Loop Heat Pipe,

A Two Phase Heat Transfer Device

A Highly Effective, Thermally Conductive Solution

With the advent of new electronic packaging developments, the role of thermal management is key to ensure that your design is successful.

Heat pipes are very common and widely used to dissipate heat in today’s electronic design. But as power densities increase, along with higher levels of integration for microelectronics design and miniaturization requirements, heat pipes on their own are unable to keep up.

Loop heat pipes are the next generation of thermal management tools. A loop heat pipe is a two-phase heat transfer device that uses capillary action to remove heat from a source and passively move it to a condenser or radiator.

In a loop heat pipe, the heat enters the evaporator and vaporizes the working fluid at the wick outer surface. The vapor then flows down the system of grooves directly to the condensor and where it condenses, as heat is removed by the radiator.

The two-phase reservoir at the end of the evaporator, the condenser is specifically designed to operate at a slightly lower temperature than the evaporator. The lower saturation pressure in the reservoir draws the condensate through the condenser and liquid return line. The fluid then flows into a central pipe where it feeds the wick. A secondary wick hydraulically links the reservoir and the primary wick.

Advantages Of A Loop Heat Pipe

• Transports heat up to 75 feet (23 meters)
• Totally passive with no external energy required
• They are efficient in transferring power against gravity.
• Resists gravity loads up to 9g, shock, vibration, freeze, and thaw.
• Greater flexibility to integrating them in to electronic packages.
• Versatile heat load capabilities for dissipating a few watts or many kW.
• Designs range from powerful, large size to miniature micro loop heat pipes.
• Flexible and flex fatigue resistance tested to more than 7.5 million flex cycles
• Broad operating temperature range for cryogenic to high-temperature applications
• They can transport a large heat load over a long distance, with only a small temperature difference.

The loop heat pipe is composed of evaporator, reservoir, capillary wick, vapor/liquid line, and condenser.

Different working fluids, different liquid filling amounts, different capillary wicks, different sizes, and different cooling methods will have an important impact on the performance of the loop heat pipe.

Therefore, if the loop heat pipe wants to have good heat transfer efficiency, it is imperative to discuss good processing steps and processing techniques.

When the loop heat pipe is running, the capillary wick is heated, the liquid in the capillary wick is heated and vaporized, and the gas passes through the vapor line to enter the condenser for condensation.

After the condensation, the liquid flows back into the reservoir and the inside of the capillary wick through the liquid line.