AEDC Tunnel 9 Coaxial Thermocouple Requirements.docx

AEDC Tunnel 9 Coaxial Thermocouple Requirements

Background The majority of the heat transfer measurements made in the AEDC Hypervelocity Wind Tunnel 9 facility have been collected using coaxial thermocouples mounted directly into a stainless steel substrate (15-5PH or 17-4PH stainless steel) test article. Typical wall thickness of the steel substrate generally ranges between 0.25”- 0.5”, and the interior volume to route lead wires can be limited. These installation limitations require the sensor length to be similar to the wall thickness, and the transition from the sensor shell to the lead wires must occur close to the base of the sensor. Finally, a thin layer of temperature sensitive paint is often applied directly on the wind tunnel model after the coaxial thermocouples have been installed and contoured to the test article.

Type-E, Chromel-Constantan, coaxial thermocouples have been successfully utilized for over 30 years in the unique and stressing Tunnel 9 hypervelocity test environment due to their high durability, fast-response times, and their ability to be contoured to the outer mold lines of the test article. Surface temperature response is acquired during the test run using a coaxial thermocouple and the heat transfer is derived using the coaxial thermocouple temperature data as a boundary condition to a finite-differencing solution of the transient heat conduction equation for a finite thickness wall.

Technical Specifications

1. NIST-traceable Type-E, Chromel-Constantan thermocouple materials (outer sheath Chromel and inner pin Constantan)

2. Outer sensor cylinder diameters of 0.061” and 0.031”

3. Sensor length options of 0.375” and 0.5” or longer

4. The sensor length may be trimmed down for installation in thinner walls or to fit into limited internal volume of the model without adverse effects to sensor operation

5. Sensor to be installed into test article using adhesives such as Loctite #271 or #620

6. Sensor can be contoured to outer-mold-lines of a test article after adhesive fully cured

7. Thermocouple junction at the outer surface of the model created by abrasion (file and/or sand paper).

8. Fast response time to metal wall surface temperature changes, typically on the order of microseconds

9. Transition from coaxial thermocouple body to lead wires to occur close to body, approximately 0.15 or less”

10. Any strain relief applied between the coaxial thermocouple body and lead wires cannot be larger than the cylindrical diameter of the coaxial thermocouple body

11. Lead wires from coaxial thermocouple assembly to be provided as Type-E thermocouple wire. Lead wires should be no larger than 30 AWG Teflon insulated solid wires.