JPH01296089A - Intermediate heat exchanger - Google Patents

Abstract

PURPOSE:To widen a gap between the bundles of tubes to reduce the flow speed of fluid and improve load bearing capacity with respect to hydrodynamic elastic vibration, by a method wherein heat transfer tubes near the inlet window of secondary cooling material are provided with elliptical sectional configuration and are arranged so that the major axis thereof coincides with the flow direction of the fluid. CONSTITUTION:In an intermediate heat exchanger for a liquid metal cooling tank type fast breeder reactor, the flow speed of secondary cooling material is quickened especially at the vicinity of the inlet window of the second cooling material and the vicinity of entrances 21 of ascending tubes and, therefore, heat transfer tubes 13 in these areas are readily damaged by hydrodynamic elastic vibration. Therefore, the heat transfer tubes 22 arranged near the inlet 21 of the ascending tubes are provided with elliptical sectional configuration and are arranged so that the major axis of the elliptical sectional configuration coincides with the flow direction of the secondary cooling material. When the hat transfer tubes are constituted of elliptical pipes having the same sectional area and the ratio of a minor axis to the major axis thereof is 1:2, the healthiness of the tubes with respect to the hydrodynamic elastic vibration may be improved to 1.62 times as compared with a circular heat transfer tube.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to an intermediate heat exchanger installed in a reactor vessel, which is applied to, for example, a liquid metal cooled tank type fast breeder reactor, and particularly The present invention relates to an intermediate heat exchanger with an improved structure of a heat exchange tube bundle.

(Prior Art) In a liquid metal cooled tank type fast breeder reactor, a liquid metal such as liquid sodium is used in both the primary coolant that circulates in the reactor vessel and the secondary coolant that circulates in the secondary coolant that includes the steam generator. is used, and an intermediate heat exchanger used for transferring heat between the primary coolant and the secondary coolant is installed in the furnace vessel.

Hereinafter, the structure inside the furnace vessel will be explained using FIG. 3. The furnace vessel 1 is covered with a roof slab 2 from above.
A plurality of intermediate heat exchangers 3 are suspended around the reactor core 4 together with primary circulation pumps 5 at regular intervals.

Note that the reference numeral 6 indicates a safety container that prevents the primary coolant filling the inside of the reactor vessel 1 from leaking to the outside.

Next, the structure of the intermediate heat exchanger 3 will be explained with reference to FIG. The intermediate heat exchanger 3 has a cylindrical upper part f! vertically suspended from the roof slab 2. It is mainly composed of the i47 and the lower part $8 connected to it.

The upper flii7 is provided with a primary coolant inlet window 9 passing through the wall surface, and the lower body 8 is provided with a primary coolant outlet 10 that opens downward. A heat exchange portion occupying the center of the lower shell 8 is formed from the primary coolant inlet window 9 to the primary coolant outlet 10. That is,
A plurality of heat transfer tubes 13 are vertically arranged, each supported by an upper tube plate 11 at the top and a lower tube plate 12 at the bottom, separated by a heat transfer wall into an inside and an outside, and are separated by a primary coolant and a secondary coolant. Heat is transferred between the

On the other hand, a secondary coolant inlet 14 and a secondary coolant outlet 15 are provided at the upper end of the upper body 7, respectively. This 2
The secondary coolant population 14 is connected to a downcomer pipe 16 installed to extend from the upper part 11ii7 to the lower body 8, and the secondary coolant outlet 15 is constituted by the downcomer pipe 16 and the heat transfer tube 13 described above. The heat exchange section consists of two types of donut-shaped baffles 18 of different thickness placed alternately.
．． The secondary coolant is separated by heat transfer tube 13.
It flows from the bottom to the top on the outside. Note that in the figure, numerals 20 and 21 indicate the secondary coolant inlet window and the riser pipe inlet, respectively.

In the above configuration, the primary coolant that has flowed to the outside of the upper body 7 flows from the primary coolant inlet window 9 into the upper part 111ii7,
While flowing roughly downward within the heat transfer tube 13, the temperature is lowered by exchanging heat with the secondary coolant flowing outside the tube 13, and then introduced into the lower shell 8. From there, the primary coolant outlet 1
0 and is discharged outside the vessel.

On the other hand, the secondary coolant enters the downcomer pipe 16 through the secondary coolant population 14, is guided by this, flows downward, flows into the heat exchange section through the secondary coolant inlet window 20, and is transferred. heat tube 1
3, the temperature rises through heat exchange with the primary coolant mentioned above, enters the riser pipe 17 through the riser pipe inlet 21, is guided by this, rises, and passes through the secondary coolant outlet 15. It is sent to a steam generator (not shown).

(Problems to be Solved by the Invention) In the intermediate heat exchanger 3 as described above, the flow velocity of the secondary coolant is particularly high near the secondary coolant inlet window 20fi and the riser pipe inlet 21, and There is a concern that the heat exchanger tubes 13 in the region may be damaged by hydroelastic vibration.

This problem will be explained in detail below with reference to the drawings.

In FIG. 5, the secondary coolant that has flowed down the downcomer pipe 16 flows into the tube bundle through the secondary coolant inlet window 20 as shown by the arrow in the figure, and then flows into the tube bundle as shown by the two-dot chain line in the figure. After passing the outer periphery of the baffle plate 18, the flow changes direction and flows perpendicular to the plane of the paper to be guided to the next span. Particularly in the flow of the secondary coolant, the flow velocity is high near the secondary coolant inlet window 20 because the tube bundle gap area, that is, the flow path area is small. In addition, since the flow is dominated by a cross flow that is perpendicular to the tube bundle, this region is caused by hydroelastic vibration of the individual heat exchanger tubes.
3 vibrations and their damage are a concern.

In addition, in FIG. 6, the secondary coolant that has risen perpendicularly to the plane of the paper between the lower shell 8 and the outer periphery of the baffle plate 18 changes its flow direction and moves in the radial direction as shown by the arrow in the figure. It flows inward, passes through the riser tube 21, rises perpendicularly to the plane of the paper again, and is guided into the flow path between the lower limit tube 16 and the riser tube 17. In this case as well, since the flow path area is small near the riser pipe inlet 21, the flow velocity of the secondary coolant is particularly high. Further, since the cross flow is similarly dominant, there is a concern that the individual heat exchanger tubes 13 may vibrate and be damaged due to the flow saw elastic vibration in this region as well.

A method for preventing such hydroelastic vibrations of the heat transfer tubes 13 is to increase the interval between the individual heat transfer tubes 13, that is, the tube pitch, which slows down the velocity of the fluid passing through the tube bundle, which leads to the ingress of debris on the outer diameter, and which also increases the This also increases the capacity of vessel-1, leading to an increase in the size of the fast breeder reactor plant. Another method for reducing the velocity of the tube-bundling fluid is to move the baffle plates 18, 19 closest to the upper tube sheet 11 and lower tube sheet 12 away from the tube sheet surface, that is, to increase the span. In this way, the flow path area becomes wider, so these two
The flow velocity in the area can be reduced. However, as the support span of the heat exchanger tube 13 has become wider, the heat exchanger tube 1
3 is lowered, and conversely, the heat exchanger tube 13 becomes easier to photograph. Therefore, this method is not necessarily convenient as a preventive measure against hydroelastic imaging.

SUMMARY OF THE INVENTION An object of the present invention is to provide an intermediate heat exchanger that can prevent damage to heat transfer tubes caused by hydroelastic vibration near the secondary coolant inlet window and the riser inlet. The cross-sectional shape of the heat exchanger tube near the secondary coolant inlet window and/or riser pipe inlet is configured to be oval or oval, and the long axis of the heat exchanger tube is arranged in the same direction as the flow direction of the secondary coolant. It is characterized by the fact that

(Function) In the intermediate heat exchanger having such a structure, the distance between the heat transfer tubes becomes wider in the circumferential direction near the secondary coolant inlet window and the riser tube inlet. That is, the gap between the tube bundle becomes wider with respect to the flow, and the flow velocity of the secondary coolant can be reduced.

On the other hand, since the natural frequency of a heat exchanger tube is proportional to the 172nd power of the adiabatic moment of inertia of the heat exchanger tube, the second moment of area of the heat exchanger tube is reduced by using a heat exchanger tube with an elliptical cross section. The effect of this is reasonably small compared to the contribution of the decrease in flow velocity due to the enlargement of the gap between the heat exchanger tubes.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of an intermediate heat exchanger according to the present invention, in which heat exchanger tubes 22 disposed near riser tubes 21 have an elliptical cross-section. The long axis of the heat transfer tube 22 is aligned with the flow direction of the secondary coolant.

Below, as an example for explanation, the initial pipe outer diameter is 25.4.
．． In a group of tubes using circular heat exchanger tubes with a wall thickness of 1.2 mm and a tube pitch in the circumferential direction of 33.02 am, that is, a ratio of tube outer diameter to tube pitch of 1:1.3, for example, a heat exchanger tube with a circular cross section The improvement of the resistance against hydroelastic imaging when replacing this with a heat exchanger tube with an elliptical cross section with the same cross-sectional area, the same wall thickness, and a ratio of short axis to long axis of 1:2 is described below. explain.

Generally, the critical flow velocity Ver that causes hydroelastic vibration is expressed by the following equation. In the formula below, (d 799 is added to the right side of the symbol) when an oval heat exchanger tube is used.

Here, fo is the natural frequency of the pipe and is based on the following equation.

Ver: Critical flow velocity me: Snow mass per unit length including added mass K: Constant determined by pipe arrangement, pitch, support method, etc. do: Representative diameter δ0: Attenuation rate A: Constant determined by distance between baffles, support method, etc. ρ: Fluid density E: Young's modulus I: By substituting the equation (2) of the second moment of area of the heat exchanger tube into the equation (2), a relational expression between the flow velocity and the second moment of area is derived as shown in the following equation.

However, it can be said that the design is more sound for hydroelastic imaging.

In the case of a circular heat exchanger tube In the case of a heat exchanger tube with an oval surface according to this embodiment, the moment of inertia of the circular heat exchanger tube is I -6695.4. On the other hand, since hydroelastic vibration in an elliptical heat transfer tube generally occurs in the direction perpendicular to the flow, if the second moment of area about the long axis is adopted, I' = 50411I
IIr&4, which is I/I-0, 753. The moment of inertia of area related to long sleeves is the smallest moment of inertia of an ellipse, and the moment of inertia of area becomes large for vibrations in directions other than perpendicular to the flow, if the flow velocity is the same. Therefore, it has more resistance against hydroelastic imaging. On the other hand, as the distance between the heat transfer tubes increases, the flow velocity of the secondary coolant increases. , 53kl
:6゜■ er = 1.62
It can be seen that by using an elliptical heat exchanger tube, the soundness against hydroelastic vibration is improved by 1.62 times compared to a circular heat exchanger tube.

According to the present invention, although there is a decrease in rigidity due to a decrease in the moment of inertia of the area, there are many effects due to the expansion of the flow path area.
q, and high resistance to hydroelastic imaging can be obtained.

Although the above description relates to the vicinity of the riser pipe inlet 21, the same can be said to the vicinity of the secondary fluid inlet window 20.

Next, another embodiment of the present invention will be described with reference to FIG. The difference from FIG. 1 is that the heat exchanger tubes 22 are arranged not in a circumferential arrangement but in a triangular arrangement.

Even if an intermediate heat exchanger with such a structure is used, the riser pipe inlet 2
The heat exchanger tubes 22 in one vicinity have a high resistance to hydroelastic vibrations in this region due to a reduction in the flow velocity of the secondary coolant due to an increase in the distance between the heat exchanger tubes on the circumference.

The same thing as ψ can be said about the vicinity of the secondary coolant inlet window 20.

Although the heat exchanger tube having an elliptical cross section has been described above, it is clear that the same thing can be said even if the shape is changed to an ellipse.

〔Effect of the invention〕

As described above, when using the intermediate heat exchanger according to the present invention, the secondary coolant flow rate is high and the heat exchanger tubes can be damaged near the secondary coolant inlet window and the riser pipe inlet, where the flow rate of the secondary coolant was high and there was concern about damage to the heat transfer tubes due to hydroelastic imaging. The flow rate suppressing effect of the secondary coolant on the tube bundle can provide a high resistance against hydroelastic imaging, and as a result, a highly reliable intermediate heat exchanger can be provided.

[Brief explanation of the drawing]

1 and 2 are partial sectional views of a tube bundle of an intermediate heat exchanger showing one embodiment of the present invention, FIG. 3 is a configuration diagram showing main equipment in a conventional furnace vessel, and FIG. 4 is a conventional FIG. 5 and FIG. 6 are cross-sectional views showing a conventional intermediate heat exchanger in an enlarged manner. 1...Furnace vessel 3...Intermediate heat exchanger 4...
・Reactor core 7... Upper shell 8... Lower shell
9...Primary coolant inlet window 10...Primary coolant outlet 13...(circular) heat transfer tube 16...Downcomer pipe
17...Rising pipe 18, 19...Baffle plate 2G...Secondary coolant inlet window 22...(elliptical) heat exchanger tube agent Patent attorney Noriyuki Noriyuki Yudo Daishimaru Kendai 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] An upper shell and a lower shell, each formed to have the same inner diameter, are vertically concentrically connected and connected, and inside the lower shell there is an upper tube plate that partitions the inside of the lower shell from the upper shell, and an outer tube plate. A lower tube plate is provided to partition the lower space in the lower shell which is communicated with the lower shell, and a heated medium led from the outside is directed from below to above the partitioned area in the lower shell, and the heating medium is A downcomer pipe having a secondary coolant inlet window and a large number of heat transfer tubes that connect the inside of the upper shell and the space below the lower shell are connected to a central region of the lower shell and a downcomer pipe having a secondary coolant inlet window so as to flow in countercurrent flow from the upper part to the lower part of the lower shell. In the intermediate heat exchangers arranged in the outer peripheral region, the heat exchanger tubes near the secondary coolant inlet window and/or the riser tube inlet have an elliptical or oval cross-sectional shape, and the length of the heat exchanger tubes is elliptical or oval. An intermediate heat exchanger characterized in that the shaft is arranged in the same direction as the flow direction of the medium to be heated.