Laser Flash Thermophysical Property Analysis

STEEL was awarded a $2 million grant in fall 2018 to determine the thermophysical properties of containment materials in the DOE’s Generation 3 Concentrating Solar Power (CSP) project. The first two generation CSP systems commercially deployed in the 1990s used both thermal oils and molten nitrate salts at heat transfer media (HTM); however, these HTM deteriorated at high (>700°C) temperatures and reached maximum efficiencies of ~40%. With higher-temperature molten salts being proposed for the Gen 3 system, thermal efficiencies of CSP plants are anticipated to exceed 50%. However, engineers are uncertain which materials will safely and effectively contain these HTM. High temperature data of both refractory materials and Inconel alloys, which are commonly used in furnace insulation or for thermal storage, are sparse in the literature. Thermophysical properties >700°C need to be established for the proper selection of Gen 3 containment materials (CMs).

csp

Karatairi, E., & Ambrosini, A. (2018). “Improving the efficiency of concentrating solar power systems”.

The STEEL lab proposed the use of a laser flash analyzer (LFA) to measure these high temperature properties. LFA is a simple, common transient measurement technique used since 1961 to directly determine the thermal diffusivity of solid or liquid samples. A small (~mm scale) disk-shaped sample is placed in an atmosphere-controlled furnace and the bottom (“front”) side of the sample is flashed with a Xenon lamp at a specific temperature. A liquid nitrogen-cooled IR detector monitors the temperature rise of the top (“rear”) of the sample. Thermal diffusivity is then determined from the raw signal voltage-time data by fitting to the 1D, time-dependent Fourier equation.

csp

LFA is advantageous as a thermal metrology method because no physical contacts are required, internal radiation within flashed samples is negligible, and radiation from the surface can be easily accounted for with corrective models. Our Netzsch LFA 467 HT is capable of furnace temperatures up to 1200°C, which is on the higher-end of the temperature scale for Gen 3 CSP containment material testing. We intend to characterize dozens of proposed containment materials selected by various national labs (NREL, ORNL) and private companies who are also participating in the Gen 3 CSP project.

 

  1. A. M. Hofmeister, “Chapter 4 – Methods Used to Determine Heat Transport and Related Properties, With Comparisons,” in Measurements, Mechanisms, and Models of Heat Transport, A. M. Hofmeister, Ed., ed: Elsevier, 2019, pp. 99-142.
  2. Generation 3 Concentrating Solar Power Systems (Gen3 CSP). Office of Energy Efficiency & Renewable Enegry.
  3. Light Flash Apparatus LFA 467 HyperFlash Series. Netzsch.