Numerical simulation to evaluate gas diffusion of turbulent flow in mine ventilation system

Tracer gas technique is a method to analyze the airflow path, measure the airflow quantity, and detect any recirculation or leakages in underground mine. In addition, it is also possible to evaluate the axial gas diffusion of gas in turbulent bulk flow by utilizing the tracer gas data. This paper discussed about the measurement using tracer gas technique in Cibaliung Underground Mine, Indonesia and the evaluation of effective axial diffusion coefficient, E, by numerical simulation. In addition, a scheme to treat network flow in mine ventilation system was also proposed. The effective axial diffusion coefficient for each airway was evaluated based on Taylor's theoretical equation. It is found that the evaluated diffusion coefficient agrees well with Taylor's equation by considering that the wall friction factor, f, is higher than those for smooth pipe flow. It also shows that the value of effective diffusion coefficient can be inherently determined and the value is constant when matching with other measurements. Furthermore, there are possibilities to utilize the tracer gas measurement data to evaluate the airway friction factors.

Effect of Digested Sewage Sludge on the Ventilation and Coughing Rates of Two Fresh Water Fish

Addition of digested sewage sludge at concentrations of 2% and 10% (v/v) to the water increased coughing rate in big head and tilapia (P<0.05). Ventilation rate was significantly decreased (P<0.05) in big head and tilapia at sludge concentrations of 6% and 2% (v/v)respectively. Copper (Cu), cadmium (Cd) and zinc (Zn) are trace metals which are commonly found in sludge. Cu caused a significant increase (P<0.05) in coughing rate in both tilapia and big head at concentrations of 0.3 and 0.2 μg/ml respectively. Zn caused significant increase (P<0.05) in coughing rate only in big head at 2 μg/ml. Neither fish responded to Cd of up to 2μg/ml in the water. However, when the levels of these trace metals in the digested sludge were measured, they were below that which can cause significant changes in the respiratory movements. Therefore, the changes in ventilation and coughing rates after addition of sludge may be due to the presence of substances other than these metals. The results of this experiment provides a guideline to control the level of sludge that can be used in rearing these fresh water fish in ponds

Study on impact factors of tracer gas method in investigations of gaseous pollutant transport and building ventilation

Building ventilation is essential to discharge indoor pollutants and improve indoor air quality for occupant health.Tracer gas method is an efficient way in the field of building ventilation to measure ventilation rate and to evaluate the ventilation performance.Literature shows notable deviation of measured ventilation rate using different tracer gases.In the present study,CFD simulations are carried out to analyze He-,CO_(2)-and SF_(6)-based tracer gas methods.The effects of tracer gas density and release rate on the concentration distribution and ventilation effectiveness are studied.Various application scenarios of different ventilation rates and airflow distribution forms are compared.The results show that the deviation of ventilation effectiveness evaluated by different tracer gases can be above 2-4 times,and the error is introduced by non-passive dispersion.Whether tracer gas dispersion is passive or not depends on the relative importance of density difference driven mass transfer to forced convection mass transfer,which is due to the combined effects of density difference,release rate,and indoor airflow velocity,and can be judged by a dimensionless number θ.Under the geometry and ventilation settings in the present study,the critical value of θ is 1.0 for the error range of 5%,and 2.0 for the error range of 10%.When θ is below the critical value,the gas transport is passive and dominated by the indoor ventilation airflow.A release of tracer gas with smaller release rate and smaller density difference into a stronger indoor airflow behaves more passive.Heavier tracer gas tends to significantly overestimate the performance of upper supply and lower exhaust ventilation,and lighter tracer gas aggravates the overestimation of the performance for lower supply and upper exhaust ventilation.In mechanical ventilation rooms with air change rate of 3.0-6.0 h^(−1),a continuous release of tracer gas SF_(6),CO_(2) or He with release rate above 8 mg/s or source concentration above 8-75 ppm should not be considered as passive.This work clarified the passive and non-passive transport characteristics and mechanisms of various tracer gases,which is helpful for the engineering applications of tracer gas method in building ventilation studies.

Mandelic Acid Single-Crystal Growth:Experiments vs Numerical Simulations

Mandelic acid is an enantiomer of interest in many areas,in particular for the pharmaceutical industry.One of the approaches to produce enantiopure mandelic acid is through crystallization from an aqueous solution.We propose in this study a numerical tool based on lattice Boltzmann simulations to model crystallization dynamics of(S)-mandelic acid.The solver is first validated against experimental data.It is then used to perform parametric studies concerning the effects of important parameters such as supersaturation and seed size on the growth rate.It is finally extended to investigate the impact of forced convection on the crystal habits.Based on there parametric studies,a modification of the reactor geometry is proposed that should reduce the observed deviations from symmetrical growth with a five-fold habit.