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Water-based ZnO nanofluids were prepared via the two-step method,and the influences of dispersant type and mass fraction on the stability and particle size distribution of the nanofluids were investigated.The spectral transmittances of the nanofluids were obtained by a UV-Vis-NIR spectrophotometer.Thermal conductivities of the nanofluids with various mass fractions were measured at different temperatures and a fitted nonlinear correlated equation was established for low-concentration application and compared with existing models.The photothermal conversion performance of the nanofluids was evaluated by theoretical and experimental methods at three optical depths.The results showed that,CTAB as the dispersant provides better physical stability of water-based ZnO nanofluids than SDBS or GA does.Effect of the temperature on the nanofluid thermal conductivity is remarkable with the increase of nanoparticle mass fraction,especially in the range 55℃ to 75℃.The maximum thermal conductivity of the studied nanofluids is 0.9488 W/(m·℃) at 75℃,43.61％ higher than that of water.The minimum thermal conductivity of the studied nanofluids is 0.6376 W/(m·℃) at 25℃,5.16％higher than that of water.The photothermal conversion performance of the nanofluids is quite good with a maximum average absorption efficiency of 0.47,135％ higher than that of water (η=0.2),and the maximum SAR is 527.5 W/g.