Enhancement of a Flow Calorimeter by Coupling a Measurement Heat Exchanger-Bypass, for Heat Capacity and Heat Transfer Measurements Using a Silicone-based Heat Transfer Fluid up to 430°C for Concentrated Solar Power Application

Kurzfassung

n concentrating solar power (CSP), the efficiency and profitability is significantly determined by the heat transfer fluid (HTF) that transports the heat from the receiver to the power block. The achievable efficiency and capacity of parabolic power plants is also limited, by the maximum operating temperature of the HTF. The novel silicone-based HTF HELISOLrXLP (HXLP) enables operating temperatures up to 430 °C, comprises reduced environmental and occupational risks and requires no exchange over a power plant lifetime of 25 years. Thus, several advantages result compared to the current benchmark eutectic mixture of biphenyl and diphenyl oxide (BP/DPO) with a maximum operating temperature of 400 °C. This thesis presents the design of a measurement bypass at the PROMETEO parabolic trough collector (PTC) loop at Plataforma Solar de Almería (PSA) to demonstrate the fluid properties such as the specific heat capacity and heat transfer coefficient of HXLP under typical PTC loop conditions up to 430 °C. An existing flow calorimeter is enhanced for the increased temperatures by coupling an HTF cooler, as previous measurements stated systematic deviations of the Coriolis mass flow sensor at temperatures above 270 °C. In order to lower the measurement uncertainty at high temperatures, an HTF cooler enables lower operating temperatures at the sensor. Furthermore, the option of in-line volume flow calibration using laser Doppler anemometry, developed and applied by the national metrology institute (PTB) is implemented. For the development of the measurement heat exchanger (MHE) to measure the heat transfer coefficient of HXLP at 430 °C the sensitivity of the measurands i.e. temperature, geometry and heat losses on the heat transfer is investigated and the derivations are respected during the design of the MHE. The selected design applying a water-HTF counter flow double pipe measurement heat exchanger enables straightforward applications of the equations given in the literature for comparison of the actual to the calculated heat transfer coefficient. An evaluation routine is developed to perform post-measurement evaluation, incorporating statistical uncertainties based on example process data of PROMETEO and known systematic uncertainties. The automated uncertainty analysis promises an overall uncertainty of 1.2 % for the specific heat capacity and 1.46 % for the heat transfer coefficient each at 430 °C.