Nucleate pool boiling of aqueous polymer solutions on a cylindrical heater

Heat transfer and ebullience behavior in saturated, nucleate pool boiling in aqueous dilute to semi-dilute solutions of a surface-active (hydroxyethyl cellulose or HEC-QP300) and a shear-thinning (polyacrylic acid or Carbopol 934) polymer on a horizontal, cylindrical heater are experimentally characterized. The influence of fluid rheology and interfacial properties (dynamic surface tension and wettability) on the heat transfer coefficient is delineated. In HEC solutions, nucleate boiling is enhanced with increasing concentration c till an optimum near the critical polymer concentration (c* ∼600 wppm); at higher concentrations, the enhancement decreases considerably. Contrarily, there is continuous deterioration in the boiling heat transfer, relative to water, in Carbopol solutions with increasing concentrations. Adsorption of macromolecules, or agglomerates of smaller monomers onto a heating surface that may favor the formation of new nucleation sites, together with a decreased dynamic surface tension, are responsible for the general growth in the number of active bubbles in surface-active HEC solutions. In HEC solutions with c > c* as well as in all Carbopol solutions, on the other hand, higher viscosity tends to suppress the micro-convection near the wall and the bubble growth, thereby weakening the boiling process.