How to choose the best heat exchanger for hydrogen refuelling stations?

Hydrogen is a clean and renewable energy source that can power vehicles with zero emissions. However, to use hydrogen as a fuel, it needs to be stored and dispensed at high pressures, which generates a lot of heat. How can we cool down the hydrogen effectively and safely? The answer is heat exchangers. In this article, we will explain what heat exchangers are, how they work, and why they are essential for hydrogen refuelling stations. We will also introduce a novel heat exchanger technology that can offer superior performance and flexibility for the pre-cooling of hydrogen.
What are heat exchangers and how do they work?
Heat exchangers are devices that allow heat to be transferred from one fluid to another, without mixing them. They are widely used in many industrial processes that involve thermal energy transfer, such as heating, cooling, condensing, evaporating, or recovering waste heat. Heat exchangers can have different designs and configurations, depending on the type and properties of the fluids, the operating conditions, and the performance requirements. The basic principle of heat exchangers is to have two fluid streams flowing in opposite or parallel directions, separated by a solid wall or a thin metal plate (Figure 1). The hot fluid transfers heat to the cold fluid through the wall or the plate, until the temperature difference between the two fluids is minimized or equalized.

Figure 1: Examples of various Heat Exchanger types. Picture from https://www.linkedin.com/pulse/what-5-types-heat-exchanger-tianjin-anton-metal-manufacture-co-isagc/
Why are heat exchangers important for hydrogen refuelling stations?
Hydrogen refuelling stations (HRS) are facilities that provide hydrogen fuel to vehicles that run on hydrogen fuel cells. Hydrogen fuel cells are a type of electrochemical device that convert hydrogen and oxygen into electricity, water, and heat. Hydrogen refuelling stations need to store and dispense hydrogen at high pressures, typically around 700 bar, to ensure sufficient driving range for the vehicles. However, compressing hydrogen to such high pressures generates a lot of heat, which can damage the storage tanks and the fuelling equipment. Therefore, it is necessary to cool down the hydrogen before it enters the storage or the dispensing system. This is where heat exchangers come in.
Heat exchangers can be used to pre-cool the hydrogen by transferring the heat from the hydrogen stream to a cooling fluid, such as water or glycol. The cooling fluid can be supplied by a chiller, a refrigeration unit, or a natural source, such as ambient air or ground water. The choice of the cooling fluid depends on the required temperature level, the availability, and the cost of the source. The design and selection of the heat exchanger also depend on several factors, such as the type of fluid, the design conditions, the cyclic behaviour, the material requirements, the size and weight constraints, the efficiency parameters, and the marketability of the equipment.
What is the best heat exchanger technology for the pre-cooling of hydrogen?
In the RHeaDHy project, a European project that aims to develop and demonstrate a novel Hydrogen Refuelling Station concept, a welded plates heat exchanger technology was selected as the most suitable option for the pre-cooling of hydrogen. This technology, also known as Printed Circuit Heat Exchanger (PCHE), consists of a series of metal plates that are welded together by diffusion welding. The plates have patterns of grooves to form channels for the fluids (Figure 2) and to create turbulence that will enhance heat transfer.

Figure 2: Typical categories of plate corrugations. (a) washboard, (b) zigzag, (c) chevron or herringbone, (d) protrusions and depressions (e) washboard with secondary corrugations, e (f) oblique washboard, from Da Silva Mota et al., 2015, Modeling and Design of Plate Heat Exchanger. In book: Heat Transfer Studies and Applications
The PCHE technology offers several advantages, such as:
· Very high efficiency, due to the high heat transfer coefficients and the high surface area to volume ratio
· Very compact and robust, due to the low thickness of the plates and the high mechanical strength of the welds
· High flexibility, due to the possibility of customizing the plate geometry, the channel configuration, and the connection type and location
· High reliability and durability, due to the absence of gaskets (Figure 3), the resistance to thermal shocks and fatigue, and the ability to handle high pressures and temperatures
These advantages have positive impacts on the whole H2 high flow refuelling line:
· Zero waiting time between refuellings, due to continuous refrigeration loops
· Minimal filling times, due to the ability to operate at very high pressures
· Robustness, ad it is a well-proven and safe technology
The PCHE technology can help to reduce the size and weight of the hydrogen refuelling station system, as well as to improve the efficiency and safety of the hydrogen fuelling process. The PCHE technology can also be applied to other applications that require high-performance heat exchangers, such as interstage compression coolers, recuperators, reformers, or evaporators.

Figure 3: 3D visual of the heat exchanger developed by Alfa Laval.
Conclusion
Heat exchangers are key elements in the design and operation of hydrogen refuelling stations, and they need to be carefully selected and optimized according to the specific process requirements and constraints. Alfa Laval’s contribution to this project includes designing and optimizing the heat transfer system, which reduces the system’s size while enhancing the efficiency and speed of refuelling. The PCHE technology is a promising solution that can meet the challenges and opportunities of the hydrogen economy and contribute to the development of a clean and sustainable mobility sector.
Authors: Laurent Doeuvre and Frédéric Rondet (Alfa Laval), and Jean Herisson (Benkei)