Heat Pipe Freeze/Thaw Cycles and Operating Temperature

When using heat pipes or vapor chambers, there may be concerns regarding damage to, or the function of, the product when exposed to extreme temperatures. Water-based heat transfer pipes are a common example, and even transporting the product via air freight could present a risk of freezing.

Operating Temperature

It is important to note the difference between the operating (functional) temperature limit of the heat pipe and a structural limit. A functional temperature limit is established by the product shape, material, internal design, and the type of fluid used. A water-based heat pipe, for example, will lose its normal capabilities once the water freezes and no longer vaporizes and condenses to transfer heat from one end to the other. A structural limit is where the product may be physically damaged beyond a certain temperature over time. These two limits can occur simultaneously, of course.

A manufacturer might only list the effective operating range—the useful efficiency percentage–without including a limit related to the physical properties of the internal fluid. In the product specifications below, for example, the temperature range for distilled water in a specific product is given as 30C to 120C.

A legitimate concern, then, would be the effects of lower temperatures at or beyond the freezing point of the working fluid inside the heat pipe.

Freeze/Thaw Cycles

This information may not be shown in a manufacturer’s documentation, though, as the main concern is damage which may occur at high temperatures (boiling point and beyond) where the working fluid is not performing normal heat transfer via evaporation and condensation while the heat-generating source is also at a high temperature. So, if there is a concern, and the data isn’t shown, the questions can be sent to the supplier (via Digi-Key or directly) for clarification. Mainly, (01) “Does the chance of freezing during shipping pose a risk to the product?” and, (02) “Is there any freeze/thaw cycle data regarding the product?”

There may not be any formal documents or testing data to share publicly, but at the very least, there may be some assurance based on the product history and the manufacturer’s customer experience with their devices. A recent inquiry regarding water-filled heat pipes produced by Advanced Thermal Solutions, Inc., for example, was answered with, “We do not have any formal documentation covering freezing of our heat pipes, but I can tell you that our heat pipes are not damaged by freezing conditions. They can go through indefinite freeze-thaw cycles. What does damage heat pipes is exposure to temperatures over 200°C.” This is more than enough information to proceed with shipping and even most plans for designs or usage.

Digi-key has a few suppliers of heat pipes and vapor chambers within our thermal management category [ Thermal – Heat Pipes, Vapor Chambers ], or they can be found by searching for keywords from our home page [ Digi-Key ].

What is your experience with heat pipes and/or vapor chambers? Please share in the ‘Reply’ section, below.

Further reading:

ATS [ ATS Engineering eBook ]
ATS [ Heat Pipes: Heat Super Conductors ]
ATS [ Thermal Performance of Heat Sinks with Heat Pipes or Vapor Chambers for Servers ]
Wakefield-Vette [ Heat Pipe Selection Guide ]