JPS61130795A - Heat exchanger - Google Patents

Abstract

PURPOSE:To make flow rate elastic oscillation hard to occur among pipes in a heat exchanger, by constituting at least one pipe among pipes comprising a group of pipes different from other pipes in one of such conditions as the quality, the thickness and the shape of a material, but a heat transfer surface is equal to the other pipes. CONSTITUTION:f1, f2, zeta1, and zeta2 respectively represent the specific frequency and the ratio of damping coefficient of each pipe 1 and 2. D represents the external diameter of a pipe, (m) represents the mass of the unit length of a pipe, and rho represents the density of a fluid, while Ucr represents the ultimate frequency causing elastic oscillation by flow energy. There is a relation shown by formula I with Kcr as a coefficient among the aforementioned functions. Accordingly, the flow rate elastic oscillation is hard to occur if the ultimate currency Ucr causing elastic oscillation by flowing energy is made large, that is, the shape of a section of one pipe where a fluid passes at the highest velocity is changed from the other pipes in a heat exchanger. If pipes neighboring to each other, of which heat transfer surface inside the pipe is equal to each other, has at least one different condition among the shape of a section, the thickness and the material of a pipe from the other, the elastic oscillation caused by flowing energy is made hard to occur among pipes as a whole group of pipes in a heat exchanger.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] This invention relates to an improvement in a heat exchanger having a group of finned tubes.

[Technical background of the invention and its problems]

In a heat exchanger having a tube group, when the velocity of the fluid flowing outside the tubes constituting the tube group exceeds a certain limit, a type of self-excited vibration called hydroelastic vibration suddenly occurs. This phenomenon will be explained based on the drawings, taking as an example the case where the tubes are arranged as shown in FIG.

Tube 1. Paying attention to No. 2, tube 1. The natural frequency and damping coefficient ratio of the tube 2 are fl+f2+ζ1. Let ζ2 (assume isotropy). In addition, the outer diameter of the tube is calculated, the mass of the unit length of the tube considering the apparent mass of the fluid is m, the density of the fluid is ρ, the critical flow velocity (vl) at which hydroelastic vibration occurs, and the minimum gap of the tube 2 is It is generally known that the following relationship can be established between Ucr and Kcr (determined experimentally depending on the arrangement of the tubes, the pitch of the tubes, etc.), which is determined experimentally by the tube arrangement, tube pitch, etc.

・・・・・・・・・(1) Conventionally, all tube groups in a heat exchanger are composed of main tubes (f1 = f2, ζl = ζ2 = ζ).
c 1 Ro.

It is also known that the constant Kcr becomes smaller as the tube pitch T (FIG. 3) becomes smaller. (When Kcr becomes smaller, the critical flow velocity Ucr becomes smaller.

In other words, hydroelastic vibration becomes more likely to occur.) Hydroelastic imaging involves imaging of a very wide excavation width, and is a serious phenomenon that can directly cause front rupture, so it must be avoided at all costs. Must be. Conventionally, the tube pitch T of the tube group of a heat exchanger is (
2; Due to the equation and the relationship between Kcr and T, it is impossible to reduce the size of the tube group, that is, the heat exchanger itself. In addition, even if the tube group does not cause hydroelastic vibration in terms of design, for example, in the case of equipment that requires higher safety than ordinary heat exchangers, such as a heat exchanger for an atomic couplant, Critical flow velocity Ucr
It is necessary to devise ways to make it larger than the purple color.

[Purpose of the invention]

This invention improves the problems of the conventional device described above, and increases the critical flow velocity Ucr for generating hydroelastic vibration in the tube group, and allows hydroelastic imaging even when the pitch T is smaller than that of the conventional tube group. The purpose is to provide a safer heat exchanger that can reduce the occurrence of

[Summary of the invention]

The present invention provides a heat exchanger in which at least one of the tubes constituting the tube group has the same heat transfer area as the other tubes, but differs in at least one of the material, material thickness, and shape.

〔Effect of the invention〕

According to this invention, it is possible to make the critical flow velocity Ucr for generating hydroelastic vibration in the tube group less than Oshima, that is, to make it difficult for hydroelastic vibration to occur. For example, suppose that only the tube 1 in FIG. 3 has a different cross-sectional shape from the other tubes. At this time, if we focus on pipes 1 and 2, the relationship of equation (1) holds; here, pipe 1. Change m and D for both tubes ζ1=ζ
2 = 0.02 If ft/fz = 1.1, the critical flow velocity Ucr in this case is 1.61 compared to the case where the clear space shape of pipe ① is the same as the other pipes (fr/fz = 1). It can be seen that the amount is doubled. Therefore, in the tube group of the heat exchanger,
By changing the cross-sectional shape of the portion through which the fluid passes at the highest speed as described above, it is possible to make hydroelastic imaging less likely to occur in this portion (the portion where hydrodynamic vibration is most likely to occur).

This effect can be observed, for example, between adjacent tubes in a plane perpendicular to the flow direction of the extratubular fluid, and the cross-sectional shapes of the adjacent tubes in the plane at least rise above each other.
If one of the material thickness and material is selected, hydroelastic vibration can be made less likely to occur in the tube group as a whole.

Furthermore, because of this effect, the tube pitch T can also be reduced, and the size of the heat exchanger body can also be expected to be reduced.

[Embodiments of the invention]

Embodiments of the invention will be described with reference to the drawings. Generally, a tube used in a heat exchanger is provided with fins 6 to increase the heat transfer area, and has a shape as shown in FIG. 2, for example. On the other hand, FIG. 1 shows an embodiment of the present invention, in which the fins 5 are spirally shaped so that the heat transfer area remains unchanged. The natural frequency of this spiral finned tube is clearly different from the finned tube shown in Figure 2 if the pitch of the fins is the same. Either arrange the tubes in a position where imaging is likely to occur (so that two tubes are not next to each other), or arrange the tubes in a plane perpendicular to the flow direction of the extratubular fluid to the finned tube shown in Figure 2 and the one shown in Figure 1. If the spiral finned tubes shown are arranged in an alternating manner, the above-mentioned effect can be obtained. Note that the structure is not limited to the above-described structure, and the material thickness and material of the fins, whether or not radial slits are provided in the fins, or the shape of the slits may be changed, and the material and material thickness of the tube may also be changed.

[Brief explanation of drawings]

Fig. 1 is a perspective view of a spiral finned tube showing an embodiment of the present invention, Fig. 2 is a perspective view showing an example of a conventional finned tube, and Fig. 3 is an arrangement of a group of tubes in a heat exchanger. FIG. ■...Pipe 2--Pipe 3...External fluid 4...Pipe 5...Spiral fin 6...Fin agent Patent attorney Noriyuki Chika (and 1 other person) Figure 1 2 illustrations included

Claims (2)

[Claims] (1) In a heat exchanger having a tube group, at least one of the tubes constituting the tube group has the same heat transfer area and differs from other tubes in at least one of the material, material thickness, and shape. A heat exchanger characterized by: (2) The heat exchanger according to claim 1, wherein adjacent finned tubes in a plane orthogonal to the flow direction of the fluid outside the tubes have the same heat transfer area and different fin shapes. .