Application note

Leak testing of fuel cell stacks

Using Flow Controller & Pressure Meter combination for quality control

Bronkhorst’s distributor, Wagner Mess- und Regeltechnik, helped a car manufacturer by supplying a flow controller & pressure meter combination for quality control purposes. 

The essence of fuel cells is that hydrogen and oxygen do not react with each other directly, but in an indirect and controlled way. These reactants are supplied to separate parts of the fuel cell, and they react with each other inside the fuel cell with water as reaction product and an electrical current as result, which can be fed to an electric motor of a vehicle. 

To prevent a premature direct reaction of hydrogen and oxygen resulting in a lower performance of the fuel cell, there should be no short circuits leaks between the hydrogen and oxygen side, and each of the sides should not be blocked. 

For car manufacturers it is important to work with high quality fuel cell stacks. Stacks are metal plates that are assembled in parallel to a fuel cell stack. The number of metal plates depends on the capacity.  During the assembly, seals or other particles could have come between the plates, which is undesirable.

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Fuel cell for automotive industry

Application requirements

Part of the incoming quality process of our customer is to check the quality of the fuel cell. A value for an optimum flow resistance window needs to be defined, and by applying a gas flow and measuring a pressure increase or drop, the flow resistance can be quantified. A too low flow resistance is a measure for a leak, and a too high flow resistance for a partly blocked fuel cell. These tests need to be performed at the hydrogen as well as the oxygen side of the fuel cell.

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Important topics

  • Quality control - incoming goods inspection of fuel cell stacks
  • Reproducibility
  • Purity of the gas
  • Flow-pressure control
  • Flexibility

Process solution

The Bronkhorst solution consists of two flow/pressure combinations. The user can determine during the tests whether he would control the pressure and measure the flow or control the flow and measure the pressure. Both options are possible. 

Each of the flow/pressure combinations is composed of an EL-FLOW Select gas mass flow controller for air or nitrogen, and an EL-PRESS pressure meter. One combination is connected to the oxygen - cathode - side of the fuel cell, and the other combination to the hydrogen - anode - side, so that the cathode and anode side are measured separately.

Filters are applied before the gas enters the flow/pressure system, in order to remove any solid particles that might be present in the gas flow. Both tests are performed in parallel, one time forward and one time backward. 

Flow scheme leak testing fuel cell stacks
Flow scheme

Depending on the type and size of the fuel cell, the client defines a pressure/flow window. When the measurement results are inside this window, the fuel cell is approved. As part of the quality control requirements to approve or disapprove a fuel cell, the reproducibility of the test results is important.

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