Modeling the convective component of the heat flow from a spill fire at railway accidence

Abstract

A significant number of emergencies that occur in the chemical, processing and transport industries begin with an accidental spill and ignition of a flammable liquid. In this case, the spread of fire to neighboring objects is of particular danger. When developing fire protection measures in areas where flammable liquids are stored, as a rule, heat transfer from a fire only by radiation is taken into account. But in some cases, the convection component of the heat flow can make a significant contribution to the overall heat transfer. Ignoring it can lead to an erroneous assessment of the safety of an industrial facility. In the paper, a model of the distribution of velocity and temperature in the upward flow, rising above the spill of a burning liquid, is constructed. The model is based on the system of Navier-Stokes equations, which, by means of simplifications, is reduced to a non-linear second-order differential equation of the parabolic type. The properties of the combustion site determine the boundary conditions of the first kind. In this case, the spill of a flammable liquid can have any shape. The presence of wind is taken into account by introducing a stable horizontal component of the flow velocity.

For the numerical solution of the equation, the method of completed differences is used. The dependence of the kinematic viscosity on the flow temperature is taken into account. An empirical formula is used as the relationship between temperature and speed. It is shown that the presence of wind leads to an inclination of the ascending flow. The angle of inclination is not constant and increases with distance from the combustion source due to a decrease in speed and cooling of the flow. An estimate of the coefficient of convection heat transfer convection of the tank wall with ascending flows over the combustion source is constructed. It is shown that the coefficient of convection heat transfer increases with increasing wind speed