Rouhollah Fatehi

Tanks containing two-phase fluid are always exposed to thermohydraulic shocks caused by the sudden condensation of steam which may create large oscillating forces to the tank by creating waves propagating to both sides of the tank. These oscillations can cause the tank connections to fail or even destroy the tank itself. In this thesis, the effects of a thermohydraulic shock on the free surface of the fluid and the velocity distribution in a long tank containing two-phase fluid are investigated by considering the effects of friction and mass exchanges resulting from the phase change. Since the tank is long, the one-dimensional shallow water model is suitable. In order to increase the accuracy of the results and select the best numerical method to solve the shallow water equations, the first-, second-, and high-order methods have been used. Energy conservation has also been used to calculate the amount of condensed fluid due to the thermal shock. The effects of the inlet and outlet flows of the tank, as well as friction, have been investigated. The effect of various variables such as the amount of sudden change in inlet water temperature, the location of the inlet water branch, changes in density and wall friction on the free surface of water and the net force on the reservoir have been calculated and plotted. Also, for better results, the problem was solved in two dimensions using Navier-Stokes equations and with the help of interFoam solver of OpenFOAM software. Although the force calculated in two-dimensional solution is less than one-dimensional due to the modeling of friction between fluid layers, it will be shown that in any case the turbulence phenomenon resulting from a thermohydraulic shock can apply forces of the order of 10^5 N to the tank.