Why Choose Liquid Cooling?

Liquid cooling beats air cooling in thermal management. It has a higher heat transfer coefficient and specific heat capacity (SHC). This boosts battery pack energy density and keeps temperatures under control.

Here’s a quick look at :

Liquid cooling comes in two types based on coolant contact: direct and indirect. It can also be active or passive. Passive systems use ambient air to exchange heat. Active systems use liquid-to-liquid heat transfer.

Direct Contact Liquid Cooling

In this system, coolant directly contacts ⇱ battery surfaces for efficient heat dissipation. Common coolants feature high thermal conductivity and electrical insulation, though limited fluidity can reduce effectiveness.

Breakthrough: Two-Phase Cooling

A cutting-edge approach uses 3M’s Novec7000 (99.5% concentration), an electronic fluorinated liquid with a boiling point of 34°C under atmospheric pressure. Tests show:

• Even at a 5C discharge rate, battery temperatures remain near 35°C.
• Below the boiling point, cooling outperforms air-based systems. At boiling, vaporization further equalizes temperatures.
• Atmospheric pressure affects boiling intensity, prompting research into pressure-controlled systems for optimized performance.

Indirect Contact Cooling

Indirect cooling uses fins or heat sinks with coolant to pull heat from batteries. For cylindrical cells, a jacket structure lets high-conductivity liquids flow freely. See the setup in follows (insert diagram of pipes around batteries).

Single-Inlet Cold Plates

Perfect for prismatic batteries with flat surfaces. Pipes or flat tubes sit between cells, carrying coolant. This indirect method avoids short circuits and boosts safety. Flow options include single-inlet single-outlet (SISO), shown in the insert diagram. Coolant can be water or a mix.

Pros: Easy to install, simple design.
Cons: High flow resistance due to battery size increases energy use. Low flow rates cause big temperature gaps.

Multiple-Inlet Cold Plates

These have 2+ inlets and outlets. Ideal for large or dense battery packs. They reduce flow resistance compared to SISO designs.

Pros: Fast cooling, high efficiency.
Cons: More complex, higher leak risk.

For prismatic lithium-ion batteries, microchannels in aluminum cold plates help. At 5C discharge, more channels cut max temps. At 5×10⁻⁶ kg/s flow, the max temp drops to 58.40°C. At 5×10⁻⁴ kg/s, temp differences shrink. In harsh conditions, water alone may not cut it—active cooling might be needed.

Serpentine Channel Cold Plates

These twist and turn to avoid uneven temps—low at the inlet, high at the outlet. Designs match battery heat patterns.

Eight shapes were tested, showing channel width and layout affect temp distribution. Uniformity matters as much as cooling power.

Ultra-Thin Fin Microchannel Cold Plates

Straight plates lose heat transfer efficiency over distance. Oblique fins fix this. At 0.1 L/min and 220 W, or 0.9 L/min and 1240 W, temps stay below 50°C. U-shaped channels and fins balance heat flow better than straight designs.

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Jacket Structure Cooling

This wraps batteries in a fluid-filled cavity. It cools in hot conditions and heats in cold ones. The system includes a battery pack, heat exchanger, and pipes.

Tests on a 5×5 cylindrical lithium-ion module showed:

• Without cooling at 5C discharge: Max temp hit 61.45°C, with a 37.63°C gap.
• With jacket cooling: Max temp was 27.86°C, with a 2.89°C gap.

Other Liquid Cooling Systems

Liquid Cooling + Heat Pump Hybrid

Combining liquid cooling with heat pump air conditioning (HPACS) lowered coolant inlet temps to 19.8°C in 42°C environments, achieving a performance coefficient of 2.36.

Dual-Loop Liquid Cooling ⇱

This system uses two circuits: a refrigerant loop and a coolant loop. A three-way valve directs coolant to radiators (low cooling demand) or condensers (high demand). While effective in extreme climates, complexity increases leakage risks.

Final Thoughts

Liquid cooling is more effective than air cooling. The following is a summary of the cooling performance based on the above literature and research:

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At Bonnen Battery, we’re pushing lithium battery tech forward. Check out bonnenbatteries.com for more. Next time, we’ll cover Heat Pipe Cooling Systems. Stay tuned!