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/m2. The 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.
Highlights
Nucleate boiling is a very efficient mode of heat transfer. It has been found in a wide range of applications such as various energy conversion systems. heat exchange systems, refrigeration, heat pump systems. and chemical thermal processes....etc
The boiling behaviuor enhancement is dependent on additive concentration, heat flux and the heater geometry
The enhancement factor for the tested surfactants solutions in this work rela tive to the pure water is found to be 1.0&- 1.3 depending upon type of surfactant, its concentration and wall heat flux
Summary
Nucleate boiling is a very efficient mode of heat transfer. It has been found in a wide range of applications such as various energy conversion systems. heat exchange systems, refrigeration, heat pump systems. and chemical thermal processes....etc. BOILING HEAT TRANSFER FOR AQUEOUS SURFACTANTS SOLUTIONS ON FLAT SURfACE The presence of surfactant (surface active agent) additives or polymer at low concentrations in solvent has been found to improve the nucleate boiling heat transfer coefficient significantl y.
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