JPH0414471B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical field to which the invention pertains] The present invention provides a battery stack in which unit batteries are stacked, particularly vertically stacked, with cooling bodies distributed at a plurality of locations in the stacking direction. The present invention relates to a method for cooling a stacked fuel cell, in which a cooling medium is caused to flow in parallel in a cooling body to cool a stacked cell body.

[Prior art and its problems]

As is well known, a practical fuel cell is constructed as a battery stack in which a large number of unit cells are stacked. However, when generating electricity, a small amount of heat is generated within each unit cell, so it is difficult to use a fuel cell. In order to operate at a proper operating temperature, it is necessary to remove the generated heat. In particular, when a large number of unit cells are stacked, the temperature at the center of the stack tends to be high, so plate-shaped cooling bodies are distributed and interposed between the stacked parts, and a cooling medium is allowed to flow through the cooling bodies. Therefore, it becomes necessary to cool the battery stack. The cooling medium flowing through this cooling body may be either gaseous or liquid, such as air or water, but from the viewpoint of cooling capacity, a liquid medium is preferable, and the generated heat is removed in the form of sensible heat. It is more advantageous to remove heat in the form of latent heat. As a cooling medium that utilizes latent heat, it is necessary to choose a cooling medium that is suitable for the operating temperature of the battery, but since the operating temperature of recent practical fuel cells is around 180 degrees, water is a cost-effective option. It is advantageous both from the point of view of vapor pressure and from the point of view of vapor pressure.

FIG. 1 shows a conventional fuel cell cooling method based on this concept. The battery stack indicated by 1 in the figure is made by stacking a large number of unit batteries 2 and cooling bodies 3 interposed at key points in the stack, and then fastening them together by fastening means (not shown) disposed above and below. It becomes. A plurality of cooling pipes 4 are embedded or inserted into each cooling body 3, and a cooling medium 5 is passed through the cooling pipes 5 in the direction of the arrow. The inlet of each cooling body is connected to a common inlet collective pipe 6, and a cooling medium 5, for example, water, energized by a pump 8 is passed through this inlet collective pipe 6 to the cooling pipe 4 of each cooling body 3 in parallel. supplied.

The temperature of the cooling medium 5 in the cooling pipe 4 increases due to the heat that the cooling body 3 receives from the unit battery 2, and reaches a boiling state where a part of the cooling medium 5 evaporates. In the figure, the coolant in pure liquid phase is shown as 5a, and the coolant that has partially vaporized in the cooling pipe 4 and contains vapor bubbles in the liquid phase is shown as 5b. ing. The cooling medium 5b in the gas-liquid mixed state enters the outlet collecting pipe 7 commonly connected to the outlet of each cooling pipe 4, enters the gas-liquid separator 9 from above through the outlet collecting pipe 7, and the gas-liquid separator 9 enters the gas-liquid separator 9 from above. Separated into a gas phase and a liquid phase in a liquid separator 9,
The liquid-phase cooling medium 5a accumulates in the lower part 9a of the gas-liquid separator 9, and the gas-phase cooling medium 5c, that is, the vapor of the cooling medium, exits the cooling system through the control valve 10 in the upper piping. The cooling medium accumulated in the lower part of the gas-liquid separator 9 is energized by the pump 8 and used again to cool the battery stack 1, but the heat generated in the battery stack 1 is mainly absorbed by the gas-phase cooling medium 5c. Since the cooling medium 5c discharged from the control valve 10 described above is heat recovered by a heat exchanger (not shown), it is simultaneously condensed and returned to the liquid phase cooling medium 5a.
It is injected into the lower part 6a of the gas-liquid separator 9 as a replenishing cooling medium 12.

Now, as can be easily seen, the pressure in the cooling system configured as described above is determined by the pressure in the upper part 9b of the gas-liquid separator 9.
Since the pressure of the gas-phase cooling medium 5c within the cooling system is approximately determined by the pressure, a pressure controller 11 is provided to maintain the prevailing pressure within the cooling system at a predetermined value. For example, the control valve 1 described above is used to detect the pressure of the cooling medium and keep the pressure constant.
Adjust the opening degree of 0. In addition, since the temperature of the cooling medium 5b in the gas-liquid two-phase mixed state is a temperature corresponding to the system pressure of the cooling system in the saturated vapor pressure diagram of the cooling medium, the pressure controller 11 maintains a predetermined temperature. The pressure value determines the operating temperature of the battery stack 1.

However, determining the operating temperature of the battery in this way does not guarantee that all parts within the battery stack 1 will be operated at the same temperature. That is, since the height difference h between the uppermost cooling body 3 and the lowermost cooling body 3 in the battery stack 1 shown in FIG. 1 reaches several meters in a practical fuel cell, A pressure difference of ρhg (g is the gravitational constant), which is obtained by multiplying the height difference h by the specific gravity ρ of the cooling medium 5b in a gas-liquid mixed state, is generated between the highest cooling pipe 4 and the bottom cooling pipe 4, This is because a temperature difference corresponding to this pressure difference occurs between the two cooling pipes and therefore between the parts of the battery stack in the vicinity thereof. The temperature difference between the top and bottom of the operating temperature distribution within the battery stack 1 that occurs due to such causes is caused by the fact that, as mentioned above, the height of the battery stack is several meters, and water is used as a cooling medium to lower the operating temperature to 180 degrees. If you choose around degree C 2~
At 3 degrees Celsius, this value itself may not seem large, but considering that fuel cell efficiency changes by more than 0.1% per degree C at operating temperatures around this range, it cannot be ignored. It's the amount.
As explained above, conventional cooling methods, especially methods using boiling cooling as described above, have sufficient cooling capacity, but when applied to cooling fuel cells with a large number of laminated layers, It has the disadvantage that the temperature distribution within the body cannot be made sufficiently uniform.

[Purpose of the invention]

An object of the present invention is to further improve the conventional cooling method to obtain a cooling method for stacked fuel cells that can sufficiently homogenize the temperature distribution within the stack even when applied to fuel cells with a large number of stacked layers.

[Summary of the invention]

In order to achieve the above object, the present invention first sets the cooling conditions in each cooling body to boiling cooling conditions that are more advanced than conventional ones. As is well known, the so-called boiling cooling region, where the cooling medium boils locally near the interface with the cooled object, has a higher heat transfer rate per cooling area than the so-called convective transfer region, where heat is transferred to the cooling medium in a pure liquid phase. However, in the present invention, boiling cooling conditions in a region where the gas phase content in the so-called nucleate boiling region is relatively high are adopted. As the nucleate boiling state progresses, the heat transfer coefficient increases, and almost all of the cooling medium
Since the heat transfer coefficient reaches its maximum when 50% of the gas phase is in the gas phase, it is always advantageous from the viewpoint of heat transfer rate to use boiling cooling conditions in areas where the gas phase content is high. However, advancing the boiling cooling conditions further to adopt local film boiling or film boiling conditions is not necessarily advantageous in terms of heat transfer coefficient, and it is difficult to maintain stable boiling cooling conditions for the cooling body over a long period of time. It is also not very desirable. In addition, the boiling cooling conditions naturally differ between the inlet and outlet of the cooling medium to the cooling body, and the cooling medium progresses from the inlet to the outlet, but in the cooling method of the present invention, the cooling medium at the outlet It is at least necessary to choose the boiling cooling conditions in such a way that the gas phase in the cooling medium predominates in the vicinity and therefore the pressure in the cooling medium near the outlet is determined by the gas phase. By doing this, the value of the specific gravity ρ of only the gas phase is much smaller than the specific gravity ρ of the cooling medium in a gas-liquid mixed state, so that the pressure difference ρgh based on the height difference h of the stacked battery mentioned above can be reduced. The value, and thus the value of the temperature difference corresponding to the pressure difference, becomes so small that it can be ignored in practice.

Further, in the present invention, the cooling medium flowing out from each cooling body operated under boiling cooling conditions as described above is guided to a common cooling medium collecting section, for example, a collecting pipe described below, and the cooling medium in the collecting section is The pressure of the gas phase is applied commonly to the cooling medium in each cooling body. In other words, as mentioned above, since the gas phase is already predominant in the cooling medium near the outlet of the cooling body, by introducing this state to the collecting section, the pressure of the cooling medium in each cooling body can be reduced. is completely unified to one pressure in the collecting section, ensuring that each cooling body is operated under the same cooling medium pressure conditions and therefore under the same temperature conditions corresponding to its pressure. In this way, in the cooling method of the present invention, it becomes possible to operate the fuel cell stack under a temperature distribution that is much more uniform than in the past.

[Embodiments of the invention]

Embodiments of the present invention will be described in detail below with reference to the drawings. In the following drawings, the same parts as in FIG. 1 are given the same reference numerals.

FIG. 2 shows a partially sectional view of a cooling system for carrying out the cooling method of the present invention. In this figure, all of the battery stacks 1 are shown in longitudinal section, and in addition to the unit batteries 2 and the plate-shaped cooling bodies 3 interposed at appropriate locations in the battery stack 1, there are also upper and lower clamping plates 13, 13.
is shown, and the battery stack 1 has a battery clamping plate 1
3 and 13 are tightened in the vertical direction from above and below by fastening means (not shown). The battery stack 1 is configured to supply a reactive gas from one of its side surfaces 1a and 1b and discharge the reactive gas from the other side, and has a manifold lid 14 for forming a reactive gas chamber through which the reactive gas flows. , 15 are connected to the side surface 1 of the battery stack 1 via the gaskets 14a and 15a.
a and 1b, respectively, in an airtight manner.
The cooling body 3 has an outer shape as shown in FIG.
A large number of cooling pipes 4a are embedded or penetrated by them, and the inlet and outlet parts of the cooling pipes are connected to common manifold pipes 4b and 4c.

An inlet collecting pipe 6 for a cooling medium is introduced into the reaction gas manifold chamber through the lower surface of the manifold lid 14 described above, and each cooling pipe 4 described above
a to manifold pipes 4b via connecting pipes 6a, respectively. On the other hand, an outlet collecting pipe 16 is introduced into the manifold chamber through the upper and lower surfaces of the other manifold lid 15, and is connected to the outlet collecting pipe 4c from each cooling pipe 4a via a connecting pipe 16a. ing. The outlet collecting pipe 1
The upper end of 6 is flange-connected as shown in the figure to a steam exhaust pipe 17a equipped with a liquid drain part 17a shown as an inverted U-shaped bent part, and the lower end thereof is connected to a cooling pipe 17a shown in the lower part of the figure. It is connected to the medium reservoir 18.

In the cooling medium system as described above, first, the liquid phase cooling medium 5 stored in the lower part of the cooling medium reservoir 18
a is energized by the pump 8 and is the inlet part on the left side of the figure of each cooling pipe 4 which is thermally tightly coupled to the cooling plate 3 through the inlet manifold pipe 6, the connecting pipe 6a; the inlet manifold pipe 4b; supplied to The liquid-phase cooling medium supplied to the inlet of the cooling pipe 4 in this way flows through the battery stack 1
It is immediately heated by the generated heat, and while cooling the cooling body 3 and the cooling pipe 4, it enters the nucleate boiling state described above, and as it flows from the inlet to the outlet, the gas phase becomes more dominant than the liquid phase. Near the outlet, the mixture becomes a gas-liquid two-phase mixture in which the gas phase is predominant. The cooling medium 5d in a state where the gas phase is dominant passes through the outlet manifold pipe 4c and the connecting pipe 16a to the outlet collecting pipe 1.
The liquid enters the outlet manifold pipe 16 through the opening indicated by 16b in the figure of 6 in a gas-liquid mixed state. The opening 16
b is opened at a lower position than the outlet manifold pipe 4c, as shown in the figure, and the liquid phase in the cooling medium 5d flows into the outlet manifold pipe 4c or the connecting pipe 1.
Consideration has been taken to avoid getting stuck within 6a.

The cooling medium 5d that enters the outlet collecting pipe 16 in a gas-liquid mixed state is separated into a gas phase and a liquid phase, and the internal liquid phase flows down the inner wall surface of the outlet collecting pipe 16 or in the form of droplets. The liquid then falls downward and enters the cooling medium reservoir 18 described above. On the other hand, the gas phase proceeds upward through the outlet collecting pipe and enters the aforementioned steam exhaust pipe 17.
Even if this vapor contains some liquid phase, it is separated at the liquid drain section 17a and returned to the outlet collecting pipe 16. Note that the outlet collecting pipe 16 is configured to have a larger diameter than the inlet collecting pipe 6, so that even when the liquid phase of the cooling medium falls downward, it is not blocked by this, so that the outlet The pressure in the collecting pipe 16 is determined by the pressure of the gas phase of the cooling medium therein. In this way, the outlet collecting pipe 16 acts as a collecting section for the cooling medium from each cooling body 3, plays the role of applying the pressure of the cooling medium therein to at least the outlet of the cooling pipe 4a of each cooling body 3, and It serves as a gas-liquid separator for the cooling medium.

Cooling medium steam 5c entering the steam exhaust pipe 17
is discharged through the control valve 19 controlled by the pressure controller 20 as in the case of FIG. 5a, cooling medium reservoir 1
8 is returned to the supply port 18a. The pressure regulator 20 controls the pressure in the steam outlet pipe 17 and therefore the outlet collecting pipe 16.
The pressure in each cooling pipe 4a, and thus the operating temperature of the cooling body 3, is determined by detecting the pressure inside and operating to keep it constant. On the other hand, the above-mentioned pump 8 is also operated under the control of the flow rate controller 21, and the electric motor adjusts the flow rate Q of the cooling medium transferred by the pump 8 to the flow rate QO at which the cooling medium in the cooling pipe 4a is in a proper boiling cooling state. controlled. The flow rate setting value QO to the flow rate controller 21 can be easily determined in relation to, for example, the electric power value and current value output by the fuel cell.

FIG. 4 shows a state where the manifold lid 15 is crossed, and details of the connecting pipe 16a are shown. This connecting pipe 16a connecting the outlet manifold pipe 4c and the opening 16b to the outlet collecting pipe 16 is configured as a flexible pipe, and when removing the manifold lid 15 from the side surface 1b of the battery stack, the connecting pipe joint 16c is It is designed so that the manifold lid 15, which is integrated with the outlet collecting pipe 16, can be separated by removing it.

5 and 6 are system diagrams of cooling systems to which different embodiments of the method of the present invention are applied. In these figures, the battery body 1 is schematically shown as a part surrounded by a broken line, and a cooling body 3 and its cooling pipe 4 are interposed at key points of the battery body 1, which is a laminate, as in the previous example. ing. Manifold covers 14 and 15 of the gas supply system are schematically indicated by dashed lines. In the embodiment shown in FIG. 5, the outlet collecting pipe 16 collects the cooling medium in a gas-liquid two-phase mixed state in which the gas phase is predominant from each cooling pipe 4, and also serves as a lower gas-liquid separation device. Although it does not have the steam exhaust pipe 17 and the liquid drain part 17a in FIG. 2, in the embodiment shown in FIG. By making the diameter large, it is possible to prevent the inside of the outlet collecting pipe 16 from being blocked by the liquid phase. Fifth
The steam exhaust pipe 17 in the figure is connected to the cooling medium reservoir 22, and the control valve 19 provided in the pipe is
A pressure controller 2 that detects the pressure in the gas phase space above the cooling medium reservoir 22 and works to keep it constant.
Controlled by 0. Therefore, in this embodiment, the outlet collecting pipe and the cooling medium reservoir 22 play the role of a collecting section for the cooling medium, and the operation of the cooling pipe 4 and therefore the battery body 1 is controlled by the pressure in the gas phase space. The temperature is determined.

On the other hand, in this embodiment, a throttle 23 is provided at the inlet of each cooling pipe 4, and the throttle 23 allows each cooling pipe 4 to operate under predetermined boiling cooling conditions, that is, near the exit of the cooling pipe 4. A liquid cooling medium is introduced into each cooling pipe at a flow rate that satisfies the condition that the gas phase is dominant. In this case, the pump 8 is controlled by a pressure controller 24 which detects the pressure in the inlet collecting pipe 6 and adjusts it to a constant level, so that the liquid phase cooling medium is always kept at a constant pressure. is given to the aperture 23 of.

In the embodiment shown in FIG. 6, a gas-liquid separator 25 integrated with the manifold lid 15 serves as a collection section for the cooling medium, and the cooling medium in a gas-liquid mixed state from the outlet of the cooling pipe 3 is The cooling medium in the vapor state is discharged upward, and the cooling medium in the liquid phase is stored in the lower part. The pressure controller 20 is
A control valve 19 provided in the steam exhaust pipe 17 so as to keep the pressure of the gas phase within the gas-liquid separator 25 constant.
operate. This figure shows a heat exchanger 26 that recovers latent heat in exhaust steam, and the cooling medium in a vapor state is condensed by giving latent heat to a heat medium 27 in this heat exchanger 26. It becomes a liquid-phase cooling medium and is returned to the cooling medium storage section in the lower part of the gas-liquid separation device 25 by the transfer pump or booster pump 28. In addition, in this embodiment, a control valve 29 provided on the discharge side of the pump 8
is controlled by a liquid level controller 30 that controls the liquid level 25a of the liquid-phase cooling medium in the gas-liquid separation device 25 to be constant.

〔Effect of the invention〕

In the method of the present invention, when uniformizing the temperature distribution within the battery stack by passing a cooling medium in parallel through the cooling bodies interposed within the battery stack as described above, the cooling conditions within each cooling body are adjusted accordingly. While maintaining boiling cooling conditions such that the gas phase is dominant near the outlet of the cooling body, the cooling medium in a gas-liquid mixed state from each cooling body is collected in a common collection compartment, and the gas in the collection compartment is Since the phase pressure is applied in common to the cooling medium in each cooling body, the operating temperature of each cooling body is uniquely and commonly determined by the pressure of the gas phase in the collective compartment, which is different from the conventional method. The disadvantage that the operating temperature varies depending on the intervening position of the cooling body is practically eliminated to a negligible extent. This effect remains more advantageous than the conventional method even when the capacity of the thermal battery power generation device increases and the number of stacked unit cells in one battery stack increases. That is, near the outlet of the cooling body, the gas phase with low specific gravity is predominant, so the pressure difference and temperature difference based on the height difference of the stacked battery is very small, and is hardly affected by the number of stacked cells. This is more advantageous than the conventional method.
By using the method of the present invention, the fuel cell is operated at an ideal temperature where the temperature of each part is equalized, so the overall efficiency is increased and there is little risk of deterioration due to local temperature increases. It disappears.
Furthermore, as mentioned above, this operating temperature is uniquely determined by the pressure of the gas phase in the cooling medium collection compartment, so it is easy and extremely effective to adjust the operating temperature of the battery based on the pressure at this single point. It also has the effect of allowing control.

[Brief explanation of drawings]

Fig. 1 is a system diagram of a cooling system schematically showing a conventional cooling method for a fuel cell, and Fig. 2 and subsequent figures all show examples of the cooling method for a stacked fuel cell according to the present invention. A system diagram showing a part of a cooling system in cross section to explain an embodiment of the present invention, FIG. 3 is a perspective external view showing the specific structure of a cooling body with cooling pipes in the cooling system, and FIG. 4 is a stacked fuel cell diagram. FIG. 5 is a cross-sectional view showing the connection state of the cooling pipe, collecting pipe, and connecting pipe of the cooling system in the manifold lid on the side of the body; FIG. 5 is a system diagram of the cooling system showing a different embodiment of the method of the present invention; FIG. FIG. 2 is a system diagram of a cooling system showing still another embodiment of the method of the present invention. In the figure, 1: battery body as a battery stack, 2: unit battery, 3: cooling body, 4: cooling pipe, 5: cooling medium, 5
a: Cooling medium in liquid phase, 5c: Cooling medium in gas phase, 5d: Cooling medium in a gas-liquid two-phase mixed state in which the gas phase is dominant, 6: Means for causing the cooling medium to flow through the cooling body in parallel. 16: Outlet collecting pipe as a cooling medium collecting section; 19: Control valve as means for controlling the pressure of the gas phase within the collecting section; 20: Pressure of the gas phase within the collecting section; 21: a flow rate controller as a means for controlling the flow rate of the cooling medium supplied to the cooling body; 22: a cooling medium reservoir as a cooling medium collection section and a gas-liquid separation device; 23; : Throttle as a means for controlling the flow rate of cooling medium supplied to the cooling body, 2
5: Gas-liquid separation device as a cooling medium collection section,
29: A control valve as means for controlling the supply flow rate of the cooling medium to the cooling body.

Claims (1)

[Claims] 1 Cooling bodies are interposed at multiple locations in the stacking direction of a battery stack formed by stacking unit batteries, and a cooling medium is flowed in parallel into the cooling bodies to cool the battery stack. In the method for cooling a fuel cell, cooling in each of the cooling bodies is performed under boiling conditions of the cooling medium, and under conditions such that the gas phase in the cooling medium is dominant at least near the outlet of the cooling medium in the cooling body. During operation, the cooling medium flowing out from the outlet of each cooling body is guided into a cooling medium collection section that is connected in common to each cooling body outlet and provided in the vertical direction, and the cooling medium is liquefied in the collection section. Cooling of a stacked fuel cell characterized in that the phase medium is separated into a liquid phase part and a gas phase part as it falls downward, and the pressure of the gas phase part in the collecting section is controlled so as to be at a predetermined value. Method. 2. The cooling method according to claim 1, wherein the flow rate of the liquid-phase cooling medium supplied to the cooling body is controlled so that the cooling medium in the cooling body satisfies boiling cooling conditions. How to cool batteries. 3. In the cooling method according to claim 1, the cooling medium collection section is configured as a bubble separator, and the cooling medium from each cooling body is separated into a gas-liquid mixed state in which the gas phase is predominant. A method for cooling a stacked fuel cell, characterized in that the cooling medium is guided to a gas phase compartment within the device. 4. In the cooling method according to claim 1 or 3, the cooling medium collecting section is configured as a collecting pipe arranged in the vertical direction, and the gas phase cooling medium is directed upwardly inside the collecting pipe. A method for cooling a stacked fuel cell, characterized in that a liquid phase cooling medium is separated and guided downward. 5. A cooling method for a stacked fuel cell according to claim 1, characterized in that the cooling inside the cooling body is operated under nucleate boiling conditions of the cooling medium.