Measurement and simulation of viscosity characteristics of coal ash slag under water vapor condition in coal gasification

•Effect of water vapor on slag viscosity depended on the slag composition.•The dividing line for the influence of water vapor on slag viscosity was A/B = 0.8.•The modified Urbain model was used to predict viscosity of homogeneous slags.•The viscosity of heterogeneous slags was predicted by modified Roscoe model.•These models can predict well slag viscosity and Tcv under water vapor condition.