Energy dissipation in a rapid filling vertical pipe with trapped air

An energy-dissipation model is developed to simulate rapid filling having an entrapped air pocket within a vertical pipe. Both convective heat transfer and transient wall shear stresses are considered. The resulting predictions are compared both to those obtained via a conventional empirical polytropic model and to experimental data. The comprehensive model accurately reproduces the experimental pressure oscillations. Results reveal that the dynamic behaviour of air pockets in all tested cases approaches a purely adiabatic process over the first two oscillations, but also that the pressure variation then gradually evolves to an isothermal variation. Moreover, the high air temperatures predicted in the numerical simulations account for the observed phenomenon of white mist in the pipe as well as the notably hot pipe wall. Significantly, the conventional empirical polytropic model associated with the adiabatic assumption for the gas phase was sufficient to reproduce the pressures and temperatures during the first two oscillations.