The direct steam generation (DSG) is an attractive option regarding the economic improvement of parabolic trough technology for solar thermal electricity generation in the multi megawatt range. According to Price, H., Lupfert, E., Kearney, D., Zarza, E., Cohen, G., Gee, R. Mahoney, R., 2002, "Advances in Parabolic Trough Solar Power Technology," J. Sol. Energy Eng., 124 and Zarza, E., 2002, DISS Phase H-Final Project Report, EU Project No. JOR3-CT 980277 a 10% reduction of the LEC is expected compared to conventional SEGS like parabolic trough power plants. The European DISS project has proven the feasibility of the DSG process tinder real solar conditions at pressures up to 100 bar and temperatures up to 400 degrees C in more than 4000 operation hours (Eck, M., Zarza, E., Eickhoff, M., Rheinlander J., Valenzuela, L., 2003, "Applied Research Concerning the Direct Steam Generation in Parabolic Troughs," Solar Energy 74, pp. 341 351). In a next step the detailed engineering for a precommercial DSG solar thermal power plant will be performed. This detailed engineering of the collector field requires the consideration of the occurring thermohydraulic phenomena and their influence on the stability of the absorber tubes.