JPS5818094A - Evaporator - Google Patents

Abstract

PURPOSE:To reduce the resistance to two-phase fluid flow of a medium to be evaporated, by forming medium fluid passages and heating fluid passages alternately between heat exchanger plates which are arranged vertically and in parallel with each other, and disposing a corrugated plate formed with hollows at its ridge portions in each of the medium fluid passages. CONSTITUTION:Liquid passages 10 for passing a medium liquid 6 therethrough and heating fluid passages 11 for passing a heating fluid 19 therethrough are formed alternately between heat exchanger plates 9 which are arranged vertically and in parallel with each other. Further, a corrugated plate 13 is disposed under a trough 12 provided in each of the liquid passages 10. Here, arrangement is such that ridge portions 13a of the corrugated plate 13 are located near to the wall 9a of the liquid passage 10 and a proper number of hollows 14 are formed at the ridge portions 13a along the width of the plate 13 with proper intervals from each other. Vapor passages 17 surrounded respectively by liquid film flows 6a, 6b are formed under the trough 12 and the corrugated plate 13.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an evaporator used in Rankine cycles, refrigerators, electronic equipment, nuclear power plants, etc., using a low boiling point medium as a working fluid.

Conventionally, the most widely used evaporator is a shell-tube heat exchanger in which a number of circular tubes are housed in a cylindrical shell. In recent years, Rankine cycle power generation plants that use a low boiling point medium as the working fluid have attracted attention in order to effectively utilize low-temperature energy such as waste heat, geothermal heat, and ocean temperature differences. There is a demand for something smaller and with higher performance than the fell-tube type. In order to satisfy this demand, three types of heat exchangers as shown in FIGS. 1 to 3 have been proposed.

As shown in Fig. 1, the first heat exchanger is made by bending a metal strip to form a small-pitch waveform.
21 and separators are installed and joined alternately and in parallel,
A horizontal flow path 23 through which hot water 24 flows and a vertical flow path 25 through which a low boiling point medium 26 flows are formed. The low boiling point medium 26 is evaporated by heat exchange with the hot water 24, and the medium vapor 27 is evaporated.
It flows out. At this time, since a large amount of steam must be generated with a small temperature difference, the fins 21 are arranged closely to increase the heat transfer area per unit volume.

The second heat exchanger creates a thin liquid film on the outer peripheral surface of the heat transfer tube and evaporates it. That is, as shown in FIG. 2, when the cleaning medium liquid 28 is sprayed horizontally and above the heat transfer tube group 29 installed in several stages, each 112 of the heat transfer tube #29 is sprayed upward.
A liquid film 30 is formed on the outer peripheral surface of 9 m. In this case, heat is transferred from the heated fluid 31 inside each heat exchanger tube 29a to the tube wall of each heat exchanger tube 29m, and this heat is transferred to each heat exchanger tube 39m.
, through the interface between the tube wall and the liquid film 30, and through the liquid film 30 to reach the liquid film surface 30a, and this surface 304
Supply latent heat of vaporization to 1.

If the liquid film 30 can be kept thin, the resistance of the liquid film portion to heat flow will be reduced, thereby improving the heat transfer vehicle. In addition, in order to prevent the negative effects caused by the presence of a large amount of liquid inside the heat exchanger, such as the generation of bubbles from the heat exchanger tubes located below, the separation of liquid from the surface, and the movement of bubbles upward, a large amount of liquid The large resistance presented by the presence of Furthermore, by providing fine grooves in front of the fins on the outer peripheral surface of the heat transfer tube, it is possible to promote the transfer of evaporative heat.

As shown in the fsa diagram, the third plan is to form a thin film layer 34 of the medium liquid on the outer peripheral surface of the vertical pipe 32 through which the heating fluid 33 flows, and to cause the liquid to evaporate by flowing down. It is something. Such a heat exchanger is suitable for use in the chemical industry and the food industry, for example, for concentrating fruit juice, to shorten the contact time between a liquid and a heated surface to prevent quality deterioration of the liquid.

In the first plan, the medium liquid 26 and the generated steam 27 are narrowly partitioned and flow in the same direction through nine channels 25. In such a two-phase flow situation, the six flows of liquid and steam interfere with each other, so that some of the liquid may separate from the heated wall surface and be swept away by the steam flow. Because the steam flow does the work of displacing the liquid film and droplets, the pressure drop in the two-phase flow increases, and the pump power to drive the medium liquid flow increases, so the Rankine system uses a low-temperature heat source. This must be avoided as it will greatly reduce the useful work for the cycle. Furthermore, among the liquids swept away by the steam flow,
Because the amount that accounts for the heat transfer rate is released from the evaporator outlet without being evaporated, even though the heat transfer area has been increased by the densely arranged fins, these heat transfer areas do not work effectively. It is highly possible.

Although the second plan has a structure with less resistance to the flow of the medium, in reality, the liquid suspends at the bottom of the heat transfer tube 29m, forming a thick liquid film 30. Furthermore, although the lower heat transfer tubes receive the dripping liquid from the upper tube group, the liquid film 30 does not necessarily become thin over the entire outer periphery of the heat transfer tubes 2951, so the expected heat transfer promoting effect cannot be obtained.

On the other hand, when fins or grooves are provided on the outer peripheral surface of the heat exchanger tube 29a, the surface area of the heat exchanger tube 29m increases.

However, although the liquid film on the ridges of the fins or the protrusions between the grooves becomes thinner, the areas between the fins or inside the grooves are covered with a thicker liquid film, so that the heat transfer coefficient does not improve significantly. As described above, in the second plan, the medium liquid flows easily, but the heat exchanger volume cannot be dramatically reduced.

Furthermore, in the third plan, the medium liquid 34 flows down along the pipe wall of the vertical pipe 32, so that the suspension liquid 34 flows down as in the second plan.
There is no risk that the effective heat transfer area will decrease. However, heat transfer tube 3
2, it is necessary to supply a sufficient amount of medium liquid 34 from above so as not to form a dry surface at the bottom. Therefore, if the liquid film thickness is averaged over the entire length of the heat transfer tube,
The average liquid film thickness does not necessarily become smaller.

Therefore, a method can be considered to keep the liquid film thin by providing liquid supply ports at small pitches in the longitudinal direction of the heat transfer tube 32 and supplying a small amount of medium liquid to these supply ports. However, providing a large number of liquid supply ports complicates the structure, and furthermore, at operating points other than the planned load of the evaporator, the medium liquid flowing down from the upper liquid supply port does not completely evaporate and flows into the lower liquid supply port. As a result, the effluent and feed liquid overlap, significantly reducing the performance of the evaporator.

Furthermore, since the liquid flowing down from the upper liquid supply port is completely evaporated before reaching the lower liquid supply port, a dry heat transfer surface appears, and the performance of the evaporator is degraded. In this way, in the third option, it is difficult to significantly improve the performance of the evaporator, and even if the planned load operator could achieve high performance, it would be difficult to adapt it to the load fluctuations of the evaporator. To -. This may cause serious problems for plums when the capacity of the heat source fluctuates greatly, such as in an evaporator that uses waste heat.

In view of the above, the present invention is compact and has high heat exchange performance,
The purpose is to provide an evaporator with low resistance to two-phase flow of the medium to be evaporated, and a heat exchange plate is installed vertically between the working medium liquid header and the working medium vapor header. A medium liquid flow path and a heating fluid flow path are arranged in parallel to alternately form, and a cavity communicating with the liquid flow path is provided on the inner wall surface of the medium liquid flow path, and a bend is formed in the medium liquid flow path. The invention is characterized in that a band is provided, a bent part of the bent band is brought close to the inner wall surface, and a notch is provided in the bent part.

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

In FIGS. 4 and 5, 2 is a liquid header to which a liquid pipe 5 for introducing the working medium liquid 6 is attached, and 3 is a liquid header with a medium vapor 8.
The steam header 9 is equipped with a steam pipe 7 that leads out the water, and 9 is a heat exchange plate installed vertically and in parallel between the liquid header 2 and the steam header 3. Medium liquid flow path through which the medium liquid 6 flows (hereinafter referred to as F liquid flow path)
10 and heating fluid passages 11 through which heating fluid 19 flows are formed in an arbitrary number alternately. In the liquid flow path 10, an arbitrary number (5 in FIG. 5) of grooves 12 are arranged in parallel at appropriate intervals.

The liquid flow path 10 is constructed as shown in FIGS. 6 and 7. That is, bending bands 13 are provided below the gutter 12, and the bending portions 13a of the bending bands 13 are connected to the liquid flow path 1.
0 wall (heat exchange plate) 9a, and an arbitrary number of notches 14 are provided in the bending portion 13a in the forward direction at appropriate intervals. A vapor passage 17 surrounded by a liquid film and streams 61 and 6b is formed in the lower part of the gutter 12 and the bent band 13, respectively.

On the inner surface of the wall (heat exchange plate) 9m of the liquid flow path 10, a large number of cavities 15 having an equivalent cross-sectional diameter of 1 - or less are provided.
These characters 1 and 15 are communicated with the liquid flow path 10 via the opening 16.

Next, the operation of this embodiment configured as described above will be explained.

The liquid medium 6 flows into the header 2 (via the liquid line 5) and flows therein at a flow rate sufficient to maintain the free liquid level 20 in place. The medium liquid 6 flowing into each gutter 12 flows at a flow rate determined by the hydraulic head, which is proportional to the flow path cross-sectional area of the liquid flow at the gutter connection port in the wall of the header 2 and the distance from the free liquid surface 20. The medium liquid 6 that has flowed into each gutter 12 flows down from the gap between the gutter 12 and the wall surface 9a along the wall surface 9a and the bending IFI: iK as a liquid film flow of 6 m, (!b) and evaporates into vapor 8. The steam 8 flows toward the steam header 3, and the steam 8 collected in the steam header 3 flows out through the pipe 7.

The wall surface 9m has a cavity 15 and is configured as a porous surface that is effective for evaporative heat transfer. Liquid enters the cavity 15 through the opening 16. When the wall surface of the cavity 15 is heated with a slight temperature difference, this intruding liquid will evaporate 1...1 in a short time,
This steam is again blown out through the opening. When the liquid film 6a is thick, the vapor turns into bubbles and crosses the liquid film 6m to reach the liquid film surface. However, when the liquid film 6a is thin, the vapor does not form a bubble shape and eliminates the liquid film 6a. Steam withdrawal takes place.

In this case, even if the temperature difference between the wall 9a and the liquid film 6a is less than IC, steam is actively generated, so the heat transfer coefficient of the porous heat transfer surface is about 10 times that of a normal smooth surface.

The flow rate of the liquid film 6a flowing down through the notch 14 provided in the bending zone 13 in the liquid flow path 10 and the flow rate of the liquid film 6b flowing down along the bending zone 13 depends on the shape and dimensions of the notch 14. controlled. At this time, a liquid pool #) 18 is often formed between the bending band 13 and the wall surface 9a;
8, the porous heat transfer surface (wall surface -9i) in contact with this
It actively generates steam. If the bending band 13 is made of metal, heat is well transferred from the wall surface 9a to the bending band 13 through the bending portion 13b between adjacent notches 14, so the bending band 13 acts as a fin and prevents liquid from flowing. Z heating the membrane flow 6b,
It can actively generate steam.

By changing the dimension of the notch 14 provided in the bend J'1a in the vertical direction, it is also possible to provide a distribution of the liquid film thickness in the vertical direction. In other words, a large amount of liquid is supplied near the evaporator inlet where the temperature of the heating fluid is relatively high (below the flow path 10 in Figure 6), and the large temperature difference is effectively used to improve the overall performance of the evaporator. can be improved. Furthermore, by changing the bending pitch of the bending band 13 in the vertical direction, the bending pitch can be increased to increase the cross-sectional area of the vapor flow path 17 at a location where a large amount of steam is generated, for example, at the lower part of the liquid flow path 10 in FIG. may be made wider.

Note that when vapor bubbles are actively generated from the porous heat transfer surface, minute droplets are scattered when the liquid film peels off from the porous heat transfer surface or the vapor bubbles separate from the liquid surface, but these separated liquid falls downward and is collected in the bend zone.

As explained above, according to the present invention, it is possible to increase the heat transfer area per unit volume and to reduce the resistance to the flow of generated steam.

Furthermore, since a high heat transfer coefficient can be maintained regardless of the thickness of the liquid film flowing down the working medium liquid flow path, it is possible to prevent a decrease in heat exchange performance due to fluctuations in the liquid flow rate. Furthermore, by changing the supply amount of the working medium in the vertical direction of the evaporator, the temperature difference between the working medium and the heating fluid can be effectively used to improve the temperature efficiency.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a conventional evaporator, FIG. 2 is a new view of a tube group in another conventional evaporator, FIG. 3 is a perspective view of heat exchange tubes in yet another conventional evaporator, and FIG. FIG. 4 is a perspective view showing an embodiment of the evaporator according to the present invention, FIG. 5 is a longitudinal sectional view of the medium liquid flow path in FIG. 4, and FIG. A perspective view, FIG. 7 is a cross-sectional perspective view of a part of the medium liquid flow path of the same embodiment.゛2...Medium liquid header, 3...Medium vapor header, 9゜9a...Heat exchange plate, 10...Medium liquid flow path, ii...
- Heating fluid flow path, 13...Bending zone % 131...Bending portion, 14...Notch, 15...Cavity. Figure 2 Figure 4 Figure 6-/i '\i 5 Figure ↑ 〆7i Figure 7

Claims (1)

[Claims] Between the working medium liquid header and the working medium vapor header,
Heat exchange plates are installed vertically and in parallel to alternately form a medium liquid flow path and a heating fluid flow path, and the inner wall rM of the medium liquid flow path is
K is provided with a cavity that communicates with the liquid flow path, a bending band is provided in the medium liquid flow path, the bending part of the bending band is brought close to the inner wall surface, and a notch is provided in the bending part. An evaporator characterized by: