Computational fluid dynamics simulation on the longwall gob breathing

In longwall mines, atmospheric pressure fluctuations can disturb the pressure balance between the gob and the ventilated working area, resulting in a phenomenon known as ‘‘gob breathing". Gob breathing triggers gas flows across the gob and the working areas and may result in a condition where an oxygen deficient mixture or a methane accumulation in the gob flows into the face area. Computational Fluid Dynamics(CFDs) modeling was carried out to analyze this phenomenon and its impact on the development of an explosive mixture in a bleeder-ventilated panel scheme. Simulation results indicate that the outgassing and ingassing across the gob and the formation of Explosive Gas Zones(EGZs) are directly affected by atmospheric pressure changes. In the location where methane zones interface with mine air, EGZ fringes may form along the face and in the bleeder entries. These findings help assess the methane ignition and explosion risks associated with fluctuating atmospheric pressures.

Efficacy of continuous tracheal gas insufflation in spontaneously breathing canine with acute lung injury

Objective To investigate the effects of continuous tracheal gas insufflation (CTGI) combined with biphasic intermittent positive airway pressure (BIPAP) ventilation on dogs with spontaneous breathing. Methods Eight canine models with oleic acid induced lung injury and spontaneous breathing were ventilated in a random order by Evita 2 (Drager Inc., Germany) in modes of BIPAP (BIPAP group) and BIPAP with CTGI flow rate of 3, 6 and 9?L/min (T3, T6 and T9 groups), respectively. The setting parameters of BIPAP were fiction of inspired oxygen 60%, inspiratory to expiratory ratio 1∶1, respiratory rate 20 and positive end expiratory pressure 5?cm?H2O. Arterial and mixed venous blood gas, lung mechanics, systemic and pulmonary hemodynamics status were monitored at the same level of PaCO2 obtained by adjusting peak inspiratory pressure of BIPAP. Results Peak inspiratory pressure in the T6 group (14±4?cm?H2O) and in the T9 group (11±3?cm?H2O) were significantly lower than that of BIPAP (20±5?cm?H2O, P<0.01), but there was no significant difference among the T3, T6 and T9 groups or between the T3 and BIPAP groups. PaO2, mean artery blood pressure, mean pulmonary artery pressure, pulmonary artery wedge pressure, cardiac ouput, oxygen delivery and oxygen consumption all remained unchanged in four different conditions.Conclusions Using BIPAP combined with CTGI does not cause asynchrony between ventilator and spontaneous breathing, but significantly decreases airway pressure with no influence on hemodynamics and oxygenation. Therefore, BIPAP with CTGI may be a useful support technique, especially in cases where the airway pressure should be limited.