Performance of a thermosiphon evaporator for concentration of uranyl nitrate solutions

The performance of a thermosiphon evaporator, with a heat transfer area of .74 m{sup 2}, for the concentration of uranyl nitrate solutions up to 1000 gU/l{sup -1} is evaluated. The effects of steam pressure, uranium concentration and liquid submergence on the overall heat transfer coefficient are reported and a method of designing thermosiphon evaporators handling concentrated uranyl nitrate solutions is proposed. Pressure drop characteristics of two packings used in the steam stripping and de-entrainment sections of the evaporator are also given. Overall heat transfer coefficients in the range 1.4 - 2.5 kW m{sup -2} K{sup -1} were obtained at uranyl nitrate concentrations up to 1000 gU/l{sup -1}. Heat transfer to uranyl nitrate solutions below a concentration of 100 gU/l{sup -1} was satisfactorily predicted by employing conventional heat transfer correlations using physical property data for water. Results for more concentrated solutions were successfully correlated using an empirical correction factor which accounts for the change in physical properties of the boiling solution with concentration. (auth)