JPS5818095A - Evaporator - Google Patents

Abstract

PURPOSE:To reduce the resistance to two-phase fluid flow of a medium to be evaporated, by arranging heat exchanger plates having corrugation with a constant pitch in the vertical direction to extend vertically and in parallel with each other, and forming cavities and grooves respectively at upward inclined sections and downward inclined sections of the corrugation on the side thereof facing the fluid passages of a work medium. CONSTITUTION:Each of heat exchanger plates 9 is formed with corrugation with a constant pitch P in the vertical direction. By connecting each two heat exchanger plates 9 facing toward each other by means of connecting plates 10, there are formed alternately medium liquid passages 11 formed with enlarged sections 11a and contracted sections 11b alternately and having an open top and a closed bottom and heating fluid passages 15 formed with contracted sections 15a and enlarged sections 15b alternately and having both of the upper and lower ends opened are formed alternately between the heat exchanger plates 9. Further, many cavities 12 are formed at upward inclined sections 9a of the passage 11, while a proper number of small grooves 14 capable of attracting liquid film 22 by the capillary action are formed at downward inclined sections 9b of the passage 11.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a two-kinnel system using a low boiling point medium as a working fluid;
It relates to evaporators used in refrigerators, electronic equipment, nuclear power plants, etc.

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 plants that use a low boiling point medium as the working fluid have been attracting 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 tube type one. In order to satisfy this demand, three types of heat exchangers as shown in FIGS. 1 to 3 have been proposed.

As shown in Figure 1, the heat exchanger of the first plan has fins 31 formed by bending metal strips to have small pitch corrugations and separators installed alternately and in parallel. join,
A horizontal flow path 33 through which hot water 34 flows and a vertical flow path 35 through which a low boiling point medium 36 flows are formed. The low boiling point medium 36 undergoes heat exchange with the hot water 34 and evaporates into medium vapor 3.
7 and flows out. At this time, since it is necessary to generate a large amount of steam with a small temperature difference, the nine fins 31 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 chamber and evaporates it. That is, as shown in FIG.
A liquid film 40 is formed on the outer peripheral surface of m. In this case, from the heating fluid 41 flowing in each heat exchanger tube 39a to each heat exchanger tube 39a
This heat is transferred to the inside of each heat transfer tube 3951, the interface between those tube walls and the liquid film 40, and the liquid film 40.
and reaches the liquid film surface 40a, supplying latent heat of vaporization to this surface 40a.

If the liquid jl[40 can be kept in a thin layer, the resistance of the liquid film portion to heat flow will be reduced, so that the heat transfer coefficient can be improved. In addition, in order to prevent adverse 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, The large resistance presented by the presence of Furthermore, by providing fine fins or grooves on the outer peripheral surface of the heat transfer tube, it is possible to promote evaporative heat transfer.

In the third plan, as shown in FIG. 3, a thin film layer 44 of a medium liquid is placed on the outer peripheral surface of a vertical pipe 42 through which a heating fluid 43 flows.
It is designed to cause evaporation by forming and flowing down. 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 36 and the generated steam 37 flow in the same direction through the narrowly partitioned channel 35. In this tight two-phase flow situation, the combined flow of liquid and steam interfere with each other, so there is a risk that some of the liquid will separate from the heated wall surface and be swept away by the steam flow. Because the vapor flow does the work of displacing the liquid film and droplets, the pressure drop in two-phase flow increases, and the pump power required to drive the media liquid flow increases, making use of a low-temperature heat source. For the Rankine cycle, this must be avoided as it will greatly reduce the effective work. Furthermore, a large proportion of the liquid flowing into the steam stream is released from the evaporator outlet without being evaporated, so even though the heat transfer area has been increased by the densely arranged fins, First, there is a high possibility that these heat transfer areas will not operate effectively.

Although the second plan has a structure with less resistance to the flow of the medium, in reality, the liquid hangs below the heat transfer tube 39a, forming a thick liquid film 4o. Furthermore, although the lower heat transfer tube receives the dripping liquid from the upper tube group, the expected heat transfer promoting effect cannot be obtained because the liquid film 4o does not necessarily become thin over the entire outer periphery of the heat transfer tube 39m.

On the other hand, when fins or grooves are provided on the outer peripheral surface of the heat exchanger tube 39m, the surface area of the heat exchanger tube 39m 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 exchange volume cannot be dramatically reduced.

Furthermore, in the third plan, the medium liquid 44 flows down along the pipe wall of the vertical pipe 42, so that the suspended liquid is used as in the second plan.
) *There is no risk that the effective heat transfer area will decrease. However, as the heat transfer tube 42 becomes longer, it is necessary to supply a sufficient amount of the medium liquid 44 from above so as not to form a dry surface in the lower part.

Therefore, when the liquid film thickness is averaged over the entire length of the heat exchanger tube, the average liquid film thickness does not necessarily become small.

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 42 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. Because it reaches
The effluent and feed liquid overlap and significantly reduce the performance of the evaporator.

In addition, 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, which reduces the performance of the evaporator.

In the third option, it is difficult to significantly improve the performance of the evaporator, and even if high performance can be obtained under the planned load, it is extremely difficult to adapt to the fluctuations in the evaporator load. be. This may pose a particularly serious problem when the capacity of the heat source fluctuates widely, such as in an evaporator that utilizes 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 the two-phase flow of the medium to be evaporated, and a waveform with a constant pitch is formed in the vertical direction between the header of the working medium liquid and the header of the working medium vapor. The heat exchange plates formed to have such a shape are installed vertically and in parallel to alternately form a working medium liquid flow path and a heating fluid flow path, and the working medium in the upwardly inclined part and the downwardly inclined part of the heat exchanger plate waveform is arranged vertically and in parallel. It is characterized in that a cavity and a groove are provided on the surface on the side of the liquid flow path.

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

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 having a medium vapor 8.
A steam header is attached with a steam pipe 7 for deriving the water, and 9 is a heat exchange plate installed in any number vertically and in parallel between the liquid ladder 2 and the steam header 3. A medium liquid channel 11 through which a medium liquid 6 flows and a heating fluid 1
An arbitrary number of two circulating heating fluid channels 15 are formed alternately.

As shown in FIG. 6, the heat exchange plate 9 is formed in a waveform with a constant pitch P in the vertical direction, that is, upwardly inclined portions 9a and downwardly inclined portions 9b are alternately arranged in series. By joining the opposing heat exchange plates 9 together at the lower ends via the coupling plate 10, the enlarged parts 11a and the reduced parts 11b are arranged in succession alternately, and the upper and lower ends are respectively opened and closed. A closed medium liquid flow path 11 is formed, and a heating fluid flow path 15 is formed in which contracted portions 15a and enlarged portions 15b are alternately arranged and open at the upper and lower ends.

The medium liquid flow path 11 has a groove 16 as shown in FIG.
An arbitrary number (5 in the figure) of .delta. are arranged in parallel at appropriate intervals, and a liquid reservoir 17 for storing a medium liquid having a free liquid surface 19 containing vapor bubbles 18 at the bottom is provided. In addition, the inner surface of the upwardly inclined portion 9a, that is, the medium liquid flow path 1
1 has an equivalent cross-sectional diameter of 1 as shown in FIG.
■ A large number of cavities 12 are provided as shown below.
is communicated with. On the other hand, an arbitrary number of fine grooves 14 are provided on the inner surface of the downwardly inclined portion 9b and have the function of adhering the inner surface film 22 by capillary force.

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

The liquid medium 6 flows into the v liquid header 2 by means of liquid piping 5 and flows within the header 2 at a flow rate sufficient to maintain the free liquid level 20 in place. The medium liquid 21 flowing into each gutter 16 flows at a flow rate determined by the liquid flow path cross-sectional area at the gutter connection port on the wall of the header 2 and the hydraulic head which is proportional to the distance from the free liquid surface 20 of the liquid header 2. . The medium liquid that has flowed into the gutter 16 passes through the gutter 16 and the heat exchange plate 9.
A liquid film flow 22 appears from the gap between the medium and liquid, and evaporates while flowing down along the corrugated surfaces of both heat exchange plates 9 forming the medium liquid flow path 11 to generate steam 8. This steam 8 flows toward the steam rudder 3 , and the steam 8 collected in the steam header 4 flows out via the pipe 7 .

On the other hand, the hot water 12 flows in from the bottom opening 15C of the heated fluid flow path 15 formed by the adjacent heat exchange plates 9, and flows alternately through the contracted portion 15a and enlarged portion 15b of the flow path 15. Due to the turbulence n of the water flow and the accelerated flow in the contraction part 15a,
Heat is transferred from the hot water 12 to the heat exchange plate 9 at a high heat transfer coefficient. This transferred heat is transferred to the liquid film flow 22 in the medium liquid flow path 11.
evaporate. Liquid film flow 2 flowing down due to the turbulence of the water
The liquid droplets peeled off from the medium liquid flow path 11 and the liquid that has not completely evaporated due to the unsteady temperature drop of the hot water 12
The liquid accumulates in a liquid reservoir 17 at the bottom of the liquid, forming a free liquid level 19.

However, the evaporative heat transfer surface (upward inclined surface) 9 of the heat exchange plate 9.
Since the porous surface 1 is configured to be effective for nucleate boiling heat transfer, bubbles 18 are actively generated from the heat transfer surface 9a in contact with the liquid reservoir 17, so that a high heat transfer coefficient can be achieved.

That is, by the ejection of steam from any aperture 13, liquid enters the cavity 1.2 from other apertures 13 in order to supplement the steam mass escaping from that cavity 12. When the wall surface of the cavity 12 is heated with a slight temperature difference, this infiltrated liquid evaporates in a short time to generate steam, which is again jetted out through the opening. When the liquid film 22 is thick,
The vapor crosses the liquid film 22 in the form of bubbles 18 and reaches the surface of the liquid film, but if the liquid film 22 is thin, the liquid film 22 does not form a bubble shape. Evacuation of steam takes place. In this case, the temperature difference between the heat exchange plate 9 and the medium liquid of the liquid film flow 22 is I
Since steam is actively generated even when the temperature is below C, the heat transfer coefficient of the porous heat transfer surface is about 10 times that of a normal smooth surface.

If steam generation from the heat exchange plate 9 is active, the turbulence of the liquid film flow 22 will be large, and there is a risk that the liquid film will peel off from the heat transfer surface. In order to prevent this peeling, let β be the inclination angle of the upwardly inclined portion 9a provided on the heat exchange plate 9 as shown in FIG. 7, and this β is set so as to satisfy the following condition.

β＞5in-'(''h) gρvhfg 4 is heat flux (W/cn1''), g is gravitational acceleration (Cr
n/S2), ρ is the vapor density (g/crr1”), ht,
is the latent heat of vaporization (J/g), f is the foaming frequency (S-1), Freon medium (R-11) is evaporated, q; IW/
cIr1! In the case of , β, ;:5.4@.

Further, the width Wm of the downwardly inclined surface 9b is provided to hold the liquid film flow 22 against gravity by capillary force, and the width Wm of this 1s14 is set as follows.

3 W = (4σ/p, II) σ is the surface tension of the fluid ('yne/cm), Pz is the density (g/cW1''), and Freon medium (R, -11)
In this case, it becomes VV-0,4cn4.

The flow rate of the medium liquid is large, for example, Freon medium (R-11
) If the liquid film thickness exceeds 4 m, the above ? With this method, it is difficult to maintain a liquid film.

In order to solve this problem, as shown in FIG. The medium liquid film flow path 26 may be formed between the downwardly inclined portion 9b and the guide 25 by installing the guide 25 so as to face the portion 9b. It would be even more effective if the lower sloped portion .

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 improving the heat transfer coefficient of the heat transfer surface of the heating fluid flow path, it is possible to generate a large amount of steam even when the volume is small and the difference between the temperature of the heating fluid and the temperature of the medium is small. It is.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a conventional evaporator, FIG. 2 is a sectional 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. The figure is a perspective view showing one embodiment of the evaporator according to the present invention, FIG. 5 is a vertical cross-sectional view of the medium liquid flow path in FIG. 4, and FIG. Near the bottom in Figure 5) cross-sectional perspective view,
FIG. 7 is a cross-sectional perspective view of the main part of the heat exchange plate of the same example, and FIG.
The figure is a cross-sectional perspective view of a main part of a heat exchange plate according to another embodiment of the present invention. 2... Medium liquid header, 3... Medium vapor header, 9...
...Heat exchange plate, 9a...Upward inclined part, 9b...Downward inclined part, 11-...Medium liquid channel, 12...Cavity,
14...Groove, 25...Guide, 26...Liquid film flow channel. FJ 4th ↑ 67'I 65 Figure ↑ 7i ¥rg Figure 1! ; 7,000 figures

Claims (1)

[Claims] 1. Between the working medium liquid header and the working medium vapor header, a heat exchange plate formed to have a waveform with a constant pitch in the vertical direction is installed vertically and in parallel to connect the medium liquid flow path and heating. Fluid channels are formed alternately, and the heat exchange plate has a large number of cavities on the surface of the upwardly inclined portion facing the medium liquid channel, and a large number of openings that communicate these cavities with the medium liquid channel, and a plurality of holes below the holes. An evaporator characterized in that a large number of grooves are provided on the surface of the heat-protecting slope on the medium liquid flow path side.・2. A guide is provided in the medium liquid flow path at an appropriate distance from the downwardly inclined part of the heat exchange plate, and a flow path for retaining the medium liquid film flow is formed between this guide and the downwardly inclined part. An evaporator according to claim 1, characterized in that: