Experimental Study of the Characteristics of Heat Transfer in an HLMC Cross Flow around Tubes

Abstract

The process of heat transfer in a heavy liquidmetal coolant (HLMC) crossflow around heattransfer tubes has not been thoroughly studied yet. Therefore, it is of great interest to carry out experimental studies for determining the heattransfer characteristics in lead coolant crossflow around tubes. It is also interesting to explore the velocity and temperature fields in an HLMC flow. To achieve this goal, experts of the R.E. Alekseev Nizhny Novgorod State Technical University performed work aimed at experimental determination of the temperature and velocity fields in hightemperature lead coolant crossflows around a tube bundle. The experimental studies were carried out in a specially designed hightemperature liquidmetal facility. The experimental facility is a combination of two hightemperature liquidmetal setups, i.e., FT2 with a lead coolant and FT1 with a leadbismuth coolant, combined by an experimental site. The experimental site is a model of the steam generator of the BREST reactor facility. The heattransfer surface is an inline tube bank of diameter 17آ mm and wall thickness of 3.5آ mm, which is made of 10H9NSMFB ferritic–martensitic steel. The temperature of the heattransfer surface is measured with thermocouples of diameter 1آ mm installed in the walls of heattransfer tubes. The velocity and temperature fields in a hightemperature HLMC flow are measured with special sensors installed in the flow crosssection between rows of heattransfer tubes. The characteristics of heat transfer and velocity fields in a lead coolant flow were studied in different directions of the coolant flow: the vertical (“topdownâ€‌ and “bottomupâ€‌ (Beznosov et al., 2013, “Experimental Studies of Thermal Hydraulics of a HLMC Flow Around Heat transfer Surfaces,â€‌ Proceedings of the 21st International Conference on Nuclear Engineering, ICONE21, Paper No. ICONE2115248)) and the horizontal directions. The studies were conducted under the following operating conditions: the temperature of lead was t=450–500آ°C, the thermodynamic activity of oxygen was a=10−5–100, and the lead flow through the experimental site was Q=3–6  m3/h, which corresponds to coolant velocities of V=0.4–0.8  m/s. Comprehensive experimental studies of the characteristics of heat transfer in a lead coolant crossflow around tubes have been carried out for the first time, and the dependences Nu=f(Pe) for a controlled and regulated content of the thermodynamically active oxygen impurity and sediments of impurities have been obtained. The effect of the oxygen impurity content in the coolant and characteristics of protective oxide coatings on the temperature and velocity fields in a lead coolant flow have been revealed. This is because the presence of oxygen in the coolant and oxide coatings on the surface, which restricts the liquidmetal flow, leads to a change in the characteristics of the walladjacent region. The obtained experimental data on the distribution of the velocity and temperature fields in an HLMC flow permit studying the heattransfer processes, and on this basis, create program codes for engineering calculations of HLMC flows around heattransfer surfaces.