Optimum Design of Heat Exchanger for the Air Conditioning System with Surfactant Drag Reduction Technique

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Basic research on the relationship between heat transfer reduction and surfactant molecular structure has been conducted in this study. This is the approach from chemical aspect to give an appropriate technique to avoid the hear transfer reduction at heat exchanger. Since the combined use of cationic surfactants with counter ion gives effective drag reduction, four cationic surfactants were selected to discuss the effect of molecular structure. These are oleyl tri-methyl ammonium chloride, oleyl hydroxyethyl di-methyl ammonium chloride, oleyl bis-hydroxyethyl methyl ammonium chloride, oleyl tri-hydroxyethyl ammonium chloride. These surfactants have different hydrophilic group, and this causes different behavior of micelle structure formation and micelle structure breakup. The concluding remarks obtained in this study are summarized as follows.(1) The drag-reducing effect depends strongly on the re-formation rate of micelles disrupted mechanically.(2) When increasing the number of hydroxyethyl groups from 0 to 2, the available temperature range of large drag reduction effect is shifted lower. But the surfactant having three hydroxyethyl groups barely exhibits the drag reduction even at the lower temperature range. This may be caused by the delayed micelle reformation by the large hydrophilic head of hydroxyethyl groups.(3) The well-known drag-reducing surfactant, oleyl bis-hydroxyethyl methyl ammonium chloride, is confirmed to be exactly excellent one, but from the view point of heat transfer reduction, this surfactant is too tough and the micelle re-formation is too rapid. Thus, we propose that the surfactant having three hydroxyethyl groups, oleyl tri-hydroxyethyl ammonium chloride, as an optimum candidate for the practical application of surfactant drag reduction system. This surfactant is now under the evaluation in practical air-conditioning system with surfactant drag reduction.