The flow pattern map of the two-phase flow of nitrogen and water based CuO nano-liquid in a horizontal capillary tube was investigated experimentally. The nano-liquid was a suspension consisting of water

CuO nano-particles and sodium dodecyl benzol sulphate solution (SDBS).The flow pattern map of nitrogen-water in a horizontal capillary tube was firstly investigated and the result was compared with previously published models for the conventional tubes. Then

different specific volumes of SDBS and CuO nano-particles were added into water to make a series of water based CuO nano-liquids. The flow pattern characteristics of the gas-nanoliquids in a horizontal capillary tube were investigated.The experimental result showed that the flow pattern maps of gas-liquid two-phase flow for capillary tube differed significantly from those for the conventional tubes. For the gas-nanoliquids flow in the capillary tube

the flow pattern transitions for gas-liquid two-phase flow occurred at lower flow gas velocities compared with the gas-water flow in the same capillary tube. The effect of the gas-nanoliquids on the two-phase flow pattern resulted mainly from the change of surface tension. Since the surfactant and nano-particles decreased the surface tension of the nano-liquid

the flow pattern transitions for gas-nanoliquids occurred at much lower velocities compared with the case of gas-water. The concentrations of the nano-particles and SDBS had no effect on the flow pattern map of the gas-nanoliquids.