Falling film flow of [EMIm]Ac ionic liquid aqueous solution on horizontal tubes considering the Marangoni effect

•The variations in thermophysical properties of the admixture of [EMIm]Ac ionic liquid and water were studied.•The physics of film flows with the Marangoni effect on horizontal tubes was analyzed.•Experiments of falling film flows on horizontal tubes in relation to the Marangoni effect were conducted. Experiments on falling film flow with a 60 wt% [EMIm]Ac (1-ethyl-3-methylimidazolium acetate) aqueous solution on cooled/heated horizontal tubes were conducted using an infrared thermal imaging camera to investigate the effect of Marangoni flow on the flow pattern and film width. The thermal stability of the [EMIm]Ac ionic liquid and the dependence of viscosity and surface tension on the temperature were presented. The physics of film flows with the Marangoni effect on horizontal tubes was analyzed. It is evidenced that the Marangoni effect exists on horizontal tubes and has significant influence on the falling film flow pattern and film width. When the film was heated, the film contracted and exhibited a sheet flow pattern, whereas a columnar pattern was observed under isothermal conditions. When the film was cooled, the film expanded and the columnar flow pattern was retained but with an increase in number of columns. Compared to the pure water, the average spreading film width with the 60 wt% [EMIm]Ac aqueous solution was narrower by approximately 20.1% and 9.8% at a liquid flow rate of 0.2473 kg m−1 s−1 as the film was cooled and heated, respectively.