The result indicates that critical flow rate at the beginning of sand production declines with the rising of oil viscosity and pH value of fluid; when pH value exceeds 12, sand production increases remarkably.

The results indicate that critical salt concentration and critical flow rate exit on the saltwater-freshwater interface.

The critical flow rate,VT could be estimated from the statistic curves.

The relation of aeration rate with wastewater flow,designed bioreactor height,and flowing section area of main and sub chamber was analyzed theoretically,as well as the relation of the critical velocity of membrane fouling outside with the internal suction pressure and the width of main chamber.

From the theoretical analysis,it can be seen that the relationship between the critical velocity of membrane outer surface and suction pressure, the width of cross-flow section and the aeration,the relationship between the critical velocity of membrane inner surface with or without gel layer and membrane pipe diameter,particle size,suction pressure,flow condition and at.

In view of the fact that raw coal in question is wide in size range, an equation for calculating the friction loss and critical velocity of this kind of coal slurry has been proposed by using dimensional and regression analysis methods based on over 5000 groups of data actually observed at five typical hydro mines.