Patent Publication Number: US-2022226788-A1

Title: Apparatus for removing thermal stratification generated by turbulent penetration by using rotation of inner ring and outer ring

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based on and claims priority under 35 U.S.C. § 119 to Korean Patent Application No. 10-2021-0006815, filed on Jan. 18, 2021, in the Korean Intellectual Property Office, the disclosure of which is incorporated by reference herein in its entirety. 
     BACKGROUND 
     1. Field 
     The present disclosure relates to an apparatus for removing thermal stratification generated by turbulent penetration by using a rotation of an inner ring and an outer ring, and more particularly, to removal of thermal stratification generated by turbulence penetrating into a branch pipe by using a rotation of an inner ring and an outer ring. The present disclosure relates to an apparatus including an inner ring and an outer ring of different polarities, wherein, when the outer ring is rotated, the inner ring automatically rotates so that a fluid inside a branch pipe is rotated to remove thermal stratification. 
     2. Description of the Related Art 
     The present disclosure relates to an apparatus for removing thermal stratification generated by penetration of turbulent eddies from a main pipe through which a high-temperature and high-flow fluid flows into a dead-end branch pipe in various industrial plants. 
     In detail, as shown in  FIG. 1 , when the branch pipe is coupled to the main pipe through which the fluid flows, and the branch pipe is isolated by a valve, turbulent eddies penetrate into the branch pipe at an initial stage of plant operation. Such turbulent penetration generates thermal stratification in a horizontal pipe portion of an elbow pipe, as shown in  FIG. 2 . 
     Such a thermal stratification phenomenon may generate a bending stress due to a difference in the thermal expansion between the upper end lower parts of a pipe wall, thereby causing serious deformation of the pipe and a support thereof. In particular, when the thermal stratification phenomenon repeats periodically, cracks due to thermal fatigue may occur. In the case of a plant where safety is important, such as a nuclear power plant, it is extremely important to prevent serious damage caused by thermal stratification. 
     SUMMARY 
     In order to solve the aforementioned problems, the present disclosure provides an apparatus for removing thermal stratification generated by turbulence penetrating into a branch pipe by using a rotation of an inner ring and an outer ring. 
     Additional aspects will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the presented embodiments of the disclosure. 
     According to an embodiment of the present disclosure, an apparatus for removing thermal stratification generated by turbulent penetration by using a rotation of an inner ring and an outer ring, which is apparatus for removing thermal stratification formed in a branch pipe branching from a main pipe through which a high-temperature fluid flows, includes: a hollow body portion coupled to the branch pipe; an inner ring being magnetic and arranged inside the body portion so that an inner circumferential surface thereof is in contact with a fluid; and an outer ring arranged outside the body portion to face the inner ring, the outer ring being magnetic of a polarity opposite to a polarity of the inner ring, wherein, when the outer ring is rotated, the inner ring rotates by a magnetic force. 
     Also, the branch pipe may include a first branch pipe branching from the main pipe, an elbow pipe connected to the first branch pipe to change a flow direction of the high-temperature fluid, and a second branch pipe connected to the elbow pipe, wherein the body portion may be between the elbow pipe and the second branch pipe. 
     Also, the inner ring may include a first magnetic portion having a certain thickness on an outer circumferential surface of the inner ring, the first magnetic portion being magnetic, and the outer ring may include a second magnetic portion having a certain thickness on an inner circumferential surface of the outer ring, the second magnetic portion being magnetic. 
     Also, an inner diameter of the body portion and an inner diameter of the inner ring may be equal to an inner diameter of the branch pipe. 
     Also, an insertion groove into which the inner ring is inserted may be formed in an inside part of the body portion, and a mounting groove in which the outer ring is mounted may be formed in an outside part of the body portion. 
     Also, magnetic materials having a same polarity as the inner ring may be provided on both sides of the insertion groove facing side surfaces of the inner ring. 
     Also, protrusions may be formed to protrude and to be spaced apart from each other at certain intervals on the inner circumferential surface of the inner ring. 
     Also, the protrusions may be arranged at intervals of 90° on the inner circumferential surface of the inner ring. 
     Also, the apparatus may further include a driving part configured to rotate the outer ring, wherein the driving part may include: a first gear portion provided on the outer ring; a second gear portion engaged with the first gear portion; and a power supply source configured to rotate the second gear portion. 
     Also, an insertion groove into which the inner ring is inserted may be formed inside the body portion, and a width of the insertion groove is greater than a width of the inner ring, and an outer diameter of the insertion groove, formed when a bottom surface of the insertion groove is connected, may be greater than an outer diameter of the inner ring. 
     Also, the body portion may include a first body coupled to one side of the branch pipe, wherein the first body includes first coupling holes spaced apart from each other in a circumferential direction, and a second body coupled to other side of the branch pipe, wherein the second body includes second coupling holes spaced apart from each other in a circumferential direction, the second coupling hole facing the first coupling hole, the first body and the second body may be fastened by a fastening member inserted into the first coupling hole and the second coupling hole, and the first body may include a groove portion having one open side so that the inner ring is inserted thereinto, and when the second body is fastened to the first body, the second body may block the open side of the groove portion to form the insertion groove into which the inner ring is inserted. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features, and advantages of certain embodiments of the disclosure will be more apparent from the following description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a diagram illustrating a state in which turbulence penetrates into a branch pipe; 
         FIG. 2  is a diagram illustrating a state in which thermal stratification is formed in a branch pipe; 
         FIG. 3  is a cross-sectional view of a state in which an apparatus for removing thermal stratification is coupled to a branch pipe; 
         FIG. 4  is a perspective view of an apparatus for removing thermal stratification; 
         FIG. 5  is an enlarged view illustrating a main part of  FIG. 3 ; and 
         FIG. 6  is a cross-sectional view of  FIG. 5  taken along line VI-VI. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. In this regard, the present embodiments may have different forms and should not be construed as being limited to the descriptions set forth herein. Accordingly, the embodiments are merely described below, by referring to the figures, to explain aspects of the present description. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Expressions such as “at least one of,” when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list. 
     Hereinafter, various embodiments of the present disclosure will be described with reference to the accompanying drawings. As the present disclosure allows for various changes and numerous embodiments, certain embodiments will be illustrated in the drawings and described in the detailed description. However, various embodiments are not intended to limit the present disclosure to certain embodiments, and should be construed as including all changes, equivalents, and/or alternatives included in the spirit and scope of various embodiments of the present disclosure. With regard to the description of the drawings, similar reference numerals may be used to refer to similar elements. 
     Expressions such as “include” or “may include” that may be used in various embodiments of the present disclosure specify the presence of a corresponding function, operation, or element, and do not preclude the presence or addition of one or more functions, operations, or elements. Also, it will be understood that terms such as “include” or “comprise” as used in various embodiments of the present disclosure specify the presence of stated features, numbers, steps, operations, elements, parts, and combinations thereof, but do not preclude in advance the presence or addition of one or more other features, numbers, steps, operations, elements, parts, combinations thereof. 
     It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it may be directly connected or coupled to the other element, or intervening elements may exist between the element and the other element. On the other hand, it will be understood that when an element is referred as being “directly connected” or “directly coupled” to another element, intervening elements may not exist between the element and the other element. 
     Terms used in various embodiments of the present disclosure are merely used to describe certain embodiments, and are not intended to limit various embodiments of the present disclosure. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. 
     Unless otherwise defined, all terms used herein including technical or scientific terms have the same meanings as commonly understood by those of ordinary skill in the art to which various embodiments of the present disclosure pertain. 
     Terms such as those defined in commonly used dictionaries should be interpreted as having meanings consistent with the meanings in the context of the related art, and should not be interpreted in an idealized or overly formal sense, unless explicitly defined in various embodiments of the present disclosure. 
     Hereinafter, preferred embodiments according to the present disclosure will be described in detail with reference to the accompanying drawings. 
       FIG. 1  is a diagram illustrating a state in which turbulence penetrates into a branch pipe, and  FIG. 2  is a diagram illustrating a state in which thermal stratification is formed in a branch pipe.  FIG. 3  is a cross-sectional view of a state in which an apparatus for removing thermal stratification is coupled to a branch pipe, and  FIG. 4  is a perspective view of an apparatus for removing thermal stratification.  FIG. 5  is an enlarged view illustrating a main part of  FIG. 3 , and  FIG. 6  is a cross-sectional view of  FIG. 5  taken along line VI-VI. 
     First, an apparatus  100  for removing thermal stratification generated by turbulent penetration by using a rotation of an inner ring and an outer ring, according to the present disclosure, is an apparatus for removing thermal stratification generated in a branch pipe  2  when a main pipe  1 , through which a high-temperature and high-flow fluid flows, is coupled to the branch pipe  2  that causes the flow of the fluid to branch from the main pipe  1 , in various industrial plants. When the branch pipe  2  is closed by a valve  6  at the initial stage of plant operation, turbulent eddies penetrate into the dead-end branch pipe  2 . The present disclosure provides an apparatus for removing thermal stratification generated by penetration of turbulence into the stagnant branch pipe  2 . 
     Referring to  FIG. 3 , the apparatus  100  for removing thermal stratification generated by turbulent penetration by using the rotation of the inner ring and the outer ring removes thermal stratification formed in the branch pipe  2  that branches from the main pipe  1  through which a high-temperature fluid flows. A flow volume flowing through the branch pipe  2  is less than a flow volume of the main pipe  1 . According to the present embodiment, the apparatus  100  for removing thermal stratification includes a body portion  10 , an inner ring  20 , and an outer ring  30 . 
     Referring to  FIGS. 3 and 4 , the body portion  10  is a hollow member coupled to the branch pipe  2 . The body portion  10  includes a first body  11  coupled to one side of the branch pipe  2  and including a first coupling hole  111  spaced apart in a circumferential direction, and a second body  12  coupled to the other side of the branch pipe  2  and including a second coupling hole  121  spaced apart in a circumferential direction, the second coupling hole  121  facing the first coupling hole  111 . The first body  11  and the second body  12  are coupled to each other to form one body portion  10  and have a hollow shape so that a fluid may flow therein. 
     The inner ring  20 , which is a circular ring arranged inside the body portion  10 , is magnetic and has an inner circumferential surface in contact with the fluid flowing through the branch pipe  2 . When the outer ring  30  to be described below is rotated, the inner ring  20  automatically rotates by a magnetic force. When the inner ring  20  rotates, it means that the inner ring  20  rotates around the center of a diameter of the branch pipe  2 . 
     According to the present embodiment, an inner diameter of the body portion  10  and an inner diameter of the inner ring  20  are formed to be equal to an inner diameter of the branch pipe  2 . An insertion groove  13  into which the inner ring  20  is inserted is formed inside the body portion  10 . In a state in which the inner ring  20  is inserted into the insertion groove  13 , the inner diameter of the inner ring  20  is formed to be equal to the inner diameter of the branch pipe  2 . The inner circumferential surface of the inner ring  20  and an inner circumferential surface of the body portion  10  form a pipe wall together with an inner circumferential surface of the branch pipe  2 . The rotation of the inner ring  20  acts as though a part of the pipe wall is rotated. 
     The outer ring  30  is arranged outside the body portion  10  to face the inner ring  20 . The outer ring  30  has a polarity opposite to a polarity of the inner ring  20 . The outer ring  30  is rotated by a driving part  60 , and when the outer ring  30  is rotated, the inner ring  20  automatically rotates by a magnetic force of the outer ring  30 . According to the present embodiment, a mounting groove  14  in which the outer ring  30  is mounted is formed outside the body portion  10 . The outer ring  30  is rotated around the center of the branch pipe  2  in a state of being mounted in the mounting groove  14 . A rolling bearing  7  is between the outer ring  30  and the body portion  10  so that the outer ring  30  may be smoothly rotated. 
     As shown in  FIG. 3 , according to the present embodiment, the branch pipe  2  includes a first branch pipe  3 , an elbow pipe  4 , and a second branch pipe  5 . The first branch pipe  3  is a pipe directly connected to the main pipe  1  so that the fluid flowing through the main pipe  1  branches therefrom. The elbow pipe  4  is a curved pipe which is connected to the first branch pipe  3  and provided to change a flow direction of the fluid. The second branch pipe  5  is a pipe connected to the elbow pipe  4  to transfer the fluid branching from the main pipe  1  to a certain location, and is provided as a straight line according to the present embodiment. 
     In the apparatus  100  for removing thermal stratification generated by turbulent penetration by using the rotation of the inner ring and the outer ring according to the present embodiment, in the case of the branch pipe  2  including the elbow pipe  4  as described above, the body portion  10  is between the elbow pipe  4  and the second branch pipe  5 . 
     As shown in  FIG. 2 , in a pipe system including the elbow pipe  4 , in which the flow direction of the fluid is changed, during operation, thermal stratification is generated at a point where the elbow pipe  4  and the second branch pipe  5  extending in a straight line come into contact and affects surrounding parts. Accordingly, the apparatus  100  for removing thermal stratification according to the present disclosure is provided at a point where the elbow pipe  4  and the second branch pipe  5  come into contact, so that concentrated formation of thermal stratification may be eliminated at an initial stage. The first body  11  is coupled to the elbow pipe  4  and the second body  12  is coupled to the second branch pipe  5 . 
     The structure and coupling relationship of the body portion  10 , the inner ring  20 , and the outer ring  30  will be described in greater detail. 
     As shown in  FIGS. 4 and 5 , according to the present embodiment, the first body  11  and the second body  12  of the body portion  10  are fastened by a fastening member  15 . The fastening member  15  is inserted into the first coupling hole  111  of the first body  11  and the second coupling hole  121  of the second body  12 , and the first and second coupling holes  111  and  121  are provided in the circumferential directions of the first and second bodies  11  and  12 , so that the fastening member  15  are provided as a plurality of fastening members  15 . The fastening member  15  may pass through the first coupling hole  111  and the second coupling hole  121 , and a nut may be coupled and fixed to an end of the fastening member  15 . 
     The first body  11  includes a groove portion having one open side so that the inner ring  20  is inserted thereinto. In addition, when the second body  12  is fastened to the first body  11 , the second body  12  blocks the open side of the groove portion to form the insertion groove  13  into which the inner ring  20  is inserted. 
     According to the present embodiment, the inner ring  20  is formed to be magnetized by a first magnetic portion  21 . The first magnetic portion  21  is formed at a certain thickness on an outer circumferential surface of the inner ring  20 . In addition, the outer ring  30  is formed to be magnetized by a second magnetic portion  31 . The second magnetic portion  31  has a polarity opposite to a polarity of the first magnetic portion  21 . The second magnetic portion  31  is formed at a certain thickness on an outer circumferential surface of the outer ring  30 . 
     The inner ring  20  and the outer ring  30  face each other with opposite polarities. The body portion  10  includes a material capable of transmitting a magnetic force. An attractive force acts between the inner ring  20  and the outer ring  30 , and when the outer ring  30  is rotated, the inner ring  20  rotates together with the outer ring  30 . The first magnetic portion  21  is provided on the outer circumferential surface of the inner ring  20  and the second magnetic portion  31  is provided on an inner circumferential surface of the outer ring  30 , so that an attractive force generated by the first and second magnetic portions  21  and  31  may act as much as possible. 
     Also, according to the present embodiment, magnetic materials  40  having the same polarity as the inner ring  20  are provided on both sides of the insertion groove  13  facing the side surfaces of the inner ring  20 . In addition, a width of the insertion groove  13  is greater than a width of the inner ring  20 , and an outer diameter of the insertion groove  13 , formed when the bottom surface of the insertion groove  13  is connected, is greater than an outer diameter of the inner ring  20 . That is, when the inner ring  20  is inserted into the insertion groove  13 , the inner ring  20  may be arranged with a certain space from both sides and the bottom surface of the insertion groove  13 . Such arrangement is made possible by polarities of the inner ring  20 , the outer ring  30 , and the magnetic materials  40 . 
     In detail, a repulsive force acts between the magnetic materials  40  and the inner ring  20 , so that the inner ring  20  is pushed from both sides of the insertion groove  13  to be spaced apart by a certain distance and to be able to rotate. That is, a certain gap is formed between the side surfaces of the inner ring  20  and both sides of the insertion groove  13 . Also, because the inner ring  20  and the outer ring  30  have the same polarity, an attractive force acts between the inner ring  20  and the outer ring  30 , and as a result of the attractive force acting in all directions in a circumferential direction because the inner ring  20  and the outer ring  30  are arranged in a circular shape, the inner ring  20  and the outer ring  30  may be spaced apart from each other by a certain space. 
     According to an embodiment of the present disclosure, the driving part  60  is provided to rotate the outer ring  30 . The driving part  60  includes a first gear portion  61 , a second gear portion  62 , and a power supply source  63 . 
     The first gear portion  61  is provided in the outer ring  30 . As shown in  FIG. 6 , the first gear portion  61  is provided on the outer circumferential surface of the outer ring  30 . The second gear portion  62  is arranged to be engaged with the first gear portion  61 . The power supply source  63  rotates the second gear portion  62 . When the first and second gear portions  61  and  62  are engaged and rotated, the outer ring  30  is rotated, and when the outer ring  30  is rotated, the inner ring  20  rotates together by a magnetic force, so that the fluid filled in the branch pipe  2  is rotated and mixed by a frictional force. 
     According to the present embodiment as described above, the driving part  60  uses the first and second gear portions  61  and  62 , and the first and second gear portions  61  and  62  are adjacent to each other, so that an excessive space is not required to install the driving part  60 . 
     According to the present embodiment, protrusions  50  that increase rotation of the fluid are formed to protrude from the inner circumferential surface of the inner ring  20 . When the valve  6  provided in the branch pipe  2  is open to allow the flow of the fluid, each of the protrusions  50  is formed in a size that does not affect the flow of the fluid in the branch pipe  2 , for example, about 3% to about 5% of the inner diameter of the branch pipe  2 . 
     According to the present embodiment, the protrusions  50  are formed to protrude and to be spaced apart from each other at certain intervals on the inner circumferential surface of the inner ring  20 . A cross-section of each of the protrusions  50  has a substantially triangular shape to increase a rotational force of the fluid when the inner ring  20  rotates in a state in which the valve  6  is closed. Also, the protrusions  50  are formed to an extent that does not interfere with the flow of the fluid and cause no pressure drop when the valve  6  is opened and the fluid flows through the second branch pipe  5 . According to the present embodiment, the protrusions  50  are provided as four protrusions  50  arranged at intervals of 90° on the inner circumferential surface of the inner ring  20 . The number of the protrusions  50  is not limited to four, but because the flow of the fluid may be inhibited as the number of the protrusions  50  increases, three or four protrusions  50  may be formed. 
     Hereinafter, the operation and effect of the apparatus  100  for removing thermal stratification generated by turbulent penetration by using the rotation of the inner ring and the outer ring according to the aforementioned configuration will be described in detail. 
     In industrial plants, the main pipe  1  through which a high-temperature and high-flow fluid flows is provided, and the branch pipe  2  branching from the main pipe  1  to supply the fluid to a desired location is provided. According to the present embodiment, the branch pipe  2  branching from the main pipe  1  is provided by being connected in order from the main pipe  1  to the first branch pipe  3 , the elbow pipe  4 , and the second branch pipe  5 . 
     When the fluid flows along the main pipe  1  and does not flow along the branch pipe  2 , the valve  6  provided in the branch pipe  2  is closed, for example, at an initial stage of operation or according to necessary conditions. In this case, a turbulent penetration phenomenon occurs in which the fluid flowing along the main pipe  1  penetrates into the branch pipe  2 , and thermal stratification is formed by the turbulent penetration phenomenon. As in the present embodiment, in the case of the branch pipe  2  including the elbow pipe  4 , thermal stratification is actively generated at a point where the elbow pipe  4  and the second branch pipe  5  are connected, and spreads to the second branch pipe  5 . 
     The apparatus  100  for removing thermal stratification generated by turbulent penetration by using the rotation of the inner ring and the outer ring, according to the embodiment of the present disclosure, is between the elbow pipe  4  and the second branch pipe  5 . According to the embodiment of the present disclosure, the apparatus  100  for removing thermal stratification is modularized and manufactured in advance, and then coupled between the elbow pipe  4  and the second branch pipe  5 . An open groove portion into which the inner ring  20  is inserted is formed in the first body  11 , the inner ring  20  is inserted into the open groove portion, and the second body  12  is arranged adjacent to the groove portion, and then the first and second bodies  11  and  12  are fastened by the fastening member  15 . By the process as described above, the inner ring  20  may be easily accommodated in the body portion  10  to be modularized. 
     According to the present embodiment, because the body portion  10  is coupled between the elbow pipe  4  and the second branch pipe  5 , the first body  11  of the body portion  10  is coupled to the elbow pipe  4 , and the second body  12  is coupled to the second branch pipe  5 . The body portion  10  is welded and coupled to the branch pipe  2 . 
     The apparatus  100  for removing thermal stratification according to the present disclosure is completely installed in a state in which the first gear portion  61  of the outer ring  30  is engaged with the second gear portion  62 . When the valve  6  that opens and closes the branch pipe  2  is closed and the fluid flows along the main pipe  1 , the first gear portion  61  is rotated as the second gear portion  62  is rotated by the power supply source  63 , and the inner ring  20  automatically rotates by a magnetic force as the outer ring  30  is rotated according to the rotation of the first gear portion  61 . The fluid is rotated and mixed according to the rotation of the inner ring  20 , so that thermal stratification at the point where the elbow pipe  4  and the second branch pipe  5  are connected is removed. 
     As described above, the apparatus  100  for removing thermal stratification generated by turbulent penetration by using the rotation of the inner ring and the outer ring, according to the embodiment of the present disclosure, efficiently removes thermal stratification generated by turbulent eddies penetrating into the branch pipe  2  closed by the valve  6 . 
     Because the inner ring  20  rotates by a magnetic force when the outer ring  30  is rotated, there is no concern about mechanical abrasion of the inner ring  20 , and because the body portion  10  is between the inner ring  20  and the outer ring  30 , a leakage of the fluid may be prevented. Also, the first magnetic portion  21  is provided on the outer circumferential surface of the inner ring  20 , and the outer ring  30  is provided on the inner circumferential surface of the outer ring  30 , so that an attractive force between the inner ring  20  and the outer ring  30  may be utilized as much as possible. 
     Also, the apparatus  100  for removing thermal stratification is modularized as described above and thus may be easily installed without changing the existing pipe network, and the apparatus  100  for removing thermal stratification is between the elbow pipe  4  and the second branch pipe  5  and thus provides easy maintenance. Accordingly, the apparatus  100  for removing thermal stratification may be easily installed in plants in operation or in which construction is completed or is in progress. 
     When the valve  6  of the branch pipe  2  is opened and the fluid flows through the branch pipe  2 , in the apparatus  100  for removing thermal stratification according to the present disclosure, a separate structure is not installed inside a pipe, which does not interfere with the flow of the fluid, and thus, pressure loss does not occur. Also, because scattered materials are not generated due to damage of the separate structure, additional device damage due to the scattered materials may be prevented in advance, and when the apparatus  100  for removing thermal stratification is applied to a nuclear power plant, safety may be greatly improved. 
     The apparatus  100  for removing thermal stratification according to the present disclosure may sufficiently remove thermal stratification without rotating the rotator  20  at a high speed. For example, a sufficient effect may be achieved at a speed of about 10 revolutions/minute to about 13 revolutions/minute (10 rpm to 13 rpm). Also, when the valve  6  of the branch pipe  2  is opened and the fluid flows through the branch pipe  2 , the apparatus  100  for removing thermal stratification according to the present disclosure may be stopped, so that a large electric load is not required for the operation. 
     In addition, because the thermal stratification is blocked in advance, a pipe integrity evaluation on thermal stratification or thermal fatigue through experiments or computational analysis may be omitted, and because there is no need to install an ultrasonic monitoring facility or the like to check the condition of the inside of a pipe, costs required for facilities may be reduced. 
     The apparatus for removing thermal stratification generated by turbulent penetration by using the rotation of the inner ring and the outer ring, according to the present disclosure, may remove thermal stratification generated by turbulence penetrating into a branch pipe by using the rotation of the inner ring and the outer ring. 
     Also, when the outer ring is rotated, the inner ring automatically rotates by a magnetic force, and a viscous fluid is rotated together by a frictional force with the rotating inner ring to remove thermal stratification, so that the thermal stratification may be removed with a relatively small rotational force, and pipe vibration or the like may not be affected. 
     In addition, the apparatus for removing thermal stratification may be modularized and installed, and thus, installation thereof is possible without changing the layout of the existing pipe network. 
     Moreover, when the branch pipe includes a first branch pipe, an elbow pipe, and a second branch pipe, during operation, thermal stratification starts at a point where the elbow pipe and the second branch pipe are connected, the apparatus for removing thermal stratification according to the present disclosure is installed at the point where the elbow pipe and the second branch pipe are connected and efficiently removes the thermal stratification with a small rotational force in the initial stage. 
     Also, because a separate structure colliding with a fluid in the pipe to remove thermal stratification is not installed, the fluid may smoothly flow to prevent pressure drop loss due to the separate structure in advance. Further, because the separate structure is not installed, not only costs may be reduced, but also device damage caused by the separate structure being damaged by the flow of the fluid may be prevented. That is, when the structure is damaged due to the flow of the fluid, fragments may be generated, and the fragments may cause serious damage not only to the pipe system but also to other devices into which the fluid flows. The present disclosure may prevent such damage. When the present disclosure is applied to a nuclear power plant, accidents caused by the fragments may be prevented, thereby greatly improving safety. 
     Also, because thermal stratification generated in the branch pipe is removed in advance, the installation of ultrasonic monitoring equipment for pipe integrity evaluation may be omitted, thereby reducing enormous costs required for such equipment. 
     It should be understood that embodiments described herein should be considered in a descriptive sense only and not for purposes of limitation. Descriptions of features or aspects within each of the embodiments should typically be considered as available for other similar features or aspects in other embodiments. While one or more embodiments have been described with reference to the figures, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the disclosure as defined by the following claims.