3 Strategies for motorsport engineers to maximize performance - passively.

Both electric and hybrid powertrains present distinct cooling challenges resulting in differing cooling architectures for each. ICE hybrids require high temperature coolant circuits (150C) for the engine in contrast to BEV's with a water-glycol battery circuit that is much lower in temperature (30-40C) . Yet both powertrains will include power electronics, batteries and e-motors simply on a larger, more powerful scale when used in isolation.

Source: Extreme E

Minimizing weight and energy consumption to maximize range

In motorsport, every gram counts. The weight of the cooling system directly impacts the vehicle's speed, handling, and energy efficiency. This is extra important in full-electric racing cars, where their range is significantly reduced in comparison to their ICE counterparts. Limited range = limited racing.

Two-phase cooling offers the ability to save energy as systems can be fully passive. This also can reduce or remove the need for a pump saving additional energy and more notably weight. In turn both offer the opportunity to maximize range.

Balancing integrated or separated cooling systems

Choosing between combined and separated cooling systems depends on the specific requirements of the vehicle.

Integrated designs, which can use a global cooling loop acting as a kind of thermal bus for multiple components, we see this in BEVs with water-glycol loops and a large heat exchanger at the front of the vehicle. The problem is running many additional lines off to cool the ever increasing number of components that require cooling creates a bunch of complexity and a maze of hoses and connectors that begin to add cost and weight. These hoses also add additional pressure drop to the global loop requiring larger pumps to force the liquid around.

Separated designs, with dedicated cooling loops for each component can be extremely effective minimizing weight through short simple loops. The challenges arise in finding cold air on the vehicle to use as a cold source, plus the cost can add up when you factor in the repeated use of small pumps.

In reality the balance is to utilize both approach's where it makes the most sense. Running a long hose to the back of a vehicle to cool an on-board charger can be overkill when it can be cooled effectively with a small isolated systems.

Achieving a high performance yet passive design

Passive, two-phase systems can be an effective tool to ease the design process. Isolated on their own they can provide lightweight, pump-free systems to cool small components/systems. While they can also be combined bringing the heat from components to the global cooling loop. In this case you are adding (investing if you like) a thermal resistance but your return on investment is from the lower pressure drop, a lighter system (one line is vapor) and a reduction in requirements for the global pump.

Two-phase cooling leverages the process of vaporization, where liquid coolant absorbs heat and transforms into vapor, boasting a significantly higher heat transfer coefficient than single-phase cooling methods. This allows it to manage much higher heat fluxes, ensuring that critical components remain within optimal temperature ranges.

Furthermore, its inherently passive design enhances reliability and reduces maintenance needs. This passive nature makes it an ideal solution for the demanding conditions experienced in motorsport.

2 well executed examples of high performance yet passive cooling.

Source: Mercedes

Example 1: Mercedes Benz Vision EQXX

Mercedes-Benz's Vision EQXX concept car incorporates a unique passive air cooling system to optimize efficiency and extend battery range. Unlike conventional liquid cooling systems that require pumps and add weight, the EQXX relies on natural airflow around the battery and an integrated heat sink. Vents on the battery pack open to allow more air circulation when temperatures rise, ensuring optimal cooling without the need for active components. The underbody plate also maximises the benefit from natural airflow during operation.

This approach works because the EQXX's battery isn't pushed to high energy outputs, reducing heat generation. The car's design—boasting an ultra-low drag coefficient of 0.17—also maximizes airflow, further aiding the cooling process. Additionally, the use of a 900V architecture minimizes energy loss due to heat, reducing the requirements for the cooling system. This method significantly contributes to the vehicle's record-setting 621-mile / 1000km range on a single charge.

More detail in the image below.

Source: Mercedes via The Drive

Example 2: Off-Road Motorsport

Here the primary objective was to avoid placing water inside the battery pack itself - instead Calyos' Micro Channel Heat Pipe system was used to passively extract the heat to the top of the pack where it can be dissipated into the water glycol loop or into the ambient air.

An inverted 'L' shape design is utilized to dissipate heat efficiently into the coolant channel above the battery. This system is capable of removing 5.5 kW of thermal energy in total, facilitated by 45 heat pipes, each dissipating 122 W. These heat pipes have a thermal resistance of 0.3 K/W, providing the effective removal of heat.

An unexpected advantage observed by the end user is a significant reduction in battery degradation over time, leading to longer battery lifetimes. This is due to better inter and intra cell temperatures.

Source: Calyos

Two-phase cooling offers numerous advantages for motorsport engineers aiming to maximize performance. Its high heat transfer coefficient, lightweight design, and passive operation make it an ideal solution for managing the intense thermal loads of modern powertrains.

By adopting two-phase cooling strategies, engineers can push the boundaries of what is possible in motorsport, achieving unparalleled performance and efficiency.