Pseudoplasticity and Dynamic Interfacial Tension Relaxation Effects on Nucleate Pool Boiling in Aqueous Polymeric Liquids

摘要

Nucleate pool boiling heat transfer and its ebullient dynamics in polymeric solutions at atmospheric pressure saturated conditions are experimentally investigated. Three grades of hydroxyethyl cellulose (HEC) are used, which have intrinsic viscosity in the range 5.29 = [eta] = 10.31 [dl/g]. Their aqueous solutions in different concentrations, with zero-shear viscosity in the range 0.0021 = eta(0) = 0.0118 [N.s/m(2)], exhibit shear-thinning rheology in varying degrees, as well as gas-liquid interfacial tension relaxation and wetting. Boiling heat transfer in solutions with constant molar concentrations of each additive, which are greater than their respective critical polymer concentration C*, is seen to have anomalous characteristics. There is degradation in the heat transfer at low heat fluxes, relative to that in the solvent, where the postnucleation bubble dynamics in the partial boiling regime is dominated by viscous resistance of the polymeric solutions. At higher heat fluxes, however, there is enhancement of boiling heat transfer due to a complex interplay of pseudoplasticity and dynamic surface tension effects. The higher frequency vapor bubbling train with high interfacial shear rates in this fully developed boiling regime tends to be influenced by increasing shear-thinning and time-dependent differential interfacial tension relaxation at the dynamic gas-liquid interfaces.