Heat transfer performance of U-tube molten salt steam generator

Heat transfer and thermal performance of U-tube molten salt steam generator was experimentally reported with inlet water flow rate of 22.4-89.6 L/h, water temperature of 20-100 degrees C, salt flow rate of 1-2.2 m(3)/h and salt temperature of 306.5-395.3 degrees C. The heat transfer mechanism of U-tube molten salt steam generator was experimentally revealed, and overall heat transfer coefficient was influenced by salt convection and water boiling, while thermal efficiency was determined by heat absorption and heat loss. As inlet water flow rate rose, overall heat transfer coefficient and thermal efficiency rose initially and decreased afterwards, while they dropped with inlet water temperature rising as subcooling boiling changed to saturation boiling. As salt temperature increased, salt convection was enhanced, while boiling heat transfer coefficient rose initially and dropped afterwards with superheat rising, so overall heat transfer coefficient and thermal efficiency rose initially and dropped afterwards. As salt flow rate rose, overall heat transfer coefficient under low salt temperature rose for boiling heat transfer coefficient increment, and that under high salt temperature first rose and then dropped as boiling curve had maximum heat flux, while thermal efficiency dropped as heat loss and wall temperature increasing. Molten salt heat transfer outside U-tube bundle was remarkably higher than that inside tube, while it was lower than that outside straight tube bundle. Heat transfer correlation of salt outside U-tube bundle was first proposed, and that had good agreement with experiment data with maximum deviation 7.8%. The heat transfer mechanism and correlation in present work can provide reliable basis for design and application of U-tube molten salt steam generator. (C) 2020 Elsevier Ltd. All rights reserved.