Abstract: A new method of enhancing heat transfer of the heating section of a two-phase closed thermosiphon was proposed.Theoretical and experimental studies were carried out on the performance of heat transfer enhancement by adding a proper amount of nanoparticles to the thermosiphon with water as working fluid.This thermosiphon showed such advantages as good startup,lower tube wall temperature,increased heat transfer coefficient by 47%—96%,and increased heat flux by 7.6%—15% in the range of the experiment.This method is simple and easy to use in chemical industry.