Experimental investigation of boiling heat transfer in helically coiled tubes at high pressure

Helically coiled once-through steam generators have been used widely during the past several decades for small nuclear power reactors. The boiling heat transfer characteristics of helically coiled tubes are important to optimal design of helically coiled steam generators. In the present work, various experiments with helically coiled tubes are performed to investigate the boiling heat transfer characteristics at high pressure with water as the working medium. Six test sections are made of thin walled stainless steel tubes having inner diameters of 12.5 mm and 14.5 mm. The system pressure is varying from 2 to 8 MP. The effects of heat flux, mass flux and system pressure on boiling heat transfer behavior are discussed in detail. Increase in heat flux increases the subcooled boiling and saturated nucleate boiling heat transfer coefficient. However, heat flux has no influence on saturated convective boiling heat transfer coefficient. Mass flux increases the saturated convective boiling heat transfer coefficient. Increase in system pressure increases the subcooled boiling and saturated nucleate boiling heat transfer coefficient but decreases the saturated convective boiling heat transfer coefficient. For the investigated experimental conditions, the results show that the Baburajan's correlation gives the best prediction in subcooled boiling region and the Gungor and Winterton's correlation predicts well with the experimental data in saturated boiling region. For the investigated experimental conditions, the results also indicate that the helically coiled tubes have similar performance of heat transfer in boiling regions compared with straight tubes.