JPS63259387A - Heat exchanging section of double-wall structured heat exchanger - Google Patents

Abstract

PURPOSE:To provide a compact, light-weight and high-performance heat exchanger by forming a spiral flow passage for fluid by disposing a spiral fin having a suitable pitch which tightly contact the inner surface of an outer pipe and the outer surface of an inner pipe and extends axially along side walls. CONSTITUTION:By a combination of an outer pipe 1, an inner pipe 2 and a spiral fin, a spiral passage 4 is formed between the inner pipe 2 and the outer pipe 1. By causing the outer thermal medium 9 and inner medium 10 to flow, heat is exchanged through the pipe wall of the inner pipe 2 by making one of them to be a high- temperature fluid and the outer a low-temperature fluid. This way, the section area of the flow passage between the outer pipe 1 and the inner pipe 2 is made more than ten times smaller, and the flow speed is made more than ten times faster. The smaller the spiral pitch, the larger the heating surface of the flow passage. When the flow speed becomes faster, turbulence is caused in the flow to improve the heat transfer performance, and so, it is generally expected that there will be about ten times more improvement. The heat exchanging section by the double-walled pipe can be economically manufactured, and the device can be made compact with a high performance.

Description

Detailed Description of the Invention 40 Object of the Invention [Field of Industrial Application] The present invention relates to the structure of a heat exchange section of a heat exchanger, and particularly relates to the structure of a heat exchange section of a cylindrical double tube structure heat exchanger. Regarding structure.

[Conventional technology]

The heat exchange section of a double-tube heat exchanger has a structure in which fluids with different temperatures flow through the gap between the outer and outer tubes and into the inner tube, and heat is exchanged between the fluids through the wall of the inner tube. The fluid is generally a liquid, and the heat transfer coefficient between the liquid and the inner wall surface is extremely good, and the distance between the two liquids is the thickness of the inner tube wall, which is generally extremely small. The bath liquid is often used as an extremely efficient heat exchange means because it completely covers the countercurrent liquid and causes little loss during heat exchange.

FIG. 5 shows a cross-sectional view of a heat exchange section with a conventional structure. In the gap between the outer tube 1 and the inner tube 2, there are riser fins 11 which also serve as supports for holding the inner tube 2 concentrically within the outer tube 1.
is mediated. As shown in the figure, the extranuclear channel fins are the inner tube 2,
Although it is often extruded integrally with the tube, it is sometimes simply press-fitted into a plurality of predetermined locations as a turbulence generating means and an inner tube support.

The heat transfer area expansion rate of the fins is about twice, which is extremely small compared to general convection heat exchange fins.

Usually, there are many cases where nothing is provided inside the inner tube 2, but
In some cases, a twisted ribbon is press-fitted as a turbulent flow generating means, or internal flow path fins 12 as shown in the figure are press-fitted. 9.10 indicate the outer flow path (and upstream heat transfer fluid) and the inner flow path (and countercurrent heat transfer fluid), respectively. Although not shown in the drawings, in the case of large-capacity heat exchange, measures such as using a hesogou to use a large number of double pipes in parallel as shown in the figure or increasing the length of the pipes are taken.

[Problem that the invention seeks to solve]

In the conventional structure, the heat exchange efficiency of the heat exchanger is improved by using several riser fins along the axial flow, or by press-fitting a turbulent flow generating means into the flow path, as described above, to increase the heat transfer coefficient. The improvement in the heat transfer area and the heat transfer area expansion rate were slight. As a means other than the above, there is an example in which a protrusion is provided facing the flow path of the above-mentioned pipe, but even if these are used in combination, it is difficult to significantly increase the amount of heat exchanged, and the length of the pipe is limited. Structures that have been significantly reduced in size or in which the number of parallel lines has been significantly reduced have not been put into practical use. This is because it is difficult and expensive to provide a complicated fin structure within the double pipe. Furthermore, the axially finned tube as described above is relatively inexpensive, easy to mass produce, and easy to maintain, so an alternative fin structure has not been easily put into practical use.

Structure of the Invention [Means for Solving the Problems] The heat exchange efficiency improvement means in the heat exchange section of the conventional double-tube structure focuses mainly on the generation of turbulence, and slightly expands the heat transfer area. It was an additional means. In the heat exchange section according to the present invention, focusing on the point that "increasing the flow velocity of the fluid increases the heat transfer coefficient", "the length of the flow path is sufficiently extended in order to sufficiently absorb the increased heat transfer coefficient". The purpose of this invention is to significantly increase heat exchange performance by providing a new structure with additional points. The means for this purpose are as follows. "A spiral fin is provided at a predetermined portion between the inner wall surface of the outer tube and the outer wall surface of the inner tube, closely interposed between both wall surfaces, and at a predetermined pitch in the axial direction along both wall surfaces. This structure forms a spiral flow path for fluid in the gap between the inner and outer tubes.''In order to further increase heat exchange performance, we developed a structure that corresponds to the spiral flow path portion described above. A structure in which spiral fins similar to the above-mentioned present structure are provided at a predetermined portion of the inner wall of the inner tube, thereby providing a spiral flow path for fluid also on the inner wall surface of the inner tube. Use it as a means of solution. FIG. 1 is a partial sectional view showing the basic structure of the heat exchange section according to the present invention described above. 1 is the outer tube,
2 is an inner tube, 3 is a spiral fin, and 4 is a spiral flow path formed in the gap between the inner tube and the outer tube by a combination of these. Reference numerals 9 and 10 denote an ascending heat medium fluid and a countercurrent heat medium fluid, one of which is a high temperature fluid and the other a low temperature fluid, and heat is exchanged with each other through the pipe wall of the inner tube 2.

The ascending heat medium fluid 9 flowing through the gap between the outer tube 1 and the inner tube 2 reaches the spiral flow path 4 of the heat exchange section, and the cross-sectional area of the flow path is reduced from a few minutes to more than ten minutes. Therefore, the flow velocity is increased several times to several times. The rate of speed increase in this case is determined by the helical pitch and wall thickness of the helical fins 3. The length of the helical channel becomes longer as the helical pitch becomes smaller, and the rate of expansion of the heat transfer area is determined by the length of the helical comb.

The basic structure shown in FIG. 1 is a structure for improving heat transfer performance between the external heat transfer fluid 9 and the outer surface of the inner tube 2.

In addition to the structure shown in Fig. 1, Fig. 2 also applies a structure based on the same points of view to the inside of the inner pipe, with countercurrent heat transfer fluid 10 and inner pipe 2.
The purpose is to improve the heat transfer performance between the heat exchanger and the inner wall surface of the heat exchanger, thereby significantly improving the performance of the heat exchanger as a whole. In the figure, reference numeral 5 denotes a second inner tube (or round bar) disposed within the inner tube, and second spiral fins 6 similarly disposed in close contact with the inner wall surface of the inner tube 2. It has the role of closely supporting the inner periphery of the tube and forming a second spiral flow path within the inner tube. As in the case of the present structure shown in FIG. 1, the countercurrent heat transfer fluid 10 reaches the second spiral flow path 6, where the flow path cross-sectional area is significantly reduced and the speed is increased several times to more than ten times. Since the second helical fin 6 has a smaller diameter than the first helical fin 3, it is desirable that the helical pitch is smaller than the latter in order to increase the heat transfer area. If the pressure loss becomes excessive for this reason, it is advisable to cause the countercurrent heat transfer fluid 10 to flow in the second inner pipe 5 as well. 8 is the second inner pipe 5
However, this sealing part may be omitted, or if the second inner tube 5 is a flow path, it may be a flow rate adjusting means.

[For production]

In the case where the inner diameter of the outer tube 1 is 70 mm, the outer diameter of the inner tube 2 is 52 m, the helical pitch of the spiral fin 3 is 201, and the fin wall thickness is 2 mm, the heat transfer area expansion magnification and flow velocity increase magnification are as follows. .

Heat transfer area expansion magnification n l =AI/At ”2.9
Double cross-sectional area of spiral flow path A3 = 142.8 Dragon 2 Flow rate increase magnification n 2 = 12.1 times According to the experimental data, the heat transfer fluid is water and turbulent heat transfer flows in a tube with an inner diameter of 50 mm. The rate α is assumed to be approximately the following value.

When the flow rate is 0.5 m/sec, Ct = 2000K
cal/m”h”C1m/sec α=
3700Kcal/m”h”C2m/sec
α=6300Kcal/m"h'c3 m/s
ec α=8700Kcal/m2h'c
That is, approximately, when the flow rate is doubled, the heat transfer coefficient increases by 1.85 times, when the flow rate is 4 times, the heat transfer coefficient is 3.15 times, and when the flow rate is 6 times, the heat transfer coefficient increases by 4.35 times. are doing. Therefore, it is considered that when the flow rate increases by 12.1 times, the heat transfer coefficient increases by about 6 to 6.5 times, and there is no large error. Therefore, the improvement ratio of the heat transfer performance of the heat exchange section according to the present invention in the above example can be considered as follows.

Since the heat transfer performance improvement factor of the conventional heat exchange section using turbulence generating means and axial fins is 2 to 3 times, it is thought that the performance of the heat exchange section according to the present invention in the above example is improved by 6 times or more. Since the helical pitch can be made even smaller, an improvement of about 10 times can generally be expected. From the above results, the flow path in the pipe.

In this case, it can be seen that increasing the flow velocity has a larger contribution to improving the heat transfer coefficient than increasing the heat transfer area.

Furthermore, the reason why the heat transfer coefficient increase factor is considered low at 6.5 times compared to the flow rate factor of 12.1 times is due to the increase in internal pressure, so in the case of large diameter pipe channels, the increase in internal pressure is small, so it can be further improved. It is thought that the multiplier will increase.

〔Example〕

First Embodiment When implementing the heat exchange section of the double-tube structure heat exchanger according to the present invention, it is important not only to have excellent heat exchange performance. It needs to be sufficiently inexpensive in terms of total cost and easy to maintain compared to the structure in which the inner tube is press-fitted. Fig. 3 shows an example of such an inexpensive and easy-to-maintain embodiment. In the heat exchanger structure for the external heat transfer fluid 9 in FIG. 3, a metal wire 3a made of a material with good thermal conductivity is spirally wound around the outer peripheral wall surface of the inner tube 2 at a predetermined helical pitch. The heat exchanger structure for the countercurrent heat transfer fluid 10 includes a material that is press-fitted into the outer tube 1.The heat exchanger structure for the countercurrent heat transfer fluid 10 includes Metal tube 6 made of material with good thermal conductivity
The inner tube 2 is formed by being press-fitted into the inner tube 2 by spirally winding a at a predetermined pitch. Metal wires and tubes are available on the market at very low prices, and they can also be wound into spirals very easily, making them easy to press into and remove from tubes. The maintainability is also good. Therefore, it is possible to construct the heat exchange section at a lower cost and easier than the conventional heat exchange section in terms of cost of 1. In the figure, the second spiral fin 6a may be a metal wire, and the spiral fin 3a may also be a metal tube. The metal wire and metal tube are not limited to those having a circular cross section, but may be oval or square.

Second Embodiment FIG. 4 shows another embodiment of the heat exchange section according to the present invention. In this embodiment, instead of the inner tube 2 and spiral fins 3 of the basic structure shown in FIG. 1, a metal tube with spiral fins is used, in which a metal tube and spiral fins for convection heat exchange are integrally rolled and molded. It is configured to be press-fitted into the inside of the outer tube 1. Such metal tubes are commercially available in various metal materials, various helical pitches, various tube diameters, and fin outer diameters. Although it is slightly more expensive than an axially finned metal tube, the heat transfer performance is dramatically improved, so the total cost can be significantly reduced compared to conventional structures.

Effects of the Invention As can be seen from its basic structure and examples, the heat exchange section of the double tube structure heat exchanger according to the present invention can be manufactured extremely simply and inexpensively, and at the same time has a heat exchange performance of 10 times or more. It is possible to improve the performance.

Therefore, it is possible to significantly shorten the length of the double tube for heat exchange, and in the case of a multi-tube heat exchange section, the number of double tubes can be significantly reduced. This makes it possible to reduce the size and weight of the entire heat exchanger, improve performance, and improve thermal response, and furthermore, it becomes possible to reduce the cost of the heat exchanger. The configuration of the heat exchange section of the double tube structure heat exchanger according to the present invention is applicable not only to temperature difference heat exchange between liquid phase fluids, but also to heat exchange between gas phases and between gas phases. You can. Moreover, it can be applied not only to a heat exchange section that uses only simple sensible heat, but also to a heat exchange section that utilizes latent heat through phase conversion in a vapor phase process. It is also possible to obtain an effect by configuring it as a steam generating part (heat receiving part) and a condensing part (heat radiating part) of a heat pipe.

[Brief explanation of drawings]

1 and 2 are a partial cross-sectional view and a vertical cross-sectional view showing the basic structure of a heat exchange section of a double-tube heat exchanger according to the present invention. FIGS. 3 and 4 are schematic cross-sectional views showing applied embodiments of FIGS. 1 and 2. FIG. FIG. 5 is a cross-sectional view of a heat exchange section of a conventional double-tube heat exchanger. 1... Outer tube, 2... Inner tube, 3... Spiral fin,
4... Spiral channel, 5... Second inner tube, 6... Second spiral fin, 7... Second spiral channel, 8...
- Sealing part, 9... external wave heat transfer fluid, 10... countercurrent heat transfer fluid, 11... rising flow path fin (or turbulence generating means),
12...Counterflow path fin (or turbulence generating means). Figure 1 Figure 2 Figure 4 Figure 5

Claims (4)

[Claims] (1) A heat exchange part of a heat exchanger in which fluids with different temperatures flow through the gap between the outer and outer pipes and the inside of the inner pipe of a double pipe, and heat exchange is performed between the fluids, and the inner wall surface of the outer pipe and Spiral fins are provided at a predetermined portion between the outer wall surfaces of the inner tube, interposed in close contact with both wall surfaces, and at a predetermined pitch in the axial direction along both wall surfaces. A heat exchange section of a double tube heat exchanger, characterized in that a spiral flow path for fluid is formed in a gap. (2) When the inner tube in the heat exchange section is the first inner tube,
A second inner tube (or round rod) is inserted into a portion of the first inner tube where the spiral fins are provided, and
The second inner tube (or round bar) is also interposed between the inner wall surface of the inner tube and the outer wall surface of the second inner tube (or round bar) in close contact with both wall surfaces, and has a predetermined pitch in the axial direction along both wall surfaces. A spiral fin is provided, and the internal through-hole of the second inner tube is sealed or a flow rate adjustment means is provided in the second inner tube. A heat exchange section of a double tube structure heat exchanger according to scope item (1). (3) The spiral fin is made of a metal wire or metal tube made of a material with good thermal conductivity, as set forth in claim (1). Heat exchange part of double tube structure heat exchanger. (4) Claim (1) characterized in that a metal tube with spiral fins is used as the inner tube and the spiral fins, and the spiral fins are integrated into a metal tube and roll-molded. The heat exchange part of the double tube structure heat exchanger described in .