To design the divertor plate for the next generation fusion machines which is subjected to high heat loads on its one side by the plasma, it is essential to evaluate performances of heat transfer efficiency. However there is little in the literature for predicting of heat transfer coefficients under such one-sided heating conditions. To establish the heat transfer correlation for water under one sided healing conditions, the authors have performed heat transfer experiments on smooth circular and swirl tubes in the regions From non-boiling to high subcooled partial nucleate boiling, Based on the experimental results, it is confirmed that the existing heat transfer correlations can be applicable at the non-boiling region. For the subcooled partial nucleate boiling region, they cannot be available so that a new heat transfer correlation has been proposed under one-sided heating conditions.