As current cooling solutions reach their limits, the industry is in need of a unique advanced cooling solution. nanoCoolers' liquid-metal cooling loops have all the attributes to fill that need. Part of the uniqueness of our thermal solutions is in its simplicity. The cooling loop consists of liquid metal as the working fluid, a heat source exchanger, an ambient heat exchanger, an electromagnetic pump, and interconnecting tubing. There are also attaching mechanisms, a fan, housing structure, etc. but the simplicity of the solution is quite unique.

The Liquid Metal

The liquid metal has significant advantages over other single phase liquid solutions. The thermal and physical properties of the material give it the ability to cool extremely high heat fluxes. With its very low vapor pressure, the boiling point of the material is in excess of 2000°C. This provides the capability to cool extremely high power densities without the liquid-metal changing phase, removing power density as the limiting factor in cooling performance. The liquid metal is non-flammable, non-toxic and environmentally friendly. As a metal, the liquid is both highly thermally conductive and highly electrically conductive. The thermal conductivity makes it ideal for heat removal and dissipation. The electrical conductivity enables the use of electromagnetic pumps to propel the liquid.

The Electromagnetic Pump

One unique benefit of liquid metal is the ability to pump this coolant efficiently with a silent, non-moving parts pump. The electromagnetic pump is located in-line with one of the fluid channels. It consists of magnets, a yoke and two electrodes, again ensuring the simplicity of the solution.

When a DC current is applied to the EM pump via the electrodes, the pump propels the liquid through the closed loop system, transporting the heat from the heat source exchanger to the ambient heat exchanger within the module. The force within the pump which produces the flow is known as the Lorentz force. The Lorentz force states that when current is applied to a conductor in the presence of a magnetic field, there is a mechanical force on the conductor in the direction of the right-hand rule (current x magnetic field). In our EM pump design, a magnetic field is generated within the fluid channel by an external magnet. Electrodes are positioned on each side of the fluid channel perpendicular to the magnetic field to provide the current that will flow through the liquid metal. The magnetic field in the pump is enhanced by the use of a yoke, which also decreases the magnetic fields external to the structure. As DC current flows through the liquid metal from one electrode to the other, the Lorentz Force generated on the liquid metal (the conductor) forces the liquid metal down the fluid channel. Since the liquid loop is a fully filled system, the fluid upstream flows into the channel and the process continually repeats itself, creating constant fluid flow. By controlling the DC current to the EM Pump, one can control the rate of fluid flow within the loop, making the cooling system scalable within its functional limits.

The Source Heat Exchanger (a.k.a Cold Plate)

The source heat exchanger is designed to be attached to the top of the heat source using a variety of mechanical methods. The source exchanger contains internal structures which direct the fluid over the heat source, facilitating heat removal. The liquid metal flows into the source exchanger, picks up heat from the heat source and exits the source exchanger with no transport losses as it flows to the ambient heat exchanger. The thermal properties of the liquid metal allow for conventional flow channels within the source exchanger, thus eliminating the need to manufacture expensive micro channels. This provides very high thermal performance with very low pressure drops, in turn lowering the pump power required to operate the loop.

The Ambient Heat Exchanger

The ambient heat exchanger is designed to transfer the heat from the liquid metal to ambient air, using ambient air as the thermal sink. Alternate sink heat exchangers may also be designed to allow primary heat transfer to be achieved through a range of different means including natural convection, forced air convection (using fans, blowers, etc.), conduction, fixed cold plates and even secondary fluid loops. The liquid metal enters the ambient heat exchanger hot, dissipates the heat to the ambient air and exits the ambient exchanger cool. Our ambient exchangers are designed to meet the thermal, mechanical and acoustic requirements of the specific application.

The Liquid-Metal Cooling Loop

These systems are designed to efficiently remove heat from high power and high power-density heat source(s), transport the heat to convenient locations and dissipate the heat to the heat sink(s) via the ambient heat exchanger(s). Integrated into a liquid-metal cooling loop are the source exchanger(s), the ambient heat exchanger(s), the electromagnetic pump(s), the piping to route the fluid and the liquid metal. Each system is fully filled with liquid metal and then sealed during our assembly process. Since the system is fully filled and the electromagnetic pump functions independent of orientation, the system is likewise orientation independent.

Advantages

The simplicity of the advanced cooling solution and the thermal and physical properties of the liquid metal combine for an impressive list of advantages for nanoCoolers' liquid-metal cooling loops to meet the need for more robust cooling solutions.

• Very low thermal resistances
• Silent performance
• High reliability due to no moving parts and the simplicity of the solution
• Small form factors
• High power efficiency
• Supports extremely high heat flux densities (no longer a limiting factor)
• Orientation independent
• Able to easily cool multiple heat sources
• Scalable heat removal via current control
• High volume solution based on commodity parts
• High heat transport capabilities