The behaviour of drops of water moving through a superheated steam atmosphere

An experimental investigation has been made into the evaporation of large freely falling, oscillating water drops in an atmosphere composed entirely of its own vapour at varying pressures. Experiments were carried out at pressures of 2, 4, 5 and 6 x 10(_5) N/m(^2). A photographic record was obtained of the drop at six observation points down the pressure vessel. From the drop diameter and the velocity of fall measured at the observation point the mass, Nusselt number, Reynolds number and coefficient of drag were calculated. With an increase in pressure the Nusselt numbers were found to increase and were much higher in value than those obtained by other investigators who had, however, used anchored drops in a moving atmosphere. Values obtained for small, freely falling drops were not comparable with the large drops investigated in this study due to the difference in dynamics of the larger drop falling within a pressurised atmosphere composed entirely of its own superheated vapour. From the experimental results it has been shown how the obtained heat-transfer coefficient decreased with the increase in excess temperature above the boiling point.