Boiling Heat Transfer for Aqueous Surfactants Solutions on Flat Surface.

Document Type : Research Studies

Author

Mechanical Eng. Dept., Higher Technological Institute, Tenth of Ramadan City, Egypt.

Abstract

Experimental study for boiling heat transfer over a flat surface was achieved by  using aqueous surfactants solutions and compared wi1h pure water. An experimental  lest loop equipped with the required measuring devices was designed and constructed  to assess the effects of surfactants type , concentration of aqueous surfactants  solutions, and the applied heat flux on the boiling heat transfer process. The tested  surfactants are Polyvinyl Alcohol (nonionic surfactant) and Sodium Laury] Sulfate  (anionic surfactant). Concentrations of aqueous surfactant solutions varied in this  work from zero up to 3000 ppm and the applied heat flux from 15300 to 31230 W/m2The experimental measurements of temperature, pressure and volume flow rate are  recorded and manipulated to calculate the boiling heat transfer coefficient and the  enhancement factor the boiling heat transfer coefficient.  
The obtained experimental results showed that, the wall temperature of flat surface  was reduced for the same heat flux by using aqueous surfactants solutions compared  with pure water. Accordingly, the boiling heat transfer coefficient increased when  using aqueous surfactants solutions and increased also with increasing heat flux in the  range of the. studied operating parameters. The enhancement factor of the boiling heat  transfer coefficient reached to a maximum value with concentration 20 ppm for  Polyvinyl Alcohol and concentration 30 ppm for Sodium Lauryl Sulfate , and then it  decreased with increasing concentrations. The enhancement facto r for the tested  surfactants solutions in this work relative to the pure water is found to be 1,08 La 1.3  depending upon type of surfactants, its concentration and wall heat flux . This improvement in the boiling heat transfer coefficient characterized by a reduction in the  bubble departure diameter, increased departure frequency , reduction in the  coalescence and increased in the number of nucleation sites. Comparison with the  previous work gave good agreement.  

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