An experimental study of void fraction and heat transfer under upward and downward flow boiling conditions

Heat transfer coefficient and actual void fraction have been measured during upflow and downflow boiling of water in an annular channel. At the same values of pressure, mass flux, heat flux and flow quality significant difference of void fraction has been established in upflow and downflow. The upflow and downflow heat transfer coefficients did not deviate significantly from each other, if compared at identical values of pressure, mass flux, heat flux and actual void fraction.