Design and Uncertainty Analysis of a Second-Generation Convective Heat Flux Calibration Facility

Abstract

The National Institute of Standards and Technology has developed a convective heat flux facility to allow calibration of heat flux sensors. The facility consists of a small wind tunnel that produces a two-dimensional laminar boundary layer across a heated isothermal copper plate. Sensors are mounted flush in the copper plate alongside a reference to measure the heat leaving the plate. Convective calibrations up to 5 kW/m2 are possible. Sensor output is compared with the reference value, and contrasted with a standard radiation calibration. Recognizing that many sensors are used in mixed radiation and convection environments, this facility provides a unique opportunity to assess a sensor’s convective response. This report describes a second-generation heated plate and provides an analysis of the system uncertainty. Redundant references, improved sensor heating and mounting, improved reference isolation, and a minimized radiation component has reduced the combined relative expanded uncertainty of the reference to ±2.5 %. The benefits of an embedded temperature sensor in the heat flux sensor are described. The facility is available for comparative calibrations and for heat transfer studies by individual researchers.