Experimental Setup of a Laser Diagnostics System for a High-Temperature Solar Receiver/Reactor

A solar receiver/reactor has been designed specifically to study high-temperature gas phase chemical reactions using a laser based metrology. It is a cavity-type receiver, lined with stabilized ZrO₂, and operated at temperatures up to 2000 K. The gas temperature is measured in situ using the coherent anti-Stokes Raman spectroscopy (CARS) of N₂. Optical access for the CARS measurement is accomplished via two side windows, each subtending a 118-mrad cone angle at the center of the cavity, providing enough clearance for the input laser beams and the output signal carrying the temperature information. Two endothermic processes were used for the initial evaluation of this method: the NH₃ dissociation into N₂ and H₂, and the CO₂-reforming of CH₄ into synthesis gas. The process flow was directly exposed to high solar fluxes in addition to infrared radiation emitted by the hot reactor walls. The laser-based metrology performed satisfactorily in spite of the presence of the intense radiation field. This paper describes in detail the technical aspects of the experimental setup, presents examples of spectra and temperature measurements, and discusses practical problems encountered during experimentation.