Characteristic curves and the promotion effect of ethanol addition on steam condensation heat transfer

Although most previous studies concerning the condensation of binary vapor mixtures report the condensation rates to be less than that for pure vapor, heat transfer enhancement can be realized by using additives to form a positive system (solutal Marangoni condensation). The objective of the present study was to clarify the effect of mixing ethanol into steam on condensation heat transfer. Precise measurements of the ethanol concentration in the vapor of water–ethanol mixtures were performed over a wide range of ethanol concentrations, and the condensation behavior was observed. The maximum heat transfer coefficients in the condensation characteristic curves were determined to be 0.12 and 0.18 MW/m2 K for vapor velocities of 0.4 and 1.5 m/s, respectively, and appeared at an ethanol vapor mass fraction of approximately 1%. The mixing was demonstrated to be extremely effective, particularly in the low-ethanol concentration range. The condensation heat transfer was enhanced approximately 2–8 times compared to pure steam.