The Pebble-Bed Heat Transfer Experiment (PBHTX) is a scaled facility designed to measure heat transfer coefficients within a pebble-bed test section for the conditions applicable to the PB-FHR. A simulant oil called Dowtherm A is used as the heat transfer fluid, which matches the Prandtl number of flibe at temperatures lower than the Mk1 PB-FHR conditions. A 3.5″ dimpled test section is filled with randomly packed 1/4″ copper pebbles, some of which are instrumented with thermocouples to measure temperature. The inlet and outlet fluid temperatures are also recorded. A coriolis flowmeter is used to measure the mass flow rate of the oil within the loop. A power supply is used to vary the heater power sinusoidally, and in this way the frequency response of the test section can be measured to a high accuracy. The facility is designed so that the range of Reynolds and Prandtl numbers are matched with the prototypical conditions. The loop has been built using flexible stainless steel piping and tri-clamp fittings. It is built in a modular fashion, implying that the pebble-bed test section could be replaced for future tests.
PBHTX during construction
PBHTX test section