Engineering topics

Finkenauer, L. R.

Publications and source records attributed to Finkenauer, L. R..

4 records

DOE OSTI2022

Binder jet additive manufacturing of ceramic heat exchangers for concentrating solar power applications with thermal energy storage in molten chlorides

Triply periodic minimal surface (TPMS) geometries can only be fabricated by additive manufacturing methods and are of interest for heat exchangers. Ceramic TPMS heat exchangers can operate at higher temperatures and pressures with superior performance and increased operating efficiencies compared to metal heat exchangers. The properties of ultra-high temperature ceramic (UHTC) materials are also favorable for heat exchangers and potentially suited to concentrated solar power (CSP) systems, such as those based on a molten chloride salt thermal energy storage (TES) medium used to heat CO 2 in a closed-loop Brayton power cycle. We intended to demonstrate binder jet additive manufacturing feasibility of a UHTC-TPMS structure by printing and sintering a null candidate. We aimed to achieve parts with a relative density ≥ 92 % of theoretical and to provide a TPMS part demonstration. The target density indicates the transition from intermediate to final stage sintering, a requirement to inhibit gas permeability and for sintering complex near net shapes to full density with sinter-HIP technology. The goal of the TPMS part demonstration was to determine if printing and sintering parameters developed from test coupons apply to the complex geometries that will eventually be used in a heat exchanger design. Our objective was to print cubic TPMS parts with a 9 cm 3 volume and sinter it without distorting and cracking. We report we were able to sinter ZrB 2 -MoSi 2 composite parts based on the Schwarz-D TPMS and achieve isotropic shrinkage up to 60 % by volume, resulting in densities ranging from 92 % to 96 % of theoretical.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Additive Manufacturing of Corrosion Resistant UHTC Materials for Chloride Salt-to-sCO2 Brayton Cycle Heat Exchangers

The objectives of the project include: (1) screen high-purity, high density ultra-high-temperature ceramics (UHTCs) for chloride salt corrosion resistance, (2) develop binder-jet additive manufacturing and sintering for ZrB 2 -MoSi 2 blends using literature and experiments to demonstrate feasibility, and (3) evaluate chloride salt corrosion resistance of additively manufactured ZrB 2 -MoSi 2 . These initial objectives support the development of a durable and reliable ultra-compact high-efficiency salt-to-sCO 2 heat exchanger for closed-loop Brayton power cycles based on corrosion resistant, high-strength, thermally conductive UHTC materials and novel designs enabled by additive manufacturing. The UHTC materials are also abrasion resistant so that they could be applicable to all three thermal carrier media pathways identified in the CSP Gen3 Roadmap.

36 MATERIALS SCIENCE↗

DOE OSTI2019

Composite 4YSZ-Al2O3 Nanofibers Prepared by Electrospinning and Thermal Processing

The relationship between solution properties and processing parameters for novel yttria-alumina-zirconia nanofibers electrospun in a constant electric field is explored through systematic variation of precursor content and aging of the polymer gel. The upper solution viscosity and conductivity limit for electrospinning with an electric field strength of 0.84 kV/cm were ~1000 cP and ~5 mS/cm, respectively. There is a predictive relationship between volumetric flow rate and solution viscosity, conductivity, and surface tension; however, there is not a strong relationship between as-spun fiber diameters, ranging between 100 and 300 nm, and any solution property. The gelation mechanism by which aqueous polyvinylpyrollidone (PVP), zirconium acetate, and aluminum/yttrium nitrate solutions age is speculated to arise from zirconium acetate hydrolysis and polymerization, facilitating intermolecular hydrogen bonding between zirconium acetate complexes, PVP functional groups, and disassociated ionic species. The 4YSZ-Al 2 O 3 ceramic nanofiber diameters ranged between 50 and 100 nm depending on the volume percent of the ceramic phases. The annealed fibers appear amorphous and without excessive grain coarsening, indicating that a heat treatment of 1000°C for 2 hours is sufficient to produce tough, refractory nanofibrous membranes relevant for high-temperature filtration applications.

36 MATERIALS SCIENCE↗

DOE OSTI2019

Fire- and Water-Resistant Prefilter

The goal of this project was to modify existing LLNL ceramic HEPA filter technology to create ceramic prefilters, which could first be implemented in nuclear facilities or hospitals and universities. The objectives were as follows: 1) Demonstrate sealing technology capable of withstand ≥ 400°C, 2) Design and fabricate a ceramic prefilter unit for flow rates ≥ 50 cfm, 3) Test prefilter prototype filtration efficiency and pressure drop before and after a relevant thermal exposure. Concurrently to prototype creation was a preliminary effort to develop a custom nuclear prefilter sealant, improving upon what is commercially available. An advantage to using prefilters that are not credited for HEPA filtration, but to protect HEPA filters in nuclear ventilation systems, is that absolute qualified performance to HEPA standards (e.g. pressure drop, filtration efficiency) is not required. This prefilter prototype aligns our technology with the more viable, lower risk market entry point which can be used to establish costs, performance and manufacturing principles necessary to overcome the primary market barrier.

36 MATERIALS SCIENCE↗