WO2018143419A1

WO2018143419A1 - Liquid supply system

Info

Publication number: WO2018143419A1
Application number: PCT/JP2018/003630
Authority: WO
Inventors: 清隆古田; 大澤　芳夫; 森　浩一
Original assignee: イーグル工業株式会社
Priority date: 2017-02-03
Filing date: 2018-02-02
Publication date: 2018-08-09
Also published as: JPWO2018143419A1; EP3578812A1; CN110192032A; KR20190098219A; US20190353148A1

Abstract

Provided is a liquid supply system which makes it possible to shorten the time spent on precooling and thus shorten the time needed until a pump can be activated. The system is characterized in that: a vessel (130) is provided with a first case part (131) in which flow passages are formed that pass through a first pump chamber (P1) and a second pump chamber (P2), and a second case part (132) which is provided so as to surround the outer wall surface of the first case part (131); and the space (fourth space K4) between the first case part (131) and the second case part (132) is configured such that an ultralow temperature liquid for precooling can flow therethrough.

Description

Liquid supply system

The present invention relates to a liquid supply system for supplying an ultra-low temperature liquid.

In order to circulate an ultra-low temperature liquid such as liquid nitrogen or liquid helium through a circulation channel, a technique using a liquid supply system having a pump chamber formed by a bellows is known (see Patent Documents 1 and 2). . In such a liquid supply system, the pump cannot be operated sufficiently unless the flow path passing through the pump chamber is filled with liquid. Therefore, it is necessary to prevent the ultra-low temperature liquid from being vaporized in the flow path by performing pre-cooling at the first start-up or at the start-up after maintenance. Therefore, before starting the liquid supply system, the flow path is cooled in advance by forcibly flowing an ultra-low temperature liquid through the flow path passing through the pump chamber.

However, in the conventional configuration, the ultra-low temperature liquid is forced to flow directly into the flow path passing through the pump chamber, and it takes a long time to cool the flow path and operate the pump. It was.

International Publication No. 2016/006648 International Publication No. 2006/003871

An object of the present invention is to provide a liquid supply system capable of shortening the time spent for precooling and shortening the time required to operate the pump.

The present invention employs the following means in order to solve the above problems.

That is, the liquid supply system of the present invention is
A container having a pump chamber therein and having a suction port and a delivery port for the cryogenic liquid;
A shaft member that reciprocates in the vertical direction in the container;
A bellows that expands and contracts as the shaft member reciprocates;
A pump chamber formed by a space surrounding the outer peripheral surface of the bellows;
A liquid supply system comprising:
The container is
A first case part in which a flow path passing through the pump chamber is formed;
A second case portion provided so as to surround the outer wall surface of the first case portion;
With
The space between the first case part and the second case part is configured to allow a pre-cooling ultra-low temperature liquid to flow therethrough.

According to the present invention, the flow path provided in the first case portion can be cooled in advance by circulating the ultra-low temperature liquid for precooling in the space between the first case portion and the second case portion. . Thereby, the said flow path can be cooled in a short time by flowing an ultra-low-temperature liquid into the said flow path after that. Therefore, it is possible to shorten the time required to operate the pump.

The space between the first case part and the second case part may be maintained in a vacuum state by removing the ultra-low temperature liquid after pre-cooling.

Thereby, the space between the first case part and the second case part can have a heat insulating function.

A sealed space different from the liquid supply flow path passing through the pump chamber is provided in the first case portion, and the space between the sealed case and the first case portion and the second case portion is provided. It is good that the space of is connected.

It is preferable that a third case portion surrounding the second case portion is provided, and a sealed space in which a vacuum state is maintained is formed between the second case portion and the third case portion.

Thereby, a heat insulating function can be given to the sealed space between the second case part and the third case part.

Therefore, it is possible to efficiently perform cooling when the ultra-low temperature liquid is circulated between the first case portion and the second case portion.

As described above, according to the present invention, the time spent for pre-cooling can be shortened, and the time required for operating the pump can be shortened.

FIG. 1 is a schematic configuration diagram of a liquid supply system according to Embodiment 1 of the present invention. FIG. 2 is a schematic configuration diagram of a liquid supply system according to Embodiment 2 of the present invention.

DETAILED DESCRIPTION Hereinafter, embodiments for carrying out the present invention will be exemplarily described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention only to those unless otherwise specified. .

Example 1
With reference to FIG. 1, the liquid supply system which concerns on Example 1 of this invention is demonstrated. The liquid supply system according to the present embodiment is suitably used, for example, to maintain the superconducting device in an ultra-low temperature state. That is, in a superconducting device, it is necessary to always cool a superconducting coil or the like. Therefore, the apparatus to be cooled is always cooled by always supplying the cryogenic liquid (liquid nitrogen or liquid helium) to the apparatus to be cooled provided with a superconducting coil. More specifically, by providing a circulation flow path that passes through the apparatus to be cooled and attaching the liquid supply system according to the present embodiment to the circulation flow path, the ultra low temperature liquid is circulated so that the apparatus to be cooled is always kept in place. It can be cooled.

<Overall configuration of liquid supply system>
FIG. 1 is a schematic configuration diagram of the entire liquid supply system according to the first embodiment of the present invention, and is a diagram showing a schematic configuration of the entire liquid supply system in cross-section. In addition, in FIG. 1, the schematic structure by the cross section cut | disconnected by the surface containing a center axis line is shown.

The liquid supply system 10 according to the present embodiment includes a liquid supply system main body (hereinafter referred to as the system main body 100), a vacuum container 200 in which the system main body 100 is installed, and piping (a suction pipe 310 and a delivery pipe 320). And. Both the suction pipe 310 and the delivery pipe 320 enter the inside of the vacuum container 200 from the outside of the vacuum container 200 and are connected to the system main body 100. The inside of the vacuum container 200 is sealed, and the space outside the system main body 100, the suction pipe 310, and the delivery pipe 320 is maintained in a vacuum state in the vacuum container 200. Thereby, this space has a heat insulating function. The liquid supply system 10 is usually installed on a horizontal plane. In the state where the liquid supply system 10 is installed, the upper side in FIG. 1 is the upper side in the vertical direction, and the lower side in FIG. 1 is the lower side in the vertical direction.

The system main body 100 includes a linear actuator 110 serving as a driving source, a shaft member 120 that reciprocates in the vertical direction by the linear actuator 110, and a container 130. The linear actuator 110 may be fixed at an arbitrary location, and the location to be fixed may be fixed to the container 130 or may be fixed to another location not shown. The container 130 includes a first case portion 131 and a second case portion 132 provided so as to surround the outer wall surface of the first case portion 131.

The shaft member 120 is installed so as to enter the inside of the container from the outside of the container 130 through the opening 131 a provided in the ceiling part of the first case part 131. Further, a suction port 131b and a delivery port 131c for fluid (ultra-low temperature liquid) are provided at the bottom of the first case portion 131. The suction pipe 310 is connected to a position where the suction port 131b is provided, and the delivery pipe 320 is connected to a position where the delivery port 131c is provided.

A plurality of members are provided inside the first case portion 131, and a plurality of pump chambers, a liquid flow path, and a vacuum chamber for heat insulation are provided by a plurality of spaces partitioned by the plurality of members. Is formed. Hereinafter, the internal configuration of the first case portion 131 will be described in more detail.

The shaft member 120 includes a shaft main body 121 having a hollow portion therein, a cylindrical portion 122 provided so as to surround the outer peripheral surface side of the shaft main body 121, and a connecting portion 123 that connects the shaft main body 121 and the cylindrical portion 122. And have. Further, an upper end side outward flange portion 122 a is provided at the upper end of the cylindrical portion 122, and a lower end side outward flange portion 122 b is provided at the lower end of the cylindrical portion 122.

The first case portion 131 includes a substantially cylindrical body portion 131X and a bottom plate portion 131Y. The body portion 131X is provided with a first inward flange portion 131Xa provided near the center in the height direction and a second inward flange portion 131Xb provided above.

Inside the body portion 131X, a plurality of first flow paths 131Xc provided below the first inward flange portion 131Xa and extending in the axial direction are formed at intervals in the circumferential direction. In addition, a second flow path 131Xd configured by a cylindrical space extending in the axial direction is further provided inside the body portion 131X at a radially outer side than a region where the first flow path 131Xc is provided. Yes. In addition, a flow path 131d that extends outward in the radial direction and is connected to the first flow path 131Xc is uniformly formed on the bottom of the first case portion 131 in a circumferential shape. Furthermore, a flow path 131e that extends radially outward is uniformly formed in the bottom plate portion 131Y of the first case portion 131 in a circumferential shape. That is, the flow channel 131d and the flow channel 131e are configured such that fluid can flow radially in all directions from 360 ° toward the radially outer side.

In addition, a first bellows 141 and a second bellows 142 that are expanded and contracted with the reciprocation of the shaft member 120 are provided inside the container 130. The first bellows 141 and the second bellows 142 are arranged side by side in the vertical direction. The upper end side of the first bellows 141 is fixed to the upper end side outward flange portion 122a of the cylindrical portion 122 of the shaft member 120, and the lower end side of the first bellows 141 is the first inward flange portion 131Xa of the first case portion 131. It is fixed to. The upper end side of the second bellows 142 is fixed to the first inward flange portion 131Xa of the first case portion 131, and the lower end side of the second bellows 142 is the lower end side outward flange of the cylindrical portion 122 of the shaft member 120. It is fixed to the part 122b. A first pump chamber P1 is formed by a space surrounding the outer peripheral surface of the first bellows 141, and a second pump chamber P2 is formed by a space surrounding the outer peripheral surface of the second bellows 142.

In addition, a third bellows 151 and a fourth bellows 152 that are expanded and contracted with the reciprocating movement of the shaft member 120 are also provided inside the container 130. The upper end side of the third bellows 151 is fixed to the ceiling portion of the first case portion 131, and the lower end side of the third bellows 151 is fixed to the shaft member 120. Thereby, the opening part 131a provided in the first case part 131 is closed. The upper end side of the fourth bellows 152 is fixed to a second inward flange portion 131Xb provided in the first case portion 131, and the lower end side of the fourth bellows 152 is fixed to the connecting portion 123 in the shaft member 120. .

The second space formed by the first space K1 formed by the hollow portion inside the shaft main body 121 of the shaft member 120, the outer peripheral surface side of the third bellows 151, the inner peripheral surface side of the fourth bellows 152, and the like. The space K2 and the third space K3 formed on the inner peripheral surface side of the first bellows 141 and the second bellows 142 are connected.

In the first case portion 131, a flow path passing through the first pump chamber P1 and a flow path passing through the second pump chamber P2 are formed. The second case portion 132 is provided so as to surround the outer wall surface of the first case portion 131. An annular fourth space K4 is formed between the first case portion 131 and the second case portion 132. It is desirable that the fourth space K4 is also connected to the first space K1, the second space K2, and the third space K3. The space formed by the first space K1, the second space K2, the third space K3, and the fourth space K4 is configured to be hermetically sealed.

Furthermore, inside the container 130, there are four check valves 160 (first check valve 160A, second check valve 160B, third check valve 160C and fourth check valve according to the position of attachment). A stop valve 160D). Each of these check valves 160 is constituted by an annular member provided coaxially with the shaft member 120. Each of these check valves 160 is configured to permit the flow of fluid from the radially inner side to the outer side and stop the fluid flow from the radially outer side to the inner side.

The first check valve 160A and the third check valve 160C are provided on the flow path passing through the first pump chamber P1. The first check valve 160A and the third check valve 160C play a role of stopping the backflow of the fluid flowing by the pumping action by the first pump chamber P1. More specifically, the first check valve 160A is provided on the upstream side with respect to the first pump chamber P1, and the third check valve 160C is provided on the downstream side. More specifically, the first check valve 160 </ b> A is provided on a flow path 131 d formed at the bottom of the first case portion 131. The third check valve 160C is provided on a flow path formed in the vicinity of the second inward flange portion 131Xb provided in the first case portion 131.

The second check valve 160B and the fourth check valve 160D are provided on the flow path passing through the second pump chamber P2. The second check valve 160B and the fourth check valve 160D play a role of stopping the backflow of the fluid flowing by the pumping action by the second pump chamber P2. More specifically, the second check valve 160B is provided on the upstream side with respect to the second pump chamber P2, and the fourth check valve 160D is provided on the downstream side. More specifically, the second check valve 160B is provided on the flow path 131e formed in the bottom plate part 131Y of the first case part 131. The fourth check valve 160D is provided in the vicinity of the first inward flange portion 131Xa of the first case portion 131.

<Operation description of the entire liquid supply system>
The overall operation of the liquid supply system will be described. When the shaft member 120 is lowered by the linear actuator 110, the first bellows 141 contracts and the second bellows 142 extends. At this time, since the fluid pressure in the first pump chamber P1 is low, the valve of the first check valve 160A is opened and the valve of the third check valve 160C is closed. Thereby, the fluid (see arrow S10) sent from the outside of the liquid supply system 10 through the suction pipe 310 is sucked into the container 130 from the suction port 131b and passes through the first check valve 160A (see arrow S11). ). Then, the fluid that has passed through the first check valve 160A is sent to the first pump chamber P1 through the first flow path 131Xc inside the body portion 131X in the first case portion 131. Further, since the fluid pressure in the second pump chamber P2 is increased, the second check valve 160B is closed and the fourth check valve 160D is opened. As a result, the fluid in the second pump chamber P2 passes through the fourth check valve 160D and is sent to the second flow path 131Xd inside the body portion 131X (see arrow T12). Thereafter, the fluid passes through the delivery port 131 c and is delivered to the outside of the liquid supply system 10 through the delivery pipe 320.

When the shaft member 120 is raised by the linear actuator 110, the first bellows 141 is extended and the second bellows 142 is contracted. At this time, since the fluid pressure in the first pump chamber P1 is increased, the first check valve 160A is closed and the third check valve 160C is opened. As a result, the fluid in the first pump chamber P1 passes through the third check valve 160C (see arrow T11) and is sent to the second flow path 131Xd inside the trunk portion 131X. Thereafter, the fluid passes through the delivery port 131 c and is delivered to the outside of the liquid supply system 10 through the delivery pipe 320. Further, since the fluid pressure in the second pump chamber P2 becomes low, the second check valve 160B is opened and the fourth check valve 160D is closed. Accordingly, the fluid (see arrow S10) sent from the outside of the liquid supply system 10 through the suction pipe 310 is sucked into the container 130 from the suction port 131b and passes through the second check valve 160B (see arrow S12). ). Then, the fluid that has passed through the second check valve 160B is sent to the second pump chamber P2.

As described above, in the liquid supply system 10 according to the present embodiment, the fluid can be flowed from the suction pipe 310 side to the delivery pipe 320 side when the shaft member 120 is lowered or raised. Therefore, so-called pulsation can be suppressed.

<Pre-cooling>
The pre-cooling will be described. As explained in the background art, in order to circulate the cryogenic liquid, the cryogenic liquid is not vaporized in the flow path by pre-cooling the entire container at the first startup or after the maintenance. It is necessary to do so. Therefore, in this embodiment, before flowing the cryogenic liquid into the flow path passing through the pump chambers (the first pump chamber P1 and the second pump chamber P2), the first case portion 131 and the second case portion 132 are interposed. The ultra-low temperature liquid is circulated through the formed fourth space K4. Hereinafter, it demonstrates in detail according to the procedure of pre-cooling.

In the fourth space K4, a first pipe 410 for introducing a precooling fluid and a second pipe 420 for discharging the precooling fluid are connected. In addition, since these 1st piping 410 and the 2nd piping 420 are not in the position of the cross section shown in FIG. 1, but are provided in another position, it has shown with the dotted line in FIG. When pre-cooling is performed, first, the inside of the fourth space K4 and the flow path from the vacuum container 200 and the suction pipe 310 to the delivery pipe 320 are exhausted, and then the inside of the fourth space K4 and the suction pipe 310 to the delivery pipe. A gas having a boiling point equal to or lower than the temperature of the ultra-low temperature liquid for precooling is introduced into the flow path up to 320. After the gas is filled into the interior of the fourth space K4 and the flow path from the suction pipe 310 to the delivery pipe 320, the ultra-low temperature liquid is introduced from the first pipe 410 into the fourth space K4. At this time, the second pipe 420 is opened, and the internal gas is discharged from the fourth space K4.

After the container 130 is cooled, the ultra-low temperature liquid is discharged from the second pipe 420 by a discharge pump (not shown) such as a dry pump. Note that the ultra-low temperature liquid is vaporized and passes through a heat exchanger to reach a temperature close to room temperature, and then released to the atmosphere. Further, it is desirable to provide a chamber capable of storing the cryogenic liquid downstream of the heat exchanger in the exhaust passage so that the ultracold liquid is not released into the atmosphere as a liquid. In order to prevent the fluid pressure in the exhaust passage from becoming abnormally high, it is desirable to provide a valve for releasing the pressure.

As described above, after the fourth space K4 is cooled, the ultra-low temperature liquid is discharged, so that the fourth space K4 is in a vacuum state. As described above, the first space K1, the second space K2, and the third space K3 may be connected to the fourth space K4. In this case, the first space K1, the second space K2, and the third space K3 are also in a vacuum state after being cooled by the precooling step.

In this way, the fourth space K4 (in the present embodiment, including the first space K1, the second space K2, and the third space K3) is cooled, and thereby the flow path passing through the first pump chamber P1, and The flow path passing through the second pump chamber P2 is cooled. Thereby, it is suppressed by flowing super low temperature liquid into these flow paths, that super low temperature liquid will be vaporized. Therefore, since the flow path is cooled in a short time by flowing the ultra-low temperature liquid through the flow path, it is possible to shorten the time required to operate the pump. Note that after the pump is operated (that is, after the linear actuator 110 starts the reciprocating movement of the shaft member 120), the cryogenic liquid may be discharged from the fourth space K4 to be in a vacuum state.

<Excellent points of the liquid supply system according to this embodiment>
According to the liquid supply system 10 according to the present embodiment, the first liquid is circulated in the space (fourth space K4) between the first case portion 131 and the second case portion 132 by circulating the ultra-low temperature liquid for precooling. The flow path provided in the case part 131 can be cooled in advance. Thereby, the said flow path can be cooled in a short time by flowing an ultra-low-temperature liquid into the said flow path after that. Therefore, it is possible to shorten the time required to operate the pump.

In the present embodiment, the fourth space K4 is configured such that the ultra-low temperature liquid is removed after pre-cooling and the vacuum state is maintained. Therefore, the fourth space K4 can have a heat insulating function.

Further, in the present embodiment, the first case portion 131 has a sealed space (a first space K1, a second space K2, and a second space different from the flow path passing through the first pump chamber P1 and the second pump chamber P2). A third space K3) is provided. And these sealed space and the 4th space K4 are connected. Accordingly, during the pre-cooling, the first space K1, the second space K2, and the third space K3 are also cooled, so that the flow path passing through the first pump chamber P1 and the second pump chamber P2 is more reliably cooled. be able to. Moreover, the heat insulation function can be exhibited also about the 1st space K1, the 2nd space K2, and the 3rd space K3.

(Example 2)
FIG. 2 shows a second embodiment of the present invention. In the first embodiment, the configuration in which the second case portion is provided so as to surround the outer wall surface of the first case portion is shown. In the present embodiment, a configuration in which a third case portion that further surrounds the second case portion is provided is shown. Since the configuration and operation other than the configuration related to the third case portion are the same as those in the first embodiment, the same components are denoted by the same reference numerals, and the description thereof is omitted as appropriate.

FIG. 2 is a schematic configuration diagram of the entire liquid supply system according to the second embodiment of the present invention, and is a diagram showing a schematic configuration of the entire liquid supply system in cross-section. FIG. 2 shows a schematic configuration of a cross section cut along a plane including the central axis. In the liquid supply system 10 according to the present embodiment, only the configuration related to the third case portion 133 is different from that in the first embodiment. Other configurations are the same as those of the liquid supply system 10 according to the first embodiment, and thus the description thereof is omitted as appropriate.

The container 130 according to the present embodiment includes a first case portion 131, a second case portion 132 provided so as to surround the outer wall surface of the first case portion 131, and a third case portion 133 surrounding the second case portion 132. It has. As in the case of the first embodiment, the first case 131 has a flow path that passes through the first pump chamber P1 and a flow path that passes through the second pump chamber P2. The second case portion 132 is provided so as to surround the outer wall surface of the first case portion 131. An annular fourth space K4 is formed between the first case portion 131 and the second case portion 132. The fourth space K4 is preferably connected to the first space K1, the second space K2, and the third space K3. And the space formed by these 1st space K1, 2nd space K2, 3rd space K3, and 4th space K4 is comprised so that sealing is possible.

The third case part 133 is provided so as to surround the outer wall surface of the second case part 132. Furthermore, the ceiling part of the third case part 133 is configured to cover these with a gap between the ceiling part of the first case part 131 and the ceiling part of the second case part 132. Note that an opening 133 a is provided in the ceiling portion of the third case portion 133. The shaft member 120 is provided so as to enter the inside of the container from the outside of the container 130 through the opening 133a. Furthermore, a fifth bellows 153 that expands and contracts with the reciprocating movement of the shaft member 120 is provided on the upper portion of the third case portion 133. The upper end side of the fifth bellows 153 is fixed to the shaft member 120, and the lower end side of the fifth bellows 153 is fixed to the third case portion 133. As a result, the opening 133a is closed.

By the third case part 133 configured as described above, a sealed space (fifth space K5) is formed between the second case part 132 and the third case part 133. And this 5th space K5 is comprised so that a vacuum state may be maintained. Accordingly, the fifth space K5 exhibits a heat insulating function.

The operation of the entire liquid supply system and the pre-cooling procedure are the same as in the case of the first embodiment, and a description thereof will be omitted.

Also for the liquid supply system 10 according to the present embodiment configured as described above, the same effect as in the first embodiment can be obtained. In the present embodiment, the heat insulation function is exhibited by the fifth space K5. Therefore, the fourth space K4 and the like can be cooled more efficiently during the precooling. Moreover, the freezing by the space used for precooling contacting a high temperature part (atmosphere) can be prevented. Specifically, since the upper part of the ceiling part of the first case part 131 and the ceiling part of the second case part 132 are covered with the fifth space K5 having a heat insulating function, the first case part is preliminarily cooled. It is possible to prevent the vicinity of the ceiling portion 131 and the ceiling portion of the second case portion 132 from freezing.

(Other)
In the configuration shown in the first embodiment and the second embodiment, the second pipe 420 used for pre-cooling is arranged up to the inside of the fourth space K4, and the opening of the second pipe 420 is formed in the fourth space K4. It is desirable to adopt a configuration that is positioned above the inside. As a result, during precooling, it is possible to suppress the occurrence of problems such as gas stagnating above the fourth space K4 and difficulty in filling the ultra-low temperature liquid.

DESCRIPTION OF SYMBOLS 10 Liquid supply system 100 System main body 110 Linear actuator 120 Shaft member 121 Shaft main body part 122 Cylindrical part 122a Upper end side outward flange part 122b Lower end side outward flange part 123 Connection part 130 Container 131 1st case part

131a Opening part 131b Inlet 131c Outlet

131d Flow path 131e Flow path 131X Body part 131Xa First inward flange part 131Xb Second inward flange part 131Xc First flow path 131Xd Second flow path 132 Second case part 133 Third case part 133a Opening part 141 1st bellows 142 2nd bellows 151 3rd bellows 152 4th bellows 153 5th bellows 160 Check valve 160A 1st check valve 160B 2nd check valve 160C 3rd check valve 160D 4th check valve 200 Vacuum container 31 0 Suction pipe 320 Delivery pipe 410 First pipe 420 Second pipe P1 First pump chamber P2 Second pump chamber

Claims

A container having a pump chamber therein and having a suction port and a delivery port for the cryogenic liquid;
A shaft member that reciprocates in the vertical direction in the container;
A bellows that expands and contracts as the shaft member reciprocates;
A pump chamber formed by a space surrounding the outer peripheral surface of the bellows;
A liquid supply system comprising:
The container is
A first case part in which a flow path passing through the pump chamber is formed;
A second case portion provided so as to surround the outer wall surface of the first case portion;
With
The space between the first case part and the second case part is configured to allow a pre-cooling ultra-low temperature liquid to flow therethrough.
The liquid supply system according to claim 1, wherein the space between the first case part and the second case part is maintained in a vacuum state by removing the ultra-low temperature liquid after pre-cooling.
A sealed space different from the flow path passing through the pump chamber is provided inside the first case portion, and the space between the sealed space and the first case portion and the second case portion. The liquid supply system according to claim 1, wherein the liquid supply system is connected.
A third case portion surrounding the second case portion is provided, and a sealed space in which a vacuum state is maintained is formed between the second case portion and the third case portion. The liquid supply system according to claim 1, 2, or 3.