ISOBAR® heat pipes are typically employed in a horizontal orientation or a similar orientation where gravity assists the charge fluid in the Isobar heat pipe to return to the evaporator section.

Ongoing research continues on ISOBAR® heat pipes to optimize performance when they are required to “work against gravity.” Acrolab consistently analyzes, investigates and tests modifications to the internal wick structure inside our ISOBAR® heat pipes to provide optimal performance for anti-gravity applications.

Optimize Isobar Heat Pipes to Work Effectively Against Gravity

In this study, our objective was to modify the design and build of Isobar heat pipes so that they will work more effectively against gravity in a vertical orientation. Several prior design and build methods used by Acrolab are specific to a given application and not necessarily as effective for other applications.  As a result, Acrolab continues to modify the design and build of our Isobars to resolve this issue and devise a reliable and repeatable process for Isobar heat pipe manufacturing for anti-gravity applications.

Engineering & Manufacturing Collaboration

Based on internal discussions between engineering and manufacturing, both copper and phosphor bronze mesh were selected in this study as the initial materials for the ISOBAR® internal wick structure required to generate the needed pumping force inside the heat pipe.

It is not unique to utilize these types of standard meshes, however, the client’s application required us to explore the compatibility of these metal meshes, and how they operated with the working fluid and the containment vessel material.  Additionally, we also needed to verify the cleaning process of the wick structure to predict the long-term performance results of the ISOBAR® heat pipe.

Test To Determine Long-Term Performance

After deciding on which mesh materials and charge fluids we were going to use, we conducted tests to determine the compatibility of these materials and fluids focusing on long-term performance, based on the client’s application and monitored the surface temperature on a scheduled regime. In one instance one of the heat pipes failed and was subsequently disassembled and analyzed to determine the failure mode of the heat pipe.

Testing Produced Positive Results

Based on the long-term temperature records for the remaining samples built at the same time and tested for 17 and 19 months respectively, the surface temperature difference (Delta-T) between top and bottom did not increase remarkably.

The two samples that were tested were charged with different fluids, one with a homogeneous fluid and the other with a hybrid fluid.

Heat Pipe With Homogeneous Fluid

The heat pipe charged with the homogeneous fluid did not show any performance degradation at all. The results of this experiment confirmed prior testing results and was important in that it provided a known performance measurement in direct relation to the other test pieces.

Heat Pipe With Hybrid Fluid

The heat pipe charged with the hybrid fluid did not show any significant performance degradation other than a small increase in delta-T along the surface, however the delta-T along the surface increased at a very slow rate.

The results of this study allowed us to modify and document changes to our design standards for similar anti-gravity heat pipe applications. We were able to validate that these anti-gravity Isobars would continue to demonstrate long-term performance improvement.