JPS586391A - Heat exchanger - Google Patents

Abstract

PURPOSE:To prevent occurrence of an unstable flowing phenomenon within the interior of a heat transfer tube by providing a finned part and a bare tube in the tube length direction and the tube row direction of the heat transfer tube to make uniform the heat load distribution of the heat transfer tube. CONSTITUTION:A tube next is constituted by use of a U-shaped heat transfer tube 26 which is formed by fitting fins 7 to the upper side of the U-shaped tube, and the lower side of said U-shaped tube is formed into a bare tube 27. Accordingly, the heat load of the bare tube section becomes at least less than 1/2 that of the finned part, and the heat load at the inlet side of the tube row decreases. Since the heat load distribution within the tube nest is made uniform, the unstable flowing phenomenon of the condensate flow is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heat exchanger, and particularly to a shell-and-tube heat exchanger suitable for using gas or steam as the heating side and heated side fluids.

BACKGROUND ART Recently, heat exchangers such as heat exchangers for waste heat recovery, heat exchangers for heat exchangers, heat exchangers for heat exchangers, and heat exchangers for heat exchangers such as one-piece heat exchangers have been increasingly used in various plants and the like from the viewpoint of energy conservation. In these heat exchangers, the heat exchanger tubes move or deform due to thermal shock during startup or uneven temperature distribution in the longitudinal direction of the heat exchanger tubes. 4t+:
In addition, in heat exchangers that utilize the phase change of steam in the tubes, a two-phase flow is formed, which complicates the flow state and, in severe cases, causes unstable flow phenomena, causing vibrations and deformation of the heat transfer tubes, and even heat loss. This is believed to be the cause of deterioration in the performance of the exchanger.

Here, the causes of such defects in the heat exchanger will be specifically explained using figures.

FIG. 1 shows an example of a heat exchanger to which the present invention applies.
This is a schematic explanation of the configuration of a cross-flow type multi-tubular heat exchanger. That is, a plurality of U-shaped heat exchanger tubes 2 are built inside the shell 1, and 13b of these heat exchanger tubes 2
A heat exchanger consisting of an end plate 4 whose mouth end is attached to a tube plate 3, which faces the heat exchanger tube 2 with the tube plate 3 in between, and constitutes partition chambers 6 and 8 that supply fluid to the heat exchanger tube 2. An example is shown. Inside the end plate 3, a partition plate 9 is provided, which constitutes a partition chamber 6 for supplying fluid before heat exchange to the heat transfer tube 2 and a partition chamber 8 for collecting fluid after heat exchange. Inside, a support plate 15 for holding the heat transfer tube 2 and partitioning the internal space, a guide plate 13 and a baffle plate 14 for guiding the fluid of the shell 1i11, etc. are provided. In these types of heat exchangers, when steam is used as the heating fluid and heat energy is transferred to the heated fluid by releasing its latent heat, the inside of the tube is the heating fluid, and the outside of the tube is the fluid to be heated. is common. That is, the heating fluid 16 enters the partition chamber 6 from the inlet pipe 5 provided on the end plate 4, and releases latent heat as it passes through the inside of the heat transfer tube 2. The condensed heating fluid 17 is collected in the partition chamber 8 and discharged from the system through an outlet pipe 10 installed on the end plate 4. On the other hand, the heated fluid 18 enters the internal space of the shell 1 from the inlet pipe 11 attached to the outer shell of the shell 1, is distributed in flow rate by the guide plate 13, and receives heat by passing through the outside of the heat transfer tube 2. , is discharged from the outlet pipe 14. In particular, when the heated fluid 18 is a gas such as gas or steam, the fins 7 are often provided on the outside of the heat exchanger tube 2 . This is because the heat transfer coefficient is generally low in the tube wall that comes into contact with gas, so the amount of heat transfer is increased by expanding the surface area.

Now, in the heat exchanger having such a configuration, the temperature rise ΔT of the fluid to be heated 18 is calculated as ΔT=(T-TIn)/(1PouL-TIn), where T: fluid temperature TI, ,: entrance temperature Tout: exit temperature, the number of pipe rows N is made dimensionless by the number of contracted pipe rows NT, and the characteristic of the temperature rise ΔT of the fluid on the heated side in the direction of the pipe rows is expressed as follows:
It will look like the solid line 6 in the figure. As can be seen from the figure, the Y blackness of the fluid to be heated, ΔT, is at half the number of condensed tube rows, that is, [in the 1-shaped heat exchanger tube 2, the lower tube occupies about 2/3 or more. It turns out.

This temperature increase ΔT is calculated as ΔT=Q/AK However, from the relationship of 1 (: heat transfer coefficient A: heat transfer area Q: heat transfer amount, if the heat transfer area A and heat transfer coefficient K change small for each tube row, , is proportional to the amount of heat transfer Q, so
This means that most of the heat transfer takes place below the tube bank. Therefore, if the amount of heat transfer is small, there will be no problem, but in a heat exchanger with a large amount of heat transfer or a heat exchanger with a large heat load per heat transfer tube (equivalent to a long heat transfer tube), The temperature distribution within the heat exchanger tube and the flow rate of condensed water become as shown in FIG. 3, which may lead to deterioration of the reliability of the heat exchanger tube. The figure shows the ratio of heating side fluid temperature, pipe wall temperature, and condensed liquid amount to the pipe length direction, respectively.
Among the heat exchanger tubes 2 in FIG. 2, those with a large heat load, such as the heat exchanger tube 25 on the outside, exhibit characteristics as shown by the solid line A in FIG. 3. That is, as shown by the solid line A in FIG. 3(C), the condensate flow becomes full inside the heat transfer tube near the outlet end of the tube length and flows downward. therefore,
Sensible heat is absorbed in the heating side fluid in that area, and the temperature rises as shown in Fig. 3(a).
The supercooling phenomenon shown in Fig. 2 occurs, and the tube wall temperature also increases to the 3rd level.
As shown in Figure (I), the temperature gradient increases in the tube length direction. For this reason, the temperature difference between the upper and lower sides of the U-shaped heat exchanger tube 25 increases, which becomes a cause of thermal deformation. On the other hand, the fourth
The figure shows the flow state of the condensate 17 inside the heat exchanger tube 25. The heating side fluid 16 releases latent heat inside the heat exchanger tube 25 and becomes the condensate 17. The liquid 17 exists in the lower part of the pipe as a laminar flow 19, and gradually forms a wavy flow 20, a slug flow 21, a plug flow 22, and a bubble flow 2.
It's 3. In such flow conditions, especially the slag flow 21
If the region occupied by the plug flow 22 is large, unstable flow phenomena are likely to occur due to load fluctuations, etc., which may lead to deterioration of heat transfer performance and damage to the heat transfer tubes. Therefore, in the prior art, in order to prevent these drawbacks, particularly unstable flow phenomena, the heating fluid 16 is allowed to flow more than necessary and the heating fluid 16 for scavenging is taken out from the discharge port 24 communicating with the partition chamber 8. Often. In this case, the thermal energy possessed by the scavenged heating fluid 16 is wasted, and in some cases, the plant performance may be degraded.

An object of the present invention is to avoid unstable flow phenomena inside the heat exchanger tubes without excessively flowing the heating fluid in a heat exchanger that utilizes phase change within the heat exchanger tubes, and to avoid unstable flow phenomena caused by supercooling of the heating side fluid. It is an object of the present invention to provide a heat exchanger that can contribute to improving the reliability of heat exchanger tubes by preventing defects in the heat exchanger tubes.

A feature of the present invention is that, as a heat exchanger tube constituting a heat exchanger, a finned section and a bare tube section are combined in the tube length direction, the section with a large heat load in the tube nest is the bare tube section, and the section with a small heat load is used as the bare tube section. By applying a finned part to the tube bundle, the heat load distribution of the heat exchanger tubes that make up the tube bundle is made uniform, and
An object of the present invention is to provide a heat exchanger technology that prevents overcooling of a heating fluid.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a heat exchanger as an embodiment of the present invention will be described in detail with reference to the drawings.

As an embodiment of the heat exchanger to which the present invention is applied, as shown in FIG.
Let us take as an example a cross-flow type shell-and-tube heat exchanger that heats 111I fluid. In the present invention, instead of the finned heat exchanger tube 20, the fifth
As shown in the figure, a fin 7 is attached to the upper side of the single-shaped tube, and a bare tube 27 is attached to the lower side [The main feature is that the tube bundle is constructed using the single-shaped heat exchanger tube 26. By the way, in general, the amount of heat dissipated from the wall surface Qb is determined by the temperature difference ΔT11 between the wall surface and the fluid.
, surface area A, b and heat transfer coefficient αt2, it is given by the following equation.

Qb=αbA−bΔT ++ On the other hand, in the case of a wall with fins, its heat radiation amount Q.

is the temperature difference between the fin root wall 1 m and the fluid Z T I % surface area A, r and heat transfer coefficient αf, and Q, −αfA
fφΔT+.

However, φ is given by fin efficiency. Here, the temperature difference ΔIll, , ΔT1. and heat transfer coefficient α
Assuming that f and αb do not change, the ratio of the amount of heat dissipated is Q, -φA, r Ql·A, b, which shows that the amount of heat dissipated from the finned tube is larger than that from the bare tube. In reality, ΔT+KΔTb) and αfKα1
1, so it becomes. Normally, the surface area Af of a finned tube is on the order of several times the surface area Ab of a bare tube. less than 1/2 of that amount. When the tube bundle of the heat exchanger shown in FIG. 1 is constructed using such heat transfer tubes 26, it can be easily seen that the temperature rise ΔT of the fluid to be heated tends to be as shown by the broken line B in FIG. It becomes possible to reduce the heat load on the inlet side of the tube array. Therefore, the heat exchanger tube 26
The heating side fluid temperature inside the tube also becomes the dashed line B shown in Figure 3 (a), and since supercooling can be prevented, the tube wall temperature is as shown in Figure 3 (1).
), and the temperature gradient in the tube length direction is reduced. If the tube wall temperature gradient in the tube length direction is not extremely large, thermal deformation etc. can be prevented. Furthermore, since the heat load distribution within the tube bundle is also made uniform, the condensate flow within the tube is also easily distributed as shown by the broken line B in Figure 3 (C), and the condensate flow becomes unstable. It is possible to prevent flow phenomena.

On the other hand, FIG. 6 shows an embodiment in which the present invention is applied to a general type of shell-and-tube heat exchanger.

In the embodiment shown in FIG. 5, the fin details are arranged on the upper side of the U-shaped heat exchanger tube 26 and the bare tube section is arranged on the lower side. Fluid 18 is inlet pipe 11
When the flow is made to pass in a zigzag manner using the guide plates 13' and 13'' from Even if a tube nest is constructed using the heat exchanger tubes 28 provided with attached portions, it is possible to achieve the same effects as in the above-mentioned embodiments.

Furthermore, even in a heat exchanger in which the heating side tube bundle is configured in two stages as shown in FIG. 7, the first stage tube bundle is made of bare tubes 30,
It is easy to imagine that the same effect can be obtained even if the second-stage tube bundle is composed of fin tubes 29.

The embodiments of the present invention have been specifically described above with reference to the drawings, and the effects obtained by the present invention are listed as follows.

By appropriately configuring finned portions and bare tubes in the tube length direction and tube row direction of the heat transfer tubes that make up the tube nest built into the heat exchanger, the heat load distribution of the heat transfer tubes can be adjusted without excessively flowing the heating fluid. This makes it possible to avoid unstable flow phenomena inside the heat transfer tube, and also prevents problems such as thermal stress and thermal deformation of the heat transfer tube caused by supercooling of the heating fluid. This can greatly contribute to improving the reliability of the exchanger.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an example of a heat exchanger according to the prior art, FIG. 2 is a thermal characteristic diagram of the fluid on the heated side of the heat exchanger, and FIG.
The figure is a thermal characteristic diagram of the heating side fluid, Figure 4 is an explanatory diagram showing the flow situation inside the heat exchanger tube according to the conventional technology, and Figure 5 d is the heat exchanger tube constituting the heat exchanger which is an embodiment of the present invention. A cross-sectional view of
FIGS. 6 and 7 are cross-sectional views showing heat exchanger tubes according to other embodiments of the present invention. 1... Heat exchanger shell, 2, 25, 26, 28° 29
．． 30... Heat exchanger tube, 3... Tube sheet, 4... End plate, 6
゜8... Partition room, 7... Fin, 9... Partition plate,
27... Bare tube, 15... Support plate. Agent Patent Attorney Akio Takahashi

Claims (1)

[Scope of Claims] ], a 7L housing a tube nest composed of a plurality of U-shaped heat exchanger tubes, a signboard for attaching the open end of the U-shaped heat exchanger tubes, and a signboard facing the heat exchanger tubes with respect to the tube temporary, 1. A heat exchanger comprising a head plate having a partition chamber communicating with a heat exchanger tube, characterized in that a finned portion and a bare tube portion are provided in the longitudinal direction of the heat exchanger tube. 2. In the heat exchanger according to claim 1, U
1. A heat exchanger incorporating a heat exchanger tube, characterized in that the second flow side of the shape-shaped heat exchanger tube is a finned part, and the downstream side is a bare tube part. 3. The heat exchanger according to claim 1, characterized in that the upstream side of the fluid to be heated is a bare tube section, and the downstream side is a finned section. vessel.