A dual system dry evaporator for central air conditioner

Abstract

The application belongs to the evaporator technical field, and discloses a double-system dry evaporator for central air conditioner, which comprises an evaporator shell, two sets of liquid inlet covers and exhaust covers installed on the outside of the evaporator shell, two sets of heat exchange pipe groups installed in the evaporator shell, the liquid inlet cover can be communicated with the corresponding exhaust cover through the heat exchange pipe group, and further comprises a gas-liquid separation mechanism installed on the liquid inlet cover. The above scheme drives the cage blade to rotate through the power motor, and the refrigerant enters the inside of the cage blade through the top end of the separation cylinder. The liquid refrigerant falls under the action of gravity and reaches the lower part of the cage blade, and then the liquid refrigerant is distributed to the flow guide plate through the flow guide pipe, and finally the liquid refrigerant at the bottom of the flow guide plate is uniformly sent into the exhaust covers, so that the problem that the liquid-phase refrigerant is naturally settled in the lower space of the header under the action of gravity and causes the difference of the liquid-phase refrigerant in each heat exchange pipe to be too large is solved.

Description

Technical Field

[0001] This invention belongs to the field of evaporator technology, specifically a dual-system dry evaporator for central air conditioning. Background Technology

[0002] Dry evaporators are the core heat exchange equipment in central air conditioning refrigeration systems. Their working principle is that the refrigerant flows and evaporates inside the heat exchange tubes, absorbing heat, while the medium being cooled flows outside the tubes, exchanging heat through the tube walls.

[0003] A dual-system dry evaporator is a high-efficiency heat exchanger that integrates two independent refrigeration circuits within its casing. The refrigerant flows and evaporates in a gas-liquid two-phase state within the heat exchange tubes. It is necessary to ensure a relatively uniform gas-liquid coexistence state within each heat exchange tube to guarantee heat exchange efficiency and reliable oil return. However, the refrigerant at the heat exchange tube supply end is centrally supplied to several heat exchanger pipes. Due to the density difference between the gas and liquid phases of the refrigerant, the liquid phase naturally settles in the lower space of the manifold under gravity. At this time, a large amount of liquid refrigerant flows into the lower heat exchange tube inlet, leading to uneven liquid distribution in each tube. This can trigger a chain reaction of problems, from decreased heat exchange efficiency and oil return failure to compressor liquid slugging or even complete unit failure. The hazards are amplified under partial load and dual-system cross-operation scenarios. Summary of the Invention

[0004] To address the problems mentioned in the background section, this invention provides a dual-system dry evaporator for central air conditioning, which solves the problem that the liquid refrigerant naturally settles in the lower space under gravity within the manifold, resulting in excessive differences in the liquid refrigerant concentration in each heat exchange tube.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a dual-system dry evaporator for central air conditioning, comprising an evaporator shell and two sets of liquid inlet covers and exhaust covers installed on the outside thereof, wherein two sets of heat exchange tube assemblies are installed inside the evaporator shell, and the liquid inlet covers can be connected to the corresponding exhaust covers through the heat exchange tube assemblies, and further comprising: a gas-liquid separation mechanism installed on the liquid inlet covers; The gas-liquid separation mechanism includes a separation cylinder fixedly installed on the liquid inlet cover. A guide block is installed at the bottom of the separation cylinder cavity. A power motor is installed inside the guide block, and the output end of the power motor can extend upward to the outside of the guide block. A cage-like blade located above the guide block is fixedly installed at the output end of the power motor. A gas guide pipe is fixedly connected to the separation cylinder. The bottom end of the gas guide pipe is fixedly connected to the liquid inlet cover. Several guide plates located inside the liquid inlet cover are vertically installed on one side of the evaporator shell. The bottom of the guide plate is located below the bottom of the two sets of heat exchange tubes and is used to send refrigerant into the heat exchange tubes. Several guide pipes are fixedly connected to the bottom of the separation cylinder and are used to send the refrigerant in the separation cylinder into several sets of guide plates respectively. The bottom end of the guide pipe extends into the liquid inlet cover. The inlet of the separation cylinder is located above the axis of the cage-like blade. The diameter of the upper part of the cage-like blade is smaller than the diameter of the lower part.

[0006] Preferably, the bottom channel cross-section of the separation cylinder is smaller than the upper channel cross-section, and the bottom end of the guide plate is provided with an opening that can communicate with the liquid inlet cover cavity; The bottom ends of the guide plate are equipped with baffles to prevent liquid refrigerant from falling downwards from both ends of the guide plate.

[0007] Preferably, the bottom end of the guide tube is flat and can extend to the top of the corresponding guide plate.

[0008] Preferably, the upper surface of the guide block is conical, and the conical portion can extend to the bottom of the cavity of the cage blade.

[0009] Preferably, an arc-shaped baffle is fixedly installed at the top of the cavity of the separation cylinder between the outer periphery of the cage-type blade and the air guide pipe, and the bottom end of the arc-shaped baffle is located below the top end of the air guide pipe.

[0010] Preferably, the guide plate is further provided with a plurality of liquid distribution plates arranged symmetrically in the direction of the guide plate. The liquid distribution plates are arranged sequentially from the bottom of the guide plate upwards at intervals, and the liquid distribution plates at the top are closer to the end of the guide plate than the liquid distribution plates at the bottom.

[0011] Preferably, the top of the cage-like blades is provided with several sets of teeth in a circular array, and the top of the separation cylinder is fixedly connected to an elastic sheet located above the cage-like blades. The bottom end of the elastic sheet extends into the gap between two teeth, and several sets of teeth can move the elastic sheet when the cage blade rotates circumferentially.

[0012] Preferably, a set of capillary tubes are fixedly installed symmetrically on the flow guide block. The top end of the capillary tubes extends above the flow guide block and to the middle and lower part of the cage blades. The bottom end of the capillary tubes passes through the flow guide block, the separation cylinder and the liquid inlet cover and can extend to the bottom of the liquid inlet cover cavity. The inner diameter of the capillary is smaller than the inner diameter of the guide tube.

[0013] Preferably, a flow guide shroud located above the capillary tube is fixedly sleeved on the shaft portion of the output shaft of the power motor.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: The above scheme uses a motor to drive the cage blades to rotate, and the refrigerant enters the cage blades through the top of the separation cylinder. The liquid refrigerant falls first under the influence of gravity and reaches the lower part of the cage blades. Inside the cage blades, the liquid refrigerant is separated outward by centrifugal force and thrown out of the cage blades, while the gaseous refrigerant is thrown outward from the upper part of the cage blades and impacts the inner wall of the separation cylinder and the arc-shaped baffle. The gaseous refrigerant is sent into the exhaust cover through the gas guide pipe and the liquid inlet cover, while the liquid refrigerant is distributed into the guide plate through the guide pipe. Finally, the liquid refrigerant at the bottom of the guide plate is evenly sent into several exhaust covers, which solves the problem of excessive differences in the liquid refrigerant in each heat exchange tube due to the natural settling of the liquid refrigerant in the lower space under the influence of gravity in the manifold.

[0015] The above solution utilizes the large diameter of the cage-like blades during rotation, which generates a strong negative pressure in the central area. This negative pressure draws the refrigerant accumulated at the bottom of the liquid inlet cover through the capillary tube and sends it back to the top of the guide block. After being thrown out again, it is sent back into the exhaust cover through the guide pipe and guide plate. This prevents some refrigerant gas from accumulating at the bottom of the liquid inlet cover when it turns into liquid inside.

[0016] The above scheme achieves separation efficiency by having the cage-like blades rotate while the teeth on their outer edges simultaneously perform circular motion. During high-speed rotation, the teeth periodically impact the elastic sheet, causing the elastic sheet to vibrate at high frequency. This vibration is then transmitted to the wall of the separation cylinder and the surface of the arc-shaped baffle. As a result, the adhesion between the mist-like refrigerant droplets adhering to the inner wall of the separation cylinder and the surface of the arc-shaped baffle and the wall is weakened, and the droplets cannot adhere stably and quickly collect and fall along the wall, effectively improving the separation efficiency. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the overall structure of the present invention; Figure 2 This is a frontal perspective view of the present invention; Figure 3 This is a front cross-sectional view of the separation cylinder of the present invention; Figure 4 for Figure 3 Enlarged view of point A in the middle; Figure 5 for Figure 3 Enlarged view of point B in the middle; Figure 6 This is a schematic diagram of the cage-type blade in the present invention; Figure 7 This is a schematic diagram of the top cross-sectional structure of the guide plate of the present invention; Figure 8 This is a schematic diagram of the capillary tube installation structure of the present invention.

[0018] In the diagram: 1. Evaporator shell; 11. Liquid inlet cover; 12. Heat exchanger tube assembly; 13. Exhaust hood; 2. Gas-liquid separation mechanism; 21. Separation cylinder; 211. Arc-shaped baffle; 212. Elastic sheet; 22. Guide block; 23. Power motor; 231. Guide shroud; 24. Cage blades; 241. Teeth; 25. Gas guide pipe; 26. Guide pipe; 27. Guide plate; 271. Liquid separator; 3. Capillary tube. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] like Figures 1 to 8 As shown, the present invention provides a dual-system dry evaporator for central air conditioning, including an evaporator shell 1 and two sets of liquid inlet covers 11 and exhaust covers 13 installed on the outside of it. Two sets of heat exchange tube groups 12 are installed inside the evaporator shell 1. The liquid inlet covers 11 can be connected to the corresponding exhaust covers 13 through the heat exchange tube groups 12. It also includes a gas-liquid separation mechanism 2 installed on the liquid inlet covers 11. The gas-liquid separation mechanism 2 includes a separation cylinder 21 fixedly mounted on the liquid inlet cover 11. A guide block 22 is installed at the bottom of the separation cylinder 21. A power motor 23 is installed inside the guide block 22, and the output end of the power motor 23 can extend upward to the outside of the guide block 22. A cage-like blade 24 located above the guide block 22 is fixedly mounted on the output end of the power motor 23. A gas guide pipe 25 is fixedly connected to the separation cylinder 21, and the bottom end of the gas guide pipe 25 is fixedly connected to the liquid inlet cover 11. (Evaporator) A number of guide plates 27 are vertically installed on one side of the outer casing 1, located inside the liquid inlet cover 11. The bottom of the guide plates 27 is located below the bottom of the two sets of heat exchange tube groups 12 for sending refrigerant into the heat exchange tube groups 12. The bottom of the separation cylinder 21 is fixedly connected to a number of guide pipes 26 for sending the refrigerant in the separation cylinder 21 into the number of guide plates 27 respectively. The bottom end of the guide pipes 26 extends into the liquid inlet cover 11. The inlet of the separation cylinder 21 is located above the axial part of the cage blade 24. The diameter of the upper part of the cage blade 24 is smaller than that of the lower part, the upper surface of the guide block 22 is conical, and the conical part can extend to the bottom of the cavity of the cage blade 24.

[0021] Using the above scheme, the cage blades 24 are rotated by the power motor 23, and the refrigerant enters the cage blades 24 through the top of the separation cylinder 21. The liquid refrigerant falls under the action of gravity and reaches the lower part of the cage blades 24. The liquid refrigerant inside the cage blades 24 is separated outward by centrifugal force and thrown out of the cage blades 24. The liquid refrigerant is distributed into the guide plate 27 through the guide pipe 26. Finally, the liquid refrigerant at the bottom of the guide plate 27 is evenly sent into several exhaust covers 13, which solves the problem that the liquid refrigerant will naturally settle in the lower space under the action of gravity in the manifold, resulting in excessive differences in the liquid refrigerant in each heat exchange tube. The liquid refrigerant inside the cage blade 24 will be separated outward by centrifugal force and thrown out of the cage blade 24. The gaseous refrigerant will be thrown outward from the top of the cage blade 24 and hit the inner wall of the separator 21 and the arc-shaped baffle 211. The gaseous refrigerant will be sent into the exhaust cover 13 through the gas guide pipe 25, the liquid inlet cover 11 and the heat exchange tube group 12 and finally output outward. It should be noted that, for guide tube 26, we will take the two upper tubes as an example: Pipe 1: Δh1 = H + L1 Pipeline 2: Δh2 = H + L2 Ignoring the constant effect of g, the flow rate ratio is: the outlet flow rate is: Flow rate Q = Av = Vπd² / 4 Let Q1 = Q2 d1 2 v1=d2 2 ·v2 conversion The length of pipe 1 is set to L1 = 20 cm, the length of pipe 2 is L2 = 30 cm, the inner diameter is d1 = 2 cm, and the liquid level in the separation cylinder 21 is H = 10 cm. Substituting into the above formula, when Q1=Q2, d2≈1.86cm.

[0022] Therefore, based on the above deduction, the inner diameter of the output end of the guide tube 26 needs to be reduced from top to bottom to avoid excessive flow differences caused by different heights of the output ends of each guide tube 26.

[0023] like Figure 3 , Figure 5 and Figure 7As shown, a number of liquid distribution plates 271 are symmetrically arranged inside the flow guide plate 27. The liquid distribution plates 271 are arranged sequentially from the bottom of the flow guide plate 27 upwards at intervals, and the liquid distribution plates 271 at the top are closer to the end of the flow guide plate 27 than the liquid distribution plates 271 at the bottom. The bottom channel cross-section of the separator 21 is smaller than that of its upper channel cross-section, and the bottom end of the guide plate 27 is provided with an opening that can communicate with the cavity of the liquid inlet cover 11; the bottom ends of the guide plate 27 are provided with baffles to prevent liquid refrigerant from falling down from the ends of the guide plate 27; the bottom end of the guide pipe 26 is flat and can extend to the top of the corresponding guide plate 27. By adopting the above scheme, the flattened bottom of the guide pipe 26 and the guide plate 27, as well as the guide plate 271, reduces the abrupt change in the flow channel cross section of the guide plate 27, avoids liquid surface fluctuation and deflection during the refrigerant flow, and ensures that the liquid refrigerant has a more uniform liquid surface when it enters the guide plate 27, thereby improving the uniform distribution of the liquid refrigerant and sending it into the corresponding exhaust cover 13.

[0024] like Figure 4 and Figure 6 As shown, an arc-shaped baffle 211 is fixedly installed on the top of the cavity of the separator 21 between the outer periphery of the cage blade 24 and the air guide pipe 25, and the bottom end of the arc-shaped baffle 211 is located below the top end of the air guide pipe 25. By adopting the above scheme, during the rotation of the cage blade 24, due to its large bottom diameter, a strong negative pressure will be generated in its central area. The negative pressure draws the refrigerant accumulated at the bottom of the liquid inlet cover 11 through the bottom of the capillary tube 3 and sends it back to the top of the guide block 22. After being thrown out again, it is sent back to the exhaust cover 13 through the guide pipe 26 and the guide plate 27. This avoids some refrigerant gas from accumulating at the bottom of the liquid inlet cover 11 when it turns into liquid inside the liquid inlet cover 11.

[0025] like Figure 4 and Figure 6 As shown, the top of the cage blade 24 is provided with several sets of teeth 241 in a ring array direction, and the top of the separation cylinder 21 is fixed with an elastic sheet 212 located above the cage blade 24. The bottom end of the elastic sheet 212 extends into the gap between two teeth 241, and several sets of teeth 241 can actuate the elastic sheet 212 when the cage blade 24 rotates circumferentially. Using the above scheme, while the cage blade 24 rotates, the teeth 241 on its outer edge also perform circular motion. During the high-speed rotation, the teeth 241 periodically impact the elastic sheet 212, causing the elastic sheet 212 to generate high-frequency vibration. This vibration is then transmitted to the wall of the separation cylinder 21 and the surface of the arc-shaped baffle 211, causing the droplets to resonate. As a result, the adhesion between the mist-like refrigerant droplets adhering to the inner wall of the separation cylinder 21 and the surface of the arc-shaped baffle 211 and the wall surface is weakened, and the droplets cannot adhere stably and quickly collect and fall along the wall surface, thus improving the separation efficiency. It should be noted that the elastic sheet 212 can be made of wear-resistant spring steel or beryllium copper alloy to improve the service life of the component.

[0026] like Figure 3 , Figure 6 and Figure 8 As shown, a set of capillary tubes 3 are fixedly installed symmetrically on the guide block 22. The top end of the capillary tube 3 extends above the guide block 22 and to the middle and lower part of the cage blade 24. The bottom end of the capillary tube 3 passes through the guide block 22, the separation cylinder 21 and the liquid inlet cover 11 and can extend to the bottom of the liquid inlet cover 11 cavity. The inner diameter of the capillary tube 3 is smaller than the inner diameter of the guide tube 26. A guide cover 231 located above the capillary tube 3 is fixedly sleeved on the shaft of the output shaft of the power motor 23. By adopting the above scheme, during the rotation of the cage blade 24, due to its large bottom diameter, a strong negative pressure will be generated in its central area. The negative pressure draws the refrigerant accumulated at the bottom of the liquid inlet cover 11 through the bottom of the capillary tube 3 and sends it back to the top of the guide block 22. After being thrown out again, it is sent back to the exhaust cover 13 through the guide pipe 26 and the guide plate 27. This avoids some refrigerant gas from accumulating at the bottom of the liquid inlet cover 11 when it turns into liquid inside the liquid inlet cover 11. The design of the flow guide shroud 231 prevents the refrigerant of the gas-liquid mixture transported from the top of the separation cylinder 21 into the top of the capillary tube 3, and ensures that the capillary tube 3 can stably extract the liquid refrigerant remaining at the bottom of the liquid inlet cover 11 under the negative pressure. It should be noted that when there is less liquid refrigerant remaining at the bottom of the liquid inlet cover 11 cavity, the gas inside the liquid inlet cover 11 will also be extracted.

[0027] Working principle and usage process of this invention: During operation, the power motor 23 drives the cage blades 24 to rotate, and the refrigerant enters the cage blades 24 through the top of the separator 21. The liquid refrigerant falls first under the action of gravity and reaches the lower part of the cage blades 24. The liquid refrigerant inside the cage blades 24 is separated outward by centrifugal force and thrown out of the cage blades 24, while the gaseous refrigerant is thrown outward from the upper part of the cage blades 24 and hits the inner wall of the separator 21 and the arc-shaped baffle 211. The droplets of refrigerant contained in the gaseous refrigerant will adhere to the inner wall of the separator 21 or the arc-shaped baffle 211. The gaseous refrigerant will be sent into the exhaust cover 13 through the gas guide pipe 25 and the liquid inlet cover 11. The liquid refrigerant will be distributed into the guide plate 27 through the guide pipe 26. Finally, the liquid refrigerant at the bottom of the guide plate 27 will be evenly sent into several exhaust covers 13.

[0028] During the rotation of the cage blade 24, due to its large bottom diameter, a strong negative pressure is generated in its central area. The negative pressure draws the refrigerant accumulated at the bottom of the liquid inlet cover 11 through the bottom of the capillary tube 3 and sends it back to the top of the guide block 22. After being thrown out again, it is sent back to the exhaust cover 13 through the guide pipe 26 and the guide plate 27. This prevents some refrigerant gas from accumulating at the bottom of the liquid inlet cover 11 when it turns into liquid inside the liquid inlet cover 11.

[0029] As the cage-like blades 24 rotate, the teeth 241 on their outer edges also rotate in a circular motion. During the high-speed rotation, the teeth 241 periodically impact the elastic sheet 212, causing the elastic sheet 212 to vibrate at high frequency. This vibration is then transmitted to the wall of the separator 21 and the surface of the arc-shaped baffle 211. As a result, the adhesion between the mist-like refrigerant droplets adhering to the inner wall of the separator 21 and the surface of the arc-shaped baffle 211 and the wall is weakened. The droplets cannot adhere stably and instead quickly gather and fall along the wall, thus improving the separation efficiency.

[0030] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0031] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A dual-system dry evaporator for central air conditioning, comprising an evaporator shell (1) and two sets of liquid inlet covers (11) and exhaust covers (13) installed outside thereon, wherein two sets of heat exchange tube assemblies (12) are installed inside the evaporator shell (1), and the liquid inlet covers (11) are connected to the corresponding exhaust covers (13) through the heat exchange tube assemblies (12), characterized in that, Also includes: Gas-liquid separation mechanism (2) installed on liquid inlet cover (11); The gas-liquid separation mechanism (2) includes a separation cylinder (21) fixedly installed on the liquid inlet cover (11). A guide block (22) is installed at the bottom of the cavity of the separation cylinder (21). A power motor (23) is installed inside the guide block (22), and the output end of the power motor (23) can extend upward to the outside of the guide block (22). A cage-like blade (24) located above the guide block (22) is fixedly installed at the output end of the power motor (23). A gas guide pipe (25) is fixedly connected to the separation cylinder (21), and the bottom end of the gas guide pipe (25) is fixedly connected to the liquid inlet cover (11). A number of guide plates (27) are vertically installed on one side of the evaporator shell (1) and located inside the liquid inlet cover (11). The bottom of the guide plate (27) is located below the bottom of the two sets of heat exchange tube groups (12) for sending refrigerant into the heat exchange tube groups (12). The bottom of the separator (21) is fixedly connected to a number of guide pipes (26) for sending the refrigerant in the separator (21) into the number of guide plates (27). The bottom end of the guide pipe (26) extends into the liquid inlet cover (11). The inlet of the separator (21) is located above the axis of the cage blade (24). The diameter of the upper part of the cage-like blade (24) is smaller than the diameter of the lower part; The bottom channel cross section of the separation cylinder (21) is smaller than the upper channel cross section, and the bottom end of the guide plate (27) is provided with an opening that can communicate with the cavity of the liquid inlet cover (11). The bottom two ends of the guide plate (27) are provided with baffles to prevent liquid refrigerant from falling down from both ends of the guide plate (27); The top of the cavity of the separation cylinder (21) is fixedly installed with an arc-shaped baffle (211) located between the outer periphery of the cage blade (24) and the air guide pipe (25), and the bottom end of the arc-shaped baffle (211) is located below the top end of the air guide pipe (25). The guide plate (27) is also provided with a number of liquid distribution plates (271) arranged symmetrically. The liquid distribution plates (271) are arranged sequentially from the bottom of the guide plate (27) upwards at intervals, and the liquid distribution plates (271) at the top are closer to the end of the guide plate (27) than the liquid distribution plates (271) at the bottom.

2. The dual-system dry evaporator for central air conditioning according to claim 1, characterized in that: The bottom end of the guide tube (26) is flat and can extend to the top of the corresponding guide plate (27).

3. The dual-system dry evaporator for central air conditioning according to claim 1, characterized in that: The upper surface of the guide block (22) is conical, and the conical part can extend to the bottom of the cavity of the cage blade (24).

4. The dual-system dry evaporator for central air conditioning according to claim 1, characterized in that: The top of the cage blade (24) is provided with several sets of teeth (241) in a ring array direction, and the top of the separation cylinder (21) is fixed with an elastic sheet (212) located above the cage blade (24). The bottom end of the elastic sheet (212) extends into the gap between two teeth (241), and several sets of teeth (241) can actuate the elastic sheet (212) when the cage blade (24) rotates circumferentially.

5. The dual-system dry evaporator for central air conditioning according to claim 1, characterized in that: A set of capillary tubes (3) are fixedly installed symmetrically on the guide block (22). The top end of the capillary tubes (3) extends above the guide block (22) and to the middle and lower part of the cage blade (24). The bottom end of the capillary tubes (3) passes through the guide block (22), the separation cylinder (21) and the liquid inlet cover (11) and can extend to the bottom of the liquid inlet cover (11) cavity. The inner diameter of the capillary (3) is smaller than the inner diameter of the guide tube (26).

6. The dual-system dry evaporator for central air conditioning according to claim 5, characterized in that: A flow guide (231) is fixedly sleeved on the shaft part of the output shaft of the power motor (23) above the capillary tube (3).

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