Synthesis of CRUD and its Effects On Pool and Subcooled Flow Boiling

摘要

Previous studies have demonstrated the potential of porous, hydrophilic surfaces to lead to more efficient boiling. CRUD (Chalk River Unidentified Deposits) is a naturally occurring porous, hydrophilic layer that forms on fuel rods during reactor operation. Therefore, CRUD deposition can have large effects on critical heat flux (CHF) and heat transfer coefficient (HTC). An investigation of such effects is being conducted by preparing synthetic CRUD on indium tin oxide-sapphire heaters. These heaters are being tested in pool and flow boiling facilities in MIT's Reactor Hydraulics Laboratory. Synthetic CRUD was created using layer-by-layer deposition of 100 nm silica nanoparticles to form porous, hydrophilic thick films. Photolithography was used to manufacture posts that were then dissolved to create characteristic boiling chimneys. Features such as CRUD thickness, wettability, pore size, and chimney diameter and pitch were verified to be representative of reactor CRUD. Silica nanoparticles were used as a surrogate for reactor CRUD nanoparticle materials (iron and nickel oxides) since they create more stable films. To ensure accurate modeling, independent of material, 10 nm silica nanoparticle and 10 nm iron oxide nanoparticle boiling tests were conducted and compared. During testing, IR thermography and high-speed video are used to obtain two dimensional temperature profiles of the active heater area to quantify properties such as HTC, nucleation site density, and bubble departure frequency. Initial testing has demonstrated that heaters with synthetic CRUD (either silica or iron oxide-based) show roughly 100% enhancement in CHF and HTC over uncoated heaters.