JP3944783B2 - Heat transfer enhancement device for natural convection boundary layer - Google Patents

Description

Detailed Description of the Invention

  The present invention is a heat transfer promotion device that is extremely useful when heat is removed from a large structure (building) such as a power facility or a spent fuel storage container in nuclear power generation by natural convection turbulent heat transfer.

  Along the heat radiating surface (including the heat transfer surface), the density of the heated fluid decreases and buoyancy is generated, thereby forming a peripheral fluid (air, water, etc.) that flows from the bottom to the top. This flow is called the natural convection boundary layer. To promote heat transfer, a method of directly installing fins (enlarged heat radiating surface) on the heat radiating surface has been adopted so far, as with forced convection. In this case, for the natural convection turbulent boundary layer, effective heat transfer cannot be promoted unless the fin height protrudes beyond the boundary layer thickness (about 20 to 30 cm) due to its turbulent characteristics. In addition, it is necessary to select the same fin material as that of the heat radiating surface or one having high thermal conductivity. This requires labor and cost to process the fins, and makes it difficult to make the heat dissipation surface compact. Also, it may be difficult to fin the heat dissipation surface. Therefore, a heat transfer acceleration method that replaces fins is more effective, and a method that is advantageous in terms of production and cost has been desired. As a means for solving this problem, by inserting a plate or the like into the boundary layer away from the heat radiating surface, the flow of the surrounding fluid is deflected to promote heat transfer. When a plate 1 (hereinafter referred to as a flow deflection plate) as shown in FIG. 1 is supported by support members 2 and 3 at a fixed angle with respect to the direction of gravitational acceleration g and inserted into a natural convection boundary layer, a flow deflection plate is obtained. The boundary layer flow is deflected outward with respect to the heat radiating surface 4 by detouring, and a large vortex (hereinafter referred to as a horizontal vortex) as shown by an arrow is generated. This transverse vortex causes the low-temperature ambient fluid at the outer edge of the boundary layer to flow to the vicinity of the heat radiating surface downstream of the deflecting plate, so that cooling becomes significant.

Problems to be solved by the invention

  As shown in Fig. 1, when a lateral vortex is generated by a single flow deflector that is long in the width direction of the heat dissipation surface, the local heat transfer rate is certainly improved in the region immediately after the surrounding fluid has passed the flow deflector. However, this effect is diminished further downstream (upward), with the disadvantage that the heat transfer coefficient becomes smaller than when the flow deflector is not inserted. This is due to the fact that the convection itself stagnates downstream from the insertion position due to the insertion of the flow deflection plate, making it difficult for the fluid near the heat dissipation surface to flow. Therefore, there has been a demand for a new heat transfer acceleration device that provides a wide effective flow area without deteriorating the heat transfer coefficient even in a region away from the flow deflector.

Means for solving the problem

Claim 1 tilts the natural convection boundary layer formed by the peripheral fluid flowing from the bottom to the top along the heat dissipation surface so that the upper edge is close to the heat dissipation surface and the lower edge is far from the heat dissipation surface Placing the plate away from the heat radiating surface deflects the flow of the surrounding fluid, discharges the high temperature fluid away from the heat radiating surface, and entrains the low temperature fluid in the outer boundary layer to promote heat transfer from the heat radiating surface In the heat transfer promoting device, a plurality of the flow deflection plates are arranged horizontally with a gap in the width direction of the heat radiating surface. By using a flow deflecting plate having a gap in the heat radiating surface width direction, heat transfer can be promoted significantly more than when a single flow deflecting plate long in the heat radiating surface width direction is used. Moreover, there is no stagnation of convection downstream of the flow deflection plate, and heat transfer coefficient does not deteriorate.
A second aspect of the present invention is the heat transfer promoting device according to the first aspect, wherein a plurality of sets of flow deflecting plates are arranged in parallel with a gap in the vertical direction of the heat radiating surface. By installing a plurality of such rows of plates at regular intervals in the height direction of the heat dissipation surface, it is possible to promote heat transfer on the heat dissipation surface over a wide basin of the surrounding fluid.
According to a third aspect of the present invention, the distance between the upper edge of the flow deflector near the heat radiating surface and the heat radiating surface is 5 mm to 10 mm. Fig. 2 shows the change in the amount of heat transfer immediately after the flow deflector by installing a flow deflector near the heat dissipating surface and changing the distance C between the upper edge of the flow deflector close to the heat dissipating surface and the heat dissipating surface. . The change in the heat transfer amount was expressed by normalizing the heat transfer coefficient (ratio of heat transfer amount and temperature difference) h at a certain C value with the maximum value h _max in the range in which the C value was changed. As shown in FIG. 2, it was confirmed that the amount of heat transfer increased most when the distance between the upper edge of the flow deflector near the heat radiating surface and the heat radiating surface was 5 mm to 10 mm.
A fourth aspect of the present invention is the heat transfer promoting device according to the first or second aspect, wherein the angle of the flow deflection plate is in the range of 30 ° to 60 ° with 0 ° in the downward direction. The change in the amount of heat transfer immediately after the flow deflection plate was investigated by changing the angle φ of the flow deflection plate with the downward direction being 0 °, and is shown in FIG. The change in the amount of heat transfer was expressed by normalizing the heat transfer coefficient h at a certain φ value with the maximum value h _max in the range in which the φ value was changed. As shown in FIG. 2, when the angle of the flow deflector is 30 ° to 60 °, the boundary layer flow is deflected outward in the vicinity of the flow deflector to form a large lateral vortex, and the boundary layer outer edge It was confirmed that the low-temperature fluid flowed and was carried to the vicinity of the heat radiating surface downstream of the deflection plate, and the amount of heat transfer increased most.
A fifth aspect of the present invention is the heat transfer promoting device according to the first or second aspect, wherein the vertical length of the flow deflection plate is in the range of 50 mm to 150 mm. The change in the amount of heat transfer immediately after the flow deflection plate was examined by changing the vertical length H of the flow deflection plate, and is shown in FIG. The change in the amount of heat transfer is standardized by the maximum value h _max in the range in which the value of H is changed with respect to the heat transfer coefficient h at a certain value of H. As shown in FIG. 2, it was confirmed that the heat transfer amount increased most when the length was 50 mm to 150 mm.
A sixth aspect of the present invention is the heat transfer promoting device according to the first or second aspect, wherein the ratio of the lateral width and the gap of the flow deflection plate is in the range of 2: 1 to 1: 2. By providing a gap in the flow deflection plate in the width direction of the heat radiating surface, the convection stagnating downstream of the flow deflection plate and the convection passing through the gap can be mixed to further promote heat transfer. In addition, the movement of the longitudinal vortex reduces stagnation of the convection downstream of the flow deflector and does not cause deterioration of the heat transfer coefficient. When the ratio of the horizontal width and gap of the flow deflection plate was changed and the change in the heat transfer amount was examined, the amount of heat transfer increased most when the ratio of the horizontal width and gap of the flow deflection plate was changed from 2: 1 to 1: 2. Was confirmed.
A seventh aspect of the present invention is the heat transfer promoting device according to the second aspect, wherein the ratio of the upper and lower gaps of the flow deflection plates to the vertical length of each flow deflection plate is in the range of 5: 1 to 8: 1. The ratio of the vertical gap of each flow deflection plate and the vertical length of each flow deflection plate was changed, and the change in heat transfer across the heat radiating surface was compared. It was confirmed that the amount of heat transfer increased in a wide flow region on the heat radiating surface when the ratio of vertical length was 5: 1 to 8: 1.

  A first embodiment of the heat transfer promoting device according to the present invention will be described with reference to FIGS.

  FIG. 3 is a perspective view of a heat transfer facilitating device configured by supporting a plurality of flow deflecting plates 1 with support members 2 and 3 and arranging them in the width direction of the heat radiating surface 4, FIG. 4 is a front view, and FIG. It is a side view. FIG. 6 is a conceptual diagram of a flow field formed by installing the heat transfer promoting device according to the present invention.

  As shown in FIGS. 3 and 4, a plurality of flow deflecting plates 1 inclined so that the upper edge is close to the heat radiating surface 4 and the lower edge is far away are provided with a gap in the width direction of the heat radiating surface 4. 2 is installed and the heat transfer promotion device is constructed. The distance between the flow deflection plate 1 having a vertical length of 50 mm to 150 mm and the heat radiation surface 4 is set to 5 mm to 10 mm, and a plurality of flow deflection plates are attached according to the size of the heat radiation surface. The ratio of the lateral width of the flow deflector and the gap length is preferably 1: 1, but may be in the range of 2: 1 to 1: 2. The length of the flow deflection plate is in the range of 0.8 to 2.0 times the lateral width. The inclination of the flow deflection plate is preferably 45 °, with the downward direction of the heat radiating surface (the direction of gravitational acceleration g) being 0 °, but may be in the range of 30 ° to 60 °. Then, as shown in FIG. 5, the heat transfer promoting device is fixed near the heat radiating surface 4 from the outside of the boundary layer by using the support material 3 of the heat transfer promoting device.

  With reference to FIG. 7, a second embodiment of the heat transfer promoting device according to the present invention will be described.

  FIG. 7 shows a heat transfer promoting device (first embodiment of the invention) in which a plurality of flow deflecting plates 1 are supported by supporting members 2 and 3 and arranged in the width direction of the heat radiating surface 4. It is the perspective view which installed the multistage in the direction. The ratio of the gap between each pair of flow deflection plates arranged vertically and the vertical length of each flow deflection plate is preferably in the range of 5: 1 to 8: 1.

The invention's effect

  By inserting the heat transfer facilitating device according to the present invention into the natural convection turbulent boundary layer, the boundary layer flow is deflected outward in the vicinity of the flow deflector plate to form a large-scale transverse vortex, and the boundary layer The low-temperature fluid at the outer edge is carried to the vicinity of the heat radiating surface downstream of the heat transfer promoting device (flow indicated by broken lines and arrows in FIG. 6). On the other hand, the flow that has passed through the gaps of the flow deflectors arranged in the width direction of the heat radiating surface is deflected in the width direction of the heat radiating surface, forming a vertical vortex. Through this series of fluid movements, the low temperature fluid at the outer edge of the boundary layer is carried to the vicinity of the heat radiating surface in the region where the flow deflector exists, and the high temperature fluid near the heat radiating surface flows along the gap of the deflecting plate due to the movement of the vertical vortex Heading away from the heat dissipation surface (flow indicated by solid line and arrow in FIG. 6). As a result, the heat transfer can be greatly accelerated compared with the case where a single flow deflector plate that is long in the width direction of the heat radiating surface is used. Moreover, there is no deterioration in the heat transfer coefficient due to the decrease in convection stagnation downstream of the flow deflection plate due to the movement of the vertical vortex. Further, if such a plate array is installed in a plurality of stages at regular intervals in the heat radiation surface height direction as shown in FIG. 7, it is possible to promote heat transfer on the heat radiation surface over a wide flow area of the surrounding fluid.

FIG. 8 shows an example in which the heat transfer promoting device of the first embodiment according to the present invention is used for a cylindrical storage container (cask, height of about 5 m, diameter of about 1.5 m) of spent fuel in nuclear power generation. . Around the storage container (heat radiating surface) 4, a plurality of flow deflecting plates 1 are attached to a circular support member 2, and are installed by the support member 3 and the column 5. The flow deflector plate is preferably made of metal, but other materials may be used as long as the surface is smooth, heat resistant and durable. Change in heat transfer when the width of one flow deflection plate and the gap in the width direction of the heat dissipation surface is about 100 mm, the distance between the flow deflection plate and the heat dissipation surface is about 5 mm, and the inclination of the flow deflection plate is about 45 ° It is shown in FIG. FIG. 9 shows the natural convection in the case where the heat transfer rate h flows and the deflection plate is not installed at x / L, where the height x with the heat radiating surface is normalized by the heat radiating surface height L (= 4 m) used in the experiment. experimental data showing how the changes with respect to the heat transfer coefficient h _0. In addition, the dashed-dotted line in a figure shows the installation position of a flow deflection plate. As shown in FIG. 9, by using a flow deflector with a gap in the heat radiating surface width direction, heat transfer can be promoted significantly more than when a single flow deflector plate long in the heat radiating surface width direction is used. Can do. Moreover, there is no deterioration of the heat transfer coefficient downstream of the flow deflection plate.

FIG. 10 shows an example in which the heat transfer promoting device according to the second embodiment of the present invention is used for a cylindrical storage container (cask, height of about 5 m, diameter of about 1.5 m) of spent fuel in nuclear power generation. . Around the storage container (heat dissipating surface) 4, a plurality of flow deflecting plates 1 attached to a circular support member 2 (form in the first embodiment) and the support member 3 and the column 5 at regular intervals in the heat dissipating surface height direction. By installing multiple stages. With respect to the second embodiment of the present invention, the change in heat transfer when two stages are installed at intervals of 500 mm is shown in FIG. FIG. 11 shows the natural convection in the case where the heat transfer rate h flows and the deflection plate is not installed at x / L where the height x having the heat dissipation surface is normalized by the heat dissipation surface height L (= 4 m) used in the experiment. experimental data showing how the changes with respect to the heat transfer coefficient h _0. A one-dot chain line in the figure indicates an installation position of the flow deflector. As shown in FIG. 11, by installing two stages of flow deflectors with a gap in the width direction of the heat radiating surface in the height direction of the heat radiating surface, compared to the case of installing one stage, Heat transfer can be promoted in a wide area.

It is a figure explaining the transverse vortex produced by the single flow deflection | deviation plate long in a thermal radiation surface width direction. It is the figure which showed the change of the amount of heat transfer when changing the distance of the upper edge of a flow deflection plate and a heat radiating surface, the angle | corner which a flow deflection plate and a heat radiating surface make, and the vertical length of a flow deflection plate. It is the perspective view which showed the position of the flow deflection plate and the heat radiating surface with the heat transfer promotion apparatus of the 1st form which concerns on this invention. It is the heat transfer promotion apparatus of the 1st form which concerns on this invention, and is the front view which showed the position of the flow deflection plate and the heat radiating surface. It is the side view which showed the position of the flow deflection plate and the heat radiating surface in the heat transfer promotion apparatus of the 1st form which concerns on this invention. It is a figure explaining the horizontal vortex and vertical vortex which arise with the flow deflection | deviation plate which concerns on this invention. It is a heat transfer promotion apparatus of the 2nd form which concerns on this invention, and is a perspective view at the time of installing the flow deflection plate in multiple steps | paragraphs in the heat sink surface height direction. It is a figure which shows the Example at the time of using the heat transfer promotion apparatus of the 1st form which concerns on this invention with respect to the storage container (cask) of the spent fuel in nuclear power generation. It is a figure explaining the effect of the heat transfer promotion apparatus of the 1st form concerning the present invention. It is a figure which shows the Example at the time of using the heat-transfer promotion apparatus of the 2nd form which concerns on this invention with respect to the storage container (cask) of the spent fuel in nuclear power generation. It is a figure explaining the effect of the heat-transfer promotion apparatus of the 2nd form which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Flow deflection plate 2 Flow deflection plate support material 3 Heat transfer promotion device support material 4 Heat radiation surface (surface of a spent fuel cylindrical storage container)
5 Mounting posts for heat transfer promotion device

Claims (7)

Tilt the natural convection boundary layer formed by the surrounding fluid flowing from bottom to top along the heat dissipation surface so that the upper edge is closer to the heat dissipation surface and the lower edge is farther from the heat dissipation surface. The flow deflecting plate to be deflected is placed away from the heat dissipation surface to deflect the flow of the surrounding fluid, discharge the high temperature fluid away from the heat dissipation surface, and entrain the low temperature fluid in the outer boundary layer, A heat transfer promoting device for promoting heat transfer, wherein a plurality of the flow deflection plates are arranged horizontally with a gap in the width direction of the heat radiating surface. 2. The heat transfer promoting device according to claim 1, wherein a plurality of sets of the flow deflecting plates are arranged in parallel with a gap in the vertical direction of the heat radiating surface. The heat transfer promoting device according to claim 1 or 2, wherein the distance between the upper edge of the flow deflector plate close to the heat radiating surface and the heat radiating surface is 5 to 10 mm. The heat transfer promoting device according to claim 1 or 2, wherein an angle of the flow deflecting plate is in a range of 30 ° to 60 ° with 0 ° in the downward direction. The heat transfer promoting device according to claim 1 or 2, wherein the vertical length of the flow deflection plate is in the range of 50 mm to 150 mm. The heat transfer promoting device according to claim 1 or 2, wherein the ratio of the lateral width and the gap of the flow deflecting plate is in the range of 2: 1 to 1: 2. The heat transfer promoting device according to claim 2, wherein the ratio of the vertical gap of the flow deflection plates to the vertical length of each flow deflection plate is in the range of 5: 1 to 8: 1.

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