JPS59122894A - Heat transfer pipe of down-flowing liquid film type evaporator - Google Patents

Abstract

PURPOSE:To stabilize and to improve the heat transfer efficiency of the heat transfer pipe by a method wherein two heat exchange promotable corrugated sections are arranged parallel to each other in different phases along the axis of the heat transfer pipe. CONSTITUTION:In the case of the down-flowing liquid film type evaporator, a heated fluid flowing out from a fluid distributor flows down as it covers the heat transfer pipe 21 in the form of a film. When the liquid film begins to flow down, the thickness of the film is not uniform but the fluid 1 flowing down in the concave sections 24 of the second heat exchange promotable corrugated section 23 in the upper stage flows down vertically and is divided into a stream 2 flowing over the convex sections 27 of the first heat exchange promotable corrugated section 22 and streams 3 and 4 flowing separately into the concave sections 26 on both sides of the concave sections 27, respectively. Further, a stream 5 of the fluid flowing down over the upper stage convex sections 25 flows into the lower stage concave sections 26 and joins together. Thus, by such tributory flow and the joined flow of the fluid, the thickness of the fluid is made uniform in the circumferential direction, a dry patch disappears in a short time and the heat transfer efficiency of the heat pipe can be maintained high.

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to a heat transfer tube for a falling film evaporator, and in particular, to improve heat transfer efficiency by providing steps on the outer surface of the heat transfer tube with different concave and convex periods. The present invention relates to a heat exchanger tube for a falling film evaporator that can improve performance.

[Technical background of the invention]

Falling film evaporators are used, for example, in ocean thermal power generation plants.

Generally, as shown in Fig. 1, in an ocean thermal power generation plant, relatively high temperature seawater at the seawater surface is introduced into an evaporator 1, and a working fluid (for example, a low boiling point medium such as fluorocarbon or ammonia) is supplied thereto. The steam is heated and evaporated and introduced into the turbine 2 to perform expansion work and drive the turbine 2. The turbine 2 is driven to rotate the generator 3, and the steam discharged from the turbine 2 is condensed with relatively low-temperature seawater in the deep seawater in the condenser 4&C, and the condensed water is temporarily stored in the tank 5. After that, it is returned to the evaporator 1 by the circulation pump 6. The amount of evaporation from the evaporator 1 is always kept constant, and the driving force of the turbine 2 is adjusted by opening and closing the turbine bypass valve 7 in response to changes in the load of the generator 3.

As the evaporator of this seawater temperature difference power generation plant, a falling liquid film type as shown in Fig. 2, Fig. 3, Fig. 4, Fig. 5, and Fig. 6 is often adopted. . Second
As shown in the figure, the falling film evaporator 11 has a heating fluid (
Surface seawater) is introduced into the vessel from the inlet port 12 and is caused to flow through the heat transfer tubes 13 arranged in a large number in the vertical direction. On the other hand, the fluid to be heated flows in from the inlet port 14 and is stored on the partition plate 15, flows down from the gap between the partition plate 15 and the heat transfer tubes 13 along the outer surface of each heat transfer tube 13, and While it is flowing down, it is heated and a part of it evaporates and flows out from the outlet port 16 (in addition, the heated fluid that has not evaporated is reintroduced into the inlet port 12 by a pump (not shown). It has become so.

Further, as shown in FIG. 3, the heat transfer tube 13 is provided so as to pass through the partition plate 15, and is a cylindrical fluid distribution tube that is fitted and fixed in a through hole formed in the partition plate 15. Vessel 1
The heat exchanger tube 13 is loosely fitted inside the tube 7.

The gap 1 between the heat transfer tube 13 and the fluid distributor 17
The fluid to be heated flows out from 8 along the periphery of the heat transfer tube 13 (.

Furthermore, as shown in FIGS. 4, 5, and 6, the heat exchanger tube 13 has recesses 13a and protrusions 13b along the circumferential direction of the outer surface in order to improve the heat transfer coefficient. A wave-shaped heat exchange enhancing uneven part formed by alternating rows is provided,
The concave portion 13a and the convex portion 13b extend in a constant shape in the tube axis direction.

[Problems with background technology]

However, the distance between the heat exchanger tubes 13 and the fluid distributor 17 is usually 0.5 m -0.111i! It is extremely difficult to uniformly provide such a small gap around the tube because the gap is set at such a small distance.

As a result, the fluid to be heated flows out from the outlet of the fluid distributor 17 in a non-uniform manner in the circumferential direction, and a liquid film of an unrestricted thickness is formed around the heat transfer tube 13 over the entire length of the tube, deteriorating the heat transfer efficiency. Furthermore, dry patches often occur in areas where the liquid film is thin, and when such dry patches occur, the fluid to be heated is no longer permanently supplied to that area, and heat transfer As a result, the amount of evaporation decreases accordingly, and the heat transfer efficiency also decreases, resulting in a decrease in the operating efficiency of the entire plant.

[Purpose of the invention]

An object of the present invention is to eliminate the above-mentioned drawbacks of conventional falling film evaporators, and to provide a falling film evaporator with uniform liquid film thickness and high heat transfer efficiency.

[Summary of the invention]

In order to achieve the above object, the present invention provides a heat exchange uneven stepped portion in which uneven portions having a predetermined length in the tube axis direction are alternately formed along the circumferential direction of the outer surface of the heat transfer tube. The pipe is characterized by having multiple stages arranged in parallel, and each adjacent heat exchange uneven step section having a different period of unevenness in the circumferential direction, so that the fluid to be heated flowing on the tube surface merges.

I am trying to repeat the diversion.

[Embodiments of the invention]

Embodiments of the present invention will be described in detail below with reference to the drawings.

As shown in FIGS. 7 to 11, the outer surface of the heat exchanger tube 21 in one embodiment of the present invention has a first heat exchange enhancing uneven portion 22 and a second heat exchange enhancing uneven portion 23 in the tube axis direction. The first and second heat exchange enhancing uneven parts 22 and 23 are formed in a wave shape by connecting a recess 25 and a convex part 25 and a recess 26 and a convex part d in the circumferential direction, respectively. has been done. The wave-shaped uneven portions 24 of the first and second heat exchange enhancing uneven portions 22 and 23 adjacent to each other in the tube axis direction
, 25, 26, and 27 are provided so as to be offset from each other in the circumferential direction, and the periodic phases of the wave-shaped uneven portions 24, 25, and 26°d of the respective heat exchange enhancing uneven portions 22, 23 are different from each other. ing. As a result, the concave portions 24 and 26 of one heat exchange enhancement uneven portion 22 are connected to the convex portion 25°γ of the other adjacent heat exchange enhancement uneven portion 23 in the tube axis direction,
Furthermore, the convex portions 25 and 27 on one side correspond to the concave portions a and 26 on the other stage.
It is connected to Therefore, the recesses 24 and 26 on both stages
The protrusions δ and 27 are not adjacent to each other. Note that the concave portions 24 and 26 and the convex portion 25% 27 are extremely smoothly connected, making it easy for the fluid to flow.

In the heat exchanger tube of the falling film evaporator having such a configuration, the fluid is provided at the upper part of the heat exchanger tube.

The fluid to be heated flows out from the inner circumferential gap of the distributor and flows down while covering the heat transfer tube 21 in a film shape. At the beginning of the flow, the thickness of the liquid film is uneven, but as shown by the arrow in FIG. As shown in , the fluid ■ that has flowed down through the concave part on the upper stage side continues to flow down in the vertical direction and flows over the convex part n on the f side.
The flow is divided into (1) and (2) which are divided into the concave portions 26 and 26 on both sides of the lower convex portion l. Further, the fluid (2) that has flown down on the upper convex portion 25 almost flows down as it is, flows into the lower concave portion 26, and is divided into flows (2) and (2) from the upper concave portion (1).

As a result, the fluid in the part where the liquid film is thick repeats the above-mentioned branch flow 9 convergence and flows into the thin part of the liquid film, and the thickness of the liquid film formed on the outer surface of the heat transfer tube 21 is The heat transfer efficiency is maintained evenly in the circumferential direction and extremely high. moreover,
Even if a dry patch occurs, fluid immediately flows into the area where the dry patch occurs from the upper stage, so the dry patch disappears in a very short time, and 1. The function as a heat transfer surface is immediately restored.

〔Effect of the invention〕

As described above, the present invention provides first and second heat exchange enhancing uneven portions formed by forming wave-shaped uneven portions of a predetermined length in the circumferential direction, which are alternately arranged in parallel along the tube axis direction of the heat exchanger tube. , the periodic phase of the irregularities of the first heat exchange enhancing uneven part and the second heat exchange enhancing uneven part are made different so that the fluid to be heated flowing down the heat exchanger tube is divided into 9 converges. The thickness of the liquid film of the fluid to be heated can be made uniform in the circumferential direction, dry patches can be immediately eliminated, and a stable falling liquid film steam generator with extremely high heat transfer efficiency can be provided.

[Brief explanation of drawings]

Figure 1 is a system diagram of a general ocean temperature difference power generation plant, Figure 2
The figure is a longitudinal sectional view of a falling film evaporator, Figure 3 is a partial enlarged view of the heat exchanger tube attachment part 9, and Figures 4, 5, and 6 are cross sectional views and partial side views of conventional heat exchanger tubes. FIG. 7 is an enlarged partial cross-sectional view, and FIG. 8 is a partial side view of a heat exchanger tube in an embodiment of the present invention. Figures 9 and 10 are cross-sectional views taken along line A-A in Figure 7;
11 is a partially developed perspective view of the heat exchanger tube shown in FIG. 7. 21... Heat exchanger tube, 22... First heat exchange enhancement uneven part,
23...Second heat exchange enhancing uneven portion, 24, 26...
Wavy concave, angry. d... Waveform convex portion. Applicant's agent Kiyoshi Inomata Figure 1 2 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 26 Figure 8 Figure 9 Figure 10 Figure 26 26 26

Claims (1)

[Claims] First and second heat exchange enhancing uneven parts are arranged alternately in the tube axis direction on the outer surface of the heat transfer tube; The heat exchange enhancing uneven portion is constituted by a series of unevenness having substantially the same waveform as the first heat exchange enhancing uneven portion, and the uneven periodic phases of the first and second heat exchange enhancing uneven portions are made to be different from each other. A heat transfer tube for a falling film evaporator characterized by: