JP2005016819A - Heat exchanger - Google Patents

Abstract

A structure for suppressing the coalescence of steam generated in a heat exchanger, reducing the diameter of bubbles and distributing them uniformly, thereby improving the heat exchange efficiency.
A heat transfer tube group including a plurality of heat transfer tubes 2 arranged in substantially parallel to each other in a non-vertical direction and in which a high-temperature fluid flows therein, and a container 1 that accommodates the heat transfer tube group. Boiling occurs between heat transfer tubes in a heat exchanger configured to contain the low temperature side fluid in the container outside the heat tube and cause the low temperature side fluid to boil on the outer surface of the heat transfer tube. The wire mesh 3 that spreads in the direction of the heat transfer tube was disposed in at least a part of the assumed portion.
[Selection] Figure 1

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a shell / tube type heat exchanger, and more particularly to a heat exchanger in which boiling occurs on the shell side.
[0002]
[Prior art]
Heat exchangers play an important role in various fields such as the chemical industry, power plant, and food industry. There are various types of heat exchangers, but shell / tube type heat exchangers are the most common, and are widely used as kettle reboilers, feed water heaters, evaporators, ventilation air conditioners and the like. This heat exchanger is a type in which a bundle of multi-tube heat transfer tubes (tubes) is inserted into a cylindrical body. Cylindrical tube plate type, U tube type, floating head type due to the connection structure of tube plate and shell (shell) And bayonet tube type (see Patent Document 1).
[0003]
The flow on the shell side varies depending on the purpose of use of the heat exchanger, but when used as an evaporator or reboiler, the liquid is heated to evaporate, so that the inside of the shell becomes a boiling two-phase flow. In fact, at least 60% of all heat exchangers are said to have a two-phase flow in the shell.
[0004]
FIG. 10 shows a schematic view of a conventional shell / tube heat exchanger. It is mainly composed of a cylindrical container 1 and a group of heat transfer tubes 2 arranged in the container 1. The container 1 is filled with a low-temperature liquid, and a high-temperature fluid flows in the heat transfer tube 2. In the example of FIG. 10, a large number of heat transfer tubes 2 parallel to each other are arranged so as to extend in the horizontal direction, and the heat transfer tubes 2 are arranged in a square lattice so as to be aligned in the horizontal direction and the height direction.
[0005]
The heat of the high-temperature fluid in the heat transfer tube 2 is transferred to the low-temperature side fluid outside the heat transfer tube 2 through the wall of the heat transfer tube 2, and the liquid on the low-temperature side boils on the outer surface of the heat transfer tube 2. It becomes a liquid two-phase flow. At this time, the fluid in the heated container 1 forms a natural circulation flow by the density difference and the rising of the generated bubbles.
[0006]
In the lower stage of the heat transfer tube group, there is very little liquid single phase or bubbles, but as the upper stage goes, more bubbles are generated and the generated bubbles are accumulated, so the volume ratio (void ratio) of bubbles in the upper stage Becomes larger. However, the void ratio does not gradually increase toward the upper stage, the void ratio is large at the upper / center portion, and the void ratio is decreased at the lower / peripheral portion, and the high void ratio region 18 and the low void ratio region 19. It has been pointed out from previous studies that it is divided into two areas.
[0007]
With regard to the local distribution of the bubbles, in the general lattice arrangement shown in FIG. 11, the bubbles are likely to accumulate because the flow backs up and stagnates due to the separation of the flow in the vertical gap between the heat transfer tubes 2, Bubble distribution occurs such that the void ratio is large behind the heat transfer tube 2 and the void ratio is small in the mainstream region.
[0008]
The larger the natural circulation flow and the greater the turbulence of the flow, the stronger the flow behind the heat transfer tube 2 and the higher the void ratio behind the heat transfer tube 2. The accumulation of bubbles in the gap between the heat transfer tubes 2 deteriorates heat transfer and easily causes dryout. When the heat exchanger is used as a cooling facility particularly related to the safety of a power plant, the rapid deterioration of heat removal due to dry-out may greatly affect the safety.
[0009]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 6-147406
[Problems to be solved by the invention]
As described above, the heat exchanger is required to have a higher heat exchange rate and to maintain a predetermined heat exchange performance without causing rapid heat transfer deterioration due to dryout or the like. However, the steam generated in the heat exchanger stagnates around the heat transfer tube, so that the heat transfer is remarkably deteriorated and dryout is easily generated.
[0011]
Therefore, the present invention provides a heat exchanger that suppresses coalescence of steam generated in the heat exchanger, reduces the diameter of bubbles, and distributes them uniformly, thereby improving the heat exchange efficiency. With the goal.
[0012]
[Means for Solving the Problems]
The present invention is in accordance with the above object, and the invention according to claim 1 is a heat transfer tube comprising a plurality of heat transfer tubes arranged in parallel to each other in a direction different from the vertical direction and through which the high temperature fluid flows. A low-temperature side fluid is stored in the container outside the heat transfer tube, and the low-temperature side fluid is boiled on the outer surface of the heat transfer tube. The heat exchanger configured as described above is characterized in that a wire mesh extending in the direction of the heat transfer tube is disposed at least at a part of the portion where boiling between the heat transfer tubes is assumed to occur.
[0013]
According to a second aspect of the present invention, a heat transfer tube group comprising a plurality of heat transfer tubes arranged in substantially parallel to each other in a direction different from the vertical direction and through which the high temperature side fluid flows, and the heat transfer tube group are accommodated. A heat exchanger configured to contain a low-temperature fluid in the container outside the heat transfer tube and to cause boiling of the low-temperature fluid on an outer surface of the heat transfer tube, By partially setting the horizontal interval between the heat transfer tubes partially larger than the horizontal interval between the other heat transfer tubes, the flow path traversing the heat transfer tube group in the vertical direction extends substantially at the center of the heat transfer tube group. It is formed at a passing position.
[0014]
According to a third aspect of the present invention, there is provided a heat transfer tube group comprising a plurality of heat transfer tubes arranged in substantially parallel to each other in a direction different from the vertical direction and through which a high temperature fluid flows, and the heat transfer tube group. A heat exchanger configured to contain a low-temperature fluid in the container outside the heat transfer tube and to cause boiling of the low-temperature fluid on an outer surface of the heat transfer tube, In the center of the upper portion of the heat transfer tube group, the interval between the heat transfer tubes is configured to be wider than the interval between the heat transfer tubes in the other part of the heat transfer tube group.
[0015]
According to a fourth aspect of the present invention, there is provided a heat transfer tube group comprising a plurality of heat transfer tubes arranged in substantially parallel to each other in a direction different from the vertical direction and through which a high temperature side fluid flows, and the heat transfer tube group. A heat exchanger configured to contain a low-temperature fluid in the container outside the heat transfer tube and to cause boiling of the low-temperature fluid on an outer surface of the heat transfer tube, A flow passage crossing the heat transfer tube group is formed by making the interval between the heat transfer tubes larger than the interval between the other heat transfer tubes from the upper center of the heat transfer tube group obliquely upward. It is characterized by.
[0016]
According to a fifth aspect of the present invention, a heat transfer tube group comprising a plurality of heat transfer tubes arranged in substantially parallel to each other in a direction different from the vertical direction and through which a high temperature fluid flows, and the heat transfer tube group are accommodated. A heat exchanger configured to contain a low-temperature fluid in the container outside the heat transfer tube and to cause boiling of the low-temperature fluid on an outer surface of the heat transfer tube, The heat transfer tube group is composed of a plurality of heat transfer tubes arranged in a substantially horizontal direction with a space between each other, and a plurality of heat transfer tubes arranged in the vertical direction with a space between each other, and adjacent to each other. The positions of the individual heat transfer tubes adjacent to each other in the vertical direction of the stage of the heat transfer tubes are arranged so as to be shifted from each other in the horizontal direction.
[0017]
According to a sixth aspect of the present invention, a heat transfer tube group comprising a plurality of heat transfer tubes arranged in substantially parallel to each other in a direction different from the vertical direction and through which a high-temperature fluid flows, and the heat transfer tube group are accommodated. A heat exchanger configured to contain a low-temperature fluid in the container outside the heat transfer tube and to cause boiling of the low-temperature fluid on an outer surface of the heat transfer tube, The cross-sectional shape of the plurality of heat transfer tubes is an ellipse that is long in the vertical direction.
[0018]
The invention according to claim 7 accommodates the heat transfer tube group including a plurality of heat transfer tubes arranged in parallel to each other in a direction different from the vertical direction and through which the high temperature fluid flows, and the heat transfer tube group. A heat exchanger configured to contain a low-temperature fluid in the container outside the heat transfer tube and to cause boiling of the low-temperature fluid on an outer surface of the heat transfer tube, The protrusion is formed in the lower end part of the outer surface of the cross section of a some heat exchanger tube, It is characterized by the above-mentioned.
[0019]
The invention according to claim 8 has a heat transfer tube group composed of a plurality of heat transfer tubes arranged in parallel to each other and through which the high temperature side fluid flows, and a container for housing the heat transfer tube group, In the heat exchanger configured to accommodate the low temperature side fluid in the container outside the heat transfer tube and to cause boiling of the low temperature side fluid on the outer surface of the heat transfer tube, the plurality of heat transfer tubes are arranged horizontally. It is characterized by being arranged in a direction that is neither a direction nor a vertical direction.
[0020]
The invention according to claim 9 includes a heat transfer tube group composed of a plurality of heat transfer tubes arranged in parallel to each other and through which a high-temperature side fluid flows, and a container accommodating the heat transfer tube group, In the heat exchanger configured to accommodate the low temperature side fluid in the container outside the heat transfer tube and to cause boiling of the low temperature side fluid on the outer surface of the heat transfer tube, a surfactant is added to the low temperature side fluid. Is included.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, with reference to FIGS. 1-9, embodiment of the heat exchanger which concerns on this invention is described. Here, parts common or similar to the prior art, or parts common or similar to each other are denoted by common reference numerals, and redundant description is omitted.
[0022]
1 and 2 show a first embodiment of a heat exchanger according to the present invention. This heat exchanger is composed of a cylindrical container (body) 1 and a large number of heat transfer tubes 2 arranged in the container 1, and a wire mesh 3 is installed between the heat transfer tubes 2. The heat transfer tubes 2 extend in parallel to each other in the horizontal direction, and are arranged in a square lattice so as to be aligned in the vertical and horizontal directions. The wire mesh 3 extends between the heat transfer tubes 2 so as to cross the container 1 in the horizontal direction.
[0023]
The temperature of the refrigerant (low temperature side fluid) outside the heat transfer tube 2 in the container 1 rises due to heat exchange with the high temperature fluid inside the heat transfer tube 2, and eventually begins to boil. Due to the convection due to the temperature rise of the refrigerant in the container 1 and the buoyancy of the generated steam, the fluid rises between the heat transfer tube groups in the container 1 and falls down along the inner wall of the container 1 outside the heat transfer tube group. And cooling is promoted. Because of the upward flow between the heat transfer tube groups, bubbles accumulate in the upper part, and the volume ratio (void ratio) of the steam increases. When the void ratio increases, the steam accumulates on the front and rear surfaces of the heat transfer tube 2. However, heat transfer deteriorates due to stagnation.
[0024]
As shown in FIG. 2, by installing the wire mesh 3 between the heat transfer tube 2 and the heat transfer tube 2, the generated steam bubbles can be reduced in diameter. Thereby, it is possible to prevent bubbles having a large diameter from staying near the side surface of the heat transfer tube 2. As shown in FIG. 1, it is effective to install the wire mesh 3 on an upper portion having a large void ratio.
[0025]
FIG. 3 shows a second embodiment of the heat exchanger according to the present invention. The void ratio in the container 1 is larger at the upper part, but does not necessarily increase in order from the lower part to the upper part of the heat transfer tube group. As shown in FIG. 10, a high void ratio region 18 is formed at the center / upper part, / It has been found that a low void ratio region 19 is formed in the lower part, so that it can be divided into two regions. In particular, it is difficult for steam to be discharged at the central portion, which increases the void ratio. Therefore, as shown in FIG. 3, the horizontal pitch of the heat transfer tubes 2 at the center is increased to form the vertical flow paths 6. Thereby, it becomes easy to discharge | evaporate the steam from the heat exchanger tube group of a center part, and it can suppress that a vapor | steam stagnates in a heat exchanger tube group.
[0026]
Next, FIG. 4 shows a third embodiment of the heat exchanger according to the present invention. This is to arrange the heat transfer tube group by increasing the pitch d2 at the center / upper part and decreasing the pitch d1 at the periphery / lower part. Thus, heat transfer can be improved by increasing the heat transfer area at the periphery / lower part where the void ratio is small and preventing bubbles from accumulating behind the heat transfer tube 2 at the center / upper part.
[0027]
FIG. 5 shows a fourth embodiment of the heat exchanger according to the present invention. This is a portion in which the heat transfer tube 2 is not installed from the center / upper part of the tube group toward the oblique upper side, that is, the V-shaped flow path 30 is provided. Thereby, the effect which accelerates | stimulates the flow of the vapor | steam outside the heat exchanger tube 2 can be anticipated similarly to 2nd Embodiment (FIG. 3).
Furthermore, FIG. 6 shows a fifth embodiment of the heat exchanger according to the present invention. As shown in the figure, the heat transfer tube groups at the respective stages are alternately shifted in the horizontal direction.
[0028]
In addition to the lattice arrangement, the conventional heat transfer tube group arrangement includes a heat transfer tube 2 in the preceding arrangement and a staggered arrangement (triangular arrangement) arranged in the center of the heat transfer tube 2. When the refrigerant is a single phase, it is generally known that the staggered arrangement is more turbulent than the lattice arrangement and thus has a high heat transfer coefficient but also a large pressure loss. On the other hand, when the refrigerant is a two-phase flow, the heat transfer coefficient is greatly influenced not only by the turbulent flow intensity but also by the vapor ratio and distribution. As shown in FIG. 11, in a generally well-used grid arrangement, the heat transfer tube 2 is formed with a wake 11 at the back, bubbles 12 are entrained, and blocked by a downstream tube, so that the heat transfer tube 2 and the heat transfer tube Air bubbles tend to accumulate between the two. This reduces the heat transfer coefficient at the front surface and the back surface of the heat transfer tube 2.
[0029]
In the present embodiment, as shown in FIG. 7, the bubbles 12 behind the heat transfer tube 2 are easily discharged upward, and the high voids due to the accumulation behind the steam as in the staggered arrangement without increasing the pressure loss so much. The rate can be prevented and the heat transfer rate can be increased.
[0030]
Further, FIG. 8 shows a sixth embodiment of the heat exchanger according to the present invention. As illustrated, the shape of the heat transfer tube 2 is an ellipse having a large diameter in the main flow direction (vertical direction). This makes it difficult for bubbles to accumulate behind the heat transfer tube as compared to a circular heat transfer tube having the same heat transfer area. Moreover, the effect that pressure loss is reduced can be expected because the separation point moves rearward and the backflow region decreases.
[0031]
FIG. 9 shows a seventh embodiment of the heat exchanger according to the present invention. This is a projection 15 provided on the lower surface of the heat transfer tube 2. Thereby, it can suppress that a bubble stagnates in the heat exchanger tube 2 lower surface.
In each of the embodiments described above, the direction of the heat transfer tube 2 is horizontal, but the same effect can be obtained if the direction is different from the vertical direction, not necessarily the horizontal direction.
[0032]
In the eighth embodiment of the heat exchanger according to the present invention, the heat transfer tubes 2 are arranged to be inclined with respect to the horizontal (not shown). As a result, the bubbles adhering to the lower surface of the heat transfer tube 2 rise and detach along the tube wall, thereby preventing stagnation on the tube wall.
[0033]
Furthermore, in the ninth embodiment of the heat exchanger according to the present invention, a small amount of a surfactant is mixed in the refrigerant in the container 1. A surfactant is a substance that can mainly activate the interface between two substances (reducing the surface tension, etc.). Therefore, by mixing this in the refrigerant, the bubbles do not merge, so that the bubbles are maintained at a small diameter, and at the same time, the distribution of gas and liquid is made uniform. Thereby, accumulation of steam in a specific portion can be suppressed.
[0034]
【The invention's effect】
As described above, according to the present invention, in the shell / tube heat exchanger, the generated steam is reduced in diameter and uniformly distributed, thereby suppressing the accumulation of bubbles in the heat transfer tube group, The heat exchange efficiency when the flow is a two-phase flow can be improved. In addition, by reducing the void rate in the heat transfer tube group by facilitating the discharge of steam from between the heat transfer tube groups, while improving the heat exchange rate, the heat transfer tubes are prevented from drying out and heating up, Safety can be improved.
[Brief description of the drawings]
FIG. 1 is a transverse cross-sectional view of a first embodiment of a heat exchanger according to the present invention.
FIG. 2 is a partial perspective view of the vicinity of a heat transfer tube of the heat exchanger of FIG.
FIG. 3 is a cross-sectional view of a second embodiment of a heat exchanger according to the present invention.
FIG. 4 is a cross-sectional view showing a heat transfer tube arrangement of a third embodiment of a heat exchanger according to the present invention.
FIG. 5 is a cross-sectional view showing a heat transfer tube arrangement of a fourth embodiment of a heat exchanger according to the present invention.
FIG. 6 is a cross-sectional view showing a heat transfer tube arrangement of a fifth embodiment of a heat exchanger according to the present invention.
7 is a partially enlarged cross-sectional view of a heat transfer tube array of the heat exchanger of FIG. 6;
FIG. 8 is a partial enlarged cross-sectional view showing a heat transfer tube arrangement of a sixth embodiment of a heat exchanger according to the present invention.
FIG. 9 is a cross-sectional view of a heat transfer tube of a seventh embodiment of a heat exchanger according to the present invention.
FIG. 10 is a cross-sectional view of a conventional heat exchanger.
FIG. 11 is a partial enlarged cross-sectional view of a heat transfer tube array of a conventional heat exchanger.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Container, 2 ... Heat transfer tube, 3 ... Wire mesh, 5 ... Bubble, 6 ... Flow path, 11 ... Wake, 12 ... Bubble, 15 ... Projection, 18 ... High void area, 19 ... Low void area, 30 ... V-shaped channel.

Claims (9)

A heat transfer tube group composed of a plurality of heat transfer tubes arranged in substantially parallel to each other in a direction different from the vertical direction and through which the high-temperature fluid flows, and a container for housing the heat transfer tube group, the outer side of the heat transfer tube In the heat exchanger configured to accommodate the low temperature side fluid in the container of the heat transfer tube and to cause boiling of the low temperature side fluid on the outer surface of the heat transfer tube,
The heat exchanger characterized by arrange | positioning the wire mesh which spreads in the direction of the said heat exchanger tube in at least one part of the part assumed that a boiling occurs between the said heat exchanger tubes. A heat transfer tube group composed of a plurality of heat transfer tubes arranged in substantially parallel to each other in a direction different from the vertical direction and through which the high-temperature fluid flows, and a container for housing the heat transfer tube group, the outer side of the heat transfer tube In the heat exchanger configured to accommodate the low temperature side fluid in the container of the heat transfer tube and to cause boiling of the low temperature side fluid on the outer surface of the heat transfer tube,
By making the horizontal interval between the heat transfer tubes partially larger than the horizontal interval between the other heat transfer tubes, the flow path traversing the heat transfer tube group in the vertical direction is substantially at the center of the heat transfer tube group. It is formed in the position which passes through, The heat exchanger characterized by the above-mentioned. A heat transfer tube group composed of a plurality of heat transfer tubes arranged in substantially parallel to each other in a direction different from the vertical direction and through which the high-temperature fluid flows, and a container for housing the heat transfer tube group, the outer side of the heat transfer tube In the heat exchanger configured to accommodate the low temperature side fluid in the container of the heat transfer tube and to cause boiling of the low temperature side fluid on the outer surface of the heat transfer tube,
A heat exchanger characterized in that, in the center of the upper part of the heat transfer tube group, the interval between the heat transfer tubes is configured to be wider than the interval between the heat transfer tubes in the other part of the heat transfer tube group. . A heat transfer tube group composed of a plurality of heat transfer tubes arranged in substantially parallel to each other in a direction different from the vertical direction and through which the high-temperature fluid flows, and a container for housing the heat transfer tube group, the outer side of the heat transfer tube In the heat exchanger configured to accommodate the low temperature side fluid in the container of the heat transfer tube and to cause boiling of the low temperature side fluid on the outer surface of the heat transfer tube,
A flow path crossing the heat transfer tube group is formed by making the interval between the heat transfer tubes larger than the interval between the other heat transfer tubes, obliquely upward from the center of the upper portion of the heat transfer tube group. A heat exchanger characterized by that. A heat transfer tube group composed of a plurality of heat transfer tubes arranged in substantially parallel to each other in a direction different from the vertical direction and through which the high-temperature fluid flows, and a container for housing the heat transfer tube group, the outer side of the heat transfer tube In the heat exchanger configured to accommodate the low temperature side fluid in the container of the heat transfer tube and to cause boiling of the low temperature side fluid on the outer surface of the heat transfer tube,
The heat transfer tube group is composed of a plurality of heat transfer tubes arranged in a vertical direction with a plurality of heat transfer tubes arranged in a substantially horizontal direction and spaced apart from each other, and adjacent to each other. The heat exchanger is characterized in that the positions of the individual heat transfer tubes adjacent to each other in the vertical direction of the stage of the heat transfer tubes are shifted from each other in the horizontal direction. A heat transfer tube group composed of a plurality of heat transfer tubes arranged in substantially parallel to each other in a direction different from the vertical direction and through which the high-temperature fluid flows, and a container for housing the heat transfer tube group, the outer side of the heat transfer tube In the heat exchanger configured to accommodate the low temperature side fluid in the container of the heat transfer tube and to cause boiling of the low temperature side fluid on the outer surface of the heat transfer tube,
A heat exchanger characterized in that the cross-sectional shape of the plurality of heat transfer tubes is an ellipse that is long in the vertical direction. A heat transfer tube group composed of a plurality of heat transfer tubes arranged in substantially parallel to each other in a direction different from the vertical direction and through which the high-temperature fluid flows, and a container for housing the heat transfer tube group, the outer side of the heat transfer tube In the heat exchanger configured to accommodate the low temperature side fluid in the container of the heat transfer tube and to cause boiling of the low temperature side fluid on the outer surface of the heat transfer tube,
A protrusion is formed at the lower end of the outer surface of the transverse section of the plurality of heat transfer tubes. A heat transfer tube group composed of a plurality of heat transfer tubes arranged in parallel with each other and through which a high temperature side fluid flows, and a container for housing the heat transfer tube group, and the low temperature side in the container outside the heat transfer tube In a heat exchanger configured to contain a fluid and to cause boiling of the low temperature side fluid on the outer surface of the heat transfer tube,
The heat exchanger is characterized in that the plurality of heat transfer tubes are arranged in directions that are neither horizontal nor vertical. A heat transfer tube group composed of a plurality of heat transfer tubes arranged in parallel with each other and through which a high temperature side fluid flows, and a container for housing the heat transfer tube group, and the low temperature side in the container outside the heat transfer tube In a heat exchanger configured to contain a fluid and to cause boiling of the low temperature side fluid on the outer surface of the heat transfer tube,
A heat exchanger characterized in that a surfactant is contained in the low temperature side fluid.

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