Reversed Heat Flux Study of Impinging-Jet Water Cooling for Helium-Cooled Finger-Type Divertors

Experimental evaluation of the thermal-hydraulic characteristics of helium-cooled divertor concepts is important in developing commercial magnetic fusion energy (MFE). Although experimental studies of a variety of concepts have been performed at the Georgia Institute of Technology (GT) over the last decade, achieving prototypical steady-state incident heat fluxes of 10 MW/m² remains a major challenge. As an alternative to heating the test section, this work presents an initial assessment of a “reversed heat flux approach” that cools the test modules (instead of heating them) with water to determine the heat transfer coefficients (HTC). This approach was pioneered by the Karlsruhe Institute of Technology (KIT) in their initial studies of the helium-cooled modular divertor with multiple jets (HEMJ).

The objectives of this design study are to: 1) determine whether such a reversed heat flux approach can be used to experimentally study the thermal-hydraulic performance of helium-cooled divertor concepts, while minimizing safety and operational issues associated with the extremely high temperatures (>1200°C) reached when testing at prototypical conditions (inlet conditions of 700°C and 10 MPa with an incident heat flux of 10 MW/m²), and 2) determine the design and operational parameters for a small-scale submerged water jet impingement cooling facility suitable for validating these numerical predictions. Numerical simulations were performed to determine the impinging-jet (water) mass flow rates required to remove heat fluxes up to 10 MW/m² from a single HEMJ module at prototypical conditions (i.e., 700°C and 10 MPa). Initial axisymmetric simulations at water pressures up to 3 MPa suggest that a submerged single-phase impinging water jet at (300 K, 1 MPa) and = 3.5 kg/s can remove heat fluxes as great as 7.5 MW/m² over a 2 cm diameter area.