Heat Pipes – A Basics Demonstration

 How a Heat Pipe Works

Heat Pipes are fully sealed, passive two-phase heat transfer devices that take advantage of a fluid’s high heat of vaporization, to achieve extremely efficient heat transfer. A heat pipe is comprised of an envelope, a wick structure, and a small amount of working fluid.

The fluid is processed under vacuum, which allows for two-phase operation across a wide temperature range, during operation. Heat is input into what is known as “the evaporator”. The heat boils the fluid and pushes the fluid vapor to the colder region of the heat pipe. The colder region, which is typically coupled to a heat sink, is known as “the Condenser”. The fluid gives up its latent heat and condenses back to a liquid, and is again absorbed in the wick structure. The wick structure then passively pumps the fluid back to the evaporator.

This entire operation results in an extremely low-temperature difference across the length of the heat pipe.

Heat Pipe Demonstration

The efficient rate of heat transfer is being compared to a solid copper rod. Both the heat pipe and the copper rod are coated with Thermochromatic paint, which will change color as it transfers heat. We’ll start by moving the copper rod to the hot zone.

Copper is known as a very strong thermal conductor. It has a thermal conductivity of roughly 400 watts per meter K. As it transfers here, you can see the color change from the base of the copper rod upward. Now we’ll move the heat pipe into the hot zone. As you can see, as the fluid vaporizes and transfers, the heat pipe rapidly isothermalizes and has a very consistent temperature across the length of the heat pipe.

Now, we’ll move the copper rod and the heat pipe back to the cold zone to show that the heat pipe can work in adverse orientation and is still able to provide the same high effective thermal conductivity.

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