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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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DOE OSTI2021

Review and Analysis of Heat Transfer Correlations For Horizontal Pseudocritical CO 2 Heat Exchanger Applications

There is significant interest in the development of supercritical carbon dioxide (sCO 2 ) power cycles because of the potential for smaller and more energy efficient systems than a steam Rankine cycle. Heat exchanger designs typically use empirical correlations, but the applicability of these correlations near the CO 2 critical point is a potential issue. Though numerous correlations have been proposed in the literature, there are some disagreements when it comes to the accuracy. The current work recognizes the role of thermophysical properties, and its impacts on the heat transfer correlations and cycle efficiency. Heat transfer correlations proposed for horizontal flow inside circular pipes were analyzed with the help of numerical simulations. Steady state RANS simulations were performed using SST k-w turbulence model to evaluate the Nusselt number empirical correlations. It was found that the most of correlations (except Yoon) produced a Nusselt number that differed significantly with the one predicted numerically. Some of the correlations were developed for pure forced convection regime and as mentioned in Lin et al. do not account for mixed convection or free convection effects. Based on the limited observation, it appears that Yoon et al. predictions match well with the numerically predicted Nusselt Numbers. However, further analysis is required understand the applicability of various correlations and is contingent on accurate measurements or predictions of wall temperature profiles in the axial and the circumferential directions.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2020

Materials Data on K3W by Materials Project

K3W is alpha bismuth trifluoride structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. there are two inequivalent K sites. In the first K site, K is bonded to four equivalent K and four equivalent W atoms to form a mixture of distorted corner, edge, and face-sharing KK4W4 tetrahedra. All K–K bond lengths are 3.91 Å. All K–W bond lengths are 3.91 Å. In the second K site, K is bonded in a body-centered cubic geometry to eight equivalent K atoms. W is bonded in a body-centered cubic geometry to eight equivalent K atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on K3W by Materials Project

K3W is alpha bismuth trifluoride structured and crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. there are two inequivalent K sites. In the first K site, K is bonded in a 4-coordinate geometry to four equivalent K and four equivalent W atoms. All K–K bond lengths are 3.99 Å. All K–W bond lengths are 3.99 Å. In the second K site, K is bonded to eight equivalent K and four equivalent W atoms to form distorted KK8W4 cuboctahedra that share corners with four equivalent KK8W4 cuboctahedra, corners with eight equivalent WK12 cuboctahedra, edges with eight equivalent KK8W4 cuboctahedra, faces with four equivalent KK8W4 cuboctahedra, and faces with six equivalent WK12 cuboctahedra. All K–W bond lengths are 4.18 Å. W is bonded to twelve K atoms to form WK12 cuboctahedra that share corners with four equivalent WK12 cuboctahedra, corners with eight equivalent KK8W4 cuboctahedra, edges with eight equivalent WK12 cuboctahedra, faces with four equivalent WK12 cuboctahedra, and faces with six equivalent KK8W4 cuboctahedra.

36 MATERIALS SCIENCE↗