Computation on pipe dynamic response induced by deflagration of H2 and air mixture

Abstract

Computation is devoted to evaluating structural safety of a heat exchanger inside a reactor whose geometry can be simplified as outer and inner pipes as well as a chamber. This paper has numerically studied deflagration of hydrogen air mixture and pipe dynamic responses. The Navier-Stokes equations coupled with multi-species mass equation are solved by TVD scheme to get flow-field solution based on MPI and multi-block methods. Combustion is described by a 11-species and 23-step reaction model. The source term is treated implicitly to involve species production and depletion. Ignition is approximated by input energy C p T per unit mass in a specified period and zone. Finally, contours of pressure and OH mass fraction at different time periods and pressure histories at fixed points are obtained. When loading is specified as wall pressure, virtual work theorem in Lagrangian frame which describes pipe response is solved by FEM to obtain stress and strain distributions. Results show that shock waves can be generated and reflected on the walls of the chamber and pipes. The shock waves and flame can not be dissipated in a narrow gap spanning 2 mm. Meanwhile, stress waves are generated. They propagate outwards on the inner and outer pipe walls. At the gap exit, shock wave diffracts and impacts on the inner pipe walls. Coupled with hot jet from the gap, re-ignition occurs on the inner pipe wall surfaces. Then, flame catches up the leading shock and shock front deforms into a planar one although the shock front passes through a short divergent section downstream. Also, stress concentrates along the intersected lines among the top, bottom and side walls. This means that the chamber is an easily damaged component. The methods provided in this paper can be used to evaluate structural safety.