This paper presents a simulation and investigation of the heat transfer coefficient, pressure drop, and thermal conductivity of two -phase flow. The simulation was performed of mixtures (Al2O3 nanoparticles with R134a refrigerant). The size of nanoparticles (Al2O3) which is used in this study is 30 nm and volume concentrations are 0.015 and 0.03. The two -phase flowing through a horizontal circular microchannel of (diameter 100 µm, and length 20 mm) under constant heat flux (3000 W/m 2 ) and constant wall temperature (330 K), also in this study used the inlet temperature at -20 o C and mass flow rates are 0.3, 0.4, 0.5, 0.6, 0.7 and 0.8 g/s using in the dissipation of heat from electronic circuits by evaporation. The simulation is achieved by CFD numerical model using FLUENT ANSYS version 15 software. The results indicate the best temperature, pressure drop, density and volume fraction for two-phase flow nanorefrigerant in the microchannel. The higher heat transfer coefficient and pressure drop of two-phase nanorefrigerant flow at a high volume concentration (0.03) of Al2O3 when the mass flow rate is maximum. Finally, compared heat transfer coefficient of this study with the results of Kumar et al. (2013) at variation the mass flow rate, and found the root mean square of error (10%), also compared heat transfer coefficient of this study with results of Hernández et al. ( 2016) at variable volume concentration of nanoparticles Al2O3, and found the root mean square of error (3.7%).