The advancement in parabolic trough technologies has led to the development of direct steam generation (DSG); an efficient and feasible solution that utilizes the sun's energy for thermal power generation as well as for heat supply in industrial processes. The complexity of the two-phase flow in the absorber tube has always remained a challenge in the development of reliable simulation tools of DSG process. The focus of this work is to improve the thermo-hydraulic modeling of DSG process by introducing a new modeling approach. A more recent flow pattern map is utilized in the prediction of flow patterns in the evaporation section. In addition, a recent development of a flow pattern oriented heat transfer model is integrated in the two-phase modeling to cover all flow regimes. Moreover, the two-phase pressure drop is modeled by following a phenomenological approach that takes the flow structure of different patterns into consideration. The validity of the model has been tested by comparing simulation results with real experimental data from DISS test facility and the results were found to be very consistent. The flow pattern analysis shows that low inlet pressures will be favorable to increase the occupation length of annular flow. On the other hand, the filling percentage of annular flow will significantly diminish in the evaporation section for increased values of inlet temperature. (C) 2015 Elsevier Ltd. All rights reserved.