Boiling heat transfer and dryout in helically coiled tubes under different pressure conditions

• Heat transfer characteristics and dryout for helically coiled tube are performed.
• A boiling heat transfer tends to increase with a pressure increase.
• Dryout occurs at high quality test conditions investigated.
• Steiner–Taborek’s correlation is predicted well based on the experimental results.

A helically coiled once-through steam generator has been used widely during the past several decades for small nuclear power reactors. The heat transfer characteristics and dryout conditions are important to optimal design a helically coiled steam generator. Various experiments with the helically coiled tubes are performed to investigate the heat transfer characteristics and occurrence condition of a dryout. For the investigated experimental conditions, Steiner–Taborek’s correlation is predicted reasonably based on the experimental results. The pressure effect is important for the boiling heat transfer correlation. A boiling heat transfer tends to increase with a pressure increase. However, it is not affected by the pressure change at a low power and low mass flow rate. Dryout occurs at high quality test conditions investigated because a liquid film on the wall exists owing to a centrifugal force of the helical coil.