A Heat Transfer Analysis and Alternative Method for Calibration of Copper Slug Calorimeters

摘要

Copper slug calorimeters are among several types of sensors that are commonly used to instrument mannequins in ASTM F1930, Standard Test Method for Evaluation of Flame Resistant Clothing for Protection Against Fire Simulations Using an Instrumented Manikin, fire simulations. In tests of protective clothing ensembles where the dressed mannequin is exposed to a 4-s-long simulated flash fire, it is necessary to acquire roughly 90s of heat flux times series data from sensors for model predictions of theoretical skin burn injury. To accurately estimate the absorbed heat flux at the sensor face from the calorimeter's temperature response, a thermal energy balance is used where internal heat loss (i.e., heat transfer from the copper slug to the body of the sensor) is accounted for. Calibration of the sensor is comprised of selecting appropriate values for parameters in the energy balance. In this work, we illustrate a method by which constants in the characterization of heat losses are determined from analysis of the cooling portion of the sensor's response occurring immediately following short-duration intense heat flux. The method is demonstrated in two experimental set-ups: a pure radiant (quartz lamp bank) exposure of single-slug calorimeters in tandem with a water-cooled Schmidt-Boelter sensor and exposure to flame engulfment conditions using a flat panel target instrumented with a cluster of twelve calorimeters surrounding a witness Medtherm thermopile heat flux sensor. Good agreement between the witness sensors and calibrated calorimeters is obtained for both nude exposures and for transmitted heat flux behind a fabric test specimen. Calibration from the cooling portion of the response provides the advantage of calibrating sensors in situ and en masse. These results suggest the technique may be extended to the calibration of 122 sensors installed on the mannequin in situ from a small number of nude exposures.