JPH06317695A - Mixed flow piping structure - Google Patents

Abstract

PURPOSE:To suppress the generation of unsteady wall temperature fluctuation caused by the heat transfer of two fluids with large temperature difference and unsteady thermal stress generated in association so as to provide mixed flow piping higher in safety and reliability by using a double/triple temperature difference reducing system. CONSTITUTION:By-pass structure is provided from a main pipe 1 after confluence to a branch pipe 2, and a throttle part 4 is installed in the branch pipe shape around the lower reaches outlet of a by-pass pipe 3. A fluid is made flow into the by-pass pipe 3 by the drop of pressure due to the throttle part 4, and the fluid in the branch pipe 2 and the fluid in the by-pass pipe 3 are mixed before the fluid in the branch pipe 2 and the fluid in the main pipe 1 are mixed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to piping of a thermal power plant and a nuclear power plant, and more particularly to suppressing the generation of thermal stress due to wall temperature fluctuation of the mixing portion piping when high temperature water and low temperature water come into contact with each other. The present invention relates to a suitable temperature difference relaxing mechanism.

[0002]

2. Description of the Related Art FIG. 5 shows a basic confluent piping structure which has been used conventionally in consideration of reduction in temperature difference. The structure shown in FIG. 5 is likely to form a laminar flow, and it is considered that the mixing reaching distance for the two fluids to reach thermal equilibrium is long, which is not desirable if the viewpoint of mixing performance is taken into consideration. Next, FIG.
This is a reactor water supply device disclosed in Japanese Patent No. 260194. The invention of FIG. 6 is similar to the invention, although it uses different objects. This is an invention for reducing repeated thermal stress due to mixing of two fluids having a temperature difference in a reactor water supply system.
It has a throttle and its pressure drop circulates the flow,
It is similar to the present invention in that the temperature difference is reduced. However, the point of the invention is to utilize a well-mixed medium temperature fluid with a bypass pipe attached, which is not seen in FIG.

A mixed flow pipe having a conventional bypass structure is shown in FIGS. 7 and 8. FIG. 7 shows a thermal shock prevention structure for piping of JP-A-60-175898, and FIG. 8 shows a reactor piping apparatus of JP-A-2-52298. The structure of FIG. 7 improves the heat transfer performance by mounting the thermal sleeves at two places, but at the confluence of the fluid A and the fluid D, the heat transfer through the tube wall of the thermal sleeve 6 is sufficient for both fluids. There is no significant decrease in temperature difference, and it is considered that the two fluids come into contact with each other in this portion with a temperature difference. Further, even in the structure of FIG. 8, the temperature difference at the merging portion is reduced, but in the mixing portion of the fluid D and the fluid B in the bypass line 5, the two fluids are in direct contact with each other with the temperature difference. Therefore, due to abrupt contact between the low temperature water and the high temperature water in a certain part of these structures, wall temperature fluctuations occur on the pipe surface. As a result, unsteady thermal stress is generated on the surface of the material, which may cause surface cracks, and concern about the reliability and safety of the piping.

[0004]

The prior art relating to the above-mentioned bypass structure is to reduce the temperature difference between hot water and cold water at a part of the contact mixing section when there is a large temperature difference between the high temperature water pipe and the low temperature water pipe. It has a structure in which almost direct contact mixing occurs without any contact, and there is a problem with the occurrence of unsteady thermal stress due to wall temperature fluctuations near the two-fluid contact area.

An object of the present invention is to prevent direct contact between the low-temperature water and the high-temperature water with a large temperature difference between the high-temperature water pipe and the low-temperature water pipe in a mixed contact portion while maintaining a simple shape at the merging portion. Especially.

[0006]

In order to achieve the above object, the present invention provides a bypass structure which leads from a main pipe at a position where fluids after merging are sufficiently mixed to a branch pipe before merging,
By allowing the fluid of the intermediate temperature after mixing to flow into the branch pipe before merging to reduce the temperature difference between the branch pipe fluid temperature and the main pipe fluid temperature, it is possible to prevent both fluids from mixing due to a large temperature difference and suppress layer separation. be able to.

[0007]

When the bypass structure is provided in the mixed flow piping structure, the fluid at the intermediate temperature in the bypass and the high temperature water (low temperature water) in the branch pipe are mixed without a large temperature difference. As a result, the temperature of the high temperature water (low temperature water) in the branch pipe is lowered (raised) by mixing. After that, the high temperature water (low temperature water) in the branch pipe where the temperature becomes low (high) becomes low temperature water (high temperature water) in the main pipe at the confluence.
, But at this point both fluids mix without a large temperature difference. By this method of stepwise mixing, it is possible to mix without having a large temperature difference,
It is possible to prevent the layer separation of the flow due to the density difference caused by the temperature difference.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 shows a cross-sectional view of a mixed flow pipe section. Further, one of the features of the present invention is that it can be easily used in combination with other systems, and FIG. 2 is shown as a simple example.

The structure of the mixed flow pipe section will be described. Here, in the mixed flow pipe, the high temperature water fluid A (hot water) and the low temperature water fluid B (cold water) join, and the intermediate temperature fluid C is generated. In this basic structure, a main pipe 1, which is a mainstream, is connected to a branch pipe 2 having a narrowed portion 4 by welding. In the throttle portion 4, the static pressure is reduced by the increase in the flow velocity due to the throttle. In the case of FIG. 2, the thermal sleeve 5 is projected at the branch pipe outlet in the direction coaxial with the tributary flow. When the bypass structure 3 that leads from the main pipe to the branch pipe is provided after the merging, part of the intermediate temperature fluid C flows in the bypass pipe 3 due to the pressure drop of the throttle portion 4. The fluid C in the bypass pipe 3 mixes with the fluid A in the throttle portion 4 without a large temperature difference, and reduces the temperature difference of the fluid in the branch pipe with respect to the fluid in the main pipe. Further, the fluid in the branch pipe is mixed with the fluid B after reducing the temperature difference by heat transfer through the thermal sleeve 5. At this time, there is no large temperature difference between the high temperature water A and the low temperature water B. In this way, the intermediate temperature fluid after mixing is used as a buffer for both fluids, and by the method of mixing both fluids stepwise, it is possible to mix without a large temperature difference,
It is possible to prevent the layer separation of the flow due to the density difference caused by the temperature difference. FIG. 3 and FIG. 4 show an embodiment of the present invention in the case where there are curved portions before and after the confluence portion. In this case,
The present invention can be used more simply as shown in FIG.

With such a mechanism, it is possible to prevent the two fluids having a large temperature difference from merging and mixing at the merging portion in the mixed flow piping portion to change in temperature. Therefore, temperature fluctuations on the piping surface are suppressed, and as a result, thermal stress associated with unsteady wall temperature fluctuations is mitigated, and the safety of the plant piping is secured.

[0011]

According to the present invention, both fluids can be mixed in a high temperature water / low temperature water mixing pipe portion without a large temperature difference. Therefore, it is possible to suppress the unsteady wall temperature fluctuation caused by the heat transfer of the two fluids having a large temperature difference and the occurrence of unsteady thermal stress accompanying it. Further, the present invention can also have the following effects.

(1) It is easy to use in combination with other methods, and it is possible to further reduce the temperature difference by using them in combination.

(2) Compared with other methods, it is possible to relatively shorten the reach of perfect mixing.

(3) The laminarization phenomenon due to the density difference caused by the temperature difference of the single-phase flow is suppressed as compared with the other methods.

(4) The merging portion of the merging pipe has a simple shape.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a mixed flow pipe section according to an embodiment of the present invention.

FIG. 2 is a sectional view of a mixed flow pipe section according to a second embodiment of the present invention.

FIG. 3 is a sectional view of a mixed flow pipe section according to a third embodiment of the present invention.

FIG. 4 is a sectional view of a mixed flow pipe section according to a fourth embodiment of the present invention.

FIG. 5 is a cross-sectional view of a conventional mixed flow pipe section.

FIG. 6 is a cross-sectional view of a conventional reactor water supply apparatus similar to the present invention.

FIG. 7 is a cross-sectional view of a mixed flow pipe section having a conventional bypass structure.

FIG. 8 is a cross-sectional view of a mixed flow pipe section having a conventional bypass structure.

[Explanation of symbols]

1 ... Main pipe, 2 ... Branch pipe, 3 ... Bypass pipe, 4 ... Throttling part, 5
… Thermal sleeve, 6… Thermal sleeve.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Hidekazu Fujimura, 502 Jinritsucho, Tsuchiura-shi, Ibaraki Hiritsu Manufacturing Co., Ltd.Mechanical Research Institute (72) Kazuhito Koyama 502, Jinritsucho, Tsuchiura-shi, Ibaraki Hiritsu Co., Ltd. Machinery Research Laboratory (72) Inventor Yukihiro Asada 3-1-1 Sachimachi, Hitachi City, Ibaraki Prefecture Hitachi Ltd., Hitachi Plant

Claims (2)

[Claims] 1. In a pipe for contacting and mixing high-temperature water and low-temperature water in pipes for thermal power and nuclear power plants, a bypass pipe communicating from a main pipe after joining to a branch pipe is provided, and a fluid at an intermediate temperature after mixing is introduced into the branch pipe. A mixed flow piping structure characterized by reducing the temperature difference at the merging / mixing part of both fluids by suppressing the wall temperature fluctuations of the pipe merging part and suppressing the thermal fatigue of the material. 2. The mixed flow piping structure according to claim 1, wherein the branch pipe near the downstream outlet of the bypass pipe has a throttle portion.