JPS603146B2 - Evaporator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field to which the Invention Pertains] The present invention relates to a double-pipe evaporator used in chemical plants, refrigerators, air conditioners, etc.

[Prior art and its problems] Generally, an evaporator is used in a cooling device as shown in FIG.
A refrigerating cycle is constructed by circulating a refrigerator (for example, R22) in the order of the condenser 2, throttle mechanism 3, and evaporator 4.
A cold water coil 5 is arranged in a heat exchange relationship to produce cold water,
This cold water is sent by the pump 6 to cooling water coils 71, 72, . . . 7n, which constitute the fan coil unit.
The fans 81, 82, . . . , 8n are used to cool the room.

Accordingly, as the evaporator used in the cooling device as described above, in order to realize the heat exchange relationship between the evaporator 4 and the chilled water coil 5, the simplest and lightest double-tube evaporator is used. It was getting worse.

In other words, an outer tube with a large diameter is placed over the outside of an inner tube with a small diameter to form an internal channel (inner channel) and an annular channel (outer channel), and one of these channels is filled with the fluid to be evaporated. Cold soot was flowed through one channel, and cold water, which was a heat exchange fluid, was flowed through another channel. However, in order to increase the amount of heat exchange using such an evaporator, it is necessary to lengthen the tube, but with a secondary structure, the amount of exchange does not increase despite the length, and the entire device There were disadvantages such as increased size. [Object of the Invention] The present invention improves the drawbacks of the prior art, and aims to provide a high-performance double-tube evaporator that has little change in local heat transfer coefficient during the evaporation process of the fluid to be evaporated. purpose.

[Summary of the invention] This invention comprises an inner pipe and an outer pipe to form an inner pipe passage and an annular passage, and a fluid to be evaporated such as cold soot is placed in one of the passages, and water or water is placed in the other passage. In a double pipe evaporator that evaporates the fluid to be evaporated by flowing a heat exchange fluid such as brine, the flow path for the fluid to be evaporated is an annular flow path in the first half of the flow separation, and the flow separation is performed in the middle of the evaporation process. In contrast, the second half is a double-tube type evaporator in which the flow path for the fluid to be evaporated is an internal flow path.

[Effects of the Invention] According to the present invention, since the regions with larger heat transfer coefficients of the channel in the pipe and the annular channel are used, a high-performance device that can obtain a large heat transfer coefficient as a whole can be achieved. Therefore, the entire evaporator can be made smaller.

[Embodiments of the Invention] Examples of the invention will be described below with reference to FIGS. 2 to 4.

FIG. 2 is a longitudinal sectional side view showing an embodiment of the double tube type evaporator according to the present invention. The double tube type evaporator of this invention has two
A set of double pipes A and B is prepared, one end of the inner pipe 11 of the double pipe A is connected to the end of the outer pipe 12 of the double pipe B at the connection part C, and the outer pipe of the double pipe A is connected to the end of the outer pipe 12 of the double pipe B. It is constituted by an integral structure of a double pipe AB in which one end of the double pipe AB is connected to the other end of the inner pipe 14 of the double pipe B at a connecting part ○. Then, a refrigerant E, which is a fluid to be evaporated, is flowed from the annular flow path end of this double pipe A, and water or brine, which is a heat exchange fluid that exchanges heat with this cold butterfly to create cold water F, is inside the pipe of the double pipe A. It is configured to flow from the end of the flow path.Next, the reason why the double pipe evaporator is constructed as described above will be explained.

In Fig. 1, the dryness of the soot flowing into the evaporator 4 is
The degree of dryness is 0.2 to 0.3 (20 to 30% of the cold soot has evaporated), and the degree of dryness gradually increases in the evaporator until it reaches a degree of dryness of about 1 (nearly 100% evaporated, or in some cases exits the evaporator in the form of slightly heated vapor). Changes in the heat transfer coefficient of the cold soot during this evaporation process are as shown by characteristic curves a and b in FIG. 3, depending on whether the cold soot flow path is inside (pipe flow path) or outside (annular flow path). This is due to the formation of a liquid film along the wall within the cross section of the channel when the mixture of cold soot liquid and vapor flows through the channel. When the refrigerant flows inside (intra-pipe flow path), all of the liquid flows as a liquid film along the inner wall of the inner pipe, which is a heat transfer surface. Especially when the dryness is low near the inlet of the evaporator, the liquid film is thick and the heat transfer coefficient is low, but as the dryness increases as evaporation progresses, the liquid film becomes thinner and the heat transfer coefficient increases. . On the other hand, when cold soot flows on the outside (annular flow separation), a liquid film is formed not only on the inner wall of the outer pipe but also on the outer wall of the inner pipe, so the liquid film on the outer wall of the inner pipe, which is the heat transfer surface, is thinner than on the inner pipe channel. As a result, the heat transfer coefficient increases. However, the liquid film that forms on the outer wall of the inner tube is unstable, and as the dryness increases and the steam flow rate increases, it becomes easier to scatter in the steam flow, resulting in a state where there is no liquid film on the heat transfer surface (dry out). begins to occur. As a result, the heat transfer coefficient decreases as the degree of dryness increases, resulting in a curve like characteristic b. Fourth
The figure is a specific example showing the relationship shown in Figure 3, with an outer diameter of 1
This is when a steel pipe with a skin thickness of 5.9, a wall thickness of 0.8 ribs, and an inner diameter of 24 skin is used as the outer pipe.

The refrigerant is 280k9'h and the heat flow rate is 7kcal's. The heat transfer coefficients on the inside (pipe flow path) and outside (annular flow path) are indicated by △ and ○ marks, respectively, and it is recognized that the same characteristic curves as in Figure 3 are obtained. In the first half of the vessel, the cold soot flow path is an annular flow path (outside), and in the middle of the evaporation process, the flow path is reversed, and in the second half, the cold soot flow path is made into an internal flow path (inside). The heat transfer coefficient can be utilized.

This state is shown by a solid line in FIG. In addition, the broken line in FIG. 3 shows the change in the heat transfer coefficient when the flow path is not reversed. In addition, the present invention is not limited to the above-mentioned embodiment, and instead of a single inner tube, a plurality of inner tubes may be provided in the outer tube flow path so as to be spaced apart from each other and facing east.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the basic concept of a cooling device, and FIG. 2 is a longitudinal sectional side view showing an embodiment of a double pipe evaporator according to the present invention.
FIG. 3 is a diagram showing changes in the fluid to be evaporated for explaining the double tube type evaporator according to the present invention, and FIG. 4 is a diagram showing a specific example of FIG. 3. 11, 14... Inner tube, 12, 13... Outer tube, 16, 17... Annular flow (outer tube), A, B...
...Double pipe, C, D...Connection part, E...
...Fluid to be evaporated, F...Heat exchange fluid. Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] 1 The inner tube and the outer tube constitute an inner tube flow path and an extra tube flow path surrounding this inner tube, and the fluid to be evaporated is placed in either of the flow paths.
In an evaporator that evaporates the fluid to be evaporated by flowing the fluid to be evaporated through another flow path, in the first half of the flow path where the degree of dryness is small, the flow path for the fluid to be evaporated is made an extra-tube flow path, and in the middle of the evaporation process, The evaporator is characterized in that the flow path is reversed in the latter half of the period when the degree of dryness is large, and the flow path for the fluid to be evaporated is made into an internal flow path.