Description:Complete Specification:
The following specification describes and ascertains the nature of this invention and the manner in which it is to be performed

Field of the invention

The present invention relates to a fuel cell system and more specifically to a method to control a coolant temperature in a fuel cell and a system thereof.

Background of the invention
[0001] Typically, the interfaces between a fuel cell stack and other components of fuel cell systems include Fuel inlet/outlet, where a fuel such as hydrogen is supplied to the cell stack through an inlet and the fuel outlet is used to remove water and other impurities. The water is collected in the storage tank. Further, the fuel cell stack also includes coolant inlets/outlets where a coolant is circulated through the cell stack to remove excess heat produced during the reactions inside the fuel cell stack. The stack coolant inlet temperature and the coolant flow-rate are the two main factors that affect the heat supplied or removed from the fuel cell stack, and hence the stack temperature. The coolant flow rate is controlled by an electric pump, while the coolant inlet temperature is regulated by appropriately flowing the coolant through a radiator or a heater, where the flow path is selected by a valve such as 2-position 3-way valve.
[0002] In a fuel cell stack, electrochemical reaction of oxygen and hydrogen generates electrical power, while heat and water are produced as by-products. The temperature of water at the outlet (as a by product) from the fuel cell stack, as experimentally and empirically observed, may be lower than the temperature of the coolant at the coolant outlet. The present invention aims to enhance the radiators performance to cool the coolant received from the coolant outlet by submerging a portion of the radiator in the exhaust water collection tank (storage tank) of the vehicle.

[0003] Brief description of the accompanying drawings
[0004] An embodiment of the invention is described with reference to the following accompanying drawings:
[0005] Figure 1 depicts a fuel cell system to control a coolant temperature
[0006] Figure 2 depicts a flowchart for a method to control a coolant temperature in a fuel cell system.

[0007] Detailed description of the drawings:

[0008] Fuel cell reaction produces water as the byproduct which is collected in a storage tank and the same (water) is drained in a single operation when the tank is full. This storage tank, with some modifications, can serve as a cooling solution for the high-temperature coolant received by the radiator from a coolant outlet of the fuel cell stack. The present invention proposes to split the existing radiator into two radiators, mainly a submerged radiator and a main radiator, while maintaining the same pressure across the two radiators. The smaller radiator may be submerged inside the water collection tank also referred to as the storage tank. The storage tank's drain valve (also referred to as the drain plug) maybe positioned at the top of the storage tank so the hot water will be released into the atmosphere.

[0009] The water will absorb a significant amount of heat from the high-temperature coolant passing through the submerged radiator, reducing the load on the fans otherwise used by the radiator to cool the coolant from the coolant outlet. When the water inside the storage tank is at a significantly lower temperature (close to environment temperature depending on the duration within which the vehicle was at stand still) compared to the coolant temperature (as received from the fuel stack outlet), this temperature difference can be used to harness additional cooling capacity for the radiator. The hot water from the tank may be removed at constant rate using the drain plug (on the upper region of the storage tank) to maintain the cooling capacity. Therefore, water in the storage tank can absorb significant amount of heat from the high temperature coolant (at fuel cell stack temperature) passing through the submerged radiator. The hot water will move to the top of the tank due to reduced density and will be removed by means of a drain plug.

[0010] If the water temperature near the submerged radiator reaches temperatures closer to or higher that the outlet coolant temperature, the coolant will be bypassed directly to the main radiator. Another advantage of this system is that during a stand-still running scenario, when the vehicle has been in a standtill for a long time, the water inside the storage tank will be cooled to environment temperatures. So, this water in the storage tank can also be used to remove excessive heat in the next driving cycle faster than Main radiator.

[0011] As a further advantage of the present invention, by keeping the radiator submerged in the water, freezing of the water inside the tank in lower temperature conditions can be avoided.

[0012] The present invention will now be described by way of example, with reference to accompanying drawings. Throughout all the figures, same or corresponding elements may generally be indicated by same reference numerals. These depicted embodiments are to be understood as illustrative of the invention and not as limiting in any way. It should also be understood that the figures are not necessarily to scale and that the embodiments are sometimes illustrated by graphic symbols, phantom lines, diagrammatic representations, and fragmentary views. In predetermined instances, details which are not necessary for an understanding of the present invention, or which render other details difficult to perceive may have been omitted.

[0013] Various embodiments of the present document may be implemented by software (for example, a program or an application) including one or more instructions stored in a storage medium (for example, a memory or) that may be read by a machine. For example, a processor of the machine may call at least one instruction among one or more instructions stored in the storage medium and may execute the instruction. This enables at least one function to be performed according to the at least one called instruction. The one or more instructions may include a code that is made by a compiler or a code that may be executed by an interpreter. The storage medium that may be read by the machine may be provided in the form of a non-transitory storage medium. Here, the "non-transitory storage medium" merely means that the storage medium is a tangible device and does not include a signal (for example, an electromagnetic wave), and with regard to the term, a case in which data is semi-permanently stored in the storage medium and a case in which data is temporarily stored in the storage medium are not distinguished from each other.
[0014] Referring to Figure 1, A fuel cell system (1) to control a coolant temperature is described. The fuel cell system (1) comprises a storage tank (3) comprising at least one temperature sensor. Said storage tank (3) is adapted to store a threshold-volume of water at a water-temperature T. Said threshold volume of water is received from a fuel cell stack (2) of the fuel cell system (1).According to an embodiment, an exhaust pipe (10) directs the threshold volume of water to the storage tank. According to an embodiment, this exhaust pipe may be exposed to the environment and the length of the said exhaust pipe may be such that a temperature of the water from the fuel cell stack may be further lowered as it passes through the exhaust pipe (10) to the storage tank (3).
[0015] The fuel cell system (1) may include a fuel cell stack (2) that generates electrical energy, a fuel supply device that supplies a fuel (hydrogen) to the fuel cell stack (2), an air supply device that supplies, to the fuel cell stack (2), oxygen in the air, which is an oxidizing agent required for electrochemical reaction, and a thermal management system (TMS) that removes reaction heat of the fuel cell stack (2) to the outside of the system to control an operating temperature of the fuel cell stack (2). The fuel cell stack (2) may further include plurality of inlets/outlets for fuel and coolant inlets and by-products and to remove hot coolant to be cooled again.
[0016] According to an embodiment of the present disclosure, the storage tank (3) comprises a first radiator (4a). Said first radiator (4a) is adapted to receive the coolant at a coolant-temperature t from a coolant-outlet (7) of the fuel cell stack (2) when the water-temperature T is less than a coolant temperature t. It is to be understood, that as an enablement requirement, the first radiator (4a) may either be completely submerged in the threshold volume of water or partially submerged in the threshold volume of water so as to provide a threshold area for heat exchange between the said water in the storage tank (3) and the coolant (received from the coolant-outlet (7) of the fuel cell stack (2)).
[0017] According to an embodiment of the present disclosure, the fuel cell system (1) comprises a second radiator (4b) in connection with the first radiator (4a) by means of at least one bypass valve (5) . Said second radiator (4b) is adapted to receive the coolant from the coolant-outlet (7) when the water temperature T is more than the coolant-temperature t. It is to be understood that the at least one bypass valve (5) s facilitate transfer of the coolant between plurality of cooling lines (9).
[0018] According to an embodiment of the present disclosure, a controller (6) is in communication with the at least one temperature sensor (10). Said controller is configured to control the at least one bypass valve (5) based on the coolant-temperature t and the water-temperature T. The controller may be a hardware device such as a processor, a micro processor unit (MPU), a micro controller unit (MCU), a central processing unit (CPU), and an electronic controller unit (ECU) or a program implemented by the processor. The controller may be connected to respective components of the fuel cell to perform overall functions related to management and operation of the fuel cell stack (2). As an example, the controller may be a fuel cell control unit (FCU) that controls the overall functions of the fuel cell system (1). The controller may communicate with the respective components, for example, the at least one bypass valve (5) , the temperature sensor and the like, constituting the fuel cell system (1) by wire or wirelessly, and may perform the communication based on, for example, controller area network (CAN) communication. According to an example, the controller may control the opening of the at least one bypass valve (5) and thus control the coolant from not to flow to a first cooling line (9a) including the first radiator (4a) but to flow to only the bypass line (9b) towards the second radiator (4b).
[0019] According to an embodiment of the present disclosure, the storage tank (3) comprises at least one drain-plug (8) to drain a first volume of water from an upper region of the storage tank (3).
[0020] According to an embodiment of the present disclosure, a first pressure drop across the first radiator (4a) is equivalent to the second pressure drop across the second radiator (4b).

[0021] Referring to Figure 2, the same depicts a flowchart for A method to control a coolant temperature in a fuel cell system (1). The method may be implemented by the Fuel cell system (1) as described in Figure 1. The method (100) comprises the first step (101) of submerging the first radiator (4a) in the threshold volume of water stored in the storage tank (3). The step (102) is receiving, by the first radiator (4a), the coolant at a coolant-temperature t from a coolant-outlet (7) of the fuel cell stack (2) when the water-temperature T is less than a coolant temperature t and step (103) is receiving by the second radiator (4b), the coolant from the coolant-outlet (7) when the water temperature T is more than the coolant-temperature t. The controller controls the the at least one bypass valve (5) based on the coolant-temperature t and the water-temperature T. A first volume of water may be drained from an upper region of the storage tank (3) by means of a drain-plug (8) in the storage tank (3).

[0022] The working of the present invention is described further. It is to be understood that several assumptions have been made for exemplary purposes. The same are examples to enable a person skilled in the art to work the present disclosure and the same are not to be construed as limiting.

[0023] According to an example, assuming a truck with an energy consumption of 1.2 kWh/km has 55% efficiency. Further considering the energy density of hydrogen, 0.0655 kg hydrogen may be needed for 1 km of travel. The same may produce 0.5895 kg of water per kilometer. Assuming further, an average speed of 60 km/h of the truck, the water production rate for the said truck may be as high as 0.009825 kg/s (0.5895 L/min = 35.37 L/hr).

[0024] The total heat energy which could be removed from the set up may be obtained by the formula = ?*c*(T1 - T) where, ? = mass flow rate of water (kg/s)c = Specific heat capacity of water, T1 = Tank outlet (drain-plug (8)) water temperature(K) and T = Tank inlet water temperature(K).

[0025] It is to be noted that based on empirical observations, the coolant temperature at the coolant-outlet (7) and water temperature at a fuel stack outlet (where water is produced post chemical reactions) already have a temperature difference of approximately~4 K. Therefore it is assumed that T is less than coolant temperature (t) (according to an embodiment T may be made even lower than t by increasing the path taken by the water to reach the storage the tank). Therefore, based on this temperature difference between T and t, the first radiator (4a) can remove heat from the coolant. Due to natural convection, as the water in the storage tank (3) gets hot from the radiator it may move to the top of the tank and this hot water may be removed through the drain-plug (8).

[0026] In a situation where the temperature T of the water in the storage tank (3) reaches closer to or higher than t (coolant temperature), the controller will control the opening of the at least one bypass valve (5) and thus control the coolant from not to flow to a first cooling line including the first radiator (4a) but to flow to only the bypass line towards the second radiator (4b).
, Claims:We Claim:

1. A method (100) to control a coolant temperature in a fuel cell system (1), the fuel cell system (1) comprising:
-a storage tank (3) comprising at least one temperature sensor, said storage tank (3) adapted to store a threshold-volume of water at a water-temperature T, said threshold volume of water received from a fuel cell stack (2) of the fuel cell system (1),
- the storage tank (3) comprising a first radiator (4a),
- a second radiator (4b) in connection with the first radiator (4a) by means of at least one bypass valve (5) , and
- a controller (6) in communication with the at least one temperature sensor, said controller configured to control the at least one bypass valve (5) ,
the method characterized by the steps of :
-submerging the first radiator (4a) in the threshold volume of water stored in the storage tank (3) (101),
- receiving, by the first radiator (4a), the coolant at a coolant-temperature t from a coolant-outlet (7) of the fuel cell stack (2) when the water-temperature T is less than a coolant temperature t (102),
-receiving by the second radiator (4b), the coolant from the coolant-outlet (7) when the water temperature T is more than the coolant-temperature t (103).

2. The method (100) as claimed in Claim 1, wherein, controlling, by the controller, the at least one bypass valve (5) based on the coolant-temperature t and the water-temperature T.

3. The method (100) as claimed in Claim 1, wherein, draining, by means of a drain-plug (8) in the storage tank (3), a first volume of water from an upper region of the storage tank (3).

4. A fuel cell system (1) to control a coolant temperature, the fuel cell system (1) comprising:
-a storage tank (3) comprising at least one temperature sensor, said storage tank (3) adapted to store a threshold-volume of water at a water-temperature T, said threshold volume of water received from a fuel cell stack (2) of the fuel cell system (1),

characterized in that,
-the storage tank (3) comprising a first radiator (4a), said first radiator (4a) adapted to receive the coolant at a coolant-temperature t from a coolant-outlet (7) of the fuel cell stack (2) when the water-temperature T is less than a coolant temperature t,
- a second radiator (4b) in connection with the first radiator (4a) by means of at least one bypass valve (5) , said second radiator (4b) adapted to receive the coolant from the coolant-outlet (7) when the water temperature T is more than the coolant-temperature t, and
-a controller (6) in communication with the at least one temperature sensor, said controller configured to control the at least one bypass valve (5) based on the coolant-temperature t and the water-temperature T.

5. The fuel cell system (1) as claimed in claim 4, wherein, the storage tank (3) comprises at least one drain-plug (8) to drain a first volume of water from an upper region of the storage tank (3).

6. The fuel cell system (1) as claimed in claim 4, wherein, a first pressure dop across the first radiator (4a) is equivalent to the second pressure drop across the second radiator (4b).