High Fidelity CFD Simulations of External Flow Around Twisted Elliptical Tubes

With the push for more advanced nuclear reactor components, advanced heat exchanger designs that incorporate the use of heat transfer enhancements (HTEs) are currently being explored. One such HTE is the twisted elliptical tube heat exchanger, which is an alternative to the standard shell and tube heat exchanger. The twisting geometry allows for more mixing of the fluid, inducing turbulence at lower Reynold’s numbers and allowing for improved mass and heat transfer characteristics with only marginal increases in the frictional pressure drop. Due to this behavior twisted elliptical tubes are advantageous for high Prandtl number fluids such as molten salts. Current correlations connect this increase in heat transfer to the modified Froude number which is defined by the twisted elliptical tube twist pitch, hydraulic diameter, and maximum diameter. However at low values of the modified Froude number, there is poor agreement for existing heat transfer coefficient correlations and there are few experimental cases available. This opens up discussion of other possible dependencies that affect the mass and heat transfer behavior of the twisted elliptical tubes. In this work, we present a Buckingham-Π analysis to determine the relevant dimensionless quantities and determine their influence by using large eddy simulations of the shell side of twisted elliptical tube heat exchangers. This project systematically simulates each of the nondimensional parameters presented in the Buckingham-Π analysis using the Nek5000 CFD code to determine their impacts on flow phenomena and heat transfer. The effects of cross-sectional tube aspect ratio, Prandtl number, and Reynolds number are being explored to better understand how twisted elliptical tubes will perform in different scenarios for various aspect ratios.

Gathering expertise On Vibration ImpaKt In Nuclear power Generation (GOVIKING) 

The GO-VIKING project is an international research effort focused on improving the understanding and prediction of fluid-induced vibrations (FIV) in nuclear reactor components, particularly steam generator tube bundles. Its primary motivation is to enhance the safety and reliability of operating nuclear reactors by developing more accurate modeling tools that can predict flow-induced forces and structural response. VCU’s contribution centers on performing high-fidelity CFD simulations using Nek5000 and NekRS to resolve the complex turbulent flow structures within cross-flow tube bundles. These simulations are used to generate detailed force and turbulence data, which are then compared against experimental measurements to validate modeling approaches. Ultimately, VCU’s work supports the development of predictive capabilities needed for safe reactor lifetime extension and improved design of future nuclear systems.

The proposed research is directed at critical aspects of making 211At more available and useful to U.S. researchers for medical applications. The research is a collaborative effort between UW Radiation Oncology, UW Material Sciences and Engineering, ORNL Isotope Science and Engineering Directorate, ORNL Physical Sciences Directorate, ORNL Fusion and Fission Energy and Science Directorate, and VCU Department of Mechanical and Nuclear Engineering. In the studies we will investigate materials and methods to produce and isolate larger quantities of 211At from irradiation of Bi targets. To achieve that goal, we will: (a) evaluate new target designs through 3D heat transfer simulations to predict which target designs allow higher beam currents to be used in production of 211At; (b) fabricate Bi targets based on thermal conductivity modeling; and (c) optimize conditions for efficient (semi-automated) recovery of 211At from newly designed bismuth targets.