JPH0727493A - Heat transfer pipe for heat exchanger - Google Patents

Abstract

PURPOSE:To enable use of a pipe-fixed plate type heat exchanger by a method wherein a part of a heat transfer pipe is formed of a short pipe which is made of shape memory material, and incorporated into the heat exchanger in a state that prestress is being given in a direction reverse to heat stress generated during operation. CONSTITUTION:A heat transfer pipe 10 to be incorporated in a linear bronze 1 having no expansive joints is formed by a short pipe 11 a part of which is made of shape memory material. Before operation, the heat transfer pipe 10 is incorporated in a heat exchanger C in a state that prestress is being given in a direction reverse to heat stress generated during the operation. In detail, as the heat transfer pipe 10 has a larger heat expansion amount than the bronze 1, at a switching point from non-operation state to operation state, compression stress is generated in the heat transfer pipe 10. Accordingly, when the heat transfer pipe 10 is incorporated in the heat exchanger C, prestress is given so that tension stress may be generated. By this, there is no need to provide the heat exchanger with bronze made expansion joints, whereby a pipe-fixed plate type heat exchanger can be used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat transfer tube for a heat exchanger used in a thermal power plant, a chemical plant, a nuclear power plant or the like, and more particularly to a heat transfer tube incorporated in a fixed tube plate type heat exchanger.

[0002]

2. Description of the Related Art A shell-and-tube type heat exchanger is a so-called fixed tube plate type heat exchanger in which tube plates supporting the ends of heat transfer tubes are fixed to both ends of a body by welding or other methods. is there. In this type of heat exchanger,
Due to the temperature of the body-side fluid and the tube-side fluid and the difference in thermal expansion coefficient between the material forming the heat transfer tube and the material forming the body, a difference in thermal expansion occurs between the body and the heat transfer tube during operation. A large amount of thermal stress may occur in the constituent members.

For this reason, a heat exchanger as shown in FIG. 3 has been developed in order to prevent the occurrence of such a great thermal stress. In the figure, reference numeral 1 is a body, 2 is a fin 2 on the outer circumference.
a is a linear heat transfer tube, 3 is a flange attached to both ends of the heat transfer tube 2, 4 is a fluid inlet on the shell side, 5
Is a fluid outlet on the body side, 6 is a fluid inlet on the tube side, 7 is a fluid outlet on the tube side, and 8 is a mount. An expansion joint 1a formed to bulge outward is provided at a substantially central portion of the body 1.
Further, flanges 1b and 1b are provided at both ends of the body 1, and these flanges 1b and 1b are fixed to flanges 3 attached to both ends of the heat transfer tube 2.

In the heat exchanger having the above-mentioned structure, when the fluid A supplied from the fluid inlet 6 on the tube side is passed through the heat transfer tube 2, it is brought into thermal contact with the fluid B supplied from the fluid inlet 4 on the shell side. , The fluid A on the tube side is heated to a predetermined temperature. Further, due to the temperature of the body fluid B and the tube side fluid A, the difference in the thermal expansion coefficient between the material forming the heat transfer tube 2 and the material forming the body 1, and the like, there is a gap between the body 1 and the heat transfer tube 2 during operation. Although a difference in thermal expansion occurs, this difference in thermal expansion is absorbed by the expansion joint 1a of the case 1, and excessive heat stress does not occur in the case 1, the heat transfer tube 2, and the like.

[0005]

However, in the above heat exchanger, when a high temperature and high pressure fluid is used as the body fluid B, not only the body 1 but also the plate thickness of the expansion joint 1a can withstand those fluid pressures. You have to set it thick,
In this case, since the amount of expansion and contraction that can be absorbed becomes small, it does not function as the expansion joint 1a, and it is conceivable that the expansion joint cannot be used. Therefore, a fixed tube plate type heat exchanger cannot be used and must be converted to a U-shaped or floating type heat exchanger. However, such a heat exchanger is compared to a fixed type heat exchanger. The cost is high.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to eliminate the need for an expansion joint of a heat exchanger barrel and to use a high-temperature, high-pressure cylinder-side fluid in which the expansion joint cannot be used. It is an object of the present invention to provide a heat transfer tube of a heat exchanger that enables the use of a heat exchanger having a fixed tube plate type structure even when using.

[0007]

In order to achieve such an object, in the present invention, a part of the heat transfer tube is composed of a short tube made of a shape memory material, and the heat transfer tube has a direction opposite to the thermal stress generated during operation. It was configured to be incorporated in the heat exchanger in a prestressed state.

[0008]

When the heat exchanger incorporating the heat transfer tube of the present invention enters a normal operating state, for example, when the thermal expansion amount of the heat transfer tube is larger than that of the shell, the heat transfer tube is pre-introduced. It changes from tensile stress due to stress to compressive stress. On the other hand, the body changes from compressive stress to tensile stress. However, the magnitude of the stresses that occur in them under operating conditions is
Compared with the case where no prestress is introduced in the state before operation, the stress is reduced by the amount of the stress in the opposite direction that was initially present.

A heat transfer tube according to the present invention will be described below with reference to FIGS. 1 and 2. In these figures, the same components as those of the conventional example described above are designated by the same reference numerals and the description thereof will be omitted.

The heat transfer tube 10 incorporated in the linear case 1 having no expansion joint is partially composed of a short tube 11 made of a shape memory material. The shape memory material forming the short tube 11 has a significantly different crystal structure on the high temperature side and the low temperature side, for example, even if plastic deformation is applied to its own shape on the low temperature side, when the temperature exceeds a certain temperature, It has the property of returning to its shape.

The heat transfer tube 10 is incorporated in the heat exchanger C in a state in which a prestress in the direction opposite to the thermal stress generated during the operation is applied before the operation. Specifically, since the heat transfer tube 10 usually has a larger thermal expansion amount than the case 1, the heat transfer tube 1 is changed from the state before operation to the operation state.
At 0, compressive stress occurs. Therefore, when the heat transfer tube 10 is incorporated into the heat exchanger C, prestress is applied so that tensile stress is generated.

A method for incorporating the heat transfer tube 10 into the heat exchanger C in a state in which a prestress in the direction opposite to the thermal stress generated during the operation before the operation is applied will be described.
As shown in FIG. 1, first, both ends of a plate-shaped shape memory material 13 are welded to form a short tube 11, and the short tube 11 is stretched along the axis in a temperature range below the transformation temperature of the shape memory material. Apply load to cause plastic deformation. Then, the plastically deformed short tube 11 is incorporated into a part of the heat transfer tube 10. That is, both ends of the short tube 11 are welded to the ends of the heat transfer tube constituent members 11a and 11b so that they are formed into a single pipe shape.

The heat transfer tube 10 is assembled in the heat exchanger C by fixing the flanges 3 to both ends of the heat transfer tube 10 produced as described above and fixing the flanges 3 to the flange portion 1b of the case 1. In this state, the heat transfer tube 10 is not prestressed.

Then, the heat transfer tube 10 incorporated in the heat exchanger C is heated so as to exceed the transformation point of the heat transfer tube (when the transformation point is lower than room temperature, it is cooled). As a result, the heat transfer tube 10 returns to the shape before the tensile work, and as a result, the heat transfer tube 10 is prestressed so that a tensile stress is generated. At the same time, a compressive stress is generated in the body 1. By the above method, the heat transfer tube 10 incorporated in the heat exchanger C can be prestressed.

When the heat exchanger C equipped with the heat transfer tube 10 is in a normal operating state and fluids A and B are introduced from the fluid inlet 4 on the shell side and the fluid inlet 6 on the tube side, respectively, the heat transfer tube The temperature of 10 and the body 1 rises. At this time, the thermal expansion of the heat transfer tube 10 is larger than that of the case 1, so that the heat transfer tube 10 turns into tensile stress and compressive stress due to pre-stress introduced in advance. On the other hand, in the case of the body 1, on the contrary, the compressive stress changes to the tensile stress. However, the magnitude of the stress in those operating states becomes smaller by the amount of the opposite stress that was initially present than in the case where no prestress was introduced before the operation and there was no stress. Therefore, by appropriately setting the prestress value, the expansion joint of the body of the heat exchanger becomes unnecessary, and even when using the high temperature and high pressure side fluid that cannot be used for the expansion joint, the fixed tube plate structure A heat exchanger can be used.

In the above embodiment, the case where the heat expansion amount of the heat transfer tube 10 is larger than that of the case 1 has been described as an example. However, the heat expansion amount of the heat transfer tube 10 is not limited to this. The present invention can be applied even when it is smaller than that of the case 1. In this case, the direction of the prestress is opposite to that of the above-described embodiment, so that the compressive stress is generated in the heat transfer tube 10 in the assembled state to the heat exchanger C before the operation so that the short tube 11 made of the shape memory alloy is preliminarily set. It may be compressed.

[0017]

As described above, according to the present invention, a part of the heat transfer tube is composed of a short tube made of a shape memory material, and a prestress in the direction opposite to the thermal stress generated during operation is applied. Since it is installed in the heat exchanger in a state where it is in a normal operating state, for example, when the thermal expansion amount of the heat transfer tube is larger than that of the shell, the heat transfer tube is It turned into compressive stress, and the body changed from compressive stress to tensile stress, and the magnitude of the stress in those operating conditions existed earlier than in the case where prestress was not introduced before operating. It becomes smaller by the amount of stress in the opposite direction. Therefore, by setting the prestress value appropriately, it is possible to eliminate the need for expansion joints on the shell of the heat exchanger, and to fix them even when using high-temperature, high-pressure fluid on the shell side, where expansion joints cannot be used. It has excellent effects such as the use of a heat exchanger having a tube plate structure.

[Brief description of drawings]

FIG. 1 is a process drawing showing a manufacturing procedure of an embodiment of such a heat transfer tube of the present invention.

FIG. 2 is a cross-sectional view of a heat exchanger incorporating the heat transfer tube according to the present invention.

FIG. 3 is a sectional view showing an example of a conventional heat exchanger.

[Explanation of symbols]

 1 Body 4 Body-side fluid inlet 5 Body-side fluid outlet 6 Tube-side fluid inlet 7 Tube-side fluid outlet 10 Heat transfer tube 11 Short pipe made of shape memory alloy C Heat exchanger

Claims (1)

[Claims] 1. A part of a heat transfer tube is formed of a short tube made of a shape memory material, and the heat transfer tube is incorporated into a heat exchanger under a prestress in a direction opposite to a thermal stress generated during operation. A heat transfer tube of a heat exchanger characterized by being.