Low-temperature wind tunnels (-80°C) present unique challenges with frost formation on pitot probes, which blocks pressure ports and invalidates measurements. Specialized selection and design features prevent frosting.Sensor Calibrationwelcome to click on the website to learn more!
Material selection prioritizes low thermal conductivity to reduce heat transfer from the probe to moist air, which causes condensation and frost. PEEK plastic (thermal conductivity 0.25 W/m·K) outperforms metal probes, as shown in a test where PEEK probes took 3x longer to frost than stainless steel ones at -80°C.
Hydrophobic coatings (e.g., perfluorinated polymers) with a contact angle >110° prevent water adhesion. A wind tunnel trial found coated probes remained frost-free for 8 hours, compared to 2 hours for uncoated probes. The coating must be thin (<5μm) to avoid altering hole dimensions.
Heated probe designs are effective for continuous operation. Embedding a 0.5W resistance heater in the probe tip, controlled to maintain 5°C above ambient, prevents frost without disturbing airflow. A aerospace cryogenic test used this design to collect uninterrupted data for 72 hours, whereas unheated probes required hourly defrosting.
Hole geometry also matters. Tapered ports (0.5mm tip, 1mm base) with a 30° internal angle allow frost to shed under airflow pressure, reducing blockage risk. In a -80°C, 90% humidity test, tapered holes maintained 90% flow through, while straight holes became 50% blocked after 4 hours.
Combining these features—PEEK material, hydrophobic coating, integrated heating, and tapered holes—ensures reliable operation in the coldest, most humid low-temperature wind tunnels.