DOI
https://doi.org/10.25772/7101-2Z63
Author ORCID Identifier
https://orcid.org/my-orcid?orcid=0000-0002-8297-9544
Defense Date
2023
Document Type
Dissertation
Degree Name
Doctor of Philosophy
Department
Mechanical and Nuclear Engineering
First Advisor
Dr. Lane B. Carasik
Second Advisor
Dr. Supathorn Phongikaroon
Third Advisor
Dr. Worth P. Longest
Fourth Advisor
Dr. Darius D. Lisowski
Fifth Advisor
Dr. Cody S. Wiggins
Sixth Advisor
Dr. Joshua D. Fishler
Abstract
Global energy consumption is expected to increase with population growth and innovative clean sources of energy are sought out that can help meet the needs of a continuously power-hungry world. Some of these innovative sources of energy use molten salts as their operating and cooling fluid, such as fission reactors, fusion reactors, and solar power with energy storage. Molten salts are considered due to their efficient heat transfer properties, thermal energy storage capabilities, and high operating temperatures. To expedite their deployment, a further understanding of the heat transfer systems is required to accurately design and develop the heat transfer components and increase their efficiency. This is typically done through experimental campaigns and computational tools, though the computational tools require further validation and verification usually done through experiments. Experimental molten salt heat transfer campaigns can be inherently costly for a university laboratory setting.
This work investigated the viability of water as a surrogate fluid for five different molten salts for heat transfer experiments. A methodology was explored to understand the inherent differences, or distortions, that arise when utilizing a surrogate fluid for heat transfer experiments, and it demonstrated water to be a viable surrogate for these five molten salts. The distortions calculated can be better accounted for and improved with improved uncertainty in the thermophysical properties of the molten salts. Thermal performance studies were conducted using water as a surrogate fluid for a passive heat transfer enhancement technique, i.e. twisted tape inserts, that is considered for high heat flux applications. Friction factor, Nusselt number, and thermal performance factor data were obtained for a variety of twisted tape insert geometries and operating conditions. A clear dependence on the width of the twisted tape insert was observed that is not fully accounted for in the leading correlations found in the literature. Friction factor and Nusselt number correlation adjustments were made to better match the current experimental data. Additionally, higher thermal performance was observed at lower Reynolds numbers when using twisted tape inserts.
Fluid flow studies were done on three different twisted tape inserts for three Reynolds numbers of 17,700, 8,000, and 4,000. Flow structures such as high-velocity islands, inflow regions, secondary flow regions, and vortices were observed similar to those found in the literature. Additionally, the flow crossing between the gap of the twisted tape and the circular pipe for smaller widths dominated the transaxial flow. This resulted in vortices near the gaps that further propagated throughout the semi-circular geometry which can lead to further flow separation, lower heat transfer, and higher wall temperatures for loose-fitting twisted tape inserts. It is thus recommended to use twisted tape inserts that have a width-to-diameter ratio (w/D) as close to one as possible.
Rights
© The Author
Is Part Of
VCU University Archives
Is Part Of
VCU Theses and Dissertations
Date of Submission
8-11-2023