Flow through calorimeter to measure fluid heat capacity in CSP applications

Performance tests of concentrating solar collectors are based on energy balance studies which require accurate measurements of fluid mass flow rate, temperature difference over the collector length and the knowledge of the specific heat capacity of the used heat transfer fluid (HTF). Especially at operation temperatures in the range of 200-400 degrees C, the accuracy of HTF manufacturer data regarding the specific heat capacity of used HTFs is insufficient. This shortcoming contributes significantly to the overall measurement uncertainty of thermal collector assessments. In the present paper, the measurement results of a flow through calorimeter measuring the specific heat capacity of SYLTHERM 800 under field conditions at temperatures up to 330 degrees C are presented. The HTF measurement shows good agreement (deviation below 1.2%) with a Differential Scanning Calorimetry (DSC) measurement for temperatures below 270 degrees C. For higher temperatures, the deviation between flow through calorimeter and DSC measurement increases to 3.7% at 330 degrees C. Furthermore, several technical design and measurement improvements over the calorimeter design presented in 2012 are described in detail. A validation measurement using water reveals deviations below 0.1% from the water reference values at ambient temperatures. A stringent uncertainty analysis reveals the largest individual measurement uncertainty. The unexpectedly large uncertainty of the Coriolis mass flow sensors at temperatures above 270 degrees C is distinguished by a large individual uncertainty and the comparison to DSC.