Uncertainty Analysis in Fan Testing

The ASME performance test codes require an uncertainty analysis as part of a code test, and some codes require both a pre-test and a post-test uncertainty analysis. ASME PTC-19.1, Test Uncertainty provides the basic approach to conducting an uncertainty analysis. The individual test codes, such as ASME PTC-11, Fans, provide specific guidance for uncertainty analysis of tests of particular equipment or processes. The following issues related to an uncertainty analysis for a PTC-11 fan test are discussed. • Evaluating uncertainties for traverse measurements — Fan testing requires one or more traverses to measure flow rate as well as various pressures, temperatures, and gas composition. Evaluating and propagating the uncertainty associated with traverse point measurements to obtain overall uncertainty is explained. • Evaluating uncertainties for non-traverse measurements — Fan testing also requires the measurement of power input, fan speed, and atmospheric temperature and pressure. Evaluating the uncertainties in these quantities is discussed. • Propagating uncertainties of the measurements into the final results — An analytical method is compared to “dithering” to obtain a sensitivity factor. • Using a pre-test uncertainty analysis to optimize the test design — Examples are provided on how a pre-test uncertainty analysis can be used to reduce the uncertainties of a fan test. The results include results of sample pre-test and post-test uncertainty analyses for fans.