Antifouling and enhancing pool boiling by TiO2 coating surface in nanometer scale thickness

AbstractThe accumulation of unwanted crystallization deposits on heat transfer surface considerably reduces the efficiency of heat transfer in heat exchangers, especially in the evaporators with vapor–liquid boiling flows. To mitigate the fouling, some measures have been taken including utilizing low‐energy surfaces made by a few kinds of surface‐coating techniques. In this article, novel applications of TiO2 material in inhibiting deposits on heat transfer surface as well as in enhancing pool boiling were developed with nanometer surface engineering method. TiO2 coatings with different layer thicknesses in nanometer scale were prepared by applying vacuum coating technique and were characterized with respect to contact angle, surface free energy, roughness, film thickness, topography by contact angle analyzer, scanning electron microscopy (SEM), and atomic force microscopy (AFM), respectively. Distilled water pool boiling and CaCO3 water solution fouling experiments in pool boiling system were performed on these coating surfaces and antifouling and heat transfer enhancement rules were investigated. The results indicate that all TiO2 coating surfaces can avoid CaCO3 deposition, and fouling induction period of TiO2 coating surface in pool boiling with film thickness of 80 × 10−9 m is about 50 times longer than that of the untreated or polished surface in the present experimental conditions. On the other hand, pool boiling was enhanced on some TiO2 coating surfaces with film thickness in nanometer scale, and heat transfer inhibiting was also observed with certain coating thickness. © 2007 American Institute of Chemical Engineers AIChE J, 2007