Influence of surfactant on characteristics of solid-liquid phase change for water-based nanofluid

Surfactant was used in the study to help dispersing TiO2 nanoparticles in deionized water.The effects of different surfactants(sodium dodecyl benzene sulfonate(SDBS),polyvinylpyrrolidone(PVP)and cetyl trimethyl ammonium bromide(CTAB))on the dispersion stability and solid-liquid phase transition of TiO2-H2O nanofluids were investigated.Surfactants SDBS and PVP significantly enhanced the dispersion stability of TiO2-H2O nanofluid,and reduced its degree of supercooling by about 37.02% and 9.65%,respectively.Whereas,surfactant CTAB showed no effect on improving the dispersion stability of TiO2-H2O nanofluid,and even worse,increased the degree of supercooling of nanofluid by about 6.11%.The adsorption structures of SDBS,PVP and CTAB were analyzed by measuring the adsorbent layer thickness on TiO2 nanoparticles(X-ray photoelectron spectroscopy).The adsorption structures of surfactants SDBS and PVP were hydrophilic while that of surfactant CTAB was micellar,which could explain the above phenomena.In addition,all three surfactants were found to extend the phase transition time of TiO2-H2O nanofluid due to the decrease in the thermal conductivity of nanofluid.