EXPERIMENTAL STUDIES OF THERMAL HYDRAULICS OF A HLMC FLOW AROUND HEAT EXCHANGE SURFACES

Temperature and velocity fields in high-temperature lead coolant flows in a circular clearance for controlled oxygen impurity content in a flow were experimentally studied at the Nizhny Novgorod State Technical University by R.E. Alekseev (NNSTU). Temperature and velocity fields were simultaneously studied in "cold" and "hot" parts of the circuit in the following operating conditions: the lead temperature is t = 400-550 degrees C, the thermodynamic activity of oxygen is a = 10(-5)-10(0); the Peclet number is Pe = 500-7000, the coolant flow velocity is w = 0.1-1.5 m/s, and the average heat flux is q = 50-160 kW/m(2). It has been found that the oxygen impurity content and characteristics of protective oxide coatings affect temperature and velocity fields in round and circular channels. This is due to the fact that oxygen in a coolant and oxide coatings on the surfaces limiting a liquid metal flow influence characteristics of the wall boundary region. The heat transfer process that occurs when HLMC transversely flows around heat exchange pipes is investigated now at the NNSTU. The experimental facility is a combination of two high-temperature liquid-metal stands, i.e., FT-2 with the lead coolant and FT-1 with the leadbismuth coolant combined with an experimental section. The temperature of a heat-exchange surface is measured by thermocouples of diameter 1 mm mounted in walls of heatexchange pipes. Velocity and temperature fields in a hightemperature HLMC flow are measured by special sensors placed in the flow cross section between rows of heat- exchange pipes. Heat transfer characteristics and temperature and velocity fields in a high-temperature lead coolant flow are studied in the following operating conditions: the lead temperature is t=450-500 degrees C, the thermodynamic activity of oxygen is a = 10(-5)-10(0), and the coolant flow rate through the experimental setup is Q=3-6 m(3)/h, which corresponds to coolant flow velocities of V=0.4-0.8 m/s. Integrated experimental studies of characteristics of the heat transfer that occurs when the lead coolant transversely or obliquely flows around pipes have been carried out for the first time and the dependences Nu=f(Pe) for controlled content of thermodynamically active oxygen impurity and sediments of impurities have been obtained. It is assumed that the obtained experimental data on distribution of velocity and temperature fields in a HLMC flow will permit to study heat transfer processes and to use them for developing program codes for engineering calculations of heat exchange surfaces (steam generators) with a HLMC flow around them.