Back pressure control plays a crucial role in fuel cell testing. Over time, PCS has built extensive knowledge of and experience in fuel cell testing applications. In this blog, we share some of this with customers who are in search of the right instrument for a fuel cell testing process.

Pressure Control Considerations in Fuel Cell Testing

Although no customer or application is the same, we do see recurring topics and questions when we compare the projects that we have seen in this field. We will discuss the most important ones below.

Consistent Operating Conditions

Fuel cells require a specific operating pressure to function optimally. Back pressure control is applied to ensure that the pressure on the exhaust side of the fuel cell is kept within the desired range. This consistency in operating conditions helps in accurate and repeatable testing, ensuring reliable and comparable test results.

Water Management

Fuel cells generate water as a by-product during the electrochemical reaction. To prevent flooding or drying out of the cell, which can adversely affect its performance, proper water management is crucial. Back pressure control plays an important role in maintaining the appropriate water balance within the fuel cell system. By controlling the exhaust pressure, the back pressure control system helps regulate the water content and prevent any issues related to excessive condensation or inadequate humidification.

Fuel Cell Performance

The back pressure in a fuel cell system can impact its overall performance. High back pressure can cause a restriction in the exhaust flow, leading to increased pressure differentials across the fuel cell stack, which – in turn – can result in reduced power output, lower efficiency, and potential damage to the fuel cell components. By controlling the back pressure, the system can operate at the desired pressure differentials, optimizing the performance of the system and preventing negative side effects.

Safety Considerations

Maintaining appropriate back pressure levels is also very important for the safe operation of a fuel cell system:
Excessive back pressure can result in pressure buildup within the system, potentially leading to leaks, component failure, or even rupture.
Insufficient back pressure can lead to inadequate flow rates, poor reactant distribution, or even air ingress into the fuel cell, which can negatively impact its performance and safety.

Adequate back pressure control ensures that the system operates within safe pressure limits, mitigating potential hazards and risks.

Summarizing the Importance of Back Pressure Control in Fuel Cell Testing

Overall, back pressure control is essential in fuel cell testing to ensure consistent operating conditions, proper water management, optimal performance, and safety. By regulating the exhaust pressure, the fuel cell system can operate efficiently, generate accurate test data, and minimize the risk of damage or unsafe operating conditions.

Instrument Selection for Fuel Cell Testing Applications

When considering the requirements for an ideal back pressure control valve for fuel cell testing, several factors come into play. These are the main considerations and concerns that are relevant in this context:

1. Pressure Control Range:
   The valve should have a wide and adjustable pressure control range to accommodate different fuel cell testing conditions. It should be capable of maintaining precise pressure control within the desired range, allowing for flexibility in testing various fuel cell types and operating conditions.
2. Accuracy and Precision:
   The back pressure regulator should provide high accuracy and precision in maintaining the desired back pressure. This ensures that the fuel cell operates at the intended pressure levels, enabling reliable and repeatable testing results. The regulator should have minimal pressure fluctuations, drift, or hysteresis to prevent any negative impact on the fuel cell performance and data accuracy.
3. Responsiveness:
   The instrument should be able to respond quickly to pressure changes. In fuel cell testing, dynamic load profiles or transient conditions may occur, requiring the regulator to adjust the back pressure rapidly and accurately. A responsive regulator ensures that the fuel cell system can adapt to varying testing conditions effectively.
4. Stability and Consistency:
   The back pressure regulator should exhibit stable performance over extended periods of operation. It should maintain a consistent back pressure, even in the presence of changes in flow rates, ambient conditions, or other system variables. This stability ensures that the fuel cell testing remains reliable and consistent throughout the entire duration.
5. Compatibility:
   The control valve should be compatible with the fuel cell system and its associated components. It should be able to handle the required flow rates, pressures, and temperature ranges without introducing additional restrictions or causing excessive pressure drops. Compatibility with the fuel cell testing setup is crucial to maintain system integrity and accurate performance evaluation.
6. Safety Features:
   The regulator should incorporate safety features to protect the fuel cell system and operators. This may include pressure relief mechanisms, overpressure protection, or fail-safe mechanisms to prevent potential damage or hazardous situations in case of regulator malfunctions or system anomalies.
7. Ease of Use:
   The back pressure regulator should be user-friendly and easy to operate. It should have clear and intuitive controls for adjusting the pressure setpoint and monitoring the back pressure. Additionally, it should be easy to install, integrate, and maintain within the fuel cell testing setup.

By fulfilling these requirements, an ideal back pressure regulator for fuel cell testing can ensure accurate pressure control, reliable performance, and safe operation of the fuel cell system throughout the testing process.

The necessity of 2-Phase Flow Capabilities

Many fuel cell systems present two-phase flow conditions. Two-phase flow refers to a situation where both a gas and a liquid phase are present in the flow stream. This can occur in fuel cell systems due to the generation of water as a byproduct during the electrochemical reaction.

This means that a back pressure regulator should be able to handle the unique challenges associated with two-phase flow, ensuring effective pressure control and system performance.

Flow Capacity

The regulator should be able to handle the combined gas and liquid flow rates that occur during two-phase flow conditions. It should have sufficient capacity to accommodate the maximum anticipated flow rates without excessive pressure drops or restrictions.

Phase Separation

The back pressure regulator should incorporate mechanisms to separate the gas and liquid phases within the flow stream. This helps to prevent liquid carryover or blockages that could impair the regulator’s performance or disrupt the fuel cell operation. Methods such as built-in separation chambers or suitable flow path designs can facilitate phase separation.

Drainage and Condensation Management

The regulator should include provisions for effective drainage and condensation management to prevent the accumulation of liquid within the regulator and associated components. This ensures that the regulator remains free from liquid blockages and maintains proper functionality during two-phase flow conditions.

Materials and Coatings

The materials used in constructing the regulator should be compatible with two-phase flow conditions. They should be resistant to corrosion, erosion, or degradation caused by the presence of liquid phases. Additionally, coatings or surface treatments can be employed to enhance the regulator’s resistance to liquid-related issues.

Maintenance and Cleaning

The regulator should be designed to facilitate maintenance and cleaning procedures specific to two-phase flow conditions. This may involve easy access to internal components for inspection, removal of any accumulated deposits or debris, and the ability to flush or purge the regulator to ensure optimal performance.

The described challenges of two-phase flow need to be addressed adequately when selecting a back pressure regulator for fuel cell testing applications. This will help select an instrument that can effectively handle the varying gas and liquid conditions within the fuel cell system, ensuring accurate pressure control, stable performance, and a longer instrument lifetime.

Want to know more?

Contact us – we are happy to discuss your process conditions and help you find the perfect back pressure regulator for your process.