JPH07159077A - Flow vibration relaxation heat exchanger - Google Patents

Abstract

(57) [Summary] [Structure] A plurality of inlets 2 for the primary side fluid are provided so as to face each other. Lead to. In order to enable highly efficient operation of the heat exchanger, it is necessary for the primary side fluid to pass through the entire outer region of the heat transfer tube 7 at a uniform flow rate. As a means for achieving a uniform flow velocity distribution, it has been dealt with by changing the diameter of the inflow hole 13 of the merging pipe 12 provided at the center of the heat exchanger. [Effect] It is possible to provide a highly efficient shell-tube heat exchanger by not only relaxing the flow vibration but also reducing the stress applied to the heat transfer tube and controlling the flow rate distribution of the primary side fluid in the heat exchanger.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shell-tube heat exchanger, and more particularly to a heat exchanger that alleviates flow vibration generated in a tube.

[0002]

2. Description of the Related Art FIG. 4 shows a general shell-tube heat exchanger. The structure is such that a shell 1 serving as an outer wall, a primary side fluid inlet nozzle 2 and an outlet nozzle 3 attached to the shell 1
Secondary side fluid inlet nozzle 4 and outlet nozzle 5, its shell 1
The flow distribution baffle plate 6 for the primary side fluid, the heat transfer tube 7 (tube) through which the secondary side fluid flows, and the heat transfer tube, which are necessary for achieving high efficiency, are fixed inside, and the primary and secondary fluids are It is composed of a tube plate 8 for separating, a baffle plate 9 for supporting the heat transfer tube 7, and a separating plate 11 for separating the secondary side fluid flowing in the header 10. Here, the primary-side fluid whose flow direction is indicated by the dotted line flows in from the inlet nozzle 2, and the heat of the fluid is transmitted to the secondary-side fluid which is indicated by the thin solid-line flow direction via the heat transfer pipe 7 and flows out from the outlet nozzle 3. To do. In addition, F shown by a thick solid line arrow in this figure represents a fluid force exerted on the heat transfer tube 7 by the primary side fluid.

FIG. 5 schematically shows the stress applied to the heat transfer tube 7 in this configuration. As can be seen from this figure, since the U-shaped heat transfer tube 7 is a cantilever beam with an evenly distributed load, a double flow force 2F acts on the tip of the bent portion, causing a large deflection. Here, the deflection constant β of the cantilever is 0.125. This deflection has a great influence on the hydroelastic vibration, and if the deflection is large, the vibration deformation of the pipe also becomes large.

[0004]

In the above-mentioned prior art, there are problems in flow vibration caused by flow force, bending of the heat transfer tube, and distribution of the flow rate of the primary side fluid for higher efficiency.

Flow vibrations are roughly classified into vibrations by Karman vortices, hydroelastic vibrations, and buffeting.

These vibration factors will be described below.

When the flow velocity is increased to some extent, a separating vortex is emitted from the surface of the pipe placed in the flow. A Karman vortex is a phenomenon in which separating vortices are generated periodically. When the generated frequency and the natural frequency of the tube match, the tube is in a resonance state. This is called "Karman vortex vibration".

When the flow velocity increases, the drag and lift acting on the pipe also increase, and the vibration deformation of the pipe also increases. As a result of this deformation, the gap between the pipe groups changes, so does the flow velocity passing through the gap and the drag force / lift force acting on the pipes. The flow vibration generated by the repeated interaction between the fluid and the structure is called hydroelastic vibration.

Turbulence that fluctuates irregularly in time or space occurs in the flow between the tube groups. Then, in the tube group, as the flow goes downstream, the turbulence such as the separation vortex generated in the upstream tube amplifies the turbulence in the downstream, and the irregular component of the flow is accumulated and the tube group is excited. This is called buffeting.

It is an object of the present invention to alleviate these flow oscillations, reduce the stress applied to the heat transfer tubes, and control the flow rate distribution of the primary side fluid in the heat exchanger to achieve high reliability. It is to provide an efficient shell-tube heat exchanger.

[0011]

[Means for Solving the Problems] Influencing the flow vibration includes the flow velocity of the fluid on the fluid side and the bending of the pipe on the structure side causing the vibration. Therefore, in order to mitigate the flow vibration, the flow velocity should be slowed to reduce the drag force on the pipe.
It is necessary to reduce the lift and the deflection of the pipe. Therefore, in the present invention, a plurality of inlets for the primary side fluid are provided so as to face each other, the flow of the fluid is made to flow toward the central portion, and the fluid is merged at the central portion and guided to the outlet.

To enable highly efficient operation of the heat exchanger,
It is necessary for the primary side fluid to pass through the entire area outside the heat transfer tube at a uniform flow velocity. In the present invention, as a means for achieving a uniform flow velocity distribution, the diameter of the inflow hole of the merging pipe provided at the center of the heat exchanger is changed.

[0013]

In the heat exchanger, the inlets for the primary side fluid are provided so as to face each other, and the flow of the fluid is made to flow toward the center, and the fluid is merged at the center and led to the outlet. Since the flow velocity of the primary side fluid can be slowed and the deflection due to the hydrodynamic force of the heat transfer tube can be reduced,
Vibration, hydroelastic vibration, and buffeting due to stress and Karman vortex on the heat transfer tube can be alleviated.

By changing the diameter of the inflow hole of the merging pipe provided at the center of the heat exchanger and adjusting the pressure loss, the flow velocity of the primary fluid flowing in the heat exchanger is made uniform to enable highly efficient operation. .

[0015]

FIG. 1 shows an embodiment of the shell tube heat exchanger according to the present invention. This embodiment shows the case where there are two inlets for the primary fluid. Here, the flow direction of the primary fluid is indicated by a dotted line, and the flow direction of the secondary fluid is indicated by a solid arrow. The primary-side fluid flows in from the opposing inlet nozzles 2 provided in the outer wall 1 (shell) of the heat exchanger, is redistributed by the flow distribution baffle plate 6, passes through the gap of the heat transfer tubes 7 group, and goes to the center of the heat exchanger. Flowing. At the center of the heat exchanger, there is a merging pipe 12 that is installed so as to penetrate through the tube plate 8, and the primary side fluid merges here and is guided to the outlet nozzle 3. At this time, the flow rate distribution in the heat exchanger is adjusted by changing the size of the inflow hole 13 into the confluence pipe 12. On the other hand, the secondary fluid flows from the inlet nozzle 4 into the header 10 partitioned by the separating plate 11, passes through the heat transfer tube 7 installed on the tube plate 8 and is guided to the outlet nozzle 5 via the header 10. . With such a structure, the flow rate distribution of the primary side fluid passing through the tube group in the heat exchanger can be made uniform, and the flow velocity can be further reduced. In this embodiment, since there are two primary-side fluid inlet nozzles, the fluid flow velocity through the tube group is half that in the case of one inlet nozzle.

With such a structure, how the fluid force of the primary side fluid acts on the heat transfer tube 7 will be described with reference to FIGS.

Since the primary side fluid is divided into two and flows in from the inlet nozzle 2, the flow velocity of the heat exchanger is half that in the case of one inlet nozzle. Therefore, the flow force F'acting on the heat transfer tube is reduced to about 1/4 of the case where there is one inlet nozzle. Next, the stress applied to the heat transfer tube 7 is U as shown in FIG.
Since the same fluid force acts from both sides of the U-shaped heat transfer tube 7, the central axis 13 of the U-shaped heat transfer tube 7 does not change. That is, the U-shaped heat transfer tube 7 as a whole does not bend. However, in the straight pipe portion of the heat transfer tube 7, stress is applied as an evenly distributed load at both end fulcrums. In this case, the deflection of the heat transfer tube 7 is a deflection constant β when compared with the cantilever beam shown in the conventional example. Is 0.01
3 is about 1/10, and the hydrodynamic force (corresponding to uniformly distributed load) is 1/4, which is about 1/40.

By making the structure of the shell-tube heat exchanger the above-mentioned embodiment, vibration due to Karman vortex which is greatly influenced by flow velocity, hydrodynamic vibration greatly influenced by flow velocity and deflection of the heat transfer tube, fluid tube group Buffeting, which is greatly affected by the time it takes to pass through, is greatly reduced. Furthermore, the stress applied to the heat transfer tubes can be reduced and the flow rate distribution of the primary side fluid in the heat exchanger can be made uniform, resulting in high efficiency operation.

[0019]

According to the present invention, not only the flow vibration is alleviated but also the stress applied to the heat transfer tube can be reduced, and the flow rate distribution control of the primary side fluid in the heat exchanger can be performed. An exchange can be provided.

[Brief description of drawings]

1 is a cross-sectional view of a shell tube heat exchanger according to the present invention.

FIG. 2 is an explanatory view showing a fluid force applied to a heat transfer tube of the shell tube heat exchanger according to the present invention.

FIG. 3 is an explanatory diagram showing stress applied to a heat transfer tube of the shell tube heat exchanger according to the present invention.

FIG. 4 is a sectional view of a shell tube heat exchanger according to the prior art.

FIG. 5 is a cross-sectional view showing stress applied to a heat transfer tube of a shell tube heat exchanger according to a conventional technique.

[Explanation of symbols]

2 ... Primary side fluid inlet nozzle, 3 ... Primary side fluid outlet nozzle, 7 ... Heat transfer tube, 12 ... Confluent tube, 13 ... Inflow hole.

Claims (2)

[Claims] 1. In a shell-tube heat exchanger, a plurality of inlet holes for primary-side fluid flowing outside the heat transfer tube are provided at opposite positions, the primary-side fluid is caused to flow toward the center of the heat exchanger, and the confluence is installed at the center. A flow vibration alleviation heat exchanger characterized by collecting the primary side fluid in a pipe and guiding the primary side fluid to an outlet. 2. In a shell-tube heat exchanger, the flow rate distribution of the primary side fluid flowing in the heat exchanger can be adjusted by changing the size of the inlet hole to the confluence pipe provided at the center of the heat exchanger. Characteristic flow vibration relaxation heat exchanger.