Adsorption type helium-4 continuous operation subKelvin refrigerating system

Abstract

The invention relates to the technical field of sub-Kelvin temperature zone refrigeration, and discloses an adsorption type helium-4 continuous operation sub-Kelvin refrigeration system. Comprising a refrigerating system, the refrigerating system comprises an evaporation module, a first helium-4 storage module, a second helium-4 storage module, a switch module and a cooling module, a blade type structure is adopted, under the condition that the helium-4 suction rate is guaranteed, heat loss caused by superfluid helium-4 is effectively reduced, the temperature change of activated carbon is accelerated through a pump core fin structure, and the heat loss is reduced; meanwhile, the condensation recovery rate of the helium-4 is remarkably increased through the densely-arranged small hole structure of the cooling main body, the thermal contact area is increased through the multi-layer nested non-contact structure adopted by the switch upper end cover, the switch lower end cover and the central pipe, and the conduction rate of the switch module is effectively improved; the suction pipe and the activated carbon increase the capacity of the helium-4 of the switch module and the effective heat conduction and resistance ratio of the switch module in the on-off state.

Description

Technical Field

[0001] The invention relates to the technical field of sub-Kelvin temperature range refrigeration, and in particular to an adsorption type helium 4 continuously operating sub-Kelvin refrigeration system. Background Art

[0002] In the field of scientific research, especially in frontier fields such as space exploration and basic physics research, there is an increasing demand for experimental equipment or detectors under sub-Kelvin (<1K) conditions. It has become a consensus among many top laboratories that the sub-Kelvin temperature range is the key to ensuring ultra-high precision measurements. For example, precision instruments such as scanning tunneling microscopes (STM) and high-end astrophysical telescopes require coolers to reduce their operating temperatures to below 1K in order to obtain precise signal measurements at the atomic and light-year scales. To achieve this goal, it is necessary to study and design a refrigeration system that is simple in structure, easy to control, and can provide a continuous and stable low-temperature environment for scientific research instruments;

[0003] Traditional adsorption helium-4 refrigeration systems are generally large in size and will inevitably vibrate during operation, which is not conducive to application in precision scientific research instruments with limited space and high vibration requirements. In addition, most of them cannot effectively suppress the "superfluid phenomenon" of helium-4. The evaporation of superfluid helium-4 at other locations in the system cannot provide effective cooling power, resulting in heat loss; at the same time, liquid helium in traditional refrigeration devices is prone to leaking into the air due to the open circulation loop, which affects the operation time. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides an adsorption-type helium-4 continuous operation sub-Kelvin refrigeration system.

[0005] The adsorption type helium-4 continuous operation sub-Kelvin refrigeration system of the embodiment of the present invention comprises a refrigeration system, wherein the refrigeration system comprises an evaporation module, a helium-4 storage module 1, a helium-4 storage module 2, a switch module and a cooling module, and the evaporation module, the helium-4 storage module 1, the helium-4 storage module 2, the switch module and the cooling module are all electrically connected to the refrigeration system;

[0006] The evaporation module includes an evaporation unit, a cooling reflux unit and an adsorption unit;

[0007] The switch module comprises an adsorption unit and a heat transfer unit, wherein the heat transfer unit is composed of two copper pieces with high thermal conductivity nested in each other;

[0008] The cooling module includes an evaporation unit and a condensation reflux unit.

[0009] In some embodiments, the interior of the evaporation module is provided with a storage module upper head, a cooling body, an adsorption pump lower head, a filter press and a pump core, the storage module upper head is located above the helium 4 storage module one, the lower surface of the storage module upper head is provided with a cooling body, one end of the helium 4 storage module one is provided with a pipe orifice, and the lower surface of the cooling body is sleeved with a disc base, the interior of the switch module is provided with a switch lower end cover, a switch upper end cover, a center tube, a switch shell, a switch suction pipe, a switch pressing cover, a switch cover, and a switch isolation cover, the switch lower end cover is connected to the disc base, the interior of the cooling module is provided with a helium 4 storage module head, a cooling pipe, a condenser, a condensation pipe, a condensation cooling head, a condensation pipe head, and a support pipe, the interfaces of the cooling pipe, the condensation pipe, and the support pipe are connected to the helium 4 storage module two, the support pipe is a fixed structure, the lower end of the support pipe is fixedly connected to the cooling module, and the upper end of the support pipe is fixedly connected to the disc base.

[0010] In some embodiments, the lower cover of the adsorption pump is located above the cooling body, a shell is provided at one end of the lower cover of the adsorption pump away from the cooling body, the filter screen press is a fixed filter screen, and the pump core adopts a fin structure.

[0011] In some embodiments, the switch upper end cover and the switch lower end cover are two copper parts that are nested with each other but not in contact, and the central tube is a hollow thin tube that is connected to the internal channel of the switch lower end cover.

[0012] In some embodiments, the switch housing fits with the switch upper end cover and the switch lower end cover, and the switch suction tube is connected to the channel inside the switch lower end cover.

[0013] In some embodiments, the switch clamping cover is located inside the switch suction tube, the switch clamping cover is fixed inside the switch suction tube by threads, the switch sealing cover is located inside the switch suction tube and above the switch clamping cover to seal the switch module, and the switch insulating cover is fixedly sleeved on the outside of the switch suction tube.

[0014] In some embodiments, the helium 4 storage module head is located at the lower end of the helium 4 storage module 2, and the upper end of the helium 4 storage module head extends into a fin structure.

[0015] In some embodiments, the condensation cooling head is located on the outside of the condenser, the condensation pipe head is located below the condenser, and the condensation pipe head is fixedly connected to the condensation pipe.

[0016] In some embodiments, a connector 1 is provided on the side surface of the evaporation module, and the connector 1 is connected to the disc base, and a connector 2 is provided on the rear surface of the helium 4 storage module 1, and the connector 2 is connected to the condensation pipe head.

[0017] Compared with the prior art, the present invention provides an adsorption type helium-4 continuous operation sub-Kelvin refrigeration system, which has the following beneficial effects:

[0018] 1. The present invention adopts a blade-shaped structure to effectively reduce the heat loss caused by superfluid helium 4 while ensuring the suction rate of helium 4. The pump core fin structure accelerates the temperature change of activated carbon and the adsorption and release rate of helium 4. At the same time, the densely packed small hole structure of the cooling body significantly increases the condensation recovery rate of helium 4, significantly reducing the refrigeration recovery cycle of the evaporation module. The lower cover of the adsorption unit simply and effectively fixes the activated carbon through the integrated design of the adsorption unit shell, the adsorption unit cover, the upper cover of the cooling body, and the conduit, as well as the mechanical connection with the filter press. The multi-layer nested non-contact structure adopted by the upper and lower end covers of the switch and the central tube increases the thermal contact area, effectively improving the conduction rate of the switch module. The suction pipe and the activated carbon increase the capacity of the switch module helium 4 and the effective thermal conductivity and heat resistance ratio of the switch module in the on and off state;

[0019] 2. The head of the helium 4 storage module of the cooling module of the present invention is placed at the lowest point of the cooling module, that is, the lowest temperature point of the refrigeration system, which improves the refrigeration effect of the system. At the same time, the head of the helium 4 storage module is located at the axial center of the refrigeration system, which is convenient for integration with the currently popular central symmetrical magnetic field. The condensation cooling head is located on the outside of the condenser and can be used as a welding flange structure and an exhaust port or an air filling port. The reserved position can also provide convenience for processing channels of the condenser. The head of the condensation pipe is located below the condenser and serves as a converter between the condenser and the condensation pipe without reducing the number of channels inside the condenser, which effectively improves the condensation effect of the condenser. The porous structure in the condenser and the inclination angle of the inner hole ensure the condensation rate of the cooling module while allowing the liquefied helium 4 to smoothly return to the storage module through gravity, effectively accelerating the liquid helium circulation of the cooling module. The channels in the flow direction of the liquid helium 4 in the refrigeration system are all smoothed and inclined to ensure that no falling vibration will occur during the recovery of the helium 4. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic diagram of the adsorption process structure of the evaporation module of the present invention;

[0021] Figure 2 This is a schematic diagram of the desorption process structure of the evaporation module of the present invention;

[0022] Figure 3 This is a schematic diagram of the switch module structure of the present invention;

[0023] Figure 4 It is a schematic diagram of the structure of the refrigeration system of the present invention;

[0024] Figure 5 It is a schematic diagram of the structure of the adsorption sub-Kelvin refrigeration system of the present invention;

[0025] Figure 6 This is a schematic diagram of the structure of the evaporation module of the present invention;

[0026] Figure 7 This is a schematic diagram of the switch module structure of the present invention;

[0027] Figure 8 This is a schematic diagram of the cooling module structure of the present invention.

[0028] Among them: 001, disc base; 002, connector one; 003, connector two; 100, evaporation module; 101, pump core; 102, lower end cap of adsorption pump; 103, cooling body; 104, upper end cap of storage module; 105, helium 4 storage module one; 200, switch module; 201, switch lower end cover; 202, switch housing; 203, switch upper end cover; 204, switch isolation cover; 205, switch suction pipe; 300, cooling module; 301, helium 4 storage module end cap; 302, helium 4 storage module two; 303, cooling pipe; 304, condensation pipe; 305, condenser; 306, support pipe; 307, condensation cooling end cap; 308, condensation pipe end cap. DETAILED DESCRIPTION

[0029] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] Embodiment 1:

[0031] See also Figure 1-4 , an adsorption type helium-4 continuous operation sub-Kelvin refrigeration system, comprising a refrigeration system, the refrigeration system comprising an evaporation module 100, a helium-4 storage module 105, a helium-4 storage module 2 302, a switch module 200 and a cooling module 300, and the evaporation module 100, the helium-4 storage module 105, the helium-4 storage module 2 302, the switch module 200, and the cooling module 300 are all electrically connected to the refrigeration system;

[0032] The evaporation module 100 includes an evaporation unit, a cooling reflux unit and an adsorption unit. The activated carbon in the adsorption unit of the evaporation module 100 absorbs the helium 4 in the helium 4 storage module 105 into the adsorption unit through adsorption, thereby generating a cooling effect. After the helium 4 in the evaporation module 100 is completely adsorbed by the adsorption unit, the evaporation module 100 loses its refrigeration effect, and it is necessary to heat the pump core 101 of the adsorption unit to release the helium 4. The released helium 4 passes through the cooling body 103 connected to the disc base 001 and is condensed into liquid helium 4 and returns to the helium 4 storage module 105. After the condensation is completed, the heating of the pump core 101 is stopped and the switch module 200 is turned on to cool the pump core 101 and the activated carbon, so that the helium in the evaporation module 100 evaporates to achieve a refrigeration effect.

[0033] The switch module 200 includes an adsorption unit and a heat transfer unit. The heat transfer unit is composed of two copper pieces with high thermal conductivity nested in each other. There is a gap between the copper pieces in the switch module 200. The switch module 200 is in a vacuum state when it is disconnected and has no heat transfer function. When the activated carbon is heated, the gap is filled with helium 4. At this time, helium 4, as a heat exchange medium, transfers the cooling power of the disc bottom plate connected to the lower end cover 201 of the switch to the upper end cover, and then transfers it to the pump core 101 of the adsorption unit of the evaporation module 100 to achieve a cooling effect. After the heating stops, the activated carbon reabsorbs the free helium 4 in the switch module 200, that is, the switch is disconnected;

[0034] The cooling module 300 includes an evaporation unit and a condensation reflux unit. Two sets of evaporation modules 100 and cooling modules 300 are operated in parallel. Cooling is performed by circulating refrigeration in the evaporation module 100. This design is that one heat exchanger is warm and the other is cold. The thermal isolation between the two systems is ensured by placing the equipment in an ultra-high vacuum. The condensation cycle efficiency of the system is ensured by using a 4K temperature disc bottom plate. A connector 002 is provided on the side surface of the evaporation module 100, and the connector 002 is connected to the disc base 001. The rear surface of the helium 4 storage module 105 is provided on a connector 003, and the connector 003 is connected to the condensation pipe cover 308.

[0035] Embodiment 2:

[0036] See also Figure 5-8, an adsorption type helium 4 continuous operation sub-Kelvin refrigeration system, the interior of the evaporation module 100 is provided with a storage module upper head 104, a cooling body 103, an adsorption pump lower head 102, a filter press and a pump core 101, the helium 4 storage module 105 is the main area for helium 4 evaporation, and is the position with the lowest temperature in the evaporation module 100, and it is necessary to reserve threaded holes for connecting heat transfer parts and process exhaust ports or charging ports, as well as welding flange structures, the storage module upper head 104 is located above the helium 4 storage module 105, and the lower surface of the storage module upper head 104 is provided with a cooling body 103, and the storage module upper head 104 can be used to heat the upper end of the helium 4 storage module 105 and the cooling body 103 The lower end provides a sealing effect. A nozzle is provided at one end of the helium 4 storage module 105. The nozzle is an extremely thin sharp blade-shaped structure that can effectively inhibit the passage of superfluid helium 4. The lower surface of the cooling body 103 is sleeved with a disc base 001. The lower head 102 of the adsorption pump is located above the cooling body 103. The end of the lower head 102 of the adsorption pump away from the cooling body 103 is provided with a shell. The middle of the two ends is a hollow capillary for the circulation of helium 4. The capillary is connected to the filter press by a thread. The filter press is a fixed filter to prevent the activated carbon in the adsorption unit from falling off and entering other structures to cause heat loss. The pump core 101 adopts a fin structure to increase the heat exchange area and improve the adsorption and release rate of the activated carbon in the adsorption unit.

[0037] The switch module 200 is provided with a switch lower end cover 201, a switch upper end cover 203, a central tube, a switch housing 202, a switch suction pipe 205, a switch pressing cover, a switch sealing cover, and a switch isolation cover 204. The switch lower end cover 201 is connected to the disc base 001. The switch upper end cover 203 and the switch lower end cover 201 are two copper parts nested in each other but not in contact, and a plurality of narrow gaps are formed between the two. The central tube is a hollow thin tube, and the central tube is connected to the internal channel of the switch lower end cover 201, providing a channel for the circulation of helium 4 and increasing the heat exchange area. The switch housing 202 is connected to the switch upper end cover 203 and the switch lower end cover 201. The switch suction pipe 205 is fitted together, the switch suction pipe 205 is connected with the channel inside the switch lower end cover 201, the switch clamping cover is located inside the switch suction pipe 205, the switch clamping cover is fixed to the inside of the switch suction pipe 205 by threads, and the fixed filter prevents the activated carbon from falling off and entering other structures to affect the conduction ability of the switch module 200. The switch sealing cover is located on the switch suction pipe 205 and is built into the switch clamping cover above the switch module 200. The exhaust port or the inflation port is processed, and the flange structure is welded. The switch isolation cover 204 is fixedly sleeved on the outside of the switch suction pipe 205, aiming to isolate the heat radiation generated by heating the activated carbon in the switch suction pipe 205.

[0038] The interior of the cooling module 300 is provided with a helium 4 storage module head 301, a cooling pipe 303, a condenser 305, a condensation pipe 304, a condensation cooling head 307, a condensation pipe head 308, and a support pipe 306. The helium 4 storage module 2 302 is used as the main area for helium 4 evaporation. The interfaces of the cooling pipe 303, the condensation pipe 304, and the support pipe 306 are connected to the helium 4 storage module 2 302. The support pipe 306 is a fixed structure. The lower end of the support pipe 306 is fixedly connected to the cooling module 300, and the upper end of the support pipe 306 is fixedly connected to the disc base 001. The helium 4 storage module head 301 is located at the helium 4 storage module 2 30 2, the upper end of the helium 4 storage module cover 301 extends into a fin structure, which is the position with the lowest temperature in the cooling module 300, that is, the working area of ​​the refrigeration system. The cooling pipe 303 is the main channel for the evaporation and circulation of helium 4 in the cooling module 300. The helium 4 is quickly condensed through the internal closely spaced circular holes in the condenser 305, and returns to the helium 4 storage module through the condensation pipe 304 by gravity. The condensation cooling cover 307 is located on the outside of the condenser 305, and is reserved for processing the exhaust port or the charging port and the welding flange structure. The condensation pipe cover 308 is located below the condenser 305, and the condensation pipe cover 308 is fixedly connected to the condensation pipe 304.

[0039] When in use, the activated carbon in the adsorption unit of the evaporation module 100 absorbs the helium 4 in the helium 4 storage module 105 into the adsorption unit through adsorption, thereby producing a cooling effect. After the helium 4 in the evaporation module 100 is completely adsorbed by the adsorption unit, the evaporation module 100 loses its cooling effect. It is necessary to release helium 4 by heating the adsorption unit pump core 101. The released helium 4 is condensed into liquid helium 4 after passing through the cooling body 103 connected to the disc base 001 and returns to the helium 4 storage module 105. After the condensation is completed, the pump core 101 is heated and the switch module 200 is turned on to cool the pump core 101 and the activated carbon, so that the helium in the evaporation module 100 evaporates to achieve a refrigeration effect. There is a gap between the copper parts in the switch module 200. The switch module 200 is in a vacuum state when it is disconnected and has no heat transfer function. When the activated carbon is heated, the helium 4 fills the gap. At this time, the helium 4, as a heat exchange medium, transfers the refrigeration power of the disc bottom plate connected to the switch lower end cover 201 to the upper end cover, and then transmits it to the pump core 101 of the adsorption unit of the evaporation module 100 to achieve a cooling effect. After the heating is stopped, the activated carbon reabsorbs the free helium 4 in the switch module 200, that is, the switch is disconnected, and two sets of evaporation modules 100 and cooling modules 300 running in parallel are used to cool by circulating refrigeration in the evaporation module 100. This design is that one heat exchanger is warm and the other is cold. The thermal isolation between the two systems is ensured by placing the equipment in an ultra-high vacuum, and the condensation cycle efficiency of the system is ensured by using a disk bottom plate with a temperature of 4K.

[0040] In view of the deficiencies in the related art, the present invention provides an adsorption-type helium-4 continuous operation sub-Kelvin refrigeration system, which adopts a blade-shaped structure to effectively reduce the heat loss caused by superfluid helium-4 while ensuring the helium-4 suction rate. The pump core fin structure accelerates the temperature change of activated carbon and the adsorption and release rate of helium-4. At the same time, the densely packed small hole structure of the cooling body significantly increases the condensation recovery rate of helium-4 and significantly reduces the refrigeration recovery cycle of the evaporation module. The lower cover of the adsorption unit simply and effectively fixes the activated carbon through the integrated design of the adsorption unit shell, the adsorption unit cover, the upper cover of the cooling body, and the conduit, as well as the mechanical connection with the filter screen pressing material. The multi-layer nested non-contact structure adopted by the upper and lower end covers of the switch and the central tube increases the thermal contact area, effectively improving the conduction rate of the switch module. The suction pipe and the activated carbon increase the helium-4 capacity of the switch module and the effective thermal conductivity-to-heat ratio of the switch module in the on and off states. The cooling module helium-4 storage The module head is placed at the lowest point of the cooling module, that is, the lowest temperature point of the refrigeration system, which improves the refrigeration effect of the system. At the same time, the head of the helium-4 storage module is located at the axial center of the refrigeration system, which is convenient for integration with the popular central symmetrical magnetic field. The condensation cooling head is located on the outside of the condenser and can be used as a welding flange structure and an exhaust port or an air filling port. The reserved position can also provide convenience for the processing of condenser channels. The condensation pipe head is located below the condenser and serves as a converter between the condenser and the condensation pipe without reducing the number of channels inside the condenser, which effectively improves the condensation effect of the condenser. The porous structure in the condenser and the inclination of the inner hole ensure the condensation rate of the cooling module while allowing the liquefied helium-4 to smoothly return to the storage module through gravity, effectively accelerating the liquid helium circulation of the cooling module. The channels in the flow direction of liquid helium-4 in the refrigeration system are smoothed and inclined to ensure that no falling vibration will occur during the recovery of helium-4.

[0041] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. An adsorption type helium-4 continuous operation sub-Kelvin refrigeration system, comprising a refrigeration system, characterized in that: The refrigeration system comprises an evaporation module (100), a helium 4 storage module 1 (105), a helium 4 storage module 2 (302), a switch module (200) and a cooling module (300), and the evaporation module (100), the helium 4 storage module 1 (105), the helium 4 storage module 2 (302), the switch module (200) and the cooling module (300) are all electrically connected to the refrigeration system; The evaporation module (100) comprises an evaporation unit, a cooling reflux unit and an adsorption unit; The switch module (200) comprises an adsorption unit and a heat transfer unit, wherein the heat transfer unit is composed of two copper pieces with high thermal conductivity nested in each other; The cooling module (300) comprises an evaporation unit and a condensation reflux unit.

2. The adsorption type helium-4 continuous operation sub-Kelvin refrigeration system according to claim 1, characterized in that: The evaporation module (100) is provided with a storage module upper cover (104), a cooling body (103), an adsorption pump lower cover (102), a filter press and a pump core (101) inside. The storage module upper cover (104) is located above the helium 4 storage module 1 (105). The lower surface of the storage module upper cover (104) is provided with a cooling body (103). One end of the helium 4 storage module 1 (105) is provided with a pipe mouth. The lower surface of the cooling body (103) is sleeved with a disc base (001). The switch module (200) is provided with a switch lower end cover (201), a switch upper end cover (203), a central tube, a switch housing (202), a switch suction pipe (205), a switch pressing cover, a switch The cooling module (300) is provided with a helium 4 storage module head (301), a cooling pipe (303), a condenser (305), a condensation pipe (304), a condensation cooling head (307), a condensation pipe head (308), and a support pipe (306). The interfaces of the cooling pipe (303), the condensation pipe (304), and the support pipe (306) are connected to the helium 4 storage module 2 (302). The support pipe (306) is a fixed structure. The lower end of the support pipe (306) is fixedly connected to the cooling module (300), and the upper end of the support pipe (306) is fixedly connected to the disc base (001).

3. The adsorption type helium-4 continuous operation sub-Kelvin refrigeration system according to claim 2, characterized in that: The lower cover head (102) of the adsorption pump is located above the cooling body (103); an outer shell is provided at one end of the lower cover head (102) of the adsorption pump away from the cooling body (103); the filter screen press is a fixed filter screen; and the pump core (101) adopts a fin structure.

4. The adsorption type helium 4 continuous operation sub-Kelvin refrigeration system according to claim 2, characterized in that: The switch upper end cover (203) and the switch lower end cover (201) are two copper parts that are nested in each other but not in contact, and the central tube is a hollow thin tube that is connected to the internal channel of the switch lower end cover (201).

5. The adsorption type helium 4 continuous operation sub-Kelvin refrigeration system according to claim 2, characterized in that: The switch housing (202) fits in contact with the switch upper end cover (203) and the switch lower end cover (201), and the switch suction pipe (205) is in communication with a channel inside the switch lower end cover (201).

6. The adsorption type helium 4 continuous operation sub-Kelvin refrigeration system according to claim 2, characterized in that: The switch clamping cover is located inside the switch suction pipe (205), the switch clamping cover is fixed inside the switch suction pipe (205) by means of threads, the switch sealing cover is located inside the switch suction pipe (205) and above the switch clamping cover for sealing the switch module (200), and the switch insulating cover (204) is fixedly sleeved on the outside of the switch suction pipe (205).

7. The adsorption type helium-4 continuous operation sub-Kelvin refrigeration system according to claim 2, characterized in that: The helium 4 storage module cover (301) is located at the lower end of the helium 4 storage module 2 (302), and the upper end of the helium 4 storage module cover (301) extends into a fin structure.

8. The adsorption type helium-4 continuous operation sub-Kelvin refrigeration system according to claim 2, characterized in that: The condensation cooling head (307) is located on the outside of the condenser (305), the condensation pipe head (308) is located below the condenser (305), and the condensation pipe head (308) is fixedly connected to the condensation pipe (304).

9. The adsorption type helium-4 continuous operation sub-Kelvin refrigeration system according to claim 1, characterized in that: The side surface of the evaporation module (100) is provided with a connector 1 (002), and the connector 1 (002) is connected to the disc base (001); the rear surface of the helium 4 storage module 1 (105) is provided on a connector 2 (003), and the connector 2 (003) is connected to the condensation pipe cover (308).

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