Gabriel Negreanu

Mathematical model and experimental tests of hydrogen diffusion in the porous system of biomass

ABSTRACT The paper deals with mathematical model and experimental tests of hydrogen (pure or mixed) diffusion in the porous system of biomass. A mathematical model has been developed for gas diffusion in a porous system and based on it a numerical simulation for hydrogen absorption gas been carried out. The results are presented graphically and they point out that the concentration variation inside the pore decreases with the increases of pore length and increases with the increase of hydrogen flux. Also, the absorbed hydrogen quantity decreases with the increase of the pore length and for a given pore length the absorbed hydrogen quantity increases with the increases of hydrogen flux and internal pore surface. Research regarding hydrogen diffusion in the porous system of biomass is part of wider research focusing on using hydrogen as an active medium for solid biomass combustion. In parallel with hydrogen diffusion in solid biomass, tests regarding biomass combustion previously subjected to a hydrogen flux will be carried out.

The Study of the Depression Occurred under Different Types of Impellers

The paper presents the analytical solution used to calculate the depression which appears under different types of impellers. This solution can be useful as a preliminary calculus to estimate the magnitude of the depression created at different rotational speeds, in order not to damage the equipment from different systems, such as hydraulic turbines. The authors obtain the variable radius of the depression zone, the pressure inside the depression zone and the depression height. The theoretical approach, the calculus itself and the numerical results presented in the article are original. In order to validate the proposed calculus, experiments were carried out using two experimental setups. The performed measurements showed a good agreement of the experimental and theoretical results.

Numerical simulation of a large power steam turbine run-up

The purpose of this paper is to propose a new behavioural evaluation of a large steam turbine during the run-up period based on a numerical simulation of the transient fluid dynamic processes that occur in the turbine during start-up. The transient process begins when the run-up valve starts its opening trip and ends when the rotor speed achieves the required value. This original approach is a follow-up of a methodology describing the steam turbine load rejection. Several primary operational parameters, such as pressure, temperature and flow-rate are revealed by the simulation, allowing the computation of secondary ones, like mechanical load and rotor speed. The results of this method are useful to equipment designers, in order to set-up both the aperture curve speed of the start-up valve and the response of the turbine protection against overspeed.