small hole at the bottom, the liquid enters the lower membrane distribution hopper 6.2 along the downcomer 6.3 in the middle. After the liquid passes through the groove 6.5 at the bottom of the downcomer 6.3 in the middle, it forms a certain liquid level in the membrane distribution hopper 6.2 and finally overflows evenly onto the guide slope 6.4 at the upper edge. Since there is only a 1-2 mm annular gap between the guide slope 6.4 and the inner wall of the heat exchange tube 5, and the liquid will be subjected to a tangential force under the action of gravity after passing through the guide slope 6.4, the liquid is more likely to form a film after passing through the annular gap, and the film formation will also be more uniform.

[0032] The structure of the film-covering head of a falling film heat exchanger according to one embodiment of the present invention is as follows: Figures 4 to 6 As shown, its structure is the same as the film head structure in the above-described falling film heat exchanger embodiment, so it will not be described again.

[0033] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and various changes and modifications can be made without departing from the spirit and scope of the invention; all such changes and modifications fall within the scope of protection claimed by the present invention.

Claims

1. A falling film heat exchanger comprising a cylinder, a tube box arranged above the cylinder, a liquid distributor arranged in the tube box, a tube plate connecting the tube box and the cylinder, and a heat exchange tube arranged in the cylinder, characterized in that: The top end of the heat exchange pipe is sealed through the tube plate, and the opening of the top end of the heat exchange pipe constitutes a tube hole. The inside of the top end of the heat exchange pipe is provided with a film distribution head. The film distribution head comprises a liquid collecting cup and a film distribution cup which are arranged in an upper-lower spaced manner. The liquid collecting cup and the film distribution cup both adopt a structure of large at the top and small at the bottom with an opening at the top. The upper edge of the liquid collecting cup is sealingly connected with the upper end of the heat exchange pipe. A downcomer is fixedly connected between the liquid collecting cup and the film distribution cup. The upper end of the downcomer is connected to the bottom of the liquid collecting cup and communicates with the inner cavity of the liquid collecting cup. The lower end of the downcomer is fixed to the bottom of the inner cavity of the film distribution cup. A plurality of grooves are uniformly arranged on the circumferential surface of the lower end of the downcomer for allowing liquid to flow into the inner cavity of the film distribution cup. An annular flow guide inclined surface is arranged at the top outer edge of the film distribution cup. The flow guide inclined surface gradually inclines downward from the film distribution cup to the heat exchange pipe. There is an annular gap between the lower edge of the flow guide inclined surface and the inner wall of the heat exchange pipe.

2. The falling-film heat exchanger according to claim 1, characterized in that: The top end of the heat exchange pipe exceeds the tube plate. The liquid collecting cup is provided with a ring-shaped outward turning flange which is clamped on the top end of the heat exchange pipe and is in close contact with the outer wall of the heat exchange pipe.

3. The falling-film heat exchanger according to claim 1, characterized in that: The grooves of the downcomer are vertical long grooves. The number of the grooves of each downcomer is more than three. The width of the annular gap between the flow guide inclined surface and the inner wall of the heat exchange pipe is 1-2 mm.

4. The falling-film heat exchanger according to claim 1, characterized in that: The liquid collecting cup and the film distribution cup adopt a bowl-shaped or basin-shaped or conical or hemispherical structure. The highest point of the downcomer is higher than the highest point of the flow guide inclined surface. The volume of the liquid collecting cup is larger than that of the film distribution cup.

5. The falling-film heat exchanger according to claim 1, characterized in that: The liquid distributor comprises an upper distributor and a lower distributor which are fixed in the tube box. The upper distributor and the lower distributor respectively comprise horizontally arranged upper distribution plates and lower distribution plates. A plurality of flow-through holes are uniformly arranged on the upper distribution plates. A plurality of distribution holes are uniformly arranged on the lower distribution plates. The distribution holes are located below the flow-through holes and are staggered with the flow-through holes. Overflow pipes are respectively fixed on the outer sides of each distribution hole on the upper surface of the lower distribution plate. Each overflow pipe is provided with a sealing plate at the bottom. A plurality of notches for allowing liquid to pass through are arranged between the sealing plate and the edge of the distribution hole. The liquid passing through each notch is used to flow into the film distribution head below.

6. The falling-film heat exchanger of claim 1, wherein: An overflow groove is arranged at the top of each overflow pipe and is uniformly distributed in the circumferential direction of the overflow pipe.

7. The falling-film heat exchanger of claim 1, wherein: The upper distributor and the lower distributor adopt a groove type structure or a plate type structure. When the groove type structure is adopted, upper groove walls and lower groove walls are respectively fixed on the outer peripheries of the upper distribution plates and the lower distribution plates. The lower groove walls are fixedly attached to the inner wall of the tube box. The upper groove walls are located inside the lower groove walls and are fixedly connected with the lower groove walls through annular plates. When the plate type structure is adopted, the outer peripheries of the upper distribution plates and the lower distribution plates are sealingly fixed with the inner wall of the tube box.

8. The falling-film heat exchanger of claim 1, wherein: The number of notches between each sealing plate and each distribution hole is three or four. Each notch of each sealing plate corresponds to one tube hole. Each tube hole is provided with three or four distribution holes above it.

9. A film distributor head for a falling film heat exchanger, characterized by: The application relates to a heat exchange tube device, which comprises a liquid collecting hopper and a membrane distributing hopper arranged in a vertical direction, the liquid collecting hopper and the membrane distributing hopper are both provided with a structure of large top and small bottom and an opening at the top, the upper edge of the liquid collecting hopper is sealingly connected with the upper end of the heat exchange tube, a downcomer is fixedly connected between the liquid collecting hopper and the membrane distributing hopper, the upper end of the downcomer is connected with the bottom of the liquid collecting hopper and communicates with the inner cavity of the liquid collecting hopper, the lower end of the downcomer is fixedly connected with the bottom of the inner cavity of the membrane distributing hopper, the circumferential surface of the lower end of the downcomer is uniformly provided with grooves for allowing liquid to flow into the inner cavity of the membrane distributing hopper, the top outer edge of the membrane distributing hopper is provided with an annular flow guide inclined surface, the flow guide inclined surface gradually inclines downwards from the membrane distributing hopper to the heat exchange tube, and an annular gap is formed between the lower edge of the flow guide inclined surface and the inner wall of the heat exchange tube.

10. The falling film heat exchanger film distributor head of claim 9, wherein: The top end of the heat exchange tube exceeds the tube plate, the upper end of the liquid collecting hopper is provided with a turn-up edge, the turn-up edge is clamped on the top end of the heat exchange tube and is attached to the outer wall of the heat exchange tube.

11. The falling film heat exchanger film distributor head of claim 9, wherein: The grooves of the downcomer are vertical long grooves, the number of the grooves of each downcomer is more than three, and the width of the annular gap between the flow guide inclined surface and the inner wall of the heat exchange tube is 1-2 mm.

12. The falling film heat exchanger film distributor head of claim 9, wherein: The liquid collecting hopper and the membrane distributing hopper are provided with a bowl-shaped or basin-shaped or conical or hemispherical structure, the highest point of the downcomer is higher than the highest point of the flow guide inclined surface, and the volume of the liquid collecting hopper is larger than that of the membrane distributing hopper.

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