JP2002267290A - refrigerator - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To reduce the pressure loss when returning refrigerant from a plurality of evaporators to a compressor, maintain good refrigerating capacity, and reliably return refrigerating machine oil to the compressor side for reliability. The purpose is to maintain good. A refrigerator (1) has a plurality of evaporators (9, 10), and at least one of the evaporators (9, 10) is compressed by a compressor (2) and then expanded with a condenser (4). The refrigerant R that has passed through the valves 7a and 7b is supplied to externally absorb heat. Outlet pipes 11 and 12 of each evaporator 9 and 10
And an inlet pipe 16 of an accumulator 18 functioning as a return pipe for returning the refrigerant to the compressor 2.
, They are joined in a substantially Y-shape.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a refrigerator, and more particularly, to a refrigerator having a plurality of evaporators.

[0002]

2. Description of the Related Art Conventionally, a refrigerator having a plurality of evaporators and supplying a refrigerant to at least one of the evaporators and absorbing external heat is known. In such a refrigerator having a plurality of evaporators, the refrigerant that has been compressed by the compressor and has become high temperature and high pressure is sent to the condenser, and radiates heat in the condenser. From the outlet pipe of the condenser, branch pipes of a number corresponding to the number of evaporators are branched, and an opening / closing valve and an expansion valve are provided in the middle of each branch pipe. Each branch pipe is connected to one evaporator. Thus, when at least one of the on-off valves is opened, the refrigerant is supplied from the condenser to at least one of the evaporators, and the evaporator absorbs heat from the outside.

[0003] The outlet pipes of each evaporator join at one collecting part, and the collecting part is connected to an accumulator. Thus, the refrigerant that has passed through the evaporator is returned to the compressor via the accumulator. In this case, during operation of the refrigerator, refrigerator oil for lubricating the compressor is mixed into the refrigerant system. The refrigerating machine oil mixed in the refrigerant system follows the flow of the refrigerant, passes through condensers, evaporators, accumulators, and the like, and is returned to the compressor.

[0004]

However, the conventional refrigerator as described above has the following problems. That is, in the conventional refrigerator, as shown in FIG. 8, the outlet pipes 101 and 102 of each evaporator are merged straight, and a refrigerant and the like for returning the refrigerant or the like to the compressor at the junction of both. The return pipe 103 is connected at a right angle. That is, the outlet pipes 101 and 102 and the return pipe 103
Has a T-shape in which the opening angle θ between the outlet pipe 101 and the outlet pipe 102 is 180 °. Accordingly, the velocity vector of the refrigerant flowing through the outlet pipe 101 and the velocity vector of the refrigerant flowing through the outlet pipe 102 are in opposite directions, and the refrigerant from the outlet pipe 101 and the velocity vector from the outlet pipe 102 The refrigerant collides. As a result, the pressure loss of the refrigerant in the collecting part 105 increases, and the refrigeration capacity of the entire refrigerator decreases.

In a refrigerator having a T-shaped collecting portion as shown in FIG. 8, one evaporator (outlet pipe 102
When the supply of the refrigerant to the evaporator on the side is stopped, the following problem occurs. That is, in this case, the refrigerant R,
And, the oil droplets O of the refrigerating machine oil conveyed by the refrigerant R are:
As shown in FIG. 9, the refrigerant flows from the outlet pipe 101 into the return pipe 103 and returns to the compressor side. At this time, the oil droplets O of the refrigerating machine oil being conveyed by the refrigerant R cause the inertia at the time of conveyance. By the force, the refrigerant R is carried to the outlet pipe 102 side where the refrigerant R is not circulated. In this case, the outlet pipe 102
The oil accumulation part 106 is formed in the inside, and the oil droplet O of the refrigerating machine oil flows to the evaporator side. For this reason, when the continuous operation is performed for a long time, the return of the refrigerating machine oil to the compressor becomes insufficient, and the amount of lubricating oil in the compressor decreases, so that the reliability of the compressor is impaired.

Accordingly, the present invention reduces the pressure loss when returning the refrigerant from the plurality of evaporators to the compressor to maintain good refrigerating capacity, and reliably returns the refrigerating machine oil to the compressor to compress the refrigerant. It is an object of the present invention to provide a refrigerator capable of maintaining good reliability of the refrigerator.

[0007]

According to a first aspect of the present invention, there is provided a refrigerator having a plurality of evaporators, at least one of the evaporators being integrally compressed by a compressor. In a refrigerator that supplies a refrigerant that has passed through a condenser and an expansion valve to externally absorb heat, an outlet pipe of each evaporator and a return pipe for returning the refrigerant to the compressor merge in a substantially Y-shape. It is characterized by being made.

This refrigerator has a plurality of evaporators, and supplies a refrigerant to at least one of the evaporators and absorbs external heat. In such a refrigerator having a plurality of evaporators, the compressor is compressed by a compressor and has a high temperature and a high temperature.
After the pressure becomes high, the refrigerant radiated by the condenser is supplied to at least one of the evaporators. Then, the refrigerant that has absorbed heat externally in the evaporator flows into one collecting portion, and is returned to the compressor via the return pipe.

In this refrigerator, the outlet pipe of each evaporator and the return pipe for returning the refrigerant to the compressor are substantially Y.
They are joined in a letter shape. That is, in this refrigerator, the gathering portion of the outlet pipe and the return pipe from each evaporator has a Y shape in which the opening angle between the outlet pipes is less than 180 °. Therefore, in this refrigerator, it is possible to reduce, in each of the components of the velocity vector of the fluid (refrigerant and refrigerating machine oil conveyed by the refrigerant) flowing through each outlet pipe, components in directions opposite to each other. it can.

Thus, in this refrigerator, it is possible to easily reduce the pressure loss caused by the collision of the refrigerant from the outlet pipes at the collecting portion. This also allows any one of the plurality of evaporators to operate (supply of refrigerant).
Can be prevented from being transported from the evaporator side (outlet pipe) during operation to the evaporator side (evaporator and outlet pipe) during operation stoppage. Is returned to the compressor side. As a result, in this refrigerator, it is possible to maintain the refrigerating capacity and the reliability of the compressor extremely well.

It is preferable that each outlet pipe is bent so that the velocity vector of the fluid flowing through the outlet end substantially matches the extending direction of the inlet end of the return pipe.

By employing such a configuration, it is possible to extremely effectively reduce the pressure loss caused by the collision of the refrigerant from the outlet pipes at the collecting portion, and to reduce the pressure loss on the side of the evaporator during operation (the outlet). It is possible to reliably prevent the refrigerating machine oil from being transported from the pipe) to the evaporator side (evaporator and outlet pipe) during which operation is suspended. Therefore, it is possible to maintain the refrigerating capacity of the refrigerator and the reliability of the compressor extremely well.

[0013] The refrigerator according to the present invention described in claim 3 is:
A refrigerator having a plurality of evaporators, at least any one of these evaporators, after being compressed by a compressor, supplies a refrigerant that has passed through a condenser and an expansion valve and externally absorbs heat. An accumulator that is provided between each evaporator and the compressor and separates a fluid flowing from at least one of the evaporators into a gas-liquid separator inside the container; and an outlet pipe of each evaporator has an accumulator. Is directly connected to the container.

This refrigerator also has a plurality of evaporators, and supplies a refrigerant to at least one of the evaporators integrally to absorb external heat. Also in this case, the refrigerant radiated by the condenser after being compressed to a high temperature and a high pressure by the compressor is discharged to at least one of the evaporators. The refrigerant that has absorbed heat externally in the evaporator is returned to the compressor via an accumulator that separates the fluid into gas and liquid.

Here, in this refrigerator, the outlet pipe of each evaporator is directly connected to the container of the accumulator. Thereby, in this refrigerator, it is possible to easily reduce the pressure loss caused by the refrigerant from each outlet pipe colliding with each other. Further, even if any operation (supply of refrigerant) of the plurality of evaporators is stopped, the fluid (refrigerant and refrigerating machine oil) flowing from the evaporator side (outlet pipe) during operation is directly guided to the accumulator. Therefore, the refrigerating machine oil is not carried to the evaporator side (evaporator and outlet pipe) during operation suspension, and the refrigerating machine oil is reliably returned to the compressor side. As a result, in this refrigerator, it is possible to maintain the refrigerating capacity and the reliability of the compressor extremely well.

It is preferable that each outlet pipe is connected to the container in a tangential direction of the inner wall surface of the container.

With such a configuration, the fluid (refrigerant liquid, refrigerant gas, and refrigerating machine oil) introduced into the container of the accumulator from the outlet pipe descends along the inner wall surface of the container. Thus, the fluid introduced into the container from the outlet pipe is centrifuged into a gas phase and a liquid phase before reaching the lower part of the container. Therefore, if such a configuration is employed, it is possible to efficiently separate the fluid into gas and liquid in the accumulator. In this case, each outlet pipe is preferably connected to the container so as to blow out the fluid in the same direction along the inner wall surface of the container. Thereby, even if the refrigerant is simultaneously supplied to each evaporator, it is possible to prevent the fluids introduced from each outlet pipe into the container of the accumulator from colliding with each other.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a refrigerator according to the present invention will be described below in detail with reference to the drawings.

[First Embodiment] FIG. 1 is a system diagram showing a first embodiment of a refrigerator according to the present invention. A refrigerator 1 shown in FIG. 1 includes a compressor 2 for compressing a refrigerant R and a refrigerant supply pipe 3.
And a condenser 4 connected to the discharge port of the compressor 2 through the compressor. The outlet pipe 5 of the condenser 4 has a plurality of (2
This is branched into branch pipes 6a and 6b. An on-off valve (electromagnetic valve) 7a and an expansion valve 8a are provided in the middle of the branch pipe 6a. The branch pipe 6a is connected to a refrigerant inlet of the evaporator 9. Similarly, the branch pipe 6b
An on-off valve (electromagnetic valve) 7b and an expansion valve 8b are provided in the middle. The branch pipe 6b is connected to a refrigerant inlet of the evaporator 10. Thus, this refrigerator 1
Has a plurality of (two) evaporators 9 and 10.

In the refrigerator 1, the refrigerant R which has been compressed by the compressor 2 and has become high temperature and high pressure is sent to the condenser 4 via the refrigerant supply pipe 3 and radiates heat in the condenser 4. During the operation of the refrigerator 1, at least one of the on-off valves 7a and 7b provided in each of the branch pipes 6a and 6b is opened. For example, when both of the on-off valves 7a and 7b are open, the refrigerant R is supplied from the condenser 4 to the evaporators 9 and 10 via the expansion valves 8a and 8b. Thereby, the refrigerant R absorbs heat from the outside in the evaporators 9 and 10. The refrigerant R that has absorbed heat in the evaporators 9 and 10 flows into one collecting part 15 and passes through the accumulator 18 to the compressor 2.
Is returned to.

FIG. 2 is a schematic configuration diagram showing the collecting section 15 provided on the subsequent stage side of each of the evaporators 9 and 10. As shown in the drawing, in the collecting section 15, an outlet pipe 11 from the evaporator 9, an outlet pipe 12 from the evaporator 10, and the compressor 2
The inlet pipe 16 of the accumulator 18 functioning as a return pipe for returning the refrigerant R to the air is merged in a substantially Y-shape.

That is, in the refrigerator 1, the outlet pipe 11 from the evaporator 9 and the outlet pipe 12 from the evaporator 10 each have a substantially semicircular arc on the tip side (opposite the condensers 9 and 10). It is bent. And the outlet end 1 of the outlet pipe 11
1a and the outlet end 12a of the outlet pipe 12 are parallel to each other, and the inlet end 1 of the inlet pipe 16 serving as a return pipe.
6a is connected straight (substantially linearly). That is, the outgoing end 11a and the outgoing end 12a are substantially parallel to the extending direction of the incoming end 16a, and
Are connected to the outlet pipes 11 and 12 (exit end portions 11a and 12a).
) Have a Y-shape with an opening angle of approximately 0 °.

Thus, when the on-off valves 7a and 7b are opened and the refrigerant R is supplied to the evaporators 9 and 10,
As shown in FIG. 2, each evaporator 9, 10 has an outlet pipe 11,
After flowing into the outlet 12, the velocity vector of the fluid (the refrigerant R and the oil droplet O of the refrigerating machine oil) flowing through the outlet ends 11 a, 12 a depends on the extending direction of the inlet end 16 a of the inlet pipe (return pipe) 16. Will almost match. As a result, in the refrigerator 1, it is possible to easily reduce the pressure loss caused by the collision of the refrigerant R from the outlet pipes 11 and 12 at the collecting portion 15, and to maintain the refrigerating capacity extremely well. It is possible to do.

Also, for example, when each on-off valve 7a is opened and the on-off valve 7b is closed to supply the refrigerant R only to each evaporator 9, the refrigerant flows from the evaporator 9 into the outlet pipe 11 and then exits. The velocity vector of the fluid (refrigerant R and oil droplets O of the refrigerating machine oil) flowing through the side end 11a is determined by the inlet pipe (return pipe) 1
6 substantially coincides with the extending direction of the entry-side end 16a. Therefore, the inertia force of the refrigerating machine oil with respect to the oil droplet O is as shown in FIG.
Therefore, the refrigerant R and the oil droplets O of the refrigerating machine oil cannot basically flow into the outlet pipe 12 from the outlet pipe 11 connected to the evaporator 9 during operation.

As a result, the oil droplets O of the refrigerating machine oil are transferred from the evaporator 9 side (outlet pipe 11) during operation to the evaporator 10 side (outlet pipe 12 and evaporator 10) during suspension of operation. Can be prevented, and the oil droplets O of the refrigerating machine oil can be reliably returned to the compressor 2. As a result, the amount of lubricating oil in the compressor 2 becomes
Since the compressor 2 is always kept sufficiently, the reliability of the compressor 2 can be maintained extremely well. Further, as shown in FIGS. 2 and 3, if the overflow wall preventing portion 14 is formed by appropriately joining the pipe wall of the outlet pipe 11 and the pipe wall of the outlet pipe 12, the Even if the oil droplets O of the refrigerating machine oil are wound up in the drawing due to the turbulence of the flow, the outlet pipe 1
Oil O of the refrigerating machine oil is on the second side (on the side of the evaporator 10 during operation suspension).
Can be effectively prevented from being carried.

It should be noted that, regarding the above-mentioned gathering portion 15, each of the outlet pipes 11, 12 (outgoing end portions 11a, 12a).
Has been described as having a Y-shape with an opening angle of approximately 0 °, but the present invention is not limited to this. That is, as shown in FIG. 4, the Y-shaped gathering portion 15A in which the opening angle θ between the outlet pipe 11 (outlet end 11a) and the outlet pipe 12 (outlet end 12a) is less than 180 ° is formed. It may be applied to the refrigerator 1.

If such a configuration is adopted, each outlet pipe 1
Of the components of the velocity vector of the fluid flowing through the fluids 1 and 12 (the refrigerant R and the oil droplets O of the refrigerating machine oil conveyed by the refrigerant R), the components in the directions opposite to each other (on the outlet pipe 11 side, The horizontal leftward component in the drawing and the horizontal rightward component in the drawing on the outlet pipe 12 side can be reduced. This makes it possible to easily reduce the pressure loss caused by the collision of the refrigerant R from each of the outlet pipes 11 and 12 at the collecting portion 15A, and to suspend the operation from the evaporator side (outlet pipe) during operation. It is possible to prevent the refrigerating machine oil from being carried to the middle evaporator side (evaporator and outlet pipe).

The angle α between the outlet pipe 11 and the inlet pipe 16 and the angle β between the outlet pipe 12 and the inlet pipe 16 are preferably set to be the same. In addition, the opening angle θ between the outlet pipes 11 and 12 (the outlet ends 11a and 12a) is preferably, for example, about 150 ° or less, and if it is about 120 ° or less, extremely good results are obtained in practical use. Can be Further, if the opening angle θ is less than 90 ° and α = β, among the components of the velocity vector of the fluid flowing through the outlet pipes 11 and 12, the downward component in FIG. It can be larger than the directional component.

[Second Embodiment] Hereinafter, a refrigerator according to a second embodiment of the present invention will be described with reference to FIGS. Note that the same reference numerals are given to the same elements as those described in regard to the above-described first embodiment, and redundant description will be omitted.

The refrigerator 1A shown in FIG. 5 also has a plurality of evaporators 9 and 10, and supplies the refrigerant R to at least one of the evaporators 9 and 10 to externally absorb heat. . That is, also in the refrigerator 1A, the refrigerant R which is compressed by the compressor 2 to have a high temperature and a high pressure and then radiates heat in the condenser 4 is supplied to at least one of the evaporators 9 or 10. The refrigerant R absorbed by the evaporators 9 and 10 is compressed by the compressor 2 via an accumulator 20 that separates fluids (refrigerant liquid, refrigerant gas, and oil droplets of refrigerating machine oil) from the evaporators 9 and 10 into gas and liquid. Is returned to.

As shown in FIGS. 6 and 7, the accumulator 20 has a cylindrical container 21 having an upper end and a lower end closed. A suction pipe (accumulator outlet pipe) 22 is inserted and fixed in the container 21. The suction pipe 22 is inserted into the inside of the container 21 from the side wall (about the upper quarter position), is bent toward the bottom, and is bent again toward the ceiling near the bottom. , Its tip 22a reaches near the ceiling of the container. The suction pipe 22 has a pressure equalizing hole 22b formed at a predetermined position, and an oil return hole 22c formed near the bottom of the container 21. Furthermore, the inside of the container 21
The suction pipe 22 is vertically partitioned by a perforated plate 23 fixed below the tip 22a of the suction pipe 22.

Then, in the refrigerator 1A, each evaporator 9, 1
The outlet pipes 11, 12 from 0 are respectively connected directly to the container 21 of the accumulator 20. As shown in FIG. 7, the outlet pipe 11 from the evaporator 9 is inserted and fixed in a tangential direction of the inner wall surface 21a from the side wall (about the upper third position) of the container 21. On the other hand, the outlet pipe 12 from the evaporator 10 is tangential to the inner wall surface 21a from a position (180 ° in this embodiment) separated from the container 21 by a predetermined angle from the insertion portion of the outlet pipe 11. Inserted and fixed to That is, the outlet pipes 11 and 12 are connected to the container 21 so as to blow fluid in the same direction (clockwise in FIG. 7) along the inner wall surface 21a of the container 21.

In the refrigerator 1A thus configured, when the on-off valves 7a, 7b are opened and the refrigerant R is supplied to the evaporators 9, 10, the refrigerant passing through the evaporators 9, 10 Is directly led into the container 21 of the accumulator 20 via the outlet pipes 11 and 12. Therefore, in the refrigerator 1A, it is possible to prevent the refrigerant from each of the outlet pipes 11 and 12 from colliding with each other, and it is possible to easily reduce the pressure loss due to such collision between the refrigerants.

The outlet pipes 11 and 12 are connected to the container 21 of the accumulator 20 so as to blow fluid in the same direction along the inner wall surface 21a. Thereby, the refrigerant is simultaneously supplied to each of the evaporators 9 and 10,
The container 21 of the accumulator 20 is connected to each of the outlet pipes 11 and 12.
Even if a fluid is introduced into the inside, it is possible to prevent the fluids blown out from the outlet pipes 11 and 12 from colliding with each other.

Further, even if any operation (supply of refrigerant) of the plurality of evaporators 9 and 10 is stopped, fluid (refrigerant and refrigerating machine oil) flowing out from the evaporator side (outlet pipe) during operation. Is directly led to the accumulator 20, so that the refrigerating machine oil cannot be conveyed to the evaporator side (evaporator and outlet pipe) during operation suspension, and the refrigerating machine oil is reliably returned to the compressor 2 side. You. As a result, in the refrigerator 1A, the refrigerating capacity and the reliability of the compressor can be maintained extremely well.

A fluid (refrigerant liquid, refrigerant gas, and refrigerating machine oil) introduced into the container 21 of the accumulator 20 from at least one of the outlet pipes 11 and 12 flows along the inner wall surface 21a of the container 21. It descends while forming a swirling flow. As a result, the fluid introduced into the container 21 from the outlet pipes 11 and 12 reaches the bottom of the container 21 before the gas phase (refrigerant gas) and the liquid phase (refrigerant liquid and refrigerating machine oil).
Then, it will be centrifuged.

The refrigerant gas is supplied to the tip 2 of the suction pipe 22.
It is sucked from 2a and returned to the compressor 2. Here, since the accumulator 20 is provided with the perforated plate 23, the liquid phase wound up toward the ceiling by the swirling flow inside the container 21 is sucked from the tip 22 a of the suction pipe 22. Can be prevented. On the other hand, the separated refrigerating machine oil is sucked from the oil return hole 22c in a state of being compatible with the refrigerant liquid or in a single state, and is returned to the compressor 2.

Therefore, according to the accumulator 20, the fluid can be efficiently separated into gas and liquid inside the container 21, and the refrigerant and the refrigerating machine oil can be reliably returned to the compressor 2. Can be. Although the refrigerator 1A according to the second embodiment has been described as including one compressor 2, the present invention is not limited to this. That is, the refrigerator according to the second embodiment of the present invention can be configured as a refrigerator having a plurality of compressors. For example, like a refrigerator for a frozen truck,
When a compressor driven by an engine and a compressor driven by a commercial power supply are provided, a plurality of suction pipes may be provided for the accumulator.

[0039]

Since the refrigerator according to the present invention is configured as described above, the following effects can be obtained. That is, the refrigerator according to the present invention includes a plurality of evaporators, and supplies the refrigerant that has been compressed by the compressor and then passed through the condenser and the expansion valve to at least any one of the evaporators. First, the outlet pipe of each evaporator and the return pipe for returning the refrigerant to the compressor are merged in a substantially Y-shape. The outlet pipes of the evaporators are each directly connected to a container of an accumulator that separates the fluid flowing from at least any one of the evaporators into a gas and a liquid. By adopting these configurations, the pressure loss when returning the refrigerant from the plurality of evaporators to the compressor is reduced to maintain good refrigeration capacity, and the refrigeration oil is reliably returned to the compressor side for compression. It is possible to maintain good reliability of the machine.

[Brief description of the drawings]

FIG. 1 is a system diagram showing a first embodiment of a refrigerator according to the present invention.

FIG. 2 is a schematic configuration diagram illustrating an assembly provided in the refrigerator of FIG. 1;

FIG. 3 is a schematic diagram showing a flow of a fluid in a collecting part when the refrigerant is supplied to only one evaporator in the refrigerator of FIG. 1;

FIG. 4 is an enlarged view of a main part for describing another mode in the first embodiment of the refrigerator according to the present invention.

FIG. 5 is a system diagram showing a second embodiment of a refrigerator according to the present invention.

FIG. 6 is a sectional view showing an accumulator provided in the refrigerator of FIG.

FIG. 7 is a sectional view taken along line VII-VII in FIG. 6;

FIG. 8 is a schematic configuration diagram showing an assembly provided in a conventional refrigerator.

FIG. 9 is a schematic view showing a flow of a fluid in a collecting part when a refrigerant is supplied to only one evaporator in a conventional refrigerator.

[Explanation of symbols]

1, 1A ... refrigerator, 2 ... compressor, 4 ... condenser, 6a, 6
b: branch pipe, 7a, 7b: on-off valve, 8a, 8b: expansion valve, 9, 10, evaporator, 11, 12: outlet pipe, 11a,
12a: exit side end, 14: overflow prevention part, 15, 15A ...
Assembling part, 16 ... entrance pipe, 16a ... entrance end, 18, 20
... accumulator, 21 ... container, 21a ... inner wall surface, 22
... Suction tube, 23 ... Perforated plate, O ... Oil drop, R ... Refrigerant.

Claims (4)

[Claims] An external endothermic device having a plurality of evaporators and supplying a refrigerant that has been compressed by a compressor and then passed through a condenser and an expansion valve to at least one of the evaporators. In the refrigerator, an outlet pipe of each of the evaporators and a return pipe for returning the refrigerant to the compressor are joined in a substantially Y-shape. 2. The method according to claim 1, wherein each of the outlet pipes is bent such that a velocity vector of a fluid flowing through the outlet end is substantially equal to an extending direction of an inlet end of the return pipe. The refrigerator according to claim 1, wherein 3. A plurality of evaporators, and at least one of the evaporators is supplied with a refrigerant that has been compressed by a compressor and then passed through a condenser and an expansion valve to provide external heat absorption. An accumulator provided between the evaporator and the compressor to separate a fluid flowing from at least one of the evaporators into a gas-liquid separator inside the container. A refrigerator, wherein the outlet pipes of the evaporator are each directly connected to the container of the accumulator. 4. The refrigerator according to claim 3, wherein each of the outlet pipes is connected to the container in a tangential direction of an inner wall surface of the container.