Author(s):

James R. Vulcanoff, Ryan P. McGuire, Lane B. Carasik.

Abstract:

To investigate the means for improving molten salt heat transfer components, helically rifled tubes, a passive heat transfer enhancement, are investigated in this study. The investigation focused on predictions of thermal performance relevant to molten salts used in fission, fusion, and concentrated solar power plants. Currently, there are limited systematic studies for helical rifling heat transfer enhancements as opposed to corrugated, internal finned, or repeating ribbed tubes. For this study, the computational fluid dynamics (CFD) code Nek5000/NekRS was used to simulate different convective flow regimes for different molten salts (i.e. fluorides, chlorides, and nitrate salts).

The outcomes from the CFD investigations involved both frictional pressure drop (friction factor) and heat transfer coefficient (Nusselt number) predictions for a range of turbulent Reynolds numbers and Prandtl numbers spanning from unity “1” to 25. The friction factor results were observed to have increased by a percent difference of 35% to 48% compared to plain tube data. This is consistent with boiler tube results from groups such as Lam et al. and Pan et al.

The CFD predictions resulted in the Nusselt number (heat transfer) increasing substantially with increasing Prandtl numbers for helically rifled tubes. It was also found that that the Nusselt number was observed to have minimal increases for all Reynolds numbers at Prandtl numbers close to unity. Using the predicted thermal performance information (friction factor and Nusselt number), the thermal performance factor of the helically rifled tubing was calculated as compared to plain tubes. It was found that the thermal performance factor was higher for Prandtl numbers larger than unity. However, it was determined that the thermal performance decreased for all Reynolds numbers when fluids with Prandtl numbers at or below unity were analyzed. Overall, this study presents a useful starting point for future investigations of helically rifled tubing in molten salt applications.

Full Article:

Full article: CFD Investigations to Understand Thermal Performance of Helically Rifled Heat Transfer Enhancements in Molten Salt Applications 

Author(s):

Trevor Franklin, Casey Icenhour, Pierre-Clément A. Simon, Paul Humrickhouse, Fande Kong, Lane B. Carasik.

Abstract:

Multiphysics modeling capabilities have a crucial role to play in the accelerated deployment of fusion energy. To that end, we developed new Multiphysics fusion blanket simulation capabilities in the Multiphysics Object-Oriented Simulation Environment (MOOSE). Firstly, we expanded on the existing capabilities of the previously published work, by coupling 3D tritium transport modeling capabilities using the Tritium Migration Analysis Program, version 8 (TMAP8) to an existing tool including thermal hydraulics, fully three-dimensional (3D) heat transfer, and loosely coupled neutronics analysis. Secondly, we performed a thorough verification of the new capabilities and increased testing code coverage to meet MOOSE’s software quality standards. The MOOSE framework follows a strict software quality assurance plan to be Nuclear Quality Assurance, Level 1 compliant. The new Multiphysics fusion blanket simulation capabilities are now held to the same standard. Thirdly, to demonstrate MOOSE’s new fusion blanket modeling capabilities, we performed a fully integrated, Multiphysics simulation of a 3D solid ceramic breeder blanket design. This proof-of-concept simulation provides the temperature and tritium distribution across the blanket. The combined efforts towards software quality and the development of Multiphysics coupling capabilities provide an effective and reliable framework for modeling solid ceramic fusion blankets using MOOSE.

Full Article:

https://www.sciencedirect.com/science/article/pii/S0920379625003254 

Author(s):

Trevor C. Franklin, Lane B. Carasik.

Abstract:

The European Go-Viking project aims to develop a deep understanding of flow-induced vibration (FIV) phenomena in cross-flow steam generator tube bundles used in operating pressurized water reactors. This understanding will be used to prevent mechanical damage and premature failure of the steam generators. To support this objective, the GOKSTAD experiment, consisting of a 7x7 cross-flow inline tube bundle (pitch-to-diameter ratio of 1.44), will be used to collect high-resolution data on flow-induced vibrations for comparison to high and low fidelity modeling efforts. The high to low fidelity modeling includes RANS and medium- to high-resolution large eddy simulations (LES) computational fluid dynamics (CFD) modeling to gather both field and integral data comparable to experimental measurements. Given the computational cost of the highest fidelity simulations, smaller unit cell computational domains of the GOKSTAD experiment were created to reduce the simulation costs while maintaining accuracy. The unit cell consists of 7 rows with 3 columns of tubes and periodic conditions in the streamwise and spanwise directions. In this reported study, the sensitivity of the simulation results to the spanwise direction parallel to the tubes was investigated. The spanwise length of the domain was varied for lengths of one, two and three diameters in size. An average bulk mass flow rate of 15 m3/hr (corresponding to a gap Reynolds number of 6650) was used for each case. The reported data was velocity signals, average streamwise velocity and RMS velocity collected at different planes within the bundle and compared. The results from this study provide guidance for future high-resolution simulations domain size requirements in the spanwise direction.

Full Article:

Impact of Simulated Tube Length in FSI Predictions of the GOKSTAD Experiment | PVP | ASME Digital Collection 

Author(s):

Sierra A. Tutwiler, Trevor C. Franklin, Ryan P. McGuire, Dillon R. Shaver, Lane B. Carasik.

Abstract:

One of the major components in fusion energy systems is the fusion blanket, which has a vacuum vessel to contain the plasma. As part of the fusion blanket/vacuum vessel, the first wall and plasma-facing components require sufficient cooling to prevent material degradation during operation from the superheated plasma. Most fusion blanket concepts involve first wall and divertor coolant channels with heat transfer enhancements (HTEs) that are intended to withstand the incident high heat fluxes of 1 to 5 MW/m2. Twisted tape inserts are a proposed HTE that have been investigated previously for first wall cooling and monoblock divertor cooling channels and in other nonfusion heat transfer components. By inserting twisted tapes into straight pipes, the amount of turbulence in the system can be increased at lower Reynolds numbers by swirling the flow. This results in better heat transfer characteristics with marginal increases in frictional pressure losses. In particular, simulations of high-Prandtl-number fluids such as the proposed molten salt FLiBe in twisted tapes, which is prototypic to liquid immersion blankets, have not been previously explored. In this study, we simulate various Prandtl numbers in pipes with twisted tape inserts using large eddy simulations to determine the effects of increasing Prandtl numbers on heat transfer performance. The quantities of particular interest are the Nusselt number and the friction factor, which were recovered using data reduction techniques to determine impacts on heat transfer and pressure losses. This work serves as a starting point for determining the feasibility of twisted tape inserts for liquid immersion blanket concepts.

Full Article:

Simulations of Heat Transfer Using Tight-Fitting Twisted Tape Inserts for First Wall Cooling in Molten Salt Breeder Blankets: Fusion Science and Technology: Vol 81, No 6