JP2564161B2 - Heat exchanger - Google Patents

Description

TECHNICAL FIELD The present invention relates to improvement of a heat exchanger such as a steam generator used in a nuclear power plant, for example.

[Prior Art and Its Problems] The upper and lower tube plates are supported at the upper and lower ends of a large number of heat transfer tubes which are overheated from outside the tube and through which the fluid to be heated flows, and are provided in the upper and lower water chambers, respectively. In a heat exchanger formed in communication with each other, when the fluid to be heated boils, a so-called unstable flow phenomenon in which the flow rate in each heat transfer tube fluctuates may occur.

When such an unstable flow phenomenon occurs, the temperature of the heat transfer tube fluctuates periodically, causing thermal fatigue of the heat transfer tube.

On the other hand, it is known that the unstable flow phenomenon does not occur if the pressure loss in the preheating region in the heat transfer tube is a certain ratio or more than the pressure loss in the nucleate boiling region, the film boiling region and the superheating region.

Therefore, it is generally practiced to provide an orifice at the inlet of the heat transfer tube to increase the pressure loss in the preheating region and prevent the occurrence of the unstable flow phenomenon.

However, the increase in pressure loss of the orifice provided at the inlet of the heat transfer tube does not contribute to the improvement of the heat transfer performance.

The present applicant has previously developed a steam generator as a heat exchanger capable of increasing the heat transfer efficiency on the heat transfer surface by increasing the in-tube mass velocity of water and steam in the heat transfer tube (Japanese Patent Application Laid-Open No. 2004-242242). (Sho 60-96803).

This steam generator has a large number of heat transfer tubes 1 as shown in FIG.
The thermal stress generated by the difference in thermal expansion between the body 2 and the body 2
In this type, the high temperature primary fluid, for example, liquid sodium, is absorbed and relaxed by elastic deformation of the curved tube portion 3 provided in the lower part of the curved pipe portion 3 enters the barrel 2 from the inlet nozzle 4 as indicated by an arrow A. Further, it enters into the inner case 5 through a distribution window 6 provided at the upper end of the inner case 5 and descends there. Then, it exits from the distribution window 7 provided at the lower end of the inner case 5 and flows out from the outlet nozzle 8 as shown by an arrow B. On the other hand, a low temperature secondary fluid,
For example, water enters the lower water chamber 9 as indicated by arrow C. Then, it rises through a large number of heat transfer tubes 1 connected to the lower tube sheet 10. During that time, heat is exchanged to vaporize the water, and the vapor thereof flows out from the upper water chamber 12 partitioned by the upper tube sheet 11 as shown by an arrow D. As shown in FIG. 6, a speed increasing core (heat transfer promoting body) 20 is arranged inside the many heat transfer tubes 1 connected to the upper tube sheet 11, and the speed increasing core 20 is made of a cylindrical body. , Its lower end 21, that is, the inflow side of the cold secondary fluid,
The shape is hemispherical or streamlined, and the upper end is the upper tube sheet.
It is a supporting device for 11. The supporting device 22 is detachably fixed to a pedestal 24 mounted on the upper tube sheet 11 with a plurality of bolts 25 by a plurality of radially extending arms 23. The speed-increasing core 20 is provided with supporting pieces 27 radially and symmetrically with a certain interval in the vertical direction on the outer peripheral surface thereof, with a slight play between the supporting pieces 27 and the inner surface of the heat transfer tube 1. Reference numeral 16 is a heat shield plate for the upper tube sheet 11 and the lower tube sheet 10, and 26 is a hook for lifting the speed increasing core 20.

Since the annular flow passage 30 for the secondary fluid is formed between the speed-up core 20 and the speed-up core 20 in the large number of heat-transfer tubes 1 in which the speed-up core 20 is arranged as described above, the heat-transfer tube 1 has a constant pressure. The secondary-side fluid that rises inside flows through the annular flow path 30 when it reaches the position of the speed-increasing core 20. Therefore, it is said that the flow passage area becomes narrower than that in the case where the speed-increasing core 20 is not provided, and the mass velocity of the secondary side fluid in the pipe is increased, so that the heat transfer efficiency on the heat transfer surface is improved.

[Problems to be Solved by the Invention] However, in the above steam generator, since the flow passage area from the preheating region to the overheating region in the electric heating pipe is equally narrow, the heat transfer performance is improved but the pressure loss is increased, and this pressure loss The increase does not contribute to the prevention of instability.

[Object of the Invention] The present invention has been made to solve the above-described problems, and can improve the heat transfer efficiency of the heat transfer tube, as well as preventing the unstable flow of the heated fluid in the heat transfer tube. It is an object of the present invention to provide a heat exchanger capable of performing.

[Means for Solving the Problems] A heat exchanger of the present invention for solving the above problems is configured such that the upper and lower ends of a plurality of heat transfer tubes that are heated from the outside of the tube and the fluid to be heated flows inside the tubes are upper tube plates. In a heat exchanger which is supported by a lower tube sheet and communicates with upper and lower water chambers, respectively,
In the preheating zone in each heat transfer tube, the flow passage area is reduced to accelerate the flow velocity to increase the pressure loss, or a heat transfer promoter having a shape with a large pressure loss coefficient is inserted, and connected to this, and each heat transfer tube From the nucleate boiling zone to the superheat zone, the flow passage area is slightly increased compared to the preheat zone to slow down the flow velocity to reduce the increase in pressure loss, or a heat transfer accelerator with a small pressure loss coefficient is inserted. It is what

[Operation] As described above, in the heat exchanger of the present invention, since the heat transfer promoting body that increases the pressure loss is inserted in the preheating area in the heat transfer tube, heat transfer in the preheating area is promoted and The occurrence of unstable flow of superheated fluid is prevented. In addition, since a heat transfer accelerator with a relatively small pressure loss is inserted from the nucleate boiling area to the superheat area in the heat transfer tube, the unstable phenomenon of the steam two-phase flow does not occur, and The heat transfer efficiency is significantly improved.

[Embodiment] An embodiment of a heat exchanger according to the present invention will be described with reference to the drawings in the case of a steam generator. FIG. 1 is a sectional view of an essential part showing a state in which the heat transfer accelerator according to the present invention is inserted and supported in the heat transfer tube in the steam generator shown in FIG. 5, and each heat transfer tube 1 has an upper end at an upper portion. The upper tube sheet is connected to the heat transfer tube communication hole 31 of the tube sheet 11.
It is connected to the lower tube sheet 10 by welding, and the lower end is connected to the heat transfer tube communicating hole 32 of the lower tube sheet 10 and is connected to the lower tube sheet 10 by welding. Inside each heat transfer tube 1, a heat transfer promoting member 33 is inserted and supported through a heat transfer tube communicating hole 31 of the upper tube sheet 11 as shown in the drawing. The heat transfer accelerating body 33 is a solid round bar 34 in the lower preheating region in the heat transfer tube 1, has a sharp lower end, and has spacers 35 symmetrically arranged at a constant interval in the vertical direction of the outer peripheral surface. Are provided so as to have a plane radial shape, with some play between the heat transfer tube 1 and the inner surface thereof. The spacer 35 is formed integrally by crushing the outer circumference of the solid round bar 34 by squeezing it and projecting it at right angles. It is connected to the upper end of the solid round bar 34 by welding, and in the upper nucleate boiling area, film boiling area, and overheating area in the heat transfer tube 1, the heat transfer promoter 33 is the torsion tape 36, and its width is transferred. It has such a size that a small clearance can be maintained between it and the inner surface of the heat tube 1, and a rod 37 is connected to the center of the upper end thereof by welding so as to pass through the heat transfer tube communication hole 31 of the upper tube sheet 11, Rod 37
The outer periphery of the upper part of the is flatly crushed to form a disk portion 38, and the disk portion 38 is locked to the opening edge of the heat transfer tube communication hole 31 to suspend and support the entire heat transfer promotion body 33.

In the steam generator of the embodiment configured as described above,
The hot primary fluid, for example, liquid sodium, enters the inner nozzle 5 through the inlet nozzle 4 as shown by an arrow A in FIG. 5, and further from the distribution window 6 provided at the upper end of the inner cylinder 5 to the inner cylinder 5. Enter and go down there. Then, it exits from the distribution window 7 provided at the lower end of the inner case 5 and flows out as shown by an arrow B. A low temperature secondary fluid such as water enters the lower water chamber 9 as indicated by arrow C. Subsequently, the heat transfer tubes 1 connected to the lower tube sheet 10 enter.

Water entering the heat transfer tube 1 flows through an annular passage 39 having a narrow flow passage area formed between the water and the outer peripheral surface of the solid round bar 34 arranged in the preheating region as shown in FIG. The mass velocity in the tube is increased, the pressure loss is increased, the heat transfer on the heat transfer surface is accelerated, the heat is exchanged with the liquid sodium, and the temperature is raised, and then passes through the annular passage 39 in the preheating region, and the heat transfer tube In the spiral flow path 40 formed between the nucleate boiling area and the outer surface of the twisting tape 36 arranged in 1 above, the mass velocity of water and water vapor in the tube is somewhat slowed, and the pressure loss is increased. Less. Then, since water and water vapor flow in the spiral flow path 40 as a swirl flow, the mist collides with the inner wall of the heat transfer tube 1. Therefore, the nucleate boiling region having an extremely high heat transfer coefficient becomes long, and the film boiling region having a low heat transfer coefficient becomes short. Further, since the pressure loss from the nucleate boiling region to the superheat region is small and the pressure loss in the preheating region is large, unstable flow in the heat transfer tube 1 is prevented.

The steam that has passed through the nucleate boiling region and the film boiling region becomes superheated steam in the superheated region, enters the upper water chamber 12 through the heat transfer pipe communicating hole 31 of the upper tube sheet 11, and enters the upper water chamber 12. Flows out as indicated by arrow D in FIG.

In the above-mentioned embodiment, the heat transfer accelerator consisting of the solid round bar 34 is arranged in the preheating zone in the heat transfer tube 1, and the heat transfer accelerator consisting of the twisting tape 36 is arranged from the nucleate boiling zone to the superheat zone. But
It is not limited to this. When the solid round bar 34 is arranged in the preheating region, the ribbon 41 having the twisting direction changed left and right alternately as shown in FIG. Mixer 43 connected by 42
It is advisable to insert a heat transfer enhancer consisting of the above to generate a swirling flow and at the same time generate a large turbulent flow to lengthen the nucleate boiling region having an extremely high heat transfer coefficient. Further, instead of the twisting tape 36, a swirl flow is generated by a heat transfer enhancer composed of a spring 44 closely inserted into the inner wall surface of the heat transfer tube 1 from the nucleate boiling area to the overheat area as shown in FIG. It is advisable to lengthen the nucleate boiling region, which has a very high rate. Further, in place of the twisting tape 36, as shown in FIG. 2c, a heat transfer enhancement consisting of a spiral rod 46 in which a wire 45 is wound around the outer circumference of a small diameter solid round bar 34 'from the nucleate boiling area to the overheat area in the heat transfer tube 1. It is advisable to insert a body to form an annular flow path in which a swirling flow is generated, and to lengthen the nucleate boiling region where the heat transfer coefficient is extremely high.

However, in the preheating region in the heat transfer tube 1, a heat transfer promoter composed of a solid round bar 34 is arranged, but as shown in FIGS. 3A to 3E, the twisting is arranged from the nucleate boiling region to the superheat region. Tape 36, mixing rod 43, spring 44, spiral rod 46,
Corresponding to the solid round bar 34, insert a heat transfer promoter consisting of a solid round bar 48 with a spacer wound with a wire 47 as a spacer around the outer circumference of the solid round bar 34 to generate a swirling flow, It is better to make it larger than the pressure loss from the nucleate boiling region to the superheat region. Further, instead of the solid round bar 48 with a spacer in this preheating region, as shown in FIGS. 4A to 4E, a rod 51 with a disc is fixed on the outer periphery of a rod 49 having a small diameter at fixed intervals in the longitudinal direction. It is advisable to insert a heat transfer accelerating body that is formed into the disk 50 to generate a large turbulent flow in the disk 50 and to make the pressure loss larger than the pressure loss from the nucleate boiling region to the superheating region. Further, even if the shape is the same from the preheating zone to the superheating zone, the pressure loss coefficient in the preheating zone can be increased. For example, in the case of a solid round bar or a rod with a disc, the diameter is increased only in the preheating zone. For twisted tape and springs, reduce the pitch only in the preheat area.

In short, in the present invention, the heat transfer promoter arranged in the heat transfer tube can reduce the flow passage area in the preheating region and accelerate the flow velocity to increase the pressure loss, or the heat transfer promoter having a shape with a large pressure loss coefficient, nucleate boiling. From the heating zone to the superheating zone, the flow passage area can be increased somewhat compared to the preheating zone, and the flow velocity can be delayed to reduce the pressure loss, or any shape can be used as long as it has a shape with a small pressure loss coefficient. Is.

Each of the solid round bars described above may be a closed circular tube.

[Effects of the Invention] As can be seen from the above description, in the heat exchanger of the present invention, heat transfer promoters that increase the pressure loss are inserted into the preheating zones in a large number of heat transfer tubes, and the heat transfer accelerators are connected to the heat transfer promoters to connect them to each heat transfer tube. Since a heat transfer enhancer is inserted from the nucleate boiling zone to the superheat zone in the tube to reduce the increase in pressure loss compared to the preheat zone, heat transfer in the preheat zone is promoted and an unstable flow of the heated fluid occurs. Is prevented, the unstable phenomenon of the water vapor bilayer flow does not occur between the nucleate boiling region and the film boiling region, and the nucleate boiling region having a high heat transfer coefficient becomes long. Therefore, the heat transfer efficiency of the heat transfer tube is remarkably improved, and the required heat transfer area, that is, the number of heat transfer tubes can be reduced to reduce the size of the heat exchanger for the same heat exchange amount demand.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view showing a heat transfer tube in a steam generator which is an embodiment of a heat exchanger according to the present invention, and FIGS. 2 a, b, and c are nucleate boiling regions in the heat transfer tube shown in FIG. To FIG. 3A to FIG. 3E are diagrams showing a modification example of the heat transfer promoting member from the heat transfer area to the superheat region, FIG. 3A to FIG. The figure which changed the heat transfer promotion body of the preheating area in the heat transfer tube of e, 5th
FIG. 6 is a schematic sectional view showing a steam generator, and FIG. 6 is a longitudinal sectional view showing a heat transfer tube in a conventional steam generator. 1 ... Heat transfer tube, 9 ... Lower water chamber, 10 ... Lower tube plate, 11 ...
… Upper tube sheet, 12 …… Upper water chamber, 33 …… Heat transfer accelerator, 34…
… Solid round bar, 36 …… Torsion tape, 43 …… Mixer, 44
...... Spring, 46 …… Spiral rod, 48 …… Solid round bar with spacer, 51 …… Disc rod.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Masanori Takemoto 2-4-25 Minamisuna, Koto-ku, Tokyo Kawasaki Heavy Industries, Ltd. Tokyo Design Office (56) References: 63-109806 (JP, U)

Claims (1)

(57) [Claims] 1. A plurality of heat transfer tubes which are heated from the outside of the tube and through which a fluid to be heated flows inside the tubes are supported by upper and lower tube plates and communicate with upper and lower water chambers, respectively. In the heat exchanger consisting of, in the preheating zone in each of the heat transfer tubes, the flow passage area is decreased to accelerate the flow velocity to increase the pressure loss, or a heat transfer accelerator having a shape with a large pressure loss coefficient is inserted, From the nucleate boiling zone to the superheat zone in each heat transfer tube, the flow passage area is slightly increased compared to the preheat zone to slow down the flow velocity to reduce the increase in pressure loss, or heat transfer with a shape with a small pressure loss coefficient. A heat exchanger having a promoter inserted therein.