2005

Lautkaski, Risto

Simple Methods to model pressure rise in confined gas explosions are reviewed. The Simplest method is based on energy conservation in an adiabatic system. Algebraic equations by which pressure and flame front radius as functions of time can be calculated have been derived by making the so-called isothermal approximation. This approximation assumes constant temperatures for the unburned and burned gases and neglects the pressure dependence of the burning velocity. At early times the overpressure is proportional to t³. Expansion factors and AICC pressure ratios were calculated for hydrogen mixed with dry or humid air at different concentrations. Only the dissociation of water vapour to hydrogen and oxygen was modelled. The values of AICC pressure ratio at 100% relative humidity calculated with this method were found to be within 2.8% of the values given in literature. Four methods to calculate pressure rise were used to calculate the amount of hydrogen whose combustion generates a 2 kPa overpressure in a 1000 m³ enclosure. The simple method based on energy conservation was taken as a reference. The method based on isothermal approximation gave results that were close to those calculated by the simple method.