JPS59100398A - Porous heat transfer surface - Google Patents

Abstract

PURPOSE:To obtain a reliable porous heat transfer surface having high heat transferring capacity and stable heat transferring property, by covering part of the upper part of a porous particle layer formed on a basic material of the heating surface with a foam inhibiting component regularly. CONSTITUTION:When resistance against an inflow and an outflow of a foam and a liquid is improved by providing a surface cover 12 obtained by providing a large number of regular openings 13 on a sintered particle layer 11, it becomes that pressure in the sintered particle layer 11 is added as a control factor, through which growth and separation of the foam and inflow of the liquid become subordinate with each other. As self-control, therefore, of the inflow and outflow-of the foam and liquid is made so that an inflow quantity of the liquid is decided according to a discharge quantity of the foam, a thin liquid film is formed within the sintered particle layer 11 always within the scope of a wide heat flux and high heat-transfer ratio can be obtained. Then discharge of the foam is performed from a large opening and the inflow of the liquid is made from a small opening by combining the large and small openings in relation to the opening 13 and replacement between the foam and the liquid begins to be carried out more smooth.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a porous heat transfer surface used in organic Rankine cycle steam generators, evaporators of refrigerators, coolers of DL devices, etc. It is.

[Prior art]

Conventional methods for improving the heat transfer performance of heat transfer surfaces used in evaporators include improving performance by expanding the heat transfer area as seen in fin tubes, and improving performance by using porous structures such as sintered particle layers. There are two ways to improve. The former is simply a passive method of enlarging the heat transfer surface, but the latter is a very effective active method of improving heat transfer performance from the viewpoint of the boiling heat transfer mechanism. To date, many types of heat transfer surfaces with this porous structure have been created, including those made of sintered particles and those made using a combination of mechanical and plastic processing.

FIG. 1 shows the principle of boiling on a porous heat transfer surface. Active pores 2 and inactive pores 4 are formed in a porous layer 8 consisting of a large number of sintered grains 1. In the active pores 2, bubbles grow and separate, and due to the accompanying pressure fluctuations in the porous layer 8 and the surface tension of the boiling liquid 70, the porous layer B shown by the arrow 5 in the inactive pores 4. An inflow of Mi liquid into the interior occurs.

This inflow liquid travels through the corners 9 existing in the connected cavities in the porous layer 8 and spreads over the entire porous layer 8 while forming a very thin liquid film. At this corner 9, since the liquid film is thin, heat transfer occurs with very low thermal resistance, and the liquid evaporates. This evaporated steam 6 turns into boiling vapor 3 from the active opening 2 and is blown out while causing a wake of boiling liquid 7. This wake promotes convective heat transfer on the outermost surface of the porous layer 8. The heat transfer coefficient of the porous heat transfer surface moves northward due to the evaporative heat transfer at the corner 9 and the convective heat transfer at the outermost surface.

Of the two methods mentioned in the prior art, the enlarged heat transfer surface has a limit in the expansion of the heat transfer area and cannot be expected to dramatically improve performance. On the other hand, the porous heat transfer surfaces that are currently commercialized have the following problems. That is, active pores, where bubbles grow and separate, and inert pores, through which liquid flows, are formed only by the non-uniformity of the porous layer, and two types of pores with different effects are:
This means that it is dispersed in an uncertain manner on the heat transfer surface. Therefore, since it depends on the production quality of the porous heat transfer surface, the heat transfer performance of each heat transfer surface varies widely, resulting in poor reliability. In addition, in order to maintain high heat transfer performance, the release of air bubbles from the porous layer and the inflow of liquid into the layer must be carried out under a balance between the vapor pressure within the layer and the surface tension of the liquid. is necessary, but since the number of openings is very large and the resistance to the inflow and outflow of gas and liquid is small, surface tension is the only governing factor. Therefore, especially in a low heat flux region, the amount of evaporation within the porous layer decreases, so the number of active pores decreases rapidly, and a large amount of liquid flows into the porous layer. Therefore, the cavities in the porous layer are filled with liquid, and a thin liquid film is not formed at the corners, resulting in a significant decrease in heat transfer performance.
One possible method to make it difficult for particles to enter the layer is to densely sinter fine particles. In this way, the liquid supply openings become smaller and the amount of liquid drawn into the porous layer is reduced. However, at the same time, the volume of the cavities within the porous layer also decreases, making it impossible to obtain a cavity volume sufficient to trap evaporated vapor within the porous layer. Furthermore, as the cross-sectional area of the cavity becomes smaller, the resistance to the flow of gas and liquid increases, which makes it difficult for vapor to escape from the inner layer of the porous layer and reduces the supply of liquid to the inner layer. I tend to become confused.

On the other hand, in a high heat flux region, most of the pores become active pores, and the inside of the porous layer becomes filled with steam. Therefore, heat transfer performance deteriorates and burnout becomes more likely.

[Purpose of the invention]

An object of the present invention is to provide a reliable porous heat transfer surface that has high heat transfer ability and stable heat transfer performance.

[Summary of the invention]

In order to achieve this object, the present invention has a porous particle layer formed on a heat transfer surface base material and a portion of the upper part of this porous particle layer that is regularly covered with a foam suppressing member. The porous heat transfer surface is made up of a layered skin.

[Embodiments of the invention]

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

The embodiment shown in FIG. 2 has regular openings 13 or slit-like narrow gaps 14 on the sintered particle layer 11 and the sintered particle layer surface, and regular openings 13 and slit-like narrow gaps. It is a porous heat transfer surface composed of a skin 12VC having both sides of 14. A sintered particle layer 11 is provided on the heat transfer wall 10, which is further covered with a skin 12 in which a large number of regular apertures 13 are made. Therefore, restrictions can be placed on the inflow of boiling liquid into the sintered particle layer 11 and the release of air bubbles from within the sintered particle layer 11. g1] Epidermis 12
When there is no bubble and the sintered particle layer 11 is exposed to the boiling liquid, the buoyancy and the surface tension of the gas-liquid interface are dominant factors in the growth and separation of bubbles at the bubble generation point.
The pressure (vapor pressure) of the cavity within the sintered particle layer 11 does not have much influence. On the other hand, at the boiling liquid supply point that covers most of the surface of the sintered particle layer 11, the capillary phenomenon (surface tension) in the narrow gap formed within the sintered particle layer 11 becomes the dominant factor.
Boiling ti is introduced into the sintered particle layer 11. therefore,
The growth and separation of bubbles and the supply of liquid are performed separately and independently, and the heat flux may cause the inside of the sintered particle layer 11 to be filled with liquid or filled with steam. Therefore, if a skin is provided on the sintered particle layer 11 to provide resistance to the inflow and outflow of bubbles and liquid, the pressure within the sintered particle layer 11 becomes the governing factor for each behavior (7). Through this pressure, the growth and separation of bubbles and the inflow of liquid become dependent on each other.Therefore, the inflow and outflow of gas and liquid is self-controlled in such a way that the amount of liquid inflow is determined according to the amount of bubble release. Therefore, a thin liquid film is always formed within the sintered particle layer 11 over a wide heat flux range, and a high thermal conductivity can be obtained.
By combining the sizes of the pores, air bubbles are released from the large pores and liquid flows from the small pores, which uniquely determines the peak opening for gas and liquid. The exchange of gas and liquid within the particle layer 11 is now performed more smoothly,
More effective. Regular openings 13 as shown in Figure 2
Instead, the same effect can be obtained by providing narrow slit-like gaps 14 obtained by regularly arranging band-shaped thin plates 15 on the sintered particle layer 11 at regular intervals as shown in FIG. I can cum. That is, the narrow slit-shaped gap 13 acts as an inflow/outlet for gas and liquid, but if the gap is sufficiently narrow, it becomes a resistance to the inflow and outflow of gas and liquid.
The pressure within the sintered particle bed 1 is a controlling factor for the inflow and outflow of gas and liquid. Therefore, the slit-shaped narrow gap 13 has the same function as the opening 13 shown in FIG.

In this case as well, by combining the width of the narrow slit-like gap 3 with the width, the inflow path for gas and liquid can be uniquely determined, and the exchange of gas and liquid can be performed more smoothly. . In addition, a strip-shaped thin plate 15 as shown in FIG.
A similar effect can be obtained by using a wire instead.

FIG. 4 shows a combination of an opening 13 and a narrow slit-like gap 14. This case also has the same effect as the two examples above, but by providing both the openings 13 and the narrow slit-like gaps 14, each having a different resistance coefficient, the number of inflow and outflow paths for gas and liquid is further increased. It is something.

Figure 2 above! The skin 12 shown in Figure t3 and Figure 4 does not need to be thermally connected to the sintered particle layer 11, for example,
When the heat transfer +bi is a vibrator, a porous heat transfer tube having high heat transfer performance according to the present invention can be obtained by wrapping the skin 12 on sintered Hiroshima a.

Furthermore, when a non-metallic plate material is used as the skin 2, the outer surface of the heat transfer surface becomes insulated, and most of the heat is transferred by evaporation within the sintered particle layer 1, especially in the low heat flux region. Active foaming also takes place.

Further, another embodiment of the present invention will be explained with reference to FIG.

Figure 5 shows a sintered particle layer 1 formed in an enemy shape at regular intervals.
1 and a skin 12 made of an adult-permeable material that covers part of this sintered particle layer 11 are constructed on the heat transfer wall 10 (an example of a porous heat transfer surface obtained by the above is shown). They are provided at regular intervals like the sintered particle layer 11 formed at the bottom.

Therefore, a narrow slit-like gap, that is, a surface opening 23
and forms an epidermal cavity 24 connected to the outer surface through this surface opening 23. - The liquid film formed at the corner inside the sintered particle layer 11 receives heat from the sintered particles and evaporates. On the other hand, this evaporated vapor is led to the epidermal cavity 24, where it is trapped for a certain period of time, and then released as bubbles to the outer surface through the surface openings 23. On the other hand, boiling liquid is
The supply to the sintered particle layer 11 is suppressed by the skin 1z, and instead of releasing the bubbles, an amount of boiling liquid commensurate with the released bubbles is guided from the surface opening 23 to the epidermal cavity 24. The eruption ma entering through the surface opening 23 spreads so as to wet the entire side wall of the epidermal cavity 24 while propagating inside the enemy-like sintered particles 1-11 by capillary action. That is, according to this example, the sintered particle layer on the heat transfer wall side, which has the highest temperature on the heat transfer surface, can be kept wet with the liquid, and furthermore, the liquid and vapor can be kept on the surface of the skin. The amount of inflow and outflow of gas and liquid is self-controlled by the cavity 24 and the surface opening 23.

In addition, by making the width of the skin 120 larger than the width of the sintered particle layer 11, the steam and liquid held in the skin F cavity 24 can be used more effectively.

FIG. 6 shows another embodiment of the invention. In this embodiment, a sintered particle layer 11 formed in a sweetfish shape and a skin 12 covering a portion of this sintered particle layer 11 are alternately combined on a heat transfer wall 10 at intervals of manual labor. 1″M of porous type M-plane
shows.

The surface opening 27 formed at the larger distance has a skin cavity 25 connected to the outer surface through this surface opening 27 . Similarly, the surface-facing openings 26 formed at the smaller interval have epidermal cavities 24 . Sintered particle layer 1
The evaporated vapor generated within 1 is directed into the epidermal cavity 25, which communicates with a large surface opening 27, where the flow resistance of the vapor to the outer surface is low. There, after being trapped for a certain period of time, it becomes a bubble and is released through the large surface opening 27 to the outer surface. On the other hand, with the foaming from the large surface openings 27,
Boiling liquid flows into the epidermal cavity 24 through small surface openings 26 . The boiling liquid introduced into the epidermal cavity 24 spreads over the entire side wall of the epidermis F cavity 24 while propagating inside the enemy-like sintered particles (11) by capillary action. According to this embodiment, the inflow path of gas and liquid can be separated, such that steam is released from the large surface opening 27 and boiling liquid flows in from the small surface opening 26, and the flow of gas and liquid is stabilized. becomes.

FIG. 7 shows another embodiment of the invention. This embodiment differs from the embodiment shown in FIG. 5 in that a plurality of openings 28 are provided in the skin 12. By providing the apertures 28 in the skin 12, vapor bubbles are released from the surface apertures 13, and the boiling liquid is sucked through the apertures 28. Therefore, the inlet and outlet of gas and liquid are separated, and the flow becomes stable. Further, unlike the embodiment shown in FIG. 6, the inflow amount of the boiling liquid is not controlled by the spacing between the skins 12, which facilitates manufacturing.

FIG. 8 shows another embodiment of the invention. In this embodiment, the skin 1 forming the surface opening 23 of the embodiment shown in FIG.
This is a waveform of 2. By waving the epidermis 12, large surface openings 30 and small surface openings 29 are formed on the same row.
is formed. Vapor bubbles are released from the large surface openings 30, and liquid is sucked through the surface openings 29. Therefore, the inlet and outlet of gas and liquid are separated, and the flow becomes stable. Further, unlike the embodiment shown in FIG. 6, the opening width is not controlled by the spacing between the skins 12, which makes manufacturing easier.

FIG. 9 shows another embodiment of the invention. In this embodiment, the upper part of the sintered particle layer 11 formed in an enemy shape is inclined, and the skin 12 covering the inclined sintered particle layer 11 is attached to the heat transfer wall 10.
An example of a porous heat transfer surface obtained by constructing the above is shown. This skin 12 forms a large side opening 31 and a small side opening 32 by the sintered particles Njjll whose upper part is inclined between the skin 12 and the heat transfer wall lO. Steam bubbles are released from the large side openings 31 and boiling liquid is sucked through the small side openings 32. Therefore, the inlet and outlet of gas and liquid are separated, and the flow becomes stable.

FIG. 10 shows another embodiment of the invention. In this example,
The surface apertures 29 and 30 of the embodiment shown in FIG. 8 are not connected to each other, but are made to be independent, making the surface apertures 33 more restricted.

By making the surface apertures 33 more restricted, the resistance to vapor bubble release is increased. Therefore, more vapor can be trapped within the epidermal cavity 24, the pressure within the epidermal cavity 24 increases, and the range of pressure fluctuations accompanying the release of vapor bubbles increases.

Therefore, the inflow of the boiling liquid into the epidermal cavity 24 is restricted, and only the amount of liquid commensurate with the amount of released vapor bubbles flows in, so that the inside of the epidermal cavity 24 and the sintered particle layer 11 is reduced. It is possible to avoid the situation of being filled with liquid.

Therefore, in particular, the amount of evaporation within the porous layer is small, and high heat transfer performance can be maintained even under low heat flux where the inside of the porous layer is filled with liquid.

FIG. 11 shows another embodiment of the invention. In this example,
The side openings 31 and 32 of the embodiment shown in FIG.
4 also covers the side surfaces of the sintered particle layer 11. Epidermis 3
By changing the size of the side surface of the sintered particle layer 11 covered with 4, a large side opening 37 through which vapor bubbles are released and a small beveled opening 36 through which boiling liquid is sucked are formed. Epidermis 34
A rectangular groove 35 whose bottom surface is the heat transfer wall 10 is formed between each of the grooves. Therefore, the inlet and outlet of gas and liquid are separated, and the flow becomes stable. In addition, the boiling liquid flows along the heat transfer wall 10 with the highest temperature between the small side surfaces [from the sintered particle layer 1
1, the evaporation performance is improved.

FIG. 12 shows another embodiment of the invention. In this example,
The side openings 36 and 37 of the embodiment shown in FIG. 11 are not formed by the size of the skin 34 covering the side surfaces of the sintered particle layer 11, but are formed by a plurality of openings 28 on the surface and a plurality of openings on both sides. The sintered particle layer 11 is entirely covered with a skin 34 having a notch 28 . The evaporated vapor generated within the sintered particle layer 11 is captured within the skin 34 and then released as bubbles through the openings 28 provided on the surface. On the other hand, the boiling liquid flows into the sintered particle layer 11 from the notches 38 provided on both sides of the skin 340 in response to foaming from the openings 28 . Therefore, the inlet and outlet of gas and liquid are separated, and the flow becomes stable. In addition, the boiling liquid flows into the sintered particle layer 11 through the notches 38 provided on both sides of the skin 34 in a self-controlled manner along the heat transfer wall 10 having the highest temperature, improving evaporation performance. do.

The porous heat transfer surface shown in the above example forms a sintered particle layer on a strip-shaped thin plate made of a liquid-permeable material.
Obtained by attaching the sintered particle layer to the heat transfer wall soil with the sintered particle layer facing down. In particular, when the heat transfer surface is a tube, as shown in FIG. A porous heat exchanger tube with good performance is obtained.

〔Effect of the invention〕

According to the present invention, a part that evaporates liquid to produce steam;
The part that releases steam as bubbles and the part that supplies liquid can be separated, and the inflow flow rate of bubbles can be self-controlled according to the required amount, so the inside of the porous layer is not filled with liquid. It is possible to prevent a situation where the porous heat transfer surface slumps or becomes filled with steam, and it is possible to realize a porous heat transfer surface that has high heat transfer performance over a wide heat flux range.

[Brief explanation of drawings]

Figure 1 is a boiling model diagram on a porous heat transfer surface, Figure 2~
FIG. 4 is an enlarged perspective sectional view illustrating an embodiment of a porous heat transfer surface according to the present invention, and FIGS. 5 to 12 are enlarged perspective sectional views each illustrating an embodiment of a porous heat transfer surface according to the present invention. It is a diagram. FIG. 13 is a front view showing an example of manufacturing a porous heat transfer surface as a pipe according to the present invention. 10... Heat transfer wall, 11... Sintered particle layer, 12...
Epidermis, 13... Opening, 14... Slit-like narrow gap, 15... Band-shaped thin plate, 23... Between surfaces ['', 2
4...Subepidermal space 1st section Y 2 / θ 3rd 4 - Fig. 14, 5 Fig. 23 ) 6 6 animals] Fig. 7 8 B 9th eye closed / ρ Fig. 9 481- 11 Fig. 122 /θ,ga /l Fig. 13 Fig. 1-687 Mimomi-cho, Narashino-shi NDC Co., Ltd. ■ Application Person NDC Co., Ltd. 1-687 Mimomi-cho, Narashino-shi

Claims (1)

[Claims] 1. On the porous particulate heat transfer surface that transmits heat, a portion of the upper part of the porous particle layer formed on the heat transfer wall base material is regularly covered with foaming suppressing parts (). A porous heat transfer surface characterized by: 2. A porous heat transfer surface according to Claim 1, characterized in that the foaming suppressing member is a strip-shaped thin plate. 3. Claim No. In item 1, the porous heat transfer surface is characterized in that the foaming suppression part nI is a perforated plate that covers all of the large number of restricted openings. 4. In the porous heat transfer surface that transfers heat, A porous heat transfer surface comprising a porous particle layer on a thermal wall base material, and a strip-shaped thin plate with reduced permeability covering the upper part of the porous particle layer. 5. Patent. A porous heat transfer surface according to claim 4, characterized in that the ridge spacing of the porous particle layer covered with the strip-shaped thin plate made of the reduced permeability member is alternately increased and decreased. 6. Patent A porous heat transfer surface according to claim 4, characterized in that a plurality of openings are provided in the strip-shaped thin plate made of the reduced permeability member. 7. In claim 4, A porous heat transfer surface characterized in that a band-shaped thin plate made of an Ail liquid-recording material that does not deteriorate is provided with wave-shaped notches at regular intervals in the longitudinal direction. 8. In claim 4, A porous heat transfer surface 9 characterized in that the northern part of the porous particle layer covered with the strip-shaped thin plate made of the reduced permeability member is sloped, according to claim 4, A porous heat transfer surface characterized in that a strip-shaped thin plate made of a permeable member is provided with individual openings between the opposing porous particle layers.10. A porous heat transfer surface characterized in that both sides of the opposing porous particle layer are also covered with strip-shaped thin plates of varying sizes made of the reduced permeability member. 11. Claim 4. , the porous particle layer is entirely covered with a strip-shaped thin plate made of the reduced permeability member so that the upper part of the porous particle layer has openings and notches are provided on both sides. heat transfer surface.