JP2007109695A - Element cooler excellent in starting characteristics - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an element cooler which can be used stably without damaging a semiconductor element by stabilizing temperature controllability at the time of starting when a substance of low global warming potential (e. g. HFC43-10mee) is used as HFC (Hydro Fluoro Carbon) refrigerant. <P>SOLUTION: The element cooler excellent in starting characteristics is a boiling cooler comprising an evaporator where a plurality of passages are arranged in parallel, a condenser stacking a refrigerant passage and an air passage communicating with the evaporator, and refrigerant used for cooling an element by circulating through the refrigerant passage. As a bubbling acceleration treatment, inner surface of the passage in the evaporator is preferably roughened by etching using acid. HFC of low global warming potential (e. g. HFC43-10mee) is preferably employed as the element cooling refrigerant. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a boiling (thermosyphon) cooler having an evaporation section and a condensation section. More specifically, even when a refrigerant for element cooling having different characteristics is used, the boiling stage of the refrigerant on the inner surface of the passage of the evaporation section. The element cooler is excellent in temperature controllability at the start-up regardless of the characteristics of the refrigerant by performing the process for promoting the bubble growth generated in the above (hereinafter referred to as “bubble promotion process”).

  A so-called inverter motor is employed as a control technology for an AC power supply in the general industrial field or as power for a railway vehicle, and the power supply is controlled by the inverter. In power electronics technology that uses semiconductor elements such as diodes, transistors, and thyristors to convert, control, and open / close power, it is essential to cool the semiconductor elements.

  Therefore, various element coolers have been proposed. For example, in Patent Document 1, as an electrically insulating heat pipe, an evaporation part and a condensation part are made of a steel pipe having an inner diameter of 16 mm, and the evaporation part and the condensation part are made of alumina ceramics. A configuration has been proposed in which perfluorocarbon (hereinafter simply referred to as “PFC”) is enclosed as a working refrigerant.

  Moreover, in patent document 2, the condensing part of the plate fin type heat exchanger which condenses a refrigerant | coolant was used as an element cooler, and the hollow surface board which has many hollow passages mutually connected, and the semiconductor element was attached to this. There has been proposed a configuration in which the evaporation parts are connected via a header tank, and fins having fine irregularities on the surface are provided in the hollow passage.

  In conventional element coolers, chlorofluorocarbon was used as the coolant, but chlorofluorocarbon gas diffused to the stratosphere, destroying the ozone layer and increasing the amount of ultraviolet rays became a serious environmental problem, and chlorofluorocarbon was abolished. It was. A change to pure water or the like has been made as a refrigerant liquid in place of chlorofluorocarbon, but when aluminum is used as the material of the heat exchanger, there is a concern about generation of hydrogen due to water corrosion. For this reason, from the viewpoint of operational stability, the use of alternative chlorofluorocarbons that are stable fluorocarbon compounds containing neither hydrogen nor chlorine and that do not destroy the ozone layer, as represented by the “PFC”, has been rapidly increasing.

In recent years, interest in global environmental issues has rapidly increased, and not only the destruction of the ozone layer, but also the impact on global warming has been evaluated. A global warming potential is used to evaluate the impact on global warming. The global warming potential is an index that represents the effect of individual greenhouse gases on global warming relative to the effect of CO _{2 in} consideration of their duration.

The above-mentioned “PFC” is a very stable fluorinated carbon-based compound (for example, CF ₄ , C ₂ F ₆ , C ₆ F _14, etc.) that does not contain any hydrogen or chlorine, and is an ozone layer as a good alternative chlorofluorocarbon. Does not destroy. However, the global warming potential is relatively high. For example, in the case of the C ₆ F ₁₄ , so-called PFC 51-14 (hereinafter sometimes simply referred to as “PFC 51-14”), it is 9000, and the number of CO ₂ It has a thousand times more powerful greenhouse effect. For this reason, as a refrigerant used for the element cooler, it is desired to use a refrigerant that does not destroy the ozone layer and has a low global warming potential instead of the “PFC”.

JP-A-3-263592 JP-A-8-204075

  In order to reduce the burden on the global environment, the present inventors have made various studies on the element cooling refrigerant, and as a result, instead of the PFC, hydrofluorocarbon (hereinafter referred to as “HFC”). ) That you can choose. Among HFCs, for example, HFC43-10mee does not destroy the ozone layer (ozone layer depletion coefficient is 0), has a lower global warming coefficient than the PFC51-14, and has a smaller greenhouse effect. is there.

  Usually, the refrigerant circulating in the element cooler is evaporated by the heat of the semiconductor element in the evaporation section, and this evaporated gas is cooled and condensed in the condensation section, so that the liquid component of the refrigerant returns to the evaporation section again. Configured. However, when a substance is used as a coolant for cooling an element, there may be a phenomenon that the controllability associated with the temperature rise becomes unstable when the element cooler is activated.

  Therefore, in order to observe unstable temperature behavior at the time of startup, it is divided into the case where PFC51-14 is used as the conventional PFC refrigerant for element cooling and the case where HFC43-10mee is newly used as the HFC refrigerant. The temperatures of the element mounting surface, the refrigerant, and the air inlet in the element cooler were measured from the time of startup to the steady state.

  FIG. 1 is a diagram showing temperature controllability at the time of activation of an element cooler when PFC 51-14 is used as a PFC refrigerant for element cooling. FIG. 2 is a diagram showing temperature controllability at the time of starting the element cooler when HFC43-10mee is used as the HFC refrigerant for element cooling. In either case, the horizontal axis indicates the elapsed time from the start-up, the vertical axis indicates the temperature of the element mounting surface, the refrigerant and the air inlet, ΔT in the figure is the degree of superheat, and the element mounting at the peak The difference between the surface temperature and the refrigerant temperature is shown.

  When PFC refrigerant is used and when HFC refrigerant is used, the temperature of the element mounting surface rises and then suddenly decreases (hereinafter simply referred to as “temperature sudden change”) during the period from startup to steady state. However, when PFC51-14 is used, the maximum value of the element mounting surface temperature does not exceed the allowable temperature before this temperature suddenly changes, but HFC43-10mee is used. In this case, the maximum value of the element mounting surface temperature exceeds the allowable temperature before the temperature suddenly changes.

  Regarding the degree of superheat ΔT, when HFC43-10mee is used, there is a large temperature difference compared to when PFC51-14 is used, and the state of exceeding the allowable temperature continues for about 6 minutes even after a sudden change in temperature. To be confirmed. The allowable temperature shown in FIGS. 1 and 2 is the upper limit of the temperature at which the semiconductor element functions normally. If the allowable temperature is exceeded, the element itself may be damaged.

  As shown in FIGS. 1 and 2, the temperature of the element mounting surface does not exceed the allowable temperature when the PFC 51-14 is used and when the HFC 43-10mee is used after reaching the steady state. It is confirmed that the element mounting surface temperature in the steady state is slightly lower than that in HFC43-10mee.

  As described above, for example, when HFC43-10mee is used as the HFC refrigerant for element cooling, the temperature controllability at the start is not stable, and the semiconductor element is damaged by the temperature behavior at the start. It became clear that there was drowning.

  The present invention eliminates the instability of temperature controllability at the start of the element cooler even when a substance having a low global warming potential (for example, HFC43-10mee) is used as the HFC refrigerant for element cooling. An object of the present invention is to provide an element cooler with excellent start-up characteristics that can be used stably without damaging the element.

  In the temperature behavior pattern at the start-up when the HFC43-10mee shown in FIG. 2 is used, the difference between the maximum temperature of the element mounting surface and the steady state temperature is, for example, 6.5 ° C.

  First, the inventors pay attention to the fact that HFC43-10mee is a mixed substance, and in view of whether the mixing ratio or boiling point difference is the cause of such a phenomenon, the component ratio of the mixed substance is The effect on boiling point was investigated. However, the simulation results show that the influence of the component ratio of the mixed substance on the boiling point is negligible, and the influence of the component ratio cannot explain the results shown in FIGS.

  Therefore, the inventors of the present invention have made a sudden change in the temperature that appears while the element mounting surface temperature reaches the steady state from the start-up, that is, the temperature drop of 6.5 ° C. occurs on the heating surface. It was noted that when the bubbles grew sufficiently and finally left the heating surface, the surrounding refrigerant flowed into the heating surface and heat transfer was rapidly accelerated.

  The inventors of the present invention have repeatedly investigated that the temperature rise of the element mounting surface exceeding the allowable temperature at the time of start-up is caused by the thermodynamic characteristics of the refrigerant and closely related to the growth of bubbles generated in the boiling stage of the refrigerant. It has been found that the bubble growth can be promoted by the bubble promotion treatment applied to the evaporation part of the element cooler, and the present invention has been completed.

  Therefore, in the element cooler of the present invention, an evaporator having a configuration in which a plurality of passages are arranged in parallel, a condensing unit in which a refrigerant passage and an air passage communicating with the evaporator are stacked, and circulating through the refrigerant passage A boiling cooler composed of a refrigerant used for element cooling is characterized in that bubble promotion processing is performed on the inner surface of the passage of the evaporation section.

  Furthermore, in the element cooler of the present invention, it is preferable that the bubble promotion treatment is performed by roughening the inner surface of the passage of the evaporation section by etching using an acid. By roughening the inner surface of the passage of the evaporation section with an etching process, it is possible to grow stably without erasing the bubbles generated on the passage surface, so that the temperature controllability at startup can be improved effectively. Can do.

In the element cooler of the present invention, it is desirable to use HFC having a low global warming potential as the element cooling refrigerant. As described above, the global warming potential is an index in which the effect of each greenhouse gas on global warming is evaluated relative to the effect of CO _2. The HFC targeted by the present invention is a global warming A coefficient smaller than PFC (for example, PFC51-14 (9000)) can be applied.

  Specifically, HFC43-10mee (1300) can be selected as an HFC applicable to the present invention. The numerical value shown in parentheses after the HFC name indicates the global warming potential.

  In the following, the description will be based on the element cooler, but the application of the present invention is not limited to the element cooler, but can be applied to a heat pipe. By applying, temperature controllability at start-up can be stabilized.

  According to the element cooler of the present invention, even when a substance having a small global warming potential (for example, HFC43-10mee) is used as the HFC refrigerant for element cooling, the control characteristics against the temperature rise of the element mounting surface at the start-up Excellent and does not damage the semiconductor element. Furthermore, since a stable use of a substance having a low global warming potential for element cooling can be realized, the burden on the global environment can be reduced.

  The inventors of the present invention have made various studies on the sudden change in temperature that appears while the element mounting surface temperature reaches the steady state from the start-up.

  Conventionally, when PFC51-14 was used as the PFC refrigerant for element cooling, this sudden change in temperature occurred in a relatively short time from the start-up, whereas when HFC43-10mee was used as the HFC refrigerant, The occurrence timing of the sudden change in temperature is delayed, and a situation occurs in which the maximum temperature of the element mounting surface before the sudden change in temperature exceeds the allowable temperature. Therefore, the present inventors tried to explain such a situation based on the theory of thermodynamics.

  FIG. 3 is a schematic diagram showing a state in which bubbles generated on the heating surface stably grow in the refrigerant. The inventors of the present invention have confirmed through experiments that the time at which the element mounting surface temperature suddenly changes corresponds to the time at which boiling starts. As shown in FIG. 3 above, boiling continues stable growth without the bubbles generated on the heating surface disappearing, and the time at which the heating surface is finally removed can be regarded as the starting point, and the bubbles are released. Since the heated surface with bubbles is rapidly cooled by the surrounding liquid at the moment, it is considered that the above-mentioned sudden change in the heated surface temperature occurs.

  In order for such bubble to stably grow, the temperature of the heating surface needs to be higher than the surrounding liquidus temperature by ΔT (degree of superheat). This ΔT is given by the following (formula 1) according to the theory of thermodynamics.

In the above (Equation 1), ΔT is the degree of superheat, T is the temperature of the heating surface (ie, the element mounting surface), T _eq is the refrigerant temperature, σ is the refrigerant surface tension, R is the bubble radius, L is the latent heat, and V _V is Represents the specific volume of bubbles.

From the above (Equation 1), the degree of superheat ΔT required for stable growth of bubbles with radius R without disappearing is theoretically determined by the thermodynamic characteristics of the refrigerant (a combined amount of surface tension, specific volume, and latent heat). You can see that By defining the thermodynamic characteristics of the refrigerant as a C value from the surface tension σ of the refrigerant, the latent heat L, the specific volume V _{V of the} bubbles, and the temperature T _{eq of the} refrigerant, the following (Expression 2) can be obtained.

  By substituting the above (Formula 2) into the above (Formula 1), the following relational expression (Formula 3) can be obtained.

  From the relational expression shown in (Expression 3), it can be seen that a refrigerant having a larger C value requires a larger degree of superheat ΔT in order to stably grow bubbles having the same radius R. That is, the degree of superheat ΔT necessary for stable growth of bubbles with a radius R does not disappear depends on the thermodynamic characteristics of the refrigerant.

  FIG. 4 is a graph showing the relationship between the C value obtained in (Expression 2) and the refrigerant temperature using the HFC43-10mee and PFC51-14 refrigerants as parameters. In the figure, the C value of PFC 51-14 at each refrigerant temperature is set to “1”, and the C value of HFC 43-10mee is shown as a ratio.

  From the results of FIG. 4, it can be seen that the analysis by (Equation 1) to (Equation 3) based on the theory of thermodynamics is in good agreement with the refrigerant characteristic experiment. The C value of HFC43-10mee is about 1.08 times the C value of PFC51-14 in the actual refrigerant use range of 50-60 ° C., so that bubbles with a radius R can grow stably without disappearing. The degree of superheat ΔT is larger in HFC43-10mee, which corresponds to the delay in the occurrence of a sudden change in temperature when HFC43-10mee is used.

  Again, when using PFC51-14, a sudden change in temperature occurs in a relatively short time from the start, whereas when using HFC43-10mee, the generation timing is delayed and the temperature The temperature of the element mounting surface exceeds the allowable temperature before sudden change occurs.

  This is because the degree of superheat ΔT required for stable growth of bubbles of radius R without annihilation depends on the C value which is the thermodynamic characteristic of the refrigerant. From the results of FIG. This is because the C value is about 1.08 times that of PFC 51-14, the degree of superheat ΔT cannot be reduced, and the transition from the startup to the stable boiling state is delayed.

  In the element cooler of the present invention, in order to reduce the degree of superheat ΔT in (Equation 3), since the C value is a thermodynamic characteristic value unique to the refrigerant, it is necessary to increase the bubble radius R as a possible means. is there. For this reason, as a result of further investigations, the present inventors changed the properties of the heating surface by applying bubble promotion treatment to the heating surface, increased the bubble generation nucleus, and activated the generation and coalescence of bubbles. By doing so, attention was paid to the effect equivalent to increasing the bubble radius in the above (Formula 3).

  Specifically, it is effective to roughen the inner surface of the passage of the evaporation unit as a means for performing bubble promotion processing on the inner surface of the passage of the evaporation unit. That is, even when HFC43-10mee is used as the HFC refrigerant for element cooling, for example, by roughening the inner surface of the passage of the evaporation section, the generation and coalescence of bubbles are promoted, and the bubble radius is increased. As a result, it is possible to reduce the degree of superheat ΔT and to control the temperature of the element mounting surface below the allowable temperature.

  The roughening of the evaporation part may be performed by blasting, grinder, etc., but in these processes, it is difficult to process the inside of a hollow shape such as an extruded mold, and the cost is also low. There is a problem of inviting a rise.

  As a means for solving the above problem, the inventors formed a long and narrow passage by roughening an inner surface that becomes a boiling surface by acid etching when forming an evaporation section using a hollow extruded mold material. It was found that even with the configuration, a predetermined rough surface can be obtained, and bubbles can be promoted in the evaporation section. Moreover, the effect of roughening by acid etching is remarkable regardless of its appearance, and the unexpectedness of the effect has also been clarified. In the roughening method by etching, an acid etching solution is appropriately selected according to the material used for the evaporation passage member, and a processing time, a liquid temperature, and the like are appropriately selected according to required surface roughness and surface properties. .

  Usually, an aluminum material is used as the evaporating passage member, but any commonly used etching solution composition and processing conditions for the aluminum material can be employed.

(Configuration example of element cooler of the present invention)
An element cooler targeted by the present invention includes an evaporator having a configuration in which a plurality of passages are arranged in parallel, a condenser having a refrigerant passage and an air passage communicating with the evaporator, and a circulation passage through the refrigerant passage. It is comprised from the refrigerant | coolant which distribute | circulates and is used for element cooling. A configuration example of the element cooler of the present invention will be described in detail with reference to the drawings.

  FIG. 5 is an exploded perspective view showing a configuration example of the boiling cooler of the present invention. As shown in FIG. 5, the cooler 1 has a basic structure in which a condensing unit 3 of a plate fin type heat exchanger is joined in an inverted T shape on an upper surface of a horizontally disposed evaporation unit 2. The evaporating section 2 has a configuration in which three evaporating passage members 4, 5, and 6 are joined and integrated at two joining sections. That is, the evaporating passage members 4 and 6 are brought into contact with both end faces of the evaporating passage member 5 located at the center, respectively, and are firmly and uniformly joined by a friction stirring joining method.

  Each of the evaporation passage members 4, 5, 6 is made of an extrusion mold material in which a partition wall 7 is formed in the depth direction and a plurality of passages 8 are provided. Fin surfaces made up of small irregularities are provided on the upper and lower surfaces in each passage to increase the surface area.

  The evaporation path member 2 is closed by brazing the closing plate material 9 at the passage opening ends of the evaporation path members 4, 5, 6 that are integrally joined to form the evaporation part 2. Further, in the planned joining portion of the condensing unit 3 on the upper surface of the evaporation unit, openings 10 having a predetermined width are provided in the parallel direction of the passages, and a plurality of openings are arranged at predetermined intervals in the direction of the passages. A communication hole portion 11 in which holes communicating with a large number of passages were arranged in a predetermined pattern was formed.

  The condensing unit 3 is a plate fin type in which a refrigerant passage 12 that communicates with the passage of the evaporation unit 2 via a communication hole portion and an air passage 14 that closes the communication hole portion with a spacer bar 13 are alternately stacked in the horizontal direction. Consists of a heat exchanger configuration.

  The refrigerant passage 12 has a structure in which serrated fins 16 having excellent fluid dispersibility are sandwiched between the plates 15 and the upper surface and both sides thereof are closed by the spacer bar 17. The refrigerant can be raised and lowered in the passage, and the air passage is The corrugated fins 18 are sandwiched between the plates and the upper and lower surfaces are joined by the spacer bar 17 so that air can pass through the gaps in the horizontal direction of the corrugated fins 18.

  The condensing unit 3 can form a plate fin type heat exchanger structure by sandwiching serrated fins or corrugated fins between plates and arranging a spacer bar at a required position to be integrated by brazing. The upper header tank 19 that communicates only with the refrigerant passages is disposed in the upper portion of the tank so as to prevent the deviation of the refrigerant amount between the refrigerant passages.

The evaporating passage members 4, 5, and 6 are manufactured as extruded molds made of an aluminum material because of their ease of assembly and airtightness, but any of them can be used. Further, in order to receive heat and function as the refrigerant evaporating unit 2, in addition to the configuration in which the element to be cooled is mounted, but the mounting screw hole is provided so that it can be directly mounted, the semiconductor element is mounted. Depending on the specifications required for the cooler, such as a configuration in which a plate or the like is installed, various configurations of the evaporating passage members 4, 5, 6 can be employed.
(Temperature controllability at startup)
Using the element cooler shown in FIG. 5, the inner surface of the passage is roughened so that each evaporation passage member is immersed in an acid etching tank of nitric acid having a low concentration to have a rough surface of about 0.3 to 0.7 μm. Turned into. HFC43-10mee was enclosed as a cooling element cooling element to obtain an element cooler. A semiconductor element was attached to the obtained cooler, and the temperatures of the element mounting surface, the refrigerant, and the air inlet were measured from the start to the steady state.

  FIG. 6 is a diagram showing the temperature controllability at the time of starting the element cooler when the roughening process is performed by acid etching and HFC43-10mee is used as the HFC refrigerant. As shown in FIG. 7, a sudden change in temperature appears from the start to the steady state, but the effect of the roughening treatment by acid etching is clearly smaller than the sudden change in temperature shown in FIG. You can see that And the temperature of the element mounting surface did not exceed the allowable temperature.

  Further, due to the heat transfer promoting effect accompanying the roughening of the evaporation passage surface, the temperature of the element mounting surface and the refrigerant in the steady state is also lower than when the roughening process by acid etching is not performed. Furthermore, even when compared with the case of FIG. 1 (when PFC51-14 is used as the PFC refrigerant), it is confirmed that the same functionality is obtained in the steady state.

  From the above results, it is confirmed that it is effective to roughen the heating surface of the evaporation section and activate bubble generation in order to reduce the degree of superheating of the HFC refrigerant (for example, HFC43-10mee) at startup. It was done. Combined with the steady-state temperature decrease due to the heat transfer promoting effect accompanying the roughening of the heating surface, if the roughening treatment by acid etching is performed, the HFC refrigerant (for example, HFC43-10mee) is a conventional PFC refrigerant (for example, , PFC51-14), and can be used as a solvent for cooling the element.

  According to the element cooler of the present invention, even when a substance having a small global warming potential (for example, HFC43-10mee) is used as the HFC refrigerant for element cooling, the control characteristics against the temperature rise of the element mounting surface at the start-up Excellent and does not damage the semiconductor element. Furthermore, since a stable use of a substance with a low global warming potential can be realized for element cooling, the load on the global environment can be reduced. Therefore, it is widely used for semiconductor element cooling in industrial technology fields such as the electronics technology field. Can be used.

It is a figure which shows the temperature controllability at the time of starting of an element cooler at the time of using PFC51-14 as a PFC refrigerant | coolant for element cooling. It is a figure which shows the temperature control property at the time of starting of an element cooler at the time of using HFC43-10mee as an HFC refrigerant | coolant for element cooling. It is the schematic diagram which showed the state which the bubble generate | occur | produced on the heating surface grew stably in a refrigerant | coolant. It is the figure which showed the refrigerant | coolant of HFC43-10mee and PFC51-14 as a parameter about the relationship between C value obtained by (Formula 2), and refrigerant | coolant temperature. It is a disassembled perspective explanatory drawing which shows the structural example of the boiling cooler of this invention. It is a figure which shows the temperature controllability at the time of starting of an element cooler at the time of performing the roughening process by acid etching and using HFC43-10mee as a HFC refrigerant | coolant.

Explanation of symbols

1. Cooler 2. Evaporation section Condensing part 4. Evaporation passage member (end)
5. 5. Evaporation passage member (central part) Evaporation passage member (end)
7). Septum 8 Passage 9. Blocking plate material 10. Opening 11. Communication hole 12. Refrigerant passage 13. Spacer bar 14. Air passage 15. Plate 16. Serrate fins17. Spacer bar 18. Corrugated fin 19. Upper header tank 20. Heating surface 21. Generated bubbles 22. Grown bubbles 23. Bubble radius R 24. Vanished bubbles

Claims (4)

An evaporation section having a configuration in which a plurality of passages are arranged in parallel, a condensing section in which a refrigerant passage communicating with the evaporation section and an air passage are stacked, and a refrigerant used for element cooling by circulating through the refrigerant passage A boiling cooler
An element cooler with excellent start-up characteristics, characterized in that a process (hereinafter referred to as “bubble promoting process”) that promotes bubble growth generated in the boiling stage of the refrigerant is applied to the inner surface of the passage of the evaporator.   2. The element cooler with excellent start-up characteristics according to claim 1, wherein as the bubble promotion treatment, the inner surface of the passage of the evaporation portion is roughened by an etching treatment using an acid.   2. The element cooler with excellent start-up characteristics according to claim 1, wherein the element cooling refrigerant is a hydrofluorocarbon having a low global warming potential. The element cooler with excellent start-up characteristics according to claim 3, wherein the bubble promotion treatment is performed by roughening the inner surface of the passage of the evaporation portion by an etching treatment using an acid.

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