JPS60253790A - Heat transfer device - Google Patents

Abstract

PURPOSE:To enhance the heat transfer coefficient on the side of a cooling surface and enhance the performance of a heat transfer device, by a construction wherein a liquid is appropriately contained in a vessel, and a bubble film formed at a boiling liquid surface part is brought into contact with a condensed liquid film formed on a top surface. CONSTITUTION:The heat transfer device in which an evaporable liquid is contained in a vessel and heat is transferred from a heating surface to a cooling surface by the boiling and condensing actions of the liquid, is so constructed that the ratio Hi/Hs of the initial distance Hi between the liquid surface with no heat applied to the heating surface and the heating surface to the distance Hs between the heating surface to the cooling surface is in the range of 0.02-0.3. Accordingly, the bubbles (bubble film) 6' generated by boiling make contact with the condensed liquid film 7 formed on the top surface 3, thereby accelerating the dropping of the film 7. Namely, when the condensed liquid film 7 makes contact with the surface of the bubble film 6', the film 7 is pulled and removed downward by the surface tension of the bubble film 6', resulting in that the quantity of a thick liquid film part at the top surface 3 is reduced, while the quantity of a thin film part is increased, thereby enhancing the heat transfer coefficient.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to the construction of a heat transfer device using boiling-condensation.

[Background of the invention]

FIG. 1 shows the configuration of a conventional heat transfer device.

Lower surface 2. Top surface 3. A container 1 is constructed by a side wall 4, and after the inside of the container 1 is evacuated, an evaporative liquid 5 (for example, fluorocarbon, alcohol, etc.) is placed therein. The lower surface 2 is a heating surface and is heated by a heater or other heat source. The upper surface 3 is a cooling surface and is cooled by natural convection or forced convection of air or water. The liquid 5 in contact with the lower surface 2 receives heat and boils, and the generated bubbles 6 rise due to buoyancy and reach the liquid level 9'. The liquid turns into vapor from the liquid level 9 and reaches the upper surface 3 due to the vapor pressure difference, where it is cooled and liquefied. From this trap, a condensate film 7 is formed at the lower part of the upper surface 3, which falls to the lower part by gravity and returns to its original state, repeating the same cycle again. The heat of condensation released at the three upper surfaces is removed by air and water flowing on the outer surface.

Such heat transfer devices have significantly lower thermal resistance than those that utilize mere heat conduction of metals, and are therefore often used to cool heat-generating objects such as semiconductor devices or electrical machines. However, in order to further improve the performance of this heat transfer device and to improve the performance of the heat generating object, it is necessary to reduce the thermal resistance of the boiling part of the liquid on the heating surface side and the thermal resistance of the condensed liquid film 7 on the cooling surface side. There is. Generally, the thermal resistance of the condensate film 7 is several times larger than the thermal resistance of the boiling part, so it is effective to reduce the thermal resistance of the condensate film 7. For this reason, various studies are currently being conducted. For example, there is one in which a large number of fins are provided at the lower part of the upper surface 3, but this has the disadvantage that machining is difficult and the number of man-hours increases significantly. As a way to solve this problem, the method shown in Figure 2 has been proposed (A+Mar
kowitz, Boilingand Condens
ation in a Liguid-FilledE
nclo6ure, MIT Re1) Of NE-D
SR29077-73Jan/1971). In this method, an auxiliary container 10 is provided on the upper part of the upper surface 3, and the auxiliary container 10 is connected to the container 1 by a pipe 10', and there is no need for a large number of fins that are difficult to process. In other words, the amount of liquid 5 to be put inside is increased, and it is poured through pipe 10' until the liquid level 9 of liquid 5 is located inside auxiliary container 10. In this way, when no input is applied to the lower surface 2, the upper surface 3 comes into contact with the liquid 5, and when input is applied, the bubbles 6 generated by boiling rise and collide violently with the upper surface 3. Therefore, on the upper surface 3, a kind of forced convection heat transfer occurs between the bubbles 6' and the liquid 5. However, when we actually measured the thermal resistance at that part, it was found to be much larger than the method shown in Figure 1, and especially when the heat flux at the lower surface 3 was small, the thermal resistance was significantly large. This is air bubbles 6,6 in liquid 5
' is precooled by the liquid 5 that is cooled on the upper surface 3 and descends to the lower part, so that the size of the bubbles 6, 6' becomes smaller.
This is because the forced convection effect of FIG. 5 shows the relationship between the heat flux Qc of the upper surface 3 and the thermal resistance αC. The solid line (conventional ■) shows the relationship between qc and αC in the method shown in FIG. (As lc increases, the thickness of the condensate film 7 formed on the lower surface 3 becomes thinner.) (As lc increases, αC decreases.) The Z double-dot chain line (conventional ■) is shown in Figure 2. In particular, in the region where qc is small, the effect of precooling the bubbles 6, 6' by the liquid 5 is large, and the size of the bubbles is small, so the forced convection effect described above is weak, and αC is significantly smaller than the solid line.Even if Qc becomes large, the two-dot chain line only matches the solid line, and the heat transfer coefficient does not become larger than that of the conventional method (■).However, this conventional method (■) This has the effect of collecting the air into the vapor space 8' in the auxiliary container 10 and preventing the heat transfer coefficient to the upper surface 3 from being drastically reduced when the air enters. The purpose of this invention is to improve the heat transfer coefficient on the cooling surface side and improve the performance of the heat transfer device, as compared to the conventional example described above.

[Summary of the Invention] The main point of the present invention is to properly adjust the liquid level in the container, bring the foam film formed at the boiling liquid surface into contact with the condensate film formed on the top surface, and eliminate it along the foam film. and improves heat transfer coefficient,
Moreover, the structure of the upper surface is modified so that this effect persists even when the heat flux qc increases.

[Embodiments of the invention]

Figures 3 and 4 are diagrams showing the configuration and principle of the present invention.
FIG. 3 shows the case where no input is entered into the lower surface 2, and FIG. 4 shows the case where the input is entered. Although the amount of liquid 5 sealed is larger than that of the conventional example shown in FIG. 1, the liquid level 9 is not in contact with the upper surface 3 as shown in FIG. Further, the auxiliary container 10 as shown in FIG. 2 of the conventional example is not provided. In the present invention, the ratio Hi/H between the initial distance Hj from the liquid level 9 to the upper surface (cooling surface) 3 and the distance H8 from the lower surface (heating surface) 2 to the upper surface 3 shown in FIG. 3 is important. It has meaning.

When the value of this ratio H1/Hs is set appropriately, the bubbles (bubble film) 6' on the boiling liquid surface 9' generated by boiling come into contact with the condensed liquid film 7 formed on the upper surface 3, and promote their fall. This is because when the condensate film 7 comes into contact with the surface of the foam film 6', the surface tension of the foam film 6' pulls the condensate film 7 and expels it to the lower part, resulting in a thick liquid film on the top 3 parts. decreases and the thin film part increases,
This increases the heat transfer coefficient αC. As shown in Figure 1, Hi
//If Hs is too large, the bubble film 6' will not come into contact with the condensate film 7 and the above-mentioned effect will not occur. On the contrary, H
i/lb is small When the boiling liquid level 9 oscillates, the liquid level 9 comes into contact with the upper surface 3, and the thickness of the liquid film 9 on the upper surface 3 is increased,
This causes a decrease in the heat transfer coefficient αC. Furthermore, when Hi 2 /Hs becomes significantly smaller, the number of points where the liquid level 9 comes into contact with the upper surface 3 increases, resulting in a decrease in the heat transfer area where steam condenses, further reducing the heat transfer coefficient αC. In such a region, when the heat flux (lc) is increased, the vapor space 8 immediately disappears, and heat transfer shifts to natural convection of the liquid 5 from the lower surface 2 to the upper surface 3, and the heat transfer coefficient decreases dramatically. This is because the temperature of the liquid 5 increases due to the increase in heat flux (lc), and the liquid 5 expands in volume, causing the vapor space 8 and the bubbles 6 to disappear.The broken line in FIG. This figure shows the change in the heat transfer coefficient αC with respect to the heat flux qc of the invention.The broken line ■ is the case when H1/H8 is appropriate, and αC is larger than the solid line (conventional ■) especially in the high heat flux region. , the highest value is about 60 cm larger than the conventional ■. The 0-touching part shows the part where αC is larger than the conventional ■.On the other hand, when Ht/as is small, as shown by the broken line ■ , in the low heat flux region, αC is rather small compared to the conventional ■, and as the heat flux increases, αC increases and αC becomes slightly larger than the conventional ■, but soon the bubbles 6 and the vapor space 8 disappear 9
, transitions to natural convection heat transfer (dotted chain line) of liquid 5 (point 1
)2. ). Figure 6 shows Hi/H5 and the heat transfer coefficient ratio αC/α in a region of high heat flux, which is industrially important, that is, when this heat transfer device is used to cool electronic elements with high heat generation density. . It shows the relationship of D (αCD represents the heat transfer coefficient of the conventional method (■)). Hi/Hs is 0.02
αC/αCD becomes 1 or more in the range of ~0.3.

When Hi/Ms is 0.02 or less, natural convection heat transfer occurs, αC/αCD is 1 or less, and Hl/H5 is 0.
3 or more, αC/αCD is 1, that is, the conventional ■
The state will be as follows. Therefore, the optimum range of the present invention is Hi/Hs
is 0.02 to 0.3.

Even in this optimum range, as shown by the broken line in Fig. 5, when the heat flux (lc) increases significantly, the volumetric tension of the liquid 5 causes the bubbles 6 and the vapor space 8 to disappear, resulting in natural convection heat transfer. (point p1). Therefore, the important point of the present invention is how to avoid this.

FIG. 7 shows an embodiment showing a method for structurally solving the above-mentioned phenomenon in which the heat transfer coefficient suddenly decreases due to transition to natural convection. As shown in the figure, a block-shaped cooling surface 12 is provided at the lower part of the upper surface 3, and vapor spaces 8 and 11 are provided between this cooling surface 12 and the side wall portion 4. Due to the existence of this large vapor space 8, even if the liquid 5 undergoes volumetric expansion, boiling will not stop. The block-shaped cooling surface 12 is made of thermally conductive copper, aluminum, etc., and steam is mainly applied to the lower part of the cooling surface 12. For this reason, it is preferable that the initial distance Hi between the boiling liquid level 9 and the lower part of the cooling surface 12 be within the optimum range shown in FIG. The side 12' of the cooling surface 12 in contact with the vapor space 8 also contributes effectively to condensation, further reducing the thermal resistance. The vapor space 8 also functions as a gas reservoir for collecting non-condensable gas generated inside or non-condensable air entering from the outside. In other words, when steam condenses on the cooling surface 12, it has the effect of alleviating an increase in thermal resistance due to non-condensable gas. Moreover, this block-shaped cooling surface 12 is thick and has a large heat capacity, so even if an excessively large input enters the lower surface 2, it will be absorbed and prevent the lower surface 2 from rising in abnormal temperature. When the steam space 8 is provided by such a method,
As shown by the broken line O in FIG. 5, even if the heat flux Qc increases, the heat flux αC does not decrease.

FIG. 8 shows another embodiment. This is a block-shaped cooling surface 12 with a horizontal hole 13, and a steam space 8.
As a result, even if the heat flux qc increases, it becomes more difficult to shift to natural convection. Reference numeral 14 denotes a welding part, and in this embodiment, the cooling surface 12 is made separately, set on the upper part of the container 1, and then fixed by welding.

FIG. 9 shows another embodiment. This is provided with a liquid cutter plate (15) on the edge of the block-shaped cooling surface 12. In this way, the liquid film condensed on the side 12' of the cooling surface 12 descends, and the cooling surface 12 is It is possible to prevent the thickness of the condensate film 7 from increasing by inserting a groove 9 in the lower part.

FIG. 10 shows another embodiment in which a large wedge-shaped cooling surface 12 is provided on the lower surface 3. Condensate film 7
descends down the wedge surface 12' and falls below its tip. It is preferable to set the initial distance Hi between the tip of the wedge and the liquid level 9 when no input is applied to the lower surface 2 to be within the optimal range shown in FIG. FIG. 11 shows another embodiment in which the space between the wedge surface 12' and the adjacent wedge surface acts as a vapor space 8. This is a rectangular cooling surface 1
2 is provided on the upper surface 3.

The space between the side 12' of the cooling surface 12 and the adjacent side is the vapor space 8.

FIG. 12 shows another embodiment. This is the case when the lower surface 2 itself is not a heating element, but has a small heating surface (for example, a semiconductor element) 2' inside it, and in this case, the total area of the heating surface 2' is The area becomes smaller. Therefore, the heat flux of the lower surface 2 in the previous embodiments and the heat flux of the heating surface 2' in FIG.
If the areas of the upper surface 3 and lower surface 20 in FIG. 2 are the same, the heat flux to the upper surface 1jj (cooling surface) 3 in this embodiment will be small. As shown in Fig. 5, when the heat flux is small, the effect of improving the heat transfer coefficient αC becomes small. Therefore, in this embodiment, the following measures are taken: a small block-shaped A cooling surface 12 is provided, and a reduction nozzle 16 is provided from the top of the heating surface 2' toward the cooling surface 12, and the air bubbles 6 are collected by the reduction nozzle 16, thereby increasing the heat flux to the cooling surface 12. , so as not to reduce the heat transfer coefficient improvement effect. - Figure 13 shows another embodiment. This is the case when the present invention is applied to a container 1 that is long in the stacking direction, such as a large-scale integrated circuit. A plurality of cooling surfaces 12 are provided on the upper surface 3, and correspondingly reducing nozzles 16 are provided. 3' is the top surface 3
FIG. 14 shows another embodiment. In this case, a cooling surface 12 having the same size as the heating surface 2' is attached to the upper surface 3 of each heating surface 2'. In such a case, the reduction nozzle 16 may be unnecessary. -The present invention can be applied not only when the container 1 is sealed but also when it is open to the atmosphere.

〔Effect of the invention〕

As explained above, according to the present invention, (1) the heat transfer coefficient of the condensing section is significantly improved, (2) there is no need to attach a large number of fine fins as in the conventional case, and (8) the side of the cooling surface The effect of the present invention can be maintained up to the high heat flux region by the steam space provided in the (5)
By adding a cooling surface, the heat capacity increases, making it possible to prevent abnormal temperature rises on the heating surface.

[Brief explanation of the drawing]

Figures 1 and 2 are configuration diagrams of conventional heat transfer devices; Figure 3;
FIG. 4 is a diagram explaining the configuration of the heat transfer device of the present invention, and FIG.
The figures are diagrams explaining the effects of the heat transfer device of the present invention, Figure 6 is a diagram explaining the optimum range in which the heat transfer device of the present invention exhibits its effects, and Figures 7 to 14 are diagrams showing other embodiments. be. 1 is the container, 2 is the bottom surface (heating surface), 3 is the top surface (cooling surface),
4 is the side wall, 5 is the liquid, 6 is the bubble, and 6' is the bubble (foam membrane).
, 7 is the condensate film, 8 and 11 are the vapor space, 9 is the liquid level, 9
' is the boiling liquid level, 10 is the auxiliary container, 12 is the cooling surface, 12'
is the side part, 13 is the hole, 14 is the welded part, 15 is the liquid drain plate, 1
6 is a reduction nozzle. Sai 1 figure, 3 3rd flash +4-m 5th evil spear 6 old Agen C. Ko (H・/ss)

Claims (1)

[Claims] 1. In a heat transfer device that transports heat from a heating surface to a cooling surface by placing an evaporative liquid in a container and using its boiling-condensation action, the liquid when no heat is applied to the heating surface. Ratio H between the initial distance Hi from the surface to the cooling surface and the distance H5 from the heating surface to the cooling surface
The heat transfer device is configured so that i/Hs is in the range of 0.02 to 0.3, and a condensed liquid film is formed on the cooling surface to form a bubble film at the boiling liquid level that is generated when heat is applied to the heating surface. A heat transfer device that effectively eliminates the condensate film by bringing it into contact with the liquid, reducing thermal resistance. 2. The heat transfer device according to claim 1, wherein a block-shaped cooling surface is provided on the upper surface of the container, and a steam space is provided at the back or side of the block-shaped cooling surface. 3. The heat transfer device according to claim 1 or 2, wherein a contraction nozzle is provided between the heating surface and the cooling surface to collect bubbles generated by boiling and increase the heat flux on the cooling surface. .