JPS6035469A - Cooling method of stacked fuel cell - Google Patents

Abstract

PURPOSE:To make uniform temperature distribution within a cell stack by gathering cooling media of gas and liquid mixture from each cooling body in a common gathering compartment, and commonly applying gas pressure in the compartment to cooling media in each cooling body. CONSTITUTION:Cooling bodies 3 in each of which a cooling pipe 4 is buried are arranged in a fuel cell. Each cooling pipe 4 is connected to a common inlet gathering pipe line 6 through pipe 4b, and connected to a common outlet gathering pipe line 16 through pipe 4c. Liquid medium 5a within a cooling medium reservoir 18 is supplied to each cooling pipe 4 with a pump 8 through the inlet gathering pipe 6. Two phase mixed media of gas and liquid generated by boiling are supplied to the outlet gathering pipe 16, and liquid phase is sent to the reservoir 18 and gas phase is to a vapor exhaust pipe 17. Since operating temperature of each cooling body 3 is set by only pressure of gas phase of the outlet gathering pipe 16, temperature of each part is uniformly kept even if the number of stacks of the cell is increased.

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 in the vertical direction, and a cooling body is interposed 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 through the cooling body to cool a battery stack.

1 [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, but during power generation operation, some amount of energy is generated within each unit cell. Heat is generated and must be removed in order to operate the fuel cell at a proper operating temperature. In particular, in the case of stacking a large number of unit cells, the temperature in 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. This makes it 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. It is necessary to select a cooling medium that is suitable for the operating temperature of the battery to utilize such latent heat, but since the operating temperature of recent practical fuel cells is around 180 degrees, water is It is advantageous both in terms of cost and steam pressure.

Figure 1 shows a conventional fuel cell cooling method based on this idea. 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 of the cooling bodies 3, and a cooling medium 5 is passed through them in the direction of the arrow. If connected to 6,
A cooling medium 5, for example water, energized by a pump 8 is supplied in parallel to the cooling pipes 4 of each cooling body 3 via this inlet collection pipe 6.

The temperature of the cooling medium 5 in the cooling pipe 4 rises due to the heat received by the cooling body 3 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 a pure liquid phase is indicated by 5a, and the coolant that has partially vaporized in the cooling pipe 4 and has come to contain vapor bubbles in a part of the liquid phase is indicated by 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, passes through the outlet collecting pipe 7, and enters the gas-liquid separator 9 from above). It is separated into a gas phase and a liquid phase in the gas-liquid separator 9, and the liquid phase cooling medium 5a is collected in the lower part 9a of the gas-liquid separator 9. Control valve 1 inside
0 and exits the cooling system. The cooling medium accumulated in the lower part of the gas-liquid separator 9 is energized by the pump 8 mentioned above and used again to cool the battery stack 1.
Since the heat generated inside is mainly latent heat in the gas phase cooling medium 5C, the cooling medium 5C coming out from the aforementioned control valve 10 is
As shown in the figure, heat is recovered by the high-power heat exchanger, and at the same time, it is condensed and returned to the liquid phase cooling medium 5a, and the replenishing cooling medium 12
The gas is injected into the lower part 9a of the gas-liquid separator 9 as a liquid.

Now, as is easily understood, the pressure within the cooling system configured as described above is approximately determined by the pressure of the gas-phase cooling medium 5C in the upper part 9b of the gas-liquid separator 9, so the pressure within the cooling system A pressure controller 11 is provided to keep the pressure at a predetermined value, and detects the pressure of the cooling medium in the upper pipe of the gas-liquid separator 9, and controls the control valve 10 described above so that the pressure remains constant. Adjust the opening. 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. Suwachi,
The height difference between the top cooling body 3 and the bottom cooling body 3 in the cell stack 1 shown in FIG. Top cooling pipe 4
This is because a temperature difference corresponding to the pressure difference generated between the surface cooling pipes and the bottommost cooling pipe 4 occurs between the surface cooling pipes, and thus between the parts in 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 caused by such causes can be explained by the fact that, as mentioned above, the height of the battery stack is several meters, water is used as a cooling medium, and the operating temperature is lowered to 180 degrees. If the temperature is chosen around 2 to 3 degrees Celsius, this value itself may not seem large, but the efficiency of the fuel cell changes by more than 0.1 inches per 1 degree C at operating temperatures around this range. Considering this, it is an amount that cannot be ignored. 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 stacked layers, It has the disadvantage that the temperature distribution 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 the heat transfer coefficient reaches its maximum when approximately 60% of the cooling medium is in the gas phase, so it is not possible to adopt boiling cooling conditions in the region where the gas phase content is high. This is also advantageous in terms of heat transfer coefficient. However, advancing the boiling cooling conditions further and adopting local film boiling or barge 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 undesirable from above. Further, the boiling cooling condition naturally occurs at the inlet and outlet of the cooling medium to the cooling body, and progresses from the inlet to the outlet, but in the cooling method of the present invention, the cooling medium at the outlet It is absolutely necessary to choose boiling cooling conditions such that the gaseous phase in the cooling medium is predominant in the vicinity, and therefore the pressure in the cooling medium in the vicinity of the outlet is determined by the gaseous phase.

Furthermore, 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 2, 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 leading this state to the collection section, the pressure of the cooling medium in each cooling body is reduced to a concentration. One pressure in the compartment is completely unified and it is thus ensured that each cooling body operates under the same cooling medium pressure conditions and therefore under the same temperature conditions corresponding to its pressure. In the cooling method of the present invention, it becomes possible to operate the fuel cell stack under a much more uniform temperature distribution 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 the figure B, 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 places in the battery stack 1, the upper and lower tightening is done by plates 13. .13 is shown, and the battery stack 1 is tightened in the vertical direction by fastening means (not shown) from above and below the battery clamping plates 13.13. The battery stack 1 is configured to supply a reactive gas from one of its side surfaces 1a and 1b and exhaust the reactive gas from the other side, and includes a manifold lid 14 for forming a reactive gas chamber through which the reactive gas flows. , 15 are airtightly attached to the side surfaces la and lb of the battery stack 1 via gaskets 14a and 15a, respectively. As shown in FIG. 3, the cooling body 3 is embedded with or penetrated by a large number of cooling pipes 4a, and the inlet and outlet portions of the cooling pipes are connected to a common manifold pipe 4b, 4c. is connected to.

An inlet collecting pipe 6 for the cooling medium is introduced into the reactant gas manifold chamber through the lower surface of the manifold lid 14 described above, and is connected to the manifold pipe 4b to each of the cooling pipes 4a through the connecting pipe 6a. each connected. 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 of each cooling pipe 4a through a connecting pipe 16a. ing. The upper end of the outlet collecting pipe 16 is shown as an inverted U-shaped bent part in the figure.
, 7a, and its lower end is connected to a cooling medium reservoir 18 shown at the bottom of the figure.

In the cooling medium system as described above, first, the cooling medium reservoir 1
The liquid phase cooling medium 5a stored in the lower part of the inlet collecting pipe 6. Connection pipe 6a; supplied to the left inlet portion of each cooling pipe 4 in the figure, which is thermally tightly coupled to the cooling plate 3 through the inlet manifold pipe 4b. The liquid phase cooling medium supplied to the inlet of the cooling pipe 4 is immediately heated by the heat generated by the battery stack 1, and the cooling medium 3. While cooling the cooling pipe 4, enter the nucleate boiling state as described above.
As it flows from the inlet to the outlet, the gas phase component becomes more dominant than the liquid phase component, and near the exit, a gas-liquid two-phase mixture state occurs where the gas phase component is dominant. The cooling medium 5d in a state where the gas phase is dominant is the outlet manifold pipe 4c.

The gas passes through the connecting pipe 16a and enters the outlet collecting pipe 16 from the opening indicated by 16b in the figure in the outlet collecting pipe 16 in a gas-liquid mixed state. As shown in the figure, the internuclear 1=' 16b is opened at a lower position than the outlet manifold pipe 4c, so that the outside of the liquid phase in the cooling medium 5d does not stagnate in the outlet manifold pipe 4c or the connecting pipe 16a. consideration is given.

The cooling medium 5d entering 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 is transferred to the outlet collecting pipe 1.
The liquid flows along the inner wall surface of the cooling medium 6 or falls downward in the form of drops, and enters the above-mentioned cooling medium reservoir 18. - The male gas phase proceeds upward through the outlet collecting pipe and the steam discharge pipe 1 mentioned above.
However, even if some liquid phase is mixed in this steam, it is separated at the liquid cutter 17a and sent to the outlet collecting pipe 16.
Return inward. The outlet collecting pipe 16 is also configured to have a larger diameter than the inlet collecting pipe 6, so that even when the outside of the liquid phase of the cooling medium falls downward, it will not be blocked by this. The pressure inside the tube 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 commonly 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 plays the role of a cooling medium gas-liquid separator.

The cooling medium steam 5c that has entered the steam exhaust pipe 17 is discharged through a control valve 19 controlled by a pressure controller 20 as in the case of FIG. 1, and its heat is recovered in a heat exchanger (not shown). At the same time, it is condensed to become a liquid phase cooling medium 5a, which is returned to the supply port 18a of the cooling medium reservoir 18. The pressure controller 20 detects the pressure in the steam discharge pipe 17, and therefore the pressure in the outlet collecting pipe 16, and operates to keep it constant, thereby controlling the pressure in each cooling pipe 4a, and thus controlling the pressure in the cooling body 3. Determine the operating temperature. On the other hand, the aforementioned pump 8 is also operated under the control of the flow 1 controller 21, and the flow 14Q of the cooling medium transferred by the pump 8 is controlled by 5ff, which brings the cooling medium in the cooling pipe 4a into a proper boiling cooling state. The motor is controlled by fi Q O. The flow rate setting value QO to the sweep controller 20 can be easily determined, for example, in relation to the 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 that connects the outlet manifold pipe 4b 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, it can be used as a connecting pipe joint. It is designed so that the manifold cover 15 integrated with the outlet collecting pipe 16 can be separated by removing the cover 16c.

5 and 6 are system diagrams of cooling systems adapted to different embodiments of the method of the present invention. In these figures, the battery body 1 is schematically shown as a hatched area surrounded by chain lines, and important parts of the battery body 1, which is a laminate, have front al'
%> A cooling body 3 and its cooling pipe 4 are interposed.

The 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 the cooling medium is provided to guide the cooling medium to the coolant reservoir 22, it does not play a role in gas-liquid separation. Therefore, in the embodiment shown in FIG.
This outlet collecting pipe 16 can also be configured to have a smaller diameter than that shown in FIG.

Along with this, the steam exhaust pipe 17 is connected to the coolant reservoir 22, and the control valve 19 provided in the pipe detects the pressure in the gas phase space above the coolant reservoir 22 and keeps it constant. It is controlled by a pressure controller 20 which acts to Therefore, in this embodiment, the cooling medium reservoir 22 serves as a collection section for the cooling medium, and the operating temperature of the cooling pipe 4 and therefore of the battery body 1 is determined by the pressure in the gas phase space.

On the other hand, in this embodiment, a throttle 2 is provided at the inlet of each cooling pipe 40.
3 is provided, and a liquid cooling medium is introduced into each cooling pipe through the throttle 23 at a flow rate suitable for each cooling pipe 4 to operate under a predetermined boiling cooling condition. In this case, the pump 8 is controlled by a pressure controller 24 that detects the pressure in the inlet collecting pipe 6 and adjusts the pumping to a constant level, so that a liquid phase cooling medium at a constant pressure is always supplied to the aforementioned throttle 23. Given.

In this embodiment, it is of course possible to obtain the same effect even if the pressure controller 24 includes a control valve on its discharge side instead of the pump 8 and operates the control valve.

In the embodiment shown in FIG. 6, the 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 flows from the outlet of the cooling pipe 3. 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 includes a control valve 19 provided in the steam exhaust pipe 17 to keep the pressure of the gas phase in the gas-liquid separation device 25 constant.
operate.

In this figure, a heat exchanger 26 is shown which recovers the latent heat in the exhaust steam, and the cooling medium in the vapor state is transferred to the heat exchanger 26.
By imparting latent heat to the heating medium 27 in the heating medium 27, the heating medium 27 is condensed and becomes a liquid phase cooling medium, which is returned to the cooling medium storage section at the lower part of the gas-liquid separation device 25 by the transfer pump or booster pump 28. .

In addition, (in this embodiment, the control valve 29 provided on the discharge side of the pump 8 is operated by a liquid level controller 30 that controls the liquid level 25 of the liquid-phase cooling medium in the gas-liquid separation device 25 to a constant level). controlled.

〔Effect of the invention〕

In the Kinoe method and method, 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 inside each cooling body is While maintaining boiling cooling conditions so that the gas phase is predominant 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. Since the configuration is such that the pressure of the gas phase in the cooling medium is commonly applied to the cooling medium in each cooling body, the operating temperature of each cooling body is commonly determined by the pressure of the gas phase in the collecting section. The drawback of the conventional method in which the operating temperature varies depending on the intervening position of the cooling body is completely eliminated. 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 unit cells stacked in one battery stack increases. 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 not only is the overall efficiency increased, but there is almost no risk of deterioration caused by localized increases in temperature. . Furthermore, as mentioned above, this operating temperature is uniquely determined by the pressure of the gas phase in the cooling medium collection compartment, so the operating temperature of the battery can be easily and extremely effectively controlled based on the pressure at this single point. It also has the effect of being able to.

[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 of the cooling system in the manifold lid on the body side, the collecting pipe, and the connecting pipe; 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, 5a: Cooling medium in liquid phase, 5c: Cooling medium in gas phase, 5d: Cooling medium in gas-liquid two-phase mixed state in which gas phase is dominant, 6 : Inlet collective piping as a means for flowing cooling medium in parallel to the cooling body, 1
6: Outlet collection pipe as a cooling medium collection section, 19:
Control valve as a means for controlling the pressure of the gas phase part in the collection compartment, 20: Pressure controller as a means for controlling the pressure of the gas phase part in the collection compartment, 21: Supply of cooling medium to the cooling body Flow rate controller as a means for controlling the flow rate; 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 supply flow rate of the cooling medium to the cooling body, 25: Gas-liquid separation device as a cooling medium collection section, 29: As a means for controlling the supply flow rate of the cooling medium to the cooling body Control valve, Figure 1, Figure 3, Figure 4

Claims (1)

[Claims] 1) Cooling bodies are interposed at a plurality of 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 form a battery stack. In the method for cooling a fuel cell, cooling in each of the cooling bodies is carried out under boiling conditions of the cooling medium, and under conditions in which the gas phase in the cooling medium is dominant at least near the outlet of the cooling medium in the cooling body. At the same time, the cooling medium flowing out from the outlet of each cooling body is guided into a common cooling medium collecting compartment, and the pressure of the gas phase in the cooling medium in the collecting compartment is applied to the cooling medium in each cooling body. A cooling method for a stacked fuel cell, characterized in that the fuel cells are cooled in common. 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. Cooling method for fuel cells. 3) In the cooling method according to claim 1, the cooling medium collection section is constructed as a bubble separator, and the cooling medium from each cooling body is separated into the gas-liquid mixture in a gas-liquid mixed state where the gas phase is dominant. A method for cooling a stacked fuel cell, characterized in that the cooling medium is guided to a gas phase compartment in a separation 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 within 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 pressure of the gas phase in the cooling medium collection section is controlled to a predetermined value. 6) A cooling method for a stacked fuel cell according to claim 1, characterized in that the cooling inside the cooling body is operated under the boiling condition of the cooling medium.