By Josh Perry, Editor
[email protected]

Researchers at the Rensselaer Polytechnic Institute (RPI) in Troy, N.Y. are studying wickless heat pipes in near-zero gravity environments on the International Space Station (ISS) as part of the Constrained Vapor Bubble (CVB) project.

RPI researchers studied wickless heat pipes in microgravity environments. (RPI)

According to an article from RPI, the research will study the distribution of vapor and liquid in a heat pipe operating in microgravity. A miniature heat pipe was created with pentane in a glass cuvette with square corners.

“An electrical resistance heater was attached to the evaporator end,” the article explained. “At the other end, a set of thermoelectric coolers kept the condenser temperature fixed. The transparent tube allowed the researchers to study the fluid dynamics in detail, and the sharp corners of the cuvette replaced the job of the wick.”

The experiment showed that in environments without gravity Marangoni forces, which are related to the change in a fluid’s surface tension due to change in temperature and drives the liquid from the evaporator to the condenser, overpowered the capillary forces of the heat pipe, which drives the fluid towards the evaporator.

“The researchers have countered this problem in the next stage of the CVB project by adding a small amount of isohexane to the pentane,” the article added. “Isohexane boils at a higher temperature and has a higher surface tension. This change in surface tension cancels out the temperature-driven Marangoni force, restoring the heat pipe’s performance.”

A paper about this study was published by Physics Today. The article can be found at https://physicstoday.scitation.org/doi/full/10.1063/PT.3.3704.