Influence of surfactants on thermosiphon reboiling

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Surfactants can increase two-phase heat transfer in aqueous solutions by depressing the surface tension and activating new bubble nucleation sites. Yet, boiling experiments are mainly conducted on a laboratory scale and hardly ever conducted under flow conditions which complicates the transfer of the results to larger scales. The present study demonstrates that the addition of an anionic secondary alkylsulfonate surfactant has a profound impact on the fluid dynamics and thermal performance of a single-tube vertical thermosiphon reboiler. At low heat flux conditions, heat transfer was enhanced by up to 26% and circulation rate was increased by up to 65% depending on the surfactant concentration. The increase in two-phase heat transfer also led to a stabilisation of the natural circulation and thus to an extension of the lower operating range of the reboiler. All experiments were conducted in the turbulent flow regime and at surfactant concentrations around the critical micelle concentration (CMC).