Investigations of an externally heated storage vessel

Storage tanks for fluids are widely used industrial facilities. As a consequence of an external fire, the heat-up of the inventory may lead to the evaporation of the liquid and to release of significant quantities of dangerous gases into the environment. Experimental investigations performed in FZ-Rossendorf have shown that the liquid inventory behaves very differently depending on the mode of heating. Bottom heating leads to an irregular thermoconvective motion of the liquid, which causes good mixing, so that saturation is reached at all places inside the tank approximately at the same time. The maximum enthalpy of the liquid always remains close to the average value. If the vessel is heated from the side, a stable temperature stratification is observed leading to large temperature gradients. Evaporation can start much earlier than the average temperature reaches saturation.
In order to clarify the physical nature of the details of the heating-up and the evaporation process in simple geometrical boundary conditions a two-dimensional mathematical model was developed, which includes also evaporation and two-phase flow. The aim of the simulations was, to understand the basic phenomena observed during the experiment.
To avoid fast temperature increase at the fluid surface in the case of side wall heating, the insertion of baffle plates inside the vessel was investigated by additional calculations using the CFD-code CFX-4.