Heat Pipes

What is a heat pipe: A heat pipe is tool used to transfer large amounts of heat very quickly. It is constructed of a vacuum sealed metal pipe, commonly copper, which is internally lined with a wick and filled with a working fluid.

How does it work: When one end of the heat pipe is exposed to temperature, the liquid inside will evaporate. The increased pressure forces the vapor towards the other, cooler, end of the pipe. Once there, the vapor rapidly condenses back into a liquid form, which releases the latent heat, and the wick pulls that liquid back to hot side once again.

Heat Pipe vs Vapor Chamber: These two are very similar. The only major difference being, a heat pipe is a round or partially flattened tube, while a vapor chamber is a large flat plate. 345-1654-ND and 345-1564-ND for reference

Why use a heat pipe: Heat pipes are essentially thermal super conductors, due to the speeds at which they are able to transport heat. To give some substance to that claim, the figure below shows a comparison of a normal copper pipe and a copper-water heat pipe.

As you can see, the heat pipe is able to transfer heat in an incredibly small fraction of the time.

Limiting factors of a heat pipe: With all this being said, heat pipes are not always the perfect solution. There are several limiting factors to consider when planning an application.

  • Power Cooling: How much cooling power will you need?
  • Diameter: Will the diameter you select allow that level of power cooling?
  • Wick style: Sintered Powder, Axially Grooved, Wire Mesh. All these styles have unique benefits and drawbacks.
  • Orientation: Some heat pipes are reliant of gravity to function properly, while some completely ignore the effect. These variables can also be changed due to the power cooling requirements, and the temperature difference.
  • Temperature Difference: There is a direct correlation between the change in temperature between the evaporator and condenser, and the amount of power able to be dissipated.
  • Length: The longer the pipe, the less efficient the system. For example, ATS2160-ND and ATS2161-ND are the same construction but different lengths. At 100mm has 70W of cooling power, while at 150mm the cooling power is reduced to 49W.

Sources and additional information: https://www.qats.com/cms/wp-content/uploads/Heat-Pipe-Engineering-eBook.pdf