JP2003114083A - Cooling water circulating system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cooling water circulating system excellent in freeze proofing of a cooling water, cooling efficiency and circulating efficiency. SOLUTION: The system is provided with a cooling water circulating means 12 cooling a device 3 to be cooled by circulating the cooling water made of water mixed with a freezing-point depressant, and a freezing-point depressant concentration regulating means 11 connected to the cooling water circulating means 12 through a pressure regulating valve 8 to regulate the concentration of the freezing-point depressant in the cooling water. The freezing-point depressant concentration regulating means 11 is provided with antifreeze containers 5 and 6 containing solutions different in the concentration of freezing-point depressant and those are connected with each other through a water separation membrane 7. The antifreeze container 5 and 6 are provided with pressure regulating means 13 and 14 respectively to regulate each internal pressure, and regulates the amount of water permeating the water separation membrane 7 to determine the concentration of the freezing-point depressant.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cooling water circulating device, and more particularly to a cooling water circulating device in a low temperature atmosphere.

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cooling water circulating device for circulating cooling water when cooling with cooling water. As a conventional technique, a cooling water circulating device is used for a polymer electrolyte fuel cell. JP-A-5-190193 used for cooling
There is something like an issue.

Generally, a fuel cell is a device for directly converting the chemical energy of the fuel into electric energy by an electrochemical reaction between a fuel gas such as hydrogen which is a reaction gas and an oxidant gas such as air. This fuel cell is classified into various types according to the difference in the electrolyte, and as one of them, a solid polymer fuel cell using a solid polymer as an electrolyte is known. The electrode reactions that proceed at both the fuel electrode and the oxidizer electrode at this time are as follows.

[0004]

[Formula 1]

When hydrogen gas is supplied to the fuel electrode, the reaction formula (1) proceeds at the fuel electrode to generate hydrogen ions.
In the hydrated state, the generated hydrogen ions move into the electrolyte, for example, in the case of a solid polymer electrolyte fuel cell, to move to the inside of the solid polymer electrolyte membrane to reach the oxidizer electrode, and the oxygen-containing gas such as air is supplied to the oxidizer electrode Then, the reaction formula (2) proceeds. The electrode reaction of (1) and (2) proceeds at each electrode, so that the fuel cell produces an electromotive force.

In the power generation using such a fuel cell, the chemical energy of the fuel, which cannot be converted into electric energy, is released as heat. Therefore, it is widely known to cool the fuel cell with circulating cooling water in order to allow the reaction to proceed smoothly.

By the way, such a polymer electrolyte fuel cell normally operates at about 80 ° C., but when used outdoors, the temperature may drop to below freezing. It is necessary to take measures to freeze the whole.

In particular, when the fuel cell system is mounted on a vehicle or the like, the cooling water obtained by mixing the water with a freezing point depressant is used as the cooling water for the fuel cell in consideration of movement to a cold region or operation without a hindrance in a cold region. Is generally used. The addition amount of the freezing point depressant mixed with water varies depending on the temperature of each region, and it is necessary to mix more freezing point depressant in a region where the outside temperature is lower.

[0009]

[Problems to be solved by the invention] However,
The polymer electrolyte fuel cell adopting such a conventional method has the following problems.

As the mixing ratio of the freezing point depressant increases, the heat capacity of the cooling water mixed with the freezing point depressant decreases. Therefore, in the cooling water mixed with the freezing point depressant, the heat exchange function for cooling the fuel cell decreases as the mixing ratio of the freezing point depressant increases. In the fuel cell, it is preferable from the viewpoint of power generation performance to control the temperature distribution uniformly in each cell and in the cell plane. From the standpoint of uniform control of heat distribution in the fuel cell during power generation, the cooling water must have a heat capacity capable of sufficiently removing heat, so the mixing ratio of the freezing point depressant should be minimized. desirable.

Further, the viscosity of the cooling water increases as the proportion of the freezing point depressant mixed increases, and as a result, the pressure required to circulate the cooling water increases. For this reason,
Since the capacity of the pump required for circulation becomes large, and as a result, it is necessary to provide a large pump, the system size becomes large and the cost increases.

As described above, by adding a freezing point depressant necessary for cooling water for a fuel cell as a measure against freezing of the fuel cell, there are problems such as poor heat exchange function and poor circulation due to increase in viscosity of the cooling water. However, it is unavoidable that a total reduction in efficiency will occur.

Therefore, the present invention prevents freezing of the cooling water especially at low outside air temperature, optimizes the cooling efficiency of the cooling water when the cooled device such as the fuel cell is in operation, and further when the cooled device is in operation. It is an object of the present invention to provide a cooling water circulation device that also improves the circulation efficiency of cooling water.

[0014]

[Means for Solving the Problems] The first invention is a cooling water circulating means in which a cooled device cooled by cooling water is installed in the middle of a path for circulating the cooling water in which water is mixed with a freezing point depressant. Freezing point depressant concentration adjusting means for adjusting the concentration of the freezing point depressant contained in the cooling water circulating means.

In a second aspect based on the first aspect, the cooled device is a fuel cell of a polymer electrolyte fuel cell power generation system.

In a third aspect based on the first or second aspect, the freezing point depressant concentration adjusting means is provided with a plurality of antifreeze containers for storing solutions having different freezing point depressant concentrations, and water is provided between the antifreeze containers. The freezing point depressant concentration is adjusted by interposing a water separation membrane that allows only the water to pass therethrough, and adjusting the amount of water in each of the antifreeze containers.

According to a fourth aspect of the present invention, in the third aspect of the present invention, pressure control means for adjusting the pressure in the antifreeze container from the outside is provided, and the amount of water that permeates the water separation membrane is adjusted by the pressure control means. Adjust the amount of water in the antifreeze container.

In a fifth aspect based on the fourth aspect, the freezing point depressant concentration adjusting means controls the pressure adjusting means in accordance with the temperature of the environment of the device to be cooled.

In a sixth aspect based on the fourth aspect, the freezing point depressant concentration adjusting means controls the pressure means according to the temperature of the device to be cooled.

In a seventh aspect based on any one of the first to sixth aspects, the cooling water circulating means and the freezing point depressant concentration adjusting means are connected via a pressure adjusting valve, and the cooling water circulating means and the freezing point are connected. The internal pressure of the depressant concentration adjusting means is independently controlled.

[0021]

According to the first aspect of the invention, the cooling water circulating means cools the device to be cooled, while the freezing point depressant concentration adjusting means for adjusting the concentration of the freezing point depressant contained in the cooling water is provided. The freezing point depressant can be adjusted to a low concentration within the range where the antifreezing of water is maintained, and the cooling / circulation efficiency in the cooling water circulation means can be improved.

According to the second aspect of the present invention, by using the polymer electrolyte fuel cell as the device to be cooled, the heat removal efficiency of the cooling water during the operation of the fuel cell can be improved from the freezing point depressant concentration required for storage in cold regions. The concentration of the freezing point depressant can be adjusted to a concentration range that optimizes the cooling water circulation efficiency. Thereby, the cooling water in consideration of the movement to the cold district or the operation without any trouble in the cold district can be used as the cooling water of the fuel cell, and the cooling / circulation efficiency in the cooling water circulation means can be improved.

According to the third aspect of the invention, a plurality of antifreezing liquid containers containing solutions having different freezing point depressant concentrations are connected through a water separation membrane, and the amount of water that permeates the water separation membrane is adjusted, respectively. It is possible to adjust the freezing point depressant concentration of the solution contained in the unreasonable liquid container, and the freezing point depressant concentration of the cooling water circulation means can be adjusted.

According to the fourth aspect of the present invention, the antifreezing liquid container, which is connected through the water separation membrane and contains the solutions having different freezing point depressant concentrations, is provided with the pressure adjusting means capable of adjusting the pressure from the outside. The pressure exerted on the water separation membrane by each of the solutions in contact with each other through the separation membrane can be adjusted, and the amount of water movement between the water separation membranes can be adjusted according to the pressure difference.

According to the fifth aspect of the invention, the freezing point depressant concentration of the cooling water can be adjusted to a low concentration within the range in which freezing can be avoided according to the temperature of the environment of the device to be cooled. The circulation efficiency and cooling efficiency can be improved.

According to the sixth aspect of the present invention, by providing the means for controlling the pressure in the antifreeze container according to the temperature of the device to be cooled, the concentration of the freezing point depressant having a heat capacity necessary for heat removal of the device to be cooled can be reduced. Since the cooling water can be circulated, the efficiency of the entire fuel cell system can be improved.

According to the seventh invention, by independently controlling the internal pressures of the cooling water circulating means and the freezing point depressant concentration adjusting means, even if the inside of the freezing point depressing agent concentration adjusting means has a high pressure, the cooling water circulating means is controlled. Cooling can be done without any effect.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION In the first embodiment, a polymer electrolyte fuel cell 3 (see FIG. 3, hereinafter referred to as "fuel cell 3") using the present invention in a polymer electrolyte fuel cell system is used as a device to be cooled. A case where this is applied to a cooling device that circulates cooling water to cool it will be described.

First, the cooling water used for cooling is water mixed with a freezing point depressant such as ethylene glycol or glycerin. In this embodiment, ethylene glycol is added to the water at a concentration of 5 to 60 Vol%. Use mixed cooling water.

FIG. 1 shows the relationship between the concentration of ethylene glycol used as a freezing point depressant in cooling water and the heat capacity and viscosity of cooling water in the first embodiment. Here, the heat capacity ratio and the viscosity ratio of the cooling water represent a relative ratio when the heat capacity and the viscosity of the water are 1. As shown in FIG. 1, the heat capacity of the cooling water gradually decreases as the concentration of the freezing point depressant increases. That is, when the concentration of the freezing point depressant increases, the amount of heat that can remove a certain amount of cooling water decreases, and the heat exchange efficiency in the cooling system of the fuel cell 3 deteriorates.

Particularly in the fuel cell 3, the temperature difference between the cooling water and the fuel cell is smaller than that in the engine and the like, so it is desired to reduce the amount of circulating cooling water to reduce the loss in the circulation system. In this case, it is desired that the heat capacity of the cooling water is large.

On the other hand, as also shown in FIG. 1, the viscosity of the cooling water increases as the concentration of the freezing point depressant in the cooling water increases. In the fuel cell 3, the flow path of the cooling water is particularly narrow as compared with the engine, etc., and as the viscosity of the cooling water increases, the pump discharge pressure required for circulation increases, so that not only the circulation efficiency of the cooling water deteriorates, but also Preparing the circulation pump 2 (see FIG. 3) having the capacity necessary for discharging is very costly and not a good idea. In addition, since a pump having a large capacity also has a large size, a large limitation is imposed on the layout for mounting on a vehicle.

Further, FIG. 2 shows ethylene glycol in the case where ethylene glycol is used as a freezing point depressant for cooling water in consideration of movement to a cold region in a vehicle equipped with a fuel cell system or operation without any trouble in the cold region. It is a general example showing the minimum mixing ratio. The lower the temperature of the environment of the fuel cell system, the greater the amount of freezing point depressant that must be mixed into the cooling water to avoid freezing.

From these, it can be seen that when the environmental temperature is low, the freezing point depressant concentration of the cooling water should be as low as possible within the range where freezing can be avoided. Therefore, FIG. 3 shows a schematic configuration of the cooling water circulation device in the present embodiment for optimally using the cooling water in the fuel cell 3.

In this cooling water circulation device, a cooling water circulation system 12 for cooling the fuel cell 3 by circulating the cooling water with the fuel cell 3 as a part of a pipe, and a freezing point depression in the cooling water flowing through the cooling water circulation system 12 It comprises a freezing point depressant concentration adjusting system 11 for adjusting the concentration of the agent.

First, the cooling water circulation system 12 is constituted by the cooling water tank 1, the circulation pump 2, the fuel cell 3 (device to be cooled) and the heat exchanger 4, and the cooling water is circulated in one direction with respect to these components. . That is, the cooling water in the cooling water tank 1 is pumped up by the circulation pump 2, and the cooling water circulation system 12
Is supplied to the cooling water pipeline in the fuel cell 3 which is a part of the fuel cell 3 to cool the fuel cell 3.

A heat exchanger 4 for removing the temperature of the circulating cooling water to a temperature required for cooling the fuel cell 3 is installed downstream of the cooling water pipe in the fuel cell 3. The cooling water that has become high in temperature by cooling the fuel cell 3 reaches a temperature at which the heat exchanger 4 can cool the fuel cell 3 again, and is returned to the cooling water tank 1 again.

Although the circulation pump 2 is installed downstream of the cooling water tank 1, the circulation pump 2 may be installed downstream of the cooling water pipe of the fuel cell 3.

On the other hand, the freezing point depressant concentration adjusting system 11 is composed of an antifreezing liquid container 5 and an antifreezing liquid container 6 containing solutions having different freezing point depressing agent concentrations. It connects through the separation membrane 7. Here, the water separation membrane 7 is installed so that the water separation membrane 7 is always in contact with the solution in the antifreezing liquid containers 5 and 6.

The antifreeze container 5 is connected to the cooling water tank 1 of the cooling water circulation system 12 via the pressure adjusting valve 8. In addition, pressure control valves 13 and 14 are provided in the antifreeze containers 5 and 6, respectively.
Is installed and the pressure in the antifreezing liquid containers 5 and 6 is adjusted to cause a pressure difference between the antifreezing liquid containers 5 and 6. By adjusting the amount of water passing through the water separation membrane 7 by this pressure difference, the freezing point depressant concentration of the solution in the antifreeze container 5 is adjusted, and finally the freezing point depressant concentration in the cooling water is adjusted. Further, the pressure adjusting valves 13 and 14 are connected to the controller 9, and the controller 9 controls the pressure adjusting valves 13 and 14 based on the measurement result from the temperature measuring device 10 that measures the environmental temperature of the fuel cell system. .

The controller 9 determines the concentration of the freezing point depressant at which the cooling water does not freeze under the measured environmental temperature according to the map shown in FIG. When the freezing point depressant temperature is determined, the amount of water required to bring the solution in the antifreezing liquid container 5 to the freezing point depressant concentration determined according to FIG. Then, the pressure difference between the antifreezing liquid containers 5 and 6 that allows water to pass through the water separation membrane 7 by that amount is calculated, and the pressure adjusting valves 13 and 14 are adjusted.

As a result, the insides of the antifreeze containers 5 and 6 adjacent to each other through the water separation membrane 7 are adjusted to the osmotic pressure necessary for water to permeate through the water separation membrane 7, and the freezing point depressant depending on the osmotic pressure. Adjusted to concentration.

The solution whose freezing point depressant concentration has been adjusted in this way is supplied to the cooling water circulation system 12 via the pressure adjusting valve 8. By adjusting the pressure adjusting valve 8 according to the pressure in the antifreeze liquid container 5, the influence on the cooling water circulation system 12 can be alleviated even when the pressure in the antifreeze liquid container 5 is high. In this way, the pressures in the cooling water circulation system 12 and the freezing point depressant concentration adjusting system 11 can be made independent.

Here, the water separation membrane 7 shown in FIG.
It consists of an ultrafiltration membrane with a pore size of less than 05 μm (a filtration membrane used when pressure is applied to control the concentration. It has strength to withstand pressure), and the molecular diameter of ethylene glycol, which is a freezing point depressant in a solution. Using the difference in the size of the water molecule, only the water molecules are allowed to pass through the filtration membrane between the antifreeze containers 5 and 6.

As the ultrafiltration membrane in the water separation membrane 7, a porous membrane is formed by membrane formation using various materials such as polyacrylonitrile, cellulose acetate and polysulfone. The material is not particularly limited, but it is preferable to select a highly durable material because water separation is performed by adjusting the pressure.

As described above, by adjusting the concentration of the cooling water to a concentration suitable for the measured environmental temperature and circulating the cooling water, the decrease of the heat capacity of the cooling water and the increase of the viscosity are suppressed, and the inside of the fuel cell 3 is suppressed. Can be prevented from freezing. Also, when a fuel cell system equipped with such a cooling device is installed in a vehicle, use cooling water for cooling the device to be cooled in consideration of movement to a cold region or operation without hindrance in the cold region. In addition, the heat removal and circulation efficiency of the cooling system can be improved.

FIG. 5 shows a schematic configuration of the cooling water circulation device in the second embodiment. Here, the temperature that determines the concentration of the freezing point depressant is the temperature of the cooling surface of the fuel cell 3, which is the device to be cooled.

That is, the temperature measuring device 10 is installed in the fuel cell 3 which is the device to be cooled, and the measured temperature is measured by the controller 9
To enter. The controller 9 calculates the amount of heat to be removed from the measured temperature, and determines the freezing point depressant concentration of the cooling water according to the map as shown in FIG. 1 in consideration of the heat capacity and the viscosity required for the removal. Once the concentration is determined, the concentration of the solution is adjusted from the pressure difference between the antifreeze containers 5 and 6 as in the first embodiment, and the solution is supplied to the cooling water circulation system 12 to obtain suitable cooling water.

By thus determining the freezing point depressant concentration according to the temperature of the fuel cell 3, the cooling water required for heat removal can be circulated, and the efficiency of the fuel cell system can be improved.

Here, if both the environmental temperature and the fuel cell temperature can be measured by the temperature measuring device 10, freezing of the cooling water is prevented by setting the freezing point depressant concentration suitable for the environmental temperature during storage in cold regions. During the operation of the fuel cell system, by setting the concentration of the freezing point depressant suitable for the temperature of the fuel cell 3, efficient circulation / cooling can be performed.

It is needless to say that the present invention is not limited to the above embodiment, and various modifications can be made within the scope of the technical idea described in the claims.

[Brief description of drawings]

FIG. 1 is a relationship between the heat capacity of water and the relative ratio of the fuel cell 3 when the viscosity is 1, and the concentration of ethylene glycol as a freezing point depressant.

FIG. 2 is a diagram showing an ethylene glycol concentration suitable for an ambient temperature.

FIG. 3 is a block diagram of a cooling water circulation device according to the first embodiment.

FIG. 4 is an image diagram of a water separation membrane for concentration adjustment.

FIG. 5 is a block diagram of a cooling water circulation device according to a second embodiment.

[Explanation of symbols]

3 Fuel Cell 5 Antifreeze Container 6 Antifreeze Container 7 Water Separation Membrane 8 Pressure Adjustment Valve 10 Temperature Measuring Device 11 Freezing Point Depressant Concentration Adjusting System (Freezing Point Depressant Concentration Adjusting Means) 12 Cooling Water Circulation System (Cooling Water Circulating Means) 13 Pressure Adjusting Valve ( Pressure adjusting means) 14 Pressure adjusting valve (pressure adjusting means)

Claims (7)

[Claims] 1. A cooling water circulating means in which a device to be cooled for cooling with cooling water is installed in the middle of a path for circulating cooling water in which water is mixed with a freezing point depressant, and a content concentration of the freezing point depressant in the cooling water circulating means. And a freezing point depressant concentration adjusting means for adjusting the cooling water circulating device. 2. The cooling water circulation device according to claim 1, wherein the cooled device is a fuel cell of a polymer electrolyte fuel cell power generation system. 3. The freezing point depressant concentration adjusting means comprises a plurality of antifreeze containers for containing solutions having different freezing point depressant concentrations, and the antifreeze containers are connected to each other with a water separation membrane interposed between them to pass only water. The cooling water circulation device according to claim 1 or 2, wherein the freezing point depressant concentration is adjusted by adjusting the amount of water in each antifreeze container. 4. An amount of water in the antifreezing liquid container is adjusted by providing a pressure adjusting means capable of adjusting the pressure in the antifreezing liquid container from the outside, and adjusting the amount of water passing through the water separation membrane by the pressure adjusting device. The cooling water circulation device according to claim 3. 5. The cooling water circulating device according to claim 4, wherein the freezing point depressant concentration adjusting means controls the pressure adjusting means in accordance with the temperature of the environment of the device to be cooled. 6. The cooling water circulating device according to claim 4, wherein the freezing point depressant concentration adjusting means controls the pressure means according to the temperature of the device to be cooled. 7. The cooling water circulating means and the freezing point depressant concentration adjusting means are connected via a pressure adjusting valve, and the internal pressures of the cooling water circulating means and the freezing point depressant concentration adjusting means are independently controlled. The cooling water circulation device according to any one of 1 to 6.