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

Abstract

The process of heat transfer in a heavy liquid-metal coolant (HLMC) cross-flow around heat-transfer tubes has not been thoroughly studied yet. Therefore, it is of great interest to carry out experimental studies for determining the heat-transfer characteristics in lead coolant cross-flow 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 high-temperature lead coolant cross-flows around a tube bundle. The experimental studies were carried out in a specially designed high-temperature liquid-metal facility. The experimental facility is a combination of two high-temperature liquid-metal setups, i.e., FT-2 with a lead coolant and FT-1 with a lead-bismuth coolant, combined by an experimental site. The experimental site is a model of the steam generator of the BREST reactor facility. The heat-transfer surface is an in-line tube bank of diameter 17 mm and wall thickness of 3.5 mm, which is made of 10H9NSMFB ferritic–martensitic steel. The temperature of the heat-transfer surface is measured with thermocouples of diameter 1 mm installed in the walls of heat-transfer tubes. The velocity and temperature fields in a high-temperature HLMC flow are measured with special sensors installed in the flow cross-section between rows of heat-transfer 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 (“top-down” and “bottom-up” (Beznosov et al., 2013, “Experimental Studies of Thermal Hydraulics of a HLMC Flow Around Heat transfer Surfaces,” Proceedings of the 21st International Conference on Nuclear Engineering, ICONE21, Paper No. ICONE21-15248)) and the horizontal directions. The studies were conducted under the following operating conditions: the temperature of lead was t=450–500°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 cross-flow 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 liquid-metal flow, leads to a change in the characteristics of the wall-adjacent region. The obtained experimental data on the distribution of the velocity and temperature fields in an HLMC flow permit studying the heat-transfer processes, and on this basis, create program codes for engineering calculations of HLMC flows around heat-transfer surfaces.