Brayton Energy (United States)

Abstract This work describes the use of deposition-based additive manufacturing (AM) techniques to fabricate air-cooled, two-fluid heat exchangers. The project focused on a Heating, Ventilation and Air Conditioning application and used an industry-standard copper/aluminum heat exchanger manufactured with conventional technology as the basis for assessing performance. The manufacturing constraints associated with using deposition-based AM technology for this application include the need for a continuous tool path within each build layer that allows uninterrupted extrusion and therefore defect-free water channel walls that correspond to a reliably leak-tight heat exchanger. A geometry that respects these constraints was developed, simulated, optimized and finally manufactured and tested. The material used was a composite of polymer filled with conductive flakes in order to provide high conductivity in the direction that heat must flow in this heat exchanger, across the wall separating the fluids. The measured performance for several test coupons matched the predicted performance and the test coupons exhibited performance that approach and in some cases exceeds conventional technology

In this design and development effort a latent-heat energy storage heat exchanger was designed for a 10MW_e sCO₂ power plant as a basis for detailed design and testing of a new phase-change heat exchanger technology. High efficiency thermal conductors of graphite foam or folded copper were employed within chloride salt phase-change volumes bounded by alternating high density compact plate-fin heat exchange cells in this new heat exchanger technology. Test articles were constructed at Brayton Energy and tested at Argonne National Laboratory. Copper-conducting samples were constructed and tested at Brayton Energy.

Materials compatibility is a major concern for the design and operation of supercritical carbon dioxide (sCO2) power cycles. Two areas were recently identified for which very little prior knowledge was available. These were the behavior of polymer materials in low-temperature sCO2 environments as well as the high-temperature corrosion behavior for alloys that have been fabricated into compact heat exchangers. A critical need exists to increase understanding in both areas. As such, the Sandia sCO2 Materials Development program initiated a series of experiments for both areas in FY19. The progress that has been made in understanding the behavior of polymers in sCO2 was summarized in the Part I report, while this Part II report describes progress in the area of compact heat exchanger corrosion. For the compact heat exchangers being developed for use in supercritical CO2 power cycles, alloy corrosion is important to understand as it may lead to reduced flow path area, reduced heat transfer, and blocked flow channels. The fabrication of these heat exchangers involve thermal processes such as brazing or diffusion bonding, where the influence of these processes on the corrosion behavior of the alloys is unknown. Candidate alloys for these heat exchangers are typically evaluated for corrosion behavior as witness coupons, without being subjected to these thermal processes. To close this gap in understanding, a series of experiments were completed that utilized small heat exchanger samples subjected to flowing CO2 for 500 hours at 750°C. Small sections of the heat exchanger samples were characterized before and after the 500 hour exposure in order to characterize the oxide growth in the channels as well as the hardness of the alloys. Results are compared to witness coupons of the same alloys.

Anaerobic digestion (AD) is a possible alternative to landfilling of food waste and conventional manure management in order to reduce methane emissions. We use the method of life cycle assessment in this study, and key results show that the AD Bio‐CH4 pathway has 15.5% lower greenhouse gas (GHG) emissions compared to the prior practice of composting of food waste and manure in Denver, CO. GHG emissions for Bio‐CH4 production from AD conversion of food waste and manure with avoiding of food waste landfilling and conventional management of dairy manure emits −3.5 kg CO2 equivalents/kg Bio‐CH4 assuming the electricity was generated using collected landfill gas. This emission intensity is favorably compared to that of fossil natural gas equal to 4.3 kg CO2 equivalents/kg CH4 equivalents. This method for carbon foot printing can be used to evaluate climate mitigation potential of other AD Bio‐CH4 projects. © 2017 American Institute of Chemical Engineers Environ Prog, 37: 1101–1111, 2018

Computed tomography (CT) has the potential to greatly enhance our understanding of the turbulent flow structures, the combustion chemistry, and the interactions between the two, which challenge us in our attempts to understand and model the details of turbulent combustion. Here, we present high-resolution and fully three-dimensional measurements of the flame surface of a turbulent reacting flow. The CT-reconstructed images show the flame front, at a single instant in time, of a turbulent, premixed propane/air flame. The significance of this powerful experimental tool is to provide new insight into turbulent combustion, allowing for the development of cleaner burning, higher power, and more efficient combustors.