Progress Report on the NIST Convective Heat Flux Calibration Facility.
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.
Available from:
For More Information on NIST SP 971 visit: WEBSITE:
http://www.bfrl.nist.gov/866/heatflux/index.htm
Keywords:
heat flux; calibration; convection; standards;
uncertainty; sensors
Abstract:
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.
