JPH01200103A - Heat exchanger - Google Patents

Abstract

PURPOSE:To improve heat transfer efficiency and to enable reduction of the size of a heat exchanger, by a method wherein a heat transfer promoter formed by twisting together at least two round rods is inserted in each heat transfer pipe and supported therein. CONSTITUTION:Water entering a heat transfer pipe 1 flows an annular flow passage 37, having a narrow flow passage in cross section, formed between the heat transfer pipe and the outer surface of a heat transfer promoter 33 formed by twisting together two round rods 34 to increase a mass velocity in the pipe. Since the outer peripheral surface of the heat transfer promoter 33 forms an uneven surface due to intertwisting of the round rods 34, the generation of turbulence is promoted. Further, since the heat transfer promoter is formed in a helical manner in a longitudinal direction, the flow of water and gasified steam in the pipe 1 forms a swirl accompanied by turbulence, and is collided with a pipe wall for gasification. This constitution lengthens a nuclear boiling area having a high heat transfer rate and shortens a film boiling area having a low heat transfer rate, and enables sharp improvement of the heat transfer efficiency of the heat transfer surface of the whole of the heat transfer pipe 1.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates primarily to improvements in heat exchangers such as steam generators used in atomic couplants.

[Prior Art] A large number of heat transfer tubes, which are heated from the outside and have a fluid to be heated inside the tubes, are supported at both upper and lower ends by an upper tube plate and a lower tube plate, and communicated with water chambers above and below, respectively. The heat exchanger consists of
It is important to improve heat transfer performance and downsize equipment.

For this reason, recently, as shown in Fig. 3, a heat transfer accelerator made of a round rod 2 is inserted into a heat transfer tube 1 to narrow the flow path area, increase the flow velocity in the tube, and improve heat transfer performance. A heat exchanger was developed (Japanese Patent Application Laid-Open No. 60-96803).

[Problems to be Solved by the Invention] By the way, in the heat transfer tube 1 of the heat exchanger described above, in heat transfer accompanied by a phase change, the nucleate boiling region has a very high heat transfer coefficient, but the length of the nucleate boiling region The flow rate tends to decrease with increasing flow velocity in the pipe.

[Object of the Invention] The present invention was made to solve the above problems, and provides a heat transfer tube that can improve the heat transfer coefficient by increasing the flow velocity in the tube and expand the nucleate boiling region, thereby further improving the heat transfer efficiency. The purpose of the present invention is to provide a heat exchanger equipped with the following.

[Means for Solving the Problems] The heat exchanger of the present invention for solving the above problems has tube sheets provided in the upper and lower parts of the shell, respectively above the upper tube sheet and below the lower tube sheet. In a heat exchanger that forms a water chamber, and in which the upper and lower ends of a large number of heat transfer tubes are supported on an upper tube sheet and a lower tube sheet and communicated with the water chamber, two heat transfer tubes are provided in each of the heat transfer tubes. It is characterized in that a heat transfer accelerator formed by twisting the above round rods is inserted and supported.

[Function] As described above, the heat exchanger of the present invention inserts and supports a heat transfer accelerator made of two or more round rods twisted together in each heat exchanger tube, so that the flow inside each heat exchanger tube is improved. The path area is reduced, which increases the mass velocity of water and steam within the pipe. Moreover, since the surface of the heat transfer promoter is uneven due to the twisting of the round rods, turbulent flow is promoted. Furthermore, since the surface irregularities of the heat transfer promoter are spiral, the flow of water and steam within the tube becomes a swirling flow, causing droplets to adhere to the tube wall. Furthermore, droplets in the steam are captured by the unevenness, and the captured droplets are blown away by the steam flow and re-attached to the tube wall. The forced attachment of these droplets to the tube wall greatly expands the nucleate boiling region.

The heat transfer performance is significantly improved due to the above synergistic effect.

[Example] An example of the 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 schematic vertical cross-sectional view of a steam generator. This steam generator uses a curved tube section provided at the bottom of the heat exchanger tubes 1 to absorb thermal stress caused by the difference in thermal expansion between a large number of heat exchanger tubes 1 and a shell 2. A high-temperature primary fluid, for example, liquid sodium, enters the shell 2 from an inlet nozzle 4 as shown by arrow A. In addition, 111i
It enters the inner shell 5 through the distribution window 6 provided at the upper end of i5 and descends there. Then, it exits from the distribution window 7 provided at the lower end of inner 1ii5 and flows out from the outlet nozzle 8 as shown by arrow B. On the other hand, the low temperature secondary fluid, such as water, flows as shown by arrow C. Enter the lower water chamber 9. Subsequently, it ascends through a large number of heat exchanger tubes 1 connected to the lower tube plate 1G. During this time, water is vaporized by heat exchange, and the steam enters an upper water chamber 12 partitioned by an upper tube plate 11, and flows out from this upper water chamber 12 as shown by the arrow.

Now, in such a steam generator, the upper end of each heat exchanger tube 1 is connected to the heat exchanger tube insertion hole 31 of the upper tube sheet 11 as shown in FIG. 2a and is joined to the upper tube sheet 11 by welding, and the lower end is The lower tube sheet 10 is connected to the heat exchanger tube communication hole 32 of the lower tube sheet lO.
It is joined by welding. A heat transfer accelerator 3 is inserted into each heat transfer tube 1 from the heat transfer tube communication hole 31 of the upper tube sheet 11 as shown in the figure.
3 is inserted and supported.

This heat transfer accelerator 33 is made by twisting two round rods 34, and spacers 35 are arranged symmetrically on the inner surface of the heat exchanger tube 1 so that the spacers 35 are arranged radially on the outer circumferential surface at regular intervals in the vertical direction. It is provided with some play between the two. A ring 36 is provided at the upper end of the heat transfer promoter 33 by bending the upper ends of two wooden round bars 34 into semicircular shapes, and this ring 36 is locked to the opening edge of the heat exchanger tube communication hole 31. , heat transfer promoter 3
3 The entire body is suspended and supported. In addition, this heat transfer accelerator 33
It is also possible to spread out a part of the spacer and use it as a spacer as shown in FIG. 2C.

In the steam generator of the embodiment configured as described above, the water that has entered the large number of heat transfer tubes 1 is transferred to the heat transfer promoter 33 made of two round rods 34 twisted together as shown in FIG. The water flows through an annular flow path 37 with a narrow cross-sectional area formed between the water and the outer surface, and the mass velocity within the pipe is increased. Further, since the outer circumferential surface of the heat transfer promoter 33 is uneven due to the twisting of the round rods 34, turbulent flow is promoted. Furthermore, since the irregularities on the outer circumferential surface of the heat transfer promoter 33 are spiral in the vertical direction (longitudinal direction), the flow of water and vaporized steam in the heat transfer tube 1 becomes a swirling flow with turbulence. The water vapor mist trapped in the concave portion of the outer circumferential surface of the heat transfer promoter 33 is carried by the swirling flow, collides with the pipe wall, and is vaporized. In this way, the nucleate boiling region where the heat transfer coefficient is high is long and the film boiling region where the heat transfer coefficient is low is shortened, and the heat transfer efficiency of the heat transfer surface of the entire heat transfer tube is significantly improved. In this way, the water vapor flowing inside the heat exchanger tube 1 becomes superheated steam in the superheated region at the upper end, and enters the upper water chamber 12 through the heat exchanger tube communication hole 31 of the upper tube plate 11. It flows out as shown by the arrow in Figure 1.

The heat transfer accelerator 33 in the heat transfer tube i of the above embodiment is made by twisting two ordinary round bars 34, but it may also be made by twisting round bars with unevenness. In this case, the outer circumferential surface of the heat transfer promoter 33 becomes extremely uneven, so that the turbulent flow of water and steam is further promoted, and the heat transfer coefficient is significantly improved.

[Effects of the Invention] As can be seen from the above explanation, the heat exchanger of the present invention has a heat transfer accelerator made of two or more twisted round rods inserted and supported in a large number of heat transfer tubes. The flow path area in each heat transfer tube decreases, which increases the flow velocity in the tube, and the unevenness of the outer circumferential surface of the heat transfer promoter promotes turbulent flow. Since the pipe has a spiral shape, the flow of water and steam inside the pipe becomes a swirling flow, and the synergistic effect of these effects significantly improves heat transfer efficiency, making it possible to downsize the heat exchanger. Further, the heat transfer accelerator formed by twisting two or more round rods together is easy to manufacture, easy to insert into a heat exchanger tube, and does not damage the inner wall of the tube.

[Brief explanation of the drawing]

Fig. 1 is a schematic sectional view showing a steam generator which is a type of heat exchanger, Fig. 2 a is a longitudinal sectional view showing a heat exchanger tube according to the present invention in the steam generator, and Fig. 2 is a view a. FIG. 3 is a partial longitudinal sectional view taken along line A-A of FIG. DESCRIPTION OF SYMBOLS 1... Heat exchanger tube, 9... Lower water chamber, io... Lower tube plate, 11... Upper tube plate, 12... Upper water chamber, 33...
... Heat transfer accelerator, 34... Round bar.

Claims (1)

[Claims] 1) Tube sheets are provided in the upper and lower parts of the shell, water chambers are formed above the upper tube sheet and below the lower tube sheet, respectively, and the upper and lower ends of a large number of heat transfer tubes are placed on the upper and lower tube sheets. In the heat exchanger which supports and communicates with the water chamber, a heat transfer accelerator made of two or more twisted round rods is inserted and supported in each of the heat transfer tubes. Heat exchanger.