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Progress Report on the NIST Convective Heat Flux Calibration Facility.

pdf icon Progress Report on the NIST Convective Heat Flux Calibration Facility. (1162 K)
Holmberg, D. G.; Womeldorf, C. A.

NIST SP 971; AJTE99-6153; August 2001.

NIST SP 971: "Collected Reports and Publications by the National Institute of Standards and Technology on Heat Flux Gage Calibration and Usage." AND ASME/JSME Joint Thermal Engineering Conference, 5th Proceedings. March 15-19, 1999, San Diego, CA, 1-9 pp, 2001.

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heat flux; calibration; convection; standards; uncertainty; sensors


The National Institute of Standards and Technology has developed a convective heat flux calibration facility to allow evaluation of heat flux sensors. This facility is a small wind tunnel that produces a two-dimensional laminar boundary layer across a heated iso-thermal copper plate. This facility has been developed to allow convection calibration of heat flux sensors to complement heat flux sensor calibrations presently conducted using standard radiation methods, recognizing that many sensors are used in mixed radiation and convection environments. By extending calibration capabilities to include a primarily convective environment, direct comparisons of sensors in controlled convective and radiative environments are possible. This report describes the first-generation heated plate design and performance. The reference heat flux on the plate is found from the electrical power input to a guarded region of the plate to the side of the sensor in the spanwise uniform flow. Tests have demonstrated a repeatability on the reference heat flux of +1.5%. A detailed uncertainty analysis of the reference heat flux value is presented showing lateral conduction to surrounding regions of the plate to be the greatest source of uncertainty with plate surface emissivity the only other significant source. The calculated relative expanded uncertainty (95% level of confidence) on the measured reference heat flux value is + 4.6%. The average reference heat flux from these tests agrees with numerical predictions within 2%. An independent measure of the reference heat flux has been employed to demonstrate absolute accuracy of the facility. Tests using a conduction calibration agree within 1% with the plate reference. This 1% difference gives increased confidence in the absolute accuracy of the convection facility and compares favorably with the calculated 4.6% uncertainty. Development of a second generation heated plate continues with the goal of reducing uncertainty on the reference heat flux. Testing of sensors in the current heated plate is on-going.