The National Institute of Standards and Technology (NIST) presently conducts heat flux sensor calibrations using standard radiation methods. In practice, however, many heat flux sensors are used in test environments where convective heat transfer dominates. Equivalent fluxes in radiation or convection can produce different sensor responses due to sensor surface properties (e.g., emissivity, roughness) and near-surface structure (e.g., transmissivity, temperature distribution). These issues are being addressed at NIST by the development of a convective heat flux facility. By extending calibration capabilities to include a primarily convective environment, direct comparisons of sensors in controlled convective and radiative environments will be possible.
This report describes the progress of the convective heat flux calibration facility under development at NIST. A low-speed wind tunnel has been built to produce a boundary layer shear flow above a constant temperature copper plate. Independently controlled heaters and temperature monitoring systems have been designed and installed to provide an isothermal surface with a known reference heat flux. Wind tunnel configuration and test section instrumentation details, as well as characterization of the flow and the temperature distribution in the plate, are described. Initial heat transfer measurements and results from numerical modeling efforts and hot-wire anemometry are reported.