[en] A method for estimating heat transfer coefficients for the evaporation of concentrated uranyl nitrate solutions is described, based on data obtained in a thermosiphon evaporator at uranium concentrations up to 1000 g ^-1. The method is also applicable to other systems when an evaporator must be designed in the absence of adequate physical data. Results are correlated using an empirical factor which accounts for the change in physical properties of the boiling solution with concentration and enables heat transfer coefficients to be predicted from conventional heat transfer correlations using physical property data for water. The performance of the thermosiphon evaporator, with a heat transfer area of 0.74 m², is reported in terms of the effects of steam pressure, uranium concentration and liquid submergence on the overall heat transfer coefficients which varied in the range 1.4-2.5 kW m^-2 K^-1. (author)