Abstract
The process of heat transfer in a HLMC cross-flow around heat-transfer tubes is not yet thoroughly studied. Therefore, it is of great interest to carry out experimental studies for determining the heat transfer characteristics in a lead coolant cross-flow around tubes. It is also interesting to explore the velocity and temperature fields in a HLMC flow. To achieve this goal, experts of the NNSTU performed the work aimed at the 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, united by an experimental site. The experimental site is a model of the steam generator of the BREST-300 reactor facility. The heat-transfer surface is an in-line tube bank of a diameter of 17 × 3.5 mm, which is made of 10H9NSMFB ferritic-martensitic steel. The temperature of the heat-transfer surface is measured with thermocouples of a diameter of 1 mm being 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 the 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”) and the horizontal ones. The studies were conducted under the following operating conditions: The temperature of lead was t = 450°C - 5000°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 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 is revealed. This is because the presence of oxygen in the coolant and oxide coatings on the surface, which restrict 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 a HLMC flow permit studying the heat-transfer processes and, on this basis, creating program codes for engineering calculations of HLMC flows around heat-transfer surfaces.
Highlights
It is not possible to obtain a package of data required to design heat-exchange equipment operating in a lead coolant medium only by means of a calculation based on the outcome of theoretical design models
The analysis shows that with an intense deoxidation of the coolant (а ≈ 10−5) by means of supplying dry hydrogen to the circulation loop, there occurs deterioration of the heat-exchange characteristics relative to similar parameters for a coolant having the content of thermodynamically active oxygen of 10−1 < a < 10−4
This difference may be explained by the change in the flow conditions of the heat-exchange surface due to variation in the characteristics of the surface wetting by the coolant on account of partial damage or alteration of the physical and chemical properties of the protective oxide coatings
Summary
It is not possible to obtain a package of data required to design heat-exchange equipment operating in a lead coolant medium only by means of a calculation based on the outcome of theoretical design models. All theoretical models are bound to introduce simplifications that do not reflect reality. An expression for calculating heat-exchange coefficients usually introduces the values of coolant mean velocities, wall temperature, characteristics of the fluid itself and its flow. This paper contains the results of an analysis and experimental research for determining heat-exchange characteristics in a heat-removing experimental section at crossflow of an in-line heat-exchange tube bank simulating lead-to-wall heat-exchange conditions within the range of operating parameters of the loop of a projected reactor installation of BREST type under a controlled and regulated content of oxygen impurity in the coolant and loop, as well as at the supply to the loop of a lead coolant of gas-air mixtures, which simulates potential malfunction during the emergency “Interloop Leakiness of Steam Generator” It is dependent on the size of heat-exchange surface elements (objects with similar heat-exchange surface geometry, but which are of smaller size, have greater heat-exchange coefficients since these objects have boundary layers of lesser thicknesses), the heat flow direction (at transfer of heat from the coolant to the wall, the heat-exchange coefficient is higher than that at flow-around of the inner wall of a pipe of the same diameter), the wall boundary layer effect, the heat flow direction (at transfer from the coolant to the wall, the heat-exchange coefficient is higher than that at transfer of heat from the wall to the coolant) and other, which has a material effect on the heat-exchange characteristics.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
