Falling film evaporator and distributor suitable for single-flow heat exchange

Abstract

A liquid supply pipe and an air suction pipe are arranged far away from the water inlet side, and the liquid supply pipe communicates with a distribution box; the distribution box main body structure is divided into a plurality of areas in the length direction of the barrel, and flow distribution of the areas is set to be in gradient distribution in the length direction, so that more flow distribution on the water inlet side is achieved, and less flow distribution on the water outlet side is achieved. The heat exchange gradient requirement of a single flow in the length direction is met, the heat exchange area and the refrigerant amount are saved, and the heat exchanger is suitable for a single-flow large-cooling-capacity unit; the processing is convenient and simple, and easy to realize; and the risk of air suction with liquid can be avoided to the greatest extent.

Description

Technical Field

[0001] This application relates to the field of air conditioning and heating technology, and more specifically, to a falling film evaporator structure for single-pass heat exchange, which includes a uniformly distributed evaporator distributor. Background Technology

[0002] A refrigeration system or chiller unit mainly consists of a compressor, evaporator, condenser, and throttling device. With increasingly stringent requirements for energy conservation and environmental protection, research on chiller units has shifted towards high performance and low energy consumption. In conventional air conditioning systems, the energy consumption of chiller units and water pumps accounts for approximately 74%, while the series counter-current arrangement of multiple chiller units is becoming increasingly widespread in large-scale units due to its significant energy-saving effects. Falling film evaporators are also widely used in the refrigeration and air conditioning field because of their advantages such as low refrigerant charge, compact structure, high heat transfer efficiency, and stable heat exchange.

[0003] Due to limitations in water-side pressure drop and increased demands on unit energy efficiency, chiller units often employ a series counter-flow configuration. In short, series counter-flow refers to connecting two chiller units in series, with specific requirements for the flow direction of chilled water and cooling water: chilled water first passes through the evaporator of the upstream chiller unit and then the evaporator of the downstream chiller unit; while cooling water flows in the opposite direction, preferentially passing through the condenser of the downstream chiller unit and then the condenser of the upstream chiller unit. Compared to conventional chiller unit arrangements, this configuration allows for the sharing of a single chilled water pump and cooling water pump, saving energy, simplifying piping layout, and conserving floor space. When using a series counter-flow chiller unit, the water circuit of a single unit system often adopts a single-pass configuration.

[0004] Because most mainstream chiller evaporators employ a two-pass or multi-pass configuration, their characteristic is a relatively uniform heat flux density distribution along the length of the evaporator. However, chillers using a series counter-flow configuration employ a single-pass evaporator. Since the temperature difference along the length of the heat exchanger decreases, the heat flux density distribution along the length is uneven, with a high heat flux density on the inlet side and a low heat flux density on the outlet side. Therefore, for falling film evaporators, if the flow distribution along the length is uniform, insufficient flow on the inlet side makes the falling film and flooded tube bundles on the inlet side very prone to drying out, resulting in decreased heat exchange efficiency. Excessive flow on the outlet side results in a thicker liquid film, but this film does not participate in heat exchange, leading to decreased heat exchange efficiency across the entire area, refrigerant waste, and insufficient utilization of the heat exchange area, with an overall heat exchange area loss potentially reaching 30%. To prevent the inlet side tubes from drying out, the common method is to increase the refrigerant quantity, which, in turn, worsens the heat exchange on the far side and wastes refrigerant. Summary of the Invention

[0005] The technical problem to be solved by this application is to propose a falling film evaporator and distributor structure suitable for single-pass heat exchange, which meets the heat exchange gradient requirements of a single pass in the length direction, saves heat exchange area and refrigerant volume, and is suitable for single-pass large-capacity cooling units; at the same time, it is easy and simple to process and easy to implement; and it can minimize the risk of liquid carryover during suction.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A falling film evaporator suitable for single-pass heat exchange, wherein the evaporator shell is horizontally positioned with the inlet and outlet sides located at opposite ends of the shell, characterized in that: Both the liquid supply pipe and the air suction pipe are located away from the water inlet side, and the liquid supply pipe is connected to the distribution box; The distribution box is located above the heat exchange tube group in the falling film zone and the heat exchange tube group in the full liquid zone, and is placed horizontally between the inlet and outlet sides. The main structure of the distribution box is divided into multiple regions along the length of the cylinder, and the flow rate of the multiple regions is set to be distributed in a gradient along the length direction, so as to achieve a larger flow rate distribution on the inlet side and a smaller flow rate distribution on the outlet side.

[0007] In the above technical solution, the main structure of the dispensing box is divided into multiple regions along the length of the cylinder. For example, typically there are 2-3 or 3-4 regions, or 3-5 regions.

[0008] In the above technical solution, the main structure of the distribution box is divided into multiple regions along the length of the cylinder, and the distribution flow rate of each region along the length is set according to the heat exchange demand gradient.

[0009] In a preferred embodiment, for example, the entire evaporator is divided into three zones along its length, with an approximate heat exchange ratio of 3:2:1 for each zone. The corresponding distribution box is then adjusted to a similar 3:2:1 ratio along its length, so that the membrane covering the heat exchange tubes can meet the heat exchange requirements.

[0010] Of course, those skilled in the art can also adjust the number of zones according to the actual heat transfer gradient, selecting typically 2-3 or 3-4 zones, or 3-5 zones. The flow rate distribution along the length of each zone is set according to the gradient as 5:3:2, 6:4:2, or 4:3:2, or other suitable ratios.

[0011] This is not a limitation of the present invention.

[0012] In the above technical solution, the distribution box is divided into two stages. The first stage distribution box adopts a rectangular pressure distribution box. The rectangular box body has uneven primary outlet holes on two corresponding side walls along the length of the cylinder. The rectangular box body is connected to the liquid inlet, which is located away from the water inlet side. The second stage adopts a gravity distribution box with uneven secondary distribution holes at the horizontal bottom. The arrangement relationship between the primary outlet holes and the secondary distribution holes is as follows: the holes closer to the water inlet side are arranged more densely, and the holes farther away from the water inlet side are arranged more sparsely.

[0013] In the above technical solution, multiple zones are set along the length of the cylinder for the primary outlet hole and the secondary distribution hole. Each zone of each stage is arranged from dense to sparse along the length, so that the flow area of ​​the opening is large near the water inlet side and small away from it.

[0014] In the above technical solution, a vent window is provided on the top of the distribution box, and a top horizontal baffle-shaped vent hood is provided on the vent window. The vent hood is positioned away from the air intake and liquid inlet, and one end of the horizontal baffle forms an opening with the cylinder body towards the water inlet side tube plate of the cylinder body. In the above technical solution, the primary outlet hole and the secondary distribution hole are respectively set in three zones along the length of the cylinder. Each zone of each stage is arranged from dense to sparse along the length, so that the flow area of ​​the opening is large near the water inlet side and small away from it.

[0015] In the above technical solution, the rectangular box sidewall of the first-stage distribution box near the liquid inlet is not perforated.

[0016] A distributor is disposed above the heat exchange tube group in the falling film zone and the heat exchange tube group in the full liquid zone, characterized in that it is horizontally positioned between the inlet side and the outlet side. It is divided into two stages. The first stage distribution box adopts a rectangular pressure distribution box. The rectangular box body has uneven primary outlet holes on two corresponding side walls along the length of the cylinder. The rectangular box body is connected to the liquid inlet, which is located away from the water inlet side. The second stage adopts a gravity distribution box with uneven secondary distribution holes at the horizontal bottom. The arrangement of the primary outlet holes and secondary distribution holes is as follows: the holes closer to the water inlet side are arranged more densely, and the holes farther away from the water inlet side are arranged more sparsely.

[0017] In the above technical solution, the holes in the first-stage and second-stage distribution boxes can be round, square, or other shapes. The first-stage distribution box has no holes on the side wall near the liquid inlet, with denser holes closer to the inlet and sparser holes further away. The second-stage distribution box has unevenly distributed holes at the bottom, with the holes also arranged in a pattern where the flow area is larger near the inlet and smaller further away.

[0018] In summary, this invention proposes a falling film evaporator and distributor structure suitable for single-pass falling film evaporators, addressing the heat exchange characteristics of such evaporators. Both the supply pipe and suction pipe of the falling film evaporator are positioned far from the inlet water side. Due to the characteristics of the inlet and outlet water, the falling film evaporator exhibits a large temperature difference and high heat flux density on the inlet side, resulting in a large heat exchange capacity, while the temperature difference, heat flux density, and heat exchange capacity are small on the outlet side. The heat exchange in the falling film evaporator gradually decreases from the inlet to the outlet water. The evaporator can be approximated by dividing it into multiple regions (two or more) along its length. The required refrigerant quantity in each region also gradually decreases from high to low. Correspondingly, the main structure of the distributor box is divided into multiple regions (two or more) along its length. Following the heat exchange characteristics of a single-pass heat exchanger, the flow rate distributed along the length is gradient-distributed, with a higher flow rate on the inlet side and a lower flow rate on the outlet side. The heat exchange capacity of the film on the surface of the heat exchange tubes in each region is also proportional to the decrease in the temperature difference between the inside and outside of the tubes in each region, thus ensuring that the film on the outside of the heat exchange tubes meets the heat exchange requirements.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention ensures that the gas-liquid two-phase mixed refrigerant, after entering the distribution box from the side furthest from the inlet, can be distributed along its length according to the temperature gradient of heat exchange. The specially structured distribution box satisfies the distribution needs of the gas-liquid mixed refrigerant while also controlling the pressure drop of the distribution box to be low. This avoids the shortcomings of existing technologies where uniform refrigerant distribution results in insufficient flow on the inlet side and excessive flow on the outlet side. Furthermore, the falling film and full-liquid zone tubes on the inlet side are prone to drying out, leading to decreased heat exchange efficiency and insufficient utilization of the heat exchange area.

[0020] Compared to traditional methods that increase refrigerant volume to prevent the inlet pipe from drying out, leading to refrigerant waste or overuse, this invention designs a distribution box along the heat flux density of the evaporator cylinder to create a gradient refrigerant distribution. The single-pass distributor initially distributes the two-phase refrigerant along the length direction according to the heat exchange ratio, ensuring that the two-phase refrigerant containing a large amount of gas is proportionally distributed into the secondary distribution box. Without increasing the refrigerant volume, the flow distribution on the inlet side is sufficient and does not cause falling film or full liquid zone tube bundles on the inlet side.

[0021] The distributor of the present invention is provided with a vent cover on the top. The vent cover is located away from the suction port and the liquid supply pipe, so that the gaseous refrigerant discharged from the top of the distribution box is discharged to the tube sheet, away from the suction port, so as to avoid the suction port from affecting the gas-liquid two-phase separation in the distribution box.

[0022] This invention relates to falling film evaporators and distributors for single-pass heat exchange, specifically a falling film evaporator structure suitable for single-pass heat exchange, incorporating an internal evaporator distributor to achieve a gradient distribution design of heat flux density and refrigerant heat exchange along the cylinder length. It can be applied in heating, ventilation, air conditioning, refrigeration, chemical, and environmental protection fields. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of a single-pass heat exchange falling film evaporator according to an embodiment of this application.

[0025] Figure 2 This is a schematic diagram of the distributor according to an embodiment of this application.

[0026] Figure 3 This is a structural diagram of the one-time distribution hole arrangement method in an embodiment of this application.

[0027] Figure 4 This is a structural diagram of the secondary distribution hole arrangement method in an embodiment of this application.

[0028] Figure 5 This is a schematic diagram illustrating the flow of gaseous refrigerant inside the distribution box and outside the evaporator tube in an embodiment of this application. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0030] Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0031] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0032] In the description of this application, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product is in use. These terms are used only for the convenience of describing this application and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application. Furthermore, the terms "first," "second," and "third," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0033] Furthermore, terms such as "horizontal," "vertical," and "sag" do not imply that components must be absolutely horizontal or suspended, but rather that they can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal relative to "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0034] In the description of this application, it should also be noted that, unless otherwise expressly specified and limited, the terms "set up," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0035] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature being directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0036] The features and performance of this application will be further described in detail below with reference to the embodiments.

[0037] Example 1 As attached Figure 1 According to the present invention, the falling film evaporator suitable for single-pass heat exchange mainly consists of an evaporator shell 1, a liquid supply pipe 2, a distribution box 3, a falling film zone pipe group 4, a full liquid zone pipe group 5, an air intake 6, a water inlet side cover 7, a water outlet side cover 8, and an evaporator tube sheet 9.

[0038] The refrigerant entering the evaporator supply pipe 2 is a two-phase gas-liquid mixture. Especially for negative pressure refrigerants, the volume fraction of the gaseous refrigerant can account for about 80% of the volume fraction of the inlet two-phase gas-liquid refrigerant.

[0039] Under normal refrigeration conditions, the inlet water temperature of the single-pass evaporator in the refrigeration unit is approximately 12℃, and the outlet water temperature is 7℃. If the evaporator temperature is 6℃, the temperature difference between the inside and outside of the tubes near the inlet side is 6℃, while the temperature difference between the inside and outside of the tubes near the outlet side is approximately 1℃. Therefore, the heat flux density is greater near the inlet side, resulting in a larger refrigerant evaporation rate. This requires a larger refrigerant distribution to ensure sufficient liquid film on the outside of the heat exchange tubes in the falling film zone near the inlet side, and for the liquid level in the full liquid zone to completely submerge the heat exchange tubes, leading to higher heat exchange efficiency. On the outlet side, due to the smaller heat exchange temperature difference, the heat flux density is lower, resulting in a smaller refrigerant evaporation rate and a smaller required refrigerant distribution. Considering the heat exchange and evaporation characteristics of this heat exchanger, the inlet side has the largest heat exchange capacity, the largest evaporation rate, and the highest airflow velocity, carrying more liquid droplets and a higher risk of liquid carryover during suction. Therefore, the suction port 6 is located away from the tube sheet 9 and vent window 33 on the inlet side to minimize the risk of liquid carryover during suction.

[0040] Meanwhile, the heat exchanger distributor proposed in this invention has a distribution structure that optimizes heat exchange and saves refrigerant. The structure is described as follows: As attached Figure 2 The distribution box structure mainly consists of a liquid supply pipe 2, a primary distribution box 31, and a secondary distribution box 32.

[0041] The distribution box 3 includes a primary distribution box 31 and a secondary distribution box 32. The liquid supply pipe 2 passes directly through the top cover of the distribution box 32 and is directly connected to the primary distribution box 31. The top of the distribution box 3 is equipped with a vent window and a mist eliminator 33 (wire mesh separator) away from the liquid inlet or the liquid supply pipe 2. The vent window is equipped with a vent hood 34 whose outlet is biased towards the evaporator tube sheet.

[0042] The gas-liquid mixture of refrigerant at the bottom of the condenser enters the primary distribution box 3 through the liquid inlet pipe 2. After initial distribution in the primary distribution box 31, the refrigerant is roughly distributed along its length according to the heat exchange ratio, with a larger flow rate on the inlet side and a smaller flow rate further away. It then enters the secondary distribution box 32, where the gas-liquid mixture undergoes gas-liquid separation. The separated gaseous refrigerant flows out through the vent at the top of the box, while the liquid refrigerant falls into the bottom of the secondary distribution box 32 under gravity. It then flows out along its length according to the heat exchange ratio, forming a film heat exchanger on the outside of the heat exchange tube bundle below. By increasing the flow rate outside the heat exchange tubes in the high heat flux density heat exchange zone, the heat exchange outside the tubes is enhanced. For the same amount of heat exchange, approximately 30% of the heat exchange area can be saved. In the distribution box 3, the refrigerant undergoes gas-liquid separation. When the gaseous refrigerant overflows from the top vent after separation, it is easily entrained by the suction port, causing secondary entrainment of the liquid inside the box. To avoid the suction port affecting the gas-liquid separation within the box, a vent guide hood 34 is added to the top of the box. After gravity separation and droplet capture by the misting device, the gaseous refrigerant overflowing from the box is guided by the vent hood 34 to the tube sheet side away from the suction port 6 (tube sheet 9 at the water inlet cap 7). At this point, the suction port 6 has almost no impact on the gas-liquid separation within the distribution box 3. The airflow direction of the gaseous refrigerant within the distribution box 3 is as follows: Figure 5 The red streamline indicates the direction of the evaporating gaseous refrigerant outside the pipe below the distribution box. Figure 5 Blue streamlined lines.

[0043] The primary distribution box 31 can be a spray box or a spray pipe structure. Preferably, the spray box 31 has a rectangular structure with spray holes 311 on the side wall of the box. The holes can be round, square or other types of holes. The opening rule is that there are no holes on the side of the liquid inlet. The liquid is roughly distributed along the length direction according to the heat exchange ratio. The flow rate distributed on the side of the liquid inlet is large, so the openings are dense or large. The flow rate distributed away from the side of the liquid inlet is small, so the openings are sparse or small. The openings gradually change from dense to sparse or from large to small along the length direction. This makes the gas and liquid two-phase refrigerant distributed along the length of the cylinder according to the heat exchange gradient in the distribution box 31. The refrigerant flows out through the spray holes 311 and enters the secondary distribution box 32.

[0044] The secondary distributor 32 has the following structural features: the secondary distribution box is a structure 32 that encloses the primary spray box (pipe) 31; the bottom has a liquid distribution hole or an outlet hole 322; the top is equipped with a vent window. In the box, the liquid refrigerant is more likely to separate and settle under the action of gravity, forming a liquid surface at the bottom of the box. The gaseous refrigerant carries some liquid refrigerant upward. Some smaller droplets collide with the angled box wall at the top under the action of the airflow and flow down the box wall and out from the lower distribution hole. Some droplets are carried by the gas to the vent window and are separated by the action of the mist eliminator 33. The droplets fall back into the box, and the gaseous refrigerant overflows. Generally, when the dryness inside the box is low and the amount of gaseous refrigerant is small, the required vent area is small enough to meet the optimal gas flow rate for mist eliminator 33. However, when the cooling capacity processed by the evaporator increases, the amount of gaseous refrigerant that needs to be separated inside the box increases, and the required vent area also increases. At this time, the distance between the vent and the suction port 6 becomes closer, the compressor's suction effect on the box increases, the fluid flow at the vent accelerates, and the flow rate increases, making it extremely easy to carry away the liquid inside the box, causing the mist eliminator 33 to fail. To avoid the interference of suction effect on the gas-liquid separation inside the box, a guide hood is added above the vent to guide the gaseous refrigerant flowing out of the box to the tube sheet 9, which is far away from the suction port 6. This does not affect the gas-liquid separation inside the box and minimizes the interference of compressor suction on the fluid inside the box. The distribution direction of the gaseous refrigerant airflow inside the box is as follows: Figure 5 The red streamline indicates the direction of the evaporating gaseous refrigerant outside the pipe below the distribution box. Figure 5 Blue streamline, Figure 5 The demonstration showed that the air intake is far from the water inlet side, and the airflow path of the distribution box and the lower part near the water inlet side is longer, making it easier for the carried droplets to fall back, and greatly reducing the risk of liquid being carried in the air intake.

[0045] The distribution holes or outlet holes 322 at the bottom of the secondary distributor 32 box follow the pattern as follows: Figure 4 The heat exchange is distributed along the length direction according to the heat exchange ratio. A larger flow rate is distributed on the inlet side, resulting in denser or larger openings; a smaller flow rate is distributed further away from the inlet side, resulting in sparser or smaller openings. The overall openings gradually change from dense to sparse or from large to small along the length direction (e.g., ...). Figure 4 The arrows point from dense to sparse, indicating that the flow rate is greater on the inlet side than on the outlet side (the tube density of the falling film heat exchanger tube group 4 gradually decreases from left to right), thus distributing the gas-liquid two-phase refrigerant along the length of the cylinder in the distribution box 32 according to the heat transfer gradient. The corresponding heat transfer on the surface of the film heat exchanger tubes is also proportional to the decrease in temperature difference between the inside and outside of the tube along the length direction, such as... Figure 1 The heat exchange capacity of the heat exchange tube group 4 in the falling film zone decreases proportionally to the temperature difference between the inside and outside of the tube along its length.

[0046] Example 2 The distribution box 3 includes a primary distribution box 31 and a secondary distribution box 32. The liquid supply pipe 2 passes directly through the top cover of the distribution box 32 and is directly connected to the primary distribution box 31. The top of the distribution box 3 is equipped with a vent window and a mist eliminator 33 (wire mesh separator) away from the liquid inlet or the liquid supply pipe 2. The vent window is equipped with a vent hood 34 whose outlet is biased towards the evaporator tube sheet.

[0047] The gas-liquid mixture of refrigerant at the bottom of the condenser enters the primary distribution box 3 through the liquid inlet pipe 2. After initial distribution in the primary distribution box 31, the refrigerant is roughly distributed along its length according to the heat exchange ratio, with a larger flow rate on the inlet side and a smaller flow rate further away. It then enters the secondary distribution box 32, where the gas-liquid mixture undergoes gas-liquid separation. The separated gaseous refrigerant flows out through the vent at the top of the box, while the liquid refrigerant falls into the bottom of the secondary distribution box 32 under gravity. It then flows out along its length according to the heat exchange ratio, forming a film heat exchanger on the outside of the heat exchange tube bundle below. By increasing the flow rate outside the heat exchange tubes in the high heat flux density heat exchange zone, the heat exchange outside the tubes is enhanced. For the same amount of heat exchange, approximately 30% of the heat exchange area can be saved. In the distribution box 3, the refrigerant undergoes gas-liquid separation. When the gaseous refrigerant overflows from the top vent after separation, it is easily entrained by the suction port, causing secondary entrainment of the liquid inside the box. To avoid the suction port affecting the gas-liquid separation within the box, a vent guide hood 34 is added to the top of the box. After gravity separation and droplet capture by the misting device, the gaseous refrigerant overflowing from the box is guided by the vent hood 34 to the outlet side of the tube sheet (tube sheet 9 at the inlet side water cover 7), away from the suction port 6. At this point, the suction port 6 has almost no impact on the gas-liquid separation within the distribution box 3. The airflow direction of the gaseous refrigerant within the distribution box 3 is as follows: Figure 5 The red streamline indicates the direction of the evaporating gaseous refrigerant outside the pipe below the distribution box. Figure 5 Blue streamlined lines.

[0048] The primary distribution box 31 can be a spray box or a spray pipe structure. Preferably, the spray box 31 has a rectangular structure with spray holes 311 on the side wall of the box. The holes can be round, square or other types of holes. The opening rule is that there are no holes on the side of the liquid inlet. The liquid is roughly distributed along the length direction according to the heat exchange ratio. The flow rate distributed on the side of the liquid inlet is large, so the openings are dense or large. The flow rate distributed away from the side of the liquid inlet is small, so the openings are sparse or small. The openings gradually change from dense to sparse or from large to small along the length direction. This makes the gas and liquid two-phase refrigerant distributed along the length of the cylinder according to the heat exchange gradient in the distribution box 31. The refrigerant flows out through the spray holes 311 and enters the secondary distribution box 32.

[0049] The secondary distributor 32 has the following structural features: the secondary distribution box 32 is a structure that encloses the primary spray box (pipe) 31; a liquid distribution hole (liquid distribution hole or outlet hole 322) is opened at the bottom; a vent window is provided at the top. In the box, the liquid refrigerant is more likely to separate and settle under the action of gravity, forming a liquid surface at the bottom of the box. The gaseous refrigerant carries some liquid refrigerant upward. Some smaller droplets collide with the angled box wall at the top under the action of airflow and flow down the box wall and out from the lower distribution hole. Some droplets are carried by the gas to the vent window and are separated by the action of the mist eliminator 33. The droplets fall back into the box, and the gaseous refrigerant overflows. Generally, when the dryness inside the box is low and the amount of gaseous refrigerant is small, the required vent area is small enough to meet the optimal gas flow rate for mist eliminator 33. However, when the cooling capacity processed by the evaporator increases, the amount of gaseous refrigerant that needs to be separated inside the box increases, and the required vent area also increases. At this time, the distance between the vent and the suction port 6 becomes closer, the compressor's suction effect on the box increases, the fluid flow at the vent accelerates, and the flow rate increases, making it extremely easy to carry away the liquid inside the box, causing the mist eliminator 33 to fail. To avoid the interference of suction effect on the gas-liquid separation inside the box, a guide hood is added above the vent to guide the gaseous refrigerant flowing out of the box to the tube sheet 9, which is far away from the suction port 6. This does not affect the gas-liquid separation inside the box and minimizes the interference of compressor suction on the fluid inside the box. The distribution direction of the gaseous refrigerant airflow inside the box is as follows: Figure 5 The red dashed arrows indicate the direction of the evaporating gaseous refrigerant outside the pipes below the distribution box. Figure 5 Blue solid lines, arrows, and streamlined shapes. Figure 5 The demonstration showed that the air intake is far from the water inlet side, and the airflow path of the distribution box and the lower part near the water inlet side is longer, making it easier for the carried droplets to fall back, and greatly reducing the risk of liquid being carried in the air intake.

[0050] The distribution holes or outlet holes 322 at the bottom of the secondary distributor 32 box follow the pattern as follows: Figure 4 The heat exchange is distributed along the length direction according to the heat exchange ratio. A larger flow rate is distributed on the inlet side, resulting in denser or larger openings; a smaller flow rate is distributed further away from the inlet side, resulting in sparser or smaller openings. The overall openings gradually change from dense to sparse or from large to small along the length direction (e.g., ...). Figure 4 The arrows point from dense to sparse, indicating that the flow rate is greater on the inlet side than on the outlet side. The tube density of the falling film heat exchanger tube group 4 gradually decreases from left to right, dividing it into three distinct open areas: densely vented area 3221, moderately densely vented area 3222, and sparsely vented area 3223. This ensures that the gas-liquid two-phase refrigerant is distributed along the length of the cylinder in the distribution box 32 according to the heat transfer gradient. The corresponding heat transfer on the surface of the film heat exchanger tubes is also proportional to the decrease in temperature difference between the inside and outside of the tube along the length direction, such as... Figure 1 The heat exchange capacity of the heat exchange tube group 4 in the falling film zone decreases proportionally to the temperature difference between the inside and outside of the tube along its length.

[0051] The embodiments described above are some, but not all, of the embodiments of this application. The detailed description of the embodiments of this application is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

Claims

1. A falling film evaporator suitable for single-pass heat exchange, wherein the evaporator shell is horizontally positioned, with the inlet and outlet sides located at opposite ends of the shell, characterized in that: Both the liquid supply pipe and the air suction pipe are located away from the water inlet side, and the liquid supply pipe is connected to the distribution box; The distribution box is located above the heat exchange tube group in the falling film zone and the heat exchange tube group in the full liquid zone, and is placed horizontally between the inlet and outlet sides. The main structure of the distribution box is divided into multiple regions along the length of the cylinder, and the flow distribution of multiple regions is set to have a gradient distribution along the length, so as to achieve a larger flow distribution on the inlet side and a smaller flow distribution on the outlet side.

2. The falling film evaporator suitable for single-pass heat exchange according to claim 1, characterized in that... The main structure of the distribution box is divided into multiple regions along the length of the cylinder.

3. The falling film evaporator suitable for single-pass heat exchange according to claim 1, characterized in that... The main structure of the distribution box is divided into multiple regions along the length of the cylinder, and the distribution flow rate of each region is set according to a gradient along the length direction.

4. The falling film evaporator suitable for single-pass heat exchange according to claim 1, characterized in that... The distribution box is divided into two stages. The first stage distribution box adopts a rectangular pressure distribution box. The rectangular box body has uneven primary outlet holes on two corresponding side walls along the length of the cylinder. The rectangular box body is connected to the liquid inlet, which is located away from the water inlet side. The second stage adopts a gravity distribution box with uneven secondary distribution holes at the horizontal bottom. The arrangement of the primary outlet holes and secondary distribution holes is as follows: the holes closer to the water inlet side are arranged more densely, and the holes farther away from the water inlet side are arranged more sparsely.

5. The falling film evaporator suitable for single-pass heat exchange according to claim 1, characterized in that... Multiple zones are set along the length of the cylinder for the primary outlet and the secondary distribution holes. Each zone of each stage is arranged from dense to sparse along the length, so that the flow area of ​​the opening is large near the water inlet and small away from it.

6. The falling film evaporator suitable for single-pass heat exchange according to claim 1, characterized in that... A vent window is provided on the top of the dispensing box, and a top horizontal baffle-shaped vent cover is provided on the vent window. The vent cover is positioned away from the air intake and liquid inlet, and one end of the horizontal baffle forms an opening with the cylinder body facing the water inlet side tube plate of the cylinder body.

7. The falling film evaporator suitable for single-pass heat exchange according to claim 1, characterized in that... The primary outlet and secondary distribution holes are each set with three zones along the length of the cylinder. Each zone of each stage is arranged from dense to sparse along the length, so that the flow area of ​​the opening is large near the water inlet and small away from it.

8. The falling film evaporator suitable for single-pass heat exchange according to claim 1, characterized in that... The first-stage dispensing box has no openings on the rectangular box sidewall near the inlet.

9. A distributor, disposed above the heat exchange tube group in the falling film zone and the heat exchange tube group in the flooded liquid zone, characterized in that... It is placed horizontally between the inlet and outlet sides; It is divided into two stages. The first stage distribution box adopts a rectangular pressure distribution box. The rectangular box body has uneven primary outlet holes on two corresponding side walls along the length of the cylinder. The rectangular box body is connected to the liquid inlet, which is located away from the water inlet side. The second stage adopts a gravity distribution box with uneven secondary distribution holes at the horizontal bottom. The arrangement of the primary outlet holes and secondary distribution holes is as follows: the holes closer to the water inlet side are arranged more densely, and the holes farther away from the water inlet side are arranged more sparsely.

10. The dispenser according to claim 9, characterized in that; The bottom of the secondary distribution box is equipped with uneven distribution holes, with a larger flow area near the water inlet and a smaller flow area further away.

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