Liquid metal magnetohydrodynamic power converters (LMMHD PC) have been recently proposed for electrical power generation. These systems contain two-phase vertical flows consisting of high density liquid metals and suitable gas-vapor. Optimum design of LMMHD power plants require accurate modeling of two-phase flows in the riser. A two-fluid model has been developed for this purpose. One-dimensional, steady state two-fluid flow equations consisting of conservation of mass, momentum of each phase along with auxiliary relations have been solved numerically by the Runge-Kutta method. Interfacial drag force corresponding to multi-bubble, churn turbulent and slug flow based on Ishii et al. and Taitel classification has been used. Effect of variation of void fraction and phase velocities of the fluids across the cross section of the pipe has been studied based on Ishii et al. model by modifying relative velocity and incorporating appropriate coefficients in the conservation equations. Bubble size at the mixer orifice exit has been calculated using the equations of Kumar et al. In order to verify the accuracy of the model, a nitrogen-mercury experimental system has been set up. Void profiles have been measured using gamma-ray attenuation method. Void fraction, slip and pressure at different locations were determined for the mass fluxes varying from 0.125 to 2.302 kg/sm(2) for nitrogen and 5.52 x 10(3) to 12.26 x 10(3) kg/sm(2) for mercury. The predicted values have been compared with the experimental data. The void fraction values matched well with the experimental data within 10% and within 20% when cross-sectional effects were included. The over all pressure values were within 13% and 8%, respectively, while the slip values deviated within 25% and 27%, respectively. In general, the model matched better with experimental data when the cross-sectional effects were not included. This is due to the high density of the liquid metal and relatively larger pipe diameter.