Evaluation of cooling channel configurations for actively cooled limiters

The purpose of the present investigation is to simulate experimentally the one-sided heating geometry encountered in fusion devices, and to assess the applicability of existing critical heat flux (CHF) and heat transfer correlations to this geometry. The Sandia National Lab. electron beam test system (EBTS) was used to heat one side of 7.7- and 12.7-mm-i.d. copper tubes. A single tube placed horizontally in the EBTS vacuum chamber was heated on the top by a rastered 30-kV electron beam. The test section was cooled with water supplied by a centrifugal pumped closed-loop system. Coolant inlet and exit pressures, flow rate, inlet temperature, and temperature rise were measured as were the target's surface and backside temperatures. Water calorimetry was used to determine the actual delivered power, with all system operation and data collection under computer control. The flow within the heated region was studied by viewing directly through the tube. Comparison of experimental data for one-sided heating of tubes with high subcooling to existing empirical correlations for CHF and heat transfer indicates that care must be taken in applying the correlations. For the range of data considered, the peak surface heat flux is indicated as the proper parameter to use when applying CHF correlations. For estimating heat transfer, a combination of Thom's equation and the Dittus-Boelter equation was reasonably successfully in analyzing one-sided heat transfer in the highly subcooled flow region