The heat transfer enhancement through turbulence augmentation is recognized as a key factor for improving the safety and economic conditions in the development of both critical and subcritical innovative advanced gas cooled fast reactors (GFR) and transmutation systems. In the present work, a new experimental facility named L-STAR has been designed and erected at the Karlsruhe Institute of Technology (KIT) to study turbulence flow behavior and its heat transfer enhancement characteristics in gas cooled annular channels under a wide range of conditions. The main objective of the experimental study is to investigate and improve the understanding of complex turbulent convective enhancement mechanisms as well as the friction loss penalties of roughened fuel rod elements compared to smooth ones and to generate an accurate database for further development of physical models. Tests are being conducted in a closed gas loop at various Reynolds numbers with nearly uniform heat release conditions.
The test section consists of an annular hexagonal cross-section channel with an inner electrical heater rod element (smooth and roughened), placed concentrically within the test section, to simulate the flow area of a fuel rod element in a fast gas cooled reactor. In the first step, experimental results of the fluid flow with a smooth heater rod are presented. The pressure drops, as well as axial temperature profiles within the heater rod surface have been measured at Reynolds numbers in the range from 3·103 to 7·104. Experimental program is continued with higher temperatures and the implementation of various artificial surface structures.