Title:
Investigation of a helium-cooled modular divertor with multiple jets using a reversed heat flux approach
Investigation of a helium-cooled modular divertor with multiple jets using a reversed heat flux approach
Author(s)
Musa, Shekaib Ahmad
Advisor(s)
Yoda, Minami
Abdel-Khalik, Said I.
Abdel-Khalik, Said I.
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Abstract
The divertor, an important plasma-facing component in future long-pulse magnetic fusion energy (MFE) reactors, is vital in sustaining fusion reactions by removing fusion products, impurities, and debris from the core plasma. This thesis focuses on the helium-cooled modular divertor with multiple jets (HEMJ) design. An HEMJ module employs an array of impinging jets to cool the inner surface of an endcap brazed to the plasma-facing surface, a tungsten tile. Originally proposed for the European demonstration DEMO fusion reactor, this concept has been experimentally shown to remove steady-state incident heat fluxes of at least 10 MW/m^2. Individual HEMJ “fingers” are initially assembled into bundles, or units, of nine fingers with a common inlet and outlet to form the divertor with a plasma-facing area of O(100 m^2). To date, most of the studies and models of the HEMJ are based on a single finger, and there are few studies of even a single HEMJ unit. The main objective of this thesis was therefore to evaluate the thermofluids characteristics of a representative HEMJ bundle to verify the results obtained from a single HEMJ finger can be used for a multi-finger bundle. Unlike a single finger outer shell, the outer shell of the HEMJ unit in the center of the bundle doesn’t have sidewalls and therefore lacks conduction paths to the manifold. The experimental studies presented here use a reversed heat flux (RHF) approach, whereby heat is removed (rather than added) at the plasma-facing surface, thereby reducing the operating temperatures for the test section. This approach was first successfully validated in experimental studies of a single HEMJ finger by comparing RHF and normal heat flux tests for dimensionless heat transfer coefficient, or Nusselt number Nu, and dimensionless pressure drop, or pressure loss coefficient K_L. Experimental studies were then conducted on a seven-finger HEMJ bundle where a central finger was surrounded by six outer fingers using the RHF method at the prototypical He pressure of 10 MPa, He temperatures as great as 300 °C and incident heat flux magnitudes as great as 5.9 MW/m^2. For this purpose, a larger helium loop with a mass flow rate as great as 100 g/s was designed and built. The results indicate that the Nu correlation developed from single-finger HEMJ studies is applicable to the seven-finger HEMJ unit at the prototypical mass flow rate of 6.8 g/s. Baring the anomalous pressure drops in the latter half of the experiments, the K_L results are higher than the single-finger HEMJ due to the inclusion of the inlet and outlet chambers in the manifold. Computational fluid dynamics (CFD) studies of a seven-finger HEMJ unit were carried out with a commercial software package ANSYS and used to design the seven-finger test section and clarify some of the experimental results, including the impact of partial blockage of the jet exit holes on Nu and K_L.
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Date Issued
2024-04-27
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Text
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Dissertation